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Research Papers: Porous Media

Parametric Study of Rarefaction Effects on Micro- and Nanoscale Thermal Flows in Porous Structures

[+] Author and Article Information
A. H. Meghdadi Isfahani

Department of Mechanical Engineering,
Islamic Azad University,
Najafabad Branch,
Najafabad 8514143131, Iran
e-mails: amir_meghdadi@pmc.iaun.ac.ir;
amir_meghdadi@yahoo.com

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF HEAT TRANSFER. Manuscript received September 8, 2016; final manuscript received March 11, 2017; published online May 9, 2017. Assoc. Editor: Peter Vadasz.

J. Heat Transfer 139(9), 092601 (May 09, 2017) (9 pages) Paper No: HT-16-1563; doi: 10.1115/1.4036525 History: Received September 08, 2016; Revised March 11, 2017

Hydrodynamics and heat transfer in micro/nano channels filled with porous media for different porosities and Knudsen numbers, Kn, ranging from 0.1 to 10, are considered. The performance of standard lattice Boltzmann method (LBM) is confined to the microscale flows with a Knudsen number less than 0.1. Therefore, by considering the rarefaction effect on the viscosity and thermal conductivity, a modified thermal LBM is used, which is able to extend the ability of LBM to simulate wide range of Knudsen flow regimes. The present study reports the effects of the Knudsen number and porosity on the flow rate, permeability, and mean Nusselt number. The Knudsen's minimum effect for micro/nano channels filled with porous media was observed. In addition to the porosity and Knudsen number, the obstacle sizes have important role in the heat transfer, so that enhanced heat transfer is observed when the obstacle sizes decrease. For the same porosity and Knudsen number, the inline porous structure has the highest heat transfer performance.

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Figures

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Fig. 1

The simulated porous structure: (a) ε=0.881, (b) ε=0.861, (c) ε=0.825, (d) ε=0.732, (e) inline ε=0.877, and (f) staggered ε=0.897

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Fig. 2

Volumetric flow rate as a function of exit

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Fig. 3

The volume flow rate versus the pressure gradient. Labels ε=0.877(L) and ε=0.897(S) represent the results of inline and staggered porous structures, respectively.

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Fig. 4

Knudsen minimum effect

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Fig. 5

The Knudsen number influence on Darcy number

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Fig. 6

Nondimensional pressure drop versus Reynolds number

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Fig. 7

Pressure drops considering the compressibility versus Reynolds number

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Fig. 8

Nusselt number obtained from the DSMC and the new LBM (Pr = 2/3)

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Fig. 9

The heat transfer control volume

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Fig. 10

The Knudsen number effect on the mean temperature along the channel for pi/po=1.1

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Fig. 11

The effect of Knudsen number at the channel outlet on the average Nusselt number

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Fig. 12

The porosity effect on the mean Nusselt number

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Fig. 13

The porosity effect on the mean temperature distribution along the channel

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Fig. 14

The particle size effect of the mean temperature distribution along the channel

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