Experimental Investigation on Thermo-Hydraulic Performance of a Fin and Tube Heat Exchanger for Battery Thermal Management

Battery thermal management is crucial for ensuring the performance, safety, and longevity of batteries, particularly in electric vehicles and energy-storage systems. Direct air-cooling systems are widely used because of their simplicity, cost-effectiveness, and reliability. However, while increasing the air velocity leads to a higher heat-dissipation efficiency, it also leads to higher power consumption and noise. This study aims to experimentally and numerically analyze the flow and heat transfer characteristics of a typical flat fin-and-tube heat exchanger used in battery thermal management. This research focuses on investigating the effects of operational parameters, including air velocity, temperature difference between the coolant and air, and coolant mass flow rate, on the heat transfer performance.

Both experimental and numerical approaches were employed to evaluate the heat transfer performance of the heat exchanger.The experimental setup featured a copper-fin and 316L stainless steel tube unit with two fans to enhance forced convection, and tests were conducted across air velocities of 2.1-6.1 m/s, coolant-to-air temperature differences of 20-40 ℃, and coolant mass flow rates of 0.35-0.55 kg/s. The performance was evaluated using the heat transfer coefficients, pressure drops, and overall heat dissipation rate, with an uncertainty of 6.5% and repeatability within 2.2%. A three-dimensional steady-state CFD model of a unit was developed by adopting noslip wall conditions, symmetry/periodic boundaries, and wall contact resistance with the corresponding boundary conditions. Mesh independence was achieved with approximately 1.41 million cells, solver residuals established at 10^-7, and parametric analysis was conducted for tube outer diameters ranging from 3 mm to 6 mm and bundle spacings from 7 mm to 11 mm.

The results illustrate the effects of air velocity, temperature difference, and coolant mass flow rate on the thermohydraulic performance of the heat exchanger. As the air velocity increases, the airside heat transfer coefficient improves owing to the enhanced convective heat transfer, with a maximum increase of 102.1% in the 2.1-6.1 m/s velocity range. Similarly, increasing thetemperature difference from 20 ℃ to 40 ℃ leads to a rise in the heat transfer coefficient by 19.1% to 28.9%, showing a nearly linear relationship. A higher coolant mass flow rate enhances the heat transfer rate, leading to a proportional increase in the heat transfer coefficient. Numerical simulations confirm these trends and provide insights into the flow behaviors, including the formation of cross-flow vortices that enhance heat transfer, particularly at higher air velocities. The simulations also reveal that transverse vortices form in the fin gaps, which shrink with increasing air velocity. Furthermore, the simulation results indicate that the optimal pipe diameter for maximizing heat transfer performance is 6 mm, with a tube bundle pitch of 9 mm.

This study concludes that the air velocity, coolant temperature difference, and coolant mass flow rate are the primary factors influencing the heat transfer performance of flat fin-and-tube heat exchangers for battery thermal management. Both the experimental and numerical results indicate that increasing the air velocity and coolant mass flow rate significantly enhances the heat transfer. Furthermore, the temperature difference between the coolant and air directly affects the heat transfer coefficient. Based on these findings, the optimal heat exchanger design should have a pipe diameter of 6 mm and tube bundle pitch of 9 mm. This configuration provides the optimum heat transfer performance and is recommended for improving the efficiency of air-cooled thermal management systems for high-performance battery applications.