微尺度核态沸腾换热的汽泡交互作用实验研究

核态沸腾换热是一种高效的换热形式,沸腾机理的研究对强化传热的研究很重要。实验采用微尺度96加热片阵列,通过独立的控制电路,加热独立的各个加热片,使其维持在恒定温度120℃上。利用高速摄像技术分别从汽泡的底部和侧面对汽泡生长及运动现象进行可视化观测,并用高速数据采集系统同步记录汽泡一个生长期间不同阶段的热流密度。实验首先单独加热每个独立的区域,产生单个汽泡,并分析汽泡脱离频率、脱离直径和热流密度;然后通过加热两个相隔一定位置的加热片区域,使得汽泡长到一定大小后能够碰撞、合并为一个新汽泡并最终脱离。这种汽泡交互作用伴随着汽泡的变形、滑移,显著增加了沸腾换热的热流密度和汽泡脱离频率。通过分析每个加热片的热流密度,得出瞬态导热是沸腾换热的主要机理。

Experimental study of bubble interactions during nucleate boiling

Nucleate pool boiling heat transfer is very effective and boiling is a very important heat transfer enhancement mechanism.A micro-scale 96 heater array was used in an experiment study of boiling heat transfer with each heater controlled by an individual feedback circuit at a constant temperature of 120℃.The bubble dynamics were observed from both sides and under the bubble by a high-speed camera.The heat fluxes during different ebullition cycles were simultaneously recorded by a high-speed data acquisition system.Each individual region was first heated to generate separate bubbles that were analyzed to calculate the bubble departure frequencies,departure diameters and heat fluxes.Two nearby regions were then heated so two bubbles could grow and coalesce to form a large bubble and depart.The bubble coalescence process is associated with a combination of bubble stretching,oscillation and sliding,which all greatly enhance the heat transfer and increase bubble departure frequencies.An analysis of the heat flux of each heater showed that transient conduction is the main heat transfer mechanism during nucleate boiling.