Temperature-Humidity Coupled Analysis in Battery Pack Based on Airflow Characteristics of Waterproof-breathable Valve

Waterproof breathable valves (WBV) are applied to the battery packs in electric vehicles due to their advantages of high efficiency waterproof and air-pressure balance. With the continuity of mass transfer of WBV and uncertain thermal conditions, the dynamic thermal characteristic of the moisture inside the battery pack is difficult to obtain by experiments, especially the phase change of the moisture. To analyze the temperature-humidity characteristic in the battery pack considering mass transfers of WBV, this study presents a temperature-humidity coupling model of the battery pack based on the mass transfer characteristic of WBV. A mass transfer model of WBV is developed with the airflow mass transfer characteristic in air pressure difference. The proposed models verified the feasibility of dynamic thermal characteristic analysis with experiments. Finally, a practical case study on a battery pack is used to study dynamic characteristics of the temperature-humidity during idle and working. Using the coupling model and the WBV model, temperature-humidity distribution and the location and time attributes of moisture condensation in the battery pack are effectively obtained. The inner walls of the pack casing and the battery surface near WBV are condensation areas during different environmental conditions.

Heat Transfer Model for Solidification Process of NH4Cl Solution

In this thesis, a unidirectional solidification model of NH4Cl solution is developed. The dynamics processes of the unidirectional solidification, such as temperature distribution and the location of phase interface are simulated timely. Based on those result data, the heat and mass transfer characteristic is analyzed. And it is found that with the stirring of the liquid zone, the temperature gradient in the liquid zone is decreased from 194 K/m to 24 K/m, and the thickness of the mush zone is enlarged.