Visualization and Prediction of Natural Convection of Water Near Its Density Maximum in a Tall Rectangular Enclosure at High Rayleigh Numbers

2000 ◽  
Vol 123 (1) ◽  
pp. 84-95 ◽  
Author(s):  
C. J. Ho ◽  
F. J. Tu
Keyword(s):  
Natural Convection ◽  
Vertical Wall ◽  
Three Dimensional ◽  
Temperature Fields ◽  
Convection Flow ◽  
Oscillatory Convection ◽  
Uniform Temperature ◽  
Density Maximum ◽  
Rectangular Enclosure ◽  
Rayleigh Numbers

An experimental and numerical investigation is presented concerning the natural convection of water near its maximum-density in a differentially heated rectangular enclosure at high Rayleigh numbers, in which an oscillatory convection regime may arise. The water in a tall enclosure of Ay=8 is initially at rest and at a uniform temperature below 4°C and then the temperature of the hot vertical wall is suddenly raised and kept at a uniform temperature above 4°C. The cold vertical wall is maintained at a constant uniform temperature equal to that of the initial temperature of the water. The top and bottom walls are insulated. Using thermally sensitive liquid crystal particles as tracers, flow and temperature fields of a temporally oscillatory convection was documented experimentally for RaW=3.454×105 with the density inversion parameter θm=0.5. The oscillatory convection features a cyclic sequence of onset at the lower quarter-height region, growth, and decay of the upward-drifting secondary vortices within counter-rotating bicellular flows in the enclosure. Two and three-dimensional numerical simulations corresponding to the visualization experiments are undertaken. Comparison of experimental with numerical results reveals that two-dimensional numerical simulation captures the main features of the observed convection flow.

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 Simulation of Natural Convection Flow in a Cube With a Horizontal Heated Strip

2008 ◽  
Author(s):  
Esam M. Alawadhi
Keyword(s):  
Heat Transfer ◽  
Numerical Simulation ◽  
Nusselt Number ◽  
High Temperature ◽  
Natural Convection ◽  
Vertical Wall ◽  
Convection Flow ◽  
Front Wall ◽  
Natural Convection Flow ◽  
Rayleigh Numbers

Natural convection flow in a cube with a heated strip is solved numerically. The heated strip is attached horizontally to the front wall and maintained at high temperature, while the entire opposite wall is maintained at low temperature. The heated strip simulates an array of electronic chips The Rayleigh numbers of 104, 105, and 106 are considered in the analysis and the heated strip is horizontally attached to the wall. The results indicate that the heat transfer strongly depends on the position of the heated strip. The maximum Nusselt number can be achieved if the heater is placed at the lower half of the vertical wall. Increasing the Rayleigh number significantly promotes heat transfer in the enclosure. Flow streamlines and temperature contours are presented, and the results are validated against published works.

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 Natural Convection Flow Of An Electrically Conducting Fluid In A Rectangular Cavity Having Internal Energy Sources With Linearly Heated Bottom Wall

2013 ◽  
Vol 32 ◽  
pp. 61-73
Author(s):  
M Obayedullah ◽  
M M K Chowdhury
Keyword(s):  
Natural Convection ◽  
Rectangular Cavity ◽  
Conducting Fluid ◽  
Bottom Wall ◽  
Temperature Fields ◽  
Convection Flow ◽  
Natural Convection Flow ◽  
Electrically Conducting ◽  
Electrically Conducting Fluid ◽  
Rayleigh Numbers

Natural convection flow in a rectangular cavity containing internally heated and electrically conducting fluid has been investigated numerically. The bottom wall of the cavity is linearly heated whereas the top wall is well insulated. The left and right vertical walls are maintained at constant hot and cold temperature respectively.Results have been obtained with respect to Rayleigh numbers and Hartmann numbers. Flow and temperature fields for these cases have been studied. Average Nusselt numbers at hot, cold and linearly heated bottom wall have been calculated. It is found that the temperature, fluid flow and heat transfer strongly depend on internal and external Rayleigh numbers and Hartmann numbers. DOI: http://dx.doi.org/10.3329/ganit.v32i0.13648 GANIT J. Bangladesh Math. Soc. (ISSN 1606-3694) 32 (2012) 61-73    

Heat Transfer in Discretely Heated Side-Vented Compact Enclosures by Combined Conduction, Natural Convection, and Radiation

1999 ◽  
Vol 121 (4) ◽  
pp. 1002-1010 ◽  
Author(s):  
E. Yu ◽  
Y. K. Joshi
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Numerical Solutions ◽  
Vertical Wall ◽  
Three Dimensional ◽  
Radiative Heating ◽  
Computational Domain ◽  
Flow Recirculation ◽  
Discrete Heat Source ◽  
Rayleigh Numbers

A three-dimensional investigation of combined conduction, natural convection, and radiation in a side-vented compact enclosure is carried out. The focus of the study is on the enhancement of overall heat transfer through the opening, and the roles of the various modes in achieving it. A discrete heat source, flush-mounted centrally on a vertical substrate, is placed in the enclosure with a single rectangular opening on the opposite vertical wall. Steady-state computations are carried out for Rayleigh numbers, Ra, at 2.6 × 106 and 2.0 × 107. The results show that radiation plays a significant role in the overall heat transfer, and the radiative transport is even more pronounced for lower Ra. It is found that natural convection is weakened by radiation, however, contrary to the existing studies on top vented enclosures, the overall heat transfer is enhanced when radiation is included in the computations. Flow recirculation by radiative heating of enclosure walls is predicted, and is also observed experimentally. Heat spreading in the substrate is found to effect both convection and radiation. The numerical solutions on an extended computational domain are found in good agreement with the experimental data, when the conjugate effects are accounted for.

