Natural convection in a cubical cavity filled with a fluid showing temperature-dependent viscosity (original) (raw)
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CFD Analysis of Heat Transfer and Flow Characteristics in A 3D Cubic Enclosure
IJMER
Flow arising “naturally” from the effect of density difference, resulting from temperature or concentration difference in a body force field such as gravity, the process is termed as natural convection. There has been growing interest in buoyancy-induced flows and the associated heat and mass transfer over the past three decades, because of the importance of these flows in many different areas such as cooling of electronic equipment, pollution, materials processing, energy systems and safety in thermal processes. Steady state laminar natural convection in a cubic enclosure with a cold vertical wall and two square heaters with constant temperature on the opposite wall is studied numerically. The enclosure is fitted with various liquids. Three-dimensional Navier Stokes equations are solved by employing SIMPLE algorithm. Computations are performed for a range of Rayleigh number from 104 to 107 while enclosure aspect ratio varies from 0.1 to 1.25. The effects of Rayleigh number, enclosure aspect ratio, and Prandtl number on heat transfer characteristics are studied in detail. The results show that the flow field is very complex and heat transfer from the two heaters is not the same. The effect of Prandtl number is negligible in the range 5 to 100 with other parameters kept constant. This allows the use of liquids such as water for studying other dielectric liquids, provided the flow geometry and other non-dimensional parameters are similar. The overall Nusselt number increased markedly with Rayleigh Number. It is also affected by enclosure aspect ratio.
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.
Numerical Modeling of the Thermal Convection of the Viscoud Fluid Flow in the Square Cavity
2014
The paper presents the results of a numerical simul ation of thermal convection in a liquid with a quad r tic dependence of viscosity on temperature in the cavit y at various angles of inclination to the horizonta l. The integral heat transfer coefficients for isothermal borders are in vestigated to plot the minimum critical Rayleigh nu mber on the angle of inclination of the cavity.
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.
American journal of heat and mass transfer, 2016
This paper presents a numerical study of fluid flow and natural convection inside cubical cavities using the finite volume method with second order schemes. Cubical cavities of various sizes with three different thermal configurations were considered, where two opposite vertical walls are isothermal and the other walls are either adiabatic or conducting (with linear temperature variation). The numerical simulations were performed for air and gases with Prandtl number 0.71 under the influence of variable Rayleigh numbers covering the range 10 3-10 7. The effects of the three thermal configurations in terms of velocities and temperatures were investigated for both steady and unsteady flow regimes. Additionally, the magnitudes of local and average Nusselt numbers in each direction of the cubical cavity were scrutinized. Using conducting walls, the heat transfer analysis in different directions divulged that the heat flow through the top/bottom walls surpasses 1/3 of the total heat flow of the cubical cavity. Overall, the collection of numerical results demonstrates good agreement when compared with experimental-based and numerical-based publications.
Natural convection in tilted rectangular cavities due to bidirectional temperature gradient
International Journal of Heat and Technology, 2017
The study by the CFD for a 3D natural convection in a tilted rectangular cavity filled by silicone oil at high Prandtl number has been compared to experimental results. A constant vertical temperature gradient has been performed by subjecting the horizontal walls to temperature Th and Tc; respectively. Other walls are adiabatic except the left small sidewall is differentially heating with temperature TA creating the horizontal temperature gradient. Different values of the lateral heating and the tilt with respect to the horizontal plane are imposed. The results draw dynamic maps. The influence of two factors (TA and ) on the flow pattern and on the convective heat transfer are analysed and discussed. The simulation flow pattern results are close to those obtained experimentally for treated cases with a minimum discrepancy between the both. A spectral analysis is done to show the fluctuations seen on the natural convective flow after the stability caused by the lateral heating and tilted angle; which based on the visualization of the amplitude as a function to the frequency. The results also show a significant impact on the flow fields and the heat transfer performance is improved.
