Experimental study of pool boiling heat transfer on novel bistructured surfaces based on micro-pin-finned structure

The pool boiling heat transfer performance of bistructured surface based on micro-pin-finned structure was experimentally investigated in this study. A high speed camera with microscope was applied to capture the micronization boiling phenomenon and study the mechanism of bistructured surfaces. The micro-pin-finned area and the smooth area are fractally distributed on the heating surface by micromaching (dry etching) method. The P-doped silicon chips with 6 different surface types -- smooth chip, PF30-60 (micro-pin-fins with 30 μm fin side length and 60 μm fin height), PF30-60LS (large smooth strips distributed in micro-pin-finned area), PF30-60SS (small strips distributed in micro-pin-finned area), PF30-60LP (large smooth passages distributed in micro-pin-finned area) and PF30-60SP (small passages distributed in micro-pin-finned area) were tested in FC-72. The experimental results indicate that the bistructured surfaces can efficiently enhance the heat transfer performance in the nucleate boiling region, and the critical heat flux (CHF) is also significantly improved. From the micronization boiling phenomenon it can be observed that the bistructured surfaces can lead to a more vitality of bubbles: large number of nucleation sites are formed in the micro-pin-finned area, and the small bubbles grow, collide, merge and move rapidly to the nearby smooth channel. When the bubble grows large enough, it will departure quickly under the force of channel pressure. The micronization phenomenon also reveals that the boundary lines between the structured and smooth areas are active nucleate site region.