ALBERT

Description: A three-dimensional numerical study on the flow and heat transfer characteristics over a rotating disk surface with discrete pins was conducted by the use of RNG k–ε turbulent model. And some experiments were also made for validation. The effects of rotating angular speed and pin configuration on the temperature maps and convective heat transfer characteristics on the rotating surface were analyzed. As the increase of rotating velocity, the impingement of pumping jet on the centre of rotating disk becomes stronger and the transition from laminar to turbulent occurs at the outer radius of rotating disk, which resulting in heat transfer enhancement. The pins on the disk make the pumping action of a rotating disk weaker. Simultaneously, they also act as perturbing elements to the cyclone flow near the rotating disk surface, making the overall heat transfer to be enhanced. The needle pins have higher convective heat transfer capacity than the discrete ring pins with the same extend pin areas.

Description: Natural convection heat transfers inside horizontal pipes were measured. The Rayleigh numbers were varied from 6.8 × 10 8 to 1.5 × 10 12 , while the Prandtl number was fixed at 2,094. Based on the analogy concept, a copper sulfate electroplating system was adopted to measure mass transfer rates in place of heat transfer rates. Test results using single-piece electrodes were in good agreement with the work of Sarac and Korkut. The angle-dependent mass transfer rates, measured using piecewise electrodes, were compared with the results of studies on natural convection in concentric annuli, and showed similar trends. The experiments were expanded to the turbulent region, and a transition criterion was proposed. Angle-dependent natural convection heat transfer correlations for the laminar and turbulent regions were derived.

Description: Molecular dynamics simulation is applied to investigate the effects of checker surface roughness geometry on the flow of liquid argon through nanochannels that the roughness is implemented on the lower channel wall. The Lennard-Jones potential is used to model the interactions between particles and periodic boundary condition is applied in the flow direction. Density and velocity profiles across the channel are investigated for channel that the lower surface is decorated with the checker surface roughness elements. Result show that as the surface attraction energy or the roughness height increase the density layering in the near the wall is enhanced by higher values or secondary layering phenomena.

Description: Heat transfer characteristics of a rolling wheel are investigated by using the naphthalene sublimation technique. The local and average Nusselt numbers are obtained. The results reveal that the local and average Nusselt numbers increase with increasing rotating Reynolds number. Under the same rotating Reynolds number they decrease along the radius direction. After comparing with similar available cases reported, it is found that the results are very close to the results of rotating disk in crossflow under the condition that rotating Reynolds number is equal the main flow Reynolds number.

Description: The precipitates, magnetism, and corrosion resistance of Fe 78 Si 9 B 13 glassy samples fabricated in vacuum and air atmospheres (labeled as VAC and AIR samples, respectively) were studied. The findings show that the fraction of the amorphous phase in VAC samples is lower than that in the AIR counterparts. The Fe phase in VAC samples grows preferentially along the 〈200〉 orientation. The distribution of magnetization M 4000 of VAC samples oriented parallel and orthogonal to the field ( H // and H ⊥ ) at H = 4000 Oe is more scattered than AIR samples. The corrosion resistance of VAC samples is lower than AIR counterparts, which can be attributed to the minor alloying effect of oxygen and the passive effect of silicon atoms supplied from the amorphous phase.

Description: Al-Si alloy A356 was modified by TiC nanoparticles. First, the nanoparticles were mechanochemically activated together with aluminum powder. Next, the activated particles were hot extruded in a home-made extruder. Finally, nanoparticles thus prepared in the aluminum matrix were added to the liquid Al-Si alloy, which was then cast into sand molds. A comparison of the microstructure and mechanical properties of the modified alloy thus produced with those of the alloy without the nanoparticles demonstrated that the grain size of the modified alloy decreased. The mechanical properties determined after T6 heat treatment indicated unusual behavior, where the elongation of the modified alloys increased by 20 to 50 pct in different regions of the cast, while the tensile strength remained unchanged and the hardness increased by 18 pct. An electron microscopy study revealed concentration of dislocations near grain boundaries in the modified alloy samples. These grain boundaries serve as obstacles to dislocation motion. It was therefore concluded that the improvement in the mechanical properties of the aluminum alloy modified by TiC nanoparticles was caused by the grain-size-strengthening mechanism.

Description: Martensite pole figures from three different steels have been studied using electron backscatter diffraction (EBSD) and mathematical models to show that the two stage transformation theory is not necessary for correct prediction of pole figure and popular orientation relationships, like Kurdjumov–Sachs. These theories can give misleading prediction. It has been proved that the use of correct crystallographic data can lead to a better texture prediction. The typical features of a pole figure in a {2 5 2} γ habit system have been studied in detail.

Description: Friction stir welding (FSW) of Al - Li alloy 2195 plate produces strong texture gradients. The microstructural characteristics evolve from the base plate, through the thermomechanically affected zone (TMAZ), to the weld nugget interface. In the current study, electron backscattered diffraction (EBSD) analyses were employed to quantify the spatial distribution of texture gradients associated with the evolution of texture within the TMAZ. The strong texture of the base plate enabled the texture evolution to be characterized as a function of location. Systematic partitioning of EBSD data relative to the degree of lattice rotation at each point accurately captured the crystallographic transitions across the advancing side TMAZ. Over a large section of this region, the texture evolves as a result of continuous rigid body rotations. The rigid body rotations were correlated with the complex material flow patterns commonly associated with the FSW process and prior observations of shear-related textures. Finally, a correlation between texture and fracture in a subscale tensile specimen is observed, where failure occurs within a visible band of low-Taylor factor grains.

Description: Sulfidation may occur even in an overall oxidizing environment beneath a corrosion product which assumes the role of a diffusion barrier allowing sulfur species transport at a faster rate when compared with that of oxygen species. The current paper presents sulfidation characteristics of an advanced single-crystal nickel-based superalloy (ANS) and compares performance with IN 792 and CMSX-4 superalloys. The results showed that all the superalloys were highly vulnerable to sulfidation and their lives were significantly reduced. Among them, the ANS was more susceptible to sulfidation and its life was reduced considerably. This is attributed to the changed chemistry of the advanced alloy. The results for ANS are compared with its oxidation data and the difference in its behavior is discussed. A degradation mechanism, which represents the deterioration of ANS under sulfidation conditions, is proposed based on the results obtained from different techniques. Finally, the necessity of protective coatings for shielding against high temperature sulfidation for potential application in enhanced efficiency of gas turbine engines is emphasized.

Description: A model is proposed to predict the room temperature austenite volume fraction as a function of the intercritical annealing temperature for medium Mn transformation-induced plasticity steel. The model takes into account the influence of the austenite composition on the martensite transformation kinetics and the influence of the intercritical annealing temperature dependence of the austenite grain size on the martensite start temperature. A maximum room temperature austenite volume fraction was obtained at a specific intercritical annealing temperature T M . Ultrafine-grained ferrite and austenite were observed in samples intercritically annealed below the T M temperature. The microstructure contained a large volume fraction of athermal martensite in samples annealed at an intercritical temperature higher than the T M temperature.

Description: Controlled rolling followed by accelerated cooling was carried out in-house to study the microstructure and mechanical properties of a low carbon dual-phase steel. The objective of the study described here was to explore the effect of cooling schedule, such as air cooling temperature and coiling temperature, on the final microstructure and mechanical properties of dual-phase steels. Furthermore, the precipitation behavior and yield ratio are discussed. The study demonstrates that it is possible to obtain tensile strength and elongation of 780 MPa and 22 pct, respectively, at the two cooling schedules investigated. The microstructure consists of 90 pct ferrite and 10 pct martensite when subjected to moderate air cooling and low temperature coiling, such that the yield ratio is a low 0.69. The microstructure consists of 75 pct ferrite and 25 pct granular bainite with a high yield ratio of 0.84 when the steel is directly cooled to the coiling temperature. Compared to the conventional dual-phase steels, the high yield strength is attributed to precipitation hardening induced by nanoscale TiC particles and solid solution strengthening by high Si content. The interphase precipitates form at a suitable ledge mobility, and the row spacing changes with the rate of ferrite transformation. There are different orientations of the rows in the same grain because of the different growth directions of the ferrite grain boundaries, and the interface of the two colonies is devoid of precipitates because of the competitive mechanisms of the two orientations.

Description: The goal of this work was to identify the inclusions in lamellar graphite cast iron in an effort to explain the nucleation of the phases of interest. Four samples of approximately the same carbon equivalent but different levels of sulfur and titanium were studied. The Ti/S ratios were from 0.15 to 29.2 and the Mn/S ratios from 4.2 to 48.3. Light and electron microscopy were used to examine the unetched, color-etched, and deep-etched samples. It was confirmed that in irons with high sulfur content (0.12 wt pct) nucleation of type-A and type-D graphite occurs on Mn sulfides that have a core of complex Al, Ca, Mg oxide. An increased titanium level of 0.35 pct produced superfine interdendritic graphite (~10  μ m) at low (0.012 wt pct) as well as at high-S contents. Ti also caused increased segregation in the microstructure of the analyzed irons and larger eutectic grains (cells). TiC did not appear to be a nucleation site for the primary austenite as it was found mostly at the periphery of the secondary arms of the austenite, in the last region to solidify. The effect of titanium in refining the graphite and increasing the austenite fraction can be explained through the widening of the liquidus-eutectic temperature interval (more time for austenite growth) and the decrease in the growth rate of the graphite because of Ti absorption on the graphite. The fact that Ti addition produced larger eutectic cells supports the theory that Ti is not producing finer graphite because of a change in the nucleation potential, but because of lower growth rate of the graphite in between the dendrite arms of a larger fraction of austenite. In the presence of high-Ti and S, (MnTi)S star-like and rib-like inclusions precipitate and act as nuclei for the austenite.

Description: This research work studied the effect of boron additions (14, 33, 82, 126, and 214 ppm) on the hot ductility behavior of a low carbon advanced ultra-high strength steel. For this purpose, specimens were subjected to a hot tensile test at different temperatures [923 K, 973 K, 1023 K, 1073 K, 1173 K, and 1273 K (650 °C, 700 °C, 750 °C, 800 °C, 900 °C, and 1000 °C)] under a constant true strain rate of 10 −3  s −1 . The reduction of area (RA) of the tested samples until fracture was taken as a measure of the hot ductility. In general, results revealed a marked improvement in hot ductility from 82 ppm B when the stoichiometric composition for BN (0.8:1) was exceeded. By comparing the ductility curve of the steel with the highest boron content (B5, 214 ppm B) and the curve for the steel without boron (B0), the increase of hot ductility in terms of RA is over 100 pct. In contrast, the typical recovery of hot ductility at temperatures below the Ar 3 , where large amounts of normal transformation ferrite usually form in the structure, was not observed in these steels. On the other hand, the fracture surfaces indicated that the fracture mode tends to be more ductile as the boron content increases. It was shown that precipitates and/or inclusions coupled with voids play a meaningful role on the crack nucleation mechanism, which in turn causes hot ductility loss. In general, results are discussed in terms of boron segregation and precipitation on austenitic grain boundaries during cooling from the austenitic range and subsequent plastic deformation.

