Numerical Investigation on Mixed Convection in a Horizontal Channel Heated From Below

2007 ◽  
Author(s):  
Giuseppe Foglia ◽  
Nicola Lanzaro ◽  
Oronzio Manca ◽  
Sergio Nardini
Keyword(s):  
Mixed Convection ◽  
Fluid Dynamic ◽  
Three Dimensional ◽  
Horizontal Channel ◽  
Uniform Heat Flux ◽  
Vertical Side ◽  
Parallel Wall ◽  
Horizontal Wall ◽  
Side Walls ◽  
Rayleigh Numbers

In this work mixed convection in a horizontal channel with the lower wall heated at uniform heat flux is studied numerically. A three dimensional problem is modeled and solved by means of the FLUENT code. The domain is made of a principal channel and two channels with adiabatic walls, one upstream the principal channel and the other downstream. The principal channel is formed by a uniformly heated horizontal wall, a parallel wall located above and two adiabatic vertical side walls. The aim of this paper is to investigate the effect of Reynolds and Rayleigh numbers on thermal and fluid dynamic behavior in mixed convection in a horizontal channel heated from below. The analysis is carried out in transient regime in order to evaluate the thermal and fluid dynamic parameters as functions of the time. The Reynolds and Rayleigh numbers investigated are between 5 and 500 and 1.37×106 and 2.75×106 respectively. The corresponding Richardson number, Ri = Gr/Re2, holds values in the range 7.76 – 1.55 × 105. Wall temperature distributions and profiles along longitudinal and transversal coordinates are reported for different time values. Air velocity and temperature in the principal channel are presented along the longitudinal and transversal sections for some time values.

Effect of Wall Thermal Boundary Conditions on the Development of Three-Dimensional, Unsteady Natural Convective Flow in a Horizontal Enclosure With a Heated Strip on the Lower Surface

2004 ◽  
Author(s):  
Patrick H. Oosthuizen ◽  
Jane T. Paul
Keyword(s):  
Boundary Condition ◽  
Rayleigh Number ◽  
Low Temperature ◽  
Cross Section ◽  
Three Dimensional ◽  
Lower Surface ◽  
Vertical Side ◽  
Thermal Boundary Conditions ◽  
Side Walls ◽  
Rayleigh Numbers

Flow in a rectangular enclosure with a square vertical cross-section normal to the longitudinal coordinate direction and having a strip on the lower horizontal surface which is heated to a uniform high temperature has been numerically studied. Two wall thermal boundary conditions have been considered. In one, the longitudinal vertical side walls are cooled to a uniform low temperature and the horizontal top surface is adiabatic while in the other the longitudinal vertical side walls and the horizontal top surface are cooled to a uniform low temperature. In both cases, the square vertical end walls of the enclosure are adiabatic. It has been assumed that the flow is laminar and that the fluid properties are constant except for the density change with temperature which gives rise to the buoyancy forces. The unsteady, three-dimensional governing equations, expressed in dimensionless form, have been solved using a finite-difference procedure. The solution was started with no flow in the enclosure. The solution, in general, has the following parameters: the Rayleigh Number, Ra, the Prandtl number, Pr, the dimensionless longitudinal length of the enclosure relative to the size of the square cross-section, Ay, the dimensionless width of the heated strip on the lower surface relative to the size of the square cross-section, wH, and the thermal boundary condition on the upper surface. Results have only been obtained for a Prandtl number of 0.7 and only results for wH = 1/3 will be presented. Results have been obtained for values of Ay between 0.5 and 2 for Rayleigh numbers up to 5×105. In all cases, three-dimensional unsteady flow has been found to exist at the higher Rayleigh numbers. The conditions under which this unsteady flow develops and the effect of Ay on the variation of the mean Nusselt number with Rayleigh number and the effect of the wall surface boundary condition on these results has been investigated.

scholarly journals Natural convection air flow in vertical upright-angled triangular cavities under realistic thermal boundary conditions

