Darcy’s law is widely used to describe the flow in porous media in which there is a linear relationship between fluid velocity and pressure gradient. However, it has been found that for high numbers of Reynolds this ...Darcy’s law is widely used to describe the flow in porous media in which there is a linear relationship between fluid velocity and pressure gradient. However, it has been found that for high numbers of Reynolds this law ceases to be valid. In this work, the Ergun equation is employed to consider the non-linearity of air velocity with the pressure gradient in casting sands. The contribution of non-linearity to the total flow in terms of a variable defined as a non-Darcy flow fraction is numerically quantified. In addition, the influence of the shape factor of the sand grains on the non-linear flow fraction is analyzed. It is found that for values of the Reynolds number less or equal than 1, the contribution of non-linearity for spherical particles is around 1.15%.展开更多
Laboratory experiments are designed in this paper using single fractures made of cement and coarse sand for a series of hydraulic tests under the conditions of different fracture apertures, and for the simulation of t...Laboratory experiments are designed in this paper using single fractures made of cement and coarse sand for a series of hydraulic tests under the conditions of different fracture apertures, and for the simulation of the evolution of the flow pattern at places far from the outlet. The relationship between the hydraulic gradient and the flow velocity at different points, and the proportion evolution of the linear and nonlinear portions in the Forchheimer formula are then discussed. Three major conclusions are obtained. First, the non-Darcian flow exists in a single fracture in different laboratory tests. Better fitting accuracy is obtained by using the Forchheimer formula than by using the Darcy law. Second, the proportion of the Darcy flow increases with the increase of the observation scale. In places far enough, the Darcy flow prevails, and the critical velocity between the non-Darcian flow and the Darcy flow decreases as the fracture aperture increases. Third, when the fracture aperture increases, the critical Reynolds number between the non-Darcian flow and the Darcy flow decreases.展开更多
In this study, the flow of a fourth order fluid in a porous half space is modeled. By using the modified Darcy＇s law, the flow over a suddenly moving flat plate is studied numerically. The influence of various parame...In this study, the flow of a fourth order fluid in a porous half space is modeled. By using the modified Darcy＇s law, the flow over a suddenly moving flat plate is studied numerically. The influence of various parameters of interest on the velocity profile is revealed.展开更多
In this paper, we present the analytic solutions of several continuum porous media models that describe the interstitial fluid flow in the interosseous membrane. We first compare the results of the Brinkman, Stokes an...In this paper, we present the analytic solutions of several continuum porous media models that describe the interstitial fluid flow in the interosseous membrane. We first compare the results of the Brinkman, Stokes and Darcy systems in describing the isotropic interstitial fluid flows. Our calculations show that the Stokes equations can well approximate the Brinkman equations when the Darcy number Da 〉 0.2, while the Darcy model is an appropriate approximation to the Brinkman model in the interosseous membrane when Da 〈 2 × 10-4. Yet, in most cases, the anisotropy dominates the interstitial fluid. Therefore, we build an anisotropic Darcy model and show that an isotropic model can be used as a suitable approximation when the ratio between the transverse and longitudinal permeabilities is no larger than 20. Lastly, we take the blood flow in capillaries into consideration as well and introduce the coupled Stokes-Darcy system to describe the cases comprising both the capillary and the interstitial domain. Our results reveal that the profile of the interface exchange flow is not exactly in the linear form as was widely adopted in the numerical simulation, instead, the flux near the artery and the vein is more significant, which in turn results in the increase of the maximum horizontal velocity in the interstitial space while the outflow rate remains the same.展开更多
