Top PDF Effect of Surface Thermal Radiation on Natural Convection and Heat Transfer in a Cavity Containing a Horizontal Porous Layer

Effect of Surface Thermal Radiation on Natural Convection and Heat Transfer in a Cavity Containing a Horizontal Porous Layer

Effect of Surface Thermal Radiation on Natural Convection and Heat Transfer in a Cavity Containing a Horizontal Porous Layer

Abstract In this paper, the effects of surface radiation on heat transfer and natural convection in a cavity containing a horizontal porous layer have been studied numerically. The governing equations for the momentum and heat transfer in both free fluid and porous medium were solved by the finite element method. The radiative heat transfer is calculated by making use of the radiosity of the surfaces that assumed to be grey. Comparisons with experimental and numerical results in the literature have been carried out. Effects of thermal radiation on natural convection and heat transfer in both free fluid and porous medium were analyzed. It was found that surface thermal radiation can significantly change the temperature fields in both the regions of free flow and porous medium. The mean temperature at the interface decreases and the temperature gradients are created on the upper two corners of the porous medium region as Ra increases.
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HEAT GENERATION EFFECTS ON NATURAL CONVECTION IN POROUS CAVITY WITH DIFFERENT WALLS TEMPERATURE

HEAT GENERATION EFFECTS ON NATURAL CONVECTION IN POROUS CAVITY WITH DIFFERENT WALLS TEMPERATURE

Natural convection heat transfer in cavity containing the porous medium with heat generation per unit volume is considered for numerical investigation. The governing parameters are Ra and λp, Ra is function of temprature difference of cold and hot boundries. Parameter λp is related to heat generation in cavity. The non-dimensional forms of the continuity, Darcy and energy equations are solved numerically. Parametric study is carried out and the results are presented to show the effect of these parameters on heat transfer and fluid flow characteristics. It is found that by increasing Ra at constant λp, the power of vortexes increases but maximum temprature of cavity, θ max decreases. Also
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Numerical study on mixed convection heat transfer in a porous L-shaped cavity

Numerical study on mixed convection heat transfer in a porous L-shaped cavity

heated porous lid-driven cavity was investigated by Oztop [2] . He concluded that heat transfer decreases as the Richardson number (Ri) increases, but that increments in the Darcy number (Da) cause heat transfer to rise. Sameh E. Ahmed [3] studied mixed convection from a discrete heat source in enclosures with two adjacent moving walls and filled with micropolar nanofluids. Numerical modeling of thermal characteristics in a microstructure filled porous cavity with mixed convection conducted by Bhuiyan et al. [4] . Javaherdeh et al. [5] studied natural convection heat and mass transfer in MHD fluid flow past a moving vertical plate with variable surface temperature and concentration in a porous medium. Khanafer and Vafai [6] carried out a numerical study of mixed convection heat and mass transport in a lid-driven square cavity filled with a non-Darcian fluid-saturated porous medium, and reported that the buoyancy ratio, Reynolds number (Re), Darcy number, and Richardson number have a profound effect on heat transfer. A numerical study on natural convection in porous media-filled an inclined triangular enclosure with heat sources using nanofluid in the presence of heat generation effect is con- ducted by Mansour and Ahmed [7] . Agarwal et al. [8] investigated double diffusive mixed convection in a lid-driven porous cavity. It was observed that convection flow was significant up to Darcy number of 0.1. Nasseddine Ouertatani et al. [9] studied the intri- cate three-dimensional flow structure and heat transfer rate in a
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Impact Of Radiation Models In CFD Simulations Of Natural Convection Heat Transfer In A Side Heated Square Cavity

Impact Of Radiation Models In CFD Simulations Of Natural Convection Heat Transfer In A Side Heated Square Cavity

