Porous Cavity Research Articles

Natural Convection and Entropy Generation in a Porous Enclosure Filled with Non-Newtonian Nanofluid

In the present work, the analysis of natural convection and entropy generation in a square porous cavity, having either a flat or a wavy vertical wall, filled with a non-Newtonian nanofluid is reported. The effect of Rayleigh number (), non-Newtonian power-law index (0.6–1.4), Darcy number (0.0001–0.01), Hartmann number (0–90), and volume fraction of CuO nanoparticles (0–0.12) on heat transfer characteristics has been thoroughly examined. It is found that the average surface Nusselt number for an undulated wall is less than that of a plane wall. for all the cases increases with and and decreases with . The mixing of the nanoparticles with both Newtonian and non-Newtonian fluids enhances the heat transfer only for of 0.01 and less than 30 for all . When is low at 0.0001, the addition of nanoparticles to a fluid enhances the heat transfer for all the cases except of at less than 1. The entropy generation is significant near the vertical wall because of the higher temperature and velocity gradient. The magnitude of is found to be very less as compared with and . , , and increase with an increase in for all cases; however, for a of 60 or 90, there exists an optimum for for a ranging from 0.0005 to 0.001. Finally, the correlation for the average surface as a function of the pertinent input parameters has been proposed for both Newtonian and non-Newtonian fluids, which can be referred in the academics and the industrial world.

Impact of injection/suction and entropy generation of the porous open cavity with the hybrid nanofluid

The objective of the current study is to investigate the convection in a porous open enclosure with the center heated baffle. The cavity walls are insulated. For the cooling purpose of the system, the water-based $$\mathrm{Cu}-\mathrm{TiO}_2$$ hybrid nanofluid allowed into the cavity either by injection or suction. The non-dimensional governing equation of the present problem is dealing numerically by the method of finite difference. The fluid flow, isotherms, rate of heat transfer, entropy generation are analyzed graphically for both the cases (injection and suction) with the various pertinent parameters. The outcome of the study shows that the entropy generation of the problem is dominated by heat transfer. The suction process yielded the most useful result with the enhancing buoyancy through Ra.

A Preliminary investigation on Mural Flora of Jalpaiguri District of the Indian State West Bengal

Plants are well adapted to wide range of habitat. Some of them design their life processes for extra terrestrial survival on walls as an additional strategy to avoid completion and exclusion from the ecosystem are often considered as murophytes. Some of the murophytes often prove destructive to wall and similar construction and must be eradicated. The intensity of destruction is dependent on their frequency and their distribution on different position of wall. In this study the vascular plant flora growing on heritage buildings of Jalpaiguri district, West Bengal, India were identified and documented. For this study, some old buildings were selected as the study area. Among the vascular mural plants, 9 species of Pteridophyte and 68 of the angiosperm belonging to a total of 33 families of vascular flora were recorded. Maximum species diversity was noted in the substrate formed on a horizontal porous surface and cavities at ground level.

Impact of Soret and Dufour on bioconvective flow of nanofluid in porous square cavity

AbstractThis article addresses the bioconvection in a porous cavity associated with Soret and Dufour effects. The bioconvective flow in a porous medium is based on Hillesdon and Pedley's model and is governed by nonlinear partial differential equations. These equations are transformed into a dimensionless form with suitable nondimensional parameters. The finite element method is employed to solve the dimensionless equations. The outcomes of the study are presented by streamlines, temperature distributions, isoconcentrations of solute, nanoparticles, and microorganisms. Furthermore, the tendency of average Nusselt number and average Sherwood number and the influence of Soret parameter, Dufour parameter, Peclet number, and bioconvective Rayleigh number is interpreted. Thermophoresis and Soret number show a strong effect on the concentration of nanoparticles. Brownian motion and thermophoresis exhibit a significant effect on the density distributions of microorganisms. The novelty of the paper is to combine the effects of Soret–Dufour and oxytactic bioconvection. The present study can be useful in the following applications: microbial‐enhanced oil recovery, toxin removal, antibiotics, and modeling of microfluidic devices.

