Fluid flow in porous media

Resume : L’objectif de cette etude, est de tester le pouvoir adsorbant d’un materiau vegetal local et abondant dans notre pays, les pedicelles de dattes, pour l’elimination d’un colorant synthetique : le Bleu de Methylene. Les essais de biosorption de BM en mode dynamique ont servi pour examiner l’influence de quelques parametres de fonctionnement intervenant dans la biosorption en lit fixe, tels que le debit d’alimentation, la hauteur du lit, la porosite du lit (compactage) et la concentration initiale de BM. La caracterisation du systeme, en utilisant la methode de la zone de transfert de matiere, nous a permis de conclure que la biosorption est favorisee pour les faibles debits (4 mL/min), aux plus grandes hauteur et porosite du lit et a la plus faible concentration initiale en BM. Abstract : The objective of this study is to test the adsorbing capacity of a local and abundant vegetable material in our country, the date pedicels, for the elimination of a synthetic dye: ¶Methylene...

Dans un contexte de protection des biens et des personnes, le CEA DAM s’intéresse aux mousses aqueuses pour leur capacité à confiner une détonation. L’objectif est, d’une part, d’atténuer les effets thermodynamiques liés à la détonation d’un engin explosif et, d’autre part, de capturer les particules solides micrométriques potentiellement nocives pouvant être émises. On s’intéresse particulièrement, ici, à la deuxième problématique.

Understanding the natural flows in porous media with specific hydraulic characteristics is crucial for advancing science and engineering. This study examines the hydraulic properties and fluid dynamics of sand samples collected from eight locations along the Osun River bed at five-meter intervals in November 2023. Significant variations in hydraulic characteristics were identified by comparing the findings with international soil classification standards. The effective grain size ranged from 0.20 mm to 0.32 mm, with most samples between 0.30 mm and 0.31 mm. Sample F had the smallest grain size, indicating finer sand. Flow velocities varied from 1.57 cm/s to 2.41 cm/s, with the highest observed at locations B and E. Flow rates ranged from 1.23 × 10² cm³/s to 1.89 × 10² cm³/s, also highest at B and E. Reynolds numbers ranged from 1.39 × 10 6 to 8.58 × 10 6 , indicating transitions from laminar to turbulent flow. Friction factors ranged from 7.46 × 10 6 to 45.85 × 10 6 , with higher values at location A, indicating greater resistance to flow. Hydraulic gradients ranged from 1.09 to 1.83, and hydraulic conductivities were between 1.14 × 10-² cm/s and 1.43 × 10-² cm/s, with the highest observed at location A. The results align with recent research showing that coarser sands exhibit higher hydraulic conductivities and flow rates, whereas finer sands demonstrate greater resistance. The study underscores the importance of monitoring friction factors, flow velocity, flow rate, and Reynolds numbers to manage potential environmental hazards and water seepage through dams.

Magnetotelluric results from 38 sites in North Iceland yield a detailed spatial distribution of conductivity versus depth. A high-conductivity layer, about 10 .Qm, marking the transition between crust and upper mantle is detected throughout the surveyed area, its depth increases from 10 km within the zones of present tectonic activity to 20-30 km at a 50-100 km distance from the rift axis. The high conductivity layer indicates some basaltic melt fraction at temperatures around 1,000 °C. The calculated average crustal temperature gradients are 100-150 °C/km at the rift axis and 50-70 °C/km at about 100 km distance. Below this anomalous zone, down to 150 km depth, the conductivity decreases to 100 .Qm due to the ultrabasic chemical composition of the upper mantle and a possible decrease of melt content with increasing depth. The temperature gradient within the upper mantle cannot be more than a few °C/km. However, a highly conducting asthenosphere exists below 150 km depth. The following petrological model for Iceland is suggested: Diapiric updoming of the asthenosphere leads to partial fusion of parent ultra basic mantle material, resulting in segregation and upward migration of basaltic melt. Lower density, lower viscosity and higher mobility relative to the solid phase causes the melt to rise faster than the ultrabasic material. This melt fraction then forms the basaltic crust of Iceland which is thickening away from the ridge axis with increasing age.

In this paper, we introduce a mathematical model to describe the nanoparticles transport carried by a two-phase flow in a porous medium including gravity, capillary forces and Brownian diffusion. Nonlinear iterative IMPES scheme is used to solve the flow equation, and saturation and pressure are calculated at the current iteration step and then the transport equation is soved implicitly. Therefore, once the nanoparticles concentration is computed, the two equations of volume of the nanoparticles available on the pore surfaces and the volume of the nanoparticles entrapped in pore throats are solved implicitly. The porosity and the permeability variations are updated at each time step after each iteration loop. Two numerical examples, namely, regular heterogeneous permeability and random permeability are considered. We monitor the changing of the fluid and solid properties due to adding the nanoparticles. Variation of water saturation, water pressure, nanoparticles concentration and p...

