IMPORTANCE OF THERMAL-DIFFUSION IN HIGH-TEMPERATURE ELECTROCHEMICAL-CELLS

The significance of thermal diffusion in liquid systems with forced co nvection has been investigated over a wide range of temperature. Numer ical calculations have been carried out for the case of dilute liquid solutions that flow into the entrance region of a tube or an annulus, and the theory has been developed for a first order chemical or electr ochemical reaction that takes place on the electrode surface. As an ex ample, dilute aqueous electrolyte solutions at sub-critical temperatur es (up to 350 degrees C) have been considered. As the Lewis number and the Soret coefficient increase, the impact of thermal diffusion on ma ss transport is predicted to become increasingly important at higher t emperatures. Simple analytical relations for describing thermal diffus ion effects in liquid solutions subject to forced convection have been derived, and good agreement between these analytical solutions and nu merical results is shown. The use of an electrochemical cell with forc ed convection could be a promising experimental technique for determin ing Soret coefficients for electrolyte solutions and liquid mixtures a t elevated temperature. (C) 1997 Elsevier Science S.A.