Porous Cavity Research Articles

Thermal performance analysis of a porous solar cavity receiver

A solar cavity receiver filled with a porous layer now is popularly found in solar energy industry. As its thermal performance will influence the efficiency of solar energy utilization systems considerably, deep understanding on it is urgent for the development of solar energy industry. In the present work, the influences of thickness, effective thermal conductivity and permeability of a porous layer on thermal performance of a porous solar cavity receiver are investigated comprehensively for the first time. The analysis is carried out not only from the viewpoint of the first law of thermodynamics but also from the second law of thermodynamics. Three new findings are obtained: (1) a critical value of thickness of the porous layer, (2) a critical value of effective thermal conductivity of the porous layer and (3) a critical value of permeability of the porous layer, across which the thermal performance of the solar receiver will alter significantly. In addition, some comparison is conducted between the observations in this research and those in previous publications to check the effects of the configuration and flow driven mechanism of a porous solar cavity receiver on its thermal performance for the first time.

Investigation of Hydrothermal Behavior of Fe3O4-H2O Nanofluid Natural Convection in a Novel Shape of Porous Cavity Subjected to Magnetic Field Dependent (MFD) Viscosity

Abstract A novel shape of cavity filled by Fe3O4-water nanofluids and porous media associated with natural convection under a constant inclined magnetic field has been studied. A novel model for viscosity named magnetic field dependent (MFD) viscosity is applied. The effects of Darcy, Hartmann and Rayleigh numbers, inclination angle and the cavity aspect ratio on heat and flow fields characteristics have been examined. The results represent that more the heat transfer rate has been constrained with any increment in the Hartmann number and therefore, the magnetic field can be utilized as an excellent controller of the heat transfer. Further, it is inferred that more values of the aspect ratio give always a greater average Nusselt number, at a given Ra.

Enhancement of heat and mass transfer rates through various porous cavities for triple convective-diffusive free convection

Convective energy and mass transfer in various porous chambers are a wide-spread physical phenomenon in natural and technical systems. The triple diffusive free convection is examined in square, trapezoidal and triangular porous chambers under an impact of internal volumetric heat generation. The top and bottom surfaces of the chambers are assumed to be adiabatic and impermeable. In this study, different concentrations of NaCl and Sucrose are utilized as solutal components with water. Governing equations written employing the linear Darcy model and non-primitive dimensionless variables were worked out by the finite element technique with the Galerkin method of weighted residuals. The influence of the internal heat generation rate, Rayleigh and Lewis numbers, buoyancy ratios on the dimensionless temperature, the concentration of both salts, Nusselt, Lewis and Sherwood numbers are scrutinized. The study reveals that the growth of the inner volumetric heat flux raises the temperature within the cavity and reduces the Nusselt number, while the Sherwood and Nusselt numbers are raised with the buoyancy ratio parameter. Also, the triangular cavity shows the highest heat and mass transfer rate.

Mono-Dispersed Microspheres Locally Assembled on Porous Substrates Formed through a Microemulsion Approach.

A cost-effective, simple, and time-saving method to fabricate mono-dispersed periodic microsphere structures on substrates with patterned sites is very meaningful due to their significance on various biological studies. Herein, a simple and facile method to fabricate mono-dispersed microsphere arrays on porous substrates was developed. The mixture of polystyrene and an organic stabilizer solution which contains aqueous solution, fabricated through shaking, was applied to prepare microemulsion solution. An ordered porous structure was produced by spreading and evaporating the solvent of microemulsion on a glass slide, accompanied by the enrichment of didodecylamine in the cavities. The porous cavities were further modified with polyacrylic acid and poly(diallyldimethylammonium chloride) which could immobilize the microspheres. The charged microspheres were incorporated into the cavities by an electrostatic interaction with the oppositely charged polyelectrolytes. The positive polyelectrolytes with abundant charges as well as a suitable content and dimension of microspheres, ensured the formation of mono-dispersed and ordered arrays. Considering that other charged particles were universally suitable for the present strategy, the reported approach opened an efficient way for the preparation of microsphere-based materials.

