There are various theories about how to scale up a solid dosage coating operation in a pan coater. This article provides a basic process understanding and scale-up theory based on first principles.
The coating process shown in Figure 1 has multiple, simultaneous, ongoing exchange processes. The first is a heat exchange between the inlet process air and the coater metal body, spray droplets, and tablets. The second is a mass exchange between the material sprayed and the inlet air stream, tablets, and coating pan.
The heat balance is shown in Equation 1:
The mass balance for the solvent is shown in Equation 2:
The mass balance for the solids sprayed is shown in Equation 3:
As with any theoretical analysis, there are assumptions built into the model described above. For example:
This model can be used to calculate process efficiency and efficiency of the inlet air heat capacity. Efficiency of coating will generally improve as the process is scaled up because the bed depth will be increased, thus increasing the heat exchange between the process air and the tablets.