Abstract
We investigate the influence of contact angle variations on spontaneous imbibition of moisture in porous materials. While the contact angle is typically assumed constant when modelling the moisture transfer in porous media, experimental findings put this assumption into question. It has been shown that during imbibition the contact angle notably rises with increasing meniscus velocity. This phenomenon resultantly affects the moisture retention curve, the relation linking the local capillary pressure to the local moisture saturation, which in turn impacts the imbibition rate and moisture distribution. This study investigates these dynamic effects via a pore network technique as well as a continuum approach. It is shown that the impacts of pore-scale contact angle variations on the imbibition process can be reproduced at the continuum scale through a modified moisture retention curve including a dynamic term. Complementarily a closed-form equation expressing the dynamic capillary pressure in terms of local saturation and saturation rate is derived. The continuum approach is then finally employed to predict measured moisture saturation profiles for imbibition in Berea sandstone and diatomite found in literature, and a fair agreement between simulated and measured outcomes is observed.
Highlights
Moisture transport and storage in porous materials play an important role in many fields of science and engineering such as concrete technology, soil science, geology, hydrology and building physics
Effect of dynamic contact angle variation on spontaneous... (Hassanizadeh and Gray 1993; Carroll et al 2010; Janssen et al 2016; Bianchi Janetti and Janssen 2020; Hassanizadeh et al 2002; Joekar-Niasar and Hassanizadeh 2011) express the local dynamic capillary pressure Pc,d S, Ṡ in a purely empirical manner, we suggest here an alternative closed-form equation expressing the dynamic local capillary pressure as a function of local saturation and saturation rate
In conformity with diffusion theory (Crank 1975; Bianchi Janetti and Wagner 2017), the saturation profiles obtained from the continuum approach collaps into a single curve, when expressed as function of the Boltzmann variable = x∕t1∕2
Summary
Moisture transport and storage in porous materials play an important role in many fields of science and engineering such as concrete technology, soil science, geology, hydrology and building physics. The material’s capability for storing and transporting moisture due to capillary forces is described by empirical material properties, i.e., the moisture retention and moisture permeability curves The former establishes a relationship between the local capillary pressure and the local moisture saturation, the latter expresses the local moisture permeability as a function of the local moisture saturation. Experimental findings reveal that this assumption may not always be valid though, having shown that the (de)saturation rate may significantly influence the moisture retention curve (Hassanizadeh and Gray 1993; Carroll et al 2010; Janssen et al 2016; Bianchi Janetti and Janssen 2020; Hassanizadeh et al 2002; JoekarNiasar and Hassanizadeh 2011) The occurrence of this phenomenon, which is still not fully explained, is addressed in the literature as “dynamic effects” on the moisture retention curve.
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