Anomalous enhancement of convective heat transfer with dispersed SiO2 particles in ethylene glycol/water nanofluid

The heat transfer coefficients and friction factor for SiO2- ethylene glycol/water (50 wt%) nanofluids, with the SiO2 particle diameter ranging from 100 to 1000 nm, and particle weight concentration ranging up to 10%, were measured for flow in a circular tube under constant temperature boundary conditions. The measurements were performed under turbulent flow conditions, wherein the temperature at the entrance of the test section was 353.15 K. Both the heat transfer coefficient and friction factor of the SiO2 nanofluids are higher than those of the ethylene glycol/water system. The heat transfer coefficient of the SiO2 nanofluids increases with particle concentration up to 7 wt% and saturates thereafter. Interestingly, the heat transfer coefficient of the SiO2 nanofluids depends on the particle diameter and it attains maximum value at the diameter of 300 nm and solid fraction of 7 wt%. The heat transfer coefficient of SiO2 nanofluids increases by up to 25% as compared with that of the ethylene glycol/water solution. Additionally, a new correlation formula is proposed to correlate the Nusselt numbers and the Reynolds numbers for the SiO2 nanofluids. (C) 2020 Elsevier Ltd. All rights reserved.