The thermal management of industrial process equipment — including pharmaceutical reactor cooling, dairy pasteuriser heat recovery, and automotive radiator circuits — faces increasing heat flux density demands as process intensification strategies reduce equipment footprint while maintaining or increasing throughput. Conventional working fluids (water, ethylene glycol, mineral oil) have inherent thermal conductivity limitations that constrain heat exchanger design, driving interest in nanofluids — colloidal suspensions of nanoparticles in base fluids — that exploit nanoparticle's high thermal conductivity and large surface-area-to-volume ratio to enhance effective fluid thermal conductivity beyond achievable with conventional fluid additives. This study presents a systematic experimental, CFD-validated, and multi-criteria optimisation investigation of Al₂O₃-Cu hybrid nanofluid (volume concentration 0-2%, prepared by two-step method with CTAB surfactant stabilisation) in a seven-shell-pass counter-flow shell-and-tube heat exchanger against water and single-component (Al₂O₃, TiO₂, Cu, SiO₂) nanofluid benchmarks. Nusselt number correlations are developed for laminar and turbulent regimes covering Re 500-8,000. ε-NTU curves for parallel, counter, and cross-flow configurations are compared experimentally and via Ansys FLUENT 3D CFD with validated mesh independence. Fin temperature distribution for three fin geometries (straight, annular, pin array) is measured by IR thermography and compared with analytical solutions. TOPSIS multi-criteria decision analysis ranks the nanofluids on Nu enhancement, pressure drop penalty, thermal conductivity, viscosity increase, and cost effectiveness. Exergy analysis quantifies the irreversibility minimisation achieved by each working fluid.
Prof. Yuki Tanaka (Sat,) studied this question.