Showing papers in "Numerical Heat Transfer Part A-applications in 2003"
TL;DR: In this article, a numerical study is conducted to investigate mixed convective cooling of a two-dimensional rectangular cavity with differentially heated side walls, where cold fluid is blown into the cavity from an inlet in the side wall of the cavity and is exited through an outlet in the opposite side wall.
Abstract: A numerical study is conducted to investigate mixed convective cooling of a two-dimensional rectangular cavity with differentially heated side walls. The horizontal walls are assumed to be adiabatic. Cold fluid is blown into the cavity from an inlet in the side wall of the cavity and is exited through an outlet in the opposite side wall. This configuration of mixed convective heat transfer has application in building energy systems, cooling of electronic circuit boards, and solar collectors, among others. The objective of the research is to optimize the relative locations of inlet and outlet in order to have most effective cooling in the core of the cavity by maximizing the heat-removal rate and reducing the overall temperature in the cavity. Various placement configurations of the inlet and outlet are examined for a range of Reynolds number and Richardson number. For a given Reynolds number, the Richardson number is varied from 0, which represents pure forced convection, to 10, which implies a dominant b...
145 citations
TL;DR: In this article, a simplified one-dimensional, parabolic, two-step model is solved numerically to predict heating, melting, and evaporation of metal under femtosecond laser irradiation.
Abstract: The short time scales and high intensities obtained during femtosecond laser irradiation of metals require that heat transfer calculations take into account the nonequilibrium that exists between electrons and the lattice during the initial laser heating period. Thus, two temperature fields are necessary to describe the process--the electron temperature and the lattice temperature. In this work, a simplified one-dimensional, parabolic, two-step model is solved numerically to predict heating, melting, and evaporation of metal under femtosecond laser irradiation. Kinetic relations at the phase-change interfaces are included in the model. The numerical results show close agreement with experimental melting threshold fluence data. Further, it is predicted that the solid phase has a large amount of superheating and that a distinct melt phase develops with duration of the order of nanoseconds.
142 citations
TL;DR: In this article, the authors studied mixed convection in an open cavity with a heated wall bounded by a horizontally insulated plate and showed that the maximum temperature values decrease as the Reynolds and the Richardson numbers increase.
Abstract: Mixed convection in an open cavity with a heated wall bounded by a horizontally insulated plate is studied numerically. Three basic heating modes are considered: (a) the heated wall is on the inflow side (assisting flow); (b) the heated wall is on the outflow side (opposing flow); and (c) the heated wall is the horizontal surface of the cavity (heating from below). Mixed convection fluid flow and heat transfer within the cavity is governed by the buoyancy parameter, Richardson number (Ri), and Reynolds number (Re). The results are reported in terms of streamlines, isotherms, wall temperature, and the velocity profiles in the cavity for Ri=0.1 and 100, Re=100 and 1000, and the ratio between the channel and cavity heights (H/D) is in the range 0.1-1.5. The present results show that the maximum temperature values decrease as the Reynolds and the Richardson numbers increase. The effect of the H/D ratio is found to play a significant role on streamline and isotherm patterns for differentheating configurations....
132 citations
TL;DR: In this article, the authors studied free convective laminar flow of a fluid with or without internal heat generation in rectangular enclosures of different aspect ratios and at various angles of inclination.
Abstract: Numerical investigations are conducted for free convective laminar flow of a fluid with or without internal heat generation in rectangular enclosures of different aspect ratios and at various angles of inclination Two principal parameters for this problem are the external Rayleigh number, Ra E , which represents the effect due to the differential heating of the side walls, and the internal Rayleigh number, Ra I , which represents the strength of the internal heat generation Results are obtained for a fixed external Rayleigh number, Ra E =2 2 10 5 , with internal Rayleigh number, Ra I =0 (without internal heat generation), and also with Ra I =2 2 10 5 (with internal heat generation) Flow patterns and isotherms do not show any significant difference between the cases with and without internal heat generation other than slight shift and changes in stream function and isotherm values as long as the internal Rayleigh number Ra I is less than or equal to the external Rayleigh number Ra E Local heat flux ra
95 citations
TL;DR: In this article, a volumetric averaging of the microscopic transport equations for the turbulent kinetic energy, k, and its dissipation rate, l, is proposed for flow in porous media.
