Role of natural convection and battery arrangement for phase change material based battery thermal management unit

Phase change material (PCM) based battery thermal management (BTM) has been of increasing interest due to the passive concept with efficient cooling and temperature uniformity performance. Due to the inherent characteristics of solid-liquid phase change during operation, it is worth in-depth investigation of the influence of buoyancy driven natural convection (NC) on battery thermal behavior. Here, a typical PCM enclosed cylindrical battery unit is considered as the benchmark problem. The effects of battery arrangement and liquid PCM NC on melting process and thermal performance are investigated numerically based on rigorously validated model. It shows that excellent cooling performance could be achieved for battery with the function of latent heat storage of PCM, whether the unit is arranged vertically or horizontally. In addition, the horizontal arrangement (4.1 K) has a better temperature uniformity than the vertical arrangement (5.7 K), which can be ascribed to the varying melting rate of PCM. To further insight into the thermal behavior of BTM unit, the relationship between the melting rate and interface length associated with differential liquid fraction curve is proposed for the first time. When the liquid PCM is full of the upper half of the BTM unit, the length reaches its maximum value and after that the differential liquid fraction is significantly declined, indicating the poor heat transfer and thermal performance. The motivation is to not only explore the fundamental mechanism of passive phase change method, but also to serve as a basis for the design of more practical and efficient PCM based BTM in the future.