THE INFLUENCE OF A VIAL STOPPER ON FLOW AND MASS TRANSFER CONDITIONS INSIDE A VIAL

In the process industry, vacuum-type dryers are becoming increasingly important. A special case of vacuum drying is lyophilization, where a solution, containing up to 90% of solvent (typically water), is dried under the conditions of very low temperatures and extremely low system pressures. As a container type, in which the solution is dried, a vial is frequently used. The intensity of drying is to a large extent controlled by the pressure conditions above the drying surface. The vial and the rubber stopper geometry present a significant pressure drop in the flow of sublimated solvent, but are experimentally difficult to determine. In order to produce realistic pressure conditions for the mass transfer computation, a CFD analysis of flow inside the vial-stopper channel is performed. The influence of imposing the no-slip and slip conditions on the solid surfaces on the pressure drop in the system is studied under the typical sublimation conditions. The effect of the increased partial pressure of the solvent on the sublimation rate is calculated by implementing the Maxwell–Stefan diffusion model.