Abstract: In the battery pack(BP) structure of electric vehicles, liquid cooling is an important form of heat dissipation. The relative humidity value in the BP is increased and the interaction of heat and mass between the internal environment and the external environment is enhanced bythe heat exchange between the cooling plate and the air in the BP, and the risk of damp and condensation in the BP is further increased, causing system safety and reliability problems. The temperature and humidity distribution in the BP and the dynamic evolution process of water evaporation and condensation are difficult to monitor in practical applications. For this purpose, the heat and mass transfer between the internal and external environments of the BPare analyzed, and theheat and mass transfer relationship between the internal and external of the BP is described through the open system model, and then the microenvironment heat and mass transfer model of the BP is established based on the heat flow control equations, the water vapor transport equations and the evaporation-condensation equations. Combined with the structural features of the small power battery pack, a numerical analysis model is established to investigate the temperature-humidity-flow multi-field coupling law in the BP. By analyzing the temperature and humidity evolution of the internal environment of the BP under different cooling intensities, it is clear that the low-temperature cold source enhances water vapor transmission and condensation. The characteristics of water vapor transport and condensation inside the BP is efficiently described by the model. The following conclusions can be drawn, the bottom area in the BP tend to be wet under the action of the low temperature cold source; the greater the cooling intensity, the greater the amount of condensation, and the greater the degree of water vapor transmission.

Key words: power battery pack, temperature and humidity coupling, transient numerical analysis, low temperature condensation