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To investigate the effects of cigarette structure parameters on the air flow field inside the cigarette, a computational fluid dynamics (CFD) method was adopted to simulate the air flow process inside a cigarette. The effects of viscous resistance coefficients of cigarette materials and cigarette length on the mouth end pressure drop and the ventilation rates of cigarette paper and filter were analyzed, and the correlation equations, which can quantitatively describe the coupling effect of cigarette structure parameters on the air field inside cigarette, were established. The results showed that: 1) The pressure drop was positively correlated with the viscosity resistance coefficients of cut tobacco, filter, cigarette paper and plug wrapper, the ventilation rate of cigarette paper was positively correlated with the viscosity resistance coefficients of cut tobacco and plug wrapper, and the ventilation rate of filter was positively correlated with the viscosity resistance coefficients of cut tobacco, filter and cigarette paper. 2) As the cigarette length decreased or the cigarette diameter increased, the pressure drop and the ventilation rates of the cigarette paper and filter decreased. 3) As the number of ventilation holes increased, the pressure drop and the ventilation rate of the cigarette paper decreased, while the ventilation rate of the filter increased. As the distance between the ventilation holes and the mouth end increased, the pressure drop and the ventilation rate of the cigarette paper increased, while the ventilation rate of the filter decreased. 4) The correlation coefficients of the established correlation equations were all higher than 0.93, and the relative errors between the predicted and measured values were small, which could accurately describe the coupling effect of cigarette structure parameters on the air flow field inside the cigarette. [ABSTRACT FROM AUTHOR]

A thorough understanding of the reactor core thermal hydraulic behavior is essential for the design and safety analysis of Sodium-cooled Fast Reactors (SFR). Due to the application of hexagonal subassembly, the core thermal hydraulic behavior is significantly affected by the flow field within the subassemblies, the inter-wrapper region and the hot pool. Analysis of the core thermal hydraulic behavior requires a model coupling the three regions mentioned above, which has been identified as one of the thermal hydraulic challenges in SFR. In the present study, a 3D model that covers the three regions was developed for the core of the China Experimental Fast Reactor (CEFR) with the Computational Fluid Dynamic (CFD) code, Fluent. The inter-wrapper region and the hot pool were modeled in detail, while the subassemblies were modeled with a special porous medium model. The core thermal hydraulics behavior under steady state was studied, more specifically, information for the flow field distribution at the core outlet, the inter-wrapper flow and the duct wall temperature distribution was obtained. Under steady state, liquid sodium in the inter-wrapper region is supplied by the inner region of the hot pool. And it enters the inter-wrapper region from the core outer region and returns back to the hot pool inner region from the core central region. The inter-wrapper flow is cooled by non-fuel subassemblies and heated up by fuel subassemblies. For non-fuel subassembly, the ratio of the total heat transfer rate between the inter-wrapper flow and the subassemblies to the heat generated within subassemblies could reaches 96%; for fuel subassemblies, the maximum ratio of the total heat transfer rate between the inter-wrapper flow and the subassemblies to the heat generated within subassemblies is 2.45%. Significant temperature gradients have been observed on the duct wall, with maximum values of 156.69 K/m in the vertical direction and 2,196.00 K/m in the circumferential direction. The largest temperature gradient appears on the duct of subassemblies adjacent to the transition region of fuel subassemblies and non-fuel subassemblies. [ABSTRACT FROM AUTHOR]

Iliac Vein Compression Syndrome (IVCS) is a common risk factor for deep vein thrombosis in the lower extremities. The objective of this study was to investigate whether employing a porous medium model to simulate the compressed region of an iliac vein could improve the reliability and accuracy of Computational Fluid Dynamics (CFD) analysis outcomes of IVCS. Pre-operative Computed Tomography (CT) scan images of patients with IVCS were utilized to reconstruct models illustrating both the compression and collateral circulation of the iliac vein. A porous medium model was employed to simulate the compressed region of the iliac vein. The agreements of times to peak between discrete phase particles in CFD analysis and contrast agent particles in Digital Subtraction Angiography (DSA) were compared. Furthermore, comparisons were made between the CFD analysis results that incorporated the porous media and those that did not. The results revealed that in the CFD analysis incorporating the porous media model, more than 80% of discrete phase particles reached the inferior vena cava via collateral circulation. Additionally, the concentration variation curve of discrete phase particles demonstrated a high concordance rate of 92.4% compared to that obtained in DSA. In comparison to CFD analysis conducted without the porous medium model, the incorporation of the porous medium model resulted in a substantial decrease in blood flow velocity by 87.5% within the compressed region, a significant increase in pressure gradient of 141 Pa between the inferior vena cava and left iliac vein, and a wider distribution of wall shear stress exceeding 2.0 Pa in collateral vessels rather than in the compressed region. The study suggests that the introduction of a porous medium model improves the hemodynamic analysis of patients with IVCS, resulting in a closer alignment with clinical observations. This provides a novel theoretical framework for the assessment and treatment of patients with IVCS.