The porous media (PM) is utilized in several industrial applications, including heating exchangers, storage tanks, and air conditioning systems. In previous studies, several researchers dealt with various methods to study the development of the coefficient of heating transfer within the channels for different cross sections including (square, rectangular, triangular, and circular). One method uses PM (glass balls, wire mesh, metal foam, and others). This research presents the most important previous studies, including theoretical (numerical simulation) and investigational ones, concerned with exploring fluid flow (air or water) and heating transfer within channels by enforced convection. Many researchers designed different types of channels and used the full PM, and some of them have focused on using the partial PM as a technique to improve the performance of systems and increase their efficiency. The conclusions demonstrated that few researchers utilized nanofluid with PM to get the optimum development in the coefficient of heating transfer and thus increase the Nusselt's Number. In addition to these recent years, most of the researchers presented in their research papers a study of heat transmission with forced or natural convection combined techniques to improve heat transmission coefficient, including the use of twisted tape with hybrid nanoparticles or having roughness for the internal surface of the channel with the addition of the PM to obtain a high-performance coefficient of systems.

Many methods are used to improve the heat transfer process of fluid flow within channels of various crosssections such as (rectangular, square, triangular, circular, and trapezoidal) and heat exchangers to increase the temperature distribution of the fluid and thus increase the heat transfer coefficient and the Nusselt number which leads to improving its performance and efficiency. The current research presents a theoretical study (numerical simulation) of heat transfer through forced convection with laminar flow inside a horizontal channel with a square cross-section (0.12 * 0.12 m 2). The test model was designed with a two-dimensional (2D) assumption. It is subjected to uniform heat flux from the top and bottom by (1500 W/ m 2). The channel was partially filled with a layer of the porous medium (glass balls with a diameter of 0.003 m) with a height of (0.06 m). Water was utilized as a working fluid for this matter, and the governing equations (mass conservation, conservation of momentum, conservation of energy) were solved numerically using the COMSOL Multiphysics 6.0 program, the test model was designed by taking different angles (0º, 15º, 30º, and 45º) of the position to study the effect of changing angles on the velocity and temperature distribution of the fluid. The outcomes of the investigation presented that the best temperature distribution appeared at an angle (15º) to the position of the test model of the channel. In addition, the porous material distorts the shape of the temperature distribution, velocity, and pressure of the fluid flow within the test model, and the temperature distribution rises gradually with the increased fluid flow along the channel at all angles.

12 especímenes) obtenida en los tres tipos de yesos para la comparativa entre marcas. (Tabla 79). Las siguientes tablas, exponen los resultados de los ensayos de R.C. (Tablas 80-82). Tabla 79 : Dureza obtenida para los yesos tipo III, IV y V.

In this work, a detailed three-dimensional numerical model of porous volumetric receivers coupled to point-focus solar concentration systems is developed and used to optimise the thermal efficiency and pressure drop. A cylindrical receiver element made of open-cell SiC ceramic foam is considered using air as heat transfer fluid, and a parabolic dish concentrator is simulated to generate the concentrated solar radiation flux at the receiver inlet. The propagation and absorption of solar radiation is modelled through an in-house Monte Carlo Ray Tracing (MCRT) algorithm, in which the asymmetry factor of the scattering phase function was determined by combining this method with experimental measurements of hemispherical diffuse reflectance for five different samples. The fluid flow and heat transfer processes are simulated through a Computational Fluid Dynamics (CFD) model based on the Local Thermal Non-Equilibrium approach, developed using an open source software (OpenFOAM). The global model is used to conduct a comprehensive parametric analysis and optimisation where the geometric parameters of the receiver (porosity and pores size) and concentration system and the fluid flow conditions that maximise the performance of porous volumetric receivers are obtained. It was found that the main thermal losses are due to the backscattering, and the conditions to achieve high thermal efficiency while not increasing pressure drop correspond to receivers with higher porosity and pores size. For a given porosity, there is a pores size that maximise thermal efficiency, being this value lower for increasing porosity. It was also found that the optimum geometric parameters do not depend significantly on the velocity at the receiver inlet, and thus the mass flow rate of heat transfer fluid can be selected as a function of the target temperature at the outlet.

The current study investigates MHD natural convection heat transfer of a hybrid nanofluid in a truncated cone along with transparent domains having the stimulus of an inherent constant magnetic field. The governing equations subject to the physical boundary conditions are solved numerically by using the Galerkin finite element method. The effects of the various parameters involved in the problem such as the Rayleigh number Ra (ranging between 103 and 106), the Hartmann number Ha (ranging between 0 and 60), and the porosity ratio ε (0.1–0.9) are examined. Moreover, the effects of Da which represents the Darcy number (between 10‑3 and 10‑1) and the volume fraction of nanoparticles ϕ for the dissipated nanoparticles of Al2O3-Cu are reported in terms of the streamlines and isotherms distributions as well as the Nusselt number. Such parameters are critical control parameters for both the fluid flow and the rate of heat transfer of the natural convection in the annular space. The solution...

In this paper, the finite volume method is used to investigate the laminar forced convection of water-copper nanofluid between two porous horizontal concentric cylinders. The effects of Reynolds number, the volume fraction of nanoparticles, the geometry, and the porous medium porosity on heat transfer have been studied. The problem is investigated in two different geometries and Re = 10, 25, 50, 75,100, and volume fraction of nanoparticles 0, 0.2, 0.5, 2, and 5% that were related to Copper nanoparticles and the porous medium porosity of 0.5, 0.9. The results indicated that in each geometry, the corresponding Nusselt number increase in the porosity of 0.9 is greater than that of the case with the porosity of 0.5. The results show that the increase in the heat transfer coefficient in the second geometry is greater than the first geometry and in porosity 0.9 is greater than porosity 0.5. These increase values are 6 and 3%, respectively. The increase in the average temperature of the inner cylinder surface in the five mentioned Reynolds values and both geometries is investigated. This increase in temperature in Re = 10 is greater than other Reynolds numbers. The corresponding temperature increases of Re = 10, for the first and second geometries, are 1.8 and 2.2%, respectively. Investigation of the effects of volume fraction of nanoparticles on Nusselt number and heat transfer coefficient shows that both parameters increase by increasing in the volume fraction of nanoparticles. The results show that the increase in the volume fraction of nanoparticles causes the increase in average temperature of the surface. The results show that these increases of temperature that take place in the volume fractions of 0.5, 2, and 5% of nanoparticles are equal to 0.6, 1.14, and 2.3% and relative to the water, respectively. Thermal conductivity coefficient (Wm -1 K -1 ) Nu Nusselt number Re Reynolds number T Temperature (K) u, v, w Velocity components in x, y, z directions (ms -1 ) * Masoud Afrand

