Radiation-Natural Convection Interactions in Two-Dimensional Complex Enclosures

1983 ◽  
Vol 105 (1) ◽  
pp. 89-95 ◽  
Author(s):  
L. C. Chang ◽  
K. T. Yang ◽  
J. R. Lloyd
Keyword(s):  
Natural Convection ◽  
Finite Thickness ◽  
Wide Band ◽  
Temperature Fields ◽  
Two Dimensional ◽  
Transfer Rates ◽  
Gas Radiation ◽  
Radiation Exchange ◽  
Radial Flux ◽  
Physical Phenomena

A numerical finite-difference study has been carried out for the two-dimensional radiation-natural convection interaction phenomena in square enclosures with equal vertical finite-thickness partitions located at the centers of the ceiling and floor. Both participating gases (CO2 and NH3) and nonparticipating gas (air) are considered. In the radiation calculations, the nongray exponential wide-band models for CO2 and NH3 are used, together with a radial flux method utilizing a more realistic polar description for the radiation exchange in the enclosure. Results on the effects of both surface and gas radiation on the velocity and temperature fields and the overall heat transfer rates as functions of the partition heights at two levels of the Grashof number are presented and discussed in terms of the physical phenomena.

scholarly journals Laser interferometry - Report #HT-01-2017

2021 ◽  
Author(s):  
David Naylor
Keyword(s):  
Heat Transfer ◽  
Light Beam ◽  
Three Dimensional ◽  
Local Heat Transfer ◽  
Laser Interferometry ◽  
Local Heat ◽  
Temperature Fields ◽  
Fluid Temperature ◽  
Two Dimensional ◽  
Transfer Rates

An introduction is given to the optical setup and principle of operation of classical and holographic interferometers that are used for convective he at transfer measurements. The equations for the evaluation of the temperature field are derived and methods of analysis are discussed for both two-dimensional and three-dimensional temperature fields. Emphasis is given to techniques for measuring local heat transfer rates. For two-dimensional fields, a method is presented for measuring the surface temperature gradient directly from a finite (wedge) fringe interferogram. This “direct gradient method” is shown to be most useful for the measurement of low convective heat transfer rates. For three-dimensional fields, the equations for calculating the beam-averaged local heat flux are presented. The measurement of the fluid temperature averaged along the light beam is shown to be approximate. However, an analysis is presented showing that for most cases the error associated with temperature variations in the light beam direction is small. Digital image analysis of interferograms to obtain fringe spacings is also discussed briefly.

Transient Natural Convection of Water in a Horizontal Pipe With Constant Cooling Rate Through 4°C

1976 ◽  
Vol 98 (4) ◽  
pp. 581-587 ◽  
Author(s):  
K. C. Cheng ◽  
M. Takeuchi
Keyword(s):  
Natural Convection ◽  
Transient Flow ◽  
Temperature Fields ◽  
Freezing Process ◽  
Horizontal Pipe ◽  
Transfer Rates ◽  
Transient Natural Convection ◽  
Anomalous Density ◽  
Horizontal Cylinders ◽  
Relationship Of

A theoretical analysis is carried out to study the influence of an anomalous density-temperature relationship of water on the transient natural convection in horizontal cylinders with wall temperature decreasing at a uniform rate. Numercial solutions are obtained for three cases involving different cooling rates, pipe diameters, and initial uniform water temperatures for temperature conditions between 0 and 7°C. The transient flow and temperature fields, and local and overall heat transfer rates are presented to study the inversion of flow patterns caused by the maximum density at 4°C. The numerical results are compared with the experimental measurements and predictions of a quasi-steady boundary-layer model reported by Gilpin [2], and generally a good agreement is observed. Some implications on the subsequent freezing process are pointed out.

scholarly journals Numerical Investigation for the Modeling of the Magnetic Buoyancy Force during the Natural Convection of Air in a Square Enclosure

2014 ◽  
Vol 6 ◽  
pp. 873260 ◽  
Author(s):  
Kewei Song ◽  
Toshio Tagawa ◽  
Liang-bi Wang ◽  
Hiroyuki Ozoe
Keyword(s):  
Magnetic Field ◽  
Natural Convection ◽  
Buoyancy Force ◽  
Nonuniform Magnetic Field ◽  
Temperature Fields ◽  
Two Dimensional ◽  
Numerical Computations ◽  
Square Enclosure ◽  
Magnetic Buoyancy ◽  
Magnetizing Force

Numerical computations are carried out for natural convection of air in a two-dimensional square enclosure under a nonuniform magnetic field and together with the gravity field. The nonuniform magnetic field is supplied by a cubic permanent magnet placed above the enclosure. Two kinds of the expressions for the magnetizing force are considered and compared in the numerical computations. The flow and temperature fields, the magnetizing force field and the Nusselt number for two kinds of magnetizing force expressions are all presented in this paper. The numerical results reveal that the natural convection inside the enclosure does not depend on the types of the expressions for magnetizing force.

