Multi-Scale Analysis of Vacuum Contact Drying

The modeling of the unit operation of vacuum contact drying is approached as a multi-scale problem. At the particle assembly length scale, effective transport properties (thermal conductivity, relative gas- and liquid-phase permeability) have been determined computationally by simulations on reconstructed porous media and verified by direct measurements. A distributed-parameter model of vacuum contact drying including liquid and vapor flow and differential energy balance has been formulated and used for the calculation of drying time as function of vacuum level, temperature, vessel diameter, and batch size at the unit operation length scale. Drying curves for a model system of sodium carbonate–isopropanol have been measured experimentally and compared with the model predictions. A very good agreement has been found.