Water filtration units have been faced problems in water turbidity removal related to their media, which is determined by qualitative indices. Moreover, Current qualitative indices such as turbidity and escaping particle number could not precisely determine the efficiency of the media in water filtration, so defining new indices is essential. In this study, the efficiency of Anthracite-Silica and LECA-Silica media in turbidity removal were compared in different operating condition by using modified qualitative indices. The pilot consisted of a filter column (one meter depth) which consisted of a layer of LECA (450 mm depth) and a layer of Silica sand (350 mm depth. Turbidities of 10, 20, and 30 NTU, coagulant concentrations of 4, 8, and 12 ppm and filtration rates of 10, 15, and 20 m/h were considered as variables. The LECA-Silica media is suitable media for water filtration. Averages of turbidity removal efficiencies in different condition for the LECA-Silica media were 85.8±5.37 p...

Curvature effects are important for a proper description of the properties of magnetic systems. In this paper, the exchange and dipolar energy of vortices on a paraboloidal shell is studied. Using analytical calculations, it is shown that the in-plane component of vortices has larger energy on a paraboloidal shell than in a planar disk with same thickness. On the other hand, the dipolar energy associated to the vortex core diminishes if the vortex core is on a paraboloidal surface. This reduction in the dipolar energy may cause a vortex pinning mechanism by a paraboloidal shaped defect in a planar nanomagnet. Regarding skyrmions, by using an in-plane anisotropy approximation to the dipolar energy, it is shown that the skyrmion must have its width shrunk in order to diminish the magnetostatic energy and satisfy geometrical constraints of the system.

The reduction from three‐ to two‐dimensional analysis of the permeability of a fractured rock mass introduces errors in both the magnitude and direction of principal permeabilities. This error is numerically quantified for porous rock by comparing the equivalent permeability of three‐dimensional fracture networks with the values computed on arbitrarily extracted planar trace maps. A method to compute the full permeability tensor of three‐dimensional discrete fracture and matrix models is described. The method is based on the element‐wise averaging of pressure and flux, obtained from a finite element solution to the Laplace problem, and is validated against analytical expressions for periodic anisotropic porous media. For isotropic networks of power law size‐distributed fractures with length‐correlated aperture, two‐dimensional cut planes are shown to underestimate the magnitude of permeability by up to 3 orders of magnitude near the percolation threshold, approaching an average fact...

The flow regimes and the dynamics of the front in miscible displacements are controlled by the interactions between the mechanisms of instability involved in such processes. The instabilities may be driven by the unfavorable relative characteristics of the fluids (like unfavorable gravity or mobility ratios) or by the heterogeneity of the medium, providing favorable paths for the more mobile fluid. This work investigates the effect of porous medium heterogeneity with two scales of permeability variations on the frontal instability and fluid mixing. The base mode of permeability variations has a smaller wavelength and higher frequency, while the imposed mode has a larger wavelength. The effect of such a bimodal heterogeneity on the growth of mixing zone length (MZL) has been studied and the development of the previously recognized flow regimes in layered porous media have been examined. The combination of a short wave which induces faster growth of instabilities at initial stages of the flow, and a relatively longer wavelength heterogeneity with elongated channeling period, distorts the consecutive appearance of the flow regimes observed in single wavelength heterogeneity profiles of previous studies. Compared to the unimodal medium comprising the base wave, in the bimodal cases with large contrast between the wavelengths of the two periodic profiles the dominance of each wavelength at a different time scale predictably enhances the growth of fingers in the early and late stages. Interestingly and less intuitively, even in cases with close wave numbers between the combined modes (e.g. 15 layers combined with 11 layers) faster growth of the mixing zone length is observed. In such cases, the coherence of equal layers in a unimodal layered medium is disturbed by the second wave number, which results in fading of the lateral diffusion regime. However, bimodal heterogeneity may attenuate the instability compared to the unimodal system with the imposed wave's frequency.

The physics of miscible flow displacements with unfavorable mobility ratios through horizontal layered heterogeneous media is investigated. The flow model is solved numerically, and the effects of various physical parameters such as the injection velocity, diffusion, viscosity, and the heterogeneity length scale and variance are examined. The flow instability is characterized qualitatively through concentration contours as well as quantitatively through the mixing zone length and the breakthrough time. This characterization allowed us to identify four distinct regimes that govern the flow displacement. Furthermore, a scaling of the model resulted in generalized curves of the mixing zone length for any flow scenario in which the first three regimes of diffusion, channeling, and lateral dispersion superpose into a single unifying curve and allowed us to clearly identify the onset of the fourth regime. A critical effective Péclet number w * c based on the layers' width is proposed to identify flows where heterogeneity effects are expected to be important and those where the flow can be safely treated as homogeneous. A similar scaling of the breakthrough time was obtained and allowed us to identify two optimal effective Péclet numbers w * opt that result in the longest and shortest breakthrough times for any flow displacement.