Natural Convection in Inclined Two Dimensional Rectangular Cavities

2009 ◽  
Author(s):  
Lyes Khezzar ◽  
Dennis Siginer
Keyword(s):  
Natural Convection ◽  
Two Dimensional ◽  
Square Cavity ◽  
Transfer Rates ◽  
Aspect Ratios ◽  
Temperature Distributions ◽  
Start Up ◽  
Side Walls ◽  
Boussinesq Fluid ◽  
Rayleigh Numbers

Steady two-dimensional natural convection in fluid filled cavities has been investigated numerically. The conservation equations of mass, momentum and energy governing the motion of a Newtonian Boussinesq fluid have been numerically solved using the finite volume technique. The computations were performed for three cavity height based Rayleigh numbers 104, 105 and 106. In all of the numerical experiments, the channel is heated from below and cooled from the top with insulated side-walls and the inclination angle is varied. The simulations have been carried out for several aspect ratios. For the case of the square cavity the calculated values are in excellent agreement with previously published benchmark results. The effects of the inclination of the cavity to the horizontal, with the angle varying from 0 to 180° and the initial start up conditions were investigated in turn for each aspect ratio. The inclination and the “initial” assumed conditions have a significant effect on the flow patterns, temperature distributions and the heat transfer rates. In particular it is found that the average Nusselt number exhibits discontinuities for rectangular cavities and that the occurrence of the discontinuity with angle of inclination is strongly influenced by the assumed start up field in the steady calculations in much the same way as the hysteresis effect that was identified by other workers.

scholarly journals Natural Convection in Undivided and Partially Divided Rectangular Enclosures

1981 ◽  
Vol 103 (4) ◽  
pp. 623-629 ◽  
Author(s):  
M. W. Nansteel ◽  
R. Greif
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Temperature Fields ◽  
Transitional Flow ◽  
Two Dimensional ◽  
Injection Flow ◽  
Stabilizing Effect ◽  
Different Temperatures ◽  
Vertical Walls ◽  
Rayleigh Numbers

Heat transfer by natural convection in a two-dimensional rectangular enclosure fitted with partial vertical divisions is investigated experimentally. The horizontal walls of the enclosure are adiabatic while the vertical walls are maintained at different temperatures. The experiments are carried out with water, Pr ≃ 3.5, for Rayleigh numbers in the range, 2.3 × 1010 ⩽ RaL ⩽ 1.1 × 1011, and an aspect ratio, A = H/L = 1/2. The effect of the partial vertical divisions on the fluid flow and temperature fields is investigated by dye-injection flow visualization and by thermocouple probes, respectively. The effect of the partitions on the heat transfer across the enclosure is also studied and correlations for the Nusselt number as a function of RaL and partition length are generated for both conducting and non-conducting partition materials. Partial divisions are found to have a significant effect on the heat transfer; especially when the divisions are adiabatic. The results also indicate that the partial divisions may have a stabilizing effect on the laminar-transitional flow on the heated vertical walls of the enclosure.

scholarly journals Laser interferometry - Report #HT-01-2017

2021 ◽  
Author(s):  
David Naylor
Keyword(s):  
Heat Transfer ◽  
Light Beam ◽  
Three Dimensional ◽  
Local Heat Transfer ◽  
Laser Interferometry ◽  
Local Heat ◽  
Temperature Fields ◽  
Fluid Temperature ◽  
Two Dimensional ◽  
Transfer Rates

An introduction is given to the optical setup and principle of operation of classical and holographic interferometers that are used for convective he at transfer measurements. The equations for the evaluation of the temperature field are derived and methods of analysis are discussed for both two-dimensional and three-dimensional temperature fields. Emphasis is given to techniques for measuring local heat transfer rates. For two-dimensional fields, a method is presented for measuring the surface temperature gradient directly from a finite (wedge) fringe interferogram. This “direct gradient method” is shown to be most useful for the measurement of low convective heat transfer rates. For three-dimensional fields, the equations for calculating the beam-averaged local heat flux are presented. The measurement of the fluid temperature averaged along the light beam is shown to be approximate. However, an analysis is presented showing that for most cases the error associated with temperature variations in the light beam direction is small. Digital image analysis of interferograms to obtain fringe spacings is also discussed briefly.

Natural Convection for Air and Molten Gallium in Square- and Elbow-Shaped Enclosures

2015 ◽  
Vol 789-790 ◽  
pp. 462-470
Author(s):  
Emel Evren-Selamet ◽  
Ahmet Selamet
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Numerical Scheme ◽  
Lead Author ◽  
Convection Flow ◽  
Two Dimensional ◽  
Natural Convection Flow ◽  
Transfer Rates ◽  
Chaotic Flow ◽  
Rayleigh Numbers

Natural convection flow of air and molten gallium in square and elbow-shaped enclosures is studied by a two-dimensional numerical scheme developed by the lead author. The dependence of the flow field and Nusselt number (Nu) on the Rayleigh (Ra) and Prandtl (Pr) numbers is examined in both enclosures. Results are obtained with sufficiently large Rayleigh numbers to observe transition from steady to damped or undamped oscillatory, and chaotic flow. Constant and oscillatory heat transfer rates are compared in both enclosures for air (Pr=0.71) and molten gallium (Pr=0.024).

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