Particle ratio optimization of Al2O3 -MWCNT hybrid nanofluid in minichannel heat sink for best hydrothermal performance

Interesting hydrothermal behavior of hybrid nanofluid containing combination of dissimilar particles (completely different in terms of shape, size and properties) by changing their ratio is unexplored yet, which is analyzed experimentally for minichannel heat sink. Nine parallel rectangular minichannels are used in the heat sink each of which has 1 mm width, 3 mm depth and 30 mm length. Al2O3-MWCNT/water hybrid nanofluid of 0.01% volume concentration with various nanoparticle mixture ratios is used as coolant to analyze the effect of Reynolds number and working fluid inlet temperature. Nanoparticles mixing ratios (5:0, 4:1, 3:2, 2:3, 1:4 and 0:5) have been taken as volume ratios. Convective heat transfer coefficient, Nusselt number, pressure drop and friction factor increase with an increase in fraction of MWCNT in hybrid nanofluid. A maximum enhancement of 44.02% has been observed for the convective heat transfer coefficient with MWCNT (5:0) hybrid nanofluid as compared to water. Maximum pressure drop has been increased by 51.2% over base fluid at an inlet temperature of 20 degrees C for the MWCNT (5:0) hybrid nanofluid. Inlet fluid temperature has negative effect on pressure drop and positive effect on heat transfer. The observed optimum volumetric mixing ratio of Al2O3 and MWCNT is around 3:2, for which hybrid nanofluid yields maximum heat transfer coefficient to pressure drop ratio. Performance evaluation criteria (PEC) has been evaluated greater than 1 for all the nanofluids, which concludes that nanofluids are better option as compared to conventional fluid (DI water). Based on the experimental data, correlations for Nusselt number and friction factor have been introduced with R-2 values of 98.8% and 96.3%, respectively, and compared with available correlations.