Diffusion Equation Applied to Isothermal Drying of a Multicomponent Liquid Film

Abstract

Liquid-side-controlled drying by convection of a multicomponent liquid film is studied. Interactive diffusion in liquid phase is considered the main mechanism for mass transfer. Assuming an isothermal drying process and a constant matrix of multicomponent diffusion coefficients, an analytical solution of the diffusion equation is developed. The equations are decoupled by a similarity transformation and solved by the method of variable separation. The solution is applied to the drying of ternary mixtures, one of them containing a component of negligible volatility. The variation of diffusion coefficients along the process trajectory was taken into account by a piecewise application of the solution in time intervals with averaged coefficients from previous time steps. Despite the simplifications made, the analytical solution gives a god insight into the selectivity of the drying process and is computationally fast. The limitations of the analytical solution and the prospect of applying the solution to the description of a nonisothermal process are discussed. It would introduce an important computational economy since the rigorous treatment of multicomponent drying leads to partial differential equations with variable coefficients, which can only be solved by time-consuming iterative procedures.

Keywords:

• Multicomponent mixtures
• Mass transfer
• Multicomponent drying

ACKNOWLEDGMENTS

The authors gratefully acknowledge the financial support provided by the Swedish Research Council for Engineering Sciences (TFR), and the Swedish Agency for Research Cooperation with Developing Countries (SIDA).