关键词: 梯度金属泡沫, 破裂, 池沸腾, 合并, 气泡, 传热

Abstract:

Pool boiling is considered to be an effective method for cooling high heat-generating electronic components with less noise and equipment. Despite many studies on boiling, opinions about the process are still disputed and there is still scope to investigate the pool boiling heat transfer mechanism, especially bubble behavior in porous materials. In this experiment, by utilizing high speed camera, the bubble departure in gradient metal foam in saturated pure deionized water and n-heptanol solutions under pool boiling conditions was investigated. To form the gradient metal foam, the foam layers were sintered together by Ag-Cu alloy sheets in a high-temperature muffle furnace. The gradient metal foam consists of a 40 PPI nickel foam layer with 4 mm thickness and a 10 PPI copper foam layer with 4 mm thickness; the foam porosity is 0.98, and n-heptanol solutions concentration is 400 mg·L^-1 and 800 mg·L^-1. The results show that n-heptanol affects the bubble parameters, and the bubbles in n-heptanol solution are smaller in size and quantity than in pure water which adversely affects the boiling heat transfer. The bubble variation is not sensitive to an increase in n-heptanol concentration. At the heat flux of 6.6×10⁴ W·m^-2, two common phenomena occur in the gradient foam:bubbles escape from the metal skeletons without cracking and bubbles separate into two smaller bubbles. When heat flux increases to 1.0×10⁵ W·m^-2, two neighboring bubbles move upwards and are sucked into the metal foam due to coalescence, then the big coalescence bubble departs from the metal foam.

Key words: gradient metal foam, cracking, pool boiling, coalescence, bubble, heat transfer