Experimental study on heat transfer and pressure drop characteristics utilizing three types of water based nanofluids in a helical coil under isothermal boundary condition

Background: Nanofluids are an innovative attractive challenging field suitable for many heat transfer applications. The helical coil is preferred due to compactness and additional curvature flow disturbance. Method: Heat transfer and pressure drop characteristics of Ag, ZnO and TiO2 water based nanofluids through helical coil tubes under isothermal boundary conditions are experimentally investigated with 0.25% nano particles volume concentration Ag/water, ZnO/water and TiO2/water nanofluids. Five coils are constructed with different coil pitches of 2, 4, 6, 8 and 10 cm. The flow rate of the nanofluid varies between 1 to 3.5 L/min with inlet temperature from 30 degrees C to 60 degrees C. Findings: The results showed that increasing the coil pitch reduces Nusselt number and pressure drop. The nanofluids have a positive impact on the enhancement of heat transfer but with a pressure drop penalty. Average Nusselt number enhancement up to 11.8 %, 17.8 % and 28.7 % was achieved at Ag/water, ZnO/water and TiO2/water with average pressure drop increasing up to 25.4%, 23.5% and 28.5% respectively. The results showed that an increase in coil pitch decreases hydrothermal performance index (HTPI) and utilizing nano fluids increases HTPI for all types of nanofluids Ag/water, ZnO/water and TiO2/water. Novel correlations were developed to predict Nusselt number and pressure drop. (c) 2021 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.