【作者】 张杰；

【导师】 舒水明；

【作者基本信息】 华中科技大学 ， 制冷及低温工程， 2008， 硕士

【摘要】 脉冲强磁场装置是开展极端条件下科学研究的重要装置。稀释制冷系统是其低温部分的重要组成部分,其系统参数的优化可以保证为科学实验提供稳定、足够制冷功率及合适制冷温度的超低温环境。根据实验装置的实际情况选择了合适的热交换器形式-套管式热交换器,并改进了换热器的形式,强化传热;在进行模拟之前,收集整理材料物性值,选取合适的数值方法—最小二乘法曲线拟合,并编制程序进行计算,得出物性的函数表达式;对换热器内部流动换热过程建立了计算数理模型,利用FLUENT流固耦合模型Coupled,并将壁面温度和对流换热系数做了合适的处理,结合实际编写Udf程序,使状态方程、边界条件、和数理模型结合起来求解。叙述了这些确定条件在FLUENT软件中的实现方法,为用FLUENT软件模拟整个传热过程做充分的准备。模拟计算结果与理论值进行了比较,变化趋势与理论一致,计算模型和结果较为正确。用FLUENT数值模拟了套管式换热器的换热特性。首先,计算了不同换热器长度L(0.8m、1m、1.2m、1.4m),不同3He进口速度V(0.001m/s、0.002m/s、0.003m/s、0.004m/s),不同的换热器管径D(0.3mm、0.5mm、0.7mm、1.0mm)对换热器出口平均温度的影响;此外,还模拟了在相同质量流量下,不同的3He循环流速V和换热器管径D的组合,换热器出口平均温度的变化趋势,进而得到L、V、D对出口平均温度的影响趋势及相互之间的影响。此外,根据气液相平衡的关系式、两相分离的原理,综合考虑超流氦分离的特点,结合脉冲强磁场装置的实际需要,对稀释制冷系统相分离装置进行了理论分析并给出相关优化措施;提出了一个尺寸结构的优化方案。更多还原

【Abstract】 Pulsed High Magnetic Field Device is important to science research under extreme conditions. Dilution refrigeration system is an important part of its cryogenic system. Stable, adequate cooling power and suitable ultra-low temperature environment for scientific experiments can be provided through the optimization of system parameters.According to the actual situation of experimental device, Casing heat exchanger is selected as the suitable form of heat exchangers. By improving the form of heat exchanger, the exchange of heat is strengthened. The materials property is collected before simulation, least squares fitting is selected as the appropriate numerical method, and then the expression of property parameters is educed by programmed calculation. The heat transfer process simulation model is established, the wall temperature and heat transfer coefficient are amended on basis of the fluid-coupling model-Coupled, and the state equations, boundary conditions, physical parameters and math model are combined calculating by UDF programmer. Meanwhile the settings and operations in FLUENT are discussed in detail. The simulation results are compared with the theoretical values, the changing trends is consistent with the theory, the simulation models and results are correct.The performance of casing heat exchanger is simulated and analyzed by FLUENT. First, different heat exchanger length L (0.8m, 1m, 1.2m, 1.4m), different 3He inlet velocity V (0.001m / s, 0.002m / s, 0.003m / s, 0.004m / s), different heat exchanger diameter D (0.3mm, 0.5mm, 0.7mm, 1.0mm) are calculated , and the impacts of these parameters on the area-weighted-average temperature are analyzed. In addition, under the combined situations of the same mass flow, different cycle velocity of 3He V and heat exchanger diameter, the outlet area-weighted-average temperature is calculated, and the changing trend of temperature is found out. Then the impacts of L, V, D parameters on area-weighted-average temperature as well as interaction impacts of these parameters are analyzed.Furthermore, in accordance with the gas-liquid equilibrium and two-phase separation principle, combining with the characteristics of super-fluid helium separation and the needs of Pulsed High Magnetic Field Device with dilution refrigeration system, phase separator of dilution refrigeration system is theoretical analyzed and optimization measures is proposed. And a proposal of structural optimization is given.更多还原