Heat Transfer Inside Tubular Heat Exchanger Using Tri-Hybrid Nanofluid at a Constant Total Volume Fraction

This study experimentally investigates the forced convective heat transfer performance of a water-based tri-hybrid nanofluid containing ZnO, CuO, and B2O3 nanoparticles flowing through an Armfield HT31X tubular heat exchanger under counter-flow. The tri-hybrid nanofluids were prepared using a two-step method with an average nanoparticle size of 50 nm and a fixed total volume concentration of 2.1%. The objective was to evaluate thermal performance of tri-hybrid nanofluids with different nanoparticle concentration while maintaining the same overall volume fraction. Four concentration configurations were examined. Experimental results reveal that the heat transfer performance is maximized when the nanoparticles are present in equal proportions. Specifically, configuration containing 0.7% ZnO, 0.7% CuO, and 0.7% B2O3 exhibited the highest convective heat transfer maximization among all tested cases with 44% enhancement compared with the base fluid. Reducing the CuO concentration to 0.6% resulted in the second-best performance, while further reductions in ZnO or B2O3 volume fractions led to comparatively lower heat transfer maximization. For all configurations, Nusselt and Peclet numbers increased with increasing Reynolds number. Although friction factor of the nanofluids was higher than that of pure water, pressure-drop remained comparable across all cases. These findings demonstrate the significant potential of tri-hybrid nanofluids for enhancing thermal performance.