Freeze-drying is a low-pressure, low-temperature condensation pumping process widely used in the manufacture of pharmaceuticals for removal of solvents by sublimation. Key performance characteristics of a freeze-dryer condenser are largely dependent on the vapor and ice dynamics in the low-pressure environment. The main objective of this work is to develop a modeling and computational framework for analysis of vapor and ice dynamics in such freeze-dryer condensers. The direct Simulation Monte Carlow (DSMC) technique is applied to model the relevant physical processes that accompany the vapor flow in the condenser chamber. Low-temperature water vapor molecular model is applied in the DSMC solver SMILE to simulate the flowfield structure. The developing ice front is tracked based on the mass flux computed at the nodes of the DSMC surface mesh. Verification of ice accretion simulations has been done by comparison with analytical free-molecular solutions. Simulations of ice buildup on the coils of a laboratory-scale dryer have been compared with experiments. The comparison shows that unsteady simulations are necessary to reproduce experimentally observed icing structures. The DSMC simulations demonstrate that by tailoring the condenser topology to the flow-field structure of the water vapor jet expanding into a low-pressure reservoir, it is possible to significantly increase water vapor removal rates and improve the overall efficiency of freeze-drying process.


Copyright (2011) American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in (A. Ganguly*, A. Venkattraman*, and A. Alexeenko, “3D DSMC Simulations of Vapor/Ice Dynamics in a Freeze-Dryer Condenser”, AIP Conf. Proc., Vol. 1333, 27th International Symposium on Rarefied Gas Dynamics, pp. 254-259, 2011.) and may be found at http://dx.doi.org/10.1063/1.3562657. The following article has been submitted to/accepted by [American Institute of Physics]. After it is published, it will be found at (http://dx.doi.org/10.1063/1.3562657). Copyright (2011) A. Ganguly*, A. Venkattraman*, and A. Alexeenko. This article is distributed under a Creative Commons Attribution 3.0 Unported License.

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