Thermal analysis in the evaporation of flowing thin liquid film confined by gradient or double-layered porous layer subjected to air jet impingement

Abstract

The porous metal foam subjected to air jet impinging is set above thin liquid fluid passing through the heating surface to maintain its thickness, in which the heat from heating surface is released in the convection with the thin liquid film to the surroundings, as well as across the thin liquid film and metal foam to the outside surface where the evaporation and convection occur. Local thermal non-equilibrium (LTNE) occurs, so the double energy equations together with Brinkman-Darcy model are employed to describe the heat transfer in metal foam, as well as N–S equations account for the flow of thin liquid film. The effects of the different porosity and particle diameter distributions (e.g. constant, linearly increasing/decreasing and stepwise increasing/decreasing), as well as thickness ratio between the bottom and upper layers with different porosities and particle diameters in stepwise variation on the cooling performances are numerically analyzed. The simulations are validated with the published experiment data. The lower heating surface and larger heat transfer coefficient (HTC) occur in the presented mode with the relatively lower porosity and particle diameter. The 67.47% rise ratio of the peak HTC in the mode with porosity of 0.3 happens than that with porosity of 0.9. The optimized thickness ratio together with the porosity and particle diameter in the bottom and upper layers influence the heat to be transported in the convection with liquid fluid to the downstream side or across the metal foam to its outside surface. All results can be considered into the promotion and application of coupling the air jet impingement and porous metal foam above thin liquid film to enhance heat transfer.