The development of predictive mathematical models can contribute to a deeper understanding of the specific stages of bone mechanobiology and the process by which bone adapts to mechanical forces. The objective of this work was to predict, with spatial accuracy, cortical bone adaptation to mechanical load, in order to better understand the mechanical cues that might be driving adaptation. The axial tibial loading model was used to trigger cortical bone adaptation in C57BL/6 mice and provide relevant biological and biomechanical information. A method for mapping cortical thickness in the mouse tibia diaphysis was developed, allowing for a thorough spatial description of where bone adaptation occurs. Poroelastic finite-element (FE) models were used to determine the structural response of the tibia upon axial loading and interstitial fluid velocity as the mechanical stimulus. FE models were coupled with mechanobiological governing equations, which accounted for non-static loads and assumed that bone responds instantly to local mechanical cues in an on-off manner. The presented formulation was able to simulate the areas of adaptation and accurately reproduce the distributions of cortical thickening observed in the experimental data with a statistically significant positive correlation (Kendall's t rank coefficient t ¼ 0.51, p , 0.001). This work demonstrates that computational models can spatially predict cortical bone mechanoadaptation to a time variant stimulus. Such models could be used in the design of more efficient loading protocols and drug therapies that target the relevant physiological mechanisms.

The study of concepts in animals is complicated by the possibility that performance reflects reinforcement learning of discriminative cues, which might be used to categorize of stimuli. To minimize that possibility, we trained seven rhesus macaques to respond, in a specific order, to four simultaneously presented exemplars of different perceptual concepts. These exemplars were drawn at random from large banks of images; in some conditions, the stimuli changed on every trial. Subjects nevertheless identified and ordered these stimuli correctly. Three subjects learned to correctly order ecologically relevant concepts; four subjects, to order close-up sections of paintings by four artists with distinctive styles. All subjects classified stimuli significantly better than that predicted by chance, and outperformed a feature-based computer vision algorithm, even when the exemplars were changed on every trial. Furthermore, six subjects (three using ecological stimuli and three using painti...

Thermoacoustic systems have been a focus of recent research due to its structural simplicity, high reliability due to absence of moving parts, and can be driven by low grade energy such as fuel, gas, solar energy, waste heat etc. There has been extensive research on both standing wave and traveling wave systems. Towards the development of such systems, simulations can be carried out by several methods such as (a) solving the energy equation, (b) enthalpy flow model, (c) DeltaEC, a free software available from LANL, USA (d) Computational Fluid Dynamics (CFD) etc. We present here the simulation studies of standing wave and traveling wave thermoacoustic prime movers using CFD and DeltaEC. The CFD analysis is carried out using Fluent 6.3.26, incorporating the necessary boundary conditions with different working fluids at different operating pressures. The results obtained by CFD are compared with those obtained using DeltaEC. Also, the CFD simulation of the thermoacoustically driven refrigerator is presented.

The performance of projection-based model order reduction methods for solving parameterdependent systems of equations highly depends on the properties of the operator, which can be improved by preconditioning. In this paper we present strategies to construct a parameter-dependent preconditioner by an interpolation of operator's inverse. The interpolation is obtained by minimizing a discrepancy between the (preconditioned) operator and the matrix defining the metric of interest. The discrepancy measure is chosen such that its minimization can be efficiently performed online for each parameter value by the solution of a small least-squares problem. Furthermore, we show how to tune the discrepancy measure for improving the quality of Petrov-Galerkin projection or residual-based error estimation. This paper also addresses preconditioning for the randomized model order reduction methods from [Balabanov and Nouy 2019, Part I]. Our methodology can be readily used for efficient and stable solution of ill-conditioned parametric systems and an effective error estimation/certification without the need to estimate expensive stability constants. The proposed approach involves heavy computations in both offline and online stages that are circumvented by random sketching. The norms of high-dimensional matrices and vectors are estimated by ℓ 2 -norms of their low-dimensional images, called sketches, through random embeddings. For this we extend the framework from [Balabanov and Nouy 2019, Part I] to random embeddings of operators.

This work describes the first detailed model of meltblowing process which allows prediction of such integral laydown properties as thickness, porosity and permeability. Also, such laydown properties as the detailed three-dimensional micro-structure, fiber-size distribution and polymer mass distribution are predicted. The effects of the governing meltblowing parameters on the variation of all these laydown properties are accounted for, with the influence of the collector screen velocity being in focus. For this aim numerical solutions of the system of quasi-one-dimensional equations of the dynamics of free liquid polymer jets moving, cooling and solidifying when driven by surrounding air jet are constructed. Multiple polymer jets are considered simultaneously when they are deposited on a moving screen and forming a nonwoven laydown. The results reveal the three-dimensional configuration of the laydown and, in particular, its porosity and permeability, as well as elucidate the dependence of the laydown structure on the forming conditions, in particular, on the velocity of the screen motion. It is shown and explained how an increase in the velocity of the collector screen increases porosity and permeability of the meltblown nonwoven laydown.

