An Experimental and Numerical Study of Natural Convection Heat Transfer in Horizontal Annuli between Eccentric Cylinders

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Numerical Simulation of Natural Convection in Circular Enclosures with Inner Polygonal Cylinders,with Confirmation by Experimental Results

Numerical computations are performed for the natural convection in circular enclosures with inner polygonalcylinders.The polygon surface and the outer envelope are at constant but different temperatures,A body-fittedcoordinate system is used,The coordinate system is generated via simple algebraic equations.The transformedgoverning equations are discretized on a control volume basis with power-law finite difference scheme.TheSIMPLE-like algorithm is used to deal with the linkage between pressure and velocities.The numerical resultsare compared with the experimental data available in the literature,and the agreement between the numericaland experimental results are very good.     

Numerical Study of Natural Convection on Horizontal Strips Embedded in an Vertical Adiabatic Substrate

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Numerical Simulations of Convective Heat Transfer in Rayleigh-Bénard Convection and a Rotating Annulus

ABSTRACT

Numerical studies of fluid and heat flows in a sealed rotating annulus having a heated outer cylinder and a cooled inner cylinder are performed. Flow is induced by buoyancy in the centrifugal field and affected by the Coriolis force. We focus on the heat transfer efficiencies characterized by correlations of Nusselt number with Rayleigh number ( Nu ～ Ra^γ); however, the flow structures are also discussed. We begin with a discussion of recent progress in Rayleigh-Bénard convection. Its connection to the rotating annulus systems used in the current study are then described. We hope to present a clearer picture of free-convective heat transfer in enclosures by comparing and interpreting results from various systems. Typical values for γ vary between 1/5 and 1/2 inclusive.     

Laminar Natural Convective Heat Transfer in the Enclosed Evacuated Collector Tube with East—West Symmetric Heat Input

INTR0DUCTI0NNaturalconvectioninenclosureshasbeenfoundinavariety0fapplications,suchassolarcollectors,nu-cleartechn0logies,thecoolingofelectronicalcircuits,etc.Amongthemnaturalconvectioninsideanen-closedrectangularcavityisthemostclassicalproblem.Correspondinglyagreatdealofexperimentalandnumericalworkhasbeendoneinsuchafieldwiththe"clean"boundaryCPnditi0nsofuniformwalltem-perature(UWT)anduniformheatflch(UHF).Re-celltlymoreattelltionispaidontheconvectioninthecirculartube.HwangandLai[11inves…     

Natural Convective Heat and Mass Transfer of Water with Corrosion Products at Super—Critical Pressures under Cooling COnditions

A numerical study is reported of laminar natural convective heat and mass transfer on a vertical cooled plate for water containing metal corrosion products at super-critical pressures. The influence of variable properties at super-critical pressures on natural convection has been analyzed. The difference between heat and mass transfer under cooling or heating conditions is also discussed and some correlations for heat and mass transfer under cooling conditions are recommended.     

Analysis of Natural Convection in an Elliptical Cavity,Using a Dini Expansion

INTRODUCTIONNaturalconvectioninanellipticalcavityheatedfrombelowwastreatednumericallybyM..him.ull],usingaFourierspectralfinitedifferencemethod,anditseffectivenesswasshownasinRef.[2].AlsopossibilityoftheextensiontovarioustypesofboundaryconditionsforthespectralfinitedeferenceschemewasproposedinReL[2-3].HerethespectralfinitedifferenceschemeisbeingextendedtoadoptDimexpansions(akindofBesselexpansions).NUMERICALANAlySISBasicAssumptionsbleatedistransiellttwo--dimensionalnaturallaminarco…     

Heat Transfer and hydrodynamics in Annular Chromatography：CFD—Simulation and Experiments

IntrotctiouAImular chrDmatography Provides the POssibility ofseparating multicomponent fixtures continuously inone single unit. The rotating annulus of thechromatotw can be filled with arbitw stationalsPhases depending on the existing separation Problem.The feed is introduced at a fixed and stationary sechonat the top of the unit, while the eluent is distributedeverywhere else around the upper circumference. At thebottom the separated Products can be collected atcendn stationals exit angle…     

Natural Convective Heat and Mass Transfer on a Vertical Heated Plate for Water Flow Containing Metal Corrosion Particles

Corrosion products of structural materials when contained in water usually are in two states:soluble state andcolloidal particles with diameter about 10~(-3)—10~(-1)μm.Deposits of such corrosion products on tube surfacesunder high pressure will jeopardize the operating economy of power plant equipment and even result in accidents.A numerical study is reported in this paper of the natural convective heat and mass transfer on a vertical heatedplate subject to the first or mixed kind of boundary conditions for high-pressure water(P=17MPa)containingmetal corrosion products with consideration of variable thermophysical properties.     