Abstract This paper presents a topology optimization approach for the surface flows on variable design domains. Via this approach, the matching between the pattern of a surface flow and the 2-manifold used to define the pattern can be optimized, where the 2-manifold is implicitly defined on another fixed 2-manifold named as the base manifold. The fiber bundle topology optimization approach is developed based on the description of the topological structure of the surface flow by using the differential geometry concept of the fiber bundle. The material distribution method is used to achieve the evolution of the pattern of the surface flow. The evolution of the implicit 2-manifold is realized via a homeomorphous map. The design variable of the pattern of the surface flow and that of the implicit 2-manifold are regularized by two sequentially implemented surface-PDE filters. The two surface-PDE filters are coupled, because they are defined on the implicit 2-manifold and base manifold, respectively. The surface Navier-Stokes equations, defined on the implicit 2-manifold, are used to describe the surface flow. The fiber bundle topology optimization problem is analyzed using the continuous adjoint method implemented on the first-order Sobolev space. Several numerical examples have been provided to demonstrate this approach, where the combination of the viscous dissipation and pressure drop is used as the design objective.

This paper presents a topology optimization approach for the surface flows on variable design domains. Via this approach, the matching between the pattern of a surface flow and the 2-manifold used to define the pattern can be optimized, where the 2-manifold is implicitly defined on another fixed 2-manifold named as the base manifold. The fiber bundle topology optimization approach is developed based on the description of the topological structure of the surface flow by using the differential geometry concept of the fiber bundle. The material distribution method is used to achieve the evolution of the pattern of the surface flow. The evolution of the implicit 2-manifold is realized via a homeomorphous map. The design variable of the pattern of the surface flow and that of the implicit 2-manifold are regularized by two sequentially implemented surface-PDE filters. The two surface-PDE filters are coupled, because they are defined on the implicit 2-manifold and base manifold, respectively. The surface Navier-Stokes equations, defined on the implicit 2-manifold, are used to describe the surface flow. The fiber bundle topology optimization problem is analyzed using the continuous adjoint method implemented on the first-order Sobolev space. Several numerical examples have been provided to demonstrate this approach, where the combination of the viscous dissipation and pressure drop is used as the design objective. [ABSTRACT FROM AUTHOR]

A thorough understanding of the reactor core thermal hydraulic behavior is essential for the design and safety analysis of Sodium-cooled Fast Reactors (SFR). Due to the application of hexagonal subassembly, the core thermal hydraulic behavior is significantly affected by the flow field within the subassemblies, the inter-wrapper region and the hot pool. Analysis of the core thermal hydraulic behavior requires a model coupling the three regions mentioned above, which has been identified as one of the thermal hydraulic challenges in SFR. In the present study, a 3D model that covers the three regions was developed for the core of the China Experimental Fast Reactor (CEFR) with the Computational Fluid Dynamic (CFD) code, Fluent. The inter-wrapper region and the hot pool were modeled in detail, while the subassemblies were modeled with a special porous medium model. The core thermal hydraulics behavior under steady state was studied, more specifically, information for the flow field distribution at the core outlet, the inter-wrapper flow and the duct wall temperature distribution was obtained. Under steady state, liquid sodium in the inter-wrapper region is supplied by the inner region of the hot pool. And it enters the inter-wrapper region from the core outer region and returns back to the hot pool inner region from the core central region. The inter-wrapper flow is cooled by non-fuel subassemblies and heated up by fuel subassemblies. For non-fuel subassembly, the ratio of the total heat transfer rate between the inter-wrapper flow and the subassemblies to the heat generated within subassemblies could reaches 96%; for fuel subassemblies, the maximum ratio of the total heat transfer rate between the inter-wrapper flow and the subassemblies to the heat generated within subassemblies is 2.45%. Significant temperature gradients have been observed on the duct wall, with maximum values of 156.69 K/m in the vertical direction and 2,196.00 K/m in the circumferential direction. The largest temperature gradient appears on the duct of subassemblies adjacent to the transition region of fuel subassemblies and non-fuel subassemblies.

