ALBERT

Description: 〈p〉Publication date: October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 International Journal of Heat and Mass Transfer, Volume 141〈/p〉 〈p〉Author(s): D.Y. Yeo, H.C. NO〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉In this paper, two-phase drag models for a packed bed of uniform-size particles were suggested, and they were applied to the calculation of pressure drop and dryout heat flux. We provided physical basis for the two-phase flow regime model through the analysis of the interfacial friction (〈em〉F〈sub〉i〈/sub〉〈/em〉). The suggested model provides flow patterns representing bubbly, slug, and channel flow and considering three criteria including d〈sup〉2〈/sup〉〈em〉F〈sub〉i〈/sub〉〈/em〉/d〈em〉α〈/em〉〈sup〉2〈/sup〉 = 0, 〈em〉F〈sub〉i〈/sub〉〈/em〉 = maximum, and 〈em〉F〈sub〉i〈/sub〉〈/em〉 = 0. The results obtained from the three criteria were drawn with several observation-based experimental ones to generate the flow regime map (void fraction vs. particle diameter). Through the current flow regime map, we clearly saw the existence of channel flow in a packed bed with particles smaller than around 3.5 mm. Then, mechanistic interfacial friction models were developed on basis of the current two-phase flow map of bubbly flow, slug flow, channel flow and annular flow. The suggested interfacial friction models were validated with top- and bottom-flooding air-water experiments and boiling experiments. We found out that the capability of pressure drop estimation by the current model were significantly improved for a bed with small particles. Finally, a zero-dimensional dryout heat flux (DHF) model was derived using the suggested interfacial friction models, and validated against DHF experimental data for beds with 1-D configuration. The root-mean-square error (RMSE) of the suggested DHF model was 35%, which was the smallest among the RMSEs of the previous DHF models.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 International Journal of Heat and Mass Transfer, Volume 141〈/p〉 〈p〉Author(s): Tianyu Ma, Lei Feng, Hu Wang, Haifeng Liu, Mingfa Yao〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Spray impingement has aroused more and more interests in recent years with the increase of injection pressure in internal combustion engines. In this paper, the near wall combustion after fuel spray impingement is studied based on an updated film development model and experiment in constant volume vessel. Relationship between spray injection and flame development under different ambient temperature is analyzed as well as the near wall distribution of combustion products. In the first part, a mathematical model that considered the effects of surface tension on spray impingement is built for better prediction of film development. Reasonable results are obtained at room temperature spray impingement case, and the split distribution of film depth is also well captured. In the second part, flame development in the near wall region is investigated based on the proposed numerical model and experiments. The result shows that the flame becomes circumferentially nonuniformed at lower ambient temperature (723 K) and the evolution of downstream flame become sensitive to the wall temperature. At lower ambient temperature (723 K), increasing wall temperature could enlarge the high temperature zone, which is helpful to accelerate the film evaporation and soot oxidation. At higher ambient temperature condition, the spray impact angle should be reduced to create more concentrated combustion (stronger stratification), which could improve the combustion efficiency in the near wall region.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 International Journal of Heat and Mass Transfer, Volume 141〈/p〉 〈p〉Author(s): Youqiang Liao, Xiaohui Sun, Baojiang Sun, Yonghai Gao, Zhiyuan Wang〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The three–phase gas–liquid–solid flow, caused by hydrate decomposition in cuttings is a main concern during drilling through gas–hydrate reservoir. In this study, a transient gas–liquid–solid flow model is developed considering the coupling interactions between hydrate dynamic decomposition, cuttings transport and heat transfer in multiphase flow. Using this model, the transient gas–liquid–solid flow behaviors are investigated. Numerical simulations show that the decomposition rate of hydrate in formation is only 1/140 of that in annular cuttings for a unit depth, therefore, the influences of hydrate decomposition in hydrate layers can be neglected. Hydrate particles undergo three processes from bottom hole to wellhead in annulus: non–decomposition, slow decomposition and rapid decomposition. In annulus where the depth is more than 400 m, hydrates decompose slowly and the decomposed gas hardly expands due to the high pressure. While, if the hydrates and decomposed gas return upwards to the position where the depth less than 400 m, the gas void fraction increases significantly, not only due to the faster decomposition rate of hydrates but also due to the more intense expansion of decomposed gas. After the hydrate particles return upwards to the wellhead, the behaviors of gas–liquid–solid flow tend to be a quasi–stable state. If there is no backpressure device at the wellhead, that is, the wellhead backpressure is 0 MPa, the gas void fraction at the wellhead can reach 0.68, which is enough to cause blowout accident. Increasing wellhead backpressure to 2 MPa through managed pressure devices and lowering the inlet temperature of drilling fluid to 17.5 °C except adjusting drilling fluid density can manage the gas void fraction within 10%.