Description: Intergranular cracking and void nucleation occur over extended periods of time in alloy 617 when subjected to stress at high temperatures. Damage occurs inhomogeneously with some boundaries suffering failure, while others are seemingly immune to creep. Crack propagation associated with grain size, and grain boundary character was investigated to determine which types of grain boundaries are susceptible to damage and which are more resistant. Electron backscatter diffraction and a stereological approach to obtain the five-parameter grain boundary distribution were used to measure the proportions of each type of boundary in the initial and damaged structures. The samples were crept at 1273.15 K (1000 °C) at 25 MPa until fracture. It was found that in addition to low-angle and coherent twin boundaries, other low index boundary plane grain boundaries with twist character are relatively resistant to creep.

Description: Microstructural characterization was used to examine the changes that occur in an Mg-6Sn-5Zn-0.3Na alloy from casting to extrusion at either 623 K or 723 K (350 °C or 450 °C) followed by artificial aging at 473 K (200 °C). In particular, the partitioning of Na was examined at each step using STEM-EDS mapping. Na atoms were found to preferentially partition to the Mg-Zn phase when present. After extrusion, when no Mg-Zn was observed, the spherical Mg 2 Sn particles were found to be enriched in Na, particularly at the higher extrusion temperature. Artificial aging following extrusion resulted in a change in Na partitioning, and a coarse distribution of Mg-Zn precipitate rods. Na microadditions led to a high as-extruded hardness, but a significant tension–compression yield asymmetry was still observed at room temperature. The compressive yield strength was found to decrease significantly after 1000 hours of aging.

Description: A metallographic method was used to determine the solvus temperature of β phase in 5083 aluminum alloy. For a more accurate investigation, experiments were carried out from two directions. Consequently, the first reported actual solvus temperature of the Mg-rich phase in the alloy was determined to be 562.5 ± 1.5 K (289.5 ± 1.5 °C), which was 50 K (50 °C) higher than that of the commonly accepted value of the alloy 5083 deduced from the binary phase diagram. A new Cu-bearing phase in the alloy was also first identified metallographically with scanning electron microscopy and its implications in determining the β solvus temperature were discussed.

Description: The durability against electromigration of an annealing twinned Ag-8Au-3Pd wire is about double that of the conventional grained wire under electrical current stressing of 1.23 × 10 5  A/cm 2 . During electromigration, a particular morphology of surface reconstruction comprising a stepwise structure and hillocks can be observed in this annealing twinned wire. The stepwise structure, which has been correlated to longer electromigration life, is postulated to result from dislocation slips driven by electron wind collisions and thermal diffusion of metallic atoms. The simultaneous processes of primary and secondary slips in crossing directions cause hillocks to form at the intersections of both slips. The results also indicated that the electrical current could enhance the grain growth in both wires but had an insignificant effect on the formation of annealing twins.

Description: Carbon enrichment in the austenite transformed from martensite during intercritical annealing was measured by electron probe microanalyzer and three-dimensional atom probe microscopy in Fe-2Mn-0.3C and Fe-0.35C alloys. At early stages of the transformation, negligible Mn partitioning occurs, and carbon content in austenite is higher than orthoequilibrium and paraequilibrium predictions. This is presumably attributed to finite intrinsic interface mobility and/or solute drag effect. The resultant free energy dissipation at interface was estimated.

Description: Nanocrystalline neodymium-doped ceria solid solutions with Nd 3+ concentrations varying from 4 to 20 mol pct have been synthesized by gel combustion method, using urea-formaldehyde as fuel for Nd doping. The combustion reaction is explained through differential scanning calorimetry (DSC)-differential thermogravimetric analysis (TGA), whereas the synthesized materials are characterized through X-ray diffractometry (XRD), field-emission scanning electron microscopy (FESEM), and transmission electron microscopy (TEM). The phase obtained from the exothermic reaction contains Nd-substituted CeO 2 . The deviation of the lattice parameter from Vegard’s law and the decrease in crystallite size with dopant concentration has been explained. The as-synthesized particles are largely nanoporous single crystallites, existing in loosely held spherical-shaped agglomerates. The size of the agglomerates increases with increasing dopant content. High-resolution TEM (HRTEM) reveals the fact that the unit cells are strained.

Description: The three-dimensional morphologies of the Fe-bearing intermetallics in a semisolid-processed Al-Mg-Si alloy were examined after extracting the intermetallics. α c -AlFeSi and β -AlFeSi are the major Fe-bearing intermetallics. Addition of Al-Ti-B grain refiner typically promotes β -AlFeSi formation. β -AlFeSi was observed with a flat, plate-like morphology with angular edges in the alloy with and without grain refiner, whereas α c -AlFeSi was observed as “flower”-like morphology in the alloy with grain refiner.

Description: The competitive grain growth in bicrystal samples during unidirectional solidification of a Ni-based superalloy was found to depend on secondary dendrites perpendicular to the grain boundary of bicrystal samples, rather than primary dendrites parallel to the thermal gradient as generally recognized. The primary dendrite orientation, however, had significance for the dendrite blocking in overgrowth processes and the resultant overgrowth rate during competitive grain growth.

Description: Additive-manufactured aluminum alloy deposits were analyzed using neutron diffraction to characterize the effect of intermediate stress relief anneal heat treatment on bulk residual stresses in the final part. Based on measured interplanar spacing, stresses were calculated at various locations along a single bead, stacked wall deposit. A comparison between an uninterrupted deposited wall and an interrupted, stress-relieved, and annealed deposited wall showed a measureable reduction in residual stress magnitude at the interface with a corresponding shift in stress character into the deposit. This shift changes the interface stresses from purely compressive to partially tensile. The residual stress profile varied along the length of the deposit, and the heat-treatment procedure reduced the overall magnitude of the stress at the interface by 10 through 25 MPa. These results are interpreted in terms of thermal gradients inherent to the process and compared with prior residual stress-characterization studies in additive-manufactured metallic structures.

Description: Microstructure, texture, and microtexture in Ti-6Al-2Sn-4Zr-2Mo-0.1Si billet/bar of three different diameters (57, 152, and 209 mm) were quantified using backscattered electron imaging and electron backscatter diffraction. All three billets exhibited a microstructure comprising a large fraction (≥70 pct) of primary alpha particles, the average size of which decreased and aspect ratio increased with increasing reduction/decreasing billet diameter, or trends suggestive of low final hot working temperatures and/or slow cooling rates after deformation. Appreciable radial variations in the volume fraction and aspect ratio of alpha particles were noticeable only for the smallest-diameter billet. Alpha-phase textures were typical of axisymmetric deformation, but were relatively weak (~3× random) for all billet diameters. By contrast, bands of microtexture, which were multiple millimeters in length along the axial direction, were relatively strong for all of the materials. The intensity and radial thickness of the bands tended to decrease with decreasing billet diameter, thus indicating the important influence of imposed strain on the elimination of microtexture and the possible influence of surface preform microstructure following the beta quench on the evolution of microstructure and microtexture.

Description: Attempts have been made to analyse the momentum and heat transfer characteristics in tortuous flow of non-Newtonian fluids such as suspensions and polymer solutions through tubes of diverging–converging geometry. The results of the study indicate that the transfer coefficients are significantly higher in such systems as compared to the conventional couette flow (through uniform cylindrical tubes). Moreover, the simultaneous increase in pressure drop due to the tortuous wall geometry has been observed to be relatively insignificant. Fluids with different rheological characteristics such as Bingham plastic fluids, pseudoplastic fluids, Ellis model fluids and fluids obeying Reiner–Philippoff rheology have been studied. The specific advantages of these geometries in providing enhanced performance efficiency have been effectively highlighted.

Description: Turbulent heat transfer in circular pipe flow with constant heat flux on the wall is investigated numerically via Large Eddy Simulations for frictional Reynolds number Re τ  = 180 and for Prandtl numbers in the range 0.1 ≤  Pr  ≤ 1.0. In our simulations we employ a second-order finite difference scheme, combined with a projection method for the pressure, on a collocated grid in cylindrical coordinates. The predicted statistical properties of the velocity and temperature fields show good agreement with available data from direct numerical simulations. Further, we study the local thermal flow structures for different Prandtl numbers. As expected, our simulations predict that by reducing the Prandtl number, the range of variations in the local heat transfer and the Nusselt number decrease. Moreover, the thermal flow structures smear in the flow and become larger in size with less sharpness, especially in the vicinity of the wall. In order to characterize the local instantaneous heat transfer, probability density functions (PDFs) for the instantaneous Nusselt number are derived for different Prandtl number. Also, it is shown that these PDFs are actually scaled by the square root of the Prandtl number, so that a single PDF can be employed for all Prandtl numbers. The curve fits of the PDFs are presented in two forms of log-normal and skewed Gaussian distributions.

Description: A 3-D numerical solution is implemented for investigating incompressible turbulent flow and thermal fields of film cooling through a single row of inclined cylindrical holes over a flat plate model. The effects of parameters of interest on the film cooling performance have been simulated. The group method of data handling (GMDH)-type neural networks successfully employed for modeling and presenting a correlation for area-weighted average adiabatic film cooling effectiveness.

Description: The heat transfer and fluid flow behavior of water based Al 2 O 3 nanofluids are numerically investigated inside a two-sided lid-driven differentially heated rectangular cavity. Physical properties which have major effects on the heat transfer of nanofluids such as viscosity and thermal conductivity are experimentally investigated and correlated and subsequently used as input data in the numerical simulation. Transport equations are numerically solved with finite volume approach using SIMPLEC algorithm. It was found that not only the thermal conductivity but also the viscosity of nanofluids has a key role in the heat transfer of nanofluids. The results show that at low Reynolds number, increasing the volume fraction of nanoparticles increases the viscosity and has a deteriorating effect on the heat transfer of nanofluids. At high Reynolds number, the increase in the viscosity is compensated by force convection and the increase in the volume fraction of nanoparticles which results in an increase in heat transfer is in coincidence with experimental results.

Description: A two region conduction-controlled rewetting model of hot surface with constant heat transfer coefficient in wet region and an adiabatic condition in the dry region is solved by the variational method. Three different models have been used for the analysis. A three parametric relation among various parameters, namely, non-dimensional dry wall temperature, Biot number and wet front velocity is obtained. Results of the present solutions are found to be in good agreement with other analytical solutions and published test data.