Gaseous flows in microsystems have attracted considerable attention in fluid dynamic communities over the last few years. When the size of the device is in the range of microns, the molecular mean free path becomes comparable with the device size, and the details of the molecular interactions need to be taken into account. The proper description of such microflows requires the consideration of the velocity distribution function of the molecules and kinetic equations. The scope of the present paper is to discuss the determination of the behavior of pressure driven rarefied gas flows in microchannels at the kinetic level. As a new application of the methodology, preliminary results are presented for pressure driven flows of single gases through long rectangular tapered microchannels, which have constant widths but varying depths along the axis of the channel. The kinetic calculation is based on the solution of the linearized Bhatnagar-GrossKrook (BGK) equation and refers to the determ...

Créée en 1997 à l'initiative de Benoît Goetz et Jean-Paul Resweber, Le Portique, revue semestrielle de philosophie et sciences humaines, est devenu un véritable lieu de recherche, garant d'une approche transdisciplinaire qui cherche à mettre en dialogue les sciences humaines et la ré exion philosophique. Tout en se voulant au carrefour de questionnements et de rencontres, la revue est aussi restée ouverte au grand public, donnant rendezvous au lecteur sous le Portique, espace ouvert dont la sagesse est conforme au modèle stoïcien d'une pensée du seuil, des degrés et des limites, et qui se risque à penser l'événement. Numéro édité sous la direction d'Anne Alombert, Michał Krzykawski et Laurent Maronneau Couverture et illustration : László Moholy-Nagy. Dessins en couleur publiés avec l'accord de Madame Natalia Hug, Directrice de la fondation Moholy-Nagy (Kinetisch-konstrukt, couverture ; Kinetisch-konstruktives System, illustration) is project has received funding from the European Commission as part of the H2020 MSCA-RISE programme under grant agreement No. 101007915 // is project has received funding from the Polish state budget under the program International Co-Financed Projects. Bernard Stiegler Panser le devenir des savoirs dans le milieu numérique LE PORTIQUE NUMÉROS 48-49 : 1 er semestre 2024 question qui touche au sens même de la condition humaine, que notre ami a amplement répondu en développant tout un art de l'habiter qui se situe au carrefour de la technique, de l'esthétique et de l'éthique. Deux jours avant sa mort, Benoît m'a redit au téléphone, en guise de testament, ce qu'il avait déjà dit à plusieurs d'entre nous : il souhaitait vivement que les publications semestrielles de la Revue Le Portique soient poursuivies au moins jusqu'au cinquantième numéro. En attendant de lui adresser un hommage o ciel plus appuyé, nous lui dédions ce numéro double qui sera bien entendu suivi, au premier semestre 2025, du numéro 50. À son épouse, à sa famille et à ses ami(e)s, l'équipe de la rédaction de la Revue adresse ses plus sincères condoléances. J.P. R. IV. L'organologie du sensible : consciences et a ects dans le milieu médiatique numérique Conscience et mimésis. Bernard Stiegler et la question du cinéma

We consider the focusing and breaking of internal waves generated by the horizontal oscillations of a very large torus mounted at the Coriolis platform, of 13 m diameter. The platform was filled with a linearly stratified fluid and rotated at a constant speed, or stood still to investigate, respectively, inertia-gravity or internal gravity waves. The wave field was measured using 2D or 3D PIV. The large torus size gives access to large Stokes numbers. Nonlinear effects and turbulence are observed in the focal region, but they can be described by linear theory with an eddy viscosity. Spectrum analysis shows the generation of higher harmonics in the focal zone even at low oscillation amplitude. The vertical vorticity field of internal gravity waves exhibits a dipolar structure in the focal zone, which transforms in the rotating case into a "Yin-Yang-shaped" structure. The overall structure of the inertial waves is close to that of internal gravity waves, though the overturning motion in the focal region is relatively intense.

Le domaine de l'émulsification en micromélangeur a connu un grand essor ces dernières années. La communauté scientifique a globalement montré que, dans ce monde miniaturisé, les forces de surface prédominent sur les forces de volume, et réussi à expliquer qualitativement le mécanisme de formation de gouttelettes au sein de dispositifs microstructurés. Toutefois, une étude plus quantitative est primordiale. Notre travail porte sur la compréhension du mécanisme de formation de gouttelettes au sein de micromélangeurs. Dans un premier temps, une étude en écoulement monophasique nous permet de nous familiariser avec la détermination de champs de vitesse obtenus au sein d'un micromélangeur possédant une jonction en T, par un dispositif de micro PIV. Il est ensuite possible, par cette même méthode d'analyse optique, d'appréhender le mécanisme de formation de gouttelette en écoulement diphasique au sein de cette jonction, en fonction de la formulation utilisée.