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 International Journal of Heat and Mass Transfer, Volume 141〈/p〉 〈p〉Author(s): Ronghui Qi, Chuanshuai Dong, Li-Zhi Zhang〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The focus of this work is on the liquid-air mass transfer mechanism that is critical for liquid desiccant dehumidification and many other absorption processes. Most existing mass transfer correlations heavily rely on specific experiments and show poor universality. Therefore, we proposed a new set of mass transfer correlations theoretically based on the film instability during falling film dehumidification. The flow dynamic, Marangoni effect and liquid/air contact conditions that affecting the interface characteristics and wetting factors are considered. The correlations were verified by comparing with experimental data from several widely-cited literatures. The tests in these literatures were conducted under a wide range of operating conditions and dehumidifier types. The newly-developed correlations provide an acceptable prediction for liquid-air mass transfer, showing close trends to all previous experimental results. The overall error of the new predictions, 20–30%, is close to those of empirical equations built in the specific literature. The factors that affect the interphase mass transfer by changing the film instability and the wetting factor are also analyzed. The increase in liquid Reynolds number shows the most significant effect as it could effectively increase the film instability and liquid-air contact area. The liquid contact angle on solid surfaces, regarding the wettability, also affects the mass transfer considerably. By reducing the contact angle from 90° to 10°, although the increase in Sherwood number is slight due to the suppression of film instability, the wetting factor is almost doubled, resulting in a significant growth in mass transfer performance. This new correlation examines the falling film mass transfer process in more detail, and is based on fewer simplifying assumptions and attempts to take more realistic situations into account. Findings presented herein contribute to a more fully understanding on the falling film behaviors during liquid/gas contact such as liquid desiccant dehumidification.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: December 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 International Journal of Heat and Mass Transfer, Volume 144〈/p〉 〈p〉Author(s): Wahiba Yaïci, Evgueniy Entchev〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉 〈p〉In recent years, considerable interest has been given to the application of solar-powered cooling technology for use in buildings. Solar cooling systems look like to be a suitable substitution to the traditional vapour-compression electrical-driven machines. Solar systems have the advantage of using harmless working fluids, especially water. They also have the capacity to decrease the peak loads for electricity utilities and can contribute to a substantial reduction of the harmful CO〈sub〉2〈/sub〉 emissions, which produce the notorious greenhouse effect that in turn is responsible for global warming and its devastating consequences. Amongst cooling technologies, low-temperature, solar-powered adsorption chillers/heat pumps are arising as a sustainable alternative to electrical vapour-compression systems.〈/p〉 〈p〉This study aims at examining the impact of design and operating factors on an adsorption cooling system’s performance in a residential application. An unsteady Computational Fluid Dynamics (CFD) combined with a heat and mass transfer model of the adsorption cooling system using adsorbent/water pair, was created in order to predict the following: (1) Flow behaviour; (2) Pressure; (3) Temperature; and (4) Water adsorption distributions. For possible adsorbents, both silica gel and zeolite 13X were considered; however, it is worth mentioning that silica gel was used at a lower working temperature range, as required by the operation. This makes silica gel an efficient option for solar/heat driven residential cooling applications. For the CFD model implemented equations, two geometries found in literature were employed for validation. Validation of the unsteady simulation results with experimental data found in literature showed favourable agreements. In a parametric study, various computation cases underwent simulation over the duration of the adsorption mode, which considered the following set of factors: heat transfer fluid (HTF) velocity (〈em〉v〈/em〉); adsorbent bed thickness (〈em〉l〈sub〉bed〈/sub〉〈/em〉); heat exchanger tube thickness (〈em〉b〈/em〉); and adsorbent particle diameter (〈em〉d〈sub〉p〈/sub〉〈/em〉) in order to perform a detailed investigation for main geometrical and operating parameters’ influence upon system performance. Results obtained from CFD disclosed the significance of 〈em〉v〈/em〉, 〈em〉l〈sub〉bed〈/sub〉〈/em〉 and 〈em〉d〈sub〉p〈/sub〉〈/em〉 whereas 〈em〉b〈/em〉 was found having relatively minor modifications within the system performance. Additionally, the development of CFD combined with heat and mass transfer model serves as an effective tool for both simulation and optimisation of adsorption cooling systems as well as for performance predicting purposes.〈/p〉 〈/div〉 〈/div〉