Description: A new numerical model predicting volatile organic compounds (VOCs) emission from a multi-layer carpet with activated carbon particles is developed with an aim to increase the VOCs emission rate in the carpet before it is used in an indoor environment. The influences of activated carbon particles, diffusion coefficient, material thickness and partition coefficient on the transient airside VOCs concentration and the VOCs emission from the carpet are investigated in detail.

Description: A two-dimensional numerical study is carried out to understand the influence of cross buoyancy on the vortex shedding processes behind two equal isothermal square cylinders placed in a tandem arrangement at low Reynolds numbers. The spacing between the cylinders is fixed with five widths of the cylinder dimension. The flow is considered in an unbounded medium, however, fictitious confining boundaries are chosen to make the problem computationally feasible. Numerical calculations are performed by using a finite volume method based on the PISO algorithm in a collocated grid system. The range of Reynolds number is chosen to be 50–150. The flow is unsteady laminar and two-dimensional in this Reynolds number range. The mixed convection effect is studied for Richardson number range of 0–2 and the Prandtl number is chosen constant as 0.71. The effect of superimposed thermal buoyancy on flow and isotherm patterns are presented and discussed. The global flow and heat transfer quantities such as overall drag and lift coefficients, local and surface average Nusselt numbers and Strouhal number are calculated and discussed for various Reynolds and Richardson numbers.

Description: A porous media theory has been proposed to characterize oxygen transport processes associated with membrane blood oxygenation devices. For the first time, a rigorous mathematical procedure based a volume averaging procedure has been presented to derive a complete set of the governing equations for the blood flow field and oxygen concentration field. As a first step towards a complete three-dimensional numerical analysis, one-dimensional steady case is considered to model typical membrane blood oxygenator scenarios, and to validate the derived equations. The relative magnitudes of oxygen transport terms are made clear, introducing a dimensionless parameter which measures the distance the oxygen gas travels to dissolve in the blood as compared with the blood dispersion length. This dimensionless number is found so large that the oxygen diffusion term can be neglected in most cases. A simple linear relationship between the blood flow rate and total oxygen transfer rate is found for oxygenators with sufficiently large membrane surface areas. Comparison of the one-dimensional analytic results and available experimental data reveals the soundness of the present analysis.

Description: Thermal vapor compressor (TVC) is a device for compressing vapor in water–steam cycles and frequently used in desalination systems. Large amounts of useless vapor can be compressed by this device and the efficiency of a desalination unit is effectively enhanced through this process. Motive steam is injected into the TVC through a convergent–divergent nozzle and accelerated to supersonic velocities. The low pressure steam is entrained at the upstream zone and mixed with this highly compressible motive flow within the TVC. In the current study, the flow field of an experimental TVC is scrutinized in both axisymmetric and three-dimensional approaches and compared with experimental measurements. Since the steam collector at the suction surface of the TVC has a curved shape and may undermine the symmetry of the flow on either side of the central axis, the second objective of this study is to reveal the deviation of the symmetric assumption from the real non-symmetric condition of entering steam flow into the TVC. Results show that the presence of a bending at the inlet side has approximately negligible effects on the mixing phenomenon and the flow remains symmetric around the central axis. Hence, there is no need to consider the collector geometry in further simulations and the performance parameters of the TVC would be sufficiently obtained through an axisymmetric method with a substantial reduction in the computational cost and time.

Description: This study presents a two dimensional analysis of coupled heat and mass transfer during the process of pasta drying. Velocity and temperature distributions of air flowing around the pasta are predicted in steady state condition. Using these profiles and the similarity between heat and mass boundary layers, local convective heat and mass transfer coefficients were determined on different points of pasta surface. By employing these values, the solution of coupled heat and mass transfer equations within the pasta object in unsteady state condition was obtained. Furthermore the effects of operating conditions such as velocity, temperature and relative humidity of air flow on drying rate of pasta were studied. Sensitivity analysis results show that the effects of air temperature and relative humidity on the rate of drying are more important than the effect of air velocity. Finally, the results obtained from this analysis were compared with the experimental data reported in the literatures and a good agreement was observed while, no adjustable parameter is used in the presented model.

Description: An inclined spray chamber with four multiple nozzles to cool a 1 kW 6U electronic test card has been designed and tested in this study. The multiple inclined sprays can cover the same heated surface area as that with the multiple normal sprays but halve the volume of the spray chamber. The spray cooling system used R134a as a working fluid in a modified refrigeration cycle. It is observed that increasing mass flow rate and pressure drop across the nozzles improved the heat transfer coefficient with a maximum enhancement of 117 %, and reduced the maximum temperature difference at the heated surface from 13.8 to 8.4 °C in the inclined spray chamber with a heat flux of 5.25 W/cm 2 , while the heat transfer coefficient of the normal spray increased with a maximum enhancement of 215 % and the maximum temperature difference decreased from 10.8 to 5.4 °C under similar operating conditions. We conclude that the multiple inclined sprays could produce a higher heat transfer coefficient but with an increase in non-uniformity of the surface temperature compared with the multiple normal sprays.

Description: In this study, steady-state turbulent forced flow and heat transfer in a horizontal smooth rectangular duct both experimentally and numerically investigated. The study was carried out in the transition to turbulence region where Reynolds numbers range from 2,323 to 9,899. Flow is hydrodynamically and thermally developing (simultaneously developing flow) under uniform bottom surface temperature condition. A commercial CFD program Ansys Fluent 12.1 with different turbulent models was used to carry out the numerical study. Based on the present experimental data and three-dimensional numerical solutions, new engineering correlations were presented for the heat transfer and friction coefficients in the form of $ {\text{Nu}} = {\text{C}}_{2} {\text{Re}}^{{{\text{n}}_{ 1} }} $ and $ {\text{f}} = {\text{C}}_{3} {\text{Re}}^{{{\text{n}}_{3} }} $ , respectively. The results have shown that as the Reynolds number increases heat transfer coefficient increases but Darcy friction factor decreases. It is seen that there is a good agreement between the present experimental and numerical results. Examination of heat and mass transfer in rectangular cross-sectioned duct for different duct aspect ratio (α) was also carried out in this study. Average Nusselt number and average Darcy friction factor were expressed with graphics and correlations for different duct aspect ratios.

Description: We visually observed that a dropwise condensation occurred initially and later changed into a filmwise condensation on hydrophobic textured surface at atmosphere pressure condition. It was observed that the condensate nucleated on the pillar side walls of the micro structure and the bottom wall adhered to the walls and would not be lifted to form a spherical water droplet using environmental scanning electron microscope.

Description: CdS/PS and ZnS/PS nanocomposites have been prepared by solution casting method with different wt% of cadmium sulphide (CdS) and zinc sulphide (ZnS) nanoparticles and characterized through X-ray diffraction and transmission electron microscope measurements. The effective thermal conductivity of polymer nanocomposites has been measured by transient plane source method over the temperature range from room to 150 °C. The experimental results showed that the thermal conductivity has been found to increase up to 4 wt% of CdS/ZnS nanoparticles and then decrease for 6 and 8 wt% of nanoparticles.

Description: This paper is aimed at estimating unknown parameters in a rectangular fin satisfying a predefined temperature. The differential transformation along with simplex method is used. The study has been done for different initial guess, random errors and measurement points. It is observed that, there is unique value of the convection-conduction parameter, but different conductivity and radiative parameters exist which will be useful in adjusting the parameters amongst various alternatives.

Description: An investigation of an analytical solution of the dynamics of a symmetrically operated parallel flow heat exchanger in the form of transfer matrix was performed. Perturbation method was used to linearize the usual non-linear model of such systems. A non-interactive controller to decouple the outputs and a controller to offset any expected disturbances in the boundary temperature was considered. A discrete model was established and found to predict the heat exchanger dynamics adequately. The results are acceptable and encouraging and the model has been found to be sufficient enough to achieve the objective of countering uncontrolled disturbance without requiring precise knowledge of process dynamics. The validity of the proposed control design is examined by comparing it with other models in the literature.

Description: Comparative study has been performed with various channel cross-sectional shapes and channel configurations of a zigzag printed circuit heat exchanger (PCHE), which has been considered as a heat exchanging device for the gas turbine based generation systems. Three-dimensional Reynolds-averaged Navier–Stokes equations and heat transfer equations are solved to analyze conjugate heat transfer in the zigzag channels. The shear stress transport model with a low Reynolds number wall treatment is used as a turbulence closure. The global Nusselt number, Colburn j-factor, effectiveness, and friction factor are used to estimate the thermal–hydraulic performance of the PCHE. Four different shapes of channel cross section (semicircular, rectangular, trapezoidal, and circular) and four different channel configurations are tested to determine their effects on thermal–hydraulic performance. The rectangular channel shows the best thermal performance but the worst hydraulic performance, while the circular channel shows the worst thermal performance. The Colburn j-factor and friction factor are found to be inversely proportional to the Reynolds number in cold channels, while the effectiveness and global Nusselt number are proportional to the Reynolds number.

Description: In this work the numerical and experimental results of heat transfer in a vertical tall closed cavity are presented. The cavity has an aspect ratio of 20, one of the vertical walls receive a constant and uniform heat flux, while the opposite wall is kept at a constant temperature. The remaining walls are assumed adiabatic. The cavity is full of air. The computational fluid dynamics software Fluent 6.3 was used for the simulation and an experimental prototype was built to obtain the heat transfer coefficients. The air temperature and the fluid velocity values are higher when emissivity (ε) is 0.03 (almost pure natural convection). The experimental total heat transfer coefficient increases between 119.9 and 159.9 % when the emissivity of the walls changes from 0.03 to 0.95.

Description: We investigated a flexible wing that can function as a folding fan by vibrating smoothly on a heated surface, and the effects of this vibration on heat transfer. For flexible up–down vibrations of the wing in a pulsating flow, we propose a novel milli-scale flexible wing shape with a relatively large body and a narrow connecting leg. The shape was optimized such that its deformation became much larger at a low air flow. We performed two-way fluid–structure interaction analyses to predict performance, and an experimental validation was also conducted. The details of flow, heat transfer, and structural deformation are summarized qualitatively. Our results show that the heat transfer coefficient of a heated surface with a single flexible wing was approximately 11.3 % greater than that of a flat plate.

Description: Increasing miniaturization of high speed multi-functional electronics demands ever more stringent thermal management. The present work investigates experimentally and numerically the use of staggered perforated pin fins to enhance the rate of heat transfer in these devices. In particular, the effects of the number of perforations and the diameter of perforation on each pin are studied. The results show that the Nusselt number for the perforated pins is 45 % higher than that for the conventional solid pins and it increases with the number of perforation. Pressure drop with perforated pins is also reduced by 18 % when compared with that for solid pins. Perforations produce recirculations in the x – y as well as the x – z planes downstream of the pins which effectively increase convective heat transfer. However, thermal dissipation decreases significantly when the ratio of pin diameter to perforation diameter exceeds 0.375. This is due to both a reduction in the number of perforation per pin and the decrease in the axial heat conduction along the pin.

