Effect of Solid Subcooling on Natural Convection Melting of a Pure Metal

1989 ◽  
Vol 111 (2) ◽  
pp. 416-424 ◽  
Author(s):  
C. Beckermann ◽  
R. Viskanta
Keyword(s):  
Heat Transfer ◽  
Steady State ◽  
Natural Convection ◽  
Numerical Study ◽  
Pure Metal ◽  
Liquid Region ◽  
Cold Wall ◽  
Fusion Temperature ◽  
Local Flow ◽  
Wide Range

A combined experimental and numerical study is reported of melting of a pure metal inside a vertical rectangular enclosure with natural convection in the liquid and conduction in the solid. The numerical model is successfully verified by conducting a series of experiments covering a wide range of hot and cold wall temperatures. It is found that solid subcooling significantly reduces the melting rate when compared to melting with the solid at the fusion temperature. Because the cooled wall is held below the fusion temperature of the metal, the solid/liquid interface eventually reaches a stationary position. For moderate values of the subcooling parameter the steady-state interface is almost vertical and parallel to the cold wall. Strong subcooling results in an early termination of the melting process, such that natural convection in the relatively small liquid region cannot fully develop. For moderate subcooling, correlations have been derived for the steady-state volume and heat transfer rates. While many aspects of melting with solid subcooling appear to be similar to ordinary nonmetallic solids, important differences in the local flow structures and heat transfer mechanisms are observed.

An Investigation of the Effect of interrupted fin arrangements on the Thermal Performance of a Heat Sink under a Free Convection Condition

2019 ◽  
Vol 7 (1) ◽  
pp. 43-53
Author(s):  
Abbas Jassem Jubear ◽  
Ali Hameed Abd
Keyword(s):  
Heat Transfer ◽  
Steady State ◽  
Natural Convection ◽  
Thermal Performance ◽  
Heat Sink ◽  
Numerical Study ◽  
Ansys Fluent ◽  
Fluent Software ◽  
Steady State Heat ◽  
Steady State Heat Transfer

The heat sink with vertically rectangular interrupted fins was investigated numerically in a natural convection field, with steady-state heat transfer. A numerical study has been conducted using ANSYS Fluent software (R16.1) in order to develop a 3-D numerical model.  The dimensions of the fins are (305 mm length, 100 mm width, 17 mm height, and 9.5 mm space between fins. The number of fins used on the surface is eight. In this study, the heat input was used as follows: 20, 40, 60, 80, 100, and 120 watts. This study focused on interrupted rectangular fins with a different arrangement and angle of the fins. Results show that the addition of interruption in fins in various arrangements will improve the thermal performance of the heat sink, and through the results, a better interruption rate as an equation can be obtained.

A Multigrid Accelerated Code for Simulating Unsteady Conjugate Natural Convection Boundary Layers

2016 ◽  
Vol 846 ◽  
pp. 30-35
Author(s):  
Mehdi Khatamifar ◽  
Emma Lee Wood ◽  
Wen Xian Lin ◽  
David Holmes ◽  
Steven W. Armfield ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Boundary Layers ◽  
Numerical Study ◽  
Viscous Boundary Layer ◽  
Central Difference ◽  
Simulation Accuracy ◽  
Conjugate Natural Convection ◽  
Wide Range ◽  
Convection Boundary

This paper presents a numerical study on the flow dynamics and heat transfer behaviour of unsteady conjugate natural convection boundary layers (CNCBLs) in a partitioned, air filled square cavity. An unsteady two-dimensional multigrid-assisted solver is developed in the C#.NET programming language on stretched Cartesian meshes. The finite volume method is used to discretise the governing equations. To solve the coupled pressure and velocity, the SIMPLE algorithm is used, and to increase simulation accuracy the Adam-Bashforth, QUICK and central difference schemes are employed for time, convection, and diffusion terms respectively. The Poisson pressure equation is solved through the use of the multigrid method. The developed code is used to model CNCBLs which typically require a large amount of simulation time. The numerical results provide detailed descriptions of unsteady CNCBLs and associated heat transfer behaviour over a wide range of Ra, such as the thermal and viscous boundary layer thicknesses, temperature and velocity distributions, and maximum velocities within the CNCBLs.

