ANOMALOUS EFFECTS DURING THERMAL DISPLACEMENT IN POROUS MEDIA UNDER NON-LOCAL THERMAL EQUILIBRIUM

2018 ◽  
Vol 21 (2) ◽  
pp. 161-196 ◽  
Author(s):  
Abiola D. Obembe ◽  
Sidqi A. Abu-Khamsin ◽  
M. Enamul Hossain
Keyword(s):  
Porous Media ◽  
Thermal Equilibrium ◽  
Local Thermal Equilibrium ◽  
Thermal Displacement ◽  
Non Local

Determination of Flow and Heat-Transfer Parameters in Porous Media With Consideration of Density Variation of Working Fluid

2000 ◽  
Author(s):  
W. H. Hsieh ◽  
W. T. Wu
Keyword(s):  
Heat Transfer ◽  
Porous Media ◽  
Equilibrium Model ◽  
Thermal Equilibrium ◽  
Density Variation ◽  
Local Thermal Equilibrium ◽  
Working Fluid ◽  
Flow And Heat Transfer ◽  
Non Local ◽  
Transfer Parameters

Abstract An experimental investigation is conducted to determine the flow and heat-transfer parameters of porous media with the consideration of density-variation effect of the working fluid. The permeability (K), inertial coefficient (F), and local convective heat transfer coefficient (hloc) are determined for two types of metal screens at Reynolds numbers ranging from 20 to 400. A single-blow transient technique combined with a compressible non-local-thermal-equilibrium model determines the hloc. The compressible non-local-thermal-equilibrium model is also adopted in a Levenberg-Marquardt optimization technique for deducing the K and F from measured steady-state pressure drops at different flow rates. Results show that the permeability increases with the increase of the porosity. A set of empirical correlations is obtained for calculating the Nusselt number. Results also show that, under the test condition of this study, consideration of the density-variation effect would improve the accuracy in deducing the K, F, and hloc.

scholarly journals Stopping power of a helium plasma under LTE or NLTE conditions

2018 ◽  
Vol 36 (4) ◽  
pp. 442-447
Author(s):  
Luis González-Gallego ◽  
Manuel D. Barriga-Carrasco ◽  
Juan Miguel Gil ◽  
Rafael Rodríguez ◽  
Guadalupe Espinosa
Keyword(s):  
Theoretical Model ◽  
Electron Temperature ◽  
Thermal Equilibrium ◽  
Stopping Power ◽  
Local Thermal Equilibrium ◽  
Helium Plasma ◽  
Slowing Down ◽  
Non Local ◽  
Argon Ions ◽  
Bound Electrons

AbstractIn this work, the stopping power of a partially ionized helium plasma due to its free and bound electrons is analyzed for an electron temperature and density in which local thermal equilibrium (LTE) or non-local thermal equilibrium (NLTE) regimes can be possible. In particular by means of collisional-radiative models, the average ionization of the plasma as well as the abundances of different helium species (HeI, HeII, and HeIII) are analyzed in both LTE and NLTE thermodynamic states. The influence of this ionization and of the different ion abundances on the stopping power of the helium plasma is shown to be quite significant. Finally, our theoretical model is compared with experimental results on slowing down of swift argon ions in helium plasma.

Heat-Transfer Study of Aluminum-Foam Heat Sink for Electronic Cooling

Volume 4 ◽  
2004 ◽  
Author(s):  
W. H. Hsieh ◽  
J. Y. Wu ◽  
W. H. Shih ◽  
W. C. Chiu
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Temperature Difference ◽  
Heat Sink ◽  
Thermal Equilibrium ◽  
Aluminum Foam ◽  
Local Thermal Equilibrium ◽  
Pore Density ◽  
Gas Phases ◽  
Non Local

The demand of high speed and miniaturization of electronic components results in increased power dissipation requirement for thermal management. In this work, the effects of porosity (ε), pore density (PPI) and air velocity on the heat-transfer characteristics of aluminum-foam heat sinks are investigated experimentally. The phenomenon of non-local thermal equilibrium (NLTE) is also observed and reported. Results show that the Nu increases as the pore density increases, due to the fact that aluminum foam with a larger pore density has a larger heat-transfer area. The Nusselt number also increases with the increase of porosity due to the same reason. It is noted that temperatures of the solid and gas phases of the aluminum foam decrease as Reynolds number increases, caused by the increased convective heat-transfer rate at higher Reynolds number. The deduced temperature difference between solid and gas phases clearly indicates the existence of non-local thermal equilibrium condition within the aluminum-foam heat sink. The increase of the porosity and the pore density enhances the phenomenon of non-local thermal equilibrium. The temperature difference increases with the decrease of Reynolds number and the distance away from the heat source.

Nanofluid Suspensions as Derivative of Interface Heat Transfer Modeling in Porous Media

2009 ◽  
Author(s):  
Peter Vadasz
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Porous Media ◽  
Heat Conduction ◽  
Thermal Equilibrium ◽  
Local Thermal Equilibrium ◽  
Interface Heat Transfer ◽  
Wire Method ◽  
Special Case ◽  
Heat Conduction Process

Spectacular heat transfer enhancement has been measured in nanofluid suspensions. Attempts in explaining these experimental results did not yield yet a definite answer. Modeling the heat conduction process in nanofluid suspensions is being shown to be a special case of heat conduction in porous media subject to Lack of Local thermal equilibrium (LaLotheq). The topic of heat conduction in porous media subject to Lack of Local thermal equilibrium (LaLotheq) is reviewed, introducing one of the most accurate methods of measuring the thermal conductivity, the transient hot wire method, and discusses its possible application to dual-phase systems. Maxwell’s concept of effective thermal conductivity is then introduced and theoretical results applicable for nanofluid suspensions are compared with published experimental data.

An Engineering Estimate for Plug-Flow Convection in Porous Media Discarding Fluid Conduction

2009 ◽  
Vol 131 (3) ◽  
Author(s):  
Nihad Dukhan
Keyword(s):  
Porous Media ◽  
Solid Phase ◽  
Plug Flow ◽  
Convection Heat Transfer ◽  
Constant Heat Flux ◽  
Heated Wall ◽  
Local Thermal Equilibrium ◽  
Equilibrium Equations ◽  
Non Local ◽  
Flow Through

Metal and graphite foam are relatively new types of porous materials characterized by having high-solid phase conductivities. In many cooling applications of these materials, including high-power electronics, low-conductivity fluids flow through them, e.g., air. A simple approximate engineering solution for the convection heat transfer inside a two-dimensional rectangular porous media subjected to constant heat flux on one side is presented. The conduction in the fluid is set to zero, and for simplicity, a plug flow is considered. As a result, the non-local-thermal equilibrium equations are significantly simplified and solved. The solid and fluid temperatures decay in what looks like an exponential fashion as the distance from the heated wall increases. The results are in good agreement with one more complex analytical solution in the literature, in the region far from the heated wall only.

The isentropic exponent of non-local thermal equilibrium plasmas

2002 ◽  
Vol 294 (1) ◽  
pp. 47-51 ◽  
Author(s):  
K.T.A.L Burm ◽  
W.J Goedheer ◽  
D.C Schram
Keyword(s):  
Thermal Equilibrium ◽  
Local Thermal Equilibrium ◽  
Isentropic Exponent ◽  
Non Local
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