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首页> 外文期刊>Experimental Thermal and Fluid Science: International Journal of Experimental Heat Transfer, Thermodynamics, and Fluid Mechanics >Evaluation of flow patterns and elongated bubble characteristics during the flow boiling of halocarbon refrigerants in a micro-scale channel
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Evaluation of flow patterns and elongated bubble characteristics during the flow boiling of halocarbon refrigerants in a micro-scale channel

机译：评估卤代烃制冷剂在微尺度通道中沸腾过程中的流型和伸长的气泡特性

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摘要

In the present study, quasi-diabatic two-phase flow pattern visualizations and measurements of elongated bubble velocity, frequency and length were performed. The tests were run for R134a and R245fa evaporating in a stainless steel tube with diameter of 2.32 mm, mass velocities ranging from 50 to 600 kg/m(2) s and saturation temperatures of 22 degrees C, 31 degrees C and 41 degrees C. The tube was heated by applying a direct DC current to its surface. Images from a high-speed video-camera (8000 frames/s) obtained through a transparent tube just downstream the heated sections were used to identify the following flow patterns: bubbly, elongated bubbles, churn and annular flows. The visualized flow patterns were compared against the predictions provided by Barnea et al. (1983) [1], Felcar et al. (2007) [10], Revellin and Thome (2007) [3] and Ong and Thome (2009) [11]. From this comparison, it was found that the methods proposed by Felcar et al. (2007) [10] and Ong and Thome (2009) [1] predicted relatively well the present database. Additionally, elongated bubble velocities, frequencies and lengths were determined based on the analysis of high-speed videos. Results suggested that the elongated bubble velocity depends on mass velocity, vapor quality and saturation temperature. The bubble velocity increases with increasing mass velocity and vapor quality and decreases with increasing saturation temperature. Additionally, bubble velocity was correlated as linear functions of the two-phase superficial velocity.
机译：在本研究中，进行了准绝热两相流模式的可视化和细长气泡速度，频率和长度的测量。对R134a和R245fa在直径2.32毫米，质量速度范围从50到600 kg / m（2）s，饱和温度分别为22摄氏度，31摄氏度和41摄氏度的不锈钢管中蒸发进行了测试。通过在其表面施加直流电来加热该管。通过位于加热部分下游的透明管从高速摄像机（8000帧/秒）获得的图像用于识别以下流动模式：气泡，细长气泡，搅动和环形流动。将可视化的流动模式与Barnea等人提供的预测进行了比较。 （1983）[1]，Felcar等。 （2007）[10]，Revellin and Thome（2007）[3]和Ong and Thome（2009）[11]。从该比较中发现，由Felcar等人提出的方法。 （2007）[10]和Ong and Thome（2009）[1]相对较好地预测了当前数据库。另外，基于高速视频的分析确定了拉长的气泡速度，频率和长度。结果表明，延长的气泡速度取决于质量速度，蒸气质量和饱和温度。气泡速度随质量速度和蒸气质量的增加而增加，而随饱和温度的增加而减小。另外，气泡速度与两相表面速度的线性函数相关。

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