4He depressurization refrigeration is a commonly used method for obtaining ultra-low temperatures at present.To improve refrigeration efficiency,orifice structures are often used to reduce the influence of superfluid helium films,which in turn restrict the circulation flow rate of 4He.This article summarizes the flow velocity models of various parts in the orifice structure and establishes a mathematical model for pumping speed,flow limiting aperture,and liquid helium evaporation flow rate.Explored the relationship between pumping speed and flow rate in the orifice structure.With the orifice diameter determined,the relationship was divided into three stages,corresponding to the maximum flow rate of superfluid helium film evaporation,1K pot liquid helium evaporation,and 1K pot liquid helium evaporation,respectively.
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