Mechanics of Liquid Transport and Swelling in Porous Media

The mechanics of liquid transport in porous cellulose foam and in a dense random packing of glass spheres are studied in this thesis. Specifically, the capillary and diffusion mechanisms are investigated by critical experiments, and appropriate theoretical models are developed for both porous media. Finally, a coupled diffusion-actuation framework is developed in 1D to predict the water-induced swelling of dry pre-compressed cellulose foam. First, a critical water discharge test via a cellulose foam siphon reveals that the liquid transport in the foam is primarily by capillary transport via a set of independent tubes. We hypothesize that the cellulose foam comprises independent cylindrical tubes of radius *a* following a probability distribution function *p*(*a*). The distribution function *p*(*a*) is experimentally measured, and it suggests that water flows primarily through the tubes of radii 0.1 µm to 100 µm. XCT scan of the wet foam supports this argument. An additional diffusion model is then proposed to explain the spread of water from a damp section of cellulose foam to an adjacent dry section. The diffusion model accounts for the deep moisture traps present in the foam. Our study suggests that the water transport in cellulose foam combines capillary transport and diffusion. The mechanics of capillary liquid rise in a random dense packing of glass spheres is then investigated. Experiments reveal the onset of a critical meniscus pinning phenomenon at a height during water or glycerol rise. The pinning is interpreted in terms of capillary rise in a wavy-walled tube, where the meniscus can get pinned at several heights when the local capillary pull balances the weight of liquid. We show that imposed pressure fluctuations at the meniscus can result in a slower capillary rise of the liquid above the first pinning height. The 1D actuation of a dry pre-compressed cellulose foam by water absorption is then studied. A Fickian diffusion model is developed to predict the concentration of water in the actuating foam. The model is suitably informed by the dynamic actuation timescale of dry pre-compressed foam and the sensitivity of the foam’s actuation of relative moisture content, measured experimentally. The model can adequately predict the early stage of the actuation response of pre-compressed foam by water absorption. The thesis concludes with recommendations for future work to further understand the nature of liquid transport mechanism and swelling in porous media.

Name dc:type.qualificationname

Doctor of Philosophy (PhD)

Level dc:type.qualificationlevel

Doctoral

Grantor dc:publisher.institution

University of Cambridge

Year dc:date.issued

2023

Author dc:creator

• Das, Ratul

Advisor dc:contributor.advisor

• Fleck, Norman

• actuation
• capillary
• cellulose foam
• diffusion
• porous media
• soft material

Licence

• https://apollo8-f-pro.lib.cam.ac.uk/bitstreams/2c862e84-77c6-42c8-ad40-de52cb5db49c/download
• https://www.rioxx.net/licenses/all-rights-reserved/

Language dc:language

eng

DOI dc:identifier.doi

https://doi.org/10.17863/CAM.106027

OAI identifier oai:identifier

oai:www.repository.cam.ac.uk:1810/364304