Thermal analysis of nanofluid saturated in inclined porous cavity cooled by rotating active cylinder subjected to convective condition

Convective heat transfer in a porous cavity conjugated with an active rotating cylinder is investigated in this paper. Copper–water nanofluid fills the porous cavity. The rotating active cylinder is positioned in such a way conveying heat from the cavity and discharges it outside. The vertical walls of the cavity are thermally insulated while the bottom wall is moving to the right and kept at a constant high temperature. The governing equations are facilitated with the ability to study the tilt of the cylinder-cavity assembly. The effects of Richardson number, Darcy number, inclination angle, conductivity ratio, rotational speed, and nanofluid volume fraction are studied at a constant Rayleigh number of 105. Galerkin finite element method of weak formulation is used to solve the dimensionless governing equation with appropriate boundary conditions. Darcy–Brinkman–Forchheimer model is adopted to govern the flow inside porous medium. Results show that the rotation of the cylinder can enlarge the average Nusselt number more than 223%, while ten times increase of thermal conductivity ratio amplifies Nusselt number by 136%. It is also found that the Richardson number plays an adverse role on the average Nusselt number. Physical explanations and thorough validations are given in the paper.

Natural convection in a partially heated porous cavity to Casson fluid

Abstract In the present study, the phenomenon of natural convection in a square porous cavity containing Casson fluid is investigated, numerically. The non-Newtonian model of Casson fluid is utilized to obtain the governing equations of a flow problem. The thermal control inside the cavity is managed by partially heating the bottom wall and symmetric cooling of the side walls while the top wall is taken to be adiabatic. The penalty finite element method is used to solve the non-linear coupled equations of the flow problem. The effect of different lengths of heated zone e, Rayleigh number Ra and Darcy number Da has been examined on flow velocity and temperature distribution inside the cavity. The impact of effective viscosity of the fluid by varying Casson fluid parameter γ on the flow of fluid and heat transport has also been investigated. The results are demonstrated by plotting streamlines, isotherms and average Nusselt number over wide ranges of governing parameters. The obtained results show that with an increase in Casson fluid parameter γ and Darcy number Da, heat transfer and flow circulation increases. It is also observed that the conduction dominant heat transfer takes place for low Darcy number over a wide range of the Rayleigh number (102 ≤ Ra ≤ 106).

Flow and heat transfer simulation in a wall-driven porous cavity with internal heat source by multiple-relaxation time lattice Boltzmann method (MRT-LBM)

Laminar mixed convection characteristics in a wall driven porous cavity with an isothermally heated square blockage inside have been investigated numerically by the Non-orthogonal multiple-relaxation time lattice Boltzmann method (MRT-LBM). Various directions of wall driven and placement of the blockage have been considered. In the current study, the geometrical and flow parameters being investigated are the directions of wall driven, blockage position (ex, ey), the Richardson number (Ri). From the analysis of the mixed convection process with different directions of wall driven, the results show that under the configuration of central placement of the blockage, the most preferable heat transfer is obtained in the right wall driven at any values of the Richardson number. Because the movement of the wall can lead to an assisting effect on the buoyancy flow in the right wall driven. Since the right wall driven has the best heat transfer effects, the influences of blockage location and Richardson number is investigated in this condition. When the value of the Richardson number is 0.1, the most preferable heat transfer is obtained when the blockage is placed at the top right and bottom right. When the value of the Richardson number is 1.0 or 10.0, both the middle left and middle right blockage placement have the best heat transfer rate. That is mainly due to the influence of the size, strength and position of the vortex, the combined effect of forced convection and natural convection is stronger when the blockage is placed at those locations.

Non-orthogonal multiple-relaxation-time lattice Boltzmann simulation of natural convection in porous square cavity with internal heat source

Non-orthogonal multiple-relaxation-time lattice Boltzmann simulation of natural convection in porous square cavity with internal heat source

Examination of CVFEM for nanofluid free convection MHD flow through permeable medium

In current attempt, a numerical code was developed to model the nanofluid free convected magnetized flow by porous cavity. Non-Darcy formula is carried out to include the term of porosity in momentum expression. Radiative phenomenon is reported for distinct nanoparticle shapes. Aspects of radiative constraint, shape factor, Rayleigh number, magnetic force, and nanoparticles’ shape on nanofluid magneto-hydrodynamic natural convection are analyzed. Result demonstrated that application of external magnetic force deteriorates the convection and this reduction is more perceptible at the greater permeability. The conductive heat transport is the dominating form of heat transportation under the impact of higher magnetic force. For the constant values of Rayleigh, Hartmann’s and Darcy number, $${\text{Nu}}_{{{\text{avg}}}}$$ is independent of shape factor and observes a direct association with the radiation parameter.

