Vacuum contact drying of crystals: Multi-scale modelling and experiments

A methodology for multi-scale modelling of the unit operation of vacuum contact drying has been developed, with the aim of parameter transfer from the laboratory scale to the pilot-plant scale. Models at three hierarchical levels - (i) lumped-parameter model of the unit operation, (ii) distributed-parameter model of heat and mass transfer in a particle bed of given size and geometry, and (iii) particle-scale model of heat and mass transfer for the estimation of effective transport properties - have been formulated and solved. Experimentally measured drying rates in a laboratory-scale vacuum dryer have been analysed using volume-averaged temperature profiles evaluated from the continuum model, and the effective heat-transfer coefficients have thus been obtained.