Gas-solid Heterogeneous Reaction Model For Thermal Protection Design

Gas-solid interface heterogeneous reaction model is the theoretical basis for thermal protection design of hypersonic vehicle.In order to effectively solve the problem of hypersonic heat and mass transfer,from the 1950s,the interdisciplinary integration among gas dynamics,thermodynamics,thermochemistry,molecular motion theory,quantum theory and statistical mechanics gradually formed aerodynamic thermodynamics theory with its own characteristics,which provides a theoretical basis for the study of this problem.However,the theoretical basis of gas-solid heterogeneous reaction model,characterization relationship and engineering application in the study of coupled heat and mass transfer between high enthalpy flow and thermal protection material properties is very weak,and can only pass a large number of but not fully simulated flight environment.The research can only be carried out through a large number of ground simulation tests,however,which is not able to fully simulate the flight environment.Whether it is possible to improve and establish the gas-solid heterogeneous reaction model,characterization relationship and engineering application evaluation method,is one of the key theoretical and engineering problems that need to be solved urgently in the thermal protection design of the new generation hypersonic vehicles.Aiming at the problems faced in current research of gas-solid heterogeneous reaction,such as the theoretical model defects,the dependence of activation energy and pre-exponential factors on a large number of experimental data,the model limitations from chemical non-equilibrium effects,the coupling prombles of active/passive oxidation and volatilization/decomposition,the following aspects are studied in this paper:The high-temperature chemical reaction model was studied.Under the conditions of engineering precision,the constraints of the Earth/Mars atmosphere mixture based on the 4-component and 7-component chemical models were established,and the gas mixture energy transfer simplified equation under the respective chemical model was derived.This equeation could provide a reliable chemical model for the rapid and efficient determination of thermal environmental parameters in the hypersonic aircraft thermal protection design.Based on the Blasius exact solution of the classical infinitely large incompressible plate boundary layer equation,the source of the relevant parameters in the stagnation point reflow heat transfer formula is analyzed.The convective heat transfer formula of the blunt-spinning stagnation point in the dissolving Mars environment is established by the analogy method.The reliability of this formula is verified by the 31 feet,Mach 10continuous hypersonic wind tunnel and the HYPULSE expansion tube wind tunnel,the deviation of less than 9%.Based on the fundamental constraint conditions of gas-solid heterogeneous reaction based on simple collision theory,and combined with the relationship between the heterogeneous reaction rate of gas-solid interface and the parameters of interfacial gas phase components in traditional aerodynamic thermodynamics theory,the relationship between gas-solid heterogeneous reaction probability and reaction rate,boundary layer finite mass transfer and reaction probility,the probability characterization model of heterogeneous reaction of gas-solid interface is established.By the Couette flow model,the effect of gas-solid heterogeneous reaction in the chemically frozen boundary layer flow on the heat and mass transfer is analyzed.The approximate processing method of heat and mass transfer for the gas-solid interface heterogeneous reaction in the chemical non-equilibrium boundary layer or shock layer is given.By comparing and analyzing the traditional theoretical model and new theoretical model of the gas-solid interface atomic catalytic recombination coefficient,combined with the new theoretical model and wind tunnel test results,the relationship of N and air atoms catalytic recombination coefficient for RCG,SiC and other materials was established,and the correctness of gas-solid atom catalytic recombination model was verified.On this basis,the quantitative influence of the difference between the flight and the ground on the heat transfer at the stagnation point gas-solid interface is analyzed when the gas-solid interface is only heterogeneous atomic catalytic recombination reaction,and the selection of ground simulation parameters is realized.The approximate treatment method of heat and mass transfer in heterogeneous reaction of chemical non-equilibrium boundary layer gas-solid interface and the interpretation method of experimental data in gas-solid interface atomic catalysis/nitriding coupling reaction are studied.The relevant reference data is used to determine the activation energy of oxidation reaction with oxygen atoms and oxygen molecules on the solid phase carbon surface.And the activation energy of gas-solid heterogeneous reaction on the surface of typical materials is given.The Nitriding/catalytic couping reaction on the surface of solid phase carbon under non-equilibrium dissociation of N atoms of the N,N₂ jet environment is studied.This experimental study verified the reliability of the activation energy determination method and the chemical non-equilibrium dissociation boundary layer heat and mass transfer method,and further determined the practicality of the theoretical model and the characterization relationshipThrough the research of this paper,the gas-solid heterogeneous reaction model with relatively solid theoretical foundation is established and improved,which could solve the main problems of the heat and mass transfer model and characteristics in the coupling thermal environment and thermal protection material performance that faced by the new generation hypersonic vehicle.