Abstract: Through the volumetric averaging of the microscopic transport equations for the turbulent kinetic energy, k , and its dissipation rate, l , a macroscopic model is proposed for flow in porous media. As an outcome of the volume-averaging process, additional terms appeared in the equations for k and l . These terms are adjusted assuming the porous structure to be modeled as an infinity array of transversally displaced elliptic rods. This adjustment is obtained by solving the microscopic flow governing equations numerically, using a low-Reynolds formulation, in the periodic cell composing the infinite medium. Different porosity and aspect ratios are investigated. The adjusted model is compared with similar results found in the literature. A general view of the effect of the medium morphology on model assumptions is obtained by comparing results for elliptic, cylindrical, and square rods.
83 citations
TL;DR: In this article, a mathematical model for simulating flow fields in porous textiles with consideration of gravity is described, which assumes that the liquid water moves in the composite network of capillaries of the porous textile and is carried to the surface by capillary action.
Abstract: A mathematical model for simulating flow fields in porous textiles with consideration of gravity is described in this article. The article focuses on the analysis of the physical model of liquid diffusion in porous textiles. The model assumes that the liquid water moves in the composite network of capillaries of the porous textile and is carried to the surface by capillary action. The analysis includes the capillary action with phase change and the gravity effects of the liquid water. The balance between capillary and gravity forces is measured by a dimensionless number (named GS number), " =3 l l l d c gL /2 cosφ l , which describes the ratio of gravity to surface tension force in porous textiles. On the basis of a fractional volume-of-fluid (VOF) method, the distributions of the temperature, moisture concentration, and liquid water content in the porous textiles the different degrees of hygroscopicity were computed numerically by this technique. The numerical solutions indicate that this model is sa...
81 citations
TL;DR: In this paper, the effects of relative surface roughness, roughness distribution, and gas rarefaction on flow were investigated and the results were presented in the form of the product of friction factor and Reynolds number.
Abstract: The paper presents direct simulation Monte Carlo (DSMC) results for nitrogen flow in a microchannel with surface roughness modeled by an array of rectangular modules placed on one side of a parallel-plate channel. The effects of relative surface roughness, roughness distribution, and gas rarefaction on flow are investigated and the results are presented in the form of the product of friction factor and Reynolds number. It was found that the effect of surface roughness is more pronounced at low Knudsen numbers. At high Knudsen numbers, rarefaction reduces the interaction between the gas molecules and the channel walls and results in a lower friction factor. The roughness distribution represented by the ratio of the roughness height to spacing of the modules has a significant effect on the flow and friction factor. Finally, the locally fully developed (LFD) flow model can be used to predict gas flow in a microchannel with low values of relative surface roughness.
81 citations
TL;DR: In this article, the authors identify models that are suitable for describing thermal transport in metal materials heated by a short-pulse laser and show that the dual-hyperbolic two-temperature model is the most suitable model for alloys.
Abstract: This article identifies models that are suitable for describing thermal transport in metal materials heated by a short-pulse laser. Three two-temperature models (dual-hyperbolic, hyperbolic, and parabolic), two one-temperature models (thermal wave and Fourier conduction), and one ultrafast thermomechanical model are investigated. A finite-difference method is used for solving the heat conduction equations, and a combined finite-difference/finite-element method is developed for solving the coupled thermomechanical equations. The numerical results, performed for gold films, suggest that for pure metals the hyperbolic two-temperature model be used for short-pulse ( 1-ns) laser heating. For alloys, the dual-hyperbolic two-temperature model is suggested for short-pulse (<10-ns) laser heating. Due to the high strain rate caused by nanosecond- and shorter-pulse lasers, a coupled thermomechanical model should be considered for more accurately predi...
