Experimental study of saturated pool boiling from downward facing surfaces with artificial cavities

Saturated pool boiling heat transfer rates were measured from downward facing and inclined surfaces with artificial cavities to study the effects of inclination angle and cavity structures on the wall superheat and critical heat flux (CHF). The inclination angles were 5°, 30°, 45°, 60°, and 90° (vertical), the artificial cavities were cylinders with diameters of 0.25 mm, 0.5 mm, and 1 mm and depths of 1 mm and 2 mm and center-to-center spacings of 8 mm, 4 mm, and 2 mm. The results show that the CHF increases as the inclination angle increases. Smaller inclination angles have higher wall superheats at a given heat flux. The structured surface had significantly smaller wall superheats than a plain surface. For the same cavity spacing and cavity depth, a larger cavity diameter gave a higher CHF. There was an optimal cavity depth that gave the highest CHF for given cavity diameter and spacing. The CHF increased as the cavity spacing decreased for a given cavity diameter and depth with larger cavity diameters leading to larger increases in the CHF. Compared with the plain surface the CHF increases on the downward-facing surfaces with cavities were not significant.