The performance of magnetohydrodynamic -MHD -generators is influenced by inhomogeneities in plasma properties. One of the sources of small scale inhomogeneity is the incomplete mixing of gas and seed, and of hot and cold gas regions (or, more generally, of electronrich and electron-poor regions) as the plasma travels from the burner of a combustion-driven generator to the working section. This question presents two different and, in a way, complementary sides: (a) gross maldistribution of electron density, arising, for instance, from combustion injection patterns, am gradually smoothed out by turbulent mixing, and (b) even after this is accomplished, the smaller eddies of higher and lower conductivity still persist on continuously decreasing scales as the r.m.s. of its fluctuations decays only slowly in time.
In this paper, we address the first of these two inhomogeneities in the plasma. A simple model is postulated for the injection pattern of seed concentration through a rectangular array of point sources. The turbulent diffusion process is followed through the plug-flow combustion, the nozzle, and finally, the generator. No account is taken of the effect of the magnetic field on the turbulence structure, but viscous decay and axial stretching of the flow in the nozzleare considered. Under these assumptions and that plasma properties are nearly constant in planes normal to the flow direction and axial diffusion is small compared to transverse diffusion, the conservation equation for the seed concentration v, is:
where D (the diffusivity in the transerve plane) and Us, (the plasma velocity) are functions of the axial distance x. It is shown that the effects of the initial maldistribution can be disregarded as soon as the lateral diffusion distance i has become '/4 to % the distance between sources where x is defined by: (a)' = J:D/Qdx Keywords. Plasma inhomogeneities; seed mixing; MHD power generators.
of only the r.m.s. of fluctuations).