ENERGETICS OF PLASMA-CHEMICAL SYSTEMS IN SELECTIVE TRANSFER PROCESSES A. V. Kasharin, B. V. Potapkin, V. D. Rusanov, and A. A. Fridman UDC 533.932 A diffusion model is proposed for the theoretical investigation of how diffusiva heat and mass transfer affects the energetics of the plasma-chemical process in highly spatially inhomogeneous discharge systems. The type of plasma-chemical systems customarily used most extensively to carry out en- doergic chemical reactions is that of discharges with a thermal plasma [i]. Products ~re obtained in such reactions according to a comparatively simple scheme: thermal heatin~- nonadiabatic cooling (quenching). In the analysis of such systems the minimum energy ,~x- penditure for obtaining a unit product is assumed not to depend on the heat and mass exchange and can be determined by the conventional method of thermodynamic calculation [2]. As was shown in [3], however, when sufficiently large external forces act on a system the flu:~ of product from the reaction zone can increase relative to the flux of thermal and chemical en- ergy (the transfer of energy and material becomes a selective process), which means a ~:educ- tion of the minimum energy expenditure. Such a situation, as will be shown below, is also characteristic of highly spatially inhomogeneous systems in which the removal of heat and products from the reaction zone is determined by molecular diffusion in this paper we study the effect of the selectivity of the transfer process on the energy efficiency of chemical processes in highly spatially inhomogeneous systems. Our analysis of how the selective nature of the heat and mass transfer, owing to the difference in the diffusion coefficients, affects the energetics of the chemical reactions will be conducted within the framework of the following model: the temperature distribution in the discharge region is uniform; the starting materials are delivered into the reaction zone and products are removed by diffusion; the temperature and concentration of the products at the periphery are kept constant at T r and O, respectively. The energy expenditure for ob- taining the product within this model is determined by the ratio of the total enthalpy flux q out of the reaction zone to the product flux Jn" N A~J- --~' (i) here h is the thermal conductivity coefficient of the gas mixture, Ji = miniVi is the mass flux of the i-th component, (mi, ni, and Vi, respectively, are the molecular mass, concen- tration, and rate of diffusion of the i-th component), and I i is the enthalpy (with all~w- ance for the enthalpy of formation) per unit mass of the i-th component. As is seen from Eq. (i), energy is removed from the reaction zone by means of ordinary thermal conductivity and diffusive transfer of chemical and thermal energy by each component. The transfer equations take on the comparatively simple form [3] q=---PDVI, j~ ..... pDvY~ (2) upon satisfaction of the following conditions:* 1) that the diffusion coefficients for all the components be equal, Dij = D; 2) that thermal diffusion does not occur, Di T = 0; and 3) *We note that in the case of turbulent exchange these conditions are satisfied antomatic.ally. Translated from Inzhinerno-Fizicheskii Zhurnal, Vol. 55, No. 5, pp. 788-797, November, 1989. Original article submitted May 13, 1988. 0022-0841/89/5705-1335512.50 9 1990 Plenum Publishin~ Corporation 1335