Description: A numerical model has been developed for plain fin of plate fin heat exchanger. Plain fin performance has been analyzed with the help of CFD by changing the various parameters of the fin, Colburn ‘ j ’ and fanning friction ‘ f ’ factors are calculated. These values compared with the standard values. The correlations have been developed between Reynolds number Re , fin height h, fin thickness t, fin spacing s, Colburn factor ‘ j ’ and friction factor ‘ f ’.

Description: This paper studies the effects of the driver housing and the resonance tube length on the temperature difference generated across the stack ends. The experiment uses air as the working fluid. The results indicate that the size of the back volume and the length of the resonance tube have affected both the optimal frequency and the temperature difference across the stack. The relationship of these parameters is necessary to the design and measurement performance of the thermoacoustic system.

Description: The focus of the first part of this numerical study is to investigate the effects of two new configurations: (1) slot with cylindrical end and (2) slot with median cylindrical hole, generated by the combination between two film cooling configurations: cylindrical hole and uniform slot. Computational results are presented for a row of coolant injection holes on each side of an asymmetrical turbine blade model near the leading edge. For each configuration, three values of the radius are taken: R = 0.4, R = 0.8 and R = 1.2. The six cases simulations, thus obtained, are conducted for the same density ratio of 1.0 and the same inlet plenum pressure. A new parameter, Rc, is defined to measure the rate of blade coverage by the film cooling. Results show that, at the pressure side; for the two new configurations, the six studied cases exceed the case baseline in cooling effectiveness term with the best result obtained for R = 0.8 (case 2). For the suction side, only configurations with R = 0.4 (cases 1 and 4) provide an increase of film effectiveness compared to the case baseline. The following configuration: Cases 1 or 4 at the suction side and case 2 at the pressure side, gets the best thermal protection because of their higher coverage and strong cooling effectiveness.

Description: Large-Eddy-Simulation of turbulent heat transfer for water flow in rotating pipe is performed, for various rotation ratios (0 ≤  N  ≤ 14). The value of the Reynolds number, based on the bulk velocity and pipe diameter, is Re  = 5,500. The aim of this study is to examine the effect of the rotating pipe on the turbulent heat transfer for water flow, as well as the reliability of the LES approach for predicting turbulent heat transfer in water flow. Some predictions for the case of non-rotating pipe are compared to the available results of literature for validation. To depict the influence of the rotation ratio on turbulent heat transfer, many statistical quantities are analyzed (distributions of mean temperature, rms of fluctuating temperature, turbulent heat fluxes, higher-order statistics). Some contours of instantaneous temperature fluctuations are examined.

Description: This paper presents an experimental–numerical method for determining heat transfer coefficients in cross-flow heat exchangers with extended heat exchange surfaces. Coefficients in the correlations defining heat transfer on the liquid- and air-side were determined based on experimental data using a non-linear regression method. Correlation coefficients were determined from the condition that the weighted sum of squared liquid and air temperature differences at the heat exchanger outlet, obtained by measurements and those calculated, achieved minimum. Minimum of the sum of the squares was found using the Levenberg–Marquardt method. The uncertainty in estimated parameters was determined using the error propagation rule by Gauss. The outlet temperature of the liquid and air leaving the heat exchanger was calculated using an analytical model of the heat exchanger.

Description: Flow and heat transfer characteristics in transition and turbulent regions are studied experimentally and numerically in a horizontal smooth regular hexagonal duct under constant wall temperature boundary condition covering a range of Reynolds number from 2.3 × 10 3 to 52 × 10 3 . Two types of k -omega (standard and shear stress transport (SST)) and three types of k - ε (standard, renormalization (RNG), and realizable) turbulence model are employed for transition and turbulent regions, respectively. Both average and fully developed Darcy friction factor and Nusselt number are presented as a function of Reynolds number. It is seen that k -omega SST and k - ε realizable turbulence models gave the best agreement with the experimental data in transition and turbulent regions, respectively. All the experimental results are correlated within an accuracy of ±13 % and ±7 % for Nusselt number and Darcy friction factor, respectively. Results obtained in this study are compared with circular duct results using hydraulic diameter.

Description: The present study focused on thermal conductivity and viscosity of alumina nanoparticles, at low volume concentrations of 0.01–1.0 % dispersed in the mixture of ethylene glycol and water (mass ratio, 60:40). Sodium dodeobcylbenzene sulfonate (SDBS) was applied for better dispersion and stability of alumina nanoparticles and study of its influence on both thermal conductivity and viscosity. The thermal conductivity established polynomial enhancement pattern with increase of volume concentration up to 0.1 % while linear enhancement was obtained at higher concentrations. In addition, thermal conductivity was enhanced with the rise of temperature. However, the augmentation was negligible compared to that obtained with increase of volume concentration. In contrast, viscosity data showed remarkable reduction with increase of temperature. Meanwhile, viscosity of nanofluids enhanced with loading of alumina nanoparticles. Thermal conductivity and viscosity measurements showed higher values over theoretical predictions. Results showed SDBS at different concentrations has distinct influence on thermal conductivity and viscosity of nanofluid.

Description: Twin roll casting has been used to produce sheet of Mg 60 Cu 29 Gd 11 bulk metallic glass (BMG). Sheet can be produced with thicknesses between 1 and 4 mm, the width of sheet produced can be between 25 and 75 mm. The dimensional stability of the produced sheet in a cast run is ±1 mm in the width direction and ±0.05 mm in the thickness direction. As with all magnesium-based BMGs the sheet produced is strong yet brittle at room temperature. The maximum flexural stress of a twin roll cast Mg 60 Cu 29 Gd 11 BMG strip is 150 MPa with a flexural strain of 0.005. The Charpy impact energy of a Mg 60 Cu 29 Gd 11 BMG strip is 0.02 J. In order to improve the toughness values of the Mg 60 Cu 29 Gd 11 , BMG strip laminates of BMG and aluminum alloy (UNS A91100) were produced via roll bonding. The introduction of aluminum layers to the sheet structure provides a barrier to shear band movement stopping the sudden catastrophic failure of the sheet. After rolling the BMG was examined via X-ray diffraction (XRD) to confirm that the BMG layer remained amorphous. The flexural stress, flexural strain, and Charpy impact energy properties of BMG-Al laminates are improved when compared to monolithic glass properties. The flexural stress values for laminates compared to the monolithic glass improve by 60 pct from 150 to 250 MPa. The flexural strain values improve by over an order of magnitude from 0.005 to 0.14. The Charpy impact energies increase by 2 orders of magnitude from 0.02 to 2.5 J.

Description: Coarse-grained commercially pure Cu was subjected to equal channel angular pressing at room temperature for 2 passes and 12 passes resulting in grain refinement down to the ultrafine scale. Uniaxial tensile testing revealed that as-ECAP Cu samples have very high strength, but low uniform elongation and elongation to failure, whereas small punch testing showed that strain in biaxial stretching of the as-ECAP Cu specimens was comparable to that in the coarse-grained Cu. Analysis of surface relief demonstrated extensive microlocalization of plastic flow into microshear bands during biaxial stretching of the as-ECAP Cu specimens. The effect of microstructure and stress state on formability of the material and the mechanisms governing its plastic deformation are discussed. It is suggested that although the high strength as-ECAP Cu exhibits poor ductility in uniaxial tension, in other strain paths such as biaxial stretching, it can show high formability which is sufficient for metal-forming processes.

Description: Two nickel-base superalloys are joined via transient liquid phase (TLP) bonding with boron as the MPD. Boride formation is observed in the parent materials at some distance from the solid/liquid interface. The boron concentration profile over the joint is measured with glow discharge optical emission spectroscopy (GDOES). Boron concentration peaks are observed corresponding to the boride formation. Boron distribution is discussed on the basis of theoretical predictions in the literature. It is concluded that diffusion of another element is necessary to explain the results with the second element influencing the solubility of boron.

Description: Microstructure evolution of a low-carbon steel with the initial microstructure of ferrite matrix plus cementite particles during hot compression deformation was investigated at the strain rates of 0.001 s −1 , 0.01 s −1 , and 1 s −1 at 973 K (700 °C) by means of field-emission scanning electron microscope, electron backscattered diffraction, and transmission electron microscopy. The results indicated that dynamic recrystallization (DRX) of ferrite took place at all of three strain rates, which can be classified as discontinuous DRX at 0.001 s −1 , 0.01 s −1 , and as continuous DRX at 1 s −1 . The formation of the nuclei of DRX of ferrite was mainly ascribed to the occurrence of particle-stimulated nucleation (PSN), accompanied with the lattice rotation and the formation of new high-angle boundaries. The occurrence of PSN was dependent on the development of a subgrain in the regions with high density of dislocations around cementite particles, without the need for the formation of the deformation zone.

Description: The primary transformation kinetics of nanoicosahedral quasicrystalline (QC) phase formation were investigated in Zr 65 Al 7.5 Ni 10 Cu 12.5 Pd 5 bulk metallic glass (BMG) in various relaxation states. A less relaxed (unrelaxed) BMG exhibited higher activation energy for atomic diffusion in the glassy structure than that of a relaxed one, which represents a change in the nucleation and grain growth kinetics of the primary phase with the relaxation state. Actually, the grain growth rate of a QC particle near the crystallization temperature was approximately 1 × 10 −9  m/s in the less relaxed BMGs, which was less than half of that in the relaxed BMGs. In contrast, the calculated homogeneous nucleation rate significantly increased in the less relaxed samples. It increased with the volume fraction transformed in the early stage. It is concluded that the relaxation state of glassy alloys markedly affects the primary transformation kinetics. The current study also indicates a necessity of development of the relaxation state for structure controlling in industrial applications of BMGs.

Description: Heat transfer and fluid flow processes of natural convection melting of a phase change material are simulated numerically inside a partially heated square cavity. The momentum and energy equations are solved by using enthalpy-based lattice Boltzmann method combined with multi distribution function model. In this communication, the dependence of liquid fraction, temperatures of vertical nodes and average Nusselt number on the positions of heated plates is investigated quantitatively.

Description: The present study focuses on the effect of conical shape in the cold side of the Ranque-Hilsch vortex tube which is shown to have a considerable influence on the system performance. A vortex tube is a simple circular tube with no moving parts which is capable to divide a high pressure flow into two relatively lower pressure flows with temperatures higher and lower than the incoming flow. A three-dimensional computational fluid dynamic model is used to analyse the mechanisms of flow inside a vortex tube. The SST turbulence model is used to predict the turbulent flow behaviour inside the vortex tube. The geometry of a vortex tube with circumferential inlet slots as well as axial cold and hot outlet is considered. Performance curves temperature separation versus cold outlet mass fraction are calculated for a given inlet mass flow rate and varying outlet mass flow rates.

