Examination of Wetting Behavior on High Superheated Surface with Chemical Thermodynamics

过热表面上重润湿现象的物理机制仍然是尚未解决的重要问题。众所周知，过渡沸腾换热和最小热流点与“一定的接触角”密切相关，但接触角如何控制沸腾现象尚不清楚。实验研究了膜沸腾坍塌过程中高过热表面的再润湿行为。实验中，在膜稳定沸腾过程中，从喷嘴中喷射液体到过热表面，然后观察湿区。实验结果表明，当局部壁温低于300℃即过热度的热力学极限时，气膜内部发生局部扰动，导致气膜局部坍塌。随后，在250℃左右开始气膜的证明性坍塌。温度随射流流量的减小而降低。随着初始壁面过热度的降低，再润湿锋面的推进速度和与壁面接触的增加。后退速度随初始壁面温度的升高而增大。液-气界面线与受热壁面的夹角分别接近于室温下的动态前进接触角和动态后退接触角。通过水平向上平面铜板的稳态传热实验，研究了水的过渡沸腾传热。在过渡沸腾中，经过核态沸腾的加热过程的传热特性与从膜沸腾开始的冷却过程的传热特性相似。根据目前的实验数据，导出了过渡沸腾传热的关系式和模型。以无因次壁面过热度为研究对象，得到了过渡沸腾过程中液固接触分数的关系式。采用宏观层模型建立了过渡沸腾传热模型。少

The physical mechanisms of the rewetting phenomena on a superheated surface are still unresolved important issues. It is common knowledge that transition boiling heat transfer and minimum-heat-flux point are related to "a certain contact angle" closely, however it is not clear how contact angles control boiling-phenomena.The behavior of rewetting on high superheated surface during collapse of film-boiling was investigated experimentally. In the experiments, a liquid jet from a nozzle was supplied on the superheated surface in the stable film-boiling, and then the wetted area was observed. The experimental results showed that the local disturbance in the vapor film occurred to induce the local collapse of the vapor film when the local wall temperature was below 300℃, i.e., the thermodynamic limit of superheat. Sequentially, the probative collapse of the vapor film began at about 250℃. The temperature was lower as the flow rate of liquid jet decreased. The wetted area right after liquid- … More wall contact and the advancing velocity of the rewetting front increased as the initial wall superheat decreased. The receding velocity increased with the initial wall temperature. The angles between the liquid-vapor inter facial line and the heated wall were close to the dynamic advancing and receding contact-angles in room temperature, respectively.Transition boiling heat-transfer of water was examined by steady heat transfer experiments for horizontal upward-facing flat copper plate. In the transition boiling, heat transfer characteristics for heating process run in transition boiling through nucleate boiling were similar to those for cooling process started from film boiling. Correlations and a model of the transition boiling heat-transfer were derived from the present experimental data. The correlations of fraction of liquid-solid contact in the transition boiling were obtained by focusing on the dimensionless wall superheat. The model of the transition boiling heat-transfer was developed by using the macrolayer model. Less