Abstract:
The paper reports on the development of a numerical model
for the simulation of a liofilization process in a vial. The lactose
and mannitol-water mixtures are used as the working medium in
the vial. Experimental analysis of lyofilization dynamics inside
a single vial and multiple vials in a laboratory scale lyofilizer is
reported, with the main focus on the primary drying phase. The
key parameter measured is the temperature distribution inside the
main axis of the vial filling. In the numerical model, a 1D vial
approximation is used, and governing equations of heat and water
vapor transport with moving front between the frozen and the
porous part of the filling are solved by a dedicated finited difference
method in a time stepping nonlinear iteration procedure.
The comparison of numerical and experimental results show, that
the developed numerical model is able to accurately capture the
transition points from primary to secondary drying, accompanied
by accurate capturing of the temperature levels inside the drying
material. The main difference in drying of lactose and mannitol
solutions lies in the fact, that the lactose shows undercooling effects
during the primary drying phase, which is not the case for
the mannitol solution. This effect is a consequence of shrinking
behavior of lacose porous matrix, loosing contact with vial
side and hence decreasing the overall heat input to the vial. The
derived numerical model is able to accurately reproduce drying
kinetics of mannitol, whereas for drying of lactose an upgrade of
the model to axysimmetric geometry would be needed.
Description:
Papers presented at the 13th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Portoroz, Slovenia on 17-19 July 2017 .