Abstract— The flow progress in a water-filled square cavity which is suddenly heated and cooled on the opposing sidewalls is noticed by using the CFD software package Fluent 6.3. Two approximations were used for CFD simulation of radiation in a liquid cavity, namely, Rosseland approximation the methods of spherical harmonic functions. Comparison of three different approaches to description of the radiation mechanism of energy transfer has made it possible to recognize the special features of these models. Temperature and stream distribution functions are acquired in a large range of the governing criterion. The horizontal boundaries of the cavity are insulated, while the heated and cooled vertical left and right walls are conducting. The present thesis continues the explanation of the flow growth until a steady state is reached. A clear visualization of the interaction between the second wave group and the laminar interruption flow across the roof of the cavity is given. The consequent collapse of the horizontal interruption cause the thermal layer in the cavity core and the adjustment of the vertical boundary layer are also observed. The final state is represented by waves which continuously travel along the boundary layers.
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Magnetic and radiation absorption effects on thermosolutal convection in a horizontal porous layer subject to cross fluxes of heat and mass

Magnetic and radiation absorption effects on thermosolutal convection in a horizontal porous layer subject to cross fluxes of heat and mass

This study investigates the effect of electromagnetic field and radiation absorption on natural convection in a horizontal shallow porous cavity filled with an electrically conducting binary fluid. subjected to cross fluxes of heat and mass. The Darcy model, Rosseland approximation for the radiative flux and the Boussinesq approximation for density variations are used in the formulation of the problem. In the limit of shallow cavity, parallel proximation is adopted and the result established that the flow intensity, heat and mass transfer are considerably affected by radiation absorption and magnetic field depending on whether the tical radiation value, depending on the thermal Rayleigh number, for the onset of unstable convection is also established in this study. The
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Lateral mass flux and thermal radiation on natural convection heat and mass transfer from a vertical flat plate in porous media considering Soret/Dufour effects

Lateral mass flux and thermal radiation on natural convection heat and mass transfer from a vertical flat plate in porous media considering Soret/Dufour effects

Partha et al. (2006) examined the Soret and Dufour effects in a non-Darcy porous medium. Lakshmi Narayana and Murthy (2008) considered both the Soret and Dufour effects on a free convection boundary layer of a horizontal flat plate in a Darcy porous medium. Cheng (2009) reported the Soret and Dufour effects on natural convection heat and mass trans- fer from a vertical cone in a porous medium with uniform wall temperature and concentration (UWT/UWC). The Soret and Dufour effects on heat and mass transfer by natural convec- tion from a vertical truncated cone in a fluid-saturated porous medium with variable wall temperature and concentration were studied by Cheng (2010) . Makinde (2011) studied the mixed convection flow with Soret and Dufour effects past a vertical plate embedded in a porous medium. Makinde et al. (2012) used a numerical method to study of chemically- reacting hydromagnetic boundary layer flow with Soret/ Dufour effects and a convective surface boundary condition.
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Heat and mass transfer by Natural convection around a hot body in a rectangular cavity

Heat and mass transfer by Natural convection around a hot body in a rectangular cavity

Gebhart and Pera [15], using the similarity method, investigated the laminar ows which arise in uids due to the interaction of the force of gravity and density dierences caused by the simultaneous diusion of thermal energy and chemical species. Bejan [16] presented a fundamental study of laminar natural convection in a rectangular enclosure with heat and mass transfer from the side. He used scale analysis to determine the scales of the ow, temperature and concentration elds in boundary layer ow for all values of Prandtl and Lewis numbers. He investigated the case of N = 0 to study the heat-transfer-driven ows. Wee et al. [17] investigated numerically and experimentally the same problem for both horizontal and vertical cavity. The experimental technique employed two porous plastic plates as two cavity walls allowing the imposition of simultaneous moisture and temperature gradients.
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The effect of temperature-dependent solubility on the onset of thermosolutal convection in a horizontal porous layer

The effect of temperature-dependent solubility on the onset of thermosolutal convection in a horizontal porous layer