On a Dirichlet problem for the Darcy-Forchheimer-Brinkman system with application to lid-driven porous cavity flow with internal square block

In this paper we are concerned with both theoretical and numerical study of a Dirichlet boundary value problem for the nonlinear Darcy-Forchheimer-Brinkman system on a bounded Lipschitz domain in Rn(n=2,3). Using the potential theory technique we obtain a well-posed theorem which implies the existence and uniqueness of a weak solution for the aforementioned Dirichlet problem when the boundary data belongs to a L2-based Sobolev space. A numerical investigation of the flow of a viscous fluid through a two dimensional lid-driven porous cavity with a solid square block is performed. The effect of the dimension and position of the internal obstacle on the flow behaviour is analysed.

Application of a Hyperelastic 3D Printed Scaffold for Mesenchymal Stem Cell-Based Fabrication of a Bizonal Tendon Enthesis-like Construct

After surgical tendon repair, the tendon-to-bone enthesis often does not regenerate, which leads to high numbers of rupture recurrences. To remedy this, tissue engineering techniques are being pursued to strengthen the interface and improve regeneration. In this study, we used hyperelastic biphasic 3D printed PLGA scaffolds with aligned pores at the tendon side and random pores at the bone side to mimic the native insertion side. In an attempt to recreate the enthesis, the scaffolds were seeded with adult human mesenchymal stem cells and then cultured in dual fluidic bioreactors, which allows the separate in-flow of tenogenic and chondrogenic differentiation media. MTS assay confirmed the ability of cells to proliferate in dual-flow bioreactors at similar levels to tissue culture plate. Hematoxylin-eosin staining confirmed a compact cell layer entrapped within newly deposited extracellular matrix attached to the scaffolds’ fibers and between the porous cavities, that increased with culture time. After 7, 14, and 21 days, samples were collected and analyzed by qRT-PCR and GAG production. Cultured constructs in dual fluidic bioreactors differentiate regionally toward a tenogenic or chondrogenic fate dependent on exposure to the corresponding differentiation medium. SOX9 gene expression was upregulated (up to 50-fold compared to control) in both compartments, with a more marked upregulation in the cartilaginous portion of the scaffold, By day 21, the cartilage matrix marker, collage II, and the tendon specific marker, tenomodulin, were found to be highly upregulated in the cartilaginous and tendinous portions of the construct, respectively. In addition, GAG production in the treated constructs (serum-free) matched that in control constructs exposed to 10% fetal bovine serum, confirming the support of functional matrix formation in this system. In summary, our findings have validated this dual fluidic system as a potential platform to form the tendon enthesis, and will be optimized in future studies to achieve the fabrication of distinctly biphasic constructs.

A mesoscopic model for thermal–solutal problems of power-law fluids through porous media

A mesoscopic method based on the lattice Boltzmann method for thermal–solutal incompressible non-Newtonian power-law fluids through porous media is introduced. The macroscopic equations of different representative element volume (REV) models of porous media are presented, and the equations of power-law fluids through porous media for various REV models reported. The general mesoscopic model for two- and three-dimensional cases are presented, and their derivations shown. To demonstrate the ability of the proposed method, natural convection and double-diffusive natural convection of Newtonian and power-law fluids in porous cavities are studied, and the results are validated against previous findings. Finally, double-diffusive natural convection in a porous cubic cavity filled with a non-Newtonian power-law fluid is simulated by the proposed method.

Mathematical Modelling of MHD Natural Convection in a Linearly Heated Porous Cavity

A linear increase in thermal boundaries towards the bottom of the porous cavity is considered for numerical flow analysis on MHD natural convection. The two-dimensional square shaped cavity is filled with the Cu-water nanofluid. The dimensionless equations are considered to interpret the fluid and heat flow inside the cavity with respect to the desired boundaries. The governing equations are solved using the finite difference techniques. The relevant dimensionless parameters used in the present study are Rayleigh number, Darcy number, solid volume fraction of the nanoparticles and Hartmann number to obtain the flow fields. Heatline flows picturization techniques involved in the study analyze the heat flow inside the cavity. As the Rayleigh number and Darcy number increases, an increase in streamlines flow velocity and convection heat transfer is observed. Convective heat transfer is interrupted by increasing the applied magnetic field effects. An improvement in the heat transfer is noticed by increasing the solid volume fraction of the particles.

