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• Permeability of tree-like branching networks with polygonal loops is studied. • Factors influencing the permeability of tree-like networks are analyzed in detail. • Good agreement between model predictions and numerical results is found. A novel tree-like branching network with polygonal loops is designed based on the network of leaf vein. In this study, analytical models are presented for the effective permeabilities through the undamaged and damaged tree-like branching networks with polygonal loops based on Hagen-Poiseuille equation and Darcy's law. These effective permeability models are explicitly related to the structural parameters and the damaged number (or points) of the tree-like branching networks. We have discussed quantitatively the influences of the length and diameter ratios of channels, Y-shaped bifurcation angle, total branching level number, and damaged number (or points) on the effective permeability. Besides, numerical simulations are performed, and compared with the model predictions. Good agreement indicates that the present models for the permeability are reasonable. These analyses of the networks may provide a basis for scientific and engineering applications. [ABSTRACT FROM AUTHOR]

• A model is built for the effective electrolyte diffusion in porous media. • Effects of microstructural and electrokinetic parameters are analyzed. • Good agreement between our present model and results is observed. Electrolyte diffusion in electrolyte solutions exists in various areas including rechargeable batteries, soil physics and chemical engineering. In this paper, a fractal model based on the capillary model and fractal theory of porous media is proposed to quantify the effective electrolyte diffusivity in porous media with consideration of the electrical double layer (EDL) effects. The present model explicitly relates to the micro-structural parameters of porous media and electrokinetic parameters. To validate this model, a comparison is carried out with experimental data and semi-analytical model results, and yields satisfying agreement. Besides, the influences of the parameters (the porosity, equivalent particle diameter, ratio of the minimum pore radius to the maximum pore radius, molar concentration, zeta potential, and dimensionless parameter β) are discussed in details. [ABSTRACT FROM AUTHOR]

An analytical model is presented for the transverse permeability of gas diffusion layer (GDL) based on an ordered array of parallel charged circular cylinders at the steady state. The formula of calculating the permeability of the transverse direction is given by solving the fluid momentum equation in a unit cell. In the present approach, the proposed model is explicitly related to the porosity and fiber radius of fibrous porous media, the zeta potential, and the physical properties of the electrolyte solution. Besides, the effects of these parameters (the porosity, unit cell aspect ratio, fiber radius, and molar concentration) on the transverse permeability are discussed detailedly. The model predictions are compared with the previous studies in the available literature, and good agreement is found. [ABSTRACT FROM AUTHOR]

Electroosmotic flow (EOF) in porous media has very important applications in various scientific and engineering fields. In this article, a fractal model for the height difference caused by the EOFs in porous media is developed based on the fractal theory of porous media and on the electrokinetic flow in capillaries, whose tortuosity is taken into account. The proposed model indicates that the height difference is a function of the physical properties of electrolyte solutions, micro-structural parameters of porous media, zeta potential on the solid surface and Debye thickness near the solid–liquid interface in porous media. Factors influencing the height difference are also analyzed. The model predictions show the same variation tendencies with the available experimental data reported in literature. It is found that the proposed fractal model is superior to the hydraulic radius model in terms of dealing with transport in porous media. [ABSTRACT FROM AUTHOR]

Based on the blood circulatory system, a model is established for living biological tissue represented by a vascular network and surrounding tissue. In this paper, we analyze the heat transfer in living biological tissue and present an analytical model for the effective thermal conductivity of living biological tissue by taking into account the effects of geometric structures of branching vascular network and convection caused by blood flow. The proposed model is expressed as a function of the thermal conductivities of solid tissue matrix and blood, structural parameters of branching vascular network, porosity and properties of blood. It is found that the effective thermal conductivity of living biological tissue decreases with the increase of branching levels, length ratio and diameter ratio. It is also found that there exists a thermal conductivity ratio, at which the effective thermal conductivity is same for different porosities, below which the effective thermal conductivity increases with the increase of porosity, and above which the effective thermal conductivity decreases with the increase of porosity. A good agreement is obtained between the proposed model predictions and available experimental data for living tissue. The present results show that blood flow plays an important role in increasing the effective thermal conductivity, and the proposed model with blood flow is more reasonable and can reveal more physical mechanisms of heat transfer in living biological tissue. [ABSTRACT FROM AUTHOR]

Abstract: The biological tissue can be treated as a porous medium consisting of randomly distributed vascular trees and solid tissue matrix. In this paper, taking into account the effects of geometric structures of vascular trees and blood flow, a fractal model for the effective thermal conductivity of living biological tissue is derived based on the assumptions that the mother channel diameters of vascular trees follow the fractal scaling law. The proposed model is expressed as a function of the thermal conductivities of solid tissue matrix and blood, structural parameters of vascular trees, porosity and properties of blood. It is found that the effective thermal conductivity of living biological tissue increases with the increase of branching levels m, length ratio α, decreases with the increase of diameter ratio β, and there exists a thermal conductivity ratio, at which the effective thermal conductivity is same for different porosities ɛ, below which the effective thermal conductivity increases with the increase of porosity ɛ, and above which the effective thermal conductivity decreases with the increase of porosity ɛ. A good agreement is obtained between the proposed model predictions and available experimental data for living tissue. The results show that blood flow plays an important role in increasing the effective thermal conductivity, and the proposed model with blood flow is more reasonable and can reveal more physical mechanisms of heat transfer in living biological tissue. [Copyright &y& Elsevier]

Reclaimed wastewater reuse represents an effective method for partial resolution of increasing urban water shortages; however, reclaimed water may be characterized by significant contaminant loading, potentially affecting receiving ecosystem (and potentially human) health. The current study examined biofilm growth and nutrient adsorption in Olympic Lake (Beijing), the largest artificial urban lake in the world supplied exclusively by reclaimed wastewater. Findings indicate that solid particulate, extracellular polymeric substance (EPS) and metal oxide (Al, Fe, Mn) constituent masses adhere to a bacterial growth curve during biofilm formation and growth. Peak values were observed after ≈30 days, arrived at dynamic stability after ≈50 days and were affected by growth matrix surface roughness. These findings may be used to inform biofilm cultivation times for future biomonitoring. Increased growth matrix surface roughness (10.0 μm) was associated with more rapid biofilm growth and therefore an increased sensitivity to ecological variation in reclaimed water. Reclaimed water was found to significantly inhibit biofilm nutrient adsorption when compared with a “natural water” background, with elevated levels of metal oxides (Al, Fe, and Mn) and EPS representing the key substances actively influencing biofilm nutrient adsorption in reclaimed water. Results from the current study may be used to provide a quantitative baseline for future studies seeking to assess ecosystem health via monitoring of biofilms in the presence of reclaimed water through an improved quantitative understanding of biofilm kinetics in these conditions. [ABSTRACT FROM AUTHOR]