Pool boiling performance on the textured hemi-wicking surfaces fabricated by nanosecond laser ablation

Today the problem of the boiling improvement is directly related to the heating surface modification at the micro-and nanoscale. As was shown by different authors the hemi-wicking surfaces demonstrate extremely high enhancement of heat transfer (HTC) and critical heat flux density (CHF) during boiling. In this paper, the laser ablation technique was used to fabricate textured hemi-wicking silicon surfaces. This surface modification technique is one of the most promising and discussed techniques today due to its high accuracy, implementation ease and high stability of the fabricated surfaces. The effect of the laser type on the silicon surface properties and boiling improvement was studied in detail. The texturing was performed using lasers with different wavelength -infrared (1064 nm) and visible (532 nm), but with the same number of pulses per unit area and laser spot diameter. The experiments showed that the water pool boiling performance differs significantly depending on the type of laser treatment. In particular, while the usage of infrared laser results in the HTC enhancement up to 78% compared to the untreated surface, the visible laser-textured surface in contrast shows the deterioration of the heat transfer rate up to 40%. At the same time, the visible laser-textured surface demonstrates the maximum CHF value of 1806 kW/m2, which is more than 2 times higher than for the untreated surface. The comparison with the models showed, that such an enhancement is explained by the highest capillary wicking of this surface. Based on the analysis of departure diameters, nucleation frequencies and the conditions for the vapor bubbles formation the observed difference in the heat transfer rate during boiling was revealed. Also using the high-speed ther-mography the dynamics of reversible and irreversible dry spots was studied during boiling on laser-textured hemi-wicking surfaces for the first time.