Prediction of degree of deformation and crystallization time of molten droplets in pastillation process.

The direct solidification process of a melt into a particulate solid is studied to achieve the desired size and shape of the product and to predict the required crystallization time. For an example, a Bisacodyl melt is chosen. The role of the contact angle of the droplet is investigated as a function of Reynolds number, degree of subcooling and characteristic of used cooled surface (substrate). The static contact angle increases with increasing degree of surface roughness of the substrate. The contact angle, however, decreases with increasing Reynolds number and degree of subcooling. The phenomena of spreading and rebouncing of droplets are used in the discussion of the deformation process. By the model of Madejski the degree of deformation is found to be proportional to the Reynolds number to the power of 0.2. On the basis of a simple droplet solidification model and experimental data, a numerical study is presented. The equations allow to estimate the normalized deformation and crystallization times, which are proportional to the Reynolds number to the power of 1.23 and help the design of solidification processes.