Numerical simulation of subcooled flow boiling of nanofluids in metal foam embedded tubes for performance enhancement

Abstract

This study numerically investigates sub-cooled flow boiling heat transfer and hydraulic performance in horizontal tubes filled with metal foam, using nano fluids as the working medium. Key measurable parameters, such as heat transfer coefficient (HTC) and pressure drop, are analyzed across various metal foam configurations, including porosity (80 %, 85 %, 90 %) and pore density (10, 20, 30 PPI), under varying mass flow rates (210–400 kg/m²s), heat flux (100–230 kW/m²), and inlet temperatures (10–80 °C). The HTC, a critical metric for quantifying energy transfer efficiency, reaches peak values of 25 kW/m²K for water and 22.5 kW/m²K and 19 kW/m²K for CuO/H₂O and Al₂O₃/H₂O nano fluids, respectively. Pressure drop, another essential performance metric, is strongly influenced by the metal foam's structure and nano fluid concentration, with denser foams exhibiting the highest pressure losses. The thermal performance index (TPI), which integrates energy efficiency improvements by balancing heat transfer enhancement with the energy losses due to pressure drop, consistently exceeds one for both water and nano fluids, with water achieving a TPI of 1.5. This indicates measurable energy efficiency improvements, highlighting the potential of optimized foam-nano fluid combinations to enhance heat exchanger performance. The numerical models used in this study are validated against experimental data, demonstrating strong agreement for both HTC and pressure drop predictions. These results offer a foundation for designing heat exchangers with a focus on maximizing energy efficiency through quantifiable improvements in heat transfer performance and pressure loss reduction.