Inclined magneto: convection, internal heat, and entropy generation of nanofluid in an I-shaped cavity saturated with porous media

A numerical investigation of entropy generation due to MHD-free convective of Cu–water nanofluid in a porous I-shaped cavity is reported. The cavity is under Darcy law with inclined uniform magnetic field. The cavity is cooled from the top and a part of bottom wall subjected to uniform heat flux, while the other parts of walls of the cavity are adiabatic. Mathematical pattern formulated employing the single-phase nanofluid approach in governing equations the problem has been solved by finite difference technique. Prime efforts have been concentrated on the impacts of the pertinent parameters on the fluid flow and heat transfer inside the cavity. Numerical data have been plotted in the form of streamlines, isotherms, and average Nusselt numbers. The results show that the Nu number decreases via increasing the Ha number. It increases when the Ra number is increased. The maximum and minimum values of Nusselt occur at B = 0.2 and B = 0.8, respectively. Exerting an angle for magnetic flux leads to the improvement in thermal performance for all amount of B. The effects of Ha, nanofluid volume fraction, heat source size, location and angle of magnetic field on heat transfer, entropy generation, and thermal performance are completely studied and discussed.

Effects of a Rotating Cone on the Mixed Convection in a Double Lid-Driven 3D Porous Trapezoidal Nanofluid Filled Cavity under the Impact of Magnetic Field.

Effects of a rotating cone in 3D mixed convection of CNT-water nanofluid in a double lid-driven porous trapezoidal cavity is numerically studied considering magnetic field effects. The numerical simulations are performed by using the finite element method. Impacts of Richardson number (between 0.05 and 50), angular rotational velocity of the cone (between −300 and 300), Hartmann number (between 0 and 50), Darcy number (between 10 and ), aspect ratio of the cone (between 0.25 and 2.5), horizontal location of the cone (between 0.35 H and 0.65 H) and solid particle volume fraction (between 0 and 0.004) on the convective heat transfer performance was studied. It was observed that the average Nusselt number rises with higher Richardson numbers for stationary cone while the effect is reverse for when the cone is rotating in clockwise direction at the highest supped. Higher discrepancies between the average Nusselt number is obtained for 2D cylinder and 3D cylinder configuration which is 28.5% at the highest rotational speed. Even though there are very slight variations between the average Nu values for 3D cylinder and 3D cone case, there are significant variations in the local variation of the average Nusselt number. Higher enhancements in the average Nusselt number are achieved with CNT particles even though the magnetic field reduced the convection and the value is 84.3% at the highest strength of magnetic field. Increasing the permeability resulted in higher local and average heat transfer rates for the 3D porous cavity. In this study, the aspect ratio of the cone was found to be an excellent tool for heat transfer enhancement while 95% enhancements in the average Nusselt number were obtained. The horizontal location of the cone was found to have slight effects on the Nusselt number variations.

Natural convection in the ferrofluid enclosed in a porous and permeable cavity

Abstract The thermal transfer in the water-based ferrofluid enclosed porous cavity attached with a novel permeable (suction/injection) chamber is investigated within this research. The mathematical analysis of the problem is fulfilled with the modified Rosensweig-model (mRm) accounting for the Darcy porous medium in cooperation with the energy equation. The relevant governing equations are numerically treated via the successive-over-relaxation method (SOR) based on a special finite difference scheme. The pertinent effects of physical parameters on the convection and heat transfer of the ferrofluid inside the cavity are examined in detail. It is determined that the Nusselt number enhances at the left wall but it is reduced at the right wall if one increases either (i) the concentration of the ferroparticles or (ii) the Lorentz force. But the effect of Kelvin force is different from the effect of the Lorentz force on the Nusselt number in the sense that; the Nusselt number decays at the left wall but it intensifies at the right wall if we increase the Lorentz force or its representative the Hartmann number. In addition, the Nusselt number at the left wall of the cavity rises about 1.4 times if the Hartmann number increases from 0 to 50. The problem setup in the current work may be useful in the applications regarding bio-medical, pharmaceutical and engineering industries. The generated results from the present work quantitatively as well as qualitatively match with the existing literature.

