Pore network model of primary freeze drying

The pore scale progression of the sublimation front during primary freeze drying depends on the local vapor fransport and the local heat fransfer as well. If the pore space is size distributed, vapor and heat fransfer may spatially vary. Beyond that, the pore size disfribution can substantially affect the physics of the fransport mechanisms if they occur in a fransitional regime. Exemplarily, if the critical mean free path is locally exceeded, the vapor fransport regime passes from viscous flow to Knudsen diffusion. At the same time, the heat fransfer is affected by the local ratio of pore space to the solid skeleton. The impact of the pore size disfribution on the transitional vapor and heat fransfer can be studied by pore scale models such as the pore network model. As a first approach, we present a pore network model with vapor transport in the fransitional regime between Knudsen diffusion and viscous flow at constant temperature in the dry region. We demonstrate the impact of pore size distribution, temperature and pressure on the vapor transport regimes. Then we study on the example of a 2D square lattice, how the presence of micro and macro pores affects the macroscopic progression of the sublimation front.