Numerical Investigation of Thermodynamic Performance and Entropy Generation in an Optimized Nanofluid Tubular Heat Exchanger

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Abstract
This numerical study investigates the thermo-hydraulic and thermodynamic performance of a rectangular-channel heat exchanger incorporating isothermal circular tubes, with particular emphasis on geometric design strategies suitable for compact thermal systems. Two configurations with identical total heat transfer surfaces are analyzed: baseline geometry comprising four aligned tubes (G1) and an optimized geometry consisting of eight tubes arranged in two parallel rows (G2) maintaining the same exchange surface. Laminar forced convection is also considered. For the baseline configuration, results show a pronounced thermal shadowing effect, leading to a reduction of nearly 50% in the heat transfer contribution of downstream tubes.In contrast, optimized geometry significantly improves flow redistribution and temperature field uniformity. An optimal inter-row spacing, equal to 0.1, is identified as a robust design parameter, maximizing the total average Nusselt number. At this spacing, all heated surfaces actively contribute to heat transfer, resulting on an overall heat transfer enhancement of approximately 20–40% compared to the baseline configuration. Entropy production analysis shows that increasing Re strongly intensifies thermal irreversibility, while viscous irreversibility exhibits a moderate increase. The impact of nanoparticles addition, carried out on the optimal configuration of G2, shows that heat transfer increases by about 8% for a nanoparticle concentration of 4% at high Re values, with an insignificant change in the Bejan number. The present findings demonstrate that geometric optimization represents a more effective and energetically sustainable enhancement strategy than nanofluid addition for compact tubular heat exchangers.

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