80 citations
TL;DR: In this paper, a meshless element free Galerkin method is used to approximate the unknown function of temperature T h (x) with Th (x), which is constructed by using a linear basis, a weight function, and a set of nonconstant coefficients.
Abstract: This article deals with the transient and steady-state solution of two-dimensional heat transfer through the fins using a meshless element free Galerkin method. Moving least-square approximants are used to approximate the unknown function of temperature T h (x) with Th (x) . These approximants are constructed by using a linear basis, a weight function, and a set of nonconstant coefficients. The variational method has been used for the development of discrete equations. Essential boundary conditions are enforced by using Lagrange multipliers. A hyperbolic weight function has been proposed. The results are obtained for a two-dimensional model and compared with the results of the finite-element method.
78 citations
TL;DR: In this article, a prediction of radiative heat transfer in a complex geometry is performed using different boundary treatments such as blocked-off, spatial-multiblock, and embedded boundary methods.
Abstract: A prediction of radiative heat transfer in a complex geometry is performed using different boundary treatments such as blocked-off, spatial-multiblock, and embedded boundary methods. The formulation of embedded boundary treatment for finite volume is derived. The finite-volume method (FVM) is used to model the radiative transfer in an absorbing and emitting medium which is maintained at an isothermal condition and enclosed by cold and black walls. While the body-fitted grid system is used for the spatial multiblock treatment, the Cartesian grid system is chosen for the others. Their results are compared and discussed for three different cases, including a trapezoidal enclosure, a semicircular enclosure with internal block, and an incinerator-shaped enclosure. The accuracy obtained by application of each treatment is shown to be highly satisfactory. Consequently, each treatment is suitable for modeling the radiative heat transfer in the complex geometry. However, the solution obtained by the blocked-off tr...
74 citations
TL;DR: In this article, the authors present a numerical implementation for solving such a hybrid medium, considering here a channel partially filled with a porous layer through which fluid flows in the laminar regime.
Abstract: A number of natural and engineering systems can be characterized by some sort of porous structure through which a working fluid permeates. Boundary layers over tropical forests and spreading of chemical contaminants through underground water reservoirs are examples of important environmental flows that can benefit form appropriate mathematical treatment. For hybrid media, involving both a porous structure and a clear flow region, difficulties arise due to the proper mathematical treatment given at the interface. The literature proposes a jump condition in which stresses at both sides of the interface are not of the same value. The objective of this article is to present a numerical implementation for solving such a hybrid medium, considering here a channel partially filled with a porous layer through which fluid flows in laminar regime. One unique set of transport equations is applied to both regions. Numerical results are compared with available analytical solutions in the literature for two cases, namel...
TL;DR: In this article, the authors extended the discrete transfer method to solve transient radiative transport problems with a one-dimensional gray planar absorbing and anisotropic scattering medium, where the incident boundary of the medium is subjected to pulse-laser irradiation, while the other boundary is cold.
Abstract: Application of the discrete transfer method is extended to solve transient radiative transport problems with participating medium. A one-dimensional gray planar absorbing and anisotropically scattering medium is considered. Both boundaries of the medium are black. The incident boundary of the medium is subjected to pulse-laser irradiation, while the other boundary is cold. For radiative parameters such as optical thickness, scattering albedo, anisotropy factor, transmittance, and reflectance at the boundaries are found. Results obtained from the present work are compared with those available in the literature. The discrete transfer method has been found to give an excellent agreement.
TL;DR: In this article, the Navier-Stokes equations are solved using a finite-volume formulation and the free surface of a circular liquid jet is tracked by the volume-of-fluid method.
Abstract: The problem of convective heat transfer of a circular liquid jet impinging onto a substrate is studied numerically. The objective of the study is to understand the hydrodynamics and heat transfer of the impingement process. The Navier-Stokes equations are solved using a finite-volume formulation. The free surface of the jet is tracked by the volume-of-fluid method. The energy equation is modeled by using an enthalpy-based formulation. The effects of several key parameters on the hydrodynamics and heat transfer of an impinging liquid jet have been examined. The numerical results are in close agreement with experimental data obtained from the literature.
