Intensified convective heat transfer using ZnO nanofluids in heat exchanger with helical coiled geometry at constant wall temperature

The present work deals with the experimental determination of enhancement in the heat transfer using ZnO nanofluid in helical copper tube heat exchanger at constant wall temperature. ZnO nanoparticles were prepared with aid of ultrasonic irradiations using zinc nitrate and KOH as raw materials. The effect of Reynolds number and ZnO nanoparticle addition to the base fluid on heat transfer coefficient and Nusselt number was examined. Around 62.80% and 136% enhancement in thermal conductivity ratio at 40 °C and 50 °C, respectively, was observed for 0.5 vol% loading of ZnO nanoparticles in nanofluids. 18.6% enhancement in the Nusselt number was observed for 0.25 vol% of ZnO nanoparticles in nanofluid at the exit of the test section. This is attributed to the combination of helical coil with ZnO nanofluid which gives significant effect on heat transfer enhancement.