Heat transfer characteristics of plate heat exchanger using hybrid nanofluids: effect of nanoparticle mixture ratio

Energetic and exergetic analyses of the plate heat exchanger are experimentally performed using Al2O3-TiO2 hybrid nanofluid as a coolant for sub-ambient temperature application to study the effect of nanoparticle volume ratio at various nanofluid flow rates ranging 2.0-4.0 lpm and inlet temperatures ranging 10-25 degrees C. The Al2O3-TiO2 hybrid nanofluids of 0.1% total volume concentration with different Al2O3-TiO2 ratios (5:0, 4:1, 3:2, 2:3, 1:4 and 0:5) are used as a coolant. Effects of nanoparticle mixture ratio, flow rate and inlet temperature on the heat transfer rate, heat transfer coefficient, pump work, performance index, and second law efficiency are investigated. Correlations are proposed to predict the Nusselt number for DI water as well as hybrid nanofluid. A maximum enhancement of around 16.91% and 4.5% are observed for convective heat transfer coefficient and heat transfer rate with Al2O3 (5:0) hybrid nanofluid along with 0.013% enhancement (insignificant) in the pump work for TiO2 (0:5) hybrid nanofluid. The maximum reduction in exergetic efficiency of 4.01% is observed for TiO2 (0:5) hybrid nanofluid. The study shows that the energetic and exergetic performances decrease continuously with the increase of the TiO2 ratio in the mixture, yielding no optimum nanoparticle mixture ratio.