Experimental and Numerical Investigation of Enhancement of Heat and Mass Transfer in Adsorbent Beds

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A numerical study of natural convection heat transfer in a composed thermal diode

The effects of inclination on the steady natural convection local heat transfer characteristics in an air-filled enclosure, which is composed of rectangular and parallelogrammic portions, are studied numerically. In this investigation, two geometrical aspect ratios are introduced: one for a parallelogrammic portion of an enclosure, the other for a rectangular one. The governing equations for a two-dimensional, laminar, natural convection process in an enclosure are discretized by the control volume approach which ensures the conservative characteristics to be satisfied in the calculation domain, and then solved by a modified SIMPLE algorithm. The momentum and energy equations are coupled through the buoyancy term. Computations are carried out for Prandtl number Pr = 1 and Rayleigh number Ra = 2.7 × 10⁸. In order to obtain a greater understanding of the flow and heat transfer behaviors, flow patterns with streamlines and isotherms at different inclination angles are shown. Also, the effects of numbers of installed guide vanes in a composed enclosure are studied to consider the enhancement of heat transfer of the inner diode. © 1999 Scripta Technica, Heat Trans Asian Res, 28(7): 573–582, 1999     

Enhancement of natural convection heat transfer from an inclined heated plate using rectangular grids

The effect of an inclination angle on the natural convection heat transfer from an inclined heated plate with rectangular grids is investigated. Heat transfer coefficients are measured in air when the plates are inclined at angles from ?30 to +60 from a vertical plane, grid heights are in the range of 5 to 10 mm, and diagonal lengths of the grid are 25, 50, 100, and 200 mm. For each configuration, the surface heat flux ranges from 50 to 200 W/m². It is found that the rectangular grids increase local heat transfer coefficients when the grids are applied to an inclined plate. The rectangular grids increase the average heat transfer coefficients along the horizontal centerline of the plate by up to 20% compared to those coefficients of a smooth plate, even when the angles of inclination are ±30° © 2002 Wiley Periodicals, Inc. Heat Trans Asian Res, 31(5): 408–419, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.10043     

Experimental study of natural convection heat transfer in a semicircular enclosure

An experimental study of natural convection heat transfer in a differentially heated semicircular enclosure was carried out. The flat surface was heated and the radial surface was cooled isothermally. The effects of angle of enclosure inclination on the heat transfer across semicircular regions of several radii were measured for Rayleigh numbers Ra_R ranging from 6.72 × 10⁶ to 2.33 × 10⁸, using water as the working fluid. The angle of inclination varied from −90 degrees to 90 degrees with radii R of 50, 40, and 30 mm. The flow patterns were sketched from the results of a visualization experiment using aluminum powder. The temperature measurements in the enclosure were carried out using liquid crystals and thermocouples. The results indicate that different flow patterns were encountered as the angle of inclination varied, and the heat transfer rate was largely dependent on the flow pattern. In particular, enhanced heat transfer rates can be obtained when plume-like flow occurs along both hot and cold walls in the case of an upward-facing hot wall. Heat transfer for the inclined enclosure can be predicted using the equation for a vertical enclosure presented in this paper. © 1998 Scripta Technica, Inc. Heat Trans Jpn Res, 26(2): 131–142, 1997     

Experimental determination of natural convection heat transfer coefficients in an attic shaped enclosure

Heat transfer by natural convection in triangular enclosures is an area of significant importance in applications such as the design of greenhouses, attics and solar water heaters. However, given its significance to these areas it has not been widely examined. In this study, the natural convection heat transfer coefficients for air in an attic shaped enclosure were determined for Grashof Numbers over the range of 10⁷ to 10⁹. It was found that the measured heat transfer coefficients could be predicted to within 5% by Ridouane and Campo's [E.H. Ridouane, A. Campo, Experimental-based correlations for the characterization of free convection of air inside isosceles triangular cavities with variable apex angles, Experimental Heat Transfer 18 (2) (2005) 81–86] equation (Eq. (1)) for natural convection in a triangular enclosure previously developed for Grashof Numbers in the range of 10⁵ to 10⁶.

equation(1)

Nu=0.286A−0.286Gr1/4.$Nu=0.286A^{-0.286}G{r}^{1/4}\text{.}$

Vibration effects on the average heat transfer characteristics of the natural convection field in a square enclosure

