梯度金属泡沫池沸腾过程中气泡脱离特性

利用实验手段对梯度金属泡沫池沸腾过程中气泡脱离行为特性进行了探究。实验工质为去离子水、浓度分别为400 mg·L^-1和800 mg·L^-1的正庚醇溶液。梯度金属泡沫材质为铜和镍，铜泡沫层和镍泡沫层厚度均为4 mm，孔密度分别为40 PPI和10 PPI。实验结果表明：添加正庚醇会使池沸腾气泡脱离直径变小，数目减少，但其浓度变化影响不明显；在热通量6.6×10⁴ W·m^-2沸腾时，观察到气泡脱离金属泡沫骨架阻碍两种常见运动形式：气泡破裂和整体滑移；当热通量增加到1.0×10⁵ W·m^-2时，相邻的两个气泡在梯度金属泡沫内合并成一个大气泡脱离金属泡沫。

Bubble departure in gradient metal foam under pool boiling conditions

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.