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 multi-walled carbon nanotubes (MWCNTs) in mono-ethylene glycol-water mixtures affect 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 MWCNTs in the base fluids, there is a remarkable increase in thermal conductivity from 15 to 24 percent. The dynamic 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. Correlations for thermal conductivity, dynamic viscosity, and Nussult 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.