Description: 〈p〉Publication date: December 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 International Journal of Heat and Mass Transfer, Volume 144〈/p〉 〈p〉Author(s): Wenzhong Gao, Qiaye Qi, Jiahao Zhang, Guangming Chen, Dawei Wu〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Spray flash evaporation is an effective desalination method, which increases specific surface area of salty water by liquid atomization, thereby improving desalination performance and maximising low-grade heat source utilization. During evaporation, explosive boiling phenomenon occurs inside superheated droplets on a heated surface. In order to understand the mechanism of explosive boiling, spray flash evaporation of distilled water and 3.5 wt% salty water in a high vacuum vessel was observed visually. Meanwhile, a parametric study was carried out to scrutinize the impacts of the variation of ambient pressure, heat flux, and surface superheat degree. The experiment data indicates that nucleate site is located in the upper layer of a droplet due to internal superheated liquid and Marangoni convection. In different operating conditions, bubble fragmentation process or crown fragmentation process happens at nucleate site. The fragmentation time of pure water, which is mainly influenced by heat flux and surface superheat degree, shrinks with higher heat flux and higher surface superheat degree. The fragmentation time of 3.5 wt% salty water decreases with ambient pressure drops and superheat degree increments.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: December 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 International Journal of Heat and Mass Transfer, Volume 144〈/p〉 〈p〉Author(s): Miaomiao Chen, Zhigang Yang, Zheyan Jin〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉In the present study, we experimentally investigated the melting process of an ice bead on the smooth and micro-grooved surfaces under a hot shear flow. One smooth silicon surface and three micro-grooved silicon surfaces were fabricated and tested. A parameter study of the substrate surface temperature and the air flow speed was conducted. During the experiment, an ice bead was first formed from a freezing water droplet on a cold substrate surface. Then, the ice bead was exposed to a hot shear flow and its melting process was recorded by a CCD camera and an infrared camera simultaneously. As for the micro-grooved surfaces, the direction of the hot shear flow was parallel to the micro-grooves. The results showed that the melting process of the ice bead on the smooth and micro-grooved surfaces under a hot shear flow could be divided into three categories. The air flow speed, the surface temperature, and the type of the surface had a significant influence on which category the melting process of the ice bead belonged to. Besides, the presence of the micro-grooves was found to apparently affect the wetting length, the removable time, and the temperature along the centerline of the ice bead. In general, the micro-grooved surfaces were found to be more favorable for the ice bead melting process than the smooth surface.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: December 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 International Journal of Heat and Mass Transfer, Volume 144〈/p〉 〈p〉Author(s): Kai Yang, Geng-Hui Jiang, Hai-Feng Peng, Xiao-Wei Gao〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉In this paper, combination of radial integration boundary element method (RIBEM) with complex variable and Levenberg-Marquardt algorithm (LMA) is firstly proposed to identify temperature-dependent conductivity in the inverse heat conduction problem. To obtain the simulative temperature, radial integration boundary element method is used to solve the transient nonlinear heat conduction problem with temperature-dependent conductivity. What’s more, RIBEM with complex variable, which transforms the real variables into complex ones in boundary element method, makes it possible to perform complex variable derivative method (CVDM) in LMA. Furthermore, because of the introduction of CVDM, the sensitivity coefficient matrix can be calculated accurately and efficiently, and then the identification of unknown variable can be achieved admirably in the inverse heat problem. Finally, different initial guess value and measurement errors are considered, respectively, and various numerical examples are presented to fully demonstrate the accuracy and feasibility of the proposed method in identifying temperature-dependent conductivity.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: December 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 International Journal of Heat and Mass Transfer, Volume 144〈/p〉 〈p〉Author(s): Wonkeun Baik, Rin Yun〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The condensation heat-transfer coefficient and pressure drop for pure CO〈sub〉2〈/sub〉 and CO〈sub〉2〈/sub〉 + N〈sub〉2〈/sub〉 mixtures were investigated under the near-critical condition, which simulates the CO〈sub〉2〈/sub〉 transporting conditions under Carbon Capture, Transportation, and Storage (CCS). The experimental apparatus consists of a test section, heat exchangers, mass flow meters, temperature sensors, a magnetic gear pump, and a differential pressure transducer. The test section made with a copper tube was assembled with Polyvinyl Chloride (PVC) pipe to form a double tube. The condensation temperature and mole fraction of N〈sub〉2〈/sub〉 of the CO〈sub〉2〈/sub〉 mixtures ranged from 20 °C to 30 °C, and 1 to 5%, respectively. The mass flux was changed from 500, 600 and 700 kg·m〈sup〉−2〈/sup〉s〈sup〉−1〈/sup〉. The average heat transfer coefficient of the CO〈sub〉2〈/sub〉 + N〈sub〉2〈/sub〉 mixtures decreased by 2.23 to 15.9% based on the average heat transfer coefficient of pure CO〈sub〉2〈/sub〉, and the pressure drop decreased by 53.4 to 77.3% at the condensation temperature of 25 °C with increase of the mole fraction of N〈sub〉2〈/sub〉.