Impact of finite wavy wall thickness on entropy generation and natural convection of nanofluid in cavity partially filled with non-Darcy porous layer

This paper investigates the natural convection inside a partially layered porous cavity with a heated wavy solid wall; the geometry is encountered in compact heat exchangers. Alumina nanoparticles are included in the water to enhance the heat exchange process. The incidental entropy generation is also studied to evaluate the thermodynamic irreversibility. The nanofluid flow is taken as 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 Darcy number (Da), porosity of the porous layer ( $$\varepsilon$$ ), number of undulations (N), and the nanoparticles volume fraction ( $$\phi$$ ) are varied to assess the heat transfer and the incidental entropy generation. It is found that the waviness of the solid wall augments the average Nusselt number and minimizes the generation of entropy. The results show for some circumstances that the Nusselt number is augmented by 43.8% when N is raised from 0 (flat solid wall) to 4. It is also found that the porosity of the porous layer is a more crucial parameter than its permeability, where a 37.4% enhancement in the Nusselt number is achieved when the porosity is raised from 0.2 to 0.8.

Analysis of hybrid nanofluid behavior within a porous cavity including Lorentz forces and radiation impacts

We investigate the hybrid nanofluid convection transportation within a permeable medium in appearance of an externally applied magnetic force by modeling it through control volume-based finite element method. To employ the permeability effect terms, one term was added in momentum and radiation was involved to show the diverse states of nanoparticles. The impact of Darcy and Rayleigh as well as magnetic and radiation parameters on the nanofluid performance is investigated and presented. We observe that the conduction mode enhances with higher values of Ha. Nusselt number Nu augments with the consideration of radiation source term. The addition of Lorentz force makes the conduction mode more sensible. The agreement with the published results makes us more confident about the validity of our numerical computations.

Simulation Examination for Nanoparticle Flow in a Permeable Enclosure via CVFEM Involving MHD Effect

In the present investigation, innovative complex porous enclosure is chosen to simulate the MHD (magnetohydrodynamic) natural convection. One side of porous cavity packed with radiative nanofluid (CuO–water) has curve-shaped triangular wave pattern. To gain insight into outputs, CVFEM (control volume-based finite element method) has been used. Nanofluid behavior is inspected by employing two-temperature model for solid matrix and nanoliquid and KKL model for effective properties of nanofluid with an extensive range of key parameters acting as Hartmann number, radiation parameter, buoyancy impact, phase interacting heat transfer factor. Not only imposing magnetic field but also wavy surface and dispersion of nanomaterial have been considered in the current paper. New numerical approach has been utilized to demonstrate the behavior of nanomaterial through the porous tank. Interrelation of average Nusselt number with involved parameters is also proposed. Outcomes reveal that radiation term has straightforward association with Nusselt number. Greater vortex generates with the rise in shape factor.

Heat Transfer in Square Porous Cavity Due to Radiation and Heat Generating Strip - Part I

Investigation of heat transfer is presented due to a vertical heat generating strip inside the square porous cavity. The heat is assumed to be generated at isothermal rate at a strip inside the medium. The vertical walls of the cavity are cooled to lower temperature Tc. The two horizontal surfaces are maintained adiabatically so that heat does not cross the boundary. Finite element method is applied as a solution tool to solve the governing equations. The impact of various parameters such as heating strip length, Rayleigh number and Radiation parameter are presented in terms of temperature and streamline distribution inside the porous cavity.

