卧式螺旋管内R134a流动沸腾迟滞现象

Flow boiling hysteresis of R134a in horizontal helically-coiled tube

为得到R134a在卧式螺旋管内的流动沸腾迟滞特性,进行增-减热流密度试验。试验时逐渐改变加热的热流密度,记录壁温变化情况,绘制增大和减小热流密度的沸腾曲线,通过曲线分析浮升力、离心力对成核滞后的影响,以及压强对成核滞后和湮灭滞后的影响。结果表明,不同位置截面处浮升力和离心力对汽泡的脱离行为影响不同,导致成核滞后的明显差异;压强越高,成核滞后、湮灭滞后现象均越明显,压强主要通过影响R134a润湿性影响成核滞后,通过影响泡核的形成影响湮灭滞后。研究结果揭示的流动沸腾迟滞特性对于提高换热器的运行可靠性具有指导意义。

In order to explore the flow boiling hysteresis characteristics of R134a in horizontal helically-coiled tube,an experiment of increasing-decreasing in heat flux was conducted.During the experiment,the heat flux was gradually changed to record the change of wall temperature,and the boiling curve of increasing and decreasing heat flux was drawn.The influence of buoyancy and centrifugal force on temperature overshoot hysteresis,as well as the influence of pressure on temperature overshoot hysteresis and temperature deviation hysteresis,were analyzed by the curve.The results showed that the two forces mentioned above had different effects on the detachment behavior of bubbles at different sections,leading to obvious differences in temperature overshoot hysteresis;the higher the pressure was,the more obvious the temperature overshoot hysteresis and the temperature deviation hysteresis were.The pressure mainly affected the temperature overshoot hysteresis by determining the wettability of R134a,and the temperature deviation hysteresis was affected by the pressure for its influence on the formation of bubble nuclei.The flow boiling hysteresis characteristics revealed by the research was of guiding significance in improving the reliability of heat exchangers in operation.