A pore network model of drying with capillary liquid rings

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Eprints ID : 17333

To cite this version : Vorhauer, Nicole and Tsotsas, Evangelos and Prat, Marc A pore network model of drying with capillary liquid rings. (2015) In: 7th International Conference on Porous Media & Annual Meeting, 18 May 2015 - 21 May 2015 (Padoue, Italy). (Unpublished)

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A Pore Network Model of Drying with Capillary Liquid Rings

AUTHORS

Nicole Vorhauer (1), Evangelos Tsotsas (2), Marc Prat (3)

1. Otto-von-Guericke University Magdeburg, Universitaetsplatz 2, 39106, Magdeburg, DE 2. Prof. Dr.-Ing. (Head of Thermal Process Engineering), Otto-von-Guericke University

Magdeburg, Universitaetsplatz 2, 39106, Magdeburg, DE

3. Chercheur (Groupe d’Études sur les Milieux Poreux), INPT, UPS, IMFT (Institut de Mécanique des Fluides de Toulouse), Université de Toulouse, 6 Allée Monso, 31400, Toulouse, FR

ABSTRACT

Modelling of drying processes without adjustable parameters is still a challenge. As emphasized in several previous works,e.g. [1-3], this might be due to the impact of liquid films trapped in the corners of the pore space. In this study, we present and analyse a drying experiment with a micromodel which clearly shows the presence of corner films. In contrast with previous works, however, the corner films do not form a system of interconnected films extending over large regions. They rather form isolated capillary rings surrounding the solid blocks of the device. These capillay rings can be regarded as a quasi-two dimensional version of liquid bridges often observed in the contact regions between grains in soils and packings of particles, [4]. These capillary rings essentially remain confined in the two-phase region. As a result, their impact on drying rate is much smaller than in the systems favouring films hydraulically connected over long distances. The capillary liquid ring formation is taken into account in a pore network model of drying [5]. This model leads to a satisfactory agreement with the experiment provided that the lateral pinning of liquid phase observed in the experiment is included in the model. This model enriches the family of pore network models of drying and can be considered as a step toward the modelling of secondary capillary effects in drying in more complex geometry, such as a random packing of particles.

The consideration of capillary rings in drying is important not only for a better prediction of evaporation rates but also for situations where the liquid phase contains particles or dissolved salt for example. For example, in the presence of salt, capillary rings are special locations where crystallization will take place as a result of ring evaporation. Since the capillary rings are likely to form in the contact regions between grains, they might play a role in the damages induced by the crystallization process [6].

REFERENCES

[1] Yiotis, A.G., Boudouvis, A.G., Stubos, A.K., Tsimpanogiannis, I.N. & Yortsos, Y.C.: Effect of liquid films on the drying of porous media. AIChE Journal 50 (2004), 2721-2731.

[2] Yiotis, A.G., Tsimpanogiannis, I.N., Stubos, A.K., Yortsos, Y.C.: Coupling between external and internal mass transfer during drying of a porous medium. Water Resources Research 43 (2007). [3] Prat, M.: On the influence of pore shape, contact angle and film flows on drying of capillary porous media. International Journal of Heat and Mass Transfer 50 (2007), 1455–1468.

[4] Wang, Y.J., Mahmood, H.T., Kharaghani, A., Tsotsas, E.: Visualization and modeling of liquid film rings observed during drying of particle packings. In Proceedings of the 19th International Drying Symposium (IDS) (August 24-27 2014), Lyon, France.

[5] Vorhauer, N., Wang, Y., Karaghani, A., Tsotsas, E., Prat, M.: Drying with formation of capillary rings in a model porous medium. Submitted to Transport in Porous Media.

[6] Scherer, G. W.: Stress from crystallization of salt. Cem. Concr. Res. 34 (2004), 1613–1624.