Experimental investigation of thermal performance and entropy generation of a flat-plate solar collector filled with porous media

•The effect of metal foam on the performance of a FPSC has been investigated.•Metal foam improves the absorbed energy parameter.•Metal foam causes a reduction of heat losses in lower values of Reynolds numbers.•The overall performance of the porous FPSC decreases with increase of flow rate.•Pressure drop irreversibility doesn’t have a main role on the entropy generation. The aim of the present experimental investigation is to examine the effect of metal foams asa passive thermal developer on the performance of water based flat plate solar collectors. Two similar wetted absorber collectors have been fabricated, the first is fully filled porous channel and the other one is empty channel. The thermal performance of the collectors is calculated based on ASHRAE standard and is compared with each other. The volume flow rate varies from 0.5 to 1.5lit/min. Results demonstrate that the porous media has a considerable effect on the characteristic curves, especially in the low flow rate. The maximum improvement of the absorbed energy parameter is 18.5%, which occurs in Reynolds number of 237 (i.e., 0.5lit/min). Moreover, porous media causes a usual pressure loss that increases nonlinearly with rising of the Reynolds number. For taking both the Nusselt number and pressure drop into account, an overall performance definition has been applied. Calculations show that the collector overall performance decreases with increasing the Reynolds number. The entropy generation analysis reveals that the portion of heat transfer irreversibility is more dominant in both collectors. Despite the greater pressure drop in porous channel, it doesn’t have considerable effect on the entropy generation.