Experimental comparison of optical properties of nanofluid and metal foam for using in direct absorption solar collectors

Abstract Open-cell porous metal foams and nanofluids are among the solar absorbers for radiation absorption in solar collectors. The optical properties of absorbers have an important role in the thermal performance of direct and volumetric absorption solar collectors. In the present work, porous foam and nanofluid are made from the same materials and their optical properties are measured experimentally. The spectrophotometric experiments are performed on the produced porous metal foams and water based nanofluids from two materials namely SiC and CuO. In water-saturated porous foams, the effect of porosity (90% and 95%), pore diameter (10PPI-30PPI) and type of material (CuO and SiC) are survived while the influence of volume fraction and kind of nanoparticles in water based nanofluids are examined. Obtained results indicate that in SiC and CuO nanofluids, by increasing concentration from 0.01 vol% to 0.1 vol%, extinction coefficient increases by 20% and 176%, respectively. Moreover, the extinction coefficient in porous foams increases by decreasing the porosity and pore diameter. Comparing the results of nanofluid with porous foam of the same material shows that there is no significant difference in extinction coefficient for CuO nanofluid (0.1 vol%) and CuO porous foam (90%, 30PPI) while the extinction coefficient of SiC porous foam (90%, 20PPI) is 4 times higher than its nanofluid (0.1 vol%).