Featured Application: The developed topology optimization approach may give a potential design idea for body shape drag reduction of micro underwater vehicles and other underwater equipment worked in low speed. This paper presents a variable density topology optimization method to numerically investigate the optimal drag-reduction shape of objects in the two-dimensional and three-dimensional flows with steady incompressible external flow conditions, taking into account material volume constraints. By introducing the porous media model, the artificial Darcy friction is added to the Navier-Stokes equation to characterize the influence of materials on the fluid. Material density is applied to implement material interpolation. By transforming the boundary integral form of viscous dissipative expression of drag into the volume integral of artificial Darcy friction and convection term, we solve the problem of drag expression on the implicit interface corresponding to the structure. The continuous adjoint method is used to analyze gradient information for iteratively solving topology optimization problems. We obtain the relevant topology optimization structures of the minimum drag shapes, investigate the effect of the low Reynolds number on the drag force corresponding to two objective functions and discuss the mechanism of drag reduction by a hydrodynamic body shape. [ABSTRACT FROM AUTHOR]

The perforated plates are commonly used for gas flow control in the wide-angle diffusers of electrostatic precipitators of large power plants. Many studies dealt with the investigation of the effects of the perforated plate's geometry on flow parameters in the cases where incoming flow is perpendicular to the plate and the plate is covering the whole cross-section of the flowing channel. These results are partially applicable in cases where flow is inclined on the plate or when the plate is not occupying the whole cross-section of the channel. The subject of this work is a numerical investigation of flow through the rectangular channel with a perforated plate in various positions in the cross-section of the channel. The aim was to investigate the effect of the plate position on the flow. The perforated plates were modeled as thin porous media of finite thickness by using the directional loss model. Numerical experiments are carried out by using CFD software ANSYS CFX. Results of pressure drop and velocity distribution behind the plate are compared to the results of CFD simulation of the full 3-D plate model. In order to obtain a reasonable agreement both of the pressure drop and velocity distribution behind the plate when using a simplified thin porous plate model, the value of streamwise permeability of the plate had to be adjusted. The level of adjustments has determined iteratively and it depends on the plate position in the channel's cross-section. [ABSTRACT FROM AUTHOR]

Chronic obstructive pulmonary disease (COPD) is a primary chronic respiratory disease associated with pulmonary congestion that restricts airflow and thereby affects the exchange of gases between the alveoli and the blood capillaries in the lungs. Dual scale-global and local-porous medium models have been developed and reported in this work, to study the effects of air-side congestion on the blood-oxygen content in the alveolar region of the human lung. The human lung is model as a global, equivalent, heterogeneous porous medium comprising three zones with distinct permeabilities related to their progressively complex branching structure. Airflow for each breathing cycle is determined by solving mass and momentum transfer equations across the three porous medium zones. The congestion is introduced by appropriate modification of the porous medium properties of the zones considered. The congestion-affected air velocity reaching Zone 3 is given as input to a separate "local model" employed at several locations of the alveoli of Zone 3. The local model determines the oxygen content in the blood flow in the capillaries of the alveoli by solving suitable mass, momentum and species transport equations. The transient simulation results performed for a long duration of multiple breathing cycles, demonstrate that a normal, healthy human lung is functional for up to 40% volume congestion or when 50% of the lung is congested to about 23.5%. Increasing congestion beyond this value, quickly-within a few hours-depletes the oxygen exchange in the blood flow of the alveolar region (of Zone 3), leading to hypoxemia. The effects of congestion progression on oxygen exchange dynamics determined through the dual-scale porous medium modelling approach provide researchers and medical professionals with in silico predictive estimates to generate treatment strategies for chronic respiratory diseases., (© 2024 John Wiley & Sons Ltd.)

• POM can reproduce the hemodynamic changes of coiled aneurysm. • Neck, pre- and postoperative inflow areas were related with aneurysm recurrence. • A large postoperative inflow area independently predicts the recurrence of coiled PAs. This study aims to investigate recurrence risk factors of simply coiled unruptured paraclinoid aneurysms based on a porous medium model (POM). Twenty unruptured coiled paraclinoid aneurysms with digital subtract angiography (DSA) follow-up were enrolled to analyze morphological and hemodynamic variables to predict recurrence. Recurrent aneurysms have larger neck areas than stable aneurysms (34.43 ± 21.46 mm2 vs. 16.12 ± 7.10 mm2; p = 0.048). For hemodynamic variables, recurrent aneurysms had larger preoperative (16.40 ± 11.38 mm2 vs. 7.87 ± 3.75 mm2; p = 0.048) and postoperative inflow areas (14.07 ± 6.80 mm2 versus 6.73 ± 4.20 mm2; p = 0.021) than the stable group. Only the postoperative inflow area (p = 0.031, OR = 1.289; 95% CI 1.024–1.624) was an independent predictor of recurrence after multivariate regression analysis. The receiver operating characteristic (ROC) curve analysis efficiently predicted recurrence (AUC = 0.833, p = 0.021) with an inflow area cutoff value (9.15 mm2; sensitivity, 0.833; specificity, 0.857). Neck area along with pre- and postoperative inflow areas were associated with aneurysm recurrence. These findings suggest that a large postoperative inflow area independently predicts the recurrence of coiled paraclinoid aneurysms. [ABSTRACT FROM AUTHOR]

