【作者】 杜宏鹏；

【导师】 王莉； 贾林祥；

【作者基本信息】 哈尔滨工业大学 ， 制冷及低温工程， 2008， 博士

【摘要】 随着现代粒子加速器、可控核聚变装置等大科学工程的建设,推进了超导磁体和超导加速腔向更大的磁场强度和更高的加速梯度发展,同时也促进为超导设备提供冷量的氦低温系统也由4.2K液氦温区向超流氦温区发展。本文以超导射频腔超流氦低温冷却系统为研究对象,采用数学模拟方法深入研究了超导射频腔的超流氦低温系统的热力循环性能,分析了超导加速腔的工作运行温度对超导腔低温系统功率消耗的影响关系等;针对4.5K氦低温系统和2K超流氦低温系统中不同设备的动态特性,采用集中参数法和分布参数法,建立了系统的动态仿真数学模型,编制了动态降温过程仿真程序,对4.5K氦低温系统以及超流氦低温系统的降温过程进行了深入的研究分析。经济合理的超流氦热力循环是进行动态降温过程分析的前提,本文首先利用大型过程分析软件及其用户自定义模块对温度为2K、制冷量为100W的超流氦低温冷却的热力循环方案进行了研究,从提高超流氦冷却系统的效率方面,对百瓦量级超流氦低温制冷系统进行了深入的冷却流程方案的热力学分析和研究,比较了不同冷却方案下超流氦制冷系统的制冷效率等因素,研究结果表明:带回收负压氦气冷量的负压换热器和预冷用低温换热器的氦制冷循环,其系统的制冷效率最大,但系统结构也较复杂,设备投入成本高,运行费用低。以广泛用于高能物理加速器的1.3GHz超导加速腔为例,深入分析研究了影响其工作性能的BCS表面电阻和制冷系统耗功与超导腔运行温度之间的关系,获得不同制冷温度下由超导腔的BCS表面电阻引起的超导腔射频损耗和制冷系统功耗,研究表明:合理选择超导加速腔的工作运行温度对于降低制冷系统的运行成本效果显著。最后,根据这两种主要损耗确定了适合该型超导腔的工作运行温度。氦系统动态仿真研究,主要是为了模拟氦系统在降温、升温以及非正常稳态运行等动态变化热力过程,研究动态过程中系统热力性能的变化规律,为系统的优化设计、实际运行操作提供理论依据。针对优化的超流氦热力循环方案,本文将相应的超流氦制冷系统划分为4.5K氦制冷系统和超流氦制冷系统两部分。运用制冷系统热动力学理论,采用集中参数法和分布参数法,分别根据各设备的工作特点,建立其动态仿真数学模型,并采用计算机编程语言FORTRAN对氦低温系统不同降温方案的降温过程进行了仿真模拟。动态仿真中考虑并研究了主要的低温调节阀门的开度、相应的氦气质量流量对降温过程系统各点热力参数的影响。结果表明,降温过程中压缩机旁通阀的开度变化直接影响系统的降温时间。进入系统的氦气质量流量受到透平膨胀机和节流阀流通能力的限制,必须在降温过程中调节压缩机的旁通阀来控制进入冷箱的氦气质量流量。通过动态仿真,获得了氦低温系统动态降温过程中沿氦气流动方向上复杂的温度变化规律,给出了氦制冷机系统内部沿氦气流动方向上温度测点的温度值在温熵图上的变化趋势。通过对4.5K液氦制冷系统以及超流氦制冷系统的动态降温过程的数值模拟还发现:采用低温换热器的超流氦制冷系统在降温过程中产生2K超流氦的时间要早于系统中产生130kPa的饱和液氦所需要的时间。仿真结果还表明,氦制冷系统的动态仿真结果可以对优化氦制冷机试车方案、节省调试费用、节约调试时间、进一步提高氦制冷机制冷效率提供可靠的理论基础。更多还原

【Abstract】 Large-scale superconducting magnets are presently widely used in modern high-energy particle accelerators and controllable nuclear fusion experimental device, which develops superconducting magnet and superconducting RF cavity technology toward higher magnetic field and higher accelerating gradient. Meanwhile the liquid helium cryogenic systems applied on superconducting devices are developed from 4.2K temperature region toward superfluid helium temperature region.In this thesis, the thermodynamic performance of superfluid helium cryogenic system cooling SRF cavities is deeply analyzed through numerical simulation. The influence of SRF cavity operating temperature on power consumption of SRF cavity system is researched also. The dynamic simulation models of key components in both 4.5K helium cryogenic system and 2K superfluid cryogenic system are built based on lumped-parameter and distributed-parameter methods. The cooling process of both 4.5K helium cryogenic system and 2K superfluid cryogenic system are deeply analyzed using reliable dynamic simulation procedure developed in this thesis.The premise of dynamic cooling process analysis is economical and reasonable thermodynamic cycle. At first, the scheme of 2K then the refrigerating output is 100W superfluid helium cryogenic thermodynamic cycle is studied using large process analysis softare and its user-defined models. Then the thermodynamic analysis of 2K superfluid helium cryogenic is deeply studied to improve the refrigerant efficiency, system reliability, and system adaptability. Compared the refrigerant efficiencies of superfluid helium cryogenic system under different cooling schemes, it shows that the helium cryogenic system with pre-cooling heat exchanger and negative pressure heat exchanger to recover cooling capacity of helium gas has the highest refrigerant efficiency, lowest operation cost, but the system structure is more complex and the equipment cost is higher.1.3GHz SRF cavities are widely applied to high-energy accelerators. The relationship between BCS surface resistance, power consumption of refrigerator and SRF cavity operating temperature are thorough analyzed. The radio-frequency losses of SRF cavity and power consumptions of refrigerator for different operating temperatures due to BCS surface resistance of SRF cavity are researched. The result shows that the reasonable operating temperature of SRF cavity can obviously reduce the operation cost, and the optimal operating temperature of this kind of SRF cavities are determined based on the two kinds of dominate losses.The dynamic simulation study of helium system is mainly on the dynamic thermodynamic process during cooling-down, warming-up and non normal operation mode. The analysis results can provide theoretical basis for the optimum design of helium system, and practice operation.In this paper, the superfluid helium refrigerator system is divided into 2 parts: 4.5K helium refrigerator system and superfluid helium refrigerator system. Based on the thermodynamics theory of the refrigeration system, the dynamic simulation model of each cryogenic component has been built according to its working characteristic, and utilizing lumped parameter and distribution parameter technique. The different cooling-down processes of superfluid helium refrigerator have been simulated using the FORTRAN program developed by this thesis.The influences of the opening of main cryogenic governor valves and helium gas flow rate on the refrigerator system parameters during cooling-down process are considered and researched in dynamic simulation. The simulation results shows that the opening variety of compressor by-pass valve affects cooling-down time of refrigerator system directly. The helium gas flow rate entering refrigerator system is limited by the negotiabilityof turbine expander and throttle valve, and must be controlled during cooling-down process by adjusting compressor by-pass valve.Through dynamic simulation the complex temperature distribution regularity along helium flow direction is obtained, and the temperature variety tendency on temperature-entropy figure of temperature measuring points along helium flow direction in helium refrigerator is presented in this thesis.The dynamic simulation of cooling down process shows that utilizing cryogenic heat-exchanger the time when the superfluid appears in the superfluid helium refrigeration system is earlier than time that the saturation liquid helium appears in the system.The dynamic simulation result also indicates that the trial-run scheme of helium refrigerator can be optimized and the debugging cost and time can be saved though dynamic simulation.更多还原