Hydrothermal and Entropy Investigation of Ag/MgO/H2O Hybrid Nanofluid Natural Convection in a Novel Shape of Porous Cavity

In this study, a new cavity form filled under a constant magnetic field by Ag/MgO/H2O nanofluids and porous media consistent with natural convection and total entropy is examined. The nanofluid flow is considered to be laminar and incompressible, while the advection inertia effect in the porous layer is taken into account by adopting the Darcy–Forchheimer model. The problem is explained in the dimensionless form of the governing equations and solved by the finite element method. The results of the values of Darcy (Da), Hartmann (Ha) and Rayleigh (Ra) numbers, porosity (εp), and the properties of solid volume fraction (ϕ) and flow fields were studied. The findings show that with each improvement in the Ha number, the heat transfer rate becomes more limited, and thus the magnetic field can be used as an outstanding heat transfer controller.

Conjugate Natural Convection in a Square Porous Cavity Filled with a Nanofluid in the Presence of Two Isothermal Cylindrical Sources

In this work, a numerical study has been performed for the problem of steady-state natural convection in a square porous cavity having a solid wall of finite thickness and conductivity filled by a nanofluid in the presence of two isothermal cylindrical sources. The external walls of the cavity are considered adiabatic and the circular sources are maintained at a hot and cold uniform temperatures. The internal thick wall has been a conducting solid. The governing dimensionless equations are solved using Galerkin finite element method and Darcy-Brinkman model assumed to be adopted. The results are presented as isotherms, streamlines, stream function values, average and local Nusselt number for various combinations of Rayleigh and Darcy numbers, concentration of nanoparticles, Thermal conductivity ratio, and dimensionless wall thickness of the solid portion. The convection heat transfer can be enhanced by increasing of these parameters except for the wall thickness.

Non-Newtonian effect on heat transfer and entropy generation of natural convection nanofluid flow inside a vertical wavy porous cavity

A numerical study on heat transfer and entropy generation in natural convection of non-Newtonian nanofluid flow has been explored within a differentially heated two-dimensional wavy porous cavity. In the present study, copper (Cu)–water nanofluid is considered for the investigation where the specific behavior of Cu nanoparticles in water is considered to behave as non-Newtonian based on previously established experimental results. The power-law model and the Brinkman-extended Darcy model has been used to characterize the non-Newtonian porous medium. The governing equations of the flow are solved using the finite volume method with the collocated grid arrangement. Numerical results are presented through streamlines, isotherms, local Nusselt number and entropy generation rate to study the effects of a range of Darcy number (Da), volume fractions (ϕ) of nanofluids, Rayleigh numbers (Ra), and the power-law index (n). Results show that the rate of heat transfer from the wavy wall to the medium becomes enhanced by decreasing the power-law index but increasing the volume fraction of nanoparticles. Increase of porosity level and buoyancy forces of the medium augments flow strength and results in a thinner boundary layer within the cavity. At negligible porosity level of the enclosure, effect of volume fraction of nanoparticles over thermal conductivity of the nanofluids is imperceptible. Interestingly, when the Darcy–Rayleigh number Ra^*gg 10, the power-law effect becomes more significant than the volume fraction effect in the augmentation of the convective heat transfer process. The local entropy generation is highly dominated by heat transfer irreversibility within the porous enclosure for all conditions of the flow medium. The particular wavy shape of the cavity strongly influences the heat transfer flow pattern and local entropy generation. Interestingly, contour graphs of local entropy generation and local Bejan number show a rotationally symmetric pattern of order two about the center of the wavy cavity.

Three-dimensional numerical investigation on melting performance of phase change material composited with copper foam in local thermal non-equilibrium containing an internal heater

This work aims to numerically study the 3D melting heat transfer of latent heat thermal energy storage (LHTES) systems with phase change material (PCM) embedded in copper foam inside an internal heated cubic cavity. The enthalpy-porosity method to model the phase change process is employed and the Darcy-Forchheimer law and local thermal non-equilibrium (LTNE) model are assumed for the metal foam. The numerical code of proposed model shows good agreement for copper foam composited PCM melting with carefully designed experiments. Special attentions are given to detect the effects of Rayleigh number (Ra), porosity (ε), Darcy number (Da) and heater size on evolvement of solid-liquid interface, temperature stratification and full melting. The results show that increasing Ra enhances convective heat transfer in the upper part of the porous cavity; though the completely melting time remains almost unchanged. For a fixed porosity, decrease of Da reduces the melting rate in the medium melting stage, and the temperature distribution of low Da is dominated by the heat conduction in porous media at the later stage, but Da shows a negligible effect on the complete melting time. For a fixed Da, increase of porosity decelerates the complete melting time. Apart from that, the heater size also plays an important role in the melting performance of composited PCM.

