Studies of mechanism of noisy film boiling in He II and its control

本研究的目的是研究He Ⅱ中有噪声的膜状沸腾过程中的可听噪声产生机理及其控制方法，为此，对沸腾过程中的热流体动力场进行了可视化研究，并利用温度传感器测量了温度，利用压力传感器测量了压力。从本研究中得出以下结论。(1)He Ⅱ中的膜沸腾有三种模式，按静水压水平、无声膜沸腾、噪声膜沸腾和过冷膜沸腾的顺序出现。明确了噪声膜沸腾的起始条件与温度、静压和加热器尺寸等参数的关系。实验结果表明，加热器表面的大汽泡破碎后，过热加热器上的He Ⅱ立即发生爆炸性蒸发，从而产生巨大的可听噪声。(2)它是由 ...更多信息 正弦振荡热扰动叠加在稳态恒热流力上诱导了从无声到嘈杂的薄膜沸腾转变。这表明向噪声沸腾的转变是一种噪声诱导的不稳定性。(3)对压力振荡测量数据的FFT分析结果进行了检验，以考虑在三种膜沸腾模式下引起的压力振荡的细节。发现过冷沸腾压力振荡的高频（kHz量级）成分是由氦Ⅱ在低温恒温器中的液柱振荡引起的。(4)弱过冷He Ⅱ中从噪声沸腾到无声膜沸腾转变的一般特征是清楚的。当温度非常接近临界温度时，过冷沸腾随着静压的降低而直接转变为无声沸腾，而不经历噪声沸腾模式。(5)描述He Ⅱ噪声沸腾机理的物理数学模型的建立尚未完成，但积累了足够的数据。从现有的实验数据来看，噪声沸腾的控制还有待进一步研究。少

The objectives of this research are the investigations of the mechanism of loud audible noise generation during noisy film boiling in He II and of the control method of it. Visualization of thermo-fluid dynamic field resulted from boiling and the measurements of the temperature by a superconductive temperature sensor and of the pressure by a pressure sensor are conducted comprehensively for the purpose. The following conclusions are drawn from the present study.(1) There are three modes of film boiling in He II appearing in the order of the hydrostatic pressure level, silent film boiling, noisy film boiling and subcool film boiling. The dependence of the onset condition of noisy film boiling on such parameters as the temperature, the static pressure and the heater size are made clear. The cause of the loud audible noise generation is found to be the explosive evaporation of He II on overheated heater immediately after the crush of a large vapor bubble on a heater surface.(2) It is foun … More d that sinusoidally oscillating thermal disturbance superposed on steady constant heat flux forces to induce the transition from silent to noisy film boiling. This indicates that the transition to noisy boiling is a kind of noise induced instability.(3) The FFT analysis result of the pressure oscillation measurement data is examined to consider the detail of the pressure oscillation caused in three film boiling modes. The high frequency (the order of kHz) components of pressure oscillation in subcool boiling are found to be resulted from the liquid column oscillation of He II in the cryostat.(4) The general feature of the transition from noisy to silent film boillings in weakly subcooled He II is made clear. At the temperatures very close to the lambda-temperature subcool boiling directly turns to silent boiling without passing through noisy boiling mode as the static pressure decreases.(5) The construction of the physico-mathematical model to describe the mechanism of noisy boiling in He II has not been completed, but sufficient amount data are accumulated for this. The control of noisy boiling is reedy to be investigated from the present experimental data. Less