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首页> 外文期刊>International Journal of Heat and Mass Transfer >The effect of sliding bubbles on nucleate boiling of a subcooled liquid flowing in a narrow channel
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The effect of sliding bubbles on nucleate boiling of a subcooled liquid flowing in a narrow channel

机译：滑动气泡对在狭窄通道中流动的过冷液体的核沸腾的影响

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An apparatus that produces flow and heat transfer in horizontal narrow channels was used to explore the physics of the onset of subcooled nucleate boiling for R-11 and Novec 649. The apparatus uses a downward-facing electrically-heated thin foil as a heater, with the outside of the heater coated with a liquid crystal to display full-field temperature distributions for the heater surface. Video recordings were made of the temperature fields for a given set of operating conditions, accompanied by video recordings of the boiling behavior of the fluids in the channel itself. These two recordings were superimposed spatially so that the influence of various bubble dynamics could be directly correlated to the temperature response of the heater. Data have been obtained in a series of experiments performed in a horizontal channel, approximately 1.2 mm high × 20 mm wide × 357 mm long at mass fluxes indicative of laminar single phase flow in the channel. These data show that the enhancement of heat transfer behind the "boiling front", i.e., the point in the channel where bubbles are observed to first nucleate, is caused primarily by sliding bubbles rather than the activation of additional nucleation sites. These results tend to confirm the speculation made with an apparatus that did not allow visual observation of the boiling phenomena that surface temperatures near the boiling front can be depressed even though active bubble nucleation is not occurring there. This leads to boiling curves that involve a "turning angle" type of behavior that connects single-phase convection heat transfer to nucleate boiling heat transfer. The results reported in this paper provide a much clearer physical description of the controlling features of the transition from convection to boiling than has been available in the past.
机译：使用一种在水平狭窄通道中产生流动和传热的装置来研究R-11和Novec 649的过冷核沸腾开始的物理过程。该装置使用朝下的电加热薄箔作为加热器，加热器的外部涂有液晶，以显示加热器表面的全场温度分布。在给定的一组操作条件下，对温度场进行了录像，同时还记录了通道中流体的沸腾行为。这两个记录在空间上叠加，因此各种气泡动力学的影响可以直接与加热器的温度响应相关。数据是在水平通道中进行的一系列实验获得的，水平通道的质量通量约为1.2 mm高×20 mm宽×357 mm长，表示通道中的层状单相流。这些数据表明，在“沸腾前沿”之后，即通道中观察到的气泡首先成核的点，传热的增强主要是由滑动气泡引起的，而不是由其他成核位置的激活引起的。这些结果趋于证实使用不允许对沸腾现象进行肉眼观察的设备进行的推测，即即使在那里没有发生主动气泡成核，也可以降低沸腾前沿附近的表面温度。这导致沸腾曲线涉及“转角”类型的行为，该行为将单相对流传热与成核沸腾传热联系起来。与过去相比，本文报道的结果对从对流到沸腾过渡的控制特征提供了更为清晰的物理描述。

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