Mixed Convection and Entropy Generation in a Double-Pipe Heat Exchanger Using Hybrid Nanofluids and Helical Baffles

Abstract

This paper reports a complete numerical and experimental study of mixed convection heat transfer and entropy generation in a double pipe heat exchanger working under the effect of hybrid nanofluids and inserted helical baffles. The working fluid is water-based hybrid nanofluids, including multi-walled carbon nanotubes and alumina nanoparticles (MWCNT-Al2O3) which are used to enhance thermal conductivity and overall heat transfer efficiency. A three-dimensional computational fluid dynamics (CFD) model is developed and solved using finite volume methods, and experimental data are collected to validate the numerical predictions. The influence of Reynolds number, nanoparticle volume concentrations and geometrical configurations of the helical baffles on the Nusselt number, friction factor and total entropy generation is analyzed in detail. Moreover, recent developments in thermophysical modeling show that hybrid suspensions possess better stability and convective transport abilities under high temperature gradients. The results show the considerable enhancement of the thermal performance of hybrid nanofluids with inserted helical baffles as compared with conventional base fluids. Finally, the total entropy generation reduces significantly at the optimum nanoparticle concentrations, thereby confirming the thermodynamic superiority of the proposed system.