Study of Hydraulic Properties of Uncoated Paper: Image Analysis and Pore-Scale Modeling

Abstract

In this study, uncoated paper was characterized. Three-dimensional structure of the layer was reconstructed using imaging results of micro-CT scanning with a relatively high resolution (0.9 μm). Image analysis provided the pore space of the layer, which was used to determine its porosity and pore size distribution. Representative elementary volume (REV) size was determined by calculating values of porosity and permeability values for varying domain sizes. We found that those values remained unchanged for domain sizes of 400 × 400 × 150 μm 3 and larger; this was chosen as the REV size. The determined REV size was verified by determining capillary pressure-saturation (P c -S) imbibition curves for various domain sizes. We studied the directional dependence of P c -S curves by simulating water penetration into the layer from various directions. We did not find any significant difference between P c -S curves in different directions. We studied the effect of compression of paper on P c -S curves. We found that up to 30% compression of the paper layer had very small effect on the P c -S curve. Relative permeability as a function of saturation was also calculated. Water penetration into paper was visualized using confocal laser scanning microscopy. Dynamic visualization of water flow in the paper showed that water moves along the fibers first and then fills the pores between them.

Characterization of the Interface Between Coating and Fibrous Layers of Paper

“…Observations have shown that penetrating liquid in a fibrous layer first follows the direction of fibers and wets them. Then, the pore space between fibers is filled up with the liquid (Aslannejad and Hassanizadeh 2017).…”

“…In an earlier work, using X-ray microtomography, the 3D structure of a fibrous layer was extracted and reconstructed (Aslannejad and Hassanizadeh 2017). Then, a pore-morphology method was used to obtain the pore size distribution, and curves of capillary pressure and relative permeability, as a functions of fluid saturation.…”

“…Therefore, here we are focusing on not the coating and fibrous layer but on the transition area from the coating to the fibrous layer.

Fig. 1 a Pore size distribution of the coating and fibrous layers, and b capillary–pressure–saturation curves of the coating and fibrous layers (Aslannejad et al 2017; Aslannejad and Hassanizadeh 2017)

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“… a Pore size distribution of the coating and fibrous layers, and b capillary–pressure–saturation curves of the coating and fibrous layers (Aslannejad et al 2017; Aslannejad and Hassanizadeh 2017)…”

Capillary pressure–saturation curves of thin hydrophilic fibrous layers: effects of overburden pressure, number of layers, and multiple imbibition–drainage cycles

“…Pore morphology modeling has been used also to determine the P c S ð Þ relationship of uncoated thin paper. 23 A few studies can be found in the literature on changes in the P c S ð Þ curves of thin fabrics due to the effect of an overburden pressure. In an experimental study by Kumbur et al, 17 the effect of compression on the drainage capillary pressure-saturation curve of thin fibrous layers with mixed wettability was investigated.…”