A hill can be regarded as an environmental carrier of heat.Water,rocks and the internal moisture naturally pre-sent in such environment constitute a natural heat accumulator.In the present study,the heat and moisture ...A hill can be regarded as an environmental carrier of heat.Water,rocks and the internal moisture naturally pre-sent in such environment constitute a natural heat accumulator.In the present study,the heat and moisture trans-fer characteristics in a representative hill cave have been simulated via a method relying on the Darcy’s law.The simulations have been conducted for both steady and unsteady conditions to discern the influence of permeability and geometric parameters on the thermal and moisture transfer processes.The reliability of the simulation has been verified through comparison of the numerical results with the annual observation data.As revealed by the numericalfindings,the internal temperature of the hill accumulator is proportional to the permeability,outside surface temperature,overground height,underground constant temperature layer depth,and underground tem-perature of the hill,and it is inversely proportional to the horizontal size of the hill.Moreover,in the considered case,the order of magnitude of the permeability of the hill is contained in the range 10-15–10-13,and displays a certain sensitivity to the rainwater seepage.展开更多
In this paper, we have discussed the linear stabil- ity analysis of the electrified surface separating two coaxial Oldroyd-B fluid layers confined between two impermeable rigid cylinders in the presence of both interf...In this paper, we have discussed the linear stabil- ity analysis of the electrified surface separating two coaxial Oldroyd-B fluid layers confined between two impermeable rigid cylinders in the presence of both interfacial insoluble surfactant and surface charge through porous media. The case of long waves interfacial stability has been studied. The dispersion relation is solved numerically and hence the ef- fects of various parameters are illustrated graphically. Our results reveal that the influence of the physicochemical pa- rameterβ is to shrink the instability region of the surface and reduce the growth rate of the unstable normal modes. Such important effects of the surfactant on the shape of in- terfacial structures are more sensitive to the variation of the βcorresponding to non-Newtonian fluids-model compared with the Newtonian fluids model. In the case of long wave limit, it is demonstrated that increasing r, has a dual role in- fluence （de-stabilizing effects） depending on the viscosity of the core fluid. It has a destabilizing effect at the large values of the core fluid viscosity coefficient, while this role is ex- changed to a regularly stabilizing influence at small values of such coefficient.展开更多
Although the two-grid finite element decoupled scheme for mixed Navier-Stokes/ Darcy model in literatures has given the numerical results of optimal convergence order, the theoretical analysis only obtain the optimal ...Although the two-grid finite element decoupled scheme for mixed Navier-Stokes/ Darcy model in literatures has given the numerical results of optimal convergence order, the theoretical analysis only obtain the optimal error order for the porous media flow and a non-optimal error order for the fluid flow. In this article, we give a more rigorous of the error analysis for the fluid flow and obtain the optimal error estimates of the velocity and the pressure.展开更多
This article concentrates on the properties of three-dimensional magneto-hydrodynamic flow of a viscous fluid saturated with Darcy porous medium deformed by a nonlinear variable thickened surface.Analysis of flow is d...This article concentrates on the properties of three-dimensional magneto-hydrodynamic flow of a viscous fluid saturated with Darcy porous medium deformed by a nonlinear variable thickened surface.Analysis of flow is disclosed in the neighborhood of stagnation point.Features of heat transport are characterized with Newtonian heating and variable thermal conductivity.Mass transport is carried out with first order chemical reaction and variable mass diffusivity.Resulting governing equations are transformed by implementation of appropriate transformations.Analytical convergent series solutions are computed via homotopic technique.Physical aspects of numerous parameters are discussed through graphical data.Drag force coefficient,Sherwood and Nusselt numbers are illustrated through graphs corresponding to various pertinent parameters.Graphical discussion reveals that conjugate and constructive chemical reaction parameters enhance the temperature and concentration distributions,respectively.展开更多
This work reports on fluid flow in a fluid-saturated porous medium, accounting for the boundary and inertial effects in the momentum equation. The flow is simulated by Brinkman-Forchheimer-extended Darcy formulation ...This work reports on fluid flow in a fluid-saturated porous medium, accounting for the boundary and inertial effects in the momentum equation. The flow is simulated by Brinkman-Forchheimer-extended Darcy formulation （DFB）, using MAC （Marker And Cell） and Chorin pressure iteration method. The method is validated by comparison with analytic results. The effect of Reynolds number, Darcy number, porosity and viscosity ratio on velocity is investigated. As a result, it is found that Darcy number has a decisive influence on pressure as well as velocity, and the effect of viscosity ratio on velocity is very strong given the Darcy number. Additional key findings include unreasonable choice of effective viscosity can involve loss of important physical information.展开更多
