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Liquid Distribution and Structural Changes During Convective Drying of Gels

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Colloid Process Engineering

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Abstract

Experimental and three-dimensional numerical simulation studies on convective drying of gels are presented in this chapter. As a physical model of a real gel, highly porous particle aggregates are produced by sintering of glass beads inside a graphite mold. A lab-scale X-ray microtomograph is used to perform a series of drying experiments with loose packings of sintered glass beads (mean diameter 700 μm) initially saturated with water. The reconstructed images (voxel size 16 μm) are analyzed to obtain the time evolution of the solid, liquid, and gas phase distributions during convective drying. A computational tool based on the volume-of-fluid approach is developed to simulate the liquid distribution over time at the microscopic scale in this model particle aggregate, which is subjected to convective drying. The simulated liquid phase distributions are found to be in good qualitative agreement with the experimental results. The major physical effect of capillary flow from large pores into small pores is easily recognized: large pores dry out first while small regions of the void space stay saturated with liquid. In addition to these pore-scale studies, resorcinol-formaldehyde (RF) hydrogels are synthesized by sol-gel polycondensation of resorcinol (R) with formaldehyde in the presence of sodium carbonate as a catalyst (C). The mechanical effects (cracks and shrinkage) in RF gels with three different R/C ratios and three different aging times are studied. The results show that the degree of shrinkage drastically increases with decreasing R/C ratio and also that the degree of shrinkage is slightly reduced by longer aging.

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Abbreviations

F :

Force (N)

f :

Volume fraction (-)

h :

Mesh size (m)

n :

(unit) normal vector (-)

α, β :

Scaling parameters (-)

θ :

Contact angle (rad)

κ :

Curvature (1/m)

σ :

Surface tension (N/m)

c :

Capillary

eq :

Equilibrium

g :

Gas

s :

Solid

w :

Liquid (water)

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Acknowledgments

This project was funded by the German Research Foundation (DFG) within the Priority Program 1273 “Colloid Process Engineering”. The X-ray tomography device used in this study was financed by the EFRD (European Fund for Regional Development) in project no. 121108002. We would like to thank Ms. Fahimeh Bahari for the synthesis of RF gels and for conducting the drying experiments described in Sect. 4.

Author information

Authors and Affiliations

  1. Thermal Process Engineering, Otto von Guericke University, 4120, 39016, Magdeburg, Germany

    Abdolreza Kharaghani & Evangelos Tsotsas

  2. Institute of Computational Physics, Zurich University of Applied Sciences, Wildbachstrasse 21, 8401, Winterthur, Switzerland

    Christoph Kirsch

  3. BASF SE, GCP/TT-L540, 67056, Ludwigshafen, Germany

    Thomas Metzger

Authors
  1. Abdolreza Kharaghani
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  2. Christoph Kirsch
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  3. Thomas Metzger
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  4. Evangelos Tsotsas
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Corresponding author

Correspondence to Abdolreza Kharaghani .

Editor information

Editors and Affiliations

  1. Institute of Thermal Process Engineering, Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany

    Matthias Kind

  2. Institute of Particle Technology, Friedrich-Alexander-Universität Erlangen, Erlangen, Germany

    Wolfgang Peukert

  3. Physical Chemistry II, TU Dortmund, Dortmund, Germany

    Heinz Rehage

  4. Institute of Process Engineering in Life Section I: Food Process Engineering, Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany

    Heike P. Schuchmann

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Kharaghani, A., Kirsch, C., Metzger, T., Tsotsas, E. (2015). Liquid Distribution and Structural Changes During Convective Drying of Gels. In: Kind, M., Peukert, W., Rehage, H., Schuchmann, H. (eds) Colloid Process Engineering. Springer, Cham. https://doi.org/10.1007/978-3-319-15129-8_5

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  • DOI: https://doi.org/10.1007/978-3-319-15129-8_5

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  • Publisher Name: Springer, Cham

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  • Online ISBN: 978-3-319-15129-8

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