Heat Transfer in Square Porous Cavity Due to Radiation and Heat Generating Strip - Part II

The current article discusses the effect of a small heating strip placed inside the porous medium enclosed in a square cavity. The left vertical surface is maintained at hot temperature and right vertical surface remains at cold temperature that allows the heat to be dissipated outside the system. The other two surfaces of the cavity are maintained adiabatic. A comparison is drawn between the present work and the work where the left vertical wall is maintained at cold temperature. The different parameters such as length of the heating strip inside the domain, Rayleigh number and Radiation parameters are discussed with respect to the square porous domain.

Mixed convection in a nanofluid-filled sloshing porous cavity including inner heated rose

In this paper, study of the heat transfer by mixed convection in sloshing enclosures heated from inside by an inner rose and filled with a porous medium using nanofluids is carried out. The Hazen–Dupain–Darcy model is applied to represent the porous medium, while the nanofluids are investigated using the one-phase model. The governing equations are converted to the dimensionless form and then solved numerically using the finite volume method. The controlling parameters in this simulation are numbers of the rose petals k, lengths of the rose petals a, the Richardson number Ri, the sloshing cavity amplitude A, the resonance frequency ω, the nanoparticle volume fraction ϕ and the Darcy number Da. It is found that rate of the heat transfer in case of the even number of the rose petals is greater than that of the odd number case. Also, the increase in either the sloshing cavity amplitude A or lengths of the rose petals a enhances the local Nusselt number, while as the resonance frequency ω increases, the average Nusselt number around the rose is reduced.

Magnetohydrodynamic natural convection and entropy generation analyses inside a nanofluid-filled incinerator-shaped porous cavity with wavy heater block

The aim of the current study is natural convection analysis conjugated with entropy generation analysis in an incinerator shaped permeable enclosure loaded with Al2O3–H2O nanofluid subjected to the magnetic field with a rectangular wavy heater block positioned on the bottom of the cavity wall. The bottom and top horizontal walls are adiabatic; the inclined and vertical walls are thought to be cooled. Firstly, the governing expressions and standard k–e turbulence model are rewritten from dimensional form to non-dimensional form using dimensionless parameters such as vorticity and stream function. In the next step, the equation of entropy generation is written in dimensionless form. Then, the system of non-dimensional governing equations is solved by the finite volume method (FVM) conjugated with a non-dimensionalization scheme using ANSYS Fluent. Fine grids (wall y+ < 2) with inflated layers have been used for the higher Rayleigh number. The effects of the Rayleigh number in the laminar region (Ra = 103, 104, and 105) and turbulent region (Ra = 108, 0.5 × 109, and 109), Darcy number (Da = 0.01 and 100), Hartmann number (Ha = 0 and 40), and the nanoparticles ( $$ \phi = 2{{\% }} $$ ) on the entropy generation number and natural convection are investigated. The validation results were in good agreement with those of the literature. The results demonstrate that for the laminar region, the Nusselt number and entropy generation number increase as the Rayleigh number and the Darcy number grow, whereas both of them abate as Hartmann number increases. In the turbulent region, the average Nusselt number decreases by ascending the Darcy number. Also, for turbulent region (Ra = 109), convection flow strength decreases 6.28% when Hartmann number increases from 0 to 40, whereas the entropy generation number increases 31.5% at Da = 0.01.

PANI-g-C3N4 grafted on cobalt acetate as an efficient precursor for synthesis of N-doped carbon contains cobalt composite: A versatile catalyst for reduction of nitro compounds

In this study, a novel nano catalyst consisted of Co oxide particles incorporated in N-doped porous carbon, named Co3O4@N-C-600, was synthesized in the one-step pyrolysis of polyaniline-graphitic carbon nitride composite grafted cobalt acetate at 600 °C. The resulting Co3O4@N-C-600 catalyst was characterized using different identification methods. In addition, specific surface area and the size of the porous carbon cavities were measured using Brunauer-Emmett-Teller (BET) analyzer. The catalytic performance of this novel nano-catalyst was examined for reduction of aromatic and aliphatic nitro-compounds using water as green solvent at 75 °C. Also the as prepared carbon catalyst resulted corresponding amine compounds in high yields and short reaction times. After the end of the reaction, the nano catalyst was easily separated using centrifuge and the recycle studies showed that it reused in five continuous runs in the model reaction without appreciable loss of its catalytic activity.