scholarly journals NUMERICAL STUDY FOR INTERRUPTED RECTANGULAR FINS IN A NATURAL CONVECTION FIELD

2019 ◽  
Vol 11 (2) ◽  
pp. 216-228
Author(s):  
Ass. Prof. Dr. Abbas Jassem Jubear ◽  
Ali Hameed Abd
Keyword(s):  
Heat Transfer ◽  
Steady State ◽  
Natural Convection ◽  
Numerical Model ◽  
Heat Sink ◽  
Numerical Study ◽  
Ansys Fluent ◽  
Fluent Software ◽  
Steady State Heat ◽  
Steady State Heat Transfer

The heat sink with vertically rectangular interrupted fins investigated numerically in a natural convection field, and with steady-state heat transfer. Numerical study has been conducted using ANSYS Fluent software (R16.1) in order to develop a 3-D numerical model.  The dimensions of fins are (305 mm length, 100 mm width, 17 mm height, and 9.5 mm space between fins). The number of fins used on the surface are eight. In this study, the heat input that is  used as follow (20, 40, 60, 80, 100, and 120 watts). The study is focused on interrupted rectangular fins with different arrangement of fins. The results show that the addition of interruption fins in various arrangements will improve the thermal performance of the heat sink, and through the results, a better interruption rate obtained as an equation.                                                         

NATURAL CONVECTION HEAT TRANSFER FROM A DISCRETE HEAT SOURCE COUPLED WITH CONDUCTION DOMINATED PHASE CHANGE

1998 ◽  
Vol 22 (3) ◽  
pp. 269-289
Author(s):  
M. Lacroix
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Steady State ◽  
Natural Convection ◽  
Thermal Diffusivity ◽  
Heat Source ◽  
Phase Change ◽  
Numerical Study ◽  
Thermal Conductivity Ratio ◽  
Discrete Heat Source

A numerical study has been conducted for the heat transfer from a discrete heat source by natural convection in air above coupled with conduction dominated melting of a phase change material (PCM) below via a wall of finite thermal diffusivity. Results indicate that the presence of a PCM layer underneath the wall significantly delays the temperature rise of the heat source. The time delay increases as the thermal diffusivity of the wail material decreases and as the thickness of the PCM layer increases. For high thermal conductivity wall materials [Formula: see text] the steady state heat source temperatures are similar and independent of the PCM layer. On the other hand, for [Formula: see text], the steady state temperatures are higher and dependent on the thickness of the PCM layer. A correlation is proposed in terms of the thickness of the PCM layer and the thermal conductivity ratio of the wall.

Transient Axial Free Jet Impinging Over a Flat Uniformly Heated Disk: Solid–Fluid Properties Effects

2000 ◽  
Author(s):  
Antonio J. Bula ◽  
Muhammad M. Rahman ◽  
John E. Leland
Keyword(s):  
Heat Transfer ◽  
Steady State ◽  
Transfer Process ◽  
Conjugate Heat Transfer ◽  
Finite Thickness ◽  
Heat Transfer Process ◽  
Transport Processes ◽  
Liquid Region ◽  
Free Jet ◽  
Wide Range

Abstract Transient conjugate heat transfer process during axial free jet impingement on a solid disk of finite thickness was considered. As the fluid reached steady state, power was turned on and a uniform heat flux was imposed on the disk at its opposite surface. The numerical model considered both solid and fluid regions. Equations for conservation of mass, momentum, and energy were solved in the liquid region taking into account the transport processes at the inlet and exit boundaries, as well as at the solid-liquid and liquid-gas interfaces. Inside the solid, only the heat conduction equation was solved. The shape and location of the free surface (liquid-gas interface) was determined iteratively as a part of the solution process by satisfying the kinematic condition as well as the balance of normal and shear forces at this interface. A non-uniform grid distribution, captured from a systematic grid-independence study, was used to adequately accommodate large variations near the solid-fluid interface. Computed results include the simulation of six different substrate materials namely, aluminum, constantan, copper, diamond, silicon, and silver, and three different impinging liquids, FC - 77, Mil - 7808, and water. The solids and fluids selected covered a wide range of possibilities of conjugate heat transfer phenomena. The analysis performed showed that the thermal storage capacity, defined as density times specific heat, is an important factor defining which material will attain steady state faster during conjugate heat transfer process, like the thermal diffusivity does it for pure conduction heat transfer.

