Investigation on immersed oil-cooled battery thermal management system for unmanned underwater vehicles

The thermal management of batteries in unmanned underwater vehicles (UUVs) faces significant challenges due to the spatial constraints and high-energy-density battery pack design. This study presents a novel immersed oil-cooling strategy, wherein batteries are directly submerged in dielectric cooling oil. By leveraging the oil's superior thermal conductivity and heat capacity, the strategy aims to augment surface heat dissipation from battery modules. The effects of battery arrangement, oil filling level, and fin designs on cooling performance are systematically evaluated. The results indicate that the proportion of natural convection heat transfer in oil-cooled systems is significantly higher than that in air-cooled systems. Compared with air-cooled battery packs, the maximum temperature of oil-cooled battery packs was reduced by 22.44 K, corresponding to a decrease of approximately 52.43%. The fully oil-immersed scheme with N-shaped fins and a battery spacing of 20 mm delivered optimal cooling performance. A dimensionless comprehensive evaluation metric integrating thermal performance, system weight, and available electrical energy was introduced. The optimal oil-immersed design lowered this metric by about 28.62% relative to the uncooled baseline. The findings provide quantitative guidance for designing and optimizing oil-cooled battery thermal management systems in UUVs.