【作者】 夏雨亮；

【导师】 金滔；

【作者基本信息】 浙江大学 ， 制冷及低温工程， 2007， 硕士

【摘要】 现代科技与工业的发展使得低温系统应用场合和使用规模日益增大，低温下材料的物理、力学性能与常温下相比有较大的差别，比如金属的低温脆性。而作为低温系统中常用部件—低温阀门会直接影响到整个系统的运行情况。不锈钢阀门材料在低温下会出现奥氏体向马氏体转变，进而带来材料性能的变化。为了消除由此可能带来的不利影响，通常需对阀门材料进行深冷处理。另外，阀门在生产出来之后还需要对其进行冷态试验(低温试验)，来检查其在低温下的密封性能和其他机械性能。本文将首先通过总结文献中的经验公式和实验结果，联立求解出不锈钢材料在液氮中沸腾对流换热系数。在此基础上，通过不锈钢圆饼的沸腾实验实测降温曲线，并将之与模拟结果进行对比，完成对对流换热系数的修正。用修正后的换热系数对低温阀门冷态试验传热过程进行数值模拟，以此来指导低温阀门的冷态试验过程，并且针对阀门冷态试验中填料处出现冻结的现象，提出了阀杆处添加绝热层的方案，并进行模拟验证。此外，还将自行设计和制作一套可控温深冷处理实验台，以供不同材料在不同低温环境下进行了深冷处理，为进一步展开深冷处理机理的研究提供一个平台。最后，利用不锈钢方板的沸腾实验中测得的内部温度分布数据，利用反传热分析方法来求解方板表面对液氮的对流换热系数，并结合公式进行分析比较。本文只是对一维反传热问题进行了初步研究，为深入开展相关研究以及进一步开展深冷处理机理的研究和深冷处理的模拟计算提供参考。更多还原

【Abstract】 Cryogenic systems have been widely applied in modern industries in recent decades. At low temperatures, change of material structure may occur, e.g., the transition of stainless steel crystal from austentite to martentite, accompanied by the change of property (including size dimension). To avoid the negative influence due to the property instability, the aforehand cryogenic treatment of structural material is required. Besides, tests at low temperatures are also usually needed to examine the sealness and mechanical properties of cryogenic valve products before puting them into use.Experiential equations and researched results have been reviewed to propose the convection heat transfer coefficient of valve material, which is immersed into liquid nitrogen. Based on this, experiments have also been conducted to obtain the cooling-down curves of a stainless steel disc, which are then compared with the simulation result to modify the convection heat transfer coefficientThe modified convection heat transfer coefficients are used to simulate the cryogenic valve’s dynamic heat transfer process, in order to guide the cryogenic treatment and product test. To solve the problem of icing on packing, a scheme of adding insulation material at the shaft position is proposed. Simulation is then carried out to check the effect of the addition of insulation layer.An experimental apparatus, with controllable operating temperature, has been built up for cryogenic treatment of different cryogenic engineering material. The platform is expected to support our further study on the mechanism of cryogenic treatment.Finally, the "inverse" heat transfer method is adopted to analyze the heat transfer coefficient through some relatively simple experimental measurement of temperature distribution inside a stainless steel plate. The preliminary work in this aspect shows the feasibility of this method, and also demonstrates the difficulties to realize it, especially the sensitivity with temperature measurement accuracy. More efforts should be devoted on this, and it will be helpful for accurate simulation of the dynamic heat transfer process.更多还原