Unveiling hysteresis of transient boiling: A multimodal perspective

Boiling is widely used in thermal management systems of electronic and energy devices due to its exceptional mass efficiency. However, hysteresis present during boiling makes the boiling curve unable to return along the same path as the rising curve, hindering a thermal management system from achieving precise temperature control. Such thermal crises increase both system instability and the likelihood of system failure. Some studies have explored hysteresis based on steady-state boiling, identifying several types of hysteresis during nucleate boiling. However, the impact of critical heat flux (CHF) on a boiling cycle has not been considered. Therefore, this paper explores hysteresis in transient boiling from a multimodal perspective, offering insights into possible indicators for active and passive thermal control. Multimodal sensing, which integrates thermal, optical, and acoustic measurements, is employed to collect data during transient pool boiling on a copper foam surface. Then, time and frequency domain analyses are conducted on these multimodal data to unveil hysteresis. Based on this research, the hysteresis observed in a complete transient boiling cycle involving CHF can be classified into three categories: nucleation hysteresis (ΔV hysteresis), burnout hysteresis (CHF hysteresis), and pressure change hysteresis (ΔP hysteresis). The mechanisms underlying these types of hysteresis and their multimodal behaviors are elucidated based on the analysis results. Finally, the impact of hysteresis and strategies for its mitigation are discussed. It is observed that smooth surfaces, such as plain copper, exhibit more pronounced nucleation hysteresis compared to hierarchical porous surfaces, such as copper foams.