There are many opportunities for further theoretical work to explore the thermosolutal reaction–convection system described here. Natural extensions of the stability analysis include considering other boundary conditions at the upper and lower surfaces (for exam- ple, heat flux conditions or chemical disequilibrium), or studying the role of effects such as anisotropic permeability or nonlinear equilibrium solubility curves. In a future study, we intend to investigate further the nonlinear dynamics of the system, with a particular focus on behaviour in the subcritical SS regime (which Mamou & Vasseur (1999) found to be particularly rich in the case of pure DDC), on quantifying heat and mass transfer across the layer, and on the long-term evolution of the porous matrix as precipitation and dissolution affects its porosity and permeability. It is likely that in this paper we have done no more than to scratch the surface of an interesting and complicated problem.
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A thermal non-equilibrium model with Cattaneo effect for convection in a Brinkman porous layer

A thermal non-equilibrium model with Cattaneo effect for convection in a Brinkman porous layer

2. Mathematical Formulation We consider a horizontal layer of Brinkman porous medium of thickness d . The lower surface is held at constant temperature T , while the upper surface is at l T (< u T ). A Cartesian l coordinate system ( , , ) x y z is chosen such that the origin is at the bottom of the porous layer and the z-axis vertically upward in the presence of gravitational field. The solid and fluid phases of the porous medium are assumed to be in local thermal non-equilibrium (LTNE) with a two-field model for temperatures. The solid temperature equation is modified to allow the heat transfer via a Cattaneo heat flux theory, while the usual Fourier heat-transfer law is used in the fluid. The basic equations governing the flow of an incompressible fluid saturating a layer of Brinkman porous medium with LTNE and Cattaneo effect in the solid are [2, 16]
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Natural convection flow and heat transfer in an enclosure containing staggered arrangement of blockages

Natural convection flow and heat transfer in an enclosure containing staggered arrangement of blockages

4.1. The 12×6 arrangements The influence of staggered arrangement of blockages on the flow and heat transfer is analysed by comparing the results with in-line arrangements. Figure 3 shows the temperature profile at mid-width and near the bottom part of the cavity. A nearly similar pattern is observed for the top part and hence is omitted to avoid repetition. The change in temperature between the two configurations is significant especially near the passive horizontal walls, with a maximum of about 2.5 ᴼC and is found to occur within the boundary layer. The effect due to staggering is more prominent up to y/H=0.15 after which a stable core region can be seen. The turbulence intensity for the two configurations is shown in Fig. 4. It can be observed that the effect is very prominent on turbulence intensity. The average Nusselt number for the two configurations presented in Table 1 shows that the staggering reduces the heat transfer by a modest 7%.
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Effect of the Wavy permeable Interface on Double Diffusive Natural Convection in a Partially Porous Cavity

Effect of the Wavy permeable Interface on Double Diffusive Natural Convection in a Partially Porous Cavity

conditions. An analytical and numerical study of natural convection heat and mass transfer through a vertical porous layer subjected to a concentration difference and a temperature difference in the horizontal direction has been studied by Trevisan and Bejan [27]. Many physical systems were modelled as a two-dimensional cavity with the vertical walls held at fixed but different temperatures or concentrations and the connecting horizontal walls considered as adiabatic or impermeable Angirasa et al. [28] were reported a numerical study of combined heat and mass transfer by natural convection adjacent to vertical surfaces situated in fluid saturated porous media. Akbal and Baytas [29] have investigated a radioactive gas transfer depending on the decay of the gas, Schmidt and concentration Grashof numbers by natural convection in a fluid saturated porous medium. Merkin and Mahmood [30] have investigated a model for the convective flow in a fluid-saturated porous medium containing a reactive component. Goyeau et al. [31] have studied the double diffusive natural convection using Darcy—Brinkman formulation in a porous cavity with impermeable boundaries. Bahloul et al. [32] have investigated the double diffusive convection in a long vertical cavity heated from the below and imposed concentration gradient from the sides both analytically and numerically.
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Free convection heat transfer of MgO-MWCNTs/EG hybrid nanofluid in a porous complex shaped cavity with MHD and thermal radiation effects