Description: It has been well known that the flaking failure in rolling contact fatigue (RCF) originates from nonmetallic inclusions in steels, and their apparent size is one of the important factors affecting RCF life. However, the influence of inclusion shape on the RCF life has not been fully clarified. In this study, attention was paid to the influence of the inclusion shape on the RCF life. This was evaluated by using carburized JIS-SCM420 (SAE4320) steels that contained two different shapes of MnS—stringer type and spheroidized type—as inclusions. Sectional observations were made to investigate the relation between the occurrence of shear crack in the subsurface and the shape of MnS. It was found that the RCF life was well correlated with the length of MnS projected to the load axis, and the initiation of shear crack in subsurface was accelerated as the length of MnS increased.

Description: There is a growing demand for single-use disposable polymer devices with features at submicron scales. This requires resilient tooling which can be patterned to scales of the order of hundreds of nanometers. The requisite topology can be imparted to silicon, but it is too brittle to be of use in a die to mold thousands of plastic parts. The polycrystalline nature of tool steel means that it cannot be patterned with submicron detail. Some bulk amorphous alloys have the requisite mechanical properties to be viable as materials for such dies, and can be patterned— e.g. , via embossing as a supercooled liquid into MEMS silicon or using focused ion beam (FIB)—with submicron features which may persevere over many thousands of molding cycles. The composition of the amorphous alloy must be carefully selected to suit the particular molding application (polymer/process). The state-of-the-art methodology is presented, along with results of our recent experimental investigations.

Description: The fracture of eutectic Si particles dictates the fracture characteristics of Al-Si based cast alloys. The morphology of these particles is found to play an important role in fracture initiation. In the current study, the effects of strain rate, temperature, strain, and heat treatment on Si particle fracture under compression were investigated. Strain rates ranging from 3 × 10 −4 /s to 10 2 /s and three temperatures RT, 373 K, and 473 K (100 °C and 200 °C) are considered in this study. It is found that the Si particle fracture shows a small increase with increase in strain rate and decreases with increase in temperature at 10 pct strain. The flow stress at 10 pct strain exhibits the trend similar to particle fracture with strain rate and temperature. Particle fracture also increases with increase in strain. Large and elongated particles show a greater tendency for cracking. Most fracture occurs on particles oriented nearly perpendicular to the loading axis, and the cracks are found to occur almost parallel to the loading axis. At any strain rate, temperature, and strain, the Si particle fracture is greater for the heat-treated condition than for the non-heat-treated condition because of higher flow stress in the heat-treated condition. In addition to Si particle fracture, elongated Fe-rich intermetallic particles are also seen to fracture. These particles have specific crystallographic orientations and fracture along their major axis with the cleavage planes for their fracture being (100). Fracture of these particles might also play a role in the overall fracture behavior of this alloy since these particles cleave along their major axis leading to cracks longer than 200 μm.

Description: In the present study, surface melting of a magnesium alloy, ZE41, was performed with an Nd:YAG laser using different laser parameters. The microstructure of the laser-treated and untreated specimens was analyzed by optical and scanning electron microscopy and X-ray diffraction. Corrosion resistance of the different laser-treated specimens along with the untreated alloy was characterized using electrochemical impedance spectroscopy and weight loss measurements in 0.001 M sodium chloride solution. Although the laser processing parameters influenced the microstructure and the melt depth of the laser-treated zone, these had little effect on the corrosion resistance of the alloy.

Description: In this paper, effects of cooling rates on glass formation and magnetic behavior of the Fe 73.0 C 7.0 Si 3.3 B 5.0 P 8.7 Mo 3.0 (at. pct) alloy were investigated via different purging gases ( i.e. , helium and argon) during suction casting. X-ray diffraction patterns and transmission electron microscopy characterization confirmed that the maximum attainable diameter for glass formation is increased from 5 to 7 mm with the helium as the purging gas, relative to the argon. Meanwhile, the coercivity value ( H c ) of the sample cast in helium is almost 5 times larger than that fabricated in argon, although the magnetization saturation in these two alloys is similar. Our pair distribution function analysis, density, and positron annihilation lifetime spectroscopy measurements indicated that the sample cast in helium possesses more free volume; however, the difference between them is insubstantial. Further, experimental results revealed that the residual stress in the samples cast under helium is much larger than that in those prepared in Argon, which could be responsible for the abrupt change in the coercivity.

Description: The effect of annealing temperature on the crystallinity, thermoelectric properties, and surface morphology of the Bi 0.5 Sb 1.5 Te 3 thin films prepared on SiO 2 /Si substrate by radio-frequency (RF) magnetron sputtering was investigated using X-ray diffraction (XRD), the four-point probe method, and scanning electron microscopy (SEM). XRD results show that the crystallite structure of the Bi x Sb 2– x Te 3 thin films belong to Bi 0.5 Sb 1.5 Te 3 . When the Bi x Sb 2– x Te 3 thin films were annealed between 423 K and 523 K (150 °C and 250 °C) for 10  minutes, the crystallinity of the thin films continuously increases with the temperature increase. In addition, the (015) reflection plane as the preferred orientation and the oxidation compound of Bi 3.73 Sb 1.5 O 3 first appeared when the Bi 0.5 Sb 1.5 Te 3 thin films were annealed at 523 K (250 °C) for 10 minutes. An activation energy of 51.66 kJ/mol for crystallite growth of Bi 0.5 Sb 1.5 Te 3 thin films annealed between 423 K and 523 K (150 °C and 250 °C) for 10 minutes was obtained. The resistivity was 2.69 × 10 2 and 5.93 × 10  μ Ω·m, respectively, for the as-deposited Bi 0.5 Sb 1.5 Te 3 thin films and annealed at 523 K (250 °C) for 10 minutes. The maximum values of the Seebeck coefficient and power factor were 256.5  μ V/K and 1.12 × 10 3   μ W/m·K 2 , respectively, for the Bi 0.5 Sb 1.5 Te 3 thin films annealing treatment at 523 K (250 °C) for 10 minutes.

Description: The accurate prediction of alloys’ properties introduced by heat treatment has been considered by many researchers. The advantages of such predictions are reduction of test trails and materials’ consumption as well as time and energy saving. One of the most important methods to predict hardness in quenched steel parts is Quench Factor Analysis (QFA). Classical QFA is based on the Johnson–Mehl–Avrami-Kolmogorov (JMAK) equation. In this study, a modified form of the QFA based on the work by Rometsch et al. is compared with the classical QFA, and they are applied to prediction of hardness of steels. For this purpose, samples of CK60 steel were utilized as raw material. They were austenitized at 1103 K (830 °C). After quenching in different environments, they were cut and their hardness was determined. In addition, the hardness values of the samples were fitted using the classical and modified equations for the quench factor analysis and the results were compared. Results showed a significant improvement in fitted values of the hardness and proved the higher efficiency of the new method.

Description: In this paper, the evolution of work-hardening and dynamic recovery rates vs the flow stress increase ( σ  −  σ y ) in Al-Mg-Si alloys is presented. The experimental data have been extracted from stress–strain curves. All curves show an initial very rapid decrease in slope of the σ –ε curve, which is associated with the elastic–plastic transition. After the elastic–plastic transition, there are typically two distinctive behaviors. For underaged alloys, there is an approximately linear decrease of work-hardening rate as ( σ  −  σ y ) increases. However, for overaged alloys after elastic–plastic transition, there is a plateau in the work-hardening rate followed by an almost linear decrease. The maximum work-hardening and dynamic recovery rates are found to be dependent on the aging state. In order to investigate these phenomena, a model has been employed to simulate the work-hardening behavior of Al-Mg-Si alloys. The model is based on a modified version of Kocks–Mecking–Estrin (KME) model, in which there are three main components: (1) hardening due to forest dislocations, grain boundaries, and sub-grains; (2) hardening due to the precipitates; and (3) dynamic recovery. The modeling results are discussed and compared with the experimental data.

Description: The effect of cobalt on bainite kinetics formation in a 1C-1.5Si wt pct steel is investigated. Two laboratory casts were manufactured with no or 2.5Co wt pct. Bainite transformation kinetics at 493 K, 523 K, and 573 K (220 °C, 250 °C, and 300 °C) were measured using dilatometry. Careful control of the alloy composition, in particular with respect to carbon content, allowed unambiguous identification of the expected accelerating effect of Co. This effect was quantified and compared to that of other possible alloying additions. It is shown that Co has an acceleration effect of around 18 to 29 pct (per wt pct added) for bainite formation between 220 °C and 300 °C. Comparison with published data indicates that this influence is orders of magnitude smaller than that achieved through reduction of C, Mn, or Cr. The influence on hardness is quantified and shown to be significant, and possible origins for hardening are discussed.

Description: In the present study, the diffusion bonding of 17-4 precipitation hardening stainless steel to Ti alloy with and without nickel alloy as intermediate material was carried out in the temperature range of 1073 K to 1223 K (800 °C to 950 °C) in steps of 298 K (25 °C) for 60 minutes in vacuum. The effects of bonding temperature on interfaces microstructures of bonded joint were analyzed by light optical and scanning electron microscopy. In the case of directly bonded stainless steel and titanium alloy, the layerwise α -Fe + χ, χ, FeTi + λ, FeTi +  β -Ti phase, and phase mixture were observed at the bond interface. However, when nickel alloy was used as an interlayer, the interfaces indicate that Ni 3 Ti, NiTi, and NiTi 2 are formed at the nickel alloy-titanium alloy interface and the PHSS-nickel alloy interface is free from intermetallics up to 1148 K (875 °C) and above this temperature, intermetallics were formed. The irregular-shaped particles of Fe 5 Cr 35 Ni 40 Ti 15 have been observed within the Ni 3 Ti intermetallic layer. The joint tensile and shear strength were measured; a maximum tensile strength of ~477 MPa and shear strength of ~356.9 MPa along with ~4.2 pct elongation were obtained for the direct bonded joint when processed at 1173 K (900 °C). However, when nickel base alloy was used as an interlayer in the same materials at the bonding temperature of 1148 K (875 °C), the bond tensile and shear strengths increase to ~523.6 and ~389.6 MPa, respectively, along with 6.2 pct elongation.

Description: Bioactive monetite (anhydrous calcium hydrogen phosphate, CaHPO 4 ) has been successfully synthesized using the sonochemical method in the presence of a ternary solvent system of water/ethylene glycol (EG)/ N , N -dimethylformamide (DMF). The morphology and chemical composition of the synthesized powders were characterized using field emission scanning electron microscopy, X-ray diffraction, and Fourier transform infrared spectroscopy. The results indicated that with increasing sonication time, the morphology changed slightly from a plate-like one to a combination of plates (flower-like). The formation of flower-like nanosheets requires an optimum time of 40 minutes, and the nanosheets have an average thickness of 210 ± 87 nm. The concentration of DMF clearly influences the morphology and crystal phase of the products. The ideal product was obtained using a water/EG DMF ratio of 1:2.

