Legitimacy of the Local Thermal Equilibrium Hypothesis in Porous Media: A Comprehensive Review

Gazy F. Al-Sumaily, Amged Al Ezzi, Hayder A. Dhahad, Mark C. Thompson and Talal Yusaf
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Gazy F. Al-Sumaily: Energy and Renewable Energies Technology Centre, University of Technology, Baghdad 19006, Iraq
Amged Al Ezzi: Department of Electrochemical Engineering, University of Technology, Baghdad 19006, Iraq
Hayder A. Dhahad: Mechanical Engineering Department, University of Technology, Baghdad 19006, Iraq
Mark C. Thompson: Department of Mechanical and Aerospace Engineering, Monash University, Clayton, VIC 3800, Australia
Talal Yusaf: School of Engineering and Technology, Central Queensland University, Brisbane, QLD 4009, Australia

Energies, 2021, vol. 14, issue 23, 1-47

Abstract: Local thermal equilibrium ( L T E ) is a frequently-employed hypothesis when analysing convection heat transfer in porous media. However, investigation of the non-equilibrium phenomenon exhibits that such hypothesis is typically not true for many circumstances such as rapid cooling or heating, and in industrial applications involving immediate transient thermal response, leading to a lack of local thermal equilibrium ( L T E ). Therefore, for the sake of appropriately conduct the technological process, it has become necessary to examine the validity of the L T E assumption before deciding which energy model should be used. Indeed, the legitimacy of the L T E hypothesis has been widely investigated in different applications and different modes of heat transfer, and many criteria have been developed. This paper summarises the studies that investigated this hypothesis in forced, free, and mixed convection, and presents the appropriate circumstances that can make the L T E hypothesis to be valid. For example, in forced convection, the literature shows that this hypothesis is valid for lower Darcy number, lower Reynolds number, lower Prandtl number, and/or lower solid phase thermal conductivity; however, it becomes invalid for higher effective fluid thermal conductivity and/or lower interstitial heat transfer coefficient.

Keywords: convection heat transfer; porous media; LTE; LTNE (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2021
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