Investigation on Heat Transfer performances of Nanofluids in Solar Collector

Nanofluids containing Al2O3, ZnO, and MgO nanoparticles were prepared with distilled water as base fluid by violent stirring and ultrasonic dispersing. The forced convective heat transfer performances of the as-prepared nanofluids in tubular solar collector were investigated. The experimental results showed that the heat transfer efficiencies of Al2O3, ZnO, and MgO nanofluids were all increased in comparison to distilled water. For 1.0% vol. Al2O3, ZnO, and MgO nanofluids, the difference in temperature between nanofluids and distilled water all could exceed 3 C in a day's cycling. In daytime, from 6:00 a.m. to 18:00 p.m., the maximum differences in temperature of nanofluids and distilled water appeared at about 10:00 a.m., while the maximum temperatures were achieved at about 15:00 p.m. for both nanofluids and distilled water. In night, the temperatures of nano-fluids still keep more than 1 degrees C higher than distilled water, which indicated that nanofluids could retain more heat energy. The viscosities and heat transfer efficiencies augmented with concentration increasing for ZnO nanofluids. Even at 0.2% vol. concentration, the difference in temperature between ZnO nanofluids and distilled could reach 2.55 degrees C. Based on low viscosity and excellent heat transfer performance, 0.2% vol. concentration ZnO nanofluid was an attractive option to be applied in solar energy utilization.