Description: The variation of morphology and mechanical properties of Al6061 automotive aluminum alloy due to friction stir welding (FSW) and gas tungsten arc welding (GTAW) was investigated by optical metallography, scanning electron microscopy, microhardness measurement, X-ray diffraction, tensile testing, and fractography. The center-line dendrite emergence and microhardness reduction in the heat-affected zone were observed in the GTAW process. Although similar microhardness reduction with respect to the base metal was observed in the FSW samples, higher HVs were obtained for the FSW rather than the GTAW process at almost all heat-affected locations. Ultimate tensile strengths of the FSW and the GTAW samples in the transverse direction were ~0.57 and ~0.35 of the base metal, respectively. Post-weld aging improved the strength, but reduced the ductility of the welding.

Description: This experimental study reports the effect of nozzle parameters on the energy separation of the vortex tube. The results indicate that maximum energy separation is achieved with tangential nozzle orientation while the symmetry/asymmetry of nozzles has a minimal effect on the performance of the energy separation. For current selected conditions and parameters, the study shows that the optimum number of nozzles for maximum energy separation is around 4 nozzles.

Description: Maxwell’s classical model for predicting effective thermal conductivity of colloidal solution predicts the thermal conductivity of nanofluids quite satisfactorily. However, Maxwell’s model does not consider the effect of interfacial layer, Brownian motion of nano-particle and nanoparticle aggregation. In this paper, the effect of interfacial layer on thermal conductivity is considered. A simple expression has been derived to determine thermal conductivity of nanofluid considering interfacial layer formed on the nano particles. The thermal conductivity of the interfacial layer has been precisely determined and results are found to be closer to the experimental values, hence, further improving the results of classical Maxwell model.

Description: The paper represents an investigation into thermohydraulic instability in flow of a supercritical fluid with respect to a “density wave”. An analytical solution was obtained for the stability boundary separating stable and unstable modes of the fluid flow. Effects of the thermophysical properties and wall thickness on the flow stability were studied. It was shown that an increase in the thermal conductivity and the thickness of the wall leads to the increase in the flow stability. The theoretically obtained stability boundary was compared with experimental data obtained for the cooling system of superconducting magnets. Taking into account the thermal conjugation “wall-coolant” lifts the problem to the new higher level: an additional parameter is involved into the mathematical description, which causes qualitative changes in the character of the solution.

Description: The effects of magnetic field, suction/injection, nanoparticles type, and nanoparticle volume fraction on heat transfer characteristics and mechanical properties of a moving surface embedded into cooling medium consists of water with Cu, Ag or Al 2 O 3 particles are studied. The governing boundary layer equations are transformed to ordinary differential equations containing, suction/injection parameter, magnetic parameter, nanoparticle and volume fraction. These equations are solved analytically. The velocity and temperature profiles within the boundary layer are plotted and discussed in details for various values of the different parameters.

Description: This study describes an investigation on the convective heat transfer performance of aqueous suspensions of multiwalled carbon nanotubes. The results suggested an increase on heat transfer coefficient of 47 % for 0.5 % volume fraction. Moreover, the enhancement observed during thermal conductivity assessment, cannot fully explain the heat transfer intensification. This could be associated to the random movements among the particles through a fluid, caused by the impact of the base fluid molecules.

Description: The paper deals with the two-dimensional stationary temperature distribution in a composite layer. The nonhomogenous body is assumed to be composed of periodically repeated two-layered laminae. The layering is inclined with an arbitrary angle to the boundary planes. The lower and upper boundary planes are assumed to be kept at given temperatures. The considered problem is solved within the framework of the homogenized model with microlocal parameters, where the continuity thermal conditions on interfaces are satisfied.

Description: Numerical simulation of Poiseuille flow of liquid Argon in a rough nano-channel using the non-equilibrium molecular dynamics simulation is performed. Density and velocity profiles across the channel are investigated in which roughness is implemented only on the lower wall. The Lennard–Jones potential is used to model the interactions between all particles. The effects of surface roughness geometry, gap between roughness elements (or roughness periodicity), surface roughness height and surface attraction energy on the behavior of the flow undergoing Poiseuille flow are presented. Results show that surface shape and roughness height have a decisive role on the flow behaviors. In fact, by increasing the roughness ratio (height to base ratio), the slip velocity and the maximum velocity in the channel cross section are reduced, and the density fluctuations near the wall increases. Results also show that the maximum density near the wall for a rough surface is less than a smooth wall. Moreover, the simulation results show that the effect of triangle roughness surface on the flow behavior is more than the cylindrical ones.

Description: Based on the “hypothetical throat area” theory and the “constant-pressure mixing” theory, a thermodynamic model for ejector was set up by introducing the real properties of refrigerants. Refrigerants which have similar normal boiling points with each other may act as replacement to each other in substitute progress. In this paper, eight environment-friendly refrigerants were divided into 4 pairs for study according to their normal boiling point. In each refrigerant pair, the entrainment ratios of ejector, system COP, pump power et al. of refrigerants were compared and analyzed. Lastly, the performances of the transcritical and subcritical ejector refrigeration cycles with propylene were calculated and compared.

Description: Ni-free austenitic steels alloyed with Cr and Mn are an alternative to conventional Ni-containing steels. Nitrogen alloying of these steel grades is beneficial for several reasons such as increased strength and corrosion resistance. Low solubility in liquid and δ -ferrite restricts the maximal N-content that can be achieved via conventional metallurgy. Higher contents can be alloyed by powder-metallurgical (PM) production via gas–solid interaction. The performance of sintered parts is determined by appropriate sintering parameters. Three major PM-processing routes, hot isostatic pressing, supersolidus liquid phase sintering (SLPS), and solid-state sintering, were performed to study the influence of PM-processing route and N-content on densification, fracture, and mechanical properties. Sintering routes are designed with the assistance of thermodynamic calculations, differential thermal analysis, and residual gas analysis. Fracture surfaces were studied by X-ray photoelectron spectroscopy, secondary electron microscopy, and energy dispersive X-ray spectroscopy. Tensile tests and X-ray diffraction were performed to study mechanical properties and austenite stability. This study demonstrates that SLPS process reaches high densification of the high-Mn-containing powder material while the desired N-contents were successfully alloyed via gas–solid interaction. Produced specimens show tensile strengths 〉1000 MPa combined with strain to fracture of 60 pct and thus overcome the other tested production routes as well as conventional stainless austenitic or martensitic grades.

Description: Effects of open-air sun drying and pre-treatment on drying characteristic of purslanes ( Portulaca oleracea L.) were investigated. Drying times were determined as 31, 24 and 9 h for natural, salted and blanched, respectively. The higher “L” value and lower “−a/b” ratio values were obtained in natural dried purslane. The Aghbashlo et al. model gave a better fit to drying data.

Description: An experimental and numerical study has been conducted to clarify fluid flow characteristics and pressure drop distributions of a cross-flow heat exchanger employing staggered wing-shaped tubes at different angels of attack. The water-side Re w and the air-side Re a were at 5 × 10 2 and at from 1.8 × 10 3 to 9.7 × 10 3 , respectively. Three cases of the tubes arrangements with various angles of attack, row angles of attack and 90° cone angles were employed at the considered Re a range. Correlation of pressure drop coefficient P dc in terms of Re a , design parameters for the studied cases were presented. The flow pattern around the staggered wing-shaped tubes bundle were predicted using the commercial CFD FLUENT 6.3.26 software package. Results indicated that the values of P dc increased with the angle of attack from 0° to 45°, while the opposite was true for angles of attack from 135° to 180°. The values of P dc for the arrangements of (θ 1,2,3  = 45°), (θ 1  = 45°, θ 2  = 0°, θ 3  = 45°), and (θ 1,2,3  = 0°) were lower than those for the arrangement of (ϕ 1  = ϕ 2  = ϕ 3  = 90°) by about 33, 53, and 91 %, respectively. Comparisons between the experimental and numerical results of the present study and those obtained by similar previous studies showed good agreements.

Description: The interface layer and discrete crystal growth in solidification are traced by analyzing the microsegregation of aluminum alloy. Based on the interface evolution and discrete crystal growth, the non-equilibrium microsegregation mechanism is qualitatively proposed. The solute content of solid is decided by the solidification temperature of interface. And the solidification temperature of interface is further decided by the evolution of interface compositions and interface temperature. The fluctuation of interface compositions and actual interface temperature persists in the whole solidification process.

Description: The weld metal of the ENiCrFe-7 nickel-based alloy-covered electrodes was investigated in terms of the microstructure, the grain boundary precipitation, and the ductility-dip cracking (DDC) susceptibility. Besides the dendritic gamma-Ni(Cr,Fe) phase, several types of precipitates dispersed on the austenitic matrix were observed, which were determined to be the Nb-rich MC-type carbides with “Chinese script” morphology and size of approximately 3 to 10 µ m, the Mn-rich MO-type oxides with size of approximately 1 to 2 µ m, and the spherical Al/Ti-rich oxides with size of less than 1 µ m. The discontinuous Cr-rich M 23 C 6 -type carbides predominantly precipitate on the grain boundaries, which tend to coarsen during reheating but begin to dissolve above approximately 1273 K (1000 °C). The threshold strain for DDC at each temperature tested shows a certain degree of correlation with the grain boundary carbides. The DDC susceptibility increases sharply as the carbides coarsen in the temperature range of 973 K to 1223 K (700 °C to 950 °C). The growth and dissolution of the carbides during the welding heat cycles deteriorate the grain boundaries and increase the DDC susceptibility. The weld metal exhibits the minimum threshold strain of approximately 2.0 pct at 1323 K (1050 °C) and the DTR less than 873 K (600 °C), suggesting that the ENiCrFe-7—covered electrode has less DDC susceptibility than the ERNiCrFe-7 bare electrode but is comparable with the ERNiCrFe-7A.

Description: Magnesium (Mg) alloys have been recently introduced as a biodegradable implant for orthopedic applications. However, their fast corrosion, low bioactivity, and mechanical integrity have limited their clinical applications. The main aim of this research was to improve such properties of the AZ91 Mg alloy through surface modifications. For this purpose, nanostructured fluoridated hydroxyapatite (FHA) was coated on AZ91 Mg alloy by micro-arc oxidation and electrophoretic deposition method. The coated alloy was characterized through scanning electron microscopy, transmission electron microscopy, X-ray diffraction, in vitro corrosion tests, mechanical tests, and cytocompatibility evaluation. The results confirmed the improvement of the corrosion resistance, in vitro bioactivity, mechanical integrity, and the cytocompatibility of the coated Mg alloy. Therefore, the nanostructured FHA coating can offer a promising way to improve the properties of the Mg alloy for orthopedic applications.