This paper presents a variable density topology optimization method to numerically investigate the optimal drag-reduction shape of objects in the two-dimensional and three-dimensional flows with steady incompressible external flow conditions, taking into account material volume constraints. By introducing the porous media model, the artificial Darcy friction is added to the Navier-Stokes equation to characterize the influence of materials on the fluid. Material density is applied to implement material interpolation. By transforming the boundary integral form of viscous dissipative expression of drag into the volume integral of artificial Darcy friction and convection term, we solve the problem of drag expression on the implicit interface corresponding to the structure. The continuous adjoint method is used to analyze gradient information for iteratively solving topology optimization problems. We obtain the relevant topology optimization structures of the minimum drag shapes, investigate the effect of the low Reynolds number on the drag force corresponding to two objective functions and discuss the mechanism of drag reduction by a hydrodynamic body shape.

Desulphurization is the key to the upgrading of oil products, and the high pressure hydrogenation reactor is a key device for desulfurization. The catalyst bed is one of the most core components of the hydrogenation reactor, and the flow characteristics of the internal multiphase fluid directly affect the reaction efficiency and product quality of the hydrogenation reactor. The multiphase flow process and the lumped reaction law of hydrodesulfurization in the catalyst bed are studied by adding the porous medium model and the laminar finite rate model in this paper. Combined the porous medium model and the laminar finite rate model, the mass fraction of hydrogen sulfide formation and Arrhenius reaction rate of desulfurization reaction with different porosity, different material inlet velocity and different hydrogen-oil ratio are studied. The result can provide theoretical basis for the optimization of the hydrogenation reaction parameters. [ABSTRACT FROM AUTHOR]

• The cooling of cargoes in the refrigerated container is enhanced. • The temperature homogeneity of the cargoes in the refrigerated container is improved. • Porous media model was used to numerically model the evaporator coil in the reefer. • Pressure drop and heat transfer of the evaporator coil are numerically modeled. The present study numerically investigates the airflow and heat transfer characteristics in a conventional refrigerated container (CRC), and an improved refrigerated container (IRC) loaded with cargoes by modeling the refrigeration unit and the cargoes in the container as porous media. The IRC design is based on a previous study by the current authors, where the airflow in the refrigerated container was enhanced by improving the refrigeration unit design. The airflow inside the refrigerated container is simulated by using the fan pressure jump boundary conditions at the location of the evaporator fans in the refrigeration unit. The CRC and IRC are simulated for three fan pressure jump conditions of 50, 100, and 150 Pa. Initially, the airflow and heat transfer results under 50 Pa fan pressure jump condition are compared for CRC and IRC to estimate the enhanced heat transfer in IRC. Then, the behavior of the heat transfer characteristics in CRC and IRC under increasing fan pressure jump conditions is studied by comparing the results of CRC and IRC under the three fan pressure jump conditions. Results show that the heat transfer and the temperature homogeneity of the cargoes in IRC are significantly improved due to the enhanced airflow by the improved design of the refrigeration unit in IRC. [ABSTRACT FROM AUTHOR]

[Display omitted] • Combining global simplified and local turbulence models to calculate flow details. • Analysis of the low-pressure heater pipe failure causes. • Simulate the low-pressure heater with the porous medium model. • Obtained flow information in the damaged local area. Low-pressure heaters are critical heat exchange equipment in thermal and nuclear power generation. The high-speed steam flow in the low-pressure heaters induces pipe vibration, causing pipe failure. The large size and complex flow make it hard to calculate directly. This paper employs a combined method of the porous medium and local models by substituting the boundary to calculate and prove steam flow trajectory and velocity are consistent with the actual situation. The analysis of the turbulent kinetic energy exhibits that the primary causes of pipe vibration are the periodic vortex shedding and the impact of the impingement plate on the pipes. The stress analysis indicates that the loosening of the pipes leads to a 368 times amplification of the shear stress by 0.1 MPa. The most crucial step in solving such a problem is to strengthen the fixation of the pipes, especially near the shell region. [ABSTRACT FROM AUTHOR]

