Study of heat transfer in the boundary layer in a nitrogen flow past a catalytic graphite wall
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DOI: 10.1134/S0869864320020031
Study of heat transfer in the boundary layer in a nitrogen flow past a catalytic graphite wall N.I. Sidnyaev Bauman Moscow State Technical University, Moscow, Russia E-mail: [email protected] (Received December 29, 2018; revised June 26, 2019; accepted for publication November 6, 2019) The results of investigating the physical and chemical processes in the wall boundary layer on graphite specimens in a nitrogen flow are reported. The effect of the catalytic wall on the heat flux is considered. The emphasis is on analyzing the distribution of the chemical species concentrations across the boundary layer based on a detailed consideration of the mechanism of heterogeneous catalytic reactions under the surface mass flux conditions. The distributions of the chemical species concentrations over the boundary layer thickness at the stagnation point of a blunted graphite body for a particular flight path segment are presented. Keywords: heat transfer, boundary layer, catalysis, graphite, wall, reaction, energy.
1. Formulation of the problem Creation of hypersonic flying vehicles is accompanied by significant practical interest in studying the interaction of multispecies gas mixtures with catalytic surfaces in a supersonic flow. A typical feature of solving the problems of aerodynamics and heat transfer at large supersonic velocities is the necessity of taking into account dissipative processes caused by viscosity, heat conduction, and diffusion simultaneously with physical and chemical processes in the gas and on the surface, which may induce qualitatively new effects as compared to the perfect gas flow [1−8]. In such problems, researchers deal with a multispecies high-temperature chemically reacting mixture in a high-velocity flow where various gas-dynamic processes can occur. In the case of a nonequilibrium flow, it is necessary to take into account some processes of chemical energy transfer, which are ignored in equilibrium flows or ideal gas flows. In particular, catalytic properties of an indestructible surface are important during its interaction with the flow. Though a considerable effect of graphite surface sublimation on heat transfer at hypersonic flight velocities has been known since the 1950s, the problem of the description of heterogeneous catalytic processes in hypersonic flows is still urgent [9]. At the atmospheric flight path, flow regimes near the vehicle surface change from subsonic to hypersonic, from continuum to free-molecular, and from laminar to turbulent. Moreover, the dimensionless Mach, Knudsen, Reynolds, and Damkohler numbers vary within wide limits. As compared to the kinetics of homogeneous reactions, the mechanism and rates of the processes responsible for gas-surface interaction have been much less studied and are basically measured quantitatively. Nevertheless, understanding and control of these processes are extremely important for the development and fabrication of thermal protection systems used for spacecraft entry to N.I. Sidnyaev, 2020
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