Behavior of Thin Liquid Film underneath a Coalesced Bubble in Nucleate Boiling at High Heat Flux

本文详细研究了窄缝间扁平气泡的汽液行为与传热的关系。在实验中，一个透明的加热表面，使加热，从下面的液体-蒸汽行为的观察和传热数据的采集同时可能。窄缝试验段的安装是为了实现重力场中的上升流，并连接到试验回路，以规定入口条件，没有歧义。实验采用蒸馏水，压力P= 0.1 - 0.18MPa，温度t_p= 100 ℃，入口过冷度Δ T_sub，in&gt;= 5 - 8 K，平均热流密度q_o= 3.2 × 10^5W/m^2，入口液速u_<in>o = 0.06m/s。重力水平的变化改变了气泡的上升速度，在狭窄的间隙中，干燥的补丁和残留的微层的溪流被确认为下面的扁平气泡。perio 关于我们 在加热表面上重复由扁平气泡覆盖并由本体液体流淬灭的DS。在气泡上升速度较慢的情况下，由于表面淬火频率降低，表面温度保持在较高的值。表面粗糙度的增加使热流密度增加，但传热系数的变化幅度较小。在极窄的间隙中，扁平气泡的流动变得不稳定，并且具有复杂轮廓的扁平气泡在加热表面上向各个方向剧烈运动。结果，干斑扩展和再润湿的迭代频率显著降低，并且在一定程度上防止了传热恶化。在本研究中，它是澄清在核态沸腾的存在的两个相互冲突的趋势的传热增强的厚度减少的微层由于蒸发和传热恶化的扩展干补丁的微层。少

The relation between the liquid-vapor behavior and heat transfer is investigated in detail for the flattened bubble generated between narrow gaps. In the experiments, a transparent heating surface was introduced to make the heating, the observation of liquid-vapor behavior from underneath and the acquisition of heat transfer data simultaneously possible. The test section of the narrow gap was installed to realize the upward flow in the gravity field and was connected to test loop to prescribe the inlet condition without ambiguity. The experiments was conducted by the use of distilled water at pressure : P= 0.1 -0.1 8MPa, temperature : t_p= 100ﾟC, inlet subcooling : DELTAT_<sub, in>= 5 -8K, averaged value of heat flux supplied q_o=*3.2 chi 10^5W/m^2, inlet liquid velocity : u_<in>= 0.06m/s. Gravity level was changed to vary the bubble rising velocity, In the narrow gap, extension of dry patches and rivulets of residual microlayers were recognized underneath a flattened bubble. The perio … More ds covered by the flattened bubble and quenched by the bulk liquid flow were iterated on the heating surface. in the case of slow bubble rising velocity, the surface temperature is maintained at high value owing to the reduced frequency of surface quenching. And the heat flux is enhanced due to the increased surface superheat, while only the deterioration is observed in the values of heat transfer coefficient. In the extremely narrow gap, the flow of flattened bubbles becomes unstable and the flattened bubbles with complicated profiles moves vigorously towards the various direction on the heating surface. As a result, the frequency in the iteration of dry patch extension and of re-wetting is markedly decreased and the heat transfer deterioration is prevented to some extent. In the present research, it was clarified in nucleate boiling the existence of two conflicting trends of heat transfer enhancement by the decreased thickness of microlayer due to evaporation and of heat transfer deterioration by the extending dry patches in the microlayer. Less