Free convection heat transfer of MgO-MWCNTs/EG hybrid nanofluid in a porous complex shaped cavity with MHD and thermal radiation effects

Complex shape enclosures and wavy geometries are utilized in various engineering designs to enhance transport performance (Sheremet et al., 2016). In this regard, many of literature studies addressed the natural convection heat transfer (Khanafer, 2014). For instance, Adjlout et al. (2002) theoretically addressed the influence of a wavy wall of the convective heat transfer for various value of Rayleigh number, cavity inclination angles. The outcomes reveal that the geometry of the cavity walls influences the flow and heat transfer rate in the cavity. Mahmud et al. (“Free convection in an enclosure with vertical wavy walls”, 2002) studied the effect of amplitude and aspect ratio of a wavy wall on the convective heat transfer characteristics in an enclosure. Yu and Xu (2018) investigated the effect of various thermal boundary conditions on the heat transfer in a cavity and revealed using a finite element method. The natural convection over vertical plates is also studied by Ahmed and Mahdy (2016) and Ahmed (2017).
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Natural Convection Flow and Heat Transfer in an Enclosure Containing Staggered Arrangement of Blockages

Natural Convection Flow and Heat Transfer in an Enclosure Containing Staggered Arrangement of Blockages

4.1. The 12×6 arrangements The influence of staggered arrangement of blockages on the flow and heat transfer is analysed by comparing the results with in-line arrangements. Figure 3 shows the temperature profile at mid-width and near the bottom part of the cavity. A nearly similar pattern is observed for the top part and hence is omitted to avoid repetition. The change in temperature between the two configurations is significant especially near the passive horizontal walls, with a maximum of about 2.5 ᴼC and is found to occur within the boundary layer. The effect due to staggering is more prominent up to y/H=0.15 after which a stable core region can be seen. The turbulence intensity for the two configurations is shown in Fig. 4. It can be observed that the effect is very prominent on turbulence intensity. The average Nusselt number for the two configurations presented in Table 1 shows that the staggering reduces the heat transfer by a modest 7%.
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Thermal radiation effect on an unsteady MHD natural convection Couette flow with Heat and mass transfer

Thermal radiation effect on an unsteady MHD natural convection Couette flow with Heat and mass transfer

In all these investigations, the radiation effects are neglected. For some industrial applications such as glass production and furnace design and in space technology applications, such as cosmical flight aerodynamics rocket, propulsion systems, plasma physics and spacecraft re – entry aerothermodynamics which operate at higher temperatures, radiation effects can be significant. Alagoaet al. [24] studied radiative and free convection effects on MHD flow through porous medium between infinite parallel plates with time – dependent suction. Bestman and Adjepong [25]analyzed unsteady hydromagnetic free convection flow with radiative heattransfer in a rotating fluid.Promise Mebine and Emmanuel MunakuroghaAdigio [26]investigates the effects of thermal radiation on transientMHD free convection flow over a vertical surface embedded in a porousmedium with periodic temperature. Analytical solutions are obtainedfor the governing coupled dimensionless partial differential equations ofvelocity and temperature.An unsteady, two – dimensional, hydromagnetic, laminar free convective boundary – layer flow of an incompressible, Newtonian, electrically conducting and radiating fluid past an infinite heated verticalporous plate with heat and mass transfer is analyzed by Ramachandra Prasad and Bhaskar Reddy [27], by takinginto account the effect of viscous dissipation. The dimensionlessgoverning equations for this investigation are solved analyticallyusing two – term harmonic and non – harmonic functions.The influence of viscous dissipation and radiation on an unsteady MHD freeconvection flow past an infinite heatedvertical plate in a porous medium with time – dependent suction was studied by Israel – Cookeyet al.[28].
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Darcian natural convection in an inclined trapezoidal cavity partly filled with a porous layer and partly with a nanofluid layer