Activated carbon from macauba endocarp (Acrocomia aculeate) for removal of atrazine: Experimental and theoretical investigation using descriptors based on DFT

In this work the properties of activated carbon obtained from macauba endocarp were evaluated, an agro-industrial waste widely produced in Brazil. This material was applied to remove the herbicide atrazine, an emerging pollutant. The biochar it was produced by vacuum pyrolysis (temperatures of 400 °C and 600 °C; heating rates 10 and 50 °C min−1) and activated with K2CO3. The characterizations of materials were performed by elemental analysis (CNHO), immediate analysis, TG/DTG, density, FTIR, DRX, SEM and surface area analysis by the N2 adsorption and desorption method. Chemical reactivity of the atrazine molecule was investigated using DFT-based reactivity descriptors. For the kinetic profile and mechanism proposal, rate equations of pseudo-first-order, pseudo-second-order and intraparticle diffusion were considered. Activated carbons showed a typical amorphous structure, with an increase in the porous cavity after chemical activation process. Surface areas of 951–1002.5 m2 g−1 were obtained after activation with pores in the range of 1.70–2.67 nm. Activated carbons showed a high affinity with atrazine with a 90–98% removal percentage. The quantum chemical parameters calculated were the energy of the HOMO (EH = −6.4649) and LUMO (EL = −0.4558) orbitals, global chemical hardness (η = 3.0045), chemical potential (μ = 3.4603) and the global electrophilicity index (ɷ = 1.9926). In the kinetic study, the pseudo-second-order model was more predictive in adsorption tests. These results suggest that macauba endocarp activated carbon is efficient in atrazine removal, in addition to being a strategy for using agro-industrial waste.

Effect of partial wall motion on MHD mixed convection heat transfer undergoing in a porous cavity filled with Cu–water nanofluid with a centrally mounted heat source

The Magneto-hydrodynamics (MHD) convective heat transfer process in a partially driven cavity (PDC) containing a centrally mounted heat source is focused in the present study. The cavity is filled with Cu–water nanofluid saturated porous medium. Heated cavity fluid is cooled through the upper half of the two sidewalls. These cold sidewalls are allowed to move in upward direction at the same velocity. The horizontal walls and lower part of the sidewalls are insulated. The cavity subjected to an externally imposed uniform magnetic field. The flow structures and mixed convection heat transfer characteristics are analyzed numerically utilizing developed CFD code adopting FVM and SIMPLE algorithm. The thermo-fluid phenomena are analyzed under a range of governing parameters like Richardson number (Ri), Hartmann number (Ha), concentrations of nanoparticles (ϕ). The results reflect that the heat transfer characteristics of the PDC are greatly influenced by all of the above parameters. Heat transfer is enhanced significantly at the higher Ri and higher volume fraction.

Analysis on the influence factors of the acoustic absorption performance of porous fiber materials

Porous fiber materials are the most widely used acoustic absorption materials at present, and they have excellent acoustic absorption performance. This paper uses the finite element method to explore the factors affecting the acoustic absorption performance of porous fiber materials, including flow resistance, thickness of the porous fiber material, incidence angle, and back cavity thickness. Due to the complex acoustic absorption mechanism of porous fiber materials, an equivalent fluid model is used to simulate the acoustic absorption properties of the porous fiber materials. The correlation of acoustic absorption performance and the model of the back cavity was analyzed. An impedance tube test was implemented to verify the simulation results.

