Due to the unique high thermal resistance bottom structure of dual-chamber cartridges, the heat input during primary drying shifts from the bottom conduction-dominated mode in traditional vials to a lateral heat transfer-dominated mode. Current research in this area remains predominantly experimental, highlighting the need for in-depth mechanistic analysis of heat and mass transfer to inform process optimization. To address this, this study develops a heat and mass transfer model for dual-chamber cartridge by modifying the boundary conditions that describe the external heat transfer pathways. This model is employed to systematically investigate the influence of key process parameters—shelf temperature, drying chamber pressure, solution fill height, and the gap distance between the shell and cartridge—on the primary drying time, maximum product bottom temperature, and the contribution proportion of different heat transfer pathways. Results demonstrate that: drying chamber pressure exhibits a counter-intuitive influence: moderately increasing the pressure shortens the drying time by enhancing lateral rarefied gas conduction, which contrary to the conventional guideline. Furthermore, the shell-cartridge gap, a unique structural parameter of this system, plays a critical role—reducing it greatly decreases lateral thermal resistance and serves as a key means to optimize drying efficiency. The model and findings provide an important theoretical foundation for understanding and optimizing the freeze-drying process for dual-chamber cartridges.
Zhou et al. (Tue,) studied this question.