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  • 1
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    Analytical Grid Generation for accurate representation of clearances in CFD for Screw Machines (2015)
    Institute of Physics (IOP)
    Details
    Publication Date: 2015-08-11
    Description: One of the major factors affecting the performance prediction of twin screw compressors by use of computational fluid dynamics (CFD) is the accuracy with which the leakage gaps are captured by the discretization methods. The accuracy of mapping leakage flows can be improved by increasing the number of grid points on the profile. However, this method faces limitations when it comes to the complex deforming domains of a twin screw compressor because the computational time increases tremendously. In order to address this problem, an analytical grid distribution procedure is formulated that can independently refine the region of high importance for leakage flows in the interlobe space. This paper describes the procedure of analytical grid generation with the refined mesh in the interlobe area and presents a test case to show the influence of the mesh refinement in that area on the performance prediction. It is shown that by using this method, the flow domains in the vicinity of the i...
    Print ISSN: 1757-8981
    Electronic ISSN: 1757-899X
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Published by Institute of Physics (IOP)
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  • 2
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    Numerical and Experimental Investigation of Pressure Losses at Suction of a Twin Screw Compressor (2015)
    Institute of Physics (IOP)
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    Publication Date: 2015-08-11
    Description: Rotary twin screw machines are used in the wide range of industrial applications and are capable of handling single and multiphase fluids as compressors, expanders and pumps. Concentration of liquid in the inlet flow can influence the performance of the machine significantly. Characteristics of the multiphase flow at the suction of a screw compressor depend on the local flow velocities and concentration. Local flow velocity measurements inside the screw compressors are difficult to obtain. However other flow properties such as local pressures are easier to attain. It is therefore useful to carry out experiments with local pressure variations in the suction which can be used to validate the 3D numerical Computational Fluid Dynamic (CFD) models that could help in studying the single and multiphase flow behaviour in screw compressors. This paper presents experimental efforts to measure the local pressure losses inside the suction plenum of the screw compressor. Pressure variat...
    Print ISSN: 1757-8981
    Electronic ISSN: 1757-899X
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Published by Institute of Physics (IOP)
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  • 3
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    Understanding the influence of Coulomb and dispersion interactions on the wetting behavior of ionic liquids (2014)
    American Institute of Physics (AIP)
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    Publication Date: 2014-11-06
    Description: We study the role of dispersion and electrostatic interactions in the wetting behavior of ionic liquids on non-ionic solid substrates. We consider a simple model of an ionic liquid consisting of spherical ions that interact via Lennard-Jones and Coulomb potentials. Bulk and interfacial properties are computed for five fluids distinguished by the strength of the electrostatic interaction relative to the dispersion interaction. We employ Monte Carlo simulations and an interface-potential-based approach to calculate the liquid-vapor and substrate-fluid interfacial properties. Surface tensions for each fluid are evaluated over a range of temperatures that spans from a reduced temperature of approximately 0.6 to the critical point. Contact angles are calculated at select temperatures over a range of substrate-fluid interaction strengths that spans from the near-drying regime to the wetting regime. We observe that an increase in the relative strength of Coulombic interactions between ions leads to increasing deviation from Guggenheim's corresponding states theory. We show how this deviation is related to lower values of liquid-vapor excess entropies observed for strongly ionic fluids. Our results show that the qualitative nature of wetting behavior is significantly influenced by the competition between dispersion and electrostatic interactions. We discuss the influence of electrostatic interactions on the nature of wetting and drying transitions and corresponding states like behavior observed for contact angles. For all of the fluids studied, we observe a relatively narrow range of substrate-fluid interaction strengths wherein the contact angle is nearly independent of temperature. The influence of the ionic nature of the fluid on the temperature dependence of contact angle is also discussed.
