Three dimensional heat transfer characteristics of superfluid helium and its mechanism

1)在大范围的实验条件下，测量了不同尺寸平板在He II中的稳态换热及其临界热流密度。2)为了研究氦气加热表面热流膨胀或收缩时的换热机理，对以下几种情况进行了传热测量：(1)热流从含有氦气的矩形管道一端的截面面积大于试板表面积的试板扩展到管道的另一开放端；(2)截面突然增大的管道；(3)带孔口的管道。测量的对象是受热面位于管道中部的壁面，热流向Duc…的两个开口端。进一步阐明了试验加热器到对壁的间隙长度对实验结果的影响。4)针对上述(2)、(3)和(4)三种情况，测量了高度高于稳态临界热流密度的阶跃热输入下试板的瞬时换热。阶梯式热输入的瞬时换热是在稳态Kapitza电导曲线外推的基础上，存在一定寿命的准稳态，然后跳跃到膜沸腾区域。阐明了热流的膨胀或升华对He II寿命与台阶高度关系的影响。5)基于湍流条件下He II的双流体模型，开发了He II中二维热和流体流动的计算机程序Super-2D。在相应条件下，阶跃热输入产生的稳态临界热流密度和瞬时换热的数值解与实验数据吻合较好。结果表明，该程序能较好地描述He II的稳态和暂态换热现象。通过计算，阐明了He II的二维换热机理

Major Results of this study are as follows.1) Steady-state heat transfer and its critical heat flux on a flat plate of various dimensions in He II were measured under wide ranges of experimental conditions. Effect of the test plate dimension was clarified and an equation which can describe the experimental data was presented.2) To investigate the mechanismof heat transfer in case of expanding or shrinkingheat flow from a heated surface in He II, measurements of heat transfer were made for the following cases : (1) the heat flow expands from a test plate located at one end of a rectangular ductcontaining He II with the cross sectional area larger than the surface area of the test plate to the other open end of the duct, (2) for a duct with a sudden increase in its cross sectional area, (3) for a duct with an orifice.3) Moreover, the measurements were made for a duct with the heated surface located on the wall at the middle of the duct and heat flowed turning to both open ends of the duc … More t. Effect of the gap length from the test heater to the opposite wall was clarified. Equations that can express the experimental data of 2) and 3) were given.4) Transient heat transfer from a test plate produced by a step heat input with the height higher than the steady-state critical heat flux was measured for the above mentioned cases of (2), (3) and (4). The transient heat transfer for a stepwise heat input is such that the quasi-steady state exists with a certain lifetime on the extrapolationof steady-stateKapitza conductance curve and then jumps to film boiling regime. Effects of expansion or sublimation of heat flow on the relation of the lifetime and step height was clarified.5) The computer code of two-dimensional heat and fluid flow in He II named SUPER-2D was developed based on the two-fluid model for He II in turbulent flow condition. The numerical solutions of the steady-state critical heat flux and transient heat transfer produced by a step heat input are in good agreement with the experimental data for the corresponding conditions. It was confirmed that the numerical code can describe the steady-state and transient heat transfer phenomena in He II. Mechanism of two-dimensional heat transfer in He II was clarified through the calculation Less