Available electronically at http://gltrs.grc.nasa.gov Level of Review: This material has been technically reviewed by technical management. An Initial Non-Equilibrium Porous-Media Model for CFD Simulation of Stirling Regenerators The objective of this paper is to define empirical parameters (or closure models) for an initial thermal non-equilibrium porous-media model for use in Computational Fluid Dynamics (CFD) codes for simulation of Stirling regenerators. The two CFD codes currently being used at Glenn Research Center (GRC) for Stirling engine modeling are Fluent and CFD-ACE. The porous-media models available in each of these codes are equilibrium models, which assume that the solid matrix and the fluid are in thermal equilibrium at each spatial location within the porous medium. This is believed to be a poor assumption for the oscillating-flow environment within Stirling regenerators; Stirling 1-D regenerator models, used in Stirling design, use non-equilibrium regenerator models and suggest regenerator matrix and gas average temperatures can differ by several degrees at a given axial location and time during the cycle. A NASA regenerator research grant has been providing experimental and computational results to support definition of various empirical coefficients needed in defining a non-equilibrium, macroscopic, porous-media model (i.e., to define "closure" relations). The grant effort is being led by Cleveland State University, with subcontractor assistance from the University of Minnesota, Gedeon Associates, and Sunpower, Inc. Friction-factor and heat-transfer correlations based on data taken with the NASA/Sunpower oscillating-flow test rig also provide experimentally based correlations that are useful in defining parameters for the porous-media model; these correlations are documented in Gedeon Associates' Sage Stirling-Code Manuals. These sources of experimentally based information were used to define the following terms and parameters needed in the non-equilibrium porous-media model: hydrodynamic dispersion, permeability, inertial coefficient, fluid effective thermal conductivity (including thermal dispersion and estimate of tortuosity effects), and fluid-solid heat transfer coefficient. Solid effective thermal conductivity (including the effect of tortuosity) was also estimated. Determination of the porous-media model parameters was based on planned use in a CFD model of Infinia's Stirling Technology Demonstration Convertor (TDC), which uses a random-fiber regenerator matrix. The non-equilibrium porous-media model presented is considered to be an initial, or "draft," model for possible incorporation in commercial CFD codes, with the expectation that the empirical parameters will likely need to be updated once resulting Stirling CFD model regenerator and engine results have been analyzed. The emphasis of the paper is on use of available data to define empirical parameters (and closure models)

Contaminant transport in a soil formation is described by advection dispersion equation. In this study, a horizontal and transversal contaminant transport along transient groundwater flow under non-linear sorption is solved numerically to examine the contaminant distribution profiles in finite soil media. The horizontal and transversal pore-water seepage velocities are defined as varying exponentially with time. Dispersion is considered directly proportional to the first power of the pore-water velocity. Axial input sources varying exponentially with time are assigned along the two-dimensional coordinate axes. For approximating the governing solute transport equation into algebraic equations, Crank-Nicolson (CN) and alternating direction implicit (ADI) methods are used. Both the numerical solutions are illustrated graphically with the help of computer software for various hydrological input data. In a special case, the numerical solutions are also compared with an approximate solution obtained by PDEtool. The comparison is performed with the help of contour plots. The CN method gives more accurate result than ADI method for the present model problem.

Handling and making decisions based on data taken at different scales is a critical issue in the design of exploration and production tasks in the oil industry. Acoustic data is the classical example of the integration of dissimilar scales (i.e. seismic, well logs, lab data) where there is a scale dependent velocity. An understanding of the acoustic dispersion phenomenon in granular samples is needed. A detailed numerical work was conducted in order to establish the relationship between frequency and propagation speed for an acoustical pulse induced in simulated granular materials. The granular samples were generated with different grain size distributions while porosity and pressure were targeted and kept invariant using the grain radii expansion method. A sinusoidal burst with frequencies from 10Hz to 1MHz was applied and the corresponding acoustical speeds were estimated for each frequency. A coherent sigmoid dispersion relationship was obtained for each granular sample. The asymptotic boundaries for the dispersion function reflect the limiting cases for the wavelength/heterogeneity ratio in the granular pack. The lower speed asymptote was explained as the mean field value while upper speed asymptote can be understood based on a ray theory approximation scaled by a parameter we defined as the "acoustic tortuosity factor". This factor reflects the intricate acoustical path due to the texture of the stress network developed in the granular samples and can be used together with the sigmoid dispersive relationship to describe and clarify the scale discrepancy between different source acoustic data in granular materials.

Groundwater pollution is a one of the major problems of our environment caused by various sources such as industries, pesticides, fertilizers, and mining activities. Convection-dispersion equation (CDE) is employed to model the transport of groundwater contamination mathematically, but it can be challenging due to complex geometries and hydrogeological characteristics. Moreover, for several realistic scenarios, the input contaminant source might be located at an intermediate location of the domain, leading to dispersion in forward and backward directions from the source point. Few previous works in this context have been approached analytically and limited to the one-dimensional (1D) assumption of the medium. In this study, a pollutant dispersion with an intermediate time-dependent point source is modelled mathematically. The forwardbackward pollutant distribution in a two-dimensional (2D) semi-infinite transient groundwater flow field is investigated. The concentration gradients are taken as zero across the final boundaries of the domain. The effect of off-diagonal dispersion is included in the model equation. The impact of various hydrological input parameters, such as dispersion, porosity, distribution coefficient, decay parameter, etc., on the pollutant transport is examined graphically. The proposed transport model problem is solved numerically and analytically using the Crank-Nicolson (CN) method, and Laplace transform technique (LTT), respectively. The accuracy of the proposed numerical method is evaluated by comparing it with the analytical solution using graphical and statistical measures. The obtained numerical solution of the 2D model problem shows a good agreement with the analytical solution. This may interest researchers working in surface water and vadose zone hydrology areas.

