Examination of Wetting Behavior on High Superheated Surface with Chemical Thermodynamics

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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