    Print ISSN: 0021-9606
    Electronic ISSN: 1089-7690
    Topics: Chemistry and Pharmacology , Physics
    Published by American Institute of Physics (AIP)
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  • 4
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    Saturation Properties of 1-Alkyl-3-methylimidazolium Based Ionic Liquids (2014)
    American Chemical Society (ACS)
    Details
    Publication Date: 2014-07-11
    Description: The Journal of Physical Chemistry B DOI: 10.1021/jp504085t
    Electronic ISSN: 1520-5207
    Topics: Chemistry and Pharmacology , Physics
    Published by American Chemical Society (ACS)
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  • 5
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    Comparative genomics of BCG vaccines by whole-genome DNA microarray (1999)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 1999-05-29
    Description: Bacille Calmette-Guerin (BCG) vaccines are live attenuated strains of Mycobacterium bovis administered to prevent tuberculosis. To better understand the differences between M. tuberculosis, M. bovis, and the various BCG daughter strains, their genomic compositions were studied by performing comparative hybridization experiments on a DNA microarray. Regions deleted from BCG vaccines relative to the virulent M. tuberculosis H37Rv reference strain were confirmed by sequencing across the missing segment of the H37Rv genome. Eleven regions (encompassing 91 open reading frames) of H37Rv were found that were absent from one or more virulent strains of M. bovis. Five additional regions representing 38 open reading frames were present in M. bovis but absent from some or all BCG strains; this is evidence for the ongoing evolution of BCG strains since their original derivation. A precise understanding of the genetic differences between closely related Mycobacteria suggests rational approaches to the design of improved diagnostics and vaccines.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Behr, M A -- Wilson, M A -- Gill, W P -- Salamon, H -- Schoolnik, G K -- Rane, S -- Small, P M -- New York, N.Y. -- Science. 1999 May 28;284(5419):1520-3.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Division of Infectious Diseases, Department of Medicine, McGill University Health Centre, Montreal H3G 1A4, Canada. mbgq@musica.mcgill.ca〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/10348738" target="_blank"〉PubMed〈/a〉
    Keywords: BCG Vaccine/*genetics/immunology ; DNA, Bacterial/genetics ; Evolution, Molecular ; *Gene Deletion ; Genetic Variation ; *Genome, Bacterial ; Humans ; Mycobacterium bovis/*genetics/immunology/pathogenicity ; Mycobacterium tuberculosis/*genetics/immunology/pathogenicity ; Nucleic Acid Hybridization ; *Oligonucleotide Array Sequence Analysis ; Open Reading Frames ; Polymerase Chain Reaction ; Vaccines, Attenuated ; Virulence
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 6
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    Numerical investigation of flow characteristics in twin-screw pump under cavitating conditions (2017)
    Institute of Physics (IOP)
    Details
    Publication Date: 2017-09-07
    Description: In order to investigate the flow characteristics and the formation process of cavitation in twin-screw pumps, three-dimensional CFD (Computational Fluid Dynamics) numerical analysis has been carried out. A conformal structured moving mesh generated by an in-house code SCORG was applied for the rotor domain. The VOF (Volume of Fluid) Method has been adopted for dealing with the liquid-gas two-phase flow, while the bubble dynamics was handled by a homogenous cavitation model. By changing the rotation speed and discharge pressure, the intensity, distribution area and variation of cavitation at different rotor angle were obtained. The effects of rotation speed and discharge pressure on cavitation characteristics have been analysed. Calculation results with cavitation model are compared with the results without cavitation and the experimentally obtained values. The influence of cavitation on the performance of a screw pump in terms of the mass flow rate, pressure distribution, rotor ...
    Print ISSN: 1757-8981
    Electronic ISSN: 1757-899X
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Published by Institute of Physics (IOP)
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  • 7
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    Manufacturing method and performance assessment for variable lead vacuum rotors (2017)
    Institute of Physics (IOP)
    Details
    Publication Date: 2017-09-07
    Description: In recent years variable lead rotors have been produced, mainly for vacuum applications, involving a multiple pass manufacturing process which is necessarily time-consuming. A faster method of manufacturing such rotors uses a full profiled disc-type milling or grinding tool but involves clearance variations along the length. These effects have been assessed by computer modelling to quantify any disadvantages. The results indicate that the effects on performance are negligible and the profiled disk tool process is suitable for such components.
    Print ISSN: 1757-8981
    Electronic ISSN: 1757-899X
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Published by Institute of Physics (IOP)
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  • 8
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    Application of numerical grid generation for improved CFD analysis of multiphase screw machines (2017)
    Institute of Physics (IOP)
    Details
    Publication Date: 2017-09-07
    Description: Algebraic grid generation is widely used for discretization of the working domain of twin screw machines. Algebraic grid generation is fast and has good control over the placement of grid nodes. However, the desired qualities of grid which should be able to handle multiphase flows such as oil injection, may be difficult to achieve at times. In order to obtain fast solution of multiphase screw machines, it is important to further improve the quality and robustness of the computational grid. In this paper, a deforming grid of a twin screw machine is generated using algebraic transfinite interpolation to produce initial mesh upon which an elliptic partial differential equations (PDE) of the Poisson’s form is solved numerically to produce smooth final computational mesh. The quality of numerical cells and their distribution obtained by the differential method is greatly improved. In addition, a similar procedure was introduced to fully smoothen the transition of the partitioning rac...
    Print ISSN: 1757-8981
    Electronic ISSN: 1757-899X
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Published by Institute of Physics (IOP)
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  • 9
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    Reply to Shanks and Brundage: Many plausible mechanisms of pandemic mortality disparities [Biological Sciences] (2017)
    National Academy of Sciences
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    Publication Date: 2017-05-02
    Description: In our recently published paper (1), we find evidence that several metrics of socioeconomic status were associated with influenza and pneumonia mortality during the 1918 pandemic. We agree with Shanks and Brundage (2) that there are many possible causal mechanisms behind this association and appreciate the hypotheses that they add...
    Keywords: Letters
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
    Published by National Academy of Sciences
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  • 10
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    Using Monte Carlo Simulation to Compute Liquid–Vapor Saturation Properties of Ionic Liquids (2013)
    American Chemical Society (ACS)
    Details
    Publication Date: 2013-06-23
    Description: The Journal of Physical Chemistry B DOI: 10.1021/jp404207x
    Electronic ISSN: 1520-5207
    Topics: Chemistry and Pharmacology , Physics
    Published by American Chemical Society (ACS)
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