Radiation effect on the natural convection flow of an optically thin viscous incompressible fluid near a vertical plate with ramped wall temperature in a porous medium has been studied. The exact solution of momentum ...Radiation effect on the natural convection flow of an optically thin viscous incompressible fluid near a vertical plate with ramped wall temperature in a porous medium has been studied. The exact solution of momentum and energy equations is obtained by the use of Laplace transform technique. The variations in fluid velocity and temperature are shown graphically whereas the numerical values of shear stress and the rate of heat transfer at the wall are presented in tabular form for various values of flow parameters. The results show that the fluid velocity increases with increase in Grashof number, Darcy number and time parameters whereas the fluid velocity decreases with increase in the radiation parameter and Prandtl number for ramped temperature as well as isothermal wall temperature. It is found that an increase in radiation parameter leads to rise the temperature for both ramped wall temperature as well as isothermal wall temperature. Further, it is found that an increase in Prandtl number leads to fall the temperature for both ramped wall temperature as well as isothermal wall temperature. The shear stress at the wall decreases with increases in either Prandtl number or porosity parameter while the result shows reverse in the case of radiation parameter. Finally, the rate of heat transfer is increased with increases in the radiation parameter for both ramped wall temperature as well as isothermal wall temperature.展开更多
The effects of two parallel porous walls are investigated, consisting of the Darcy number and the porosity of a porous medium, on the behavior of turbulent shear flows as well as skin-friction drag. The turbulent chan...The effects of two parallel porous walls are investigated, consisting of the Darcy number and the porosity of a porous medium, on the behavior of turbulent shear flows as well as skin-friction drag. The turbulent channel flow with a porous surface is directly simulated by the lattice Boltzmann method （LBM）. The Darcy-Brinkman- Forcheimer （DBF） acting force term is added in the lattice Boltzmann equation to simu- late the turbulent flow bounded by porous walls. It is found that there are two opposite trends （enhancement or reduction） for the porous medium to modify the intensities of the velocity fluctuations and the Reynolds stresses in the near wall region. The parametric study shows that flow modification depends on the Darcy number and the porosity of the porous medium. The results show that, with respect to the conventional impermeable wall, the degree of turbulence modification does not depend on any simple set of param- eters obviously. Moreover, the drag in porous wall-bounded turbulent flow decreases if the Darcy number is smaller than the order of O（10-4） and the porosity of porous walls is up to 0.4.展开更多
New approximate analytical solutions for steady flow in parallel-plates channels filled with porous materials governed by non-linear Brinkman-Forchheimer extended Darcy model for three different physical situations ar...New approximate analytical solutions for steady flow in parallel-plates channels filled with porous materials governed by non-linear Brinkman-Forchheimer extended Darcy model for three different physical situations are presented. These results are compared with those obtained from an implicit finite-difference solution of the corresponding time dependent flow problem. It is seen that the time dependent flow solutions yield the almost same steady state values as obtained by using the new approximate analytical展开更多
We established a model for the chemical reaction kinetics of biomass pyrolysis via the hightemperature thermal cracking of liquid products. We divided the condensable volatiles into two groups, based on the characteri...We established a model for the chemical reaction kinetics of biomass pyrolysis via the hightemperature thermal cracking of liquid products. We divided the condensable volatiles into two groups, based on the characteristics of the liquid prdoducts., tar and biomass oil. The effects of temperature, residence time, particle size, velocity, pressure, and other parameters on biomass pyrolysis and high-temperature tar cracking were investigated numerically, and the results were compared with experimental data. The simulation results showed a large endothermic pyrolysis reaction effect on temperature and the reaction process. The pyrolysis reaction zone had a constant temperature period in several layers near the center of large biomass particles. A purely physical heating process was observed before and after this period, according to the temperature index curve.展开更多
