Experimental investigation on the performance and evaluation correlations of the expanded flow channel in refrigerant-based direct-cooling thermal management system

Refrigerant direct-cooling has emerged as a prominent trend in battery thermal management due to its structural simplicity and high efficiency. However, owing to the complexity of boiling process, direct cooling exhibits high sensitivity to pressure loss. Applying conventional uniform cross-section channels to meter-scale scenarios results in significant pressure drop and suboptimal heat transfer performance. This study conducts parametric experiments on meter-scale long-flow expanded cross-section channels with different expansion ratios, analyzing the effects of expansion, saturation pressure, and heat flux on cooling performance including flow parameters and thermal distribution indicators. Expanded channels of both expansion ratios reduce the pressure drop by 7.47% and 11.49% in average compared to the uniform cross-section channel. As for the thermal distribution, expansion ratio of 1.5 delivers optimal flow stability and temperature distribution within 640-670 kPa, reducing temperature difference and maximum temperature by 19.4% and 14.3% compared to uniform-channel values, respectively. However, excessive expanding ratio of 2.0 further decreases pressure drop at the cost of deteriorated temperature distribution across all operating conditions. Finally, to comprehensively characterize the performance of expanded flow channels in battery direct-cooling applications, the pressure-drop correlation and the temperature distribution correlation are proposed with fitting errors of 10.23% and 16.27%, respectively. These provide practical guidance for designing and evaluating expanded-channel direct cooling plates.