ZnO⿿propylene glycol⿿water nanofluids with improved properties for potential applications in renewable energy and thermal management

Abstract

ZnO⿿propylene glycol⿿water (ZnO⿿PG⿿water) nanofluids of higher thermal conductivity and lower viscosity than PG⿿water mixture were prepared by the sequential method. The unsteady state heat transfer performance of ZnO⿿PG⿿water nanofluids revealed 16.5% increase in heat transfer rate for 2vol% nanofluids under constant heat flux conditions. The coolant side heat transfer coefficient increased by 29% on use of 2vol% ZnO⿿PG⿿water nanofluid for heat removal from constant temperature source (simulated thermal energy storage). The collection efficiency of solar collectors employing ZnO⿿PG⿿water nanofluid was found to increase linearly with nanoparticle concentration with about 9% increase in collection efficiency for 2vol% nanofluid. These results summarily indicate that ZnO⿿PG⿿water nanofluids perform better than PG⿿water mixture for solar energy collection and discharging of solar thermal energy storage.