In this paper, we consider the mixed Navier-Stokes/Darcy model with BeaversJoseph interface conditions. Based on two-grid discretizations, a local and parallel finite element algorithm for this mixed model is proposed...In this paper, we consider the mixed Navier-Stokes/Darcy model with BeaversJoseph interface conditions. Based on two-grid discretizations, a local and parallel finite element algorithm for this mixed model is proposed and analyzed. Optimal errors are obtained and numerical experiments are presented to show the efficiency and effectiveness of the local and parallel finite element algorithm.展开更多
A three-dimensional Darcy Forchheimer mixed convective flow of a couple stress hybrid nanofluid flow through a vertical plate by means of the double diffusion Cattaneo-Christov model is presented in this study.The inf...A three-dimensional Darcy Forchheimer mixed convective flow of a couple stress hybrid nanofluid flow through a vertical plate by means of the double diffusion Cattaneo-Christov model is presented in this study.The influence of highorder velocity slip flow,as well as a passive and active control,is also considered.The motive of the research is to develop a computational model,using cobalt ferrite(Co Fe_(2)O_(4))and copper(Cu)nanoparticles(NPs)in the carrier fluid water,to magnify the energy and mass communication rate and boost the efficiency and performance of thermal energy conduction for a variety of commercial and biological purposes.The proposed model becomes more significant,with an additional effect of non-Fick's mass flux and Fourier's heat model to report the energy and mass passage rate.The results are obtained through the computational strategy parametric continuation method.The figures are plotted to reveal the physical sketch of the obtained solution,while the statistical assessment has been evaluated through tables.It has been observed that the dispersion of Cu and Co Fe_(2)O_(4)NPs to the base fluid significantly enhances the velocity and thermal conductivity of water,which is the most remarkable property of these NPs from the industrial point of view.展开更多
The seepage characteristics of multiscale porous media is of considerable significance in many scientific and engineering fields.The Darcy permeability is one of the key macroscopic physical properties to characterize...The seepage characteristics of multiscale porous media is of considerable significance in many scientific and engineering fields.The Darcy permeability is one of the key macroscopic physical properties to characterize the seepage capacity of porous media.Therefore,based on the statistically fractal scaling law of porous media,fractal geometry is applied to model the multiscale pore structures.And a two-dimensional fractal orifice-throat model with multiscale and tortuous characteristics is proposed for the seepage flow through porous media.The analytical expression for Darcy permeability of porous media is derived,which is validated by comparing with available experimental data.The results show that the Darcy permeability is significantly influenced by porosity,orifice-throat fractal dimension,minimum to maximum diameter ratio,orifice-throat ratio and tortuosity fractal dimension.The present results are helpful for understanding the seepage mechanism of multiscale porous media,and may provide theoretical basis for unconventional oil and gas exploration and development,porous phase transition energy storage composites,CO2 geological sequestration,environmental protection and nuclear waste treatment,etc.展开更多
The need to understand flow within aquiferous formations for a complete evaluation of groundwater resource and quality control prompts the determination of groundwater velocities through well dilution technique. Well ...The need to understand flow within aquiferous formations for a complete evaluation of groundwater resource and quality control prompts the determination of groundwater velocities through well dilution technique. Well dilution techniques utilize tracer solutions after establishing an initial homogenous condition to monitor the flow rate of ambient groundwater into the wells. Application of dilution techniques in wells makes it feasible to determine the velocities of groundwater in the aquiferous formation surrounding the well. In this study, a simple trigger-tube tracer dilution technique was employed to determine the Darcy and apparent velocities of groundwater in the phreatic aquiferous formation in Bamenda, Cameroon. Eighteen (18) hand dug-wells at different locations within Bamenda were sampled by utilizing sodium chloride (NaCl) as the conservative tracer. Field estimates of