Effect of the thermal boundary conditions and physical properties variation on transient natural convection of high Prandtl number fluids (original) (raw)
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Transient natural convection cooling of a high Prandtl number fluid in a cubical cavity
Meccanica, 2011
This work presents a numerical analysis of the effects of thermal boundary conditions, fluid variable viscosity and wall conduction on transient laminar natural convection of a high Prandtl number (Pr = 4 × 10 4 ) fluid (Golden Syrup) in a cubical cavity. The simulations consider physical situations realizable at laboratory scale using a cavity with Plexiglas walls of 1 cm of thickness, and inside dimension of L = 20 cm. The initial Rayleigh (Ra) number is 10 6 . The cavity is initially full of fluid at rest and at constant temperature (T i = 45°C) higher than the temperature of the walls (T w = 25°C). The time evolution of the flow patterns, the temperature contours, the mean temperature of the fluid and the Nusselt number (Nu) of eight different cases of cooling are presented and analyzed.
Proceedings of World Academy of Science, …, 2007
This paper presents and discusses the numerical simulations of transient laminar natural convection cooling of high Prandtl number fluids in cubical cavities, in which the six walls of the cavity are subjected to a step change in temperature. The effect of the fluid Prandtl number on the heat transfer coefficient is studied for three different fluids (Golden Syrup, Glycerin and Glycerin-water solution 50%). The simulations are performed at two different Rayleigh numbers (5 · 10 6 and 5 · 10 7 ) and six different Prandtl numbers (3 · 10 5 ≥Pr≥ 50). Heat conduction through the cavity glass walls is also considered. The propsed correlations of the averaged heat transfer coefficient (Nu) showed that it is dependant on the initial Ra and almost independent on P r. The instantaneous flow patterns, temperature contours and time evolution of volume averaged temperature and heat transfer coefficient are presented and analyzed.
Heat and Mass Transfer, 2007
This paper presents and discusses the numerical simulations of transient laminar natural convection cooling of high Prandtl number fluids in cubical cavities, in which the six walls of the cavity are subjected to a step change in temperature. The effect of the fluid Prandtl number on the heat transfer coefficient is studied for three different fluids (Golden Syrup, Glycerin and Glycerin-water solution 50%). The simulations are performed at two different Rayleigh numbers (5 · 10 6 and 5 · 10 7 ) and six different Prandtl numbers (3 · 10 5 ≥Pr≥ 50). Heat conduction through the cavity glass walls is also considered. The propsed correlations of the averaged heat transfer coefficient (Nu) showed that it is dependant on the initial Ra and almost independent on P r. The instantaneous flow patterns, temperature contours and time evolution of volume averaged temperature and heat transfer coefficient are presented and analyzed.
Natural convection in a cubical cavity filled with a fluid showing temperature-dependent viscosity
International Journal of Thermal Sciences, 2015
We present a numerical and experimental study of laminar natural convection flow in a fluid filled cubical cavity. The fluid is a dielectric oil used for cooling distribution and power transformers. As most liquids, this oil exhibits temperature-dependent viscosity. The cubical cavity of interest has an imposed temperature difference between two opposite vertical walls while the other walls are insulated. The cavity dimensions are 0.1 m  0.1 m  0.1 m. Four characteristic Rayleigh numbers ranging from 1.7  10 8 to 6.3  10 8 were analyzed. The numerical study was carried out by applying the Finite Element Method to solve the 3D NaviereStokes and heat equations using the in-house developed Par-GPFEP code. The influence of temperature-dependent viscosity on the total transferred heat and on the flow pattern, have been evaluated. Although there are several studies regarding the flow in a square cavity in this configuration, there is limited information in the literature on the 3D flow in cubical cavities with variable properties of the working fluid. We could not find in the open literature experimental measurements that we could use to validate our numerical results. For this reason an experimental setup was developed. The velocity field was visualized and measured by Particle Image Velocimetry (PIV). The temperature profiles in the vertical mid-axis at mid-plane of the cavity were measured and compared with the numerical results. We found reasonable agreement between numerical simulations and experimental measurements.