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: December 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 International Journal of Heat and Mass Transfer, Volume 144〈/p〉 〈p〉Author(s): Yong Jin, Mohammed Albaity, Yusuf Shi, Noreddine Ghaffour, Peng Wang〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Water condensation is an important phase change phenomenon whose applications range from power generation to water desalination. In the present study, we compared condensation occurring on two different substrates (namely square and strip) and demonstrated the effect of substrate geometry on water condensation. It is found that condensation on different regions of the same substrate is dramatically different due to different local vapor flux. In general, the condensation rate is linearly proportional to vapor flux while average vapor flux can be improved by creating geometrical discontinuity (strip substrate) within rigid substrates. Experimental result of water collection confirms that the condensation rate is increased by around 40% on the strip substrate compared to the square substrate. This study demonstrates that water condensation can be enhanced by rationally tuning the geometry of the condensation substrate. Performance of water condensation of a specific substrate can be predicated by simulating the vapor flux over the substrate.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: December 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 International Journal of Heat and Mass Transfer, Volume 144〈/p〉 〈p〉Author(s): Hao Zhang, Ningfei Wang, Zhiwen Wu, Wanzhi Han, Rui Du〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉A new theoretical model has been developed to calculate the regression rate of solid fuel scramjet (SF-Scramjet). This model obtains the local regression rate by calculating the local heat flux on the fuel surface, which is obtained by a standard wall function. A two-dimensional, axisymmetric, turbulent, one-reaction model which used the new method was developed to study the solid fuel regression rate for SF-Scramjet numerically with a flight environment of 25 km and a Mach number of 6. The quasi-steady state numerical method has been adopted to calculate the regression rate at different times. Experiments were carried out on the ground dedicated connected-pipe static test facility under the same boundary conditions to verify the correctness of the model. The results demonstrate that the numerical results agree well with the experimental results in the first few seconds. In the next few seconds of combustion, the numerical results of the regression rate gradually deviate from the experimental results. This may be due to the gradual accumulation of errors in the quasi-steady method.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: December 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 International Journal of Heat and Mass Transfer, Volume 144〈/p〉 〈p〉Author(s): Fan Wu, Liang Li, Jiefeng Wang, Xiaojun Fan, Changhe Du〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉In this paper, four swirl and impingement composite cooling structures are established to deeply study the flow and heat transfer characteristics, where the swirl nozzles and impingement nozzles are reasonably arranged. Numerical simulation is conducted by solving the Reynolds Averaged Navier-Stokes (RANS) equations with the standard 〈em〉k〈/em〉-〈em〉ω〈/em〉 model. Meanwhile, numerical results are compared with the cooling behaviors of swirl cooling and impingement cooling under the same condition. Results revealed that the pressure distribution of four composite cooling structures is quite different from that of swirl cooling and impingement cooling. Hence, the nozzle mass flow ratio distribution of composite cooling structures displays a large fluctuation with the variation of the nozzle location, which has an influence on the flow and heat transfer characteristics. Moreover, the heat transfer characteristics of swirl and impingement composite cooling combine the advantages of impingement cooling and swirl cooling, where there both exists extremely high local heat transfer regions and uniform heat transfer regions. As for composite cooling 3 and composite cooling 4, the alternate locations of impingement nozzles and swirl nozzles could effectively increase the band-shaped high heat transfer area. Meanwhile, the low heat transfer area caused by the continuous arrangement of impingement nozzles is reduced. Among four composite cooling structures, the composite cooling 4 has the highest average heat transfer coefficient and the minimum pressure loss. The globally average heat transfer of composite cooling 4 is 3.49% lower than swirl cooling but is 19.12% higher than impingement cooling. Its total pressure loss is 4.29% lower than swirl cooling and is slightly lower compared with impingement cooling.〈/p〉〈/div〉 〈/div〉