Heat Sink Distribution Characteristics Of Steam Reforming Process Of Supercritical Hydrocarbon Fuel

Hypersonic aircraft with a Mach number greater than 5 is a hot spot in the field of aerospace research today.Its power unit,the scramjet engine,has the largest thermal load among all advanced aeroengines.The engine has serious heat dissipation problems,and thermal management is an effective solution.The chemical regenerative cycle uses an endothermic chemical reaction to provide additional heat absorption capacity for the engine wall,which is called chemical heat sink.The maximal theoretical heat sink that can be provided by the thermal cracking reaction is 3.5 MJ/kg,which cannot satisfy the flight with a Mach number greater than 7,and the theoretical total heat sink of the steam reforming reaction can reach 10 MJ/kg.For effective utilization of chemical heat sink,deep understanding of underlying physicochemical mechanism and factors is necessary,which affects the distribution of chemical heat sink.Therefore,one-dimensional and two-dimensional numerical models of the steam reforming process of hydrocarbon fuels under supercritical conditions are established,and the distribution of chemical heat sink is simulated and studied.A one-dimensional numerical model of the steam reforming process of hydrocarbon fuels in the micro channel is established.The semi-discretization method of partial differential equations is used to discretize the one-dimensional unsteady control equations.The pipe section is averaged by the one-dimensional model,the characteristics of the wall reaction on the inner surface of the pipe cannot be reflected.To solve this problem,the surface reaction is equivalent to the volume reaction.The established numerical model is verified,and the key factors affecting the energy conversion of the steam reforming process are analyzed through the derivation of the one-dimensional energy equation.The flow and endothermic coupling characteristics of the steam reforming process of hydrocarbon fuels under supercritical conditions are analyzed,and the influence of different factors on the flow direction distribution characteristics of the chemical heat sink is studied.As inlet velocity increases,the maximal value of chemical heat sink decreases slightly.As the working pressure increases from 3MPa to 5MPa,and the maximal value of chemical heat sink reduces by approximately 15%.The inlet water content has the most significant impact on the chemical heat sink,and as the water content increases from 5% to 10%,the maximal value of chemical heat sink is approximately doubled.Based on the analysis of the flow direction distribution of the chemical heat sink,the inhomogeneity of the radial flow and the complex coupling characteristics of the endothermic steam reforming process in the two-dimensional model are further analyzed,and the product and the chemical heat sink on different cross-sections are analyzed in detail.The influence of different factors on the radial distribution characteristics of chemical heat sink is studied.As inlet velocity increase,the chemical heat sink decreases first and then increases in the radial direction.The maximal value of the chemical heat sink is almost the same.As working pressure increases,the chemical heat sink decreases in the radial direction.As inlet water content increases,the chemical heat sink increases in the radial direction.The competitive relationship between the endothermic reaction and the exothermic reaction in the steam reforming process causes the chemical heat sink to gradually decrease after reaching the maximal value.To solve this problem,a model of the secondary water addition in the middle of the pipe is established.On the premise of avoiding additional burden on the engine,the distribution of the chemical heat sink is optimized,which effectively improves the chemical heat sink.As inlet velocity increases,the chemical heat sink increases in the second half of the pipe.As the secondary water addition within a reasonable range increases,the distribution of chemical heat sink can be effectively improved and the maximal value of chemical heat sink increases significantly.