Investigation on Heat Transfer performances of Nanofluids in Solar Collector

摘要

Nanofluids containing Al_2O_3, 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 Al_2O_3, ZnO, and MgO nanofluids were all increased in comparison to distilled water. For 1.0% vol. Al_2O_3, 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 nanofluids still keep more than 1 °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 °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.