Thermal and thermo-hydraulic behaviour of alumina-graphene hybrid nanofluid in minichannel heat sink: An experimental study

Thermal and pressure drop aspects of a minichannel heat sink have been investigated experimentally using distilled water as base fluid with alumina, graphene and alumina-graphene hybrid composition at 0.01% volume concentration. The reasons to select alumina-graphene as a potential nanomaterials combination for hybrid nanofluids are as: (i) thermal conductivity enhancement and (ii) to investigate the effect of morphology (shape and size of nanoparticles). Alumina (Al2O3) is oxide and has spherical shape whereas graphene is allotrope of carbon and has platelet shape. To examine the effect of different nanoparticles (in terms of shape, size and properties) dispersed hybrid nanofluid on hydrothermal bahaviour is an interesting study. Effects of Reynolds number (80-450), flow rate (0.1-0.5 L/min) and fluid inlet temperature (20-40 degrees C) are studied. The effects of uniform heat flux of 50 and 66.7 W/cm(2) on hydrothermal behaviour of a minichannel are also examined. The increment in convective heat transfer coefficient (HTC) is 30.93% at 30 degrees C with graphene/water composition nanofluid than water base fluid. A penalty of 23.82% has been observed in pressure drop with graphene/water nanofluid over base fluid. As inlet temperature increases, Nusselt number (Nu) increases while adverse effect is found in case of friction factor. Performance evaluation criteria (PEC) has been observed more than 1 for all nanofluids and hybrid nanofluids, which ensured that nanofluids act as a better electronic cooling agent than water. Al2O3 + graphene hybrid nanofluid delivers optimum comparison factor (HTC to pressure drop ratio) and lower entropy generation rate among used working fluids. Graphene/water nanofluid yields less comparison factor compared to other working fluids irrespective of high HTC. h/Delta p is favourable for nanofluid of unlike particles of hybrid composition (in terms of particle size, properties and shape) as compared to mono nanofluid and hybrid nanofluid having similar particles.