The Experts below are selected from a list of 216789 Experts worldwide ranked by ideXlab platform
Michael J Russell - One of the best experts on this subject based on the ideXlab platform.
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modelling the influence of the process inputs on the removal of surface contaminants from ti 6al 4v linear friction welds
Materials & Design, 2015Co-Authors: Anthony R Mcandrew, Adrian C Addison, Bertrand C D Flipo, Paul A Colegrove, Michael J RussellAbstract:Abstract The linear friction welding (LFW) process is finding increasing interest from industry for the fabrication of near-net-shape, titanium alloy Ti–6Al–4V, aerospace components. Currently, the removal of surface contaminants, such as oxides and foreign particles, from the weld interface into the flash is not fully understood. To address this problem, two-dimensional (2D) computational models were developed using the finite element analysis (FEA) software DEFORM and validated with experiments. The key findings showed that the welds made with higher applied forces required less burn-off to completely remove the surface contaminants from the interface into the flash; the interface Temperature increased as the applied force was decreased or the rubbing velocity increased; and the Boundary Temperature between the rapid flash formation and negligible material flow was approximately 970 °C. An understanding of these phenomena is of particular interest for the industrialisation of near-net-shape titanium alloy aerospace components.
Hua Meng - One of the best experts on this subject based on the ideXlab platform.
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numerical studies of liquid water behaviors in pem fuel cell cathode considering transport across different porous layers
International Journal of Hydrogen Energy, 2010Co-Authors: Hua MengAbstract:Abstract In this paper, a two-phase two-dimensional PEM fuel cell model, which is capable of handling liquid water transport across different porous materials, is employed for parametric studies of liquid water transport and distribution in the cathode of a PEM fuel cell. Attention is paid particularly to the coupled effects of two-phase flow and heat transfer phenomena. The effects of key operation parameters, including the outside cell Boundary Temperature, the cathode gas humidification condition, and the cell operation current, on the liquid water behaviors and cell performance have been examined in detail. Numerical results elucidate that increasing the fuel cell Temperature would not only enhance liquid water evaporation and thus decrease the liquid saturation inside the PEM fuel cell cathode, but also change the location where liquid water is condensed or evaporated. At a cell Boundary Temperature of 80 °C, liquid water inside the catalyst layer and gas diffusion media under the current-collecting land would flow laterally towards the gas channel and become evaporated along an interface separating the land and channel. As the cell Boundary Temperature increases, the maximum current density inside the membrane would shift laterally towards the current-collecting land, a phenomenon dictated by membrane hydration. Increasing the gas humidification condition in the cathode gas channel and/or increasing the operating current of the fuel cell could offset the Temperature effect on liquid water transport and distribution.
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A PEM fuel cell model for cold-start simulations
Journal of Power Sources, 2008Co-Authors: Hua MengAbstract:Abstract In this paper, a transient multiphase multi-dimensional PEM fuel cell model has been developed in the mixed-domain framework for elucidating the fundamental physics of fuel cell cold start. Cold-start operations of a PEM fuel cell at a subfreezing Boundary Temperature of −20 °C under both constant current and constant cell voltage conditions have been numerically examined. Numerical results indicate that the water vapor concentration inside the cathode gas channel affects ice formation in the cathode catalyst layer and thus the cold-start process of the fuel cell. This conclusion demonstrates that high gas flow rates in the cathode gas channel could increase fuel cell cold-start time and benefit the cold-start process. It is shown that the membrane plays a significant role during the cold-start process of a PEM fuel cell by absorbing the product water and becoming hydrated. The time evolutions of ice formation, current density and water content distributions during fuel cell cold-start processes have also been discussed in detail.
Sujit Kumar Khan - One of the best experts on this subject based on the ideXlab platform.
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on heat and mass transfer in a viscoelastic Boundary layer flow over an exponentially stretching sheet
International Journal of Thermal Sciences, 2006Co-Authors: Emmanuel Sanjayanand, Sujit Kumar KhanAbstract:A comprehensive mathematical analysis has been carried out on momentum, heat and mass transfers in a viscoelastic Boundary layer fluid flow over an exponentially stretching continuous sheet. The contributions of the viscous dissipation and elastic deformation have been taken into account in this study. Zeroth order analytical local similar solution of the highly non-linear stream function equation and confluent hypergeometric solutions of heat and mass transfer equations are obtained. These solutions involve an exponential dependence of stretching velocity, prescribed Boundary Temperature and concentration, prescribed Boundary heat flux and concentration flux on the flow directional coordinate. The contribution of elastic deformation on various heat transfer characteristics is examined. The effects of various physical parameters like local viscoelastic parameter, Prandtl number, local Reynolds number, local Eckert number and Schmidt number on various momentum, heat and mass transfers characteristics are presented in this paper.
