Legitimacy of the local thermal equilibrium hypothesis in porous media: A comprehensive review
Local thermal equilibrium (LTE) 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 (LTE). Therefore, for the sake of appropriately conduct the technological process, it has become necessary to examine the validity of the LTE assumption before deciding which energy model should be used. Indeed, the legitimacy of the LTE 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 LTE 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.
History
Volume
14Issue
23Start Page
1End Page
47Number of Pages
47eISSN
1996-1073Publisher
MDPIPublisher DOI
Full Text URL
Additional Rights
CC BY 4.0Language
enPeer Reviewed
- Yes
Open Access
- Yes
Acceptance Date
2021-11-26External Author Affiliations
University of Technology, IraqEra Eligible
- Yes