Thermal Management Analysis and Design Considerations for a Battery Pack Used in a High-Altitude Pseudo-Satellite

Abstract

A three-dimensional computational thermal analysis of an air-cooled battery system for a High-Altitude Pseudo-Satellite (HAPS), created by Sion Power, is conducted. In addition, design modifications are implemented aimed at enhancing the battery's thermal management system to improve its overall performance. The objective of the thermal management system is to maintain the cell temperatures between 15 – 40° C for optimal performance. Two levels of analysis are carried out. The first level, called the Module Level Analysis, involves a preliminary examination of a single battery module comprising 36 cells. The second level, known as the Battery Level Analysis, consists of a comprehensive analysis of the complete battery system, encompassing 18 modules, individual components for each module, and a casing. A parametric study using Ansys Fluent is conducted where various external conditions are studied in both steady-state and transient simulations. In addition, different inlet and outlet combinations for airflow through the battery system are examined to observe the heat distribution and the velocity profile of the air through the system. A final transient simulation is carried out reflecting the 14.8 hour discharging period profile of the battery system using the University of Arizona’s high-performance computing (HPC) center. The module level analysis revealed that the inclusion of additional components, such as a casing or insulation layer around the cells, leads to a significant increase in cell temperature. Furthermore, a linear relationship between the heat generation rate and overall cell temperatures was observed. In the battery level analysis, various inlet and outlet configurations were explored through transient simulations. The design with 3 vertical slits as inlets and a circular outlet proved to be the most effective, providing improved cooling with a temperature rise of 1.8 °C during a single cycle of heat generation. To further enhance the thermal management system, an insulation layer was added to the casing, leading to better cooling and a maximum temperature of 26.3 °C in the cells during transient simulations. The complex geometry, representing the actual battery pack, was analyzed with individual cells, foam, and module cases enclosed in the gondola casing. Transient simulations with a full discharge cycle of 14.8 hours demonstrated a maximum temperature of 31.1 °C, with a temperature rise of 6.1 °C. The selected inlet and outlet design optimized the airflow, ensuring uniform cooling and efficient performance. Overall, this research successfully improved the thermal management system of the HAPS battery, leading to extended battery life and safer operation during real-time flight conditions. The findings provide valuable insights into the design considerations for enhancing the thermal performance of battery systems for high-altitude applications.