Laminar Natural Convection Study in a Quadrantal Cavity Using Heater on Adjacent Walls
Frontiers in Heat and Mass Transfer, 2013
A numerical analysis of laminar natural convection in a quadrantal cavity filled with water having variable length heaters attached on the adjacent walls have been made to examine heat and fluid flow. Numerical solutions are obtained using a commercial computational fluid dynamics package, FLUENT, using the finite volume method. Effects of the Rayleigh number, Ra, on the Nusselt number, Nu, as well as velocity and temperature fields are investigated for the range of Ra from 10 3 to 10 7 . Computations were carried out for the non-dimensional heater lengths on the vertical wall (m=0.2, 0.4 and 0.6) and horizontal wall (n=0.2, 0.4 and 0.6). It is observed that heat transfer increases with increase in Rayleigh number and the flow strength increases with increase in size of heater on the vertical wall compared to the bottom wall and temperature fields are also affected. In contrast, with increase in size of heater on both side of adjacent walls flow strength does not changes significantly.
Steady natural convection in a cylindrical cavity
International Communications in Heat and Mass Transfer, 2002
We present a numerical and experimental study of steady natural convection in a small aspect ratio cylindrical cavity with circular cross section. The main objective of the present communication is to highlight some difficulties encountered when a comparison of theoretical and experimental velocity results is attempted. We keep the aspect ratio (radius/height), the Prandtl number and the Rayleigh number tixed to 0.28, 6 and 2.25 x 10' respectively and make observations in a vertical plane that contains the axis of symmetry of the cylinder with a particle image velocimetty (PIV) technique. The' main structure present in the flow is a single nonaxisymmetric cell with a horizontal rotation axis. Due to the symmetry of the geometry of the cavity and of the heating and cooling systems, the orientation of the convective &ucture is undefined by the boundaries. In order to make a theoretical-experimental comparison, it is necessary to make a full description of the three dimensional velocity field to End the phme that corresponds to the one observed in the experiment. (0 2002 glsewer &lence Ltd The phenomenon of natural convection has been the subject of intense scientific research since the classical experiments of B6nard in the early 20th century. Con&red natural convection is a phenomenon related to the well known Rayleigh-B6nard problem where the walls have determinant influence. The interest in this phenomenon arises on the one hand due to the large variety 'of dynamic behaviors that can be generated in simple experimental facilities and on the other, due to its many appticatiom in technology. Out of these, two important examples are: crystal growth using the Czochralzki method
Boundary condition investigation for cavity flow natural convection.
Natural Convection in confined enclosures has been one of the research interests because of the application in a wide range of engineering areas such as power plants, cooling systems, solar collectors and energy storage technologies. It seems that a rectangular cavity exhibits a simple geometry for experimental purposes; however, the existence of low range of velocity and heat transfer in natural convection remains the measurement challenges. Also, complete modeling (the cavity and heat exchangers) is so complicated from the aspects of the flow regime and heat transfer, especially with the presence of turbulence. In this research, both experimental and numerical models of water natural convection inside a cavity are presented. The experiment aims to keep the hot and cold walls in constant temperature. The numerical simulation consists of 3D full model of the experimental setup and a 2D model of the cavity as well. A comparison among results proves that the existence of a small gradient of temperature in both cold and hot walls is unavoidable.
In the present study, natural convection problem has been solved in a cavity having three flat walls and the right vertical wall consisting of one undulation and three undulations. The two vertical and bottom walls are cold walls maintained at a fixed temperature whereas the top wall is heated with spatially varying temperature distribution. Air has been taken as the working fluid with Pr =0.71. This problem is solved by SIMPLE algorithm with deferred QUICK scheme in curvilinear coordinates. A wide range of Rayleigh number (10 3 to 10 6) has been chosen for this study. For small Ra, the heat transfer was dominated by conduction across the fluid layers. With increase of Ra, the process began to be dominated by convection. In the presence of undulation the peak point of the heat rejection (negative local Nusselt number) in the right wall increases by 5.54% than left wall for Ra = 10 4. The three undulations case had maximum heat transfer to the uppermost undulation compared to that of the one undulation case.