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

为了生产高质量、低成本、节能的钢材，热机械控制技术应运而生。本研究的目的是研究TMCP避免冷却不稳定性的机理，着重于热工技术，即沸腾换热。首先，利用水平铂丝在常压下过冷水中研究了汽膜在膜沸腾中的传播塌陷。通过改变测试导线两边局部低温点的温度，测量了塌陷前沿的传播速度和塌陷时的表面温度。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。用热传导模型较好地描述了汽膜崩塌的传播速度。这一事实支持了膜沸腾汽膜坍塌时，再湿锋温度低于过热度热力学极限。其次，实验研究了润湿对池膜沸腾的影响，重点观察了汽膜坍塌和接触角的变化。实验使用直径为2 mm的铂丝，在常压下对饱和水进行了实验。实验中，在稳定的膜沸腾过程中，从喷嘴向过热面提供液体射流，观察了液固接触行为。实验结果表明，对于顶喷流情况，当壁面过热度低于334K时，汽膜发生传播性坍塌。根据热传导模型，温度与过热的热力学极限有关。在室温下，气液界面与受热壁的夹角接近动态推进接触角。

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.