Immersion coupled direct cooling with non-uniform cooling pipes for efficient lithium-ion battery thermal management

Lithium-ion batteries (LIBs) are widely employed in electric vehicles (EVs) and energy storage systems, but managing the heat they generate is challenging. Immersion cooling stands out for its high efficiency and temperature uniformity. This paper proposes an immersion coupled direct cooling (ICDC) system with non-uniformly spaced cooling pipes to simplify cooling circuits and reduce energy consumption. It explores the effects of various parameters in the ICDC system, including the use of four different dielectric coolants (transformer oil, PAO-4, HFE-7100, and Noah3000A), ambient temperature, coolant temperature, and flow rate on the thermal performance. Simulation results demonstrate that under ambient temperature of 25 °C and 2C discharge rate, transformer oil and PAO-4 exhibit superior cooling performance under comprehensive conditions, reducing the maximum battery temperature to 21.8 °C and 25.4 °C, respectively, and controlling the temperature difference within 3.66 °C and 4.40 °C. The maximum temperature of the battery pack decreases as the coolant flow rate increases, and the maximum temperature difference diminishes with rising coolant temperature. To balance thermal performance and economy, this study introduces the cooling efficiency coefficient (CEC) as an evaluation metric. The calculation results and analysis suggest that the flow rate should be maintained around 0.075 m/s and the coolant temperature should be kept below 15 °C. Given practical application conditions, the structure effectively controls the battery temperature under a wide range of ambient temperatures, from 25 to 40 °C, indicating its reliability in terms of environmental adaptability and safety. This study provides strong data support for the application of ICDC systems in LIBs thermal management and offers theoretical guidance for the design of efficient and economical battery thermal management systems.