Numerična analiza tokovnih razmer v viali

Lyophilization or freeze-drying is a widely used process in the pharmaceutical and food industry. In the process the solvent will be removed under extreme conditions of low temperature and low system pressures, whereby sublimation happens, the transition from the solid phase to the gas phase, with skipping the liquid phase, which happens bellow the triple point. This study focuses on numerical modeling at the start of the process, the so called primary drying. For this stage the highest mass flow rates of vapor are typical, since the driving force of the process is the pressure difference between the sublimation front and surrounding area. In this stage the non-bonded solvent is removed. Because of the extreme conditions the typical computational fluid dynamics approach is not suitable anymore and has to be corrected. One way to do this is to use additional models for fluid behavior at the solid wall. The study focuses on the influence of different boundary conditions on the solid wall, No-Slip, Free Slip and Maxwell Slip, and their effect on fluid flow inside the vial. A quantitative and qualitative comparison of the results is presented.Izdelki v farmacevtski in prehrambni industriji so zaradi svoje kemijske sestave pogosto občutljivi na visoke temperature, zaradi česar je potrebno z njimi ravnati drugače, kot z običajnimi materiali. V primeru kadar je potrebno izdelke sušiti, torej odstraniti topilo iz že obstoječe zmesi, se posega po procesu liofilizacije. Liofilizacija je proces odstranjevanja topila iz zamrznjene zmesi, pri čemer pride do faznega prehoda iz trdnine v plin (sublimacija), kar pa je mogoče izvesti pri zelo nizkih temperaturah in obratovalnih tlakih. Gonilna sila procesa je tlačna razlika med uparjalno fronto in okolico. Nanjo vplivajo predvsem tokovne razmere v okolici, geometrija in prenos toplote znotraj liofilizatorja. Z dobrim poznavanjem vseh dejavnikov je mogoče proces dodatno optimirati in s tem zagotoviti željen rezultat