2016 ◽  
Vol 20 (5) ◽  
pp. 1407-1420 ◽  
Author(s):  
Jaime Sieres ◽  
Antonio Campo ◽  
José Martínez-Súarez
Keyword(s):  
Natural Convection ◽  
Vertical Wall ◽  
Aperture Angle ◽  
Temperature Fields ◽  
Uniform Heat Flux ◽  
Thermal Boundary Conditions ◽  
Nusselt Numbers ◽  
Horizontal Wall ◽  
Rayleigh Numbers

This paper presents an analytical and numerical computation of laminar natural convection in a collection of vertical upright-angled triangular cavities filled with air. The vertical wall is heated with a uniform heat flux; the inclined wall is cooled with a uniform temperature; while the upper horizontal wall is assumed thermally insulated. The defining aperture angle ? is located at the lower vertex between the vertical and inclined walls. The finite element method is implemented to perform the computational analysis of the conservation equations for three aperture angles ? (= 15?, 30? and 45?) and height-based modified Rayleigh numbers ranging from a low Ra = 0 (pure conduction) to a high 109. Numerical results are reported for the velocity and temperature fields as well as the Nusselt numbers at the heated vertical wall. The numerical computations are also focused on the determination of the value of the maximum or critical temperature along the hot vertical wall and its dependence with the modified Rayleigh number and the aperture angle.

Numerical Study on Mixed Convection in Porous Media in a Channel With an Open Cavity Below

2010 ◽  
Author(s):  
Bernardo Buonomo ◽  
Oronzio Manca ◽  
Paolo Mesolella ◽  
Sergio Nardini
Keyword(s):  
Mixed Convection ◽  
Numerical Study ◽  
Fluid Dynamic ◽  
Vertical Wall ◽  
Open Cavity ◽  
Temperature Fields ◽  
Forced Flow ◽  
Heated Wall ◽  
Local Thermal Equilibrium ◽  
Uniform Heat Flux

A numerical analysis of mixed convection in gas saturated metal foam in a horizontal channel with an open cavity heated at uniform heat flux on a vertical wall is studied numerically. Non-local thermal equilibrium and Brinkman-Forchheimer-extended Darcy model are assumed. Boussinesq approximation with constant thermophysical proprieties are considered. Results are carried out for an aluminium foam with 10 PPI and ε = 0.909, the fluid is air and for the assisting case. Results, for different Peclet and Rayleigh numbers, are given in terms of solid and fluid wall temperatures and local Nusselt numbers and stream function and temperature fields. Results show that diffusive effect determined lower temperature values inside the solid and the fluid temperatures are higher in all considered cases. The interaction between the forced flow in the channel and the buoyancy due to the heated wall determines different thermal and fluid dynamic behaviors.

Numerical Calculation of Three-Dimensional Turbulent Natural Convection in a Cubical Enclosure Using a Two-Equation Model for Turbulence

1986 ◽  
Vol 108 (4) ◽  
pp. 806-813 ◽  
Author(s):  
H. Ozoe ◽  
A. Mouri ◽  
M. Hiramitsu ◽  
S. W. Churchill ◽  
N. Lior
Keyword(s):  
Natural Convection ◽  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Vertical Wall ◽  
Three Dimensional ◽  
Spiral Flow ◽  
Vertical Side ◽  
Turbulent Natural Convection ◽  
Cubical Enclosure ◽  
Side Walls

This paper presents a model and numerical results for turbulent natural convection in a cubical enclosure heated from below, cooled on a portion of one vertical side wall and insulated on all other surfaces. Three-dimensional balances were derived for material, energy, and the three components of momentum, as well as for the turbulent kinetic energy k and the rate of dissipation of turbulent kinetic energy ε. The constants used in the model were the same as those used by Fraikin et al. for two-dimensional convection in a channel. Illustrative transient calculations were carried out for Ra = 106 and 107 and Pr = 0.7. Both the dominant component of the vector potential and the Nusselt number were found to converge to a steady state. Isothermal lines and velocity vectors for vertical cross sections normal to the cooled wall indicated three-dimensional effects near the side walls. A top view of the velocity vectors revealed a downward spiral flow near the side walls along the cooled vertical wall. A weak spiral flow was also found along the side walls near the wall opposing the partially cooled one. The highest values of the eddy diffusivity were 2.6 and 5.8 times the molecular kinematic viscosity for Ra = 106 and 107, respectively. A coaxial double spiral movement, similar to that previously reported for laminar natural convection, was found for the time-averaged flow field. This computing scheme is expected to be applicable to other thermal boundary conditions.

