| The 7W/4.5K G-M/J-T helium refrigerator manufactured at Institute of Cryogenics and Superconductivity Technology in Harbin Institute of Technology in 2003 has some drawbacks such as: slow cooling down spade, inefficiency and so on, and the system needs to be improved. The improved work will consider both the dynamic and steady characteristic. To achieve this goal, research on dynamic simulation on this system was done in this dissertation, a dynamic simulation test plant was built up based on SIMULINK and the characteristic of cooling down process has been obtained.Based on the investigation result of relational study at home and abroad, the SIMULINK package was adopted as the simulation tool, S Function was used to build up the unit module and the masking technology was used to design GUI. The matter thermophysical properties were calculated using looking up table method and applicable correlations formula to calculate the convection heat transfer coefficient was selected. The distributed parameter model of partial differential equations, derived form energy conversation and mass conversation, solved using numerical method was used to build up the dynamic model of tube heat exchanger. The dynamic model of the G-M heat exchangers were obtained from the experimental data based on the energy conversation. Based on isenthalpic process the dynamic model of adjustable J-T valve was build up. A dynamic simulation test plant was build up in SINULINK and the research on dynamic simulation has been completed.In this dissertation, the temperature and pressure drop change trend in the cooling down process has been obtained and analysed. The deviation between the model and the real plants has been discussed.The dynamic simulation test plant built up in this dissertation makes it possible to analysis the dynamic and steady characteristic of the system by the mean of computer simulation. This test plant will help the system to be optimized and improved.
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