Heat transfer in reacting gas mixtures with large pressure gradients

Mechanical Engineering

Marxman, Gerald Albert ; Marble, Frank E. (advisor)

University:California Institute of Technology

Department:Engineering and Applied Science

关键词: Mechanical Engineering;   

Others  :  https://thesis.library.caltech.edu/6573/1/Marxman_ga_1962.pdf

美国|英语

来源: Caltech THESIS

【 摘 要 】

Energy transport by conduction and diffusion is considered in chemically-reacting, gaseous mixtures which have a pressure gradient parallel to the temperature gradient. As a consequence of pressure diffusion and other mechanisms, the pressure gradient can influence energy transport, and this effect is given particular emphasis. The use of an idealized flow model and a perturbation technique makes it possible, with a relatively simple analysis, to deduce many of the features of energy transport in multicomponent, gaseous media.

The dissociation reaction of a diatomic gas, with the ratio (reaction rate/diffusion rate) either large or small, is studied. When the flow is chemically frozen, the extension of the analysis to include any number of components would be straightforward, in principle. However, when the gas is in local chemical equilibrium, the binary case is unique in that the diffusion velocities are then proportional to the local temperature gradient, but independent of the local pressure gradient. Consequently, there exists an effective thermal conductivity. The order of the governing set of equations is therefore the same as for a simple, single-component gas, and the effect of the wall surfaces on reaction rates is confined to reaction boundary layers. Two other examples illustrate that the order of the equations is higher when the equilibrium flow comprises more than two components, although there are still reaction boundary layers. The additional boundary conditions associated with the higher order are determined, through integral conditions, by the proportions of the chemical elements present.

The results show that in many high-temperature gasdynamics problems of current interest the presence of a pressure gradient may have an important influence on energy transport.