Experimental investigation on a solar parabolic trough collector for absorber tube filled with porous media

In the present work the efficiency of a solar parabolic trough has been investigated experimentally. An absorber filled with metal foam is used in order to improve the heat transfer and increase the efficiency of PTC (parabolic trough collector). The porosity of copper foam is 0.9 and the pore density is 30 PPI (pores per inch). The experiments were performed in different volume flow rates from 0.5 to 1.5 Lit/min and the standard of ASHRAE 93 was used to test the solar collector's performance. Friction factor and Nu number have been investigated for both cases. It was found that by increasing the mass flow rate, the efficiency of the collector was enhanced and the same pattern can be seen when absorber filled with copper foam. When absorber filled with metal foam the overall loss coefficient UL decreases by 45% and it causes to increase efficiency because less energy is lost.