Numerical study of natural melt convection in cylindrical cavity with hot walls and cold bottom sink (original) (raw)
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International Journal of Heat and Technology, 2020
Cooling process of a heat source placed at the bottom side of a cold-walled cavity (TC) by means of natural convection has been studied numerically in this work. Two thermal conditions have been assumed at the source (q-imposed or T-imposed). The effects of Rayleigh number (Ra=10+3→10+6), source length (SL=0.1→1.0), source position (D) compared to left side, in addition to the effect of the number of Prandtl (Pr=0.71→10+2) were analyzed with ample details. For a source at the center of the bottom side, results showed an increase of flow and temperature disturbance with increasing Ra and/or SL, with an enhancement of both local and mean Nusselt numbers. Particular exceptions were noticed for high Ra values for the second heating type. For all considerations, the case of SL=0.1 makes an exception where a very good heat exchange rate is recorded. When the source is no longer centered, Clearer difference between this case and the previous one was recorded, especially for small D values....
IOP Conference Series: Materials Science and Engineering, 2019
Effects of cavity aspect ratios and cavity inclination angles to natural convection in a rectangular cavity are numerically investigated. Investigation is performed at the Rayleigh number (Ra) equal to 104, the cavity aspect ratios from 1 to 50 and the cavity inclination angles from 0 to 180°. Consequently, Heat transfer enhancement or decreasing due to the effects is exposed. In addition, streamline contours in the rectangular cavity are illustrated. Multi-cellular flow figuring on the appropriate conditions is exhibited. A new correlation of the average Nusselt number, the cavity aspect ratio and the cavity inclination angle is formulated at Ra equal to 104.
2020
In the current study, the effect of an inner heated circular cylinder placed inside a cooled square enclosure on the heat transfer and fluid flow is numerically studied. The main parameters that were investigated are the position of the inner cylinder which was varied both in the vertical and diagonal directions from -0.2 to +0.2 and the aspect ratio which was from 0.05 to 0.25. The Rayleigh number and the Prandtl number were kept constant at 10 and 0.7, respectively. However, for the comparison study, three Prandtl numbers were examined 10, 10, and 10. The numerical study is conducted using (FORTRAN 90) code which is built to perform the calculations for the Navier-Stokes equation of the stream-vorticity expression using finite-difference approach that relates with the non-orthogonal body-fitted coordinate system. The results revealed that the highest local Nu number was achieved at the top surface of the cylinder when the cylinder is moved both in the vertical and diagonal directi...
2003
In this work, a experimental study of the natural convection heat transfer in a cavity with discrete heat sources flush mounted in one of the walls, simulating electronic components, is carried out. The inferior and superior walls are insulated and the temperature of the opposite wall to the one with heat sources is maintained constant, lower than the environment temperature. The influence of power dissipated by the sources, the cooling temperature, the aspect ratio and the inclination angle of the cavity with respect to the horizontal plane, on the flow and the heat transfer, have all been evaluated. Cubic cavities were built and experimental tests for measure of the temperature was realized by using thermocouples and a data acquisition system controlled by computer, being obtained the temperature fields inside the cavity, as well as the temperature distribution in the wall where the heat sources are mounted. The results were compared with respect to the maximum temperature in the ...