Description: Microstructural evolution of an Fe-22 pct Mn-0.4 pct C twinning-induced plasticity (TWIP) steel during high strain rate deformation has been investigated. When subjected to low strain rate deformation, the steel shows the typical TWIP phenomenon. On the other hand, when subjected to high strain rate deformation, there is a formation of nanostructured austenite, due to the occurrence of deformation twinning forming nanoscale twin/matrix lamellae followed by dynamic recovery induced by adiabatic heating during high strain rate deformation.

Description: The presence of Fe aids in establishing the mechanical and physical properties of AlSi alloys and is also one of the main impurities leading to formation of β -Al 5 FeSi intermetallics. This study aims to understand the effect of fluid flow on the dendritic microstructure with intermetallics in Al-5/7/9 wt pct Si-0.2/0.5/1.0 wt pct Fe alloys that are directionally solidified under defined thermal and fluid flow conditions. We made extensive use of 3D X-ray tomography to obtain a better insight into the morphology and formation of the intermetallics. Three-dimensional (3-D) distribution of intermetallics presented here shows that the growth of large β -Al 5 FeSi due to forced flow occurs in the eutectic specimen center and together with an increase in the number density of β precipitates. The 3D reconstructions have verified the β shaped to be curved, bent with twining, branched, and to have imprints, holes, and propeller-shaped platelets. The 3D views showed that hole-shaped β arose from the lateral growth around α -Al dendrites. These views also confirmed the phenomenon of shortening of β as an effect of flow in the dendritic region, where β could be fragmented or completely remelted, and ultimately resulting in microstructures with shorter β -Al 5 FeSi and increases in number density. The analysis revealed an interaction between melt flow, 3D distribution, and the morphology of β -Al 5 FeSi. The growth of a large and complex group of β intermetallics can reduce the melt flow between dendrites and strengthen pore nucleation and eutectic colonies nucleation, leading to lower permeability of the mushy zone and increased porosity in the castings.

Description: We present a numerical analysis of the sensitivity of the density driven CO 2 convection results in a vertical Hele-Shaw cell with respect to different modeling assumptions. The role of density driven convection phenomenon in CO 2 geological storage capacity and safety has already been pointed out in several studies. We showed that in order to accurately simulate the phenomenon occurring in lab experiments, multi-phase transfer has to be considered and variations in the permeability field should also be taken into account. Taylor dispersion has been found to have no significant effect on the results. Experimental results of the convection fingering process development and of quantitative determination of the total mass of dissolved CO 2 were used to validate the numerical simulation results. Understanding how accurate numerical models can simulate lab experiments is an important step in confirming their reliability to predict underground CO 2 storage capacity.

Description: Due to the miniaturization of the solder joints in micro/nanoelectronic devices, the volume ratio of intermetallic (IMCs) materials has substantially increased. This increased ratio could affect the reliability of solder joints depending on the regime and the rate of the loading. Cu 6 Sn 5 is the primary IMC layer in the solder joint, and the primary crack initiation is observed in Cu 6 Sn 5 site in the literature. As the size of the joints becomes closer to the grain size, joints may only contain a few numbers of grains of Cu 6 Sn 5 . This manifests itself in statistical grain size effects, as well as anisotropy. Modeling these joints using bulk properties of Cu 6 Sn 5 does not capture the actual behavior of these joints especially when plastic deformation is involved. Plastic deformation, starting at yield point, happens to be associated with the activation of slip systems. Deformation of a slip system of single crystal largely rests on the slip parameters such as critical resolved shear stress (CRSS), initial hardening modulus, and saturation stress (Stage I stress when large plastic flow occurs). However, no efforts have been made to capture the slip parameters of Cu 6 Sn 5 experimentally or analytically because of the difficulties of using conventional mechanical tests to measure the slip parameters of HCP single crystals. Due to wide range of CRSS values, it becomes difficult to isolate a specific slip system in testing without activating the other slip systems. The crystal plasticity finite-element (CPFE) method takes into account the effect of anisotropy and slip system behavior in modeling materials. This work uses a combined strategy based upon experiments, modeling, and a comparative analysis to obtain slip system parameters that could predict the slip process of Cu 6 Sn 5 . Nanoindentation tests were performed on Cu 6 Sn 5 single crystal to extract the load–displacement curves, and a CPFE nanoindentation model analysis along with custom user material was utilized to obtain set of crystal plasticity material parameters which can represent the plastic behavior of Cu 6 Sn 5 IMC. These parameters were then used to predict shear yield strength and shear modulus of Cu 6 Sn 5 , and the findings were compared with the previously published values in the literature.

Description: Most research related to dendrite coherency point (DCP) has been done on cast aluminum alloys and at a low cooling rate condition. In this research, the DCP of a wrought aluminum alloy is calculated in the range of high cooling rates used in the direct-chill casting process. The two-thermocouple thermal analysis technique was used to determine the DCP of Al2024 alloy. The aim of this work is to investigate the effect of different cooling rates on the dendrite coherency characteristics of Al2024. The cooling rates used in the present study range from 0.4 to 17.5 °C s −1 . Also, the effect of 1.2 wt pct Al-5Ti-1B grain refiner on the DCP was studied. To calculate the solid fraction at dendrite coherency, solid fraction versus time is plotted based on Newtonian technique. The results show that by increasing the cooling rate, both time and temperature of dendrite coherency are decreased. Also, by adding the Al-5Ti-1B master alloy, dendrite coherency temperature is reduced and dendrite impingement is postponed. To reduce casting defects occurring during equiaxed solidification, e.g ., macrosegregation, porosities, and hot tearing, these two operations which lead to postpone the transition from mass to inter-dendritic feeding, or dendrite coherency, can be useful. By increasing the cooling rate, solid fraction at dendrite coherency increases initially and then decreases at higher cooling rates. Presence of grain refiner leads to increasing of solid fraction at DCP. Thus, by delaying the dendrite coherency and increasing the solid fraction at DCP, semi-solid forming can be performed on parts with higher solid fraction and less shrinkage. Microstructural evaluation was carried out to present the correlation between the cooling rate and solid fraction in 2024 aluminum alloy.

Description:    Numerical simulation has been made on heat and mass transfer of vapor absorption by wavy lithium bromide aqueous solution films. The velocity fields and interface positions are obtained by VOF model. Solitary waves are generated by periodically disturbed inflow boundary. Based on these, the temperature and concentration fields are obtained with a stationary interface shape. The effect of solitary waves on the heat and mass transfer across the film is investigated. It is shown that due to the mixing of circulation and stretch of large film thickness, the gradient of concentration and absorption rate decrease for solitary wave region. The region of capillary waves shows a significant amount of absorption enhancement. The percentage of absorption for the different regions is quantified. Content Type Journal Article Pages 1-9 DOI 10.1007/s00231-011-0820-x Authors Shoushi Bo, Institute of Chemical Engineering, Dalian University of Technology, 2# Linggong Road, 116024 Dalian, China Xuehu Ma, Institute of Chemical Engineering, Dalian University of Technology, 2# Linggong Road, 116024 Dalian, China Hongxia Chen, Institute of Chemical Engineering, Dalian University of Technology, 2# Linggong Road, 116024 Dalian, China Zhong Lan, Institute of Chemical Engineering, Dalian University of Technology, 2# Linggong Road, 116024 Dalian, China Journal Heat and Mass Transfer Online ISSN 1432-1181 Print ISSN 0947-7411

Description:    In this paper, the influence of both the hydrodynamic and the thermal boundary layer on the solidification process of the flowing liquid on a cold plate is theoretically analyzed. Heat transfer between a frozen layer which is created and a laminar flowing liquid over that layer is considered. The development of the boundary layers and the relation between them on the solidification process are studied. An integral method for the solution of the boundary layer equations was used to obtain approximative solutions. The influence of the Prandtl and Reynolds number on the formation of the solid crust is shown and discussed for time dependent and steady-state solutions. Content Type Journal Article Pages 1-7 DOI 10.1007/s00231-011-0823-7 Authors Z. Lipnicki, Institute of Environmental Engineering, University of Zielona Góra, 65-516 Zielona Góra, Poland B. Weigand, Institut für Thermodynamik der Luft- und Raumfahrt, Universität Stuttgart, Pfaffenwaldring 31, 70569 Stuttgart, Germany Journal Heat and Mass Transfer Online ISSN 1432-1181 Print ISSN 0947-7411

Description:    The evolution of γ/γ′ eutectic during the solidification of Ni-base superalloys CMSX-10 and CMSX-4 was investigated over a wide range of cooling rates. The microsegregation behavior during solidification was also quantitatively examined to clarify the influence of elemental segregation on the evolution of γ/γ′ eutectic. In the cooling rate ranges investigated (0.9 to 138.4 K/min (0.9 to 138.4 °C/min)), the γ/γ′ eutectic fraction in CMSX-10 was found to be more than 2 times higher than that in CMSX-4 at a given cooling rate. However, the dependence of the γ/γ′ eutectic fraction on the cooling rate in both alloys showed a similar tendency; i.e. , the γ/γ′ eutectic fraction increased with increasing the cooling rate and then exhibited a maximum plateau at and above the certain critical cooling rate in both alloys. This critical cooling rate was found to be dependent on the alloy composition and was estimated to be about 12 K/min (12 °C/min) and 25 K/min (25 °C/min) for CMSX-10 and CMSX-4, respectively. The calculated solid compositions based on the modified Scheil model revealed that even a small compositional difference of total γ′ forming elements in the initial composition of the alloy can play a significant role in the as-cast eutectic fraction during the solidification of Ni-base superalloys. The evolution of the γ/γ′ eutectic fraction with respect to the cooling rate could be rationalized by taking into account the effects of back-diffusion in solid and dendrite arm coarsening on decreasing the extent of microsegregation. Content Type Journal Article Pages 1-10 DOI 10.1007/s11661-011-0738-4 Authors S. M. Seo, High Temperature Materials Group, Korea Institute of Materials Science, Changwon, 641-010 South Korea J. H. Lee, Department of Metallurgy and Materials Engineering, Changwon University, Changwon, 641-773 South Korea Y. S. Yoo, High Temperature Materials Group, Korea Institute of Materials Science, Changwon, 641-010 South Korea C. Y. Jo, High Temperature Materials Group, Korea Institute of Materials Science, Changwon, 641-010 South Korea H. Miyahara, Department of Materials Science and Engineering, Kyushu University, Fukuoka, 819-0395 Japan K. Ogi, Oita National College of Technology, Oita, 870-0152 Japan Journal Metallurgical and Materials Transactions A Online ISSN 1543-1940 Print ISSN 1073-5623