TL;DR: In this paper, a pin-fin heat sink, placed horizontally in a channel, is modeled as a hydraulically and thermally anisotropic porous medium, and a uniform heat flux is prescribed at the bottom of the heat sink.
Abstract: A numerical study has been carried out to optimize the thermal performance of a pin-fin heat sink. A pin-fin heat sink, which is placed horizontally in a channel, is modeled as a hydraulically and thermally anisotropic porous medium. A uniform heat flux is prescribed at the bottom of the heat sink. Cool air is supplied from the top opening of the channel and exhausts to the channel outlet. Comprehensive numerical solutions are derived from the governing Navier-Stokes and energy equations using the Brinkman-Forchheimer extended Darcy model and the local thermal nonequilibrium (LTNE) porous model for the region occupied by the heat sink. Results from this study indicate that the anisotropy in permeability and solid-phase effective thermal conductivity changes substantially with the variation of porosity. Optimum porosity for maximum heat dissipation depends on the pin-fin thickness, the pin-fin height, and the Reynolds number. A correlation for predicting the optimum porosity for a pin-fin heat sink is prop...
TL;DR: In this article, the effect of surface undulations on natural convection in a thermally stratified vertical porous enclosure has been analyzed numerically by the finite-element method, and the influence of increasing number of surfaces undulations with different wave phases (φ) and different wave amplitudes (a ) on the Nusselt number is analyzed.
Abstract: The effect of surface undulations on natural convection in a thermally stratified vertical porous enclosure has been analyzed numerically by the finite-element method. The influence of increasing number of surface undulations ( N ) with different wave phases (φ) and different wave amplitudes ( a ) has been analyzed. Increasing either number of waves per unit length ( N ) or wave amplitudes ( a ) or thermal stratification ( S ) is seen to decrease Nusselt number (Nu). Interestingly, the periodic variation in Nu with wave phase in the presence of thermal stratification is seen to be sensitive to the number of waves ( N ) per unit length. Maximum heat flux is obtained when the wave phase 210° h φ h 240° for 0 h S h 1. Features such as secondary circulations near the wavy wall and multicellular circulations in the core of the flow field have been noticed.
TL;DR: In this article, the delta winglet-type vortex generators are mounted behind the tubes of a fin-tube heat exchanger for generating streamwise longitudinal vortices to enhance heat transfer in geothermal power plants.
Abstract: This investigation stems from the area of augmentation of heat transfer by generating streamwise longitudinal vortices. The vortex generators are arranged in a common-flow-up configuration. Existing air-cooled condensers in geothermal power plants use fin-tube heat exchangers with circular tubes. The heat exchangers are huge, and often the cost of the condensers is more than one-third of the plant cost. The size of the condensers can be reduced through enhancement of heat transfer from fin surfaces. The enhancement strategy involves introduction of strong swirling motion in the flow field. The swirl can be generated by the longitudinal vortices. In this study, the longitudinal vortices are created by delta winglet-type vortex generators, which are mounted behind the tubes. An element of a heat exchanger has been considered for detailed study of the flow structure and heat transfer analysis. Biswas and colleagues have obtained significant enhancement of heat transfer by deploying the winglet pair behind ea...
TL;DR: In this paper, a local subgrid diffusivity model for the large-eddy simulation of natural-convection flows in cavities is presented. But this model does not make use of the Reynolds analogy with a constant subgrid Prandtl number.
Abstract: We present a local subgrid diffusivity model for the large-eddy simulation of natural-convection flows in cavities. This model, which does not make use of the Reynolds analogy with a constant subgrid Prandtl number, computes the subgrid diffusivity independently from the subgrid viscosity along the lines of the mixed scale model for eddy viscosity. First, an a-priori test is performed from a direct numerical simulation (DNS) approach in order to compare the respective effects of the subgrid viscosity model and that introduced by the QUICK scheme used to discretize the convective terms in the momentum equations. Then the subgrid diffusivity model is applied to the case of a two-dimensional square cavity filled with air for a Rayleigh number of 5 2 10 10 . Comparisons with DNS reference results demonstrate significant improvements in capturing the general pattern of the flow and particularly in predicting the transition to turbulence in the boundary layers as compared with Reynolds analogy results. The infl...