Natural Convection in Collector Cavities With an Isoflux Absorber Plate

1983 ◽  
Vol 105 (1) ◽  
pp. 19-22 ◽  
Author(s):  
W. M. M. Schinkel ◽  
C. J. Hoogendoorn
Keyword(s):  
Heat Transfer ◽  
Boundary Condition ◽  
Natural Convection ◽  
Solar Collector ◽  
Numerical Study ◽  
Cold Wall ◽  
Solar Collectors ◽  
Absorber Plate ◽  
Hot Plate ◽  
Expected Values

The boundary condition at the hot absorber plate in a solar collector will influence the natural convection in the enclosure. For the isoflux boundary condition and an isothermal cold wall an experimental and numerical study has been made for Ra numbers from 105 to 107 and inclinations from 20 to 90 deg with the horizontal. For vertical enclosures the heat transfer by natural convection was about 19 percent above that for an isothermal hot plate. This decreases with angle of inclination, to 9 percent at 20 deg. For solar collectors it means that for cases where the absorber plate is not isothermal the convective losses can be about 10 percent above the usually expected values.

Interaction of Natural Convection Wakes Arising From Thermal Sources on a Vertical Surface

1985 ◽  
Vol 107 (4) ◽  
pp. 883-892 ◽  
Author(s):  
Y. Jaluria
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Natural Convection ◽  
Numerical Study ◽  
Finite Difference Methods ◽  
Heat Removal ◽  
Temperature Fields ◽  
Electronic Components ◽  
Wide Range ◽  
Wall Plume

A numerical study of the interacting natural convection flows generated by isolated thermal energy sources, such as electronic components, located on a vertical adiabatic surface is carried out. Of particular interest were the effects of the wake on the heat transfer from and the flow over a downstream heat source and the nature of the wall plume far from the sources. This consideration is related to the positioning of finite-sized electronic components and the relevant heat removal process. A two-dimensional flow is considered, without making the boundary-layer assumptions. The full elliptic equations governing the flow are solved numerically, employing finite-difference methods. The results are compared with the boundary layer solutions, obtained in earlier studies, in order to determine the nonboundary-layer effects. This is an important consideration in several practical circumstances that involve small heat inputs, sources of relatively small heights, and small separation distances between the sources. It is found that the flow downstream rapidly approaches the characteristics of an idealized wall plume due to a line source. A boundary-layer flow arises far from the heat sources and this flow provides the boundary conditions for the elliptic problem. The nature of the velocity and temperature fields is studied in detail for a wide range of governing parameters and the heat transfer coefficients for the heated elements determined. The relevance of the results obtained to practical systems is outlined, particularly for small Grashof numbers which necessitate a solution of the full equations.

scholarly journals Numerical Study of Natural Convection within a Wavy Enclosure Using Meshfree Approach: Effect of Corner Heating

2014 ◽  
Vol 2014 ◽  
pp. 1-18 ◽  
Author(s):  
Sonam Singh ◽  
R. Bhargava
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Rayleigh Number ◽  
Prandtl Number ◽  
Numerical Study ◽  
Numerical Procedure ◽  
Side Wall ◽  
Integration Scheme ◽  
Square Enclosure ◽  
Wide Range

This paper presents a numerical study of natural convection within a wavy enclosure heated via corner heating. The considered enclosure is a square enclosure with left wavy side wall. The vertical wavy wall of the enclosure and both of the corner heaters are maintained at constant temperature,TcandTh, respectively, withTh>Tcwhile the remaining horizontal, bottom, top and side walls are insulated. A penalty element-free Galerkin approach with reduced gauss integration scheme for penalty terms is used to solve momentum and energy equations over the complex domain with wide range of parameters, namely, Rayleigh number (Ra), Prandtl number (Pr), and range of heaters in thex- andy-direction. Numerical results are represented in terms of isotherms, streamlines, and Nusselt number. It is observed that the rate of heat transfer depends to a great extent on the Rayleigh number, Prandtl number, length of the corner heaters and the shape of the heat transfer surface. The consistent performance of the adopted numerical procedure is verified by comparison of the results obtained through the present meshless technique with those existing in the literature.

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