Transient Natural Convection From a Vertically Embedded Heat Source in a Thermally Stratified Porous Layer

2008 ◽  
Author(s):  
J. Zhang ◽  
F. C. Lai
Keyword(s):  
Natural Convection ◽  
Heat Source ◽  
Porous Layer ◽  
Negative Temperature ◽  
Transient Natural Convection ◽  
Wide Range ◽  
Underground Disposal ◽  
Saturated Porous Layer ◽  
Induced Flow ◽  
The Heat Transfer Coefficient

Numerical results are presented for transient natural convection from a heat source vertically embedded in a saturated porous layer. The porous layer is initially thermally stratified with a negative temperature gradient. The effects of the source strength and its buried depth on the penetration of convective flows are investigated. The results, which include the buoyancy-induced flow patterns and temperature profiles, as well as the heat transfer coefficient in terms of the Nusselt number, are presented for a wide range of base Rayleigh number and stratification parameter. The results thus obtained have important implications for applications in geothermal energy and underground disposal of nuclear wastes.

Measurements and Calculations of Transient Natural Convection in Water

1982 ◽  
Vol 104 (4) ◽  
pp. 644-648 ◽  
Author(s):  
B. Sammakia ◽  
B. Gebhart ◽  
Z. H. Qureshi
Keyword(s):  
Natural Convection ◽  
Temperature Response ◽  
Vertical Surface ◽  
Constant Heat Flux ◽  
Thermal Capacity ◽  
Transient Natural Convection ◽  
Heating And Cooling ◽  
Dependent Form ◽  
Induced Flow ◽  
Explicit Finite Difference

Transient natural convection adjacent to a flat vertical surface with appreciable thermal capacity is investigated both experimentally and numerically. The surface is immersed in initially quiescent water, and has the same uniform temperature distribution. It is then suddenly loaded with a uniform and constant heat flux thereby generating a buoyancy induced flow adjacent to the surface. Surface temperature response was recorded by means of thermocouples embedded inside the surface, and boundary layer temperature measurements were also taken. An explicit finite difference numerical scheme is used to obtain solutions to the partial differential equations describing the conservation of mass, momentum, and energy in their time dependent form. Good agreement between the calculated and measured results is observed for both the heating and cooling transient processes.

scholarly journals NUMERICAL ANALYSIS OF THE NATURAL CONVECTION IN HORIZONTAL ANNULI AT LOW AND MODERATE Ra

2006 ◽  
Vol 5 (2) ◽  
pp. 58
Author(s):  
E. L. M. Padilla ◽  
R. Campregher ◽  
A. Silveira-Neto
Keyword(s):  
Natural Convection ◽  
Three Dimensional ◽  
Staggered Grid ◽  
Governing Equations ◽  
Concentric Cylinders ◽  
Wide Range ◽  
Horizontal Annuli ◽  
Rayleigh Numbers ◽  
The Heat Transfer Coefficient ◽  
Good Agreement

The natural convection at low and moderate Rayleigh numbers (Ra) incylindrical horizontal annuli with imposed temperatures in both surfaces isnumerically studied. This flow inside concentric cylinders classic configuration has a wide range of practical and technological applications, which justifies its growing studies efforts. In this work, the governing equations are discretized by the volume finite technique over a staggered grid, with second-order accuracy in space and time. The flow pattern is presented by several Rayleigh numbers, with an analysis of the heat transfer coefficient and flow properties. Furthermore, a three-dimensional field is shown at a moderate Ra number. The results showed a good agreement with the experimental data.

Mixed Convection Heat Transfer From Thermal Sources Mounted on Horizontal and Vertical Surfaces

1990 ◽  
Vol 112 (4) ◽  
pp. 975-987 ◽  
Author(s):  
S. S. Tewari ◽  
Y. Jaluria
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Heat Source ◽  
Mixed Convection ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Finite Width ◽  
Heat Sources ◽  
Wide Range ◽  
Thermal Sources

An experimental study is carried out on the fundamental aspects of the conjugate, mixed convective heat transfer from two finite width heat sources, which are of negligible thickness, have a uniform heat flux input at the surface, and are located on a flat plate in the horizontal or the vertical orientation. The heat sources are wide in the transverse direction and, therefore, a two-dimensional flow circumstance is simulated. The mixed convection parameter is varied over a fairly wide range to include the buoyancy-dominated and the mixed convection regimes. The circumstances of pure natural convection are also investigated. The convective mechanisms have been studied in detail by measuring the surface temperatures and determining the heat transfer coefficients for the two heated strips, which represent isolated thermal sources. Experimental results indicate that a stronger upstream heat source causes an increase in the surface temperature of a relatively weaker heat source, located downstream, by reducing its convective heat transfer coefficient. The influence of the upstream source is found to be strongly dependent on the surface orientation, especially in the pure natural convection and the buoyancy dominated regimes. The two heat sources are found to be essentially independent of each other, in terms of thermal effects, at a separation distance of more than about three strip widths for both the orientations. The results obtained are relevant to many engineering applications, such as the cooling of electronic systems, positioning of heating elements in furnaces, and safety considerations in enclosure fires.

Measurements of Transient Natural Convection on Flat Vertical Surfaces

1963 ◽  
Vol 85 (1) ◽  
pp. 25-28 ◽  
Author(s):  
B. Gebhart ◽  
D. E. Adams
Keyword(s):  
Natural Convection ◽  
Thermal Capacity ◽  
Complete Agreement ◽  
Experimental Measurements ◽  
Integral Analysis ◽  
Transient Natural Convection ◽  
Surface Temperatures ◽  
Input Flux ◽  
Wide Range ◽  
Infrared Techniques

Experimental measurements of natural convection transients in air and in water are compared with the results of the integral analysis presented by the first author. An application of infrared techniques to the measurement of transient surface temperatures is described. The measurements, over a wide range of thermal capacity, are reduced to the variables which arose in the analysis and the measured responses are in essentially complete agreement with the results of that analysis for the case of a step in input flux. None of the measurements of natural convection transients on vertical plates has indicated temperature overshoot for the step condition.

Sign in / Sign up

Export Citation Format

Share Document