TL;DR: In this article, an inverse analysis is employed to estimate the unknown heat flux distribution over the heater surface of an irregular 2D domain with participating media from the knowledge of a desired temperature and heat flux distributions over a given design surface.
Abstract: An inverse analysis is employed to estimate the unknown heat flux distribution over the heater surface of an irregular 2-D domain with participating media from the knowledge of a desired temperature and heat flux distributions over a given design surface. The discrete transfer method is employed to solve the radiative transfer equation and a conjugate gradient method is used for minimization of an objective function, which is expressed by the sum of square residuals between estimated and desired heat fluxes. The performance of the present technique for inverse radiation analysis is evaluated by several numerical experiments.
TL;DR: In this article, three-dimensional numerical simulations are performed of freckling during directional solidification of a binary metal alloy, and it is shown that, while it is possible to simulate freckle formation with a relatively coarse grid, local details are predicted inaccurately.
Abstract: Three-dimensional numerical simulations are performed of freckling during directional solidification of a binary metal alloy. The purpose of the study is to evaluate the sensitivity of the predictions to the grid resolution. Detailed results are provided for the liquid concentration, solid fraction, and liquid velocity distributions at different times. It is shown that, while it is possible to simulate freckle formation with a relatively coarse grid, many local details are predicted inaccurately. The results for the finest grid indicate that complete grid independence is difficult to achieve given present-day computing resources.
TL;DR: In this paper, the effects of Rayleigh number, Prandtl number, baffle height, and baffle location on the heat transfer in partially divided trapezoidal cavities representing industrial buildings were investigated.
Abstract: Numerical results are reported for natural-convection heat transfer in partially divided trapezoidal cavities representing industrial buildings. Two thermal boundary conditions are considered. In the first, the left short vertical wall is heated while the right long vertical wall is cooled (buoyancy-assisting mode along the upper inclined surface of the cavity). In the second, the right long vertical wall is heated while the left short vertical wall is cooled (buoyancy-opposing mode along the upper inclined surface of the cavity). The effects of Rayleigh number, Prandtl number, baffle height, and baffle location on the heat transfer are investigated. Results are displayed in terms of streamlines, isotherms, and local and average Nusselt number values. For both boundary conditions, predictions reveal a decrease in heat transfer in the presence of baffles, with its rate generally increasing with increasing baffle height and Pr. For a given baffle height, greater decrease in heat transfer is generally obtain...
TL;DR: In this paper, numerical computations were carried out for natural convection of air in a cubic enclosure under both magnetizing and gravitational force fields, where the air in the cubic enclosure is heated from one vertical wall and cooled from an opposing cold wall.
Abstract: Numerical computations were carried out for natural convection of air in a cubic enclosure under both magnetizing and gravitational force fields. The air in the cubic enclosure is heated from one vertical wall and cooled from an opposing cold wall. Two electric wires to produce a magnetic field are located outside the vertical side walls, perpendicular to the hot and cold walls. Computation for a nongravity field revealed that the magnetizing force attracts the cold air and repels the hot air. As a result, convection roll cells can be seen from the top plate, although usual natural-convection roll cells can be seen through a vertical side wall. Computations were carried for the combined force field of gravity and magnetism for the ranges of parameters Pr=0.71, Ra=10 4 , 10 5 , 10 6 , and 10 7 , and n =0, 0.1, 1, and 10, where n represents the strength of magnetic field. As n increases, the effect of the magnetizing force prevails. This can be understood from the model equation and the flow modes computed....
TL;DR: In this article, a numerical analysis was carried out to study the performance of mixed convection in a horizontal duct with two heated blocks mounted on the bottom plate and baffles arranged on the up plate.