Description:    The present study reports the effect of several operating parameters on the thermal performance of the vortex tube. The experimental results indicate that the inlet pressure and the cold fraction are the most significant parameters influencing the vortex tube performance. The experimental data point out that insulation has minimal effect on the vortex tube performance. The same inlet pressure tests show that energy separation increases as number of inlet nozzle increases. Content Type Journal Article Pages 1-6 DOI 10.1007/s00231-011-0824-6 Authors Mohammad O. Hamdan, Mechanical Engineering Department, United Arab Emirates University, P.O. Box 17555, Al-Ain, United Arab Emirates Ahmed Alawar, Mechanical Engineering Department, United Arab Emirates University, P.O. Box 17555, Al-Ain, United Arab Emirates Emad Elnajjar, Mechanical Engineering Department, United Arab Emirates University, P.O. Box 17555, Al-Ain, United Arab Emirates Waseem Siddique, Mechanical Engineering Department, United Arab Emirates University, P.O. Box 17555, Al-Ain, United Arab Emirates Journal Heat and Mass Transfer Online ISSN 1432-1181 Print ISSN 0947-7411

Description:    Austenite formation during intercritical annealing was studied in a cold-rolled dual-phase (DP) steel based on a low-carbon DP780 composition processed in the mill. Two heating rates, 10 and 50 K/s, and a range of annealing temperatures from 1053 K to 1133 K (780 °C to 860 °C) were applied to study their effects on the progress of austenitization. The effect of these process parameters on the final microstructures and mechanical properties was also investigated using a fixed cooling rate of 10 K/s after corresponding annealing treatments. It was found that the heating rate affects the austenite formation not only during continuous heating, but also during isothermal holding, and the effect is more pronounced at lower annealing temperatures. Faster heating delays the recrystallization kinetics of the investigated steel. The rate of austenite formation and its distribution are strongly influenced by the extent of overlapping of the processes of recrystallization and austenitization. It appeared that the heating rate and temperature of intercritical annealing have a stronger effect on the final tensile strength (TS) of the DP steel than holding time. Both higher annealing temperatures and long holding times minimize the strength difference caused by a difference in heating rate. Content Type Journal Article Pages 1-11 DOI 10.1007/s11661-011-0753-5 Authors R. R. Mohanty, ArcelorMittal Global R&D, East Chicago, IN 46312, USA O. A. Girina, ArcelorMittal Global R&D, East Chicago, IN 46312, USA N. M. Fonstein, ArcelorMittal Global R&D, East Chicago, IN 46312, USA Journal Metallurgical and Materials Transactions A Online ISSN 1543-1940 Print ISSN 1073-5623

Description:    This paper presents both a numerical and analytical study in connection with the steady boundary layer flow and heat transfer induced by a moving permeable semi-infinite flat plate in a parallel free stream. Both the velocities of the flat plate and the free stream are proportional to x 1/3 . The surface temperature is assumed to be constant. The governing partial differential equations are converted into ordinary differential equations by a new similarity transformation. Numerical results for the flow and heat transfer characteristics are obtained for various values of the moving parameter, transpiration parameter and the Prandtl number. Approximate analytical solutions are also obtained when the suction or injection parameter is very large. It is found that dual solutions exist for the case when the fluid and the plate move in the opposite directions. Content Type Journal Article Pages 1-7 DOI 10.1007/s00231-011-0821-9 Authors Norfifah Bachok, Department of Mathematics, Faculty of Science, Universiti Putra Malaysia, 43400 UPM Serdang, Malaysia Mihaela Anghel Jaradat, Bogdan Voda University, Cluj-Napoca, Romania Ioan Pop, Faculty of Mathematics, University of Cluj, CP 253, 3400 Cluj, Romania Journal Heat and Mass Transfer Online ISSN 1432-1181 Print ISSN 0947-7411

Description:    Extremely thin plates of bainitic ferrite can now routinely be induced in steels by heat–treatment at low homologous temperatures. Given the atomic mechanism by which the transformation occurs, morphology should be dominated by the minimization of strain energy due to the displacements necessary to accomplish the change in crystal structure when austenite decomposes into bainite. Experiments were conducted using atomic force microscopy in an attempt to characterize these displacements, with a surprising outcome that the shear strain is much larger than associated with conventional, coarser bainitic structures. It appears that this might explain why the plates of bainitic ferrite tend to be slender in this new class of nanostructured alloys. Content Type Journal Article Pages 1-5 DOI 10.1007/s11661-011-0755-3 Authors M. J. PEET, Materials Science and Metallurgy Department, University of Cambridge, Cambridge, CB2 3QZ United Kingdom H. K. D. H. BHADESHIA, Materials Science and Metallurgy Department, University of Cambridge, Cambridge, CB2 3QZ United Kingdom Journal Metallurgical and Materials Transactions A Online ISSN 1543-1940 Print ISSN 1073-5623

Description:    A numerical method for calculation of strong radiation for 2D reactive air is developed. Governing equations are taken to be 2D, compressible Reynolds-average Navier–Stokes and species transport equations. Also, radiation heat flux is evaluated using a model of discrete ordinate method. A multiband model is used to construct absorption coefficients. Tangent slab approximation is assumed to determine the characteristic parameters needed in the Discrete Ordinates Method. Content Type Journal Article Pages 1-12 DOI 10.1007/s00231-011-0828-2 Authors Morteza Rahmanpour, Department of Mechanical Engineering, Islamic Azad University, Khameneh Branch, Khameneh, Shabestar, Iran Reza Ebrahimi, Faculty of Aerospace Engineering, K.N. Toosi University of Technology, Tehran, Iran Mehrzad Shams, Faculty of Mechanical Engineering, K.N. Toosi University of Technology, Tehran, Iran Journal Heat and Mass Transfer Online ISSN 1432-1181 Print ISSN 0947-7411

Description:    The aim of this work is to partially substitute Fe and Mn for Ni in the 3HA piston alloy and to study the consequences through microstructural evaluation and the thermal analysis technique. Three types of near-eutectic alloys containing (2.6 wt pct Ni-0.2 wt pct Fe-0.1 wt pct Mn), (1.8 wt pct Ni-0.75 wt pct Fe-0.3 wt pct Mn), and (1 wt pct Ni-1.15 wt pct Fe-0.6 wt pct Mn) were produced, and their solidification was studied at the cooling rate of 0.9 K/s (°C/s) using the computer-aided thermal analysis technique. Optical microscopy and scanning electron microscopy were used to study the microstructure of the samples, and energy dispersive X-ray (EDX) analysis was used to identify the composition of the phases. Also, the quantity of the phases was measured using the image analysis technique. The results show that Ni mainly participates as Al 3 Ni, Al 9 FeNi, and Al 3 CuNi phases in the high Ni-containing alloy (2.6 wt pct Ni). In addition, substitution of Ni by Fe and Mn makes Al 9 FeNi the only Ni-rich phase, and Al 12 (Fe,Mn) 3 Si 2 appears as an important Fe-rich intermetallic compound in the alloys with the higher Fe and Mn contents. Content Type Journal Article Pages 1-12 DOI 10.1007/s11661-011-0764-2 Authors R. Gholizadeh, Center of Excellence for Advanced Materials Processing (CEAMP), School of Metallurgy and Materials Engineering, Iran University of Science and Technology (IUST), 16846 Narmak, Tehran, Iran S. G. Shabestari, Center of Excellence for Advanced Materials Processing (CEAMP), School of Metallurgy and Materials Engineering, Iran University of Science and Technology (IUST), 16846 Narmak, Tehran, Iran Journal Metallurgical and Materials Transactions A Online ISSN 1543-1940 Print ISSN 1073-5623

Description:    Microstructure and mechanical properties of cold-spray coatings are usually required in order to explore the potential industrial application of the latter. This article demonstrates the successful formulation of Ni-20Cr and Ni-50Cr coatings on two boiler steels, namely, SAE 213-T22 and SA 516 steel by cold-spray process. The microstructure, coating thickness, phase formation, and microhardness properties of the coatings were evaluated. The coatings were subjected to cyclic heating and cooling cycles at an elevated temperature of 1173.15 K (900 °C) to ascertain their high-temperature oxidation behavior. Moreover, these cyclic exposures can give useful information regarding the adhesion of the coatings with the substrate steels. Of all the coatings, the Ni-50Cr coating on SA 516 steel had a maximum average hardness value of 469 Hv. As observed from the surface field emission–scanning electron microscopy (FE-SEM) analysis, the coatings were found to have nearly dense microstructure with the sprayed particles in interlocked positions. It was concluded that the cold-spray process is suitable for spraying the preceding powders onto the given boiler steels to produce nearly dense and low oxide coatings. The coatings, in general, were found to follow the parabolic rate of oxidation and were successful in maintaining their surface contact with their respective substrate steels. Content Type Journal Article Pages 1-18 DOI 10.1007/s11661-011-0759-z Authors Niraj Bala, Baba Banda Singh Bahadur Engineering College, Fatehgarh Sahib, Punjab, India Harpreet Singh, School of Mechanical, Materials and Energy Engineering, Indian Institute of Technology Ropar, Rupnagar, India Satya Prakash, Metallurgical and Materials Engineering Department, Indian Institute of Technology Roorkee, Uttrakhand, India Journal Metallurgical and Materials Transactions A Online ISSN 1543-1940 Print ISSN 1073-5623

Description:    Interdiffusion in the face-centered-cubic (fcc) Co-Al binary alloys was studied by the diffusion-couple approach in the temperature range of 1173 K to 1573 K (900 °C to 1300 °C). Interdiffusion coefficients of the fcc Co-Al alloys were then evaluated by using the Sauer–Freise method. The effect of magnetic ordering on the Co-Al interdiffusion was observed at 1273 K (1000 °C) by examining the Arrhenius plots. The interdiffusion data were assessed to develop the atomic mobility for the fcc Co-Al alloys, and their validity was tested by simulating the diffusion-couple experiments. Content Type Journal Article Pages 1-5 DOI 10.1007/s11661-011-0758-0 Authors Y.-W. Cui, Computational Alloy Design Group, IMDEA Materials Institute, Madrid, 28040 Spain B. Tang, State Key Laboratory of Solidification Processing, Northwestern Polytechnical University, Xi’an, 710072 People’s Republic of China R. Kato, Department of Materials Science, Graduate School of Engineering, Tohoku University, Sendai, 980-8579 Japan R. Kainuma, Department of Materials Science, Graduate School of Engineering, Tohoku University, Sendai, 980-8579 Japan K. Ishida, Department of Materials Science, Graduate School of Engineering, Tohoku University, Sendai, 980-8579 Japan Journal Metallurgical and Materials Transactions A Online ISSN 1543-1940 Print ISSN 1073-5623