Search

Fractured porous media is of great significance to the exploration and development of unconventional reservoirs. In this paper, a fractal model for permeability through micro-fractured porous media with consideration of the electric double layer (EDL) effect is proposed based on the fractal theory. The present model indicates that the permeability is a function of the electrokinetic parameters and micro-structural parameters of fractured porous media, and each parameter has a clear physical meaning, the results from the proposed model are found to be in good agreement with experimental data. Moreover, factors influencing the permeability are also analyzed in detail. The results indicate that the more obvious EDL effects will lead to permeability becoming lower. The present fractal model for the permeability with the EDL effect can provide guidance for tight reservoir development or other micro-porous media transportation. [ABSTRACT FROM AUTHOR]

Based on the fractal geometry science and the model of flow friction resistance when fluid flows through rough microcapillaries, the formula of diffusion layer thickness and the spatial charge density distribution of the pipe were derived. The relationship between the amount of space charge and the structural parameters of rough elements, relative roughness, liquid conductivity, pipeline diameter, and other physical quantities was discussed. It was found that the height of rough elements is directly proportional to the thickness of the diffusion layer, and also positively proportional to the amount of current. The predicted results of the model are in good agreement with existing models and various published experimental data, verifying the accuracy and reliability of the model. [ABSTRACT FROM AUTHOR]

The seepage in tree-like bifurcating networks is a very common phenomenon in nature. The research on the transport characteristics of tree-like bifurcating networks has always been a hot topic. In this paper, a novel permeability model for fluid flow in damaged tree-like bifurcating networks is proposed. In the proposed model, the influence of roughness on permeability is considered by means of the fractal method. It is found that the permeability is not only related to the structural parameters of the network but also related to the damaged position and the number of damaged tubes at the damaged position. The effects of these parameters and damaged structure on permeability are discussed separately. The results show that the permeability reduces along with an increase in the roughness level, the length ratio, the number of damaged tubes, and the number of total bifurcating levels. Another major finding is that the permeability increases with an increase in the diameter ratio. Besides, we found that the damaged position and the number of damaged tubes at the damaged position have an important effect on the permeability. Increasing the number of damaged tubes and bringing the damaged position close to the front end of the network will reduce the permeability. Compared with the undamaged network, the permeability of damaged network has a significant decline. The proposed model may provide potential applications for the analysis of fluid flow in damaged tree-like bifurcating network. [ABSTRACT FROM AUTHOR]

In this paper, a novel fractal model for the invasion depth of fluid through the tortuous capillary bundle with roughened surfaces in porous media is proposed. The capillary pressure effect is considered in the proposed model. The proposed model is expressed as a function of structure parameters of porous media, including the relative roughness, the fractal dimension for pore size distribution, the contact angle, the density, the gravitational acceleration, the tortuosity and porosity. The invasion depth can be quantitatively characterized by the proposed model. By using the fractal theory, the effect of relative roughness on the invasion depth is discussed. It is observed that the invasion depth decreases with increasing the relative roughness of the tortuous capillary bundle with roughened surfaces. In addition, it is found that the invasion depth increases with the increase of the invasion time. The proposed model predictions are in good agreement with the available experimental data. Each parameter in our model has clear a distinct physical meaning, which may contribute to comprehend the better understanding of seepage mechanisms. [ABSTRACT FROM AUTHOR]

The tree-like branching network widely exists in nature and human society. The heat and mass transfer of tree-like branching network has been studied for a long time. The research indicates that a tree-like branching network has excellent heat and mass transfer performance. In this paper, a model of spontaneous imbibition in the tree-like branching network with fractal roughened surfaces is proposed. Based on the series-parallel equivalent model, the analytical expression of the time-varying imbibition height and the expression of the equilibrium height are derived. It is found that the structural parameters of the branching network have an important influence on the imbibition process, including the diameter in the 0th branching level, the length ratio, the diameter ratio, the branching number, the total number of branching levels, the relative roughness and the branching angle. For instance, the equilibrium height increases with the increase in the total number of branching levels, but the time required to reach the equilibrium height also increases with the increase in the total number of branching levels. It is also seen that the equilibrium height increases with the increase in fractal dimension of roughened elements and length ratio, and decreases with the increase in diameter ratio. In addition, an interesting phenomenon is that the time required to reach the equilibrium height increases with the increase in branching angle, but the equilibrium height remains the same. Every parameter of the presented model has a clear physical meaning, revealing the imbibition mechanism of the tree-like branching network. [ABSTRACT FROM AUTHOR]

