SELF-SIMILAR SOLUTIONS OF THE NONLINEAR DIFFUSION EQUATION AND APPLICATION TO NEAR-CRITICAL FLUIDS

We use analytic self-similar solutions of both the linear and non-linear diffusion equation to determine the behavior of a heat conducting system experiencing a time-dependent energy production. Supposing a power law evolution of the system parameters, we calculate the corresponding exponents to describe the temporal behavior of the system. in the non-linear case, we are able to introduce a variation of both the coefficient of diffusion and the amplitude of the heat source. The analytic solutions are checked numerically. These results can be considered, for example, as the basis for further developments on the non-linear behavior of supercritical fluids in a microgravity environment, e.g. the ''Piston Effect'' (M. Bonetti et al., Phys. Rev. E 49 (1994) 4779) or the ''Jet Instability'' (D. Beysens et al., Near-critical Fluids in Space, in: Lectures on Thermodynamics and Statistical Mechanics, M, Costas et al., eds. (World Scientific, Singapore, 1994) p. 88).