Study On The Transfer Parameters And Obtaining Of He II

The key technologies of the CGSE system are of the filling and transferring of He I, and the achieving of 1.8 K He II by vacuum pumping. It is necessary to set up a simulating experimental system because the practical CGSE system is so complicated and large. The experimental system will simulate the flow process of He I in real operating condition and obtain He II. So that we can gain the key physical and technical parameters, information and the operation experience for the real engineering system. In the paper, both the theoretical studies and numerical simulations are carried out to analyze the physical characteristics of He I and He II, to obtain He II by vacuum-pumping method, and to study the temperature rise model of He II forced flow. The major works are summarized as follows:1.Study on the dependence of the viscosities of He II on the experimental techniques: Based on the summary of experimental data of the viscosities, it is found that the viscosities of He II have different values under different experimental technologies. The key work of this chapter is of finding the detail values of the viscosities of He II in terms of operating conditions to propose a simple equation to calculate them at practical operating conditions.2.Study on the viscosities of LJ fluid and helium by molecular dynamics. The LJ potential function is adopted to simulate the viscosities of supercritical argon and supercritical helium. The results show that the values of supercritical argon are close to that provided by NIST (National Institute of Standards and Technology) in comparison of the simulation results of supercritical helium. The reason is that helium is a quantum fluid and has quantum effect that has not been considered in the LJ potential function. Therefore, the quantum effect must be considered in order to obtain the accurate values for quantum fluid. In this chapter, the FH(Feynman-Hibbs)potential function has been used to solve the problem. It is found that the quantum effect becomes stronger with the decreasing of the temperatures and the calculation time becomes much longer.3.Study on the schemes of obtaining He II. The mass and energy conservation model are used to analyze the liquid ratio of He II at different temperatures by vacuum pumping method. There are four methods to obtain He II, i.e. direct throttling process, throttling process with pre-cooling, vacuum pumping and vacuum-pumping with throttling process. Limited by the charging time and the assembly space, the He II should be quickly produced by a compact system with high working reliabilities. Therefore, selection of a scheme for producing He II is also a crucial work to the construction of the CGSE system. Based on the thermodynamic analyses of the processes in those four methods, the scheme of vacuum-pumping has been selected and the pumping speed has been also determined for choosing the vacuum pump.4.Set up the experimental system. Based on the characteristics and the performance of the CGSE system a simulating experimental system has been set up in order to test its major equipments and functions. Several essential technical problems are solved during the construction process, including how to leading-out the signal wires from the device, how to warm up and purge the system after the accident of system block. Data acquisition system and software are also developed. Test of the static evaporative rate of LHe Dewar, the heat leak of the coupling and the cryogenic pipe in the experimental system. Experimental studies on the liquid ratio of producing different temperatures of He I and He II, on the transferring performance of He I, and on the heat leak of the special four layer cryogenic pipeline. There are two aims for the experimental studies on the producing and transferring low temperature helium (lower than 4.2 K):(1) Producing the low temperature helium by vacuum-pumping method. Comparing the results of liquid ratio with the theory model. Obtaining engineering information and experience of producing He II and determining the liquid ratio;(2) Determining the performance of heat-insulating properties of the special four layer structure pipeline and supply the analysis data for the engineering design and application. The performance test of cryogenic transfer pipeline PL3 and PL14 in the CGSE system are also carried out by mass flowmeter in order to supply the analysis data for the operation of the real system;5.Theoretical analyses and calculations are carried out for the forced flow characteristics of He II. The results explain that the limit heat leak permitted by per meter line will be decreased with the length of the transfer lines increase. So more restrict requirement on the thermal insulation structure will be presented to the longer lines. Larger limit heat leak will be permitted when the transfer differential pressure increases. The temperature rise of He II transfer system due to the negative Joule-Thomson (JT) effect is one of the major problems in the system design for the He II forced flow system. The equation considering the pressure gradient effect is adopted to analyze the temperature distribution along the transfer pipeline for the He II forced flow system. Results are compared with those obtained by the simplified equation. The results calculated by the simplified equation are modified by the negative JT effect therefore the total temperature rises along the pipeline are obtained. The results show that the total temperature rises along the pipeline are similar to the values calculated by the complicated equation. So the simplified equation can also give good results of temperature rise when the negative JT effect of He II is known. The transfer properties of He II, obtaining of He II and the performance of the cryogenic pipes are experimentally and theoretically researched. The results are reasonable and helpful, especially for the engineering application of He I and He II.