Numerical Study of Natural Convection Inside a Square Cavity with Non-uniform Heating from Top
Journal of The Institution of Engineers (India): Series C, 2020
The prime objective of the present numerical study is to analyse buoyancy-driven thermal flow behaviour inside an enclosure with the application of nonlinear heating from top surface which is commonly essential in glass industries. A fluid-filled square cavity with sinusoidal heating from top surface, adiabatic bottom wall and constant temperature side walls is considered here. The thermal flow behaviour has been numerically observed with the help of relevant parameters like stream functions, isotherms and Nusselt number. For the present investigation, Rayleigh number (Ra), Prandtl number (Pr) and heating frequency of the wall (x) are varied from 10 3 to 10 6 , 0.7 to 7 and 0.5 to 2, respectively. It has been noticed from the investigation that flow dynamics drastically alter with Ra, x and Pr. However, the effect of Ra on heat transfer rate has been found to be significantly higher while compared with the influences by x and Pr. Keywords Free convection Á Buoyancy Á Rayleigh number Á Pr number Á Sinusoidal heating Greek letters a Thermal diffusivity (m 2 s-1) b Volumetric expansion coefficient (K-1) q Kinetic viscosity (m 2 s-1) t Density of fluid (kg m-3) h Dimensionless temperature x Heating frequency of the top wall
Natural convection in a two dimensional circular headed cavity filled with Ferro-fluid (water + Fe3O4) is numerically investigated for different heater positions. In this study, two discrete heat sources at constant temperature are located on the bottom wall. The vertical and circular top walls are cooled at constant low temperature. The Ferro-fluid is assumed to be homogenous and Newtonian. The physical problem is represented mathematically by sets of governing equations and the developed mathematical model is solved by employing Galerkin finite element formulation. The influence of pertinent parameter such as Rayleigh number (Ra) ranges from 10 3 to 10 6 for different aspect ratios (λ) of 0, 0.4 and 0.7 and also the solid volume fraction of Ferro-fluid (φ) from 0 to 0.15 on heat transfer are studied. The present study analyzes and discusses the flow patterns (streamline structures and isotherm distributions) set up by the buoyancy force and the heat transfer rate is quantified by the average Nusselt number (Nu) along the heat source. The results show that the heat transfer rate increases with the increase of the Rayleigh number and solid volume fraction of Ferro-fluid. It is also evident from results that heat transfer is maximum for λ=0.7 up to Ra=10 6 but the increasing rate of heat transfer is higher for λ=0.4 beyond Ra=10 4 .
Journal of Mechanical Science and Technology, 2015
Finite element method was used to investigate the effects of heater location and heater size on the natural convection heat transfer in a 2D square cavity heated partially or fully from below and cooled from above. Rayleigh number (5Í10 2 ≤ Ra ≤ 5Í10 5), heater size (0.1 ≤ D/L ≤ 1.0), and heater location (0.1 ≤ x h /L ≤ 0.5) were considered. Numerical results indicated that the average Nusselt number (Nu m) increases as the heater size decreases. In addition, when x h /L is less than 0.4, Nu m increases as x h /L increases, and Nu m decreases again for a larger value of x h /L. However, this trend changes when Ra is less than 10 4 , suggesting that Nu m attains its maximum value at the region close to the bottom surface center. This study aims to gain insight into the behaviors of natural convection in order to potentially improve internal natural convection heat transfer.
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.
Effects of thermal boundary conditions on natural convection flows within a square cavity
International Journal of Heat and Mass Transfer, 2006
A numerical study to investigate the steady laminar natural convection flow in a square cavity with uniformly and non-uniformly heated bottom wall, and adiabatic top wall maintaining constant temperature of cold vertical walls has been performed. A penalty finite element method with bi-quadratic rectangular elements has been used to solve the governing mass, momentum and energy equations. The numerical procedure adopted in the present study yields consistent performance over a wide range of parameters (Rayleigh number Ra, 10 3 6 Ra 6 10 5 and Prandtl number Pr, 0.7 6 Pr 6 10) with respect to continuous and discontinuous Dirichlet boundary conditions. Non-uniform heating of the bottom wall produces greater heat transfer rates at the center of the bottom wall than the uniform heating case for all Rayleigh numbers; however, average Nusselt numbers show overall lower heat transfer rates for the non-uniform heating case. Critical Rayleigh numbers for conduction dominant heat transfer cases have been obtained and for convection dominated regimes, power law correlations between average Nusselt number and Rayleigh numbers are presented.
In this paper, we analyze the fluid flow and heat transfer characteristics inside a two dimensional quadrantal cavity filled with air. The cavity is heated non-uniformly from the bottom wall and the vertical wall is cooled to a constant temperature while the curved wall is thermally insulated. Finite element method is used to solve the transport equations. The results are illustrated in the form of streamlines, isotherms, local Nusselt number and average Nusselt number. It reveals that the local Nusselt number at the bottom wall follows a sinusoidal variation and moreover at some location, the Nusselt number is negative because of the imposed temperature distribution on the wall. It further reveals that the mechanism of heat transfer is conduction at lower values of Rayleigh number, while heat transfer is due to convection at higher values of Rayleigh number.