Numerical Investigation and Optimization of Heat transfer and ExergyLoss in Geometrically Modified Tube Heat Exchangers Using Nanofluids

Abstract

This study numerically investigates the thermal and energy performance of double helical and conical coil heat exchangers using CFD simulations under turbulent flow conditions. The analysis focuses on optimizing key design parameters—coil geometry, coil pitch (16 mm and 20 mm), and hot and cold flow rates (1.5 to 6 LPM)—while evaluating the impact of different working fluids: water, 0.4% CuO, 0.4% Al₂O₃, and 0.4% Fe₂O₃ nanofluids. The Taguchi method (L₁₆ orthogonal array) was employed to identify optimal parameter combinations for maximizing heat transfer and minimizing exergy loss across 16 simulation cases. Simulation results revealed that Nusselt number increases with both cold rates, particularly for Al₂O₃ nanofluid, which demonstrated the highest heat transfer performance. In contrast, exergy loss increases with increasing cold flow rate, while water exhibits the lowest and most stable exergy loss across flow conditions. Additionally, increasing coil pitch was found to reduce the heat transfer coefficient, especially in helical configurations. The Taguchi analysis identified that: The optimum combination for maximum heat transfer is a conical coil with 16 mm pitch, 0.4% Al₂O₃ nanofluid, cold flow rate 6 LPM, and hot flow rate 1.5 LPM. The optimum condition for minimizing exergy loss is a conical coil with 16 mm pitch, water, and both cold and hot flow rates at 1.5 LPM. This study provides a comprehensive framework for enhancing the design of compact coil heat exchangers for energy-efficient applications.