Featured Application: Two-stage finger seal is a novel and revolutionary compliant seal, which has the characteristics of high speed, pressure and temperature capacity, low leakage, low cost, and long life time. It can be used in the secondary flow system of aeroengines. To solve the high leakage and high wear problems faced by sealing devices in aeroengines under the condition of high axial pressure difference, the two-stage finger seal is proposed in this paper. The finite element method and computational fluid dynamics (FEM/CFD) coupling iterative algorithm of the two-stage finger seal is developed and validated. Then the performance advantages of two-stage finger seal compared to the one-stage finger seal are studied, as well as the leakage and the inter-stage pressure drop characteristics of two-stage finger seal are investigated. Finally, the measure to improve the inter-stage imbalance of pressure drop of two-stage finger seal is proposed. The results show that the two-stage finger seal has lower leakage and lower contact pressure than the one-stage finger seal at high axial pressure difference, but there exists an inter-stage imbalance of pressure drop. Increasing the axial pressure difference and the root mean square (RMS) roughness of finger element can aggravate the imbalance of pressure drop, while the radial displacement excitation of rotor has little influence on it. The results also indicate that the inter-stage imbalance of pressure drop of the two-stage finger seal can be improved by increasing the number of finger elements of the 1st finger seal and decreasing the number of finger elements of the 2nd finger seal. [ABSTRACT FROM AUTHOR]

Copyright of China Sciencepaper is the property of China Sciencepaper and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

• The reefer was modeled considering the pressure drop from the refrigeration unit. • Porous media model was used to numerically model the evaporator coil in the reefer. • Airflow distribution in the refrigerated container was improved. • An improved refrigeration unit design is proposed for enhanced airflow in the reefer. An improved design of the refrigeration unit that provides enhanced airflow distribution inside the refrigerated container is proposed by numerically analyzing the airflow patterns in the refrigerated container with several design models of the refrigeration unit. Fifteen different models have been considered by changing effective dimensions and design parameters of the refrigeration unit, which play a major role in affecting the airflow patterns inside the refrigerated container. The numerical simulation of the airflow inside the refrigerated container is performed by considering the pressure drop and flow characteristics in the refrigeration unit. The pressure drop in the refrigeration unit is obtained by modeling the evaporator coil of the refrigeration unit as a porous medium. Results show that the improved design of the refrigeration unit provides significantly higher jet velocity, higher vertical velocity distributions, improved Coanda effect, higher mass averaged velocity, and reduced areas of dead zones in the container compared to the base case refrigeration unit. The mass averaged velocity in the refrigerated container with the improved refrigeration unit is 33.66% higher than that of the base case refrigerated container. [ABSTRACT FROM AUTHOR]

Copyright of Tunnel Construction / Suidao Jianshe (Zhong-Yingwen Ban) is the property of Tunnel Construction Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

We analyze the hydrodynamic behavior of the porous medium model (PMM) in a discrete space { 0 , ... , n } , where the sites 0 and n stand for reservoirs. Our strategy relies on the entropy method of Guo et al. (Commun Math Phys 118:31–59, 1988). However, this method cannot be straightforwardly applied, since there are configurations that do not evolve according to the dynamics (blocked configurations). In order to avoid this problem, we slightly perturbed the dynamics in such a way that the macroscopic behavior of the system keeps following the porous medium equation (PME), but with boundary conditions which depend on the reservoirs' strength. [ABSTRACT FROM AUTHOR]

To solve the high leakage and high wear problems faced by sealing devices in aeroengines under the condition of high axial pressure difference, the two-stage finger seal is proposed in this paper. The finite element method and computational fluid dynamics (FEM/CFD) coupling iterative algorithm of the two-stage finger seal is developed and validated. Then the performance advantages of two-stage finger seal compared to the one-stage finger seal are studied, as well as the leakage and the inter-stage pressure drop characteristics of two-stage finger seal are investigated. Finally, the measure to improve the inter-stage imbalance of pressure drop of two-stage finger seal is proposed. The results show that the two-stage finger seal has lower leakage and lower contact pressure than the one-stage finger seal at high axial pressure difference, but there exists an inter-stage imbalance of pressure drop. Increasing the axial pressure difference and the root mean square (RMS) roughness of finger element can aggravate the imbalance of pressure drop, while the radial displacement excitation of rotor has little influence on it. The results also indicate that the inter-stage imbalance of pressure drop of the two-stage finger seal can be improved by increasing the number of finger elements of the 1st finger seal and decreasing the number of finger elements of the 2nd finger seal.

