A hybrid thermal management system with liquid cooling and composite phase change materials containing various expanded graphite contents for cylindrical lithium-ion batteries

To improve the temperature uniformity and cooling performance of the battery module, a hybrid battery thermal management system (BTMS) with liquid cooling and phase change materials (PCM) containing different expanded graphite contents is proposed. To adjust the heat transfer efficiency of composite phase change material (CPCM) along the direction of liquid flow, the segments of CPCM matrix contain different expanded graphite (EG) contents. Subsequently, the effects of the layout of CPCM matrix, length distribution of each segment, the structure parameters and cooling strategy on cooling performance of the battery module are investigated using computational fluid dynamics (CFD) model at 4C discharge rate and ambient temperature of 308.15 K. The results demonstrate that the maximum temperature (Tmax) and temperature difference (ΔT) of BTMS adopting segmented layout III are significantly reduced by 1.3 K and 1.4 K respectively compared with layout Ⅰ. Additionally, the layout III exhibits optimal cooling performance when length of each segment is 110 mm, 120 mm and 120 mm, respectively. Moreover, the Tmax and ΔT decrease with increase of cell-to-cell spacing (L) and diameter of liquid channel (d), and ΔT is only 2.2 K under the condition of L24d5 (L = 24 mm, d = 5 mm). During the 1C-charging and 4C-discharging cycles, the Tmax of BTMS with normal strategy remains at 319.5 K and ΔT lower than 3 K; furthermore the strategy of delayed liquid cooling can significantly reduce power consumption by 33.3 % without sacrificing the cooling performance.