Systematic numerical analysis of thermal and hydraulic performance of nanofluids in double-tube heat exchangers

Abstract Heat exchangers are central to thermal management in industrial, energy, and HVAC systems, motivating continued interest in advanced working fluids that enhance thermal performance. This study presents a computational investigation of the thermo-hydraulic performance of three nanofluids (MWCNT, SiO₂, and ZnO) flowing through a double-tube heat exchanger under identical geometrical and boundary conditions. An experimentally validated CFD model is used to isolate the effects of flow rate, nanoparticle concentration, and operating temperature on heat-transfer enhancement and pressure drop. Relative to water, nanofluids enhance heat transfer rates by approximately 6–40%, with a pressure drop of 8–106%. Increasing the volumetric flow rate to 600 l/h and the nanoparticle concentration to 0.25% yields the most significant thermal enhancement among all nanofluids. However, thermo-hydraulic evaluation shows that maximum heat-transfer enhancement alone does not guarantee optimal performance. When thermal and hydraulic effects are combined using the performance evaluation criterion (PEC), SiO₂ at 0.25% concentration yields a thermo-hydraulic improvement of approximately 11% relative to water, whereas ZnO, despite enhanced heat-transfer performance, incurs substantially higher-pressure losses. At high operating temperatures, heat transfer is further intensified, with ZnO exhibiting the highest sensitivity to thermal loading. The results establish a controlled reference for nanofluid comparison and provide practical guidance for selecting working fluids for compact, high-efficiency heat exchangers in HVAC, energy recovery, and industrial thermal management applications.