A special issue concerned in the current study is the supersonic ejector-based cooling system in an oil radiator air-cooled passage. To match the geometric feature of mixing chamber (variable sectional configuration with a big aspect ratio of cross section), a novel piccolo-tube multi-nozzles supersonic ejector is designed and numerically assessed. In the current 3-D numerical simulations, a simplified approach by utilizing an isotropic porous medium model is adopted for modeling the flow through a compact oil radiator. Simultaneously, a scaled-model experimental test is conducted for the purpose of validation. From a scaled-model test, it is suggested that the CFD simulation based on the porous medium approach is generally acceptable. In the presence of porous matrix, approximately 20%–40% decrease of the ejector pumping ratio is produced in relative to the situation without oil radiator, due to the flow resistance across the porous matrix. A conjunctive parameter considering the nozzle numbers, nozzle throat diameter, and piccolo-tube length is proposed. Either from the CFD-based analysis or from the scaled-model test, it is confirmed that there is an optimal conjunctive parameter for achieving the best ejector performance. [ABSTRACT FROM AUTHOR]

Ultrasound-enhanced drug delivery through the cornea has considerable therapeutic potential. However, our understanding of how ultrasound enhances drug transport is poor, as is our ability to predict the increased level of transport for given ultrasound parameters. Described here is a computational model for quantifying changes in corneal porosity during ultrasound exposure. The model is calibrated through experiments involving sodium fluorescein transport through rabbit cornea. Validation was performed using nylon filters, for which the properties are known. It was found that exposure to 800-kHz ultrasound at an intensity 2 W/cm2 for 5 min increased the porosity of the epithelium by a factor of 5. The model can be useful for determining the extent to which ultrasound enhances the amount of drug transported through biological barriers, and the time at which a therapeutic dose is achieved at a given location, for different drugs and exposure strategies. [ABSTRACT FROM AUTHOR]

The strategy of particle-resolved computational fluid dynamics (CFD) has been widely used to study the hydrodynamic properties of fluid flow in small-sized pebble bed, but generally suffers from the tedious creation of body-fitted grids. Previously, we proposed a novel particle-resolved CFD strategy, p-IBM, which combines mesh-adaption and the immersed boundary method. The primary objective of this work is to test different mesh-adaption strategies and evaluate the quantitative accuracy degree of p-IBM simulations. For this purpose, two packed bed systems reported in the literature are simulated based on the p-IBM strategy. The flow behavior and heat transfer properties of the interstitial gas are analyzed and compared with published experimental results. Comparisons show that the simulation results are in quantitative agreement with the experimental data. This work thus lays a solid foundation for future detailed investigations of the flow and transfer performance of fluid in a small-sized pebble bed. [Display omitted] • The quantitative accuracy of a novel particle-resolved CFD strategy is evaluated. • A mesh adaption strategy reducing the grid number by several times is proposed. • The predicted results are in quantitative agreement with experimental data. [ABSTRACT FROM AUTHOR]

Water alternating gas (WAG) technique is used in the petroleum industry to inject carbon dioxide (CO2) into underground formations either for sequestration or enhanced oil recovery (EOR) processes. CO2 injection causes reactions with formation brine or aquifer and produces carbonic acid, the acid dissolves calcite and changes flow behavior significantly. Modeling and investigating effects of CO2 injection into carbonate formations during WAG processes, investigating parameters related to chemical reactions between reservoir rock and injecting fluid and also better understanding of the process theory for future experiments are the most important goals of this paper. To achieve these experimental data were used. Changes of output calcium concentration from a calcite core sample during three WAG cycles have been studied in laboratory works. The sample is modeled as a medium consisting of a set of capillary pipes and two pore size distribution models are used. Plug flow model and mass conservation law are used for modeling and Darcy law and Hagen-Poiseuille equation are also used to determine characteristics of the porous model. The model is built for linear, miscible and one-dimensional flow. The results show that experimental and model data coincide well in the first and second cycles of both porous models however; they are not coincided in the third cycle. It is because of precipitation and dissolution that cause permeability alternations. Results of the two porous models are compared also.

