Characterizing the hydraulic properties of paper coating layer using FIB-SEM tomography and 3D pore-scale modeling

AbstractPaper used in the printing industry generally contains a relatively thin porous coating covering a thicker fibrous base layer. The three-dimensional pore structure of coatings has a major effect on fluid flow patterns inside the paper medium. Understanding and quantifying the flow properties of thin coating layers is hence crucial. Pore spaces within the coating have an average size of about 180nm. We used scanning electron microscopy combined with focused ion beam (FIB-SEM) to visualize the nano-scale pore structure of the paper coating layer. Post-processing of the FIB-SEM images allowed us to reconstruct the three-dimensional pore space of the coating. The 3D FIB-SEM images were analyzed in detail to obtain pore size distribution and porosity value. The permeability was estimated using the GeoDict software, based on solutions of the Stokes equation. By determining the porosity and permeability of increasingly larger domain sizes, we estimated the size of a representative elementary volume (REV) for the coating layer to be 60µm3, which is well within the volume analyzed using FIB-SEM. The estimated porosity and permeability of the REV domain were 0.34 and 0.09 mDarcy, respectively. Using the pore morphology method, capillary pressure-saturation (Pc-S) and relative permeability curves of the REV domain could be constructed next. The Pc-S curves showed that the coating had a high air entry suction, which is very favorable for printing in that ink will invade the coating as soon as it is applied to the coating. Our results are essential for macroscale modelling of ink penetration into a coating layer during inkjet printing. Macroscopic models can be valuable tools for optimization of the penetration depth and the spreading of ink on and within paper substrates

Alternate furrow irrigation can radically improve water productivity of okra

Alternate furrow irrigation (AFI) is gaining interest as a means of saving water while minimising loss in crop production. Given the potential water savings of AFI, a field experiment was conducted in the Tandojam region of Pakistan by growing okra with AFI and conventional furrow irrigation (CFI) in which every furrow is irrigated. Our results show that total irrigation water applied in the AFI treatment was roughly half (248 ± 2.9 mm) that applied to the CFI treatment (497 ± 1.7 mm). Despite the very significant reduction in irrigation water used with AFI there was a non-significant (p>0.05) reduction (7.3 %) in okra yield. As a result, we also obtained a significantly (p<0.001) higher crop water productivity (CWP) of 5.29 ± 0.1 kg m-3 with AFI, which was nearly double the 2.78 ± 0.04 kg m-3 obtained with CFI. While this reduction in yield and/or potential income may appear small, it could be critical to the welfare of individual farmers, who may as a result hesitate to make changes from CFI to AFI if they are worse off than farmers who don’t adopt AFI. This situation exists because current water charges are based on crop and land area rather than the volume of water being accessed for irrigation. Transitioning from the current crop and land area based method of charging for water to a volumetric method may require investment in irrigation system changes and may take time to accomplish. These are important lessons for other countries, and particularly developing countries who are trying to improve the environmental, social and economic performance of their irrigated systems. We recommend that further studies be carried out using AFI to determine whether similar water savings and flow-on benefits can be achieved across a wide range of cropping systems in arid and semi-arid environments.http://www.elsevier.com/locate/agwat2017-07-31hb2016Plant Production and Soil Scienc