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Viscoelastic Boundary layer flow and heat transfer over an exponential stretching sheet
International Journal of Heat and Mass Transfer, 2005Co-Authors: Sujit Kumar Khan, Emmanuel SanjayanandAbstract:Abstract Viscoelastic Boundary layer flow and heat transfer over an exponential stretching continuous sheet have been examined in this paper. Approximate analytical similarity solution of the highly non-linear momentum equation and confluent hypergeometric similarity solution of the heat transfer equation are obtained. Accuracy of the analytical solution for stream function is verified by numerical solutions obtained by employing Runge–Kutta fourth order method with shooting. These solutions involve an exponential dependent of stretching velocity, prescribed Boundary Temperature and prescribed Boundary heat flux on the flow directional coordinate. The effects of various physical parameters like viscoelastic parameter, Prandtl number, Reynolds number, Nusselt number and Eckert number on various momentum and heat transfer characteristics are discussed in detail in this work.
X Meng - One of the best experts on this subject based on the ideXlab platform.
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buoyancy driven convection heat transfer of copper water nanofluid in a square enclosure under the different periodic oscillating Boundary Temperature waves
Case Studies in Thermal Engineering, 2015Co-Authors: Xilian Han, X MengAbstract:This study investigates natural convective heat transfer of copper–water nanofluids in a square enclosure with alternating Temperature at one vertical wall, relatively low Temperature at the opposite sidewall and adiabatic at the other walls. The transport equations are solved numerically with finite volume approach using SIMPLEC algorithm. Calculations are performed for nanoparticle volume fractions from 0 to 0.2 and dimensionless amplitude from 0 to 1.0 with consideration of three typical alternating waves (trapezoid wave, sine wave and triangle wave). Results show the utilization of nanoparticles enhances heat transfer and the percentage increase in the time-averaged Nusselt number is around 38% d from ϕ=0 to ϕ=0.2 under the certain conditions. The oscillating waveform has a degree effect on the heat transfer enhancement and the trapezoid wave is more conducive to the enhancement of heat transfer than sine and triangle waves. And the oscillating area is introduced to combine the oscillating waveform and its amplitude and the percentage increase in the time-averaged Nusselt number is around 14.5% from S=0 to S=0.075. In the end, the regression equation about the time-averaged Nusselt number is obtained as parameters of the solid volume fraction and the oscillating area.
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natural convection heat transfer of copper water nanofluid in a square cavity with time periodic Boundary Temperature
Heat Transfer Engineering, 2014Co-Authors: G Wang, X Meng, Min Zeng, Hiroyuki Ozoe, Qiuwang WangAbstract:This paper presents a numerical study of natural convective heat transfer of copper–water nanofluid in a square enclosure where the Temperature of the left vertical sidewall is sinusoidally oscillated with a constant average Temperature, the right sidewall is cooled at a relatively low Temperature, and the other walls are kept adiabatic. The influence of pertinent parameters such as Rayleigh number, solid volume fraction of copper nanoparticles, and dimensionless time period on the heat transfer characteristics is studied. The results show that the heat transfer rate increases using copper nanoparticles.
Emmanuel Sanjayanand - One of the best experts on this subject based on the ideXlab platform.
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on heat and mass transfer in a viscoelastic Boundary layer flow over an exponentially stretching sheet
International Journal of Thermal Sciences, 2006Co-Authors: Emmanuel Sanjayanand, Sujit Kumar KhanAbstract:A comprehensive mathematical analysis has been carried out on momentum, heat and mass transfers in a viscoelastic Boundary layer fluid flow over an exponentially stretching continuous sheet. The contributions of the viscous dissipation and elastic deformation have been taken into account in this study. Zeroth order analytical local similar solution of the highly non-linear stream function equation and confluent hypergeometric solutions of heat and mass transfer equations are obtained. These solutions involve an exponential dependence of stretching velocity, prescribed Boundary Temperature and concentration, prescribed Boundary heat flux and concentration flux on the flow directional coordinate. The contribution of elastic deformation on various heat transfer characteristics is examined. The effects of various physical parameters like local viscoelastic parameter, Prandtl number, local Reynolds number, local Eckert number and Schmidt number on various momentum, heat and mass transfers characteristics are presented in this paper.
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Viscoelastic Boundary layer flow and heat transfer over an exponential stretching sheet
International Journal of Heat and Mass Transfer, 2005Co-Authors: Sujit Kumar Khan, Emmanuel SanjayanandAbstract:Abstract Viscoelastic Boundary layer flow and heat transfer over an exponential stretching continuous sheet have been examined in this paper. Approximate analytical similarity solution of the highly non-linear momentum equation and confluent hypergeometric similarity solution of the heat transfer equation are obtained. Accuracy of the analytical solution for stream function is verified by numerical solutions obtained by employing Runge–Kutta fourth order method with shooting. These solutions involve an exponential dependent of stretching velocity, prescribed Boundary Temperature and prescribed Boundary heat flux on the flow directional coordinate. The effects of various physical parameters like viscoelastic parameter, Prandtl number, Reynolds number, Nusselt number and Eckert number on various momentum and heat transfer characteristics are discussed in detail in this work.