Driven by the growing need for high-efficiency thermal systems, the optimization of heat exchanger performance at low Reynolds numbers has become a crucial area of research. To enhance the thermohydraulic performance of heat exchangers at low Reynolds numbers, this study investigates the synergistic use of twisted elliptical tubes and nanofluids. A comparative analysis of the heat transfer and pressure drop performance was conducted for circular, elliptical, and twisted elliptical tubes under both single-phase and two-phase model. The impact of nanofluid type on heat transfer enhancement was further examined. The two-phase mixture model provided more accurate predictions than the single-phase model. Results also demonstrate that the twisted elliptical tube exhibits optimal performance due to intensified secondary flows and swirl. Among the nanofluids, graphite nanofluids achieved the most effective heat transfer enhancement. Higher nanoparticle concentrations led to more pronounced improvements in heat transfer coefficient for the twisted elliptical tube. Performance evaluation criteria consistently indicate superior overall thermo-hydraulic efficiency for the twisted elliptical tube configuration. In conclusion, the combination of twisted elliptical tubes and higher-concentration nanofluids offers the best thermo-hydraulic performance at low Reynolds numbers. The findings provide valuable insights for designing efficient heat exchangers in low-velocity thermal systems.
 

Nanofluids;,Twisted elliptical tube;,Two-phase flow;,Performance evaluation criteria.