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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 >Experimental investigation of velocity and length of elongated bubbles for flow of R-134a in a 0.5 mm microchannel
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Experimental investigation of velocity and length of elongated bubbles for flow of R-134a in a 0.5 mm microchannel

机译：R-134a在0.5 mm微通道中流动的细长气泡的速度和长度的实验研究

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摘要

The length and velocity of elongated bubbles have been experimentally investigated for R-134a flowing in a 0.5 mm microchannel, where 440 experimental data points were obtained at the exit of a microevaporator using an optical laser measurement technique. The variation of the elongated bubble velocity u(v) as a function of its length L-v shows firstly, a nearly linear increase of uv with L, and secondly, a region where the velocity tends towards a plateau and where it varies little with further increase in length. This behavior is the starting point to explain merging between elongated bubbles in microchannels during flow boiling. No influence of a small variation in the inlet subcooling (ranging from 2 to 5 degrees C) and the microevaporator length (ranging from 30 to 70 mm) was observed on the bubble velocity and the bubble length. On the other hand, when decreasing the saturation temperature, the bubble length and the bubble velocity both increased due to the decrease in the vapor density. Almost 92% of the new database obtained here is predicted by the elongated bubble velocity model of Agostini et al. [B. Agostini, R. Revellin, J.R. Thome, Elongated bubbles in microchannels. Part 1: Experimental study and modelisation of elongated bubble velocity. Int. J. Multiphase Flow, in press] within a +/-20% error band. Furthermore, this model shows that during diabatic flow boiling of elongated bubbles in horizontal microchannels, the drift flux distribution parameter C is close to unity and the drift velocity is not necessarily equal to zero as predicted by the original drift flux model of Zuber and Findlay [N. Zuber, J.A. Findlay, Average volumetric concentration in two-phase flow systems. J. Heat Transfer 87 (1965) 458-463]. Rather the drift velocity can deviate substantially from the average bubble velocity given by the homogeneous model. (C) 2007 Elsevier Inc. All rights reserved.
机译：对于在0.5毫米微通道中流动的R-134a，已经通过实验研究了细长气泡的长度和速度，其中使用光学激光测量技术在微蒸发器的出口获得了440个实验数据点。细长气泡速度u（v）随长度Lv的变化首先显示uv随L线性增加，其次显示速度趋于平稳且随进一步增加几乎没有变化的区域长。此行为是解释流沸腾过程中微通道中细长气泡之间合并的起点。对于气泡速度和气泡长度，未观察到入口过冷度（2至5℃）和微蒸发器长度（30至70mm）的小变化。另一方面，当降低饱和温度时，气泡长度和气泡速度都由于蒸气密度的降低而增加。 Agostini等人的拉长气泡速度模型预测了这里获得的新数据库的几乎92％。 [B. Agostini，R.Revellin，J.R.Thome，微通道中的气泡伸长。第1部分：拉长气泡速度的实验研究和建模。诠释J.多相流，印刷中）在+/- 20％的误差范围内。此外，该模型表明，在水平微通道中细长气泡的绝热流沸腾过程中，漂移通量分布参数C接近于1，并且漂移速度不一定等于Zuber和Findlay的原始漂移通量模型所预测的零。 N. Zuber，J.A. Findlay，两相流系统中的平均体积浓度。热传递87（1965）458-463]。而是，漂移速度可以大大偏离均质模型给出的平均气泡速度。 （C）2007 Elsevier Inc.保留所有权利。

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