Abstract: A numerical analysis was carried out to study the performance of mixed convection in a horizontal duct with two heated blocks mounted on the bottom plate and baffles arranged on the up plate. The effects of the dimensionless height of baffle H b , the dimensionless distance between the block and baffle D , and the number of baffle N on the flow structure and heat transfer characteristics were investigated for the system at various Reynolds number Re and ratio of Grashof number to square of Reynolds number Gr/Re 2 . With the two baffles installed at D 1 =0 and D 2 =0, results show that the maximum augmentation in the average Nusselt number of the second heated block exceeds 320% for H b1 = H b2 =0.4, Pr = 0.7, 100 h Re h 1,000, and 0 h Gr/Re 2 h 10, while the maximum augmentation is about 130% for the first heated block. When a single baffle is located between the two heated blocks, the heat transfer performance of both the first and second heated blocks can be significantly promoted. However, only the hea...
TL;DR: In this paper, a finite-volume model has been developed to study the gas flow and heat transfer of an optical fiber as it travels through a CVD reactor, with temperature changes over 50% observed under the conditions studied.
Abstract: A fundamental understanding of how reactor parameters influence the fiber surface temperature is essential to manufacturing high-quality optical fiber coatings by chemical vapor deposition (CVD). In an attempt to understand this process better, a finite-volume model has been developed to study the gas flow and heat transfer of an optical fiber as it travels through a CVD reactor. This study showed that draw speed significantly affects fiber temperature inside the reactor, with temperature changes over 50% observed under the conditions studied. Other parameters affecting fiber temperature include fiber radius, fiber coating emissivity, and gas flow velocity at inlet. Multiple heat transfer modes contribute to these phenomena, with convection and radiation heat transfer dominating the process. The numerical model is validated against analytical cases.
TL;DR: In this paper, the authors considered the heat and mass transfer problem in a trapezoidal cavity, where the lower part of the cavity is heated and the top inclined part is cooled.
Abstract: The heat and mass transfer problem in a trapezoidal cavity is treated in this article. The lower part of the cavity is heated and the top inclined part is cooled. Phenomenological equations are solved using the alternating direction implicit (ADI) method combined with a fourth-order compact Hermitian method. The results are compared to those obtained experimentally and numerically by other authors in the triangular and trapezoidal cavity cases. The thermoconvective instabilities obtained are similar to those obtained in rectangular cavities. The influence of geometric parameters, global solicitations, and Lewis numbers on fluid flow configurations and on heat and mass transfer ratios is also studied.
TL;DR: In this paper, pressure drop and heat transfer characteristics are investigated in the fully developed region of three-dimensional wavy channels whose aspect ratios (width over height) range from one to infinity.
Abstract: Pressure drop and heat transfer characteristics are investigated in the fully developed region of three-dimensional wavy channels whose aspect ratios (width over height) range from one to infinity. Numerical simulations show that Nusselt numbers and friction factors increase with decreasing aspect ratios, in such a way that global performances improve. In all the channels considered, friction factors always increase with the Reynolds number, while Nusselt numbers significantly increase only above the critical value of the Reynolds number at which self-sustained flow oscillations begin. In turn, the critical value of the Reynolds number decreases with the aspect ratio, down to a minimum that is reached asymptotically.
TL;DR: In this paper, the authors investigate the heat transfer characteristics of a silicon microstructure irradiated by picosecond-to-femtosecond ultrashort laser pulses from a microscopic point of view.
Abstract: This work aims to investigate the heat transfer characteristics of a silicon microstructure irradiated by picosecond-to-femtosecond ultrashort laser pulses from a microscopic point of view. Carrier-lattice nonequilibrium interactions are simulated with a set of governing equations for the carrier and lattice temperatures to obtain the time evolutions of the lattice temperatures, the carrier number densities, and carrier temperatures. In particular, the relaxation time for approaching the thermal equilibrium between carriers and lattices is introduced to estimate duration of the nonequilibrium state. An appropriate regime map to make a distinction between one-peak and two-peak structures is also established for picosecond laser pulses. It is noted that a substantial increase in carrier temperature is observed for pulse lasers of a few picoseconds duration, whereas the lattice temperature rise is relatively small with decreasing laser pulse widths. It is also found that the laser fluence significantly affec...