Numerical Simulation of Natural Convection in a Square Cavity with Two Partitions and Two Fluids
International Review of Mechanical Engineering (IREME), 2018
The present work enlightens the study of laminar natural convection in an isosceles right-angled triangular cavity filled with water. The bottom wall of the cavity contains a caterpillar (C)-curve shape wavy wall, having different width (w = 0.20b, 0.25b, 0.33b and 0.50b) and aspect ratio (d) with 0 6 d 6 0.15. Vertical and incline walls of the cavity are considered individually and together for cooling purpose. The physical model is solved to examine the effect of constrained parameters such as hot wall profiles, configurations of cold walls and Rayleigh number (10 5-10 7) on the fluid flow and heat transfer. The study is carried out numerically by commercially available software FLUENT 6.3. The deviation in the flow pattern and temperature profile is displayed by streamlines and isotherms contours whereas the variation in heat transfer rate is presented by local and average Nusselt number. It is found from the investigation that the heat transfer rate is enhanced significantly for caterpillar curved shape wavy wall than the flat hot wall. Moreover, the rate of heat transfer is varied profoundly with the location of cold walls.
Simulation of Natural Convection in a Square Cavity with Partially Heated and Cooled Vertical Walls
Proceeding of 5th Thermal and Fluids Engineering Conference (TFEC)
Natural convection driven by temperature differences between partially heated and cooled vertical walls in a square cavity is studied numerically. Steady or unsteady cellular flow structures and temperature patterns are illustrated along with the evolution of heat transfer rates in terms of Nusselt number. The cavity is filled with fluids of various Prandtl number, including .024 (liquid metal), .71 (air), 6 (water), and 450 (silicon oil). The effect of Prandtl and Rayleigh numbers on the flow regime and heat transfer is established along with two different thermal boundary conditions.
Computers & Fluids, 2007
In this article, we present a two-dimensional study of laminar natural convection in porous enclosure. The horizontal walls of the enclosure are thermally insulated , where as the left and right vertical walls are maintained respectively at different temperatures (warm temperature) and (cold temperature).we present the differential equations modeling the phenomenon studied according to Darcy-Brinkman-Forcheimer model. after the dimensionless form of the equation we have four dimensionless numbers : the Prandtl number the thermal Grashof , the aspect ratio A, the Darcy number .The results allowed us to conclude the following: Increasing of Grachof number with a constant Darcy number, so we areThe increase of convection and as a result the increase in flow velocity and heat transfer.at constant of Grachof number whith decreasing of the Darcy number, the medium is impermeable which slow motion of the convection phenomenon. so we are a degradation speed and heat transfer .Finaly We executed the program calculates with the real data of oil reservoir.
International Journal of Heat and Mass Transfer, 2005
Natural convection in two-dimensional enclosure with three flat and one wavy walls is numerically investigated. One wall is having a sinusoidal temperature profile. Other three walls including the wavy wall are maintained at constant cold temperature. This problem is solved by SIMPLE algorithm with deferred QUICK scheme in curvilinear co-ordinates. The tests were carried out for different inclination angles, amplitudes and Rayleigh numbers while the Prandtl number was kept constant. The geometrical configurations considered were namely one, two and three undulations.
Transient natural convection heat transfer in a large-diameter cylinder
Experimental Thermal and Fluid Science, 1988
The transient two-dimensional laminar natural convection of water, enclosed in rectangular cavities with wall temperature maintained at 0°C is studied analytically. This investigation is carried out in order to study the inversion of flow patterns caused by the maximum density of water at 4°C. Numerical solutions are obtained for cases involving different aspect ratios and initial water temperatures varying between 4 and 21°C. Solutions of the governing coupled system ofpartial differential equations are obtained using an alternating direction implicit finite difference method. The results are presented graphically in the form of stream function and isotherm contour plots. The heat transfer through each wall is evaluated in order to study the effect of the density inversion on the cooling process. It is established numerically that one of the consequences of the nonlinearity of the water is to change the maximum heat transfer from the top wall of the cavity to the bottom one.
Natural convection in a rectangular cavity with wall temperature decreasing at a uniform rate
W�rme - und Stoff�bertragung, 1982
The transient natural convection in a fluid contained in a rectangular enclosure, the wall of which is maintained at a uniform temperature which changes at a steady rate, is approached by a numerical method. Numerical solutions are obtained for Pr = 0.73, 7.3 and 73 and a range of Rayleigh numbers Ra = 102 ~ l0 s. At relatively low Rayleigh numbers the flow is characterized by the development of double cells with flow up the center and down the sidewalls. However it was found that an increase of the Rayleigh number leads to the development of strong secondary circulation on the axis of symmetry of the cavity near the top wall. Thus, as the Rayleigh number is increased the secondary cells grow in size. The effects of the secondary cells on the temperature field and heat transfer coefficients are discussed. Most results are obtained for the case of a square cavity (E ~-2) but the influence of the aspect ratio of the cavity is also studied for E = 1 and 4. Freie Konvektion in reehtwinkeligen Riiumen bei mit der Zeit linear fallenden Wandtemperaturen