groundwater flow velocities in the phreatic aquiferous formation in Bamenda reveal Darcy's groundwater velocity in the range of 0.39 m/d at Nacho to 130.64 m/d at Foncha Street and apparent velocity in the range of 0.78 m/d at Nacho to 277.86 m/d at Foncha Street. The immense variations in the velocities of groundwater indicate that the groundwater flows at different rates and directions within the aquiferous formation in Bamenda, possibly due to variations in their hydraulic conductivities. Moreover, the spatial variations in the formation types, facies changes, thickness, and layering of the aquiferous formation also contribute to the variation of velocities. Areas with low groundwater velocities are associated with a lower contaminant transport rate when compared to areas with high groundwater velocities. The findings of this study are important for assessing the rates of pollutant movement in the subsurface, as well as the effectiveness and efficacy of the trigger-tube technique in evaluating the hydraulic properties of aquiferous formations.展开更多
文摘Darcy’s law is widely used to describe the flow in porous media in which there is a linear relationship between fluid velocity and pressure gradient. However, it has been found that for high numbers of Reynolds this law ceases to be valid. In this work, the Ergun equation is employed to consider the non-linearity of air velocity with the pressure gradient in casting sands. The contribution of non-linearity to the total flow in terms of a variable defined as a non-Darcy flow fraction is numerically quantified. In addition, the influence of the shape factor of the sand grains on the non-linear flow fraction is analyzed. It is found that for values of the Reynolds number less or equal than 1, the contribution of non-linearity for spherical particles is around 1.15%.
基金Project supported by the National Natural Science Foun-dation of China(Grant Nos.41272251,41372245)
文摘Laboratory experiments are designed in this paper using single fractures made of cement and coarse sand for a series of hydraulic tests under the conditions of different fracture apertures, and for the simulation of the evolution of the flow pattern at places far from the outlet. The relationship between the hydraulic gradient and the flow velocity at different points, and the proportion evolution of the linear and nonlinear portions in the Forchheimer formula are then discussed. Three major conclusions are obtained. First, the non-Darcian flow exists in a single fracture in different laboratory tests. Better fitting accuracy is obtained by using the Forchheimer formula than by using the Darcy law. Second, the proportion of the Darcy flow increases with the increase of the observation scale. In places far enough, the Darcy flow prevails, and the critical velocity between the non-Darcian flow and the Darcy flow decreases as the fracture aperture increases. Third, when the fracture aperture increases, the critical Reynolds number between the non-Darcian flow and the Darcy flow decreases.
文摘In this study, the flow of a fourth order fluid in a porous half space is modeled. By using the modified Darcy＇s law, the flow over a suddenly moving flat plate is studied numerically. The influence of various parameters of interest on the velocity profile is revealed.
基金Project supported by the National Natural Science Foundation of China(Grant No.11202053)the Shanghai Science Foundation(Grant No.12ZR1401100)the National Key Basic Research Program of China(973 Program,Grant No.2012CB518502)
文摘In this paper, we present the analytic solutions of several continuum porous media models that describe the interstitial fluid flow in the interosseous membrane. We first compare the results of the Brinkman, Stokes and Darcy systems in describing the isotropic interstitial fluid flows. Our calculations show that the Stokes equations can well approximate the Brinkman equations when the Darcy number Da 〉 0.2, while the Darcy model is an appropriate approximation to the Brinkman model in the interosseous membrane when Da 〈 2 × 10-4. Yet, in most cases, the anisotropy dominates the interstitial fluid. Therefore, we build an anisotropic Darcy model and show that an isotropic model can be used as a suitable approximation when the ratio between the transverse and longitudinal permeabilities is no larger than 20. Lastly, we take the blood flow in capillaries into consideration as well and introduce the coupled Stokes-Darcy system to describe the cases comprising both the capillary and the interstitial domain. Our results reveal that the profile of the interface exchange flow is not exactly in the linear form as was widely adopted in the numerical simulation, instead, the flux near the artery and the vein is more significant, which in turn results in the increase of the maximum horizontal velocity in the interstitial space while the outflow rate remains the same.
