Experimental correlation for pool boiling heat transfer on metallic foam surface and bubble cluster growth behavior on grooved array foam surface

The pool boiling heat transfer of deionized water on copper foams was experimentally studied under saturation conditions. Bubble growth behavior was captured by a high-speed camera. Two opposing factors, namely, surface area and bubble escaping resistance, governed the pool boiling heat transfer performance. The former dominated at large pore sizes, whereas the latter prevailed at small pore sizes. An experimental correlation was proposed for the heat transfer coefficient, which was applied at a porosity range of 0.9-0.98, pore density range of 5-40 PPI, and foam thickness of 5-7 mm. The bubble departure diameter and frequency of the high pore density (130 PPI) foam sample with V-shaped grooved arrays were further examined. The departure of the lotus-shaped bubble cluster caused by grooves was observed. Bubble cluster pulsation occurred at a high heat flux. The average departure diameter and frequency increased with the increase in heat flux. A typical bubble cluster pulsation period included four stages, namely, suction of the previous bubble cluster, fresh liquid supplement, liquid vaporization, and bubble cluster departure. The relationships between bubble cluster diameter and growth frequency were consistent in the boiling heat transfer performance of the three groove-arrayed foam surfaces.