Thermal enhancement in a flat-plate solar water collector by flow pulsation and metal-foam blocks

This study presents a numerical analysis of forced pulsating convection flow in a parallel-plate channel of solar water collector mounted with multiple metal-foam blocks. Both transient Darcy-Brinkman-Forchheimer flow model and two-equation energy model based on local thermal non-equilibrium (LTNE) are used to characterize the thermo-flow fields inside the porous regions. Solution of the coupled governing equations for the fluid/porous composite system is obtained by utilizing a control-volume method through the use of a stream function-vorticity approach. This study details the effects of variations in the Darcy number, pulsation frequency and amplitude, Reynolds number, and porosity, to illustrate important fundamental and practical results. The results show that the periodic alteration in the structure of recirculation flows, caused by metal-foam blocks and flow pulsation, will significantly enhance the heat transfer rate on heat source surface. For fixed Re, the findings show that an increase in the solid-fluid interfacial heat exchange results in a more obvious local thermal equilibrium (LTE) phenomenon, and a larger heat transfer augmentation of solar thermal collector. Besides, two useful correlated equations to predict Num are proposed.