Research On The Model Of Flow And Heat Transfer In The Catalytic Bed Of Monopropellant Engine

Monopropellant liquid rocket engine is widely used in attitude and orbit control of spacecraft.Because the main processes of flow,reaction and heat transfer occur in catalytic bed,it is necessary to simulate the physical process in the catalytic bed of monopropellant engine.However,in simulation,it is difficult to determine the flow resistance coefficient and heat transfer coefficient of the catalytic bed accurately.In order to obtain the empirical formulas of the flow resistance coefficient and the heat transfer coefficient of the catalytic bed,this paper studies the flow and heat transfer process in catalytic bed in detail by numerical simulation and test on the basis of the catalytic bed of hydroxylamine nitrate-based monopropellant engine.Firstly,according to the theory of porous media,the flow and heat transfer process of gas in catalytic bed is simplified,and then the one-dimensional calculation program of flow and heat transfer in catalytic bed is developed.On this basis of the research,it is proposed to modify the empirical coefficient of flow resistance in catalytic bed based on the Ergun equation,and an inverse problem is proposed to obtain the convective heat transfer coefficient of the catalytic bed.In this paper,a test platform for the flow and heat transfer process of catalytic bed is built,the properties of catalyst particles and the structural parameters of catalytic bed is measured,and the cold flow test is carried out.Then,the empirical formula of flow resistance coefficient of catalytic bed is obtained by numerical simulation.The result shows that the compressibility of the gas must be considered in the calculation of Ergun equation,and the resistance coefficient obtained in this paper can more accurately simulate the pressure drop of catalytic bed.Furthermore,the convective heat transfer coefficient of the catalytic bed is concluded by comparing the hot flow tests under several conditions in the catalytic bed and numerical simulations,from which the correlation of Nusselt number in the catalytic bed is obtained.Meanwhile,the one-dimensional calculation program of flow and heat transfer in catalytic bed and the reasonableness of the inverse problem for the convective heat transfer coefficient are proven effective.Research shows that the convective heat transfer coefficient obtained in this paper can accurately describe the heat transfer process in the catalytic bed,and the heat capacity of particles has more impact on the calculation results than the convective heat transfer coefficient.Finally,in accordance with the previous empirical correlation,the simulation parameters of the catalyst bed of a hydroxylamine nitrate-based monopropellant engine are analyzed,and the unsteady startup process of the engine is simulated by one-dimensional model and twodimensional model respectively.The results show that the inlet pressure is 1.6 MPa,which is close to the test data,and the temperature distribution in the catalytic bed of engine is accurate.In addition,the heat capacity of particles and the specific surface area of the catalytic bed are important for the simulation of the catalytic bed of the engine,which means the effect of temperature on the specific heat capacity of particles cannot be ignored.All these above results indicate that the method of obtaining the flow resistance coefficient and heat transfer coefficient is reasonable,and it is helpful for the design of monopropellant engine.