A comprehensive pore scale and volume average study on solid/liquid phase change in a porous medium

Purpose The purpose of this study is to investigate the applicability of volume average which is extensively used for analyzing the heat and fluid flow (both for single-phase and solid/liquid-phase change) in a closed cell porous medium numerically. Design/methodology/approach Heat conduction equations for the solid frame and fluid (or phase change material) are solved for pore scale and volume average approaches. The study mainly focuses on the effect of porosity and the number of porous media unit cell on the agreement between the results of the pore scale and volume average approaches. Findings It is observed for the lowest porosity values such as 0.3 and the number of porous media unit cell as 4 in heat transfer direction, the results between two approaches may be questionable for the single-phase fluid. By increasing the number of porous media unit cell in heat transfer direction, the agreement between two approaches becomes better. In general, for high porosity values (such as 0.9) the agreement between the results of two approaches is in the acceptable range both for single-phase and solid/liquid-phase change. Two charts on the applicability of volume average method for single-phase and solid/liquid-phase change are presented. Originality/value The authors’ literature survey shows that it is the first time the applicability of volume average which is extensively used for analyzing the heat and fluid flow in a closed cell porous medium is investigated numerically.

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Analysis of Solid-Liquid Phase Change Under Pulsed Heating

Heat Transfer, Part A ◽

10.1115/imece2005-82553 ◽

2005 ◽

Author(s):

Shankar Krishnan ◽

Jayathi Y. Murthy ◽

Suresh V. Garimella

Keyword(s):

Porous Medium ◽

Natural Convection ◽

Liquid Phase ◽

Phase Change ◽

Pulse Width ◽

Energy Transport ◽

Metal Foams ◽

Governing Equations ◽

Pulsed Heating ◽

Solid Liquid

Solid/liquid phase change occurring in a rectangular container with and without metal foams subjected to periodic pulsed heating is investigated. Natural convection in the melt is considered. Volume-averaged mass and momentum equations are employed, with the Brinkman-Forchheimer extension to Darcy’s law to model the porous-medium resistance. A local thermal non-equilibrium model, assuming equilibrium melting at the pore scale, is employed for energy transport through the metal foams and the interstitial phase change material (PCM). Separate volume-averaged energy equations for the foam and the PCM are written and are closed using a heat transfer coefficient. The enthalpy method is employed to account for phase change. The governing equations for the PCM without foam are derived from the porous medium equations. The governing equations are solved implicitly using a finite volume method on a fixed grid. The coupled effect of pulse width and natural convection in the melt is found to have a profound effect on the overall melting behavior. The influence of pulse width, Stefan number, Rayleigh number and interstitial Nusselt number on the temporal evolution of the melt front location and the melting rate for both the cases with and without metal foams is investigated.

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