Experimental investigation on the heat transfer performance of evacuated tube solar collector using CuO nanofluid and water

The efficiency of an evacuated tube solar collector was experimentally measured and analyzed according to the size of CuO nanoparticle and the concentration of the CuO nanofluid. In addition, the efficiency of the evacuated tube solar collector using CuO nanofluid as a working fluid was compared with that when water was used. As a result, the efficiency of the evacuated tube solar collector improved as the concentration of the CuO nanofluid increased at low concentration. Further, the efficiency of the evacuated tube solar collector was higher at a mass flux rate of 598 kg/sm(2) than at 420 kg/sm(2). The highest efficiency of the solar collector with 40 nm-CuO nanofluid was 69.1 %, an improvement of 2.0 % compared to 80 nm-CuO nanofluid. The most optimal concentration of the 40 nm-CuO nanofluid was 0.5 vol% and an improvement of thermal efficiency was 7.2 % compared to water. In addition, at this concentration, the efficiency improved by 4.4 %, 2.3 % and 0.3 % compared to that at concentrations of 0.1 vol%, 0.3 vol% and 0.7 vol%, respectively. The use of CuO nanofluid in the evacuated tube solar collector can improve the efficiency and can maintain the high efficiency for wide operating conditions compared to water.