International Journal of Energy Research, Vol.45, No.3, 4370-4384, 2021
Experimental study on thermal conductivity of mono and hybridAl(2)O(3)-TiO(2)nanofluids for concentrating solar collectors
Hybrid nanofluids with Therminol-55 as base fluid and TiO(2)and Al(2)O(3)as nano additives are investigated for parabolic trough collectors. Stable mono nanofluids based on Therminol-55 with Al(2)O(3)and TiO(2)nanoparticles, and hybrid Al2O3-TiO(2)nanopowder as additives are prepared by the two-step method. Oleic acid has been made as a surfactant. The impact of nanoparticle content and fluid temperature on thermal conductivity was studied using the transient hot-wire technique. Thermal conductivity exhibited an increase with an increase in both temperature and nanoparticle concentration. Al2O3-TiO(2)Therminol-55 hybrid nanofluids exhibit the highest increase of 33.5% in thermal conductivity followed by 27.06% in Al2O3-Therminol-55, and lowest rise of 21% is found in TiO2-Therminol-55 nanofluids. Synergetic effect of Al(2)O(3)and TiO(2)nanoparticles, increased Brownian motion, and filling of vacant spaces by smaller-sized TiO(2)nanoparticles in Al2O3-TiO(2)hybrid nanofluids lead to effective thermal network for enhanced thermal conductivity. Maximum thermal conductivity of 0.15 W/m-K is observed in the case of hybrid Al2O3-TiO(2)Therminol-55 nanofluid with 0.5 wt% concentration. Augmented thermal conductivity of HNF's leads to the efficient photothermal conversion in concentrating solar collectors. Further, a correlation for thermal conductivity with variation in nanoparticle content and the fluid temperature is proposed with R-2= 0.92.