Forward-backward solute dispersion with an intermediate point source in one-dimensional semi-infinite homogeneous porous media is studied in this paper. Solute transport under sorption conditions, firstorder decay and zero-order production terms are included. The first type of boundary condition is taken as a constant point source at an intermediate point from where forward and backward solute dispersion is examined. The Laplace transform method is adopted to solve the governing equation analytically. All the analytical results are obtained in graphical form to investigate the forward-backward solute transport in porous media for various hydrological input data. The graphical nature of the analytical solution is compared with numerical data taken from existing literature and similar results are obtained. Also, numerical solution of the governing equation is obtained by the Crank-Nicolson finite difference scheme and validated with the analytical solution, which demonstrates good agreement between them. Accuracy of the solution is also observed by using RMSE.

The objective of the study is to investigate the fluid flow and heat transfer characteristics applying Artificial Neural Networks (ANN) analysis in triangular-shaped cavities for the analysis of magnetohydrodynamics (MHD) mixed convection with varying fluid velocity of water/ Al 2 O 3 nanofluid. No study has yet been conducted on this geometric configuration incorporating ANN analysis. Therefore, this study analyzes and predicts the complex interactions among fluid flow, heat transfer, and various influencing factors using ANN analysis. The process of finite element analysis was conducted, and the obtained results have been verified by previous literature. The Levenberg-Marquardt backpropagation technique was selected for ANN. Various values of the Richardson number (0.01 � Ri � 5), Hartmann number (0 � Ha � 100), Reynolds number (50 � Re � 200), and solid volume fraction of the nanofluid (ϕ = 1%, 3% and 4%) have been selected. The ANN model incorporates the Gauss-Newton method and the method of damped least squares, making it suitable for tackling complex problems with a high degree of non-linearity and uncertainty. The findings have been shown through the use of streamlines, isotherm plots, Nusselt numbers, and the estimated Nusselt number obtained by ANN. Increasing the solid volume fraction improves the rate of heat transmission for all situations with varying values of Ri, Re, and Ha. The Nusselt number is greater with larger values of the Ri and Re parameters, but it lessens for higher value of Ha. Furthermore, ANN demonstrates exceptional precision, as evidenced by the Mean Squared Error and R values of 1.05200e-6 and 0.999988, respectively.

The aim of this study is to examine the unsteady hydromagnetic flow of non-Newtonian nanofluid past a stretching sheet in the presence of variable magnetic field and chemical reaction. The system of non-linear partial differential equations governing the flow was solved using finite difference numerical approximation method. The resulting numerical schemes were simulated in MATLAB software. Furthermore, the skin-friction coefficient, Sherwood number, and Nusselt number have been presented in tabular form and discussed. The findings demonstrated that increasing Reynolds number increases velocity profiles while increasing permeability parameter, suction parameter and angle of inclination for the applied magnetic field reduces the velocity profiles of the fluid flow. Temperature of the fluid increases as the angle of inclination, magnetic number, Reynolds number and Eckert number increase but decreases as Prandtl number increases. Induced magnetic field profiles decrease as magnetic Prandtl number and suction parameter increase. Concentration profiles decrease as the chemical reaction parameter and Schmidt number increase but increase as the Soret number increases. The study is significant because fluid flow and heat transfer mechanisms with the variable magnetic considerations play an important role in magnetohydrodynamic generator or dynamo and magnetohydrodynamic pumps, nuclear reactors, vehicle thermal control, heat exchangers, cancer therapy, wound treatment and hyperthermia.

Heat exchanger research is mainly exploited to develop and optimiseoptimize new engineering systems with high thermal efficiency. Passive methods based on nanofluids, fins, wavy walls, and the porous medium are actually the most attractive ways to achieve this goal.This investigation focuses on heat transferand entropy production in a nanofluid laminar flow inside a plate corrugated channel (PCC).The channel geometry comprises three sections, partially filled with a porous layer located at the intermediate corrugate channel section.The physical modeling is based on the laminar, two-dimensional Darcy–Brinkman–Forchheimer formulation for nanofluid flow and the local thermal equilibrium model for the heat equation, includingthe viscous dissipation term. Numerical solutions arewere obtained using ANSYS Fluent software based on the finite volume technique and the appropriate meshed geometries.The numerical results are validated with theoretical, numerical, and experimental studies. The simulations are performed for CuO–water nanofluid and AISI 304 porous medium. The coupled effects of porous layer thickness (δ), Reynolds number (Re), and nanoparticle fraction (φ) on velocity, streamlines, isotherm contours, Nusselt number (Nu), and entropy generation (S) are analyzed and illustrated. The simulation results demonstrate that heat transfer enhancement in clear PCC can be achieved using a porous layer insert. For the porous thickness range of [0.1–0.6], the corresponding range of average Nusselt number increase is [35.7%–176.9%], and the average entropy generation is [105.4%–771.9%]. The effect of the Reynolds number is more important in a porous duct than in aclear one. For δ = 0.4 and φ = 5%, the increase of Rein the range of [200–500] induces an increase ofin average Nusselt number in the range of [80.9%–108.4%] and average entropy in [222.9%–309.1%] comparatively to clear PCC.The effect of φ is practically the same for porous and clear channels. For φ = 5%, the increase inon average Nu is about 9%,and entropy generation is 5%. Accordingly, important improvements in heat transfer in PCC can be achieved through the combined effect of flow Reynolds numberand porous layer thickness.

