Effects of functionalized single walled carbon nanotubes on thermal performance of antifreeze: An experimental study on thermal conductivity

In this experimental work, the antifreeze composed of 50 vol.% water and 50 vol.% ethylene glycol has been used as the base fluid. The functionalized single walled carbon nanotubes (F-SWCNTs) with different volume fractions (0.025, 0.055, 0.08, 0.125, 0.25, 0.53 and 0.65%) have been suspended to the base fluid by ultrasonic waves. The KD2 Pro Thermal Properties Analyzer was employed to measure thermal conductivity of the prepared samples at different temperatures. Results showed that the thermal conductivity improves proportionally with augmenting the concentration and temperature. Measurements also indicated that in greater volume fractions (φ > 0.53%), temperature rise has a greater influence on the nanofluids thermal conductivity. Since no valid and applicable correlation is available to predict the thermal conductivity of F-SWCNTs/EG-water nanofluid, a correlation has been offered for predicting the thermal conductivity of this nanofluid using experimental results. The maximum value of deviation boundary was 2.4%. Finally, forced convective heat transfer in a smooth tube in absence and presence F-SWCNTs was investigated. Thermal performance of antifreeze (η), defined as the ratio of heat transfer coefficient to pressure drop, was analyzed and results made a border for the use of present nanofluids. The argumentations indicated that the present nanofluid was efficient as long as relative viscosity is lower than the 0.465 power of the thermal conductivity ratio.