Stability and Thermo-Physical Properties of Ethylene Glycol Based Nanofluids for Solar Thermal Applications

Abstract

This article summarizes research involving the evaluation of the thermo-physical properties of ethylene- glycol-based solar thermic fluids oxidized multi-walled carbon nanotubes. Nanofluids were prepared with Ethylene glycol and water as base fluids in 100:0, 90:10 and 80:20 ratios. Base fluids of three categories were dispersed with surfactant-assisted multi-walled carbon nanotubes (MWCNTs) and oxidized MWCNTs in the weight fractions of 0.125, 0.25, and 0.5 percentages to check the influence of surface modification technique on the thermophysical properties. The variation in zeta potential is studied to examine the dispersion stability during 2 months. Thermal conductivity and dynamic viscosity were measured by hot disk method and Anton paar viscometer, respectively. Significant enhancement of thermal conductivity by 15 to 24 % was observed when the base fluids are dispersed with oxidized MWCNTs. In the case of nanofluids dispersed with surfactant-assisted MWCNTs, the improvement is significantly less compared to oxidized MWCNTs. Nanofluids' dynamic viscosity is found to be higher compared to base fluids in the temperature range of 50 to 70 oC. A comprehensive mathematical equation suitable for all weight fraction of MWCNTs and volume percentages of Ethylene glycol was developed, which can forecast the temperature range. The correlation could fit well with the experimental data in reasonable limits.