Roles of heating power, gravity, coolant temperature and heat source on the thermal performance of an ultra-thin vapor chamber

Ultra-thin vapor chambers (UTVCs), known for their excellent thermal diffusion performance and lightweight, show strong potential for thermal management of chips and batteries. This study experimentally investigates the heat transfer performance of UTVCs under various operating conditions. A dedicated test platform was developed to examine the effects of heating power, gravity orientation, cooling water temperature, and heat source size. Results reveal a critical heating power of 4–8 W, below which evaporator temperature and temperature difference increase slowly with increased heating power, while thermal resistance decreases. Above this threshold, thermal resistance increases sharply. Gravity orientation significantly affects performance only beyond the critical heating power where gravity-assisted cases yield the best performance, followed by horizontal ones, with gravity-opposed being the worst. At a coolant temperature of 20 °C, gravity-assisted cases reduce the maximum evaporator temperature by 11.75 °C at most compared to gravity-opposed cases. The effect of coolant temperature is twofold. At low power, higher temperature increases evaporator temperature. At high power, a “temperature reversal” occurs where evaporator temperature drops as coolant temperature rises, due to enhanced working fluid reflux. Heat source size also plays a critical role. Smaller heat sources concentrate heat flux, leading to earlier critical power and temperature reversal. Under identical conditions, smaller heating source results in higher evaporator temperature, temperature difference, and thermal resistance. For instance, at 6 W, 25 °C coolant, and gravity-opposed orientation, the smaller heat source shows increases of 9.12 °C, 9.82 °C, and 1.71 °C/W, respectively, compared to the larger one.