关键词: 成像, 电解液, 两相流, 图像预处理, 速度场

Abstract:

The ternary lithium battery is increasing being used in the field of electric vehicles. Studying the jet velocity field of the jet valve during thermal runaway of the battery is crucial for deducing critical pressure and pressure changes inside the battery. This information holds significant importance in optimizing battery design and accurately predicting flame propagation. However, lithium batteries often have two ejections during the thermal runaway process. The ejections comprise chemical reaction gas production, electrolyte evaporation, as well as particles and fragments from various battery components. In addition, the evaporated electrolyte condenses after cooling, resulting in a gas-liquid-solid three-phase mixed state within the jet valve jet process. This complexity increases the difficulty of identifying and testing the velocity field. Therefore, in order to realize the visualization of the jet flow of the jet valve and the identification and calculation of the velocity field under high temperature conditions, an experimental bench composed of a high-speed camera, a laser system and a battery explosion-proof box was constructed in this study. The high-speed camera was used to capture and process the thermal runaway jet process of the battery. Firstly, a preliminary analysis of the flow field flow pattern was carried out. Then, the adaptive filtering algorithm effectively reduced imaging noise and enhanced droplet edge detail information. Histogram equalization was then used to further improve image contrast. Finally, the cross-correlation algorithm based on sub-pixel precision interpolation was used to analyze and calculate the velocity field of the jet flow field. This approach yielded velocity field data on a two-dimensional plane at different times intervals. The velocity characteristics of different regions at different times were further analyzed, which provides a foundation for the subsequent research on the mechanism of battery thermal runaway and the improvement of battery safety performance.

Key words: imaging, electrolyte, two-phase flow, image preprocessing, velocity field