Three-Dimensional Laminar Natural Convection in an Inclined Air Slot With Hexagonal Honeycomb Core

1991 ◽  
Vol 113 (4) ◽  
pp. 906-911 ◽  
Author(s):  
Y. Asako ◽  
H. Nakamura ◽  
Z. Chen ◽  
M. Faghri
Keyword(s):  
Natural Convection ◽  
Numerical Solutions ◽  
Transfer Problem ◽  
Three Dimensional ◽  
Convection Heat Transfer ◽  
Temperature Fields ◽  
Honeycomb Core ◽  
Inclination Angles ◽  
Side Walls ◽  
Rayleigh Numbers

Numerical solutions are obtained for a three-dimensional natural convection heat transfer problem in an inclined air slot with a hexagonal honeycomb core. The air slot is assumed to be long and wide such that the velocity and temperature fields repeat themselves in successive enclosures. The numerical methodology is based on an algebraic coordinate transformation technique, which maps the complex cross section onto a rectangle, coupled with a calculation procedure for fully elliptic three-dimensional flows. The calculations are performed for Rayleigh numbers in the range of 103 to 105, inclination angles in the range of −90 to 80 deg, Prandtl number of 0.7, and for five values of the aspect ratio. Three types of thermal boundary condition for the honeycomb side walls are considered. The average Nusselt number results are compared with those for a rectangular two-dimensional enclosure.

scholarly journals Large-scale numerical simulations: Convection in an annular channel rotating about a vertical axis with side-walls

2008 ◽  
Vol 4 (S252) ◽  
pp. 111-112
Author(s):  
Yingli Chang ◽  
Yu Liu
Keyword(s):  
Large Scale ◽  
Fluid Dynamic ◽  
Three Dimensional ◽  
Annular Channel ◽  
Vertical Axis ◽  
Jet Flows ◽  
Nonlinear Convection ◽  
Strongly Nonlinear ◽  
Convection Model ◽  
Side Walls

AbstractFor the purpose of understanding the dynamics of planetary atmospheres, we use the annular convection model to simulate the dynamics of atmospheres of Jupiter and Saturn. The model (annular channel) rotates about a vertical axis with side-walls, and it is heated from below.We use the software NaSt3DGP (a parallel software package to solve the 3D incompressible fluid dynamic problems in Cartesian coordinates by using Finite Difference Method) for the computation. It's reliability is tested by our application to simulate fully three-dimensional nonlinear convection in a box with lateral stress-free side-walls, uniformly heated from below. We found that, at moderately large Rayleigh numbers, the complex formation of multiple-jet flows can be maintained by the traveling convective eddies; we also found that the type of the sidewall velocity condition does not play an essential role in determining the primary properties of strongly nonlinear convection.

scholarly journals Thermal Convection Inside Three-Dimensional Differentially Heated Cavity Under Laminar and Transitional Flow Conditions

2020 ◽  
Vol 9 (4) ◽  
pp. 31-34
Keyword(s):  
Three Dimensional ◽  
Transitional Flow ◽  
Navier Stokes ◽  
Flow Conditions ◽  
Vertical Side ◽  
Square Enclosure ◽  
Fortran Code ◽  
Buoyancy Driven Flows ◽  
Flow Phenomena ◽  
Side Walls

The study presents the heat transfer phenomena of steady buoyancy driven flows inside a three-dimensional square enclosure. The thermal boundary condition of this enclosure are the vertical side walls are maintained at constant temperature difference and all the other walls are adiabatic. Reynolds averaged Navier stokes (RANS) equations are used to model the flow phenomena inside the enclosure, these equations are discretized using finite difference method (FDM) based Fortran code which was developed in house. The study is done for varying Grashof numbers 105 ≤ Gr ≤ 107 and a constant Prandtl number 6.2. The results indicated that as the Grashof number increases the temperature along the enclosure decreases by 24.2% and the rate of transfer of heat inside the enclosure increased by 26%.

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