Optimized modeling and experimental investigation on the thermal/electrical characteristics of MWCNT nanofluid for effective solar thermal applications

Abstract

In this study, a multi-objective optimization tool, response surface methodol-ogy (RSM) was utilized to determine the optimum thermal and electrical con-ductivity characteristics of a nanofluid consisting of solar glycol (SG)-water(H2O) (50:50) blend with multiwall carbon nanotube (MWCNT) for efficientsolar thermal applications. A three-level factorial optimization design involvedevaluating the effects of volumetric concentration and operating temperatureon the electrical and thermal conductivities of MWCNT-SG/H2O nanofluid.Further several experiments were carried out to establish a second-order poly-nomial correlation for evaluating of electrical and thermal conductivity proper-ties of the nanofluid. Optimization results indicated that higher operatingtemperature and volume concentration of MWCNT contributed to higher ther-mal and electrical conductivities in the MWCNT-SG/H2O nanofluid, respec-tively, demonstrating that the inherent physical and operational propertiespredominantly influence the behavior of the nanofluid. Further experimentalresults substantiated the optimization results with good agreement, indicatingthe direct effect of temperature and volume concentration on the performanceof the nanofluid. Thus, the optimum conditions for achieving competent ther-mal and electric characteristics in MWCNT-SG/H2O nanofluid were identifiedto be the operational temperature of 66.2 C and MWCNT volume concentra-tion of 0.125% in SG/H2O base fluid, respectively.