NATURAL CONVECTION STUDY IN AN ENCLOSURE WITH DIFFERENT ASPECT RATIOS

2007 ◽  
Vol 18 (12) ◽  
pp. 1903-1923 ◽  
Author(s):  
YI DONG ◽  
QINGLAN ZHAI
Keyword(s):  
Natural Convection ◽  
Present Model ◽  
Distribution Functions ◽  
Temperature Fields ◽  
Convection Flow ◽  
Natural Convection Flow ◽  
Aspect Ratios ◽  
Boltzmann Method ◽  
Rayleigh Numbers ◽  
Good Agreement

Natural convection in an enclosure with different ratios are investigated with the lattice Boltzmann method, and double distribution functions (DDF) are proposed to simulate the velocity and the temperature fields. Meanwhile, compared with other existing results, we studied the effect of the different aspect ratios on heat transfer, and 2D numerical simulation of natural convection flow in a square cavity are performed at Rayleigh numbers 103–106 with fixed Prandtl number 0.71 in detail. The numerical results of the Nusselt number along the two sidewalls and the maximum velocities along the horizontal and vertical lines through the cavity center are in good agreement with existing results, which shows the accuracy of the present model.

On the Natural Convection in a Cavity With a Cooled Top Wall and Multiple Protruding Heaters

1995 ◽  
Vol 117 (1) ◽  
pp. 34-45 ◽  
Author(s):  
C. P. Desai ◽  
K. Vafai ◽  
M. Keyhani
Keyword(s):  
Natural Convection ◽  
Critical Rayleigh Number ◽  
Vertical Wall ◽  
Side Wall ◽  
Temperature Fields ◽  
Length Ratio ◽  
Numerical Work ◽  
Steady Solutions ◽  
Heater Length ◽  
Rayleigh Numbers

Natural convection in rectangular enclosures with multiple protruding heaters mounted on one side wall is of relevance to the cooling of electronic equipment. In some configurations, the top wall behaves as the heat sink while the opposing vertical wall and the bottom wall are insulated. The present work examines the peculiarities introduced in the natural convection process for such configurations. The enclosure considered had five protrusions, cavity width to heater length ratio of 1.2 and cavity height to heater length ratio of 11. It is shown that for such configurations, a stable flow exists only at lower Rayleigh numbers and that above a certain critical Rayleigh number, only quasi-steady solutions exist. At low Rayleigh numbers(Ra* ≤ 1.5 × 107), the flow is stable and characterized by the presence of a primary flow cell and a counter-rotating secondary cell at the top of the enclosure. At higher Rayleigh numbers (Ra* ≥ 3 × 108), however, the isothermal top wall causes a periodic flow pattern to develop within the enclosure. Several interesting characteristics of the flow and temperature fields are presented. Results compared with previous experimental and numerical work are found to be in good agreement.

scholarly journals Numerical study of the effects of natural convection in a thermoacoustic configuration

2019 ◽  
Vol 20 (8) ◽  
pp. 807
Author(s):  
Omar Hireche ◽  
Catherine Weisman ◽  
Diana Baltean-Carlès ◽  
Virginie Daru ◽  
Yann Fraigneau
Keyword(s):  
Porous Medium ◽  
Natural Convection ◽  
Numerical Study ◽  
Three Dimensional ◽  
Boussinesq Approximation ◽  
Acoustic Resonator ◽  
Operating Conditions ◽  
Temperature Fields ◽  
Convection Flow ◽  
Conductivity Anisotropy

This study focuses on natural convection flows within a cylindrical guide containing a porous medium. This configuration is applicable to standing-wave thermoacoustic engines, usually composed of an acoustic resonator where a (short) stack (or porous medium) is inserted, with a heat exchanger placed at one of its ends. The resulting horizontal temperature gradient, when high enough, triggers the onset of an acoustic wave. Natural convection effects are usually neglected in thermoacoustics so that axisymmetry is often assumed. Here a 3D numerical study of natural convection flow is performed using a finite volume code for solving mixed Navier-Stokes and Darcy-Brinkman equations under Boussinesq approximation. The influence of the porous medium’s physical characteristics (permeability, thermal conductivity, anisotropy) on the flow and temperature fields is investigated. It is shown that such flows are fully three-dimensional and therefore can modify significantly starting as well as steady operating conditions of the thermoacoustic engine.

scholarly journals Numerical Study of Three- Dimensional Natural Convection in a Differentially Heated Cubical Enclosure

2020 ◽  
Vol 14 ◽  
Keyword(s):  
Steady State ◽  
Natural Convection ◽  
Numerical Study ◽  
Vertical Wall ◽  
Three Dimensional ◽  
Three Dimensional Flow ◽  
Cubical Enclosure ◽  
Side Walls ◽  
The Right ◽  
Rayleigh Numbers

—A high-resolution, finite difference numerical studyis reported on three-dimensional steady-state natural convectionof air, for two Rayleigh numbers, in a cubical enclosure, which isheated differentially at one side walls. The temperature of thewall is TC except for the right vertical wall, in which is TH.Thedetails of the three-dimensional flow and thermal characteristicsare described.

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