Performance evaluation and heat transfer mechanism for battery thermal management of autonomous underwater vehicles based on phase change material cooling

Battery thermal management is of great significance to enhance the comprehensive performance of autonomous underwater vehicles(AUVs). However, few relevant studies have been conducted on the AUV's battery thermal management (BTM). In this work, the phase change material (PCM) cooling was proposed for AUV's BTM with taking into account natural convection. The temperature behavior of the battery and the melting behavior of PCM were studied under different parameters including thickness of PCM and eccentricity between PCM and battery. In addition, the enhanced heat transfer mechanism of the PCM melting process was further revealed based on the temperature deviation index. More importantly, the dimensionless temperature control rate (TCR) factor and the dimensionless heat storage rate (HSR) factor were introduced to quantitatively evaluate and optimize the eccentricity on the enhancement performance. The results show that PCMs have an excellent performance in the battery thermal management of AUVs. Unlike the traditional view, the whole PCM melting process was further subdivided into three stages according to the thermal energy storage mode or heat transfer types. Increasing the eccentricity can accelerate the melting of the PCM, while the reduced time of complete PCM melting was not linearly correlated with the eccentricity. The optimal eccentricity between PCM and battery was 10 mm, i.e., the eccentricity ratio ε = 0.625. The temperature control performance rate and heat storage performance rate were enhanced by 29.4 % and 5.7 % at e = 10 mm, respectively. These findings can provide guidelines for accurate design of the PCM cooling system for the AUV's battery thermal management.