Abstract:

Nucleate pool boiling in ethane was studied at 0.15, 0.2 and 0.3 MPa at heat flux between 14.27 and 81.22 kW·m^-2 by visualization technique. Images of departure ethane bubbles at upper smooth surface of the vertical 20 mm-diameter heating copper rod were recorded at a frame rate of 2619 fps and a full resolution of 960×720 pixels by Phantom high-speed digital camera. The departure bubble diameters were got by image processing and analyzed relationship with Jacob number(Ja). With the increase in Ja, bubble departure diameter tended to increase but not monotonically. Compared experimental diameter data with predictions of six most used correlations, it was found that Kim and Kim(2006) model had the best prediction with absolute average deviation (AAD) below 30% at all three pressures and 50% of the predicted values within 30%-40% deviations at 0.15 MPa. Finally, a new correlation was proposed on a basis of fitting bubble departure data and Kim and Kim (2006) power law model, which has within ±30% difference between prediction and experimental data. The prediction for methane departure diameters at four different pressures were within ±30% (only one over ±30%) of the literature data. The new correlation works well for both methane and ethane at various operating conditions, however, its application range is limited because the correlation is obtained from data under low Ja.

Key words: thermodynamics, phase change, nucleate pool boiling, ethane, bubble, departure diameter, correlation

摘要：

针对0.15、0.2、0.3 MPa 3个压力进行乙烷池内核态沸腾可视化实验研究，实验测量的热通量范围是14.27～81.22 kW·m^-2。高速摄像机采集得到竖直铜棒的光滑上表面的乙烷气泡的脱离图像，利用图像处理软件获得气泡脱离直径，并分析了Jacob数（Ja）与气泡脱离直径的变化关系。实验所测直径与引用广泛的6个关联式进行比较，Kim和Kim（2006）模型的预测效果较好，绝对平均偏差均在30%以内，但在0.15 MPa工况下，50%的预测值偏差为30%～40%。Kim和Kim（2006）模型提出Bo^1/2和Ja呈幂函数的关系。在对比基础上，用乙烷的气泡脱离直径数据拟合得到的新关联式与实验数据偏差在±30%以内。另外，选取文献中甲烷的气泡脱离直径与新关联式进行对比，在4种压力下的预测值偏差几乎均在±30%以内（只有一个预测值在±30%以外）。新关联式对甲烷和乙烷的工况具有良好的预测效果，但是由于拟合数据所用的Ja较小，在使用范围上具有一定的局限性。

关键词: 热力学, 相变, 池内核态沸腾, 乙烷, 气泡, 脱离直径, 关联式