Pool boiling inside micro-nano composite pores: Thermofluids behaviors and heat transfer enhancement

Pool boiling has been considered as an effective method for heat transfer, which is extensively used in semiconductor microprocessors and aerospace. The prevention of critical heat flux (CHF) and improvement of heat transfer coefficient (HTC) are the keys to strengthen the pool boiling heat transfer. It has been reported that porous pillars can delay CHF by reducing vapor-liquid counter flow and nano-porous structure can significantly improve the liquid replenishment capacity and HTC. Herein, we modulate micro-nano porous structures by etching nanostructures on the surface of microporous pillars in order to utilize the advantages of above two structures. The boiling phenomenon inside the micro-nano composite pores is clearly demonstrated based on our visualization experiment. It is observed that the main vapor motion is regular periodic growth and recession. Through the quantitative analysis of the vapor-liquid interface area and vapor movement frequency, we find that they are both positively correlated with the heat transfer performance of porous structures. Hence, it is proved that the vapor-liquid phase distribution is the decisive factor affecting the heat transfer performance of micro-nano porous structures. Following the principle of maintaining larger vapor-liquid interface area and accelerating vapor movement frequency, the micro-nano porous structures with better performance can be obtained. Our approach establishes the relationship between the internal boiling phenomenon and the performance of micro-nano porous structures. In addition, it also provides a feasible direction for improving the performance of engineered boiling micro-nano structures.