Darcian natural convection in an inclined trapezoidal cavity partly filled with a porous layer and partly with a nanofluid layer

Some important conclusions from the study are provided as follows: It is found that when the nanoparticle volume fraction is applied, the circulation intensity increases due to the increase in thermal conductivity of the nanofluid. The conduction heat transfer pushes the isotherms within the porous layer to take almost a diagonal shape, while the convection mode heat transfer forces the isotherms within the nanofluid layer to appear almost horizontal to the sloping walls. A higher nanoparticle volume fraction (φ = 0.2) leads to a higher overall Nusselt number due to higher thermal conductivity. The smaller porous layer thickness (S = 0.3) has stronger effect on the heat transfer rate, which has the higher average Nusselt number due to lower thermal conductivity of pure fluid compared to that of nanofluid. Qualitatively, the enhanced-heat transfer situation is seen in all the three nanofluids compared to that of the base fluid but the following general result holds: Nu water–Ag > Nu water–Cu > Nu water–TiO2 . The ramification of this
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Effect of Rayleigh Numbers on Natural Convection and Heat Transfer with Thermal Radiation in a Cavity Partially Filled with Porous Medium

Effect of Rayleigh Numbers on Natural Convection and Heat Transfer with Thermal Radiation in a Cavity Partially Filled with Porous Medium

In this paper, the effects of Rayleigh numbers on natural convection and heat transfer with thermal radiation in a cavity partially filled with a porous medium have been studied numerically. The governing equations for the momentum and heat transfer in both free fluid and porous medium were solved by the finite element method. The radiative heat transfer is calculated by making use of the radiosity of the surfaces that assumed to be grey. Comparisons with experimental and numerical results in the literature have been carried out. Effects of Rayleigh number on natural convection and heat transfer in both free fluid and porous medium were analyzed. It was found that Rayleigh numbers can significantly change the temperature fields in both the regions of free flow and porous medium. The mean temperature at the interface decreases and the temperature gradients are created on the upper two corners of the porous medium region as Ra increases.
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Natural convection heat transfer of nanofluids along a vertical plate embedded in porous medium

Natural convection heat transfer of nanofluids along a vertical plate embedded in porous medium

very few studies have been done for the natural convec- tion of nanofluids in porous media. Nield and Kuznetsov [24] studied the Cheng-Minkowycz problem for natural convection boundary layer flow in a porous medium satu- rated by a nanofluid. In the modeling of the problem, they used nanofluids by incorporating the effects of Brownian motion and thermophoresis. For the porous medium, the Darcy model was taken. Aziz et al. [25] found the numer- ical solution for the free convection boundary layer flow past a horizontal flat plate embedded in porous medium filled by nanofluid containing gyrotactic microorganisms. Recently, Rana et al. [26] found the numerical solution for steady-mixed convection boundary layer flow of a nano- fluid along an inclined plate embedded in a porous medium. In the studies of natural convection of nanofluids in porous media, the authors did the parametric study only. However, they did not account any effect of para- meters influencing the thermal conductivity and dynamic viscosity, such as particle concentration, particle size, temperature, nature of base fluid, and the nature of nano- particle, which satisfy the experimental data for the ther- mal conductivity and dynamic viscosity of the nanofluids. In the best knowledge of the authors of this article, no such study has been done with regard to the natural con- vection of nanofluids in porous media. It is known that heat transfer in a fluid depends upon the temperature dif- ference in fluid and heated surface and the thermophysical properties of the fluid. Heat transfer also depends upon the fluid flow rate, which depends upon the viscosity of the fluid.
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Effect of Sinusoidal Heating on Natural Convection Coupled to Thermal Radiation in a Square Cavity Subjected to Cross Temperature Gradients

