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Article

Freeze-Drying with Structured Sublimation Fronts—Visualization with Neutron Imaging

by
Nicole Vorhauer-Huget
1,*,
David Mannes
2,
Mathias Hilmer
3,
Sebastian Gruber
3,
Markus Strobl
2,
Evangelos Tsotsas
1 and
Petra Foerst
3
1
Institute of Process Engineering, Otto von Guericke University Magdeburg, 39106 Magdeburg, Germany
2
Laboratory for Neutron Scattering and Imaging, Paul Scherrer Institute, 5232 Villigen, Switzerland
3
Chair of Process Systems Engineering, Technical University of Munich, 80333 München, Germany
*
Author to whom correspondence should be addressed.
Processes 2020, 8(9), 1091; https://doi.org/10.3390/pr8091091
Submission received: 31 July 2020 / Revised: 28 August 2020 / Accepted: 30 August 2020 / Published: 2 September 2020
(This article belongs to the Special Issue Modern Freeze Drying Design for More Efficient Processes)
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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.
Keywords: neutron tomography; image analysis; freeze-drying; drying front; front structure neutron tomography; image analysis; freeze-drying; drying front; front structure

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MDPI and ACS Style

Vorhauer-Huget, N.; Mannes, D.; Hilmer, M.; Gruber, S.; Strobl, M.; Tsotsas, E.; Foerst, P. Freeze-Drying with Structured Sublimation Fronts—Visualization with Neutron Imaging. Processes 2020, 8, 1091. https://doi.org/10.3390/pr8091091

AMA Style

Vorhauer-Huget N, Mannes D, Hilmer M, Gruber S, Strobl M, Tsotsas E, Foerst P. Freeze-Drying with Structured Sublimation Fronts—Visualization with Neutron Imaging. Processes. 2020; 8(9):1091. https://doi.org/10.3390/pr8091091

Chicago/Turabian Style

Vorhauer-Huget, Nicole, David Mannes, Mathias Hilmer, Sebastian Gruber, Markus Strobl, Evangelos Tsotsas, and Petra Foerst. 2020. "Freeze-Drying with Structured Sublimation Fronts—Visualization with Neutron Imaging" Processes 8, no. 9: 1091. https://doi.org/10.3390/pr8091091

APA Style

Vorhauer-Huget, N., Mannes, D., Hilmer, M., Gruber, S., Strobl, M., Tsotsas, E., & Foerst, P. (2020). Freeze-Drying with Structured Sublimation Fronts—Visualization with Neutron Imaging. Processes, 8(9), 1091. https://doi.org/10.3390/pr8091091

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