Metal oxide nanofluid-enhanced closed-loop pulsating heat pipes considering the characteristics of base solution: Thermal performance improvement for battery thermal management in cryogenics

The short-term operational performance and long-term performance degradation of batteries are substantially affected by low temperatures, emphasizing the urgent need for efficient thermal management. Traditional heat pipe systems using conventional working medium suffer from persistent challenges such as low-temperature condensation, start-up difficulties, and limited heat transfer capacity. In this study, the properties of various base solutions and the application potential of metal oxide nanofluids in pulsating heat pipes (PHPs) are explored for the first time. Titanium dioxide (TiO2) nanofluids with different base solutions are innovatively prepared, and a PHP utilizing these TiO2 nanofluids (TiO2-PHP) is designed and experimentally evaluated. This design effectively addresses common issues such as start-up difficulties and slow heat transfer response. Building on these findings, a novel battery thermal management system (BTMS) incorporating TiO2-PHP is proposed and tested under representative low-temperature conditions. Experiment results reveal a considerable difference in the start-up behavior between PHPs using ethanol and water (Ethanol-PHP and H2O-PHP), with Ethanol-PHP demonstrating smoother initiation. Considering the favorable thermal characteristics of ethanol, the PHP using ethanol-based TiO2 nanofluids (Ethanol-TiO2-PHP) achieved optimal performance at a nanofluid concentration of 2.0 % and filling rate of 50 %. This system exhibited rapid start-up and stable heat transfer at low temperatures. Across various scenarios, the battery temperature reached 0 °C in under 503 s, and the maximum temperature difference remained below 2.6 °C. compared with pure batteries, the temperature difference was reduced by up to 48 %. When compared to previously published results, this approach offers clear advantages in preheating time and temperature uniformity. PHP is regarded as a breakthrough technology for battery thermal management. This study is the first to verify the high efficiency of PHP-based systems for low-temperature thermal management at the battery module level, paving the way for future integration into pack-level thermal management. Overall, this study provides a strong case for the adoption of PHP technology in vehicle thermal management applications.