TL;DR: In this article, the P-1 radiation model and the renormalization group (RNG) k-k model are applied to simulate the turbulent convective heat transfer with thermal radiation in the curved pipe at a constant wall temperature.
Abstract: The combined turbulent forced-convective and radiative heat transfer of a participating medium in the entrance region of a curved pipe is investigated numerically. The P-1 radiation model and the renormalization group (RNG) k- k model are applied to simulate the turbulent convective heat transfer with thermal radiation in the curved pipe at a constant wall temperature. A control-volume finite-element method (CVFEM) with second-order accuracy is used to solve the governing equations. This study explores the interaction phenomena between turbulent forced convection and thermal radiation in a participating medium inside a curved pipe at different temperature ratio, optical thickness, and wall emissivity.
TL;DR: In this paper, the numerical modeling of heat and moisture transfer during the drying process of a two-dimensional (2D) rectangular object subjected to convective boundary conditions is dealt with, and a computer code is developed to predict the temperature and moisture distributions inside the object.
Abstract: The present article deals with the numerical modeling of heat and moisture transfer during the drying process of a two-dimensional (2-D) rectangular object subjected to convective boundary conditions. As is common in solids drying, it is assumed that drying takes place as a simultaneous heat and moisture transfer whereby moisture is vaporized by means of a drying fluid (e.g., air), which passes over a moist object. The governing equations representing the drying process in a 2-D rectangular object are discretized using an explicit finite-difference approach, and a computer code is developed to predict the temperature and moisture distributions inside the object. Moreover, the results obtained from the present model are compared with the experimental data available in the literature, and considerably high agreement is found.
TL;DR: In this article, the performance of the low Reynolds number k - y model of Wilcox (1994) and the low Reynal number k m l turbulence model of Lam and Bremhorst (1981) in predicting buoyancy-driven flow in a noninclined enclosure is evaluated numerically.
Abstract: Turbulent natural convection at a moderately high Rayleigh number (4.9 2 10 10 ) in a two-dimensional side-heated square cavity at various angles of inclination is studied numerically. Initially, the performance of the low Reynolds number k - y model of Wilcox (1994) and the low Reynolds number k m l turbulence model of Lam and Bremhorst (1981), in predicting buoyancy-driven flow in a noninclined enclosure, is evaluated against experimental measurements. The evaluation is focused on the prediction of the flow patterns and convective heat transfer in the boundary layer and corner regions. The performance of the Wilcox k m y model is found to be superior in capturing the flow physics such as the strong streamline curvature in the corner regions. The Lam and Bremhorst k m l model is not capable of predicting these features but provides reasonable predictions away from the corners. None of these models, however, is capable of predicting the boundary-layer transition from laminar to turbulent. In order to stud...
TL;DR: In this paper, a three-dimensional flow structure in a rectangular channel with a built-in oval tube is quite complex due to the formation of horseshoe vortices near the front stagnation region of the tube and the Karman Vortices behind it.
Abstract: Three-dimensional flow structure in a rectangular channel with a built-in oval tube is quite complex due to the formation of horseshoe vortices near the front stagnation region of the tube and the Karman vortices behind it. The presence of a winglet pair in conjunction with the oval tube makes the flow structure even more complex. The interaction of the horseshoe vortices with the longitudinal vortices generated by the winglets and the interaction of the longitudinal vortices with the transverse Karman vortices culminate as a flow field dominated by the tangle of vortices. The existence of more than one pair of longitudinal vortices would further complicate the flow structure and the heat transfer behavior in the channel. The interaction between the secondary flows generated by the tube and by the winglets, as well as the interaction of the longitudinal vortices due to different arrangement of the winglets, play an important role in heat transfer enhancement. In the present article, effect of the streamwi...