In order to study the chaotic behavior of vibrational thermal convection in a square enclosure, a calculation method and the features of the average Nusselt number with vibration frequency were precisely examined. In the computation, the Prandtl number, the Rayleigh number, and the vibration Grashof number were held constant at 0.71, 10⁴, and 10⁶, respectively. The angular frequency of vibration was changed in the range between 10 and 7680. The results showed that the phenomena could be predicted with the calculation method adopted in this paper and the change in the time‐dependent characteristics of surface‐averaged Nusselt number with the angular frequency of vibration could be analyzed well with the power spectra. These changes were characterized by the five regimes proposed by Fu and Shieh. Moreover, it was clarified that the region where the hysteresis phenomena were detected corresponded to the one where the variation of the surface‐averaged Nusselt number was irregular and aperiodic. © 2000 Scripta Technica, Heat Trans Asian Res, 29(7): 545–558, 2000     

Suppression of natural convection heat transfer coefficients in an attic shaped enclosure

The use of convection suppression devices has been widely discussed in the literature as a means of reducing natural convection heat loss from enclosed spaces. In this study the use of a single baffle was examined as a possible low cost means of suppressing heat loss by natural convection in an attic shaped enclosure.     

Fluid flow and heat transfer in the transition process of natural convection over an inclined plate

The present study deals with fluid flow and heat transfer in the transition process of natural convection over an inclined plate. In order to examine the mechanism of the transition process, experiments on the flow and heat transfer were performed for various plate inclination angles in the range of 20 to 75°. The wall temperature and fluid flow fields were visualized using a liquid crystal sheet and fluorescent paint, respectively. The visualization confirmed that separation of a boundary layer flow took place, and the onset point of streaks appeared over the plate wall when the modified Rayleigh number exceeded a characteristic value for each inclination angle. The local Nusselt number in the transition range was proportional to the one‐third power of the local modified Rayleigh number. By introducing a nondimensional parameter, a new correlation between visualizations of the flow and temperature fields and heat transfer was proposed. © 2001 Scripta Technica, Heat Trans Asian Res, 30(8): 648–659, 2001     

Numerical predictions of natural convection with liquid fluids contained in an inclined arc-shaped enclosure

In the present paper a numerical study has been performed of the flow behavior and natural convection heat transfer characteristics of liquid fluids contained in an inclined arc-shaped enclosure. The governing equations are discretized using the finite-volume method and curvilinear coordinates. The Prandtl number (Pr) of the liquid fluids is assigned to be 4.0 and the Grashof number (Gr) is ranged within the regime 1 × 10⁵ ≦ ≦ 4 × 10⁶. On the other hand, the inclination angle (θ) of the enclosure is varied within 0° ≦ θ ≦ 360°. Of major concern are the effects of the inclination and the buoyancy force on the flow and the thermal fields, and based on the numerical data of the thermal field the local and overall Nusselt numbers are calculated. Results show that the arc-shaped enclosure for Pr = 4.0 at Gr = 4 × 10⁶ and θ = 90° exhibits the best heat transfer performance. The poor heat transfer performance for Pr = 4.0 fixed at Gr = 1 × 10⁵ and θ = 180° exhibits the arc-shaped enclosure, respectively. As the value of Grashof number is elevated from 10⁵ to 4 × 10⁶, at θ = 90°, the magnitude of Nu is elevated from 13.946 to 25.3 (81.4% increase); however, at θ = 180°, the magnitude is elevated from 11.655 to 13.475 (15.6% increase) only.     

Lattice Boltzmann simulation of natural convection heat transfer in an elliptical-triangular annulus

A numerical study for steady-state, laminar natural convection in a horizontal annulus between a heated triangular inner cylinder and cold elliptical outer cylinder was investigated using lattice Boltzmann method. Both inner and outer surfaces are maintained at the constant temperature and air is the working fluid. Study is carried out for Rayleigh numbers ranging from 1.0 × 10³ to 5.0 × 10⁵. The effects of different aspect ratios and elliptical cylinder orientation were studied at different Rayleigh numbers. The local and average Nusselt numbers and percentage of increment heat transfer rate were presented. The average Nusselt number was correlated. The results show that by decreasing the value of aspect ratio and/or increasing the Rayleigh number, the Nusselt number increases. Also the heat transfer rate increases when the ellipse positioned vertically.     

Conjugate natural convection heat transfer in an inclined square cavity containing a conducting block

The present work is concerned with computation of natural convection flow in a square enclosure with a centered internal conducting square block both of which are given an inclination angle. Finite volume method through the concepts of staggered grid and SIMPLE algorithm have been applied. Deferred QUICK scheme has been used to discretize the convective fluxes and central difference for diffusive fluxes. The problem of conjugate natural convection has been taken up for validating the code. The abrupt variation in the properties at the solid/fluid interface are taken care of with the harmonic mean formulation. Solution has been performed in the computational domain as a whole with proper treatment at the solid/fluid interface. Computations have been performed for Ra = 10³–10⁶, angle of inclination varying from 15° to 90° in steps of 15° and ratio of solid to fluid thermal conductivities of 0.2 and 5.0. Results are presented in terms of streamlines, isotherms, local and average Nusselt number.