Numerical investigation of laminar heat transfer and fluid flow characteristics of Al2O3 nanofluid in a double tube heat exchanger

Purpose - The purpose of the study is to numerically investigate the characteristics of laminar heat transfer and fluid flow in a double tube heat exchanger (DTHE) using water-aluminum oxide (Al2O3) nanofluid. The study examines the effects of nanofluid in both counter and parallel flow configurations. Furthermore, an exergy analysis is conducted to assess the impact of nanofluid on exergy destruction. Design/methodology/approach - The single-phase method has been used for Al2O3 nanoparticles in water as base fluid in a laminar regime for Reynolds numbers from 400 to 2,000. The effects of nanoparticle volume fractions (0 to 0.1), Nusselt number, Reynolds number, heat transfer coefficient, pressure drop, performance evaluation criteria (PEC) and the impact of counter and parallel flow direction have been studied. Findings - The findings indicate that the incorporation of nanoparticles into the water enhances the heat transfer rate of DTHE. This enhancement is attributed to the improved thermal properties of the working fluid and its impact on the thermal boundary layer. Nusselt number, heat transfer coefficient, and PEC increase by approximately 19.5%, 58% and 1.2, respectively, in comparison to pure water. Conversely, the pressure drop experiences a 5.3 times increase relative to pure water. Exergy analysis reveals that nanofluids exhibit lower exergy destruction compared to pure water. The single-phase method showed better agreement with the experimental results compared to the two-phase method. Originality/value - Dimensionless correlations were derived and validated with experimental and numerical results for the Nusselt number and PEC for both counter and parallel flow configurations based on the Reynolds number and nanoparticles volume fraction with high accuracy to predict the performance of DTHE without performing time-consuming simulations. Also, an exergy analysis was performed to compare the exergy destruction between nanofluid and pure water.