Effect of Sinusoidal Heating on Natural Convection Coupled to Thermal Radiation in a Square Cavity Subjected to Cross Temperature Gradients

Natural convection coupled with surface radiation in closed cavities has been extensively studied using nu- merical simulations and experiments, owing to the prac- tical importance of such configurations in many engi- neering applications (convective heat losses from solar collectors, thermal design of buildings, air conditioning and, recently, electronic cooling). The majority of the existing studies, which are of numerical nature, con- cerned with rectangular cavities where the temperature gradient is either horizontal or vertical, including differ- ent kinds of boundary conditions [1-6]. Results of these studies show that radiation affects the dynamical and thermal structures of the fluid, reduces natural convec- tion heat transfer component, and contributes to increase the total amount of heat exchanged in the configurations considered. Most of the works conducted in the past on natural convection coupled with radiation inside rectan-
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Mixed Convection Heat Transfer in a Lid Driven Cavity with Wavy Bottom Surface

Mixed Convection Heat Transfer in a Lid Driven Cavity with Wavy Bottom Surface

transfer occurs due to the temperature difference across the fluid layer, one horizontal solid surface being at a temperature higher than the other. If the upper plate is the hot surface, then the lower surface has heavier fluid and by virtue of buoyancy, the fluid would not come to the lower plate. Because in this case the heat transfer mode is restricted to only conduction. Convection is the heat transfer mechanism affected by the flow of fluids. The amount of energy and matter are conveyed by the fluid can be predicted through the convective heat transfer. The convective heat transfer splits into two branches; the natural convection and the forced convection. Forced convection regards the heat transport by induced fluid motion which is forced to happen. This induced flow needs consistent mechanical power. However, natural convection differs from the forced convection through the fluid flow driving force, which happens naturally. The flows are driven by the buoyancy effect due to the presence of density gradient and gravitational field. As the temperature distribution in the natural convection depends on the intensity of the fluid currents which is dependent on the temperature potential itself, the qualitative and quantitative analysis of natural convection heat transfer is very difficult. Numerical investigation instead of theoretical analysis is more needed in this field.
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Natural Convection Heat Transfer in Cylindrical Enclosure of Porous Media with Periodic Boundary Conditions

Natural Convection Heat Transfer in Cylindrical Enclosure of Porous Media with Periodic Boundary Conditions

Free convection heat transfer from inclined wavy surface has received attention because of its vast applications. Some of these applications include ground water flows, oil recovery processes, thermal insulation engineering food processing etc. Extensive literature on the topic is availed for porous media, Slimi et. al. 1998[1] studied two – dimensional and transient fluid flow and heat transfer by natural convection in a vertical cylinder opened at both ends filled with a saturated porous medium and heated with a uniform lateral heat flux. The study was carried out using the forchheimer – extended Darcy flow model. Taofik et.al. 1999[2] studied unsteady natural convection which occurs in a vertical cylindrical enclosure opened at both ends, filled with a fluid saturated porous medium with a periodic lateral heat flux density. The study was carried out by the use of the Darcy law and it takes in to account heat conduction in the wall. The set of equations was solved numerically by the standard finite volume method. Saaed 2000[3] proposed a simple numerical expression for average Nusselt numbers over isothermal horizontal cylinder for all Rayleigh by using Darcy flow model. And also Khalid Abd.Al-hussein 2001[4] obtained a simple relation for Nusselt number which is a strong function of modified Rayleigh number, time, radius ratio, and aspect ratio. AL-Najar 2004[5] used the finite difference method to investigate the steady free convection from a two separated horizontal cylinders embedded in saturated porous media bounded by rectangular cavity. The cylinders kept isothermally hot while the bounded cavity is isothermally. It found that the large heat gained to the cavity been at the upper horizontal wall above cylinders. Saleh 2008[6] studied numerically unsteady natural convection heat transfer through a fluid–saturated porous media in inclined pipe enclosure. The temperature at cylindrical sidewall Tw was
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