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Title: Freeze-drying with structured sublimation fronts : visualization with neutron imaging
Author(s): Vorhauer-Huget, Nicole
Mannes, David
Hilmer, Mathias
Gruber, Sebastian
Strobl, Markus
Tsotsas, Evangelos
Foerst, Petra
Issue Date: 2020
Type: Article
Language: English
URN: urn:nbn:de:gbv:ma9:1-1981185920-366925
Subjects: Neutron tomography
Image analysis
Front structure
Drying front
Abstract: The particular structure of the sublimation front in vacuum freeze-drying of porous media is, in most situations, not accessible at the pore scale. The classical measurement techniques access the process only globally. Knowledge about the structure of the front, however, is necessary for prescriptive analysis of freeze-drying, as it dictates not only drying velocity, drying time, and overall energy consumption, but also the material properties after drying. This is especially relevant in situations in which the freeze-drying process is carried out close to the collapse temperature of the product. We, therefore, study the sublimation of ice with neutron tomography and analyze the spatial formation of the dry space using the example of frozen cylindrical maltodextrin with drying parameters at the limit of material collapse. We show that the sublimation front forms unique fractal structures that differ strongly from the usual form of a flat front. Distinct dry fingers covering the sample, in addition to a fractal peripheral sublimation front, were observed. The findings are important for the understanding of freeze-drying processes and will serve as a basis for the development of microscale models of freeze-drying.
Open Access: Open access publication
License: (CC BY 4.0) Creative Commons Attribution 4.0(CC BY 4.0) Creative Commons Attribution 4.0
Sponsor/Funder: DFG-Publikationsfonds 2020
Journal Title: Processes
Publisher: MDPI
Publisher Place: Basel
Volume: 8
Issue: 9
Original Publication: 10.3390/pr8091091
Page Start: 1
Page End: 12
Appears in Collections:Fakultät für Verfahrens- und Systemtechnik (OA)

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