The CNC machining of nephrite is increasingly used in the jade engraving industry. As the most important standard for quality evaluation, surface roughness is influenced by cutting parameters. In this paper, taking the Buddha head as the machining object, the influence of cutting parameters on the surface quality of was studied by SYIL S7 CNC milling machine. The grooving experiment was carried out at spindle speed of 24,000 rpm, then the CAXA manufacturing engineer and JDpiant software were comparatively applied in machining. Furtherly, the influence of the spindle speed on the roughness was investigated. The research results were summarized as follows: (1) No edge breakage appeared when feed speed lower than 300 mm/min with the maximum depth of cut of 0.1 mm. In this case, when the jade is machined with the spindle speed range of 16,000–24,000 rpm, the mean roughness R a was in the range of 1,496.111–891.842 nm. (2) JDpiant software is more suitable for CNC jade engraving than CAXA manufacturing engineer. (3) In roughing stage, only the high-speed grinding contdition is satisfied, the integrity of side profile could be guaranteed. The higher spindle speed was conducive to achieve the fine surface quality. (4) The tungsten steel cutter in finish machining stage shows better grinding ability than diamond cutter used in rough machining stage. In order to formulate an economic spindle speed, the finishing surface roughness should be considered in conjunction with the requirement of polishing. [ABSTRACT FROM AUTHOR]

The arch is an important component of a biomass boiler. Initial arch design of most boilers is generally gained through manual computation, thus resulting in uncertain reasonability of flue gas flow. Moreover, biomass fuels in the market have instable characteristics, which influence the utilization of biomass energies considerably. To address the problems concerning reasonable flue gas flow caused by the collaborative design of arch and air staging and the combustion adaptability of fuels, a cold modeling experiment of a 1 t/h biomass boiler under different staged air distribution ratios when the rear arch coverage varies was conducted using Fluent software in this study after thermal performance computation and initial structural design of grate and furnace. Furthermore, a boiler performance test based on main fuels and a combustion adaptation test of auxiliary fuels were also performed. The experiments show that the best flue gas flow in the furnace is achieved when the rear arch coverage is 60% and the primary–secondary air distribution ratio is 4:6. The mean boiler efficiency and the mean boiler heat output are 81.26% and 715.76 by using Pinus koraiensis pellets, wood–straw mixed pellets, and cotton straw briquettes as main fuels; and the tested pollutant emissions are in compliance with the limits of the national standard. The results of the combustion adaptation test reveal that the excessive particle size, the high ash content and the relatively low calorific value of biomass molded fuels are all against the combustion of biomass boilers. Fuel upgrading based on washing process and other methods is suggested. This study can provide references to the performance optimization of traditional small-scale biomass chain heating boilers. [ABSTRACT FROM AUTHOR]

In this paper, the Fractal-Monte Carlo has been employed to simulate the effective thermal conductivity of porous media with roughened surfaces. The proposed probability model for the effective thermal conductivity of porous media with roughened surfaces can be expressed as a function of the relative roughness, porosity, minimum and maximum diameter of pores, fractal dimensions, and random number. The proposed model is validated by a satisfying agreement of our Fractal-Monte Carlo simulations and the experimental data. In our Fractal-Monte Carlo model, there is no extra empirical constant and each parameter has clear physical meaning. Then, the effects of micro-structural parameters of porous media on the effective thermal conductivity of porous media with roughened surfaces have been analyzed in detail. It can be found that the effective thermal conductivity of porous media with roughened surfaces decreases with the increase of relative roughness and tortuosity fractal dimension. Our results demonstrate that the proposed Fractal-Monte Carlo model can be used to characterize other transport properties such as mass transfer of porous media. [ABSTRACT FROM AUTHOR]