Biodegradable Nanocomposite Film Based on Gluten/Silica/Calcium Chloride: Physicochemical Properties and Bioactive Compounds Extraction Capacity

In this study, a biodegradable wheat gluten (WG) film containing calcium chloride and nano silica (WG/CaCl2/SiO2) was prepared and the physicochemical properties of the film were investigated. Finally, the WG/CaCl2/SiO2 film was used as a polymeric adsorbent for extraction of bioactive compounds from red grape pomace. The properties of the composite film, including thickness, water vapor permeability (WVP), solubility, antioxidant activity and mechanical property were investigated. FT-IR, SEM, XRD and DSC tests were performed to investigate the physical, morphology and thermal properties of film. The results showed that the addition of SiO2 decreased the WVP because these nanoparticles can fill the porous cavities of the film matrix. Furthermore, SiO2 caused to improve the water resistance of the film. With the addition of SiO2, the antioxidant content of the films increased compared to the control film. The addition of SiO2 to the film decreased the crystal property and addition of CaCl2 increased the crystal property of the film. In the second step, the optimum film as adsorbent was used to extract of the bioactive compounds from the red grape pomace. For this purpose, total phenol, flavonoid and anthocyanin content were measured before and after the extraction by film, and the optimum extraction conditions were obtained by the desirability function method. At optimum extraction condition, the phenolic compounds were extracted with 76.9% efficiency and optimum extraction temperature and time were 20.5 °C and 27.1 h, respectively. Due to the low solubility of WG/CaCl2/SiO2 film in water and its appropriate thermal and mechanical stability, the WG/CaCl2/SiO2 film in different aquatic environments can be used to extract bioactive compounds of fruit pomace.

Navigating Copper-Atom-Pair Structural Effect inside a Porous Organic Polymer Cavity for Selective Hydrogenation of Biomass-Derived 5-Hydroxymethylfurfural

In recent times, selective hydrogenation of biomass-derived 5-hydroxymethylfurfural (5-HMF) to produce the novel difuranic polyol scaffold 2,5-dihydroxymethylfuran (DHMF) has attracted the interest...

Local Thermal Nonequilibrium Natural Convection in a Cavity with Heat-Generating Porous Layer

Natural convection in a partially porous cavity with a heat generating source in the solid phase is studied numerically under a local thermal nonequilibrium condition. The right and left walls of the cavity are maintained at hot and cold temperatures, respectively. The horizontal walls are thermally insulated. The finite volume method and the semi-implicit method for pressure-linked equations (SIMPLER) algorithm are used to solve the conservation equations. The effects of relevant parameters, such as internal and external Rayleigh numbers , , interphase heat transfer coefficient , modified thermal conductivity ratio , and dimensionless porous layer thickness are discussed. The results revealed that at high values of the interphase heat transfer coefficient, the impact of an internal Rayleigh number on the dynamic and thermal fields decreases with an increase in the modified thermal conductivity ratio.

Double-diffusive convection of a rotating circular cylinder in a porous cavity suspended by nano-encapsulated phase change materials

The main objective of this study is to simulate the suspension of a nano-encapsulated phase change material (NEPCM) during the double-diffusive convection flow inside a compound cavity. A novel cavity shape is formed from a central circular cylinder mounted with two rectangular shapes. An incompressible smoothed particle hydrodynamics (ISPH) method is used to solve the governing equations of the present physical problem. A heat capacity of the core-shell layers assisted the phase changes of the encapsulated nanoparticles. The main findings of the performed simulations showed that a fusion temperature controls both location and intensity of a phase change zone inside a cavity. Regardless of the impacts of a buoyancy ratio parameter on the flow speed, the melting-solidification zones are not changing under the variations in a buoyancy ratio parameter. An increase in a radius of a circular cylinder enhances the double diffusive convection and it reduces the intensity of a phase change zone. In addition, the increase in the radius of the circular cylinder powers the average Nusselt and Sherwood numbers. Increasing nanoparticles concentration enhances a phase change zone.

Onset of Convection in Two-Dimensional Porous Cavities with Open and Conducting Boundaries

The onset of thermal convection in two-dimensional porous cavities heated from below is studied theoretically. An open (constant-pressure) boundary is assumed, with zero perturbation temperature (thermally conducting). The resulting eigenvalue problem is a full fourth-order problem without degeneracies. Numerical results are presented for rectangular and elliptical cavities, with the circle as a special case. The analytical solution for an upright rectangle confirms the numerical results. Streamlines penetrating the open cavities are plotted, together with the isotherms for the associated closed thermal cells. Isobars forming pressure cells are depicted for the perturbation pressure. The critical Rayleigh number is calculated as a function of geometric parameters, including the tilt angle of the rectangle and ellipse. An improved physical scaling of the Darcy–Bénard problem is suggested. Its significance is indicated by the ratio of maximal vertical velocity to maximal temperature perturbation.