文摘A hill can be regarded as an environmental carrier of heat.Water,rocks and the internal moisture naturally pre-sent in such environment constitute a natural heat accumulator.In the present study,the heat and moisture trans-fer characteristics in a representative hill cave have been simulated via a method relying on the Darcy’s law.The simulations have been conducted for both steady and unsteady conditions to discern the influence of permeability and geometric parameters on the thermal and moisture transfer processes.The reliability of the simulation has been verified through comparison of the numerical results with the annual observation data.As revealed by the numericalfindings,the internal temperature of the hill accumulator is proportional to the permeability,outside surface temperature,overground height,underground constant temperature layer depth,and underground tem-perature of the hill,and it is inversely proportional to the horizontal size of the hill.Moreover,in the considered case,the order of magnitude of the permeability of the hill is contained in the range 10-15–10-13,and displays a certain sensitivity to the rainwater seepage.
文摘In this paper, we have discussed the linear stabil- ity analysis of the electrified surface separating two coaxial Oldroyd-B fluid layers confined between two impermeable rigid cylinders in the presence of both interfacial insoluble surfactant and surface charge through porous media. The case of long waves interfacial stability has been studied. The dispersion relation is solved numerically and hence the ef- fects of various parameters are illustrated graphically. Our results reveal that the influence of the physicochemical pa- rameterβ is to shrink the instability region of the surface and reduce the growth rate of the unstable normal modes. Such important effects of the surfactant on the shape of in- terfacial structures are more sensitive to the variation of the βcorresponding to non-Newtonian fluids-model compared with the Newtonian fluids model. In the case of long wave limit, it is demonstrated that increasing r, has a dual role in- fluence （de-stabilizing effects） depending on the viscosity of the core fluid. It has a destabilizing effect at the large values of the core fluid viscosity coefficient, while this role is ex- changed to a regularly stabilizing influence at small values of such coefficient.
基金Subsidized by NSFC(11571274 and 11171269)the Ph.D.Programs Foundation of Ministry of Education of China(20110201110027)
文摘Although the two-grid finite element decoupled scheme for mixed Navier-Stokes/ Darcy model in literatures has given the numerical results of optimal convergence order, the theoretical analysis only obtain the optimal error order for the porous media flow and a non-optimal error order for the fluid flow. In this article, we give a more rigorous of the error analysis for the fluid flow and obtain the optimal error estimates of the velocity and the pressure.
文摘This article concentrates on the properties of three-dimensional magneto-hydrodynamic flow of a viscous fluid saturated with Darcy porous medium deformed by a nonlinear variable thickened surface.Analysis of flow is disclosed in the neighborhood of stagnation point.Features of heat transport are characterized with Newtonian heating and variable thermal conductivity.Mass transport is carried out with first order chemical reaction and variable mass diffusivity.Resulting governing equations are transformed by implementation of appropriate transformations.Analytical convergent series solutions are computed via homotopic technique.Physical aspects of numerous parameters are discussed through graphical data.Drag force coefficient,Sherwood and Nusselt numbers are illustrated through graphs corresponding to various pertinent parameters.Graphical discussion reveals that conjugate and constructive chemical reaction parameters enhance the temperature and concentration distributions,respectively.
