Optimal Nanoparticle Size in SiO₂/Al₂O₃-Water Nanofluids for Enhancing Intercooler Thermal Enhancement: A Conjugate Heat Transfer Study

This study investigates the optimal nanoparticle size selection in SiO₂/Al₂O₃-water nanofluids for enhancing the thermal performance of gas turbine intercoolers. A novel numerical model is developed for fluid-solid conjugate heat transfer analysis within the intercooler, considering the impact of nanofluid viscosity on flow dynamics and thermal exchange. Unlike conventional models using constant properties, the proposed approach incorporates experimentally fitted, temperature-dependent viscosity and thermal conductivity updated via UDF and fully coupled with the energy and fluid-solid interface equations. This yields a more accurate representation of nanofluid behaviour under varying loads, achieving < 3% prediction error in experimental validation. The effects of nanoparticle size and volume fraction on cooling performance are systematically explored using the enhanced heat transfer factor, η. Results demonstrate that increasing the nanoparticle volume fraction enhances liquid-side heat transfer by up to 24.7% (30 nm SiO₂/water at 100% load), albeit with a concomitant rise in gas-side pressure drop (up to 4.02%). With fixed volume fractions, SiO₂/water nanofluid exhibits an optimal particle size of 30 nm, whereas heat transfer capacity of Al₂O₃/water nanofluid decreases with increasing particle size. Overall, 30 nm SiO₂/water nanofluid is identified as the most effective coolant, and no Al₂O₃/water formulation exceeds its performance.