Study On The Mechanism Of Low Temperature Throttling Refrigeration In The Middle Time Of Space Cold Shield System

With the development of low-temperature refrigeration,space low-temperature refrigeration technology has become a topic of common concern around the world.Infrared stealth technology uses space low-temperature technology to reduce the intensity of infrared radiation on the surface of the cold-shield.The specific method is that the refrigerant in the cold-shield absorb heat by evaporating to reduce the temperature of the cold-shield system,thereby reducing the intensity of infrared radiation on the surface of the cold-shield and achieving the effect of infrared stealth.In actual conditions,the cold-shield surface receives radiation from the external environment that changes with the change of the space environment.In order to achieve the temperature of the cold-shield surface to meet the requirements of infrared stealth,the cooling capacity caused by the phase change of the refrigerant must also change accordingly.The amount of saturated steam generated inside the cold-shield is also different,which leads to changes in the steam pressure inside the system,especially when the space environment changes drastically,a large amount of refrigerant will quickly evaporate and generate a large amount of saturated steam.If these saturated steam cannot be discharged in time,the internal pressure of the cold screen will be too high,causing unnecessary safety hazards to the aircraft.In view of the above problems,this paper proposes a throttle pressure reducing valve device.This device mainly plays a role in controlling the internal pressure and throttling of the cold shield system.Firstly,passing different mass flow saturated steam to explore the effect of mass flow on throttling refrigeration,secondly change the structure of the throttle valve,pass in saturated steam with a certain mass flow rate,and explore the effect of the structure on the throttling refrigeration.This article takes the decompression throttle valve of space cold shield system as the research object,and the relevant theories are taken as the research basis to analyze the throttling effect of the reducing and throttling valve in the space cold-shield system.Firstly,establish a three-dimensional single channel throttle and pressure reducing valve model,using numerical simulation calculation method to obtain the distribution of temperature field,pressure field,velocity field and density field under saturated nitrogen with different mass flow rates.The origin is used to draw the distribution curve of each parameter along the streamline to analyze the effect of mass flow on throttling refrigeration of space cold shielding system.Secondly,in view of the mass flow of saturated nitrogen is too large and the throttling refrigeration effect is not good,a multi-channel throttle valve is established,and the method of multi-channel simultaneous throttling is used to divide a large mass flow fluid into several small mass flow streams.The fluid is passed into each throttle valve for numerical simulation,and obtain the distribution of each parameter cloud,and drawn a curve chart to analyze the throttling cooling effect and compared with a single channel.Finally,explore the influence of the structure of the decompression throttle valve on the throttling refrigeration effect.It is mainly used to change the outlet cross-sectional area of the single-channel decompression throttle valve,the shape of the valve core and the shape of the diffusion chamber.Carry on the numerical simulation to the above three situations separately,and carry on comparative analysis with the result,obtain the influence of the throttle reducing valve structure on the throttle cooling effect.The conclusion is as follows: the temperature of saturated steam decreases after reducing and throttling valve,and then it will turn into supercooled steam and enter the secondary expansion pipe to realize the secondary refrigeration,so as to reduce the filling of liquid nitrogen and the total mass of the aircraft;The magnitude of saturated steam mass flow will affect the effect of throttling refrigeration.The simulation results show that the greater the mass flow,the greater the fluctuation of various parameters within the fluid,and the smaller the temperature difference and pressure difference between the inlet and outlet,the throttle effect is not good.Therefore,the mass flow should not to be too large;multi-channel throttle valve is more stable than single-channel throttle valve at high flow throttle,and the throttle effect is better;The outlet cross-sectional area also has a great influence on the throttling effect of the throttle valve.The main performance is that the smaller the outlet cross-sectional area is,the abnormal phenomenon will appear in the internal parameters of the fluid,which will seriously affect the throttling cooling effect.Therefore,the outlet cross-sectional area of the throttle valve should not be too small;Removing the upper part of the valve core has little effect on the cooling effect of throttling,but after changing the shape of the diffuser cavity,the internal fluid change of the throttling valve is unstable,so the throttling effect becomes worse.