基金sponsored by Institute of Crustal Dynamics (Grant Nos. ZDJ2007-06 and ZDJ2008-08)National 973 Project (2006CB705802)
文摘This work reports on fluid flow in a fluid-saturated porous medium, accounting for the boundary and inertial effects in the momentum equation. The flow is simulated by Brinkman-Forchheimer-extended Darcy formulation （DFB）, using MAC （Marker And Cell） and Chorin pressure iteration method. The method is validated by comparison with analytic results. The effect of Reynolds number, Darcy number, porosity and viscosity ratio on velocity is investigated. As a result, it is found that Darcy number has a decisive influence on pressure as well as velocity, and the effect of viscosity ratio on velocity is very strong given the Darcy number. Additional key findings include unreasonable choice of effective viscosity can involve loss of important physical information.
文摘Radiation effect on the natural convection flow of an optically thin viscous incompressible fluid near a vertical plate with ramped wall temperature in a porous medium has been studied. The exact solution of momentum and energy equations is obtained by the use of Laplace transform technique. The variations in fluid velocity and temperature are shown graphically whereas the numerical values of shear stress and the rate of heat transfer at the wall are presented in tabular form for various values of flow parameters. The results show that the fluid velocity increases with increase in Grashof number, Darcy number and time parameters whereas the fluid velocity decreases with increase in the radiation parameter and Prandtl number for ramped temperature as well as isothermal wall temperature. It is found that an increase in radiation parameter leads to rise the temperature for both ramped wall temperature as well as isothermal wall temperature. Further, it is found that an increase in Prandtl number leads to fall the temperature for both ramped wall temperature as well as isothermal wall temperature. The shear stress at the wall decreases with increases in either Prandtl number or porosity parameter while the result shows reverse in the case of radiation parameter. Finally, the rate of heat transfer is increased with increases in the radiation parameter for both ramped wall temperature as well as isothermal wall temperature.
基金Project supported by the National Natural Science Foundation of China(Nos.10972132 and 11272198)
文摘The effects of two parallel porous walls are investigated, consisting of the Darcy number and the porosity of a porous medium, on the behavior of turbulent shear flows as well as skin-friction drag. The turbulent channel flow with a porous surface is directly simulated by the lattice Boltzmann method （LBM）. The Darcy-Brinkman- Forcheimer （DBF） acting force term is added in the lattice Boltzmann equation to simu- late the turbulent flow bounded by porous walls. It is found that there are two opposite trends （enhancement or reduction） for the porous medium to modify the intensities of the velocity fluctuations and the Reynolds stresses in the near wall region. The parametric study shows that flow modification depends on the Darcy number and the porosity of the porous medium. The results show that, with respect to the conventional impermeable wall, the degree of turbulence modification does not depend on any simple set of param- eters obviously. Moreover, the drag in porous wall-bounded turbulent flow decreases if the Darcy number is smaller than the order of O（10-4） and the porosity of porous walls is up to 0.4.
文摘New approximate analytical solutions for steady flow in parallel-plates channels filled with porous materials governed by non-linear Brinkman-Forchheimer extended Darcy model for three different physical situations are presented. These results are compared with those obtained from an implicit finite-difference solution of the corresponding time dependent flow problem. It is seen that the time dependent flow solutions yield the almost same steady state values as obtained by using the new approximate analytical
文摘We established a model for the chemical reaction kinetics of biomass pyrolysis via the hightemperature thermal cracking of liquid products. We divided the condensable volatiles into two groups, based on the characteristics of the liquid prdoducts., tar and biomass oil. The effects of temperature, residence time, particle size, velocity, pressure, and other parameters on biomass pyrolysis and high-temperature tar cracking were investigated numerically, and the results were compared with experimental data. The simulation results showed a large endothermic pyrolysis reaction effect on temperature and the reaction process. The pyrolysis reaction zone had a constant temperature period in several layers near the center of large biomass particles. A purely physical heating process was observed before and after this period, according to the temperature index curve.
文摘In this paper, we consider the mixed Navier-Stokes/Darcy model with BeaversJoseph interface conditions. Based on two-grid discretizations, a local and parallel finite element algorithm for this mixed model is proposed and analyzed. Optimal errors are obtained and numerical experiments are presented to show the efficiency and effectiveness of the local and parallel finite element algorithm.
