Simulation Of Multi-Channel Cryogenic Throttle Valve In Space Cold Shield System

The built-in throttle valve of the cold-shield system is the core equipment for the safe and stable operation of the space cold-shield system,which is also the core equipment for the infrared shielding effect of the cold-shield system.The heat transfer process of the aircraft in the middle of space is complicated.When the surface of the cold-shield system is heated by high heat flux,the refrigerant in the cold-shield system evaporates rapidly to produce a large amount of saturated vapor.If this part of the saturated steam cannot be removed in time,it may cause safety risks to the normal working of the cold-shield system.In addition,if a large amount of saturated vapor be discharged in a non-throttling form,the surface temperature of the cold-shield system will rise and the infrared shielding effect will be lost.There are few studies on the built-in throttle valve of the space cold shielding system,and there is no research on how to deal with the problem of large flow throttling in space.According to the existing low temperature throttle valve technology,this article presents a multi-channel throttle valve structure of cold-shield system,which based on the space cold-shield system near three-phase points throttling refrigeration principle.It can deal with the phenomenon that the surface temperature of the cold screen risen when the large flow saturated nitrogen be discharged from the inside of the cold-shield system.Determine the basic parameters and dimensions of the multi-channel throttle valve of the cold-shield system according to the built-in pipeline requirements of the cold-shield system,and establishing a three-dimensional model.Using numerical simulation method,the multi-channel throttle valve produces the throttling effect area,that is,the flow field at the outlet of the diffuser chamber and the spool.After determining the maximum evaporation of the cooling screen system,analyze the changes in related parameters of the throttle valve outlet flow field under different working conditions,and analyze the entropy changes before and after the throttling process with the help of the T-S diagram.On this basis,the numerical calculation method is used to determine the change of the unit refrigeration capacity of each channel of the multi-channel throttle valve,and the relationship between the throttle refrigeration capacity of the multi-channel throttle valve and the mass flow rate,the relationship of this change is simulated by the MATLAB software.By changing the number of valve channels and the way of channel arrangement,a new structure attempt was made on the multi-channel throttle model,and models with different channel numbers were established according to the two structural relationships of with and without central channels.By comparing two different structure models,the influence of valve structure and channel number on throttling refrigeration effect is obtained.Under the corresponding number of channels,the distribution law of throttling outlet parameters,the unit cooling capacity of each channel and the valve cooling capacity.The conclusion is as follows: the temperature of saturated nitrogen is reduced after being throttled by the multi-channel throttle valve and enters the secondary expansion pipeline.The cooling capacity produced by throttling refrigeration can effectively prevent the increase of the surface temperature of the cold-shield system caused by the overflow of saturated nitrogen.It can also reduce the amount of liquid nitrogen in the system and reduce the total mass of the aircraft.As the mass flow rate of saturated nitrogen at the inlet of the valve increases,the temperature of the fluid at the outlet decreases,the velocity and pressure increase.At the same time,the outlet temperature and pressure of the central channel are higher than the equilibrium channel.The mass flow rate of saturated nitrogen increases,the unit refrigeration capacity shows a decreasing trend,the refrigeration capacity of the valve channel increases.The refrigeration capacity of the multi-channel valve increases,which meets the working requirements that the throttling refrigeration effect can still be produced under the maximum mass flow.This fitting equation can also effectively predict the relationship between the valve refrigeration capacity and the mass flow rate.Under the same mass flow,the unit refrigeration capacity of the center channel is less than the balance channel,indicating that the throttling cooling effect of the balance channel is better than the center channel.