In this paper, fluid transport through fibrous porous media is studied by the fractal theory with a focus on the effect of surface roughness of capillaries. A fractal model for Kozeny–Carman (KC) constant and dimensionless permeability of fibrous porous media with roughened surfaces is derived. The determined KC constant and dimensionless permeability of fibrous porous media with roughened surfaces are in good agreement with available experimental data and existing models reported in the literature. It is found that the KC constant of fibrous porous media with roughened surfaces increases with the increase of relative roughness, porosity, area fractal dimension of pore and tortuosity fractal dimension, respectively. Besides, it is seen that the dimensionless permeability of fibrous porous media with roughened surfaces decreases with increasing relative roughness and tortuosity fractal dimension. However, it is observed that the dimensionless permeability of fibrous porous media with roughened surfaces increases with porosity. With the proposed fractal model, the physical mechanisms of fluids transport through fibrous porous media are better elucidated. [ABSTRACT FROM AUTHOR]

The Ni–Zn–P alloy coating has excellent physical and chemical properties that have been exploited for various industrial applications. Using sodium citrate as a complexing agent and lactic acid as a stabilizer, the effects of temperature and pH on the deposition rate and corrosion resistance of electroless plated Ni–Zn–P coating were studied. The results indicated that, when the temperature was 85 ∘ C, a good deposition rate was obtained with stable plating solution. pH value of 9.0 is preferred for the coating process by considering the stability of plating bath and deposition rate. The Ni–Zn–P alloy coating deposited with plating temperature of 85 ∘ C and bath pH of 9.0 has good quality, and a uniform and smooth surface texture without porosity. [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]

The capillary pressure is one of the crucial parameters in many science and engineering applications such as composite materials, interface science, chemical engineering, oil exploration, etc. The drop/bubble formation and its mechanisms that affect the permeability of porous media have steadily attracted much attention in the past. When a drop/bubble moves from a larger capillary to a smaller one, it is often obstructed by an additional pressure difference caused by the capillary force. In this paper, a comprehensive model is derived for the capillary pressure difference when a drop/bubble flows through a constricted capillary, i.e. a geometrically constricted passage with an abrupt change in radius. The proposed model is expressed as a function of the smaller capillary radius, pore-throat ratio, contact angle, surface tension and length of the drop/bubble in the smaller capillary. The model predictions are compared with the available experimental data, and good agreement is found between them. [ABSTRACT FROM AUTHOR]

Biofilms, abundantly attached on the surfaces of multiple media (such as pebbles and aquatic plants) in rivers or lakes reusing reclaimed water (RW), are of great significance to contaminants' self-purification of water bodies. In this paper, the nitrogen and phosphate adsorption characteristics of such biofilms were studied by the batch method, using biofilms cultivated under an outdoor simulative process. Two types of RW treated by anaerobic-anoxic-oxic process (A/O) and cyclic activated sludge technology (CASS), and surface water (NW) were chosen as the experimental water bodies. And the glasses of surface roughness of 0.1, 1.0, and 10 μm, respectively, were used as the substrates, where the biofilms adhere to them. The results indicated that the isothermal adsorption of biofilms for ammonia nitrogen and phosphates was proved to conform to the Langmuir and the Freundlich equation, whereas the adsorption capacity was significantly lower than that of soils and sediments limited by the pore structure and surface area. There were also significant differences between the adsorption behaviors. The distribution coefficients were ranked as K > K > K, and the maximum adsorption capacities ( S), under these conditions were ranked as S > S > S, while other parameters did not change regularly. Extracellular polymers ( $$R^{ 2}_{\text{N}}$$ = 0.95**, $$R^{ 2}_{\text{p}}$$ = 0.84**), iron oxides ( $$R^{ 2}_{\text{N}}$$ = 0.86**, $$R^{ 2}_{\text{p}}$$ = 0.68*), and aluminum oxides ( $$R^{ 2}_{\text{N}}$$ = 0.95**, $$R^{ 2}_{\text{p}}$$ = 0.81**) in the biofilms had a significant impact on the S for ammonia and phosphates. The roughness of media surfaces also had a considerable influence on the S, which was in the order of S > S > S, whereas other parameters did not change regularly. The research aimed to provide theory reference for in situ decontamination of RW in rivers or lakes. [ABSTRACT FROM AUTHOR]

The analytical expressions for the normalized average mass flux and pressure drop for power law fluids for wall effects in porous media are presented by using the fractal theory and technique for porous media. The proposed models are expressed as functions of power law index and structure parameters. These model predictions show that the proposed models can provide a good agreement with the experimental and other analytical results. This indicates that the fractal models may be helpful to much better understand the mechanisms of flow than other analytical models for porous media. [ABSTRACT FROM AUTHOR]

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]