基金Deanship of Scientific Research at King Khalid University for funding this work through Large Groups Project under grant number(RGP.2/155/43)。
文摘A three-dimensional Darcy Forchheimer mixed convective flow of a couple stress hybrid nanofluid flow through a vertical plate by means of the double diffusion Cattaneo-Christov model is presented in this study.The influence of highorder velocity slip flow,as well as a passive and active control,is also considered.The motive of the research is to develop a computational model,using cobalt ferrite(Co Fe_(2)O_(4))and copper(Cu)nanoparticles(NPs)in the carrier fluid water,to magnify the energy and mass communication rate and boost the efficiency and performance of thermal energy conduction for a variety of commercial and biological purposes.The proposed model becomes more significant,with an additional effect of non-Fick's mass flux and Fourier's heat model to report the energy and mass passage rate.The results are obtained through the computational strategy parametric continuation method.The figures are plotted to reveal the physical sketch of the obtained solution,while the statistical assessment has been evaluated through tables.It has been observed that the dispersion of Cu and Co Fe_(2)O_(4)NPs to the base fluid significantly enhances the velocity and thermal conductivity of water,which is the most remarkable property of these NPs from the industrial point of view.
文摘The seepage characteristics of multiscale porous media is of considerable significance in many scientific and engineering fields.The Darcy permeability is one of the key macroscopic physical properties to characterize the seepage capacity of porous media.Therefore,based on the statistically fractal scaling law of porous media,fractal geometry is applied to model the multiscale pore structures.And a two-dimensional fractal orifice-throat model with multiscale and tortuous characteristics is proposed for the seepage flow through porous media.The analytical expression for Darcy permeability of porous media is derived,which is validated by comparing with available experimental data.The results show that the Darcy permeability is significantly influenced by porosity,orifice-throat fractal dimension,minimum to maximum diameter ratio,orifice-throat ratio and tortuosity fractal dimension.The present results are helpful for understanding the seepage mechanism of multiscale porous media,and may provide theoretical basis for unconventional oil and gas exploration and development,porous phase transition energy storage composites,CO2 geological sequestration,environmental protection and nuclear waste treatment,etc.
文摘The need to understand flow within aquiferous formations for a complete evaluation of groundwater resource and quality control prompts the determination of groundwater velocities through well dilution technique. Well dilution techniques utilize tracer solutions after establishing an initial homogenous condition to monitor the flow rate of ambient groundwater into the wells. Application of dilution techniques in wells makes it feasible to determine the velocities of groundwater in the aquiferous formation surrounding the well. In this study, a simple trigger-tube tracer dilution technique was employed to determine the Darcy and apparent velocities of groundwater in the phreatic aquiferous formation in Bamenda, Cameroon. Eighteen (18) hand dug-wells at different locations within Bamenda were sampled by utilizing sodium chloride (NaCl) as the conservative tracer. Field estimates of groundwater flow velocities in the phreatic aquiferous formation in Bamenda reveal Darcy's groundwater velocity in the range of 0.39 m/d at Nacho to 130.64 m/d at Foncha Street and apparent velocity in the range of 0.78 m/d at Nacho to 277.86 m/d at Foncha Street. The immense variations in the velocities of groundwater indicate that the groundwater flows at different rates and directions within the aquiferous formation in Bamenda, possibly due to variations in their hydraulic conductivities. Moreover, the spatial variations in the formation types, facies changes, thickness, and layering of the aquiferous formation also contribute to the variation of velocities. Areas with low groundwater velocities are associated with a lower contaminant transport rate when compared to areas with high groundwater velocities. The findings of this study are important for assessing the rates of pollutant movement in the subsurface, as well as the effectiveness and efficacy of the trigger-tube technique in evaluating the hydraulic properties of aquiferous formations.
