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 0.2 to 1.5vol%, 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 1.5vol%. the results indicated that thermal conductivity enhanced with decreasing particle size and increasing with temperature. for nanofluids containing 10-15 nm and 45-50 nm particle sizes, the enhancements were 26.3 and 22.8% at 40oc, 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 (1.5 vol%). for nanofluids with 10-15 nm and 45-50 nm particle sizes, the average heat transfer coefficient enhancement was 18.1 and 14.9% at re=1115, respectively.