Study on Mechanism to Avoid Cooling-Instability for Thermo-Mechanical Control Process

采用热-机械控制工艺（TMCP）生产高质量、低成本、节能的钢材。本研究的目的是探讨避免TMCP因添加氧化物而导致冷却不稳定的机理，重点是热工，即沸腾传热。首先，用水平铂丝实验研究了常压下过冷水沸腾过程中汽膜的传播坍缩现象。通过改变试样两端局部低温点的温度，测量了崩溃锋的传播速度和崩溃时的表面温度。实验结果表明，随着局部温度的降低，崩塌时的传播速度减小，表面温度升高。热传导模型能很好地反映气膜崩塌的传播速度。这一事实支持了再润湿锋的温度低于过热度的热力学极限时，膜沸腾的蒸汽膜崩溃。其次，对池膜沸腾过程中的润湿行为进行了实验研究，重点研究了汽膜的坍塌和接触角的变化。实验采用直径为2mm的铂丝，在常压下对饱和水进行实验。在稳定沸腾膜的过程中，用喷嘴向过热表面喷射液体，观察了液固接触行为。实验结果表明，在顶喷工况下，壁面过热度低于334 K时，汽膜发生了传播性坍缩。根据热传导模型，温度与过热度的热力学极限有关。汽液界面线与受热壁面之间的角度与室温下的动态推进接触角接近。

The technology of Thermo-Mechanical Control Process (TMCP) is advanced to produce steel with high quality and low cost on saving energy. The aim of the study is examined the mechanism to avoid cooling-instability for TMCP caused it to add oxide, focusing on thermal engineering, i.e., boiling heat-transfer.First, Propagative collapse of a vapor film in film boiling was investigated experimentally with a horizontal platinum-wire for subcooled water at atmospheric pressure. The propagation velocity of collapse front and the surface temperature at the collapse were measured by changing the temperature of the local low-temperature-spot at both edges of the test wire. The experimental results showed that the propagation velocity decreased and the surface temperature at the collapse increased with decreasing the local temperature. The propagation velocities of the collapse of the vapor film were represented well by the heat-conduction model. This fact supports that the temperature of the rewetting front is lower than the thermodynamic limit of superheat when the vapor film of the film boiling collapses.Second, the behavior of wetting on pool film-boiling, focusing on observations of a collapse of a vapor-film and a contact angle was investigated experimentally. The experiments, used a platinum wire with 2 mm diameter, were performed for saturated water at atmospheric pressure. In the experiments, a liquid jet from a nozzle was supplied on the superheated surface in the stable film-boiling, then the behavior of liquid-solid contact was observed. The experimental results showed that the propagative collapse of the vapor film occurred when the wall superheat was below 334 K for the top-jet case. The temperature was related to the thermodynamic limit of superheat, according to the heat conduction model. The angles between the liquid-vapor interfacial line and the heated wall were close to the dynamic advancing contact-angles in room temperature.