Investigation of Thermal Conductivity and Convective Heat Transfer Coefficient of Water-Based ZnO Nanofluids

Nanofluids are stable suspensions of nanoparticles in a conventional fluid. They have shown superior potential in heat transfer enhancement. In this research, ZnO/water nanofluids were prepared at various concentrations from ۰.۲ to ۱.۵vol%, and their thermal conductivity was measured. The results showed that the thermal conductivity of ZnO/water nanofluids depends on particle concentration and increases non-linearly with the volume fraction of nanoparticles. The effects of particle size and temperature on the thermal conductivity were also investigated at ۱.۵vol%. The results indicated that thermal conductivity enhanced with decreasing particle size and increasing with temperature. For nanofluids containing ۱۰-۱۵ nm and ۴۵-۵۰ nm particle sizes, the enhancements were ۲۶.۳ and ۲۲.۸% at ۴۰oC, respectively. In this research, the convective heat transfer coefficient of ZnO/water nanofluids with the above particle sizes was also measured under laminar flow in a horizontal tube heat exchanger. It was observed that both nanofluids showed higher heat transfer coefficients compared to the base fluid at a constant concentration (۱.۵ vol%). For nanofluids with ۱۰-۱۵ nm and ۴۵-۵۰ nm particle sizes, the average heat transfer coefficient enhancement was ۱۸.۱ and ۱۴.۹% at Re=۱۱۱۵, respectively.

کلیدواژه ها:

Nanofluid ، Thermal conductivity ، heat exchanger ، laminar flow ، Convective heat transfer ، ZnO nanoparticles