In this study, a semi-analytical solution is developed to investigate the wave interference and corresponding dynamic responses of an array of submersible flexible fish cages. The net chamber is modelled as a perforated cylindrical shell, and the penetration flow through the cage interface is described by a porous medium model. Based on the potential flow theory, the solution to this physical problem is expanded as a series of eigenfunctions in the local coordinate system of each cage, and the scattered wave potentials generated by all cages are superimposed wherein Graf's addition theorem is employed for the coordinate transformation. The mean wave drift effect is also explored, which is a nonlinear phenomenon derivable from the first-order solution. The results indicate that the interference of waves is determined by wavenumbers, cage spacings or net porosities, and significant wave responses are manifested near the top part of the cage. Additionally, the first-order wave force vanishes at a ratio of cage diameter to wavelength = 0.59, and, along the direction of wave incidence, the rear cages experience opposite mean wave drift loads relative to those on the front cages. These studies provide benchmark results for understanding the hydroelastic characteristics of multi-cage systems. • The shell-membrane theory introduced in the semi-analytical solution of waves and an array of fish cages interactions. • Prediction of the mean wave drift loads on fish cages based on the first-order solutions of the wavefield. • The total wave force acting on all cages is zero if the ratio of cage diameter to wavelength is approximately 0.59. • Wave interference in a cage array depends on the ratio of cage spacing or size to wavelength and the net porosity. [ABSTRACT FROM AUTHOR]

Surface flows can represent the motions of the viscous and incompressible fluid at the solid/fluid interfaces. This paper presents a topology optimization approach for surface flows and extends the design space of topology optimization of fluidic structures onto the curved surfaces in the forms of 2-manifolds corresponding to the geometrical configurations of the solid/fluid interfaces. The presented approach is implemented by filling a porous medium onto the 2-manifolds. An artificial Darcy friction is correspondingly added to the area force term of the surface Navier-Stokes equations used to describe the surface flows and the physical area forces are penalized to eliminate their existence in the fluidic regions and to avoid the invalidity of the porous medium based topology optimization model. Topology optimization for the steady and unsteady surface flows has been executed by iteratively evolving the impermeability of the porous medium, where the impermeability is interpolated by the material density derived from a design variable. The related partial differential equations are solved by using the surface finite element method. Numerical examples have been provided to demonstrate this topology optimization approach for the surface flows, including the boundary velocity driven flows, the area force driven flows and the convection-diffusion flows. [ABSTRACT FROM AUTHOR]

Based on the porous medium model, the monolayer coolant-side flow and heat transfer in the plate-fin oil coolers with 5 kinds of structures were numerically simulated by means of the finite volume method. The results indicate that the distribution of pressure and temperature is more even and the temperature difference is larger when the inlet and outlet are diagonally positioned than they are positioned on the same side, with the fins' layouts in the same direction. Given the same outlet positions, the distribution of pressure and temperature in the case of transverse arrangement of fins is more even, and the pressure difference is larger than those in the case of vertical arrangement, while similar temperature differences occur in both cases. The plate-fin oil cooler with clapboards has the biggest temperature difference as well as pressure difference 1 order of magnitude higher than that of other structures. [ABSTRACT FROM AUTHOR]

Highlights: [•] The fluid dynamic behaviour of the filter housing of a production ICE is studied. [•] A 3D CFD analysis is performed and an experimental validation is proposed. [•] The adopted CFD model appears very accurate for complex industrial applications. [•] The effect of the filter element on the mean flow is investigated. [ABSTRACT FROM AUTHOR]

Abstract: Present investigation analyzes the issue of entropy generation in a uniformly heated microchannel heat sink (MCHS). Analytical approach used to solve forced convection problem across MCHS, is a porous medium model based on extended Darcy equation for fluid flow and two-equation model for heat transfer. Simultaneously, closed form velocity solution in a rectangular channel is employed to capture z-directional viscous effect diffusion and its pronounced effect on entropy generation through fluid flow. Subsequently, governing equations are cast into dimensionless form and solved analytically. Second law analysis of problem is then conducted on the basis of obtained velocity and temperature fields and expressions for local and average entropy generation rate are derived in dimensionless form. Average entropy generation rate is then utilized as a criterion for assessing the system performance. Finally, the effect of influential parameters such as, channel aspect ratio (αS ), group parameter (Br/Ω), thermal conductivity ratio (C) and porosity (ε) on thermal and total entropy generation is investigated. In order to examine the accuracy of the analysis, the results of thermal evaluation are compared to one of the previous investigations conducted for thermal optimization of MCHS. [Copyright &y& Elsevier]

The hydrologic significance of spatial variability and anisotropic permeability in fault zones has been studied through two sets of numerical experiments using a integrated model of fracture network model and porous medium model. The steady-state flow conditions were established for specific fluid flow and hydraulic head boundary conditions, after which particle migration was tracked through the model domain from the repository to the model boundaries. The first set is for a fractured rock mass overla in by an impermeable cover rock, and second set by a permeable cover rock. The particle travel paths and residence times were compared for different fault zone configurations. [ABSTRACT FROM AUTHOR]

