HEAT-TRANSFER ENHANCEMENT OF MONO ETHYLENE GLYCOL-WATER-BASED SOLAR THERMIC FLUIDS DISPERSED WITH MULTIWALLED CARBON NANOTUBES IN A COILED TUBE HEAT EXCHANGER

The current research focuses on how the inclusion of multiwalled carbon nanotubes (MWCNTs) in mono ethylene glycol-water mixtures affects thermal conductivity, heat transfer, and dynamic viscosity for solar thermal applications. To achieve high stability in mono ethylene glycol-water mixtures, MWCNTs were oxidized and then dispersed at concentrations of 0.5, 0.25, and 0.125 wt.%. Zeta potential analysis was used to track the stability of the nanofluids over a two-month period. With the dispersion of MW-CNTs in the base fluids, there is a remarkable increase in thermal conductivity from 15 to 24%. The dy-namic viscosity variation is found to be minimal at high temperatures. Heat-transfer studies conducted on a specially designed test rig consisting of a coiled heat exchanger show that ethylene glycol-water mixtures dispersed with MWCNTs exhibit excellent performance under laminar conditions. Correla-tions for thermal conductivity, dynamic viscosity, and Nusselt number were obtained for all temperature conditions, mass fractions, and percentages of ethylene glycol. In the case of 100% mono ethylene glycol and mono ethylene glycol-water mixtures (90:10 and 80:20) as base fluids, the increase in heat-transfer coefficients of the corresponding nanofluids is up to 30, 26, and 25%, respectively.