Entropy Generation of Graphene Nanoplatelets in Micro and Mini Channels: Nanofluid Flow in Automotive Cooling Applications

Abstract

The present study examines the entropy generation of graphene nanoplatelet (GnP) suspended in different basefluids, theoretically. GnP in water (W), ethylene glycol (EG) and ethylene glycol- water (EGW, 1:1) was examined under laminar flow state in a unit length mini and micro-channel of 3mm and 0.05mm diameter. The coefficient of conductivity (Ck) and viscosity (Cμ) of the nanofluid were determined from experimental analysis and their order of magnitude were established for analysis of entropy generation in mini and micro-channels. Entropy generation by fluid friction (Ṡgen, ff) in the channels containing EG was higher than with W and EGW by 75.6% and 79.9%, respectively. Thermal irreversibility (Ṡgen, th) of W was lower by132.9% and 58.2% compared to EG and EGW. Sgen,th in all the fluids decreased with increased solid volume fraction in mini-channels, while, Ṡgen,ff increased with increase in volume fraction for micro-channels. Total entropy generation (Ṡgen, tot) of water was lower by 75.6% and higher by 64.8% compared to EG and EGW, respectively in a micro-channel, whereas Ṡgen, tot of water was lower by 123.7% and 38.4% compared to EG and EGW, respectively. As GnP volume fraction was increased in the basefluids, entropy generation ratio decreased, highlighting the positive influence of thermal properties of the nanofluid. A lower Bejan number for water (Bew), 36.8% and 358.9% were observed compared to EG and EGW in micro-channel, whereas Bew was lower by 3.8% and 13.8% when compared to EG and EGW nanofluids in the mini channel.