A three-dimensional analysis of protein redistribution in the extracapillary space (ECS) of ultrafiltration membrane hollow-fiber bioreactors (HFBRs), used for mammalian cell culture, is presented. Homogeneous distribution of growth-factor proteins in the ECS is essential for a successful startup and efficient operation of HFBRs. The ECS protein transport under most startup conditions of practical interest is strongly influenced by gravity and represents a complex interaction of forced- and free-convective phenomena. These effects were investigated using a comprehensive porous medium model (PMM) that accounts for local variations of fluid density, fluid viscosity, and osmotic pressure resulting from time-dependent changes in the protein concentration field. In addition, the model considers the influence of fiber-free manifolds, which are adjacent to the fiber bundle and are accessible to ECS proteins and cells. The PMM predictions of the ECS protein distributions at different bioreactor orientations were in good agreement with the observed distributions of a colored test protein in an experimental HFBR cartridge. The results of this study can provide useful insights for optimizing HFBR operation strategies. [ABSTRACT FROM AUTHOR]

An idealized model of a porous rock consisting of a bundle of capillary tubes whose cross-sections are regular polygons is used to assess the importance of viscous coupling or lubrication during simultaneous oil-water flow. Fluids are nonuniformly distributed over tubes of different characteristic dimension because of the requirements of capillary equilibrium and the effect of interfacial viscosity at oil-water interfaces is considered. With these assumptions, we find that the importance of viscous coupling depends on the rheology of the oil-water interface. Where the interfacial shear viscosity is zero, viscous coupling leading to a dependence of oil relative permeability on oil-water viscosity ratio for viscosity ratios greater than one is important for a range of pore cross-section shapes and pore size distributions. For nonzero interfacial shear viscosity, viscous coupling is reduced. Using values reported in the literature for crude oil-brine systems, we find no viscous coupling. [ABSTRACT FROM AUTHOR]

• A 3-D detailed porous medium model for wire wrapped fuel bundles has been proposed. • The prediction results of the model proposed agree well with experimental results. • The model has been validated under various conditions. • The model could simulate wire-wrapped fuel bundles with low computing cost. Wire-wrapped fuel bundles have been widely used in SFRs, and the conjugate heat transfer between wire-wrapped fuel bundles plays a key role in safety characteristics of SFRs. However, due to the existence of helical wire spacers, the geometry of fuel bundle becomes quite complicated, bringing challenges to realistic CFD modeling. A porous medium model for simulating conjugate heat transfer between fuel bundles have been proposed in this study. The geometries of fuel rods and wrapper tubes are preserved and helical wire spacers are treated as solid body of porous medium in this model. The flow resistance induced by helical wire spacers is considered by adding additional flow resistance source terms to momentum equation and the transverse mixing effects caused by wire spacers and thermal plumes are accounted by modifying diffusion terms in energy equation of porous medium model. The sodium experiment of 19-pin wire-wrapped fuel bundle under forced convection performed by ORNL and sodium experiments of multi-bundle systems named CCTL-CFR and PLANDTL-DHX under mixed convection conducted by JNC were selected as benchmark. Comparison results show that under both forced and mixed convection, this model could attain considerable accuracy in the prediction of conjugate heat transfer between fuel bundles with relatively low computational cost and have the potential to simulate core-wide temperature distribution of SFR. [ABSTRACT FROM AUTHOR]

• A tubular exhaust reformer for LNG engine was investigated by numerical simulation. • The simulation coupled fluid flow, reaction and heat recovery in the reactor. • There was an optimum M/O value (about 2) for maximum hydrogen production. • There was an optimum W/M value (about 1.25) for maximum hydrogen production. • Addition of steam helped to reduce hot spot and carbon deposition. A three-dimensional tubular exhaust reformer was investigated to study the effects of EGR ratio and the amount of the steam addition on the methane-exhaust gas reforming process under different excess air coefficients. The objective was to maximize hydrogen production economically, by regulating the amount of exhaust gas and the steam addition at the inlet of the reaction tube with the amount of methane addition fixed. Coupled with the detailed catalytic reaction mechanism based on Rh-Al 2 O 3 catalyzer, the exhaust gas reforming process in a fixed bed reactor was simulated by using a porous media model. The results showed that, in the entry region of the reaction zone, oxidation reaction dominates with significant heat release; whilst after the entry region steam reforming reaction dominates with heat absorbing. The exhaust gas outside the reaction tube played the role of preheating the mixture before the reaction zone and heat preservation in the reaction zone. Results showed that with the methane addition fixed, there is an optimum M/O value (about 2) and W/M value (about 1.25) for maximum hydrogen production. In addition, the surface coverage ratio of coke deposit in the reaction bed decreases with the increase of EGR ratio and steam addition. [ABSTRACT FROM AUTHOR]