Research On The Decompression Process Of High Pressure Hydrogen And Optimization Of Decompression System

In hydrogen fuel cell vehicles,hydrogen is usually stored in high-pressure tank.In order to achieve a higher range of hydrogen fuel cell vehicles,the pressure of the tank is constantly increasing,and the optimal operating pressure of the fuel cell is only0.1 ～ 0.3MPa.Therefore,higher requirements are put forward for the performance of the decompression system.The effective decompression of high pressure hydrogen in the pressure reducing system is the key to the safety and stability of hydrogen fuel cell vehicles.Therefore,it is necessary to study the valve of high pressure hydrogen pressure reduction.In this paper,the three-dimensional computational fluid dynamics(CFD)model of compressible high pressure hydrogen flow is established,considering the influence of high compressibility of hydrogen on the thermal physical parameters.The model accurately predicts the thermal and physical properties of high pressure fluid by Peng Robinson(PR)real gas state equation.Compared with experimental data,it is proved that the model can accurately simulate the real flow state of high pressure hydrogen in complex structure of pressure reducing system.The main research contents and achievements of this paper are as follows:(1)In the verification of hydrogen thermophysical properties,it is found that the ideal gas equation of state overestimates the density of hydrogen under high pressure.This directly leads to a 73% decrease in the maximum flow rate and a 72% decrease in the Mach number of the single-stage Tesla valve compared with the traditional orifice valve under the same decompression effect,which means that the Tesla valve has less noise and the hydrogen flow in the Tesla valve is more stable;With the decrease of the two-stage spacing of Tesla valve,the backflow of hydrogen in the main channel of the later stage valve will hinder the flow of hydrogen in the main channel of the previous stage valve.The smaller the two-stage spacing,the stronger the blocking effect,so that greater pressure drop can be obtained;The unidirectional conductivity of Tesla valve is due to the obstruction of the fluid in the curved channel of each stage valve to the fluid in the straight channel,and the pressure drop will increase linearly with the increase of stages.(2)Tesla valve was successfully introduced into the traditional perforated plate pressure relief valve,and the pressure drop of the new Tesla type orifice valve increased by 238% compared with the traditional DC channel orifice pressure relief valve.Tesla type two-stage orifice pressure reducing valve has high pressure drop performance under small inlet mass flow.At the same mass flow rate,the maximum Mach number of Tesla orifice relief valve is higher than that of orifice relief valve before hydrogen supersonic flow.When supersonic flow occurs,the maximum Mach number of the two is almost the same.Increasing the number of parallel Tesla valves can effectively reduce the maximum Mach number.Due to the structural asymmetry of Tesla type orifice relief valve,hydrogen flows out of the orifice and forms a wall sticking effect on the lower wall,while eddy current is generated on the upper wall.When the valve inlet mass flow rate increases to a certain value,there will be expansion wave at the outlet of the orifice.When hydrogen flows through the expansion wave,a small fanshaped region of low pressure,low temperature and high speed will be formed.(3)A multi-stage high-pressure hydrogen pressure reducing valve was constructed by combining Tesla type orifice plate pressure reducing valve and sleeve type pressure reducing valve.When the opening of the valve is small,the pressure reduction effect of the first stage spool is high,followed by the Tesla orifice valve,and the pressure drop performance of the multi-stage sleeve is low.With the increase of valve opening,the role of Tesla orifice relief valve in the whole decompression process becomes larger,the decompression efficiency of the two-stage sleeve will be improved,and the decompression efficiency of the first stage spool will be reduced due to the increase of valve opening,the flow channel area will be increased.The research on the flow state of multi-stage high-pressure hydrogen pressure reducing valve shows that the mutual impact of hydrogen ejected from the valve core orifice and the change of flow direction in the outlet valve chamber lead to different degrees of eddy current in the inlet section of the valve core,outlet valve chamber and Tesla type orifice pressure reducing valve.Eddy current may cause valve vibration,noise,flow obstruction,etc.,which can be improved by changing the flow direction of the valve and increasing the pressure drop performance of multi-stage sleeve and primary spool.