Purpose-This paper aims to present a numerical study that investigates the flow of MgO-Al 2 O 3 /water hybrid nanofluid inside a porous elliptical-shaped cavity, in which we aim to examine the performance of this thermal system when exposed to a magnetic field via heat transfer features and entropy generation. Design/methodology/approach-The configuration consists of the hybrid nanofluid out layered by a cold ellipse while it surrounds a non-square heated obstacle; the thermal structure is under the influence of a horizontal magnetic field. This problem is implemented in COMSOL multiphysics, which solves the related equations described by the "Darcy-Forchheimer-Brinkman" model through the finite element method. Findings-The results illustrated as streamlines, isotherms and average Nusselt number, along with the entropy production, are given as functions of: the volume fraction, and shape factor to assess the behaviour of the properties of the nanoparticles. Darcy number and porosity to designate the impact of the porous features of the enclosure, and finally the strength of the magnetic induction described as Hartmann number. The outcomes show the increased pattern of the thermal and dynamical behaviour of the hybrid nanofluid when augmenting the concentration, shape factor, porosity and Darcy number; however, it also engenders increased formations of irreversibilities in the system that were revealed to enhance with the permeability and the great properties of the nanofluid. Nevertheless, this thermal enhanced pattern is shown to degrade with strong Hartmann values, which also reduced both thermal and viscous entropies. Therefore, it is advised to minimize the magnetic influence to promote better heat exchange. Originality/value-The investigation of irreversibilities in nanofluids heat transfer is an important topic of research with practical implications for the design and optimization of heat transfer systems. The study's findings can help improve the performance and efficiency of these systems, as well as contribute to the development of sustainable energy technologies. The study also offers an intriguing approach that evaluates entropy growth in this unusual configuration with several parameters, which has the potential to transform our understanding of complicated fluid dynamics and thermodynamic processes, and at the end obtain the best thermal configuration possible.

The current study investigates MHD natural convection heat transfer of a hybrid nanofluid in a truncated cone along with transparent domains having the stimulus of an inherent constant magnetic field. The governing equations subject to the physical boundary conditions are solved numerically by using the Galerkin finite element method. The effects of the various parameters involved in the problem such as the Rayleigh number Ra (ranging between 103 and 106), the Hartmann number Ha (ranging between 0 and 60), and the porosity ratio ε (0.1–0.9) are examined. Moreover, the effects of Da which represents the Darcy number (between 10‑3 and 10‑1) and the volume fraction of nanoparticles ϕ for the dissipated nanoparticles of Al2O3-Cu are reported in terms of the streamlines and isotherms distributions as well as the Nusselt number. Such parameters are critical control parameters for both the fluid flow and the rate of heat transfer of the natural convection in the annular space. The solution...

Sports played in or on the water represent a large proportion of human competitive and recreational activity. However, the level of our knowledge and understanding of technique in these activities seems to lag behind those of other popular activities. There are some somewhat obvious reasons for this discrepancy. First, motion in or on the water is dependent on a person's interaction with the fluid environment. Explaining this motion requires measurement of fluid forces acting on the limbs and body of a competitor or their blade or craft. These forces include drag forces, defined as forces in the direction of fluid flow across an object, or lift, defined as forces in a plane perpendicular to the direction of flow. Direct measurement of drag and lift forces acting on individual segments of a system is fraught with difficulties. Estimation of forces using indirect methods is also fraught with difficulty due to the problems involved in collecting accurate kinematic data in an environment in which there is an interface of two media -air and water. A fundamental question in aquatic sports is how propulsive forces may be produced in an energetically economical way while minimising resistive forces. In some cases, a technique in which the body is propelled by drag forces may optimise performance. In others, a technique in which the body is propelled by lift forces may optimise performance. Therefore, one of the key tasks in analysing technique in aquatic sports is to determine the relative contributions of drag forces and lift forces. The purpose of this presentation is to review the evidence relating to the use of drag forces and lift forces in three aquatic skills. These skills are freestyle swimming, flatwater kayak paddling, and the water polo 'eggbeater' kick. The implications for technique are discussed. Given the lack of definite findings, the presenter seeks to stimulate further investigation into aquatic sports rather than to draw conclusions. The issue of whether propulsion in freestyle swimming is due primarily to lift or drag appeared to have been settled in the early 1970s. Prior to that time coaches believed that the best way to propel the body forward was to pull the hand directly backwards, that is, to use drag forces. The drag force produced is opposite the direction of hand motion. It was thought that the hand plane should be almost square to the direction of motion. Coaches applied this idea by teaching swimmers to pull directly backwards with the hand at right angles to the pulling direction. Following observations that the hands of champion freestyle swimmers scribed curved paths during the pull phase of the stroke, and promoted the idea that good swimmers use 'sculling actions' with their hands pitched to utilise lift forces as the dominant means of propulsion. By definition, lift forces are perpendicular to the flow relative to the hand. Assuming that the hand moves into 'still' water, this means that the lift forces are also perpendicular to the line of motion of the hand. Initially, the lift in freestyle

WII, as accelerometer was used to study push-off phase in breaststroke swim turn. The accelerometer could not be used directly into the water; therefore necessary modifications had to be done in order to use it in water. The results have been compared with the results of Qualisys ...

In the present chapter, we examined the flow of a Newtonian fluid passing through complex porous medium between two coaxial cylinders which are rotating about the axis of the flow and moving parallel to the axis of the cylinders with different velocities. Flow under different situations is studied. In each case, the results are obtained when the permeability of the medium is very large and is very small. The classical Darcy's effect is found very near to the axis of the cylinders and the non-Darcian effect is found near the boundaries of the flow. The effect of the permeability coefficient of the porous medium is examined in each case.