An Application of the Optical Correlation Computer to the Detection of the Malkus Transitions in Free Convection

1982 ◽  
Vol 104 (2) ◽  
pp. 255-263 ◽  
Author(s):  
E. F. C. Somerscales ◽  
H. B. Parsapour
Keyword(s):  
Heat Transfer ◽  
Quantitative Analysis ◽  
Free Convection ◽  
Optical Method ◽  
Fluid Layer ◽  
Flow Patterns ◽  
Optical Correlation ◽  
Scale Size ◽  
Heated Fluid ◽  
Rayleigh Numbers

This paper presents the results of an investigation concerned with measurements of the scale-size of the flow patterns near the so-called Malkus transitions. The flow patterns in a heated fluid layer were photographed at various Rayleigh numbers and these photographs subjected to quantitative analysis using an optical correlation computer. The results showed that the method provides a very sensitive technique for locating the transitions. Transitions reported by other investigators have been confirmed for Rayleigh numbers between 5.0 × 103 and 1.0 × 106, and an additional, previously unobserved, transition has been detected. Heat-transfer measurements were also made. This data demonstrated the limitations, compared to the optical method, of this approach to the detection of transitions.

Effective Thermal Conductivity for Combined Radiation and Free Convection in an Optically Thick Heated Fluid Layer

1981 ◽  
Vol 103 (1) ◽  
pp. 114-120 ◽  
Author(s):  
M. Epstein ◽  
F. B. Cheung ◽  
T. C. Chawla ◽  
G. M. Hauser
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Free Convection ◽  
Effective Thermal Conductivity ◽  
Radiative Heat ◽  
Fluid Layer ◽  
Convection Heat Transfer ◽  
Turbulent Heat ◽  
Free Convection Heat ◽  
Heated Fluid

The effective thermal conductivity for radiative heat transfer within an optically thick fluid layer undergoing high Rayleigh number convection is derived. This result is combined with available “pure” free-convection heat-transfer correlations to obtain closed-form analytical descriptions of the gross properties of a radiating fluid layer heated internally or from below. These simple solutions compare favorably with recent work in which the governing energy equation incorporating both turbulent heat transport and thermal radiation is solved numerically.

Natural Convection in Horizontal Thin-Walled Honeycomb Panels

1973 ◽  
Vol 95 (4) ◽  
pp. 439-444 ◽  
Author(s):  
K. G. T. Hollands
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Fluid Layer ◽  
Convection Heat Transfer ◽  
Correlation Equation ◽  
Wave Number ◽  
Equivalent Wave ◽  
Side Walls ◽  
The Stability ◽  
Rayleigh Numbers

This paper presents an experimental study of the stability of and natural convection heat transfer through a horizontal fluid layer heated from below and constrained internally by a honeycomb. Examination of the types of boundary conditions exacted on the fluid at the cell side-walls has shown that there are three limiting cases: (1) perfectly conducting side-walls; (2) perfectly adiabatic side-walls; and (3) side-walls having zero thickness. Experiments described in this paper approach the latter category. The fluid used is air and the honeycomb used is square-celled. Measured critical Rayleigh numbers are found to be intermediate between those applying to cases (1) and (2), and consistent with an “equivalent wave number” of approximately 0.95 times that for case (1). The measured natural convective heat transfer after instability is found to be significantly less than that predicted by the Malkus-Veronis power integral technique. However, it is found to approach asymptotically the heat transfer which would take place through a similar fluid layer unconstrained by a honeycomb. A general correlation equation for the heat transfer is given.

Laminar and Turbulent Free Convection From Elliptic Cylinders, With a Vertical Plate and Horizontal Circular Cylinder as Special Cases

1976 ◽  
Vol 98 (1) ◽  
pp. 72-80 ◽  
Author(s):  
G. D. Raithby ◽  
K. G. T. Hollands
Keyword(s):  
Heat Transfer ◽  
Circular Cylinder ◽  
Free Convection ◽  
Vertical Plate ◽  
Constant Heat Flux ◽  
Special Cases ◽  
Flux Boundary Conditions ◽  
Large Eccentricity ◽  
Rayleigh Numbers ◽  
Horizontal Circular Cylinder

Heat transfer by free convection from thin elliptic cylinders is predicted, accounting for both the effect of thick boundary layers at low Rayleigh numbers and the influence of turbulence at higher Rayleigh numbers. Isothermal and constant heat flux boundary conditions are treated. The results are compared with experimental data, which are available for the limiting cases of large eccentricity (vertical plate) and small eccentricity (horizontal circular cylinder); the agreement is excellent. Accurate correlation equations, from which the average heat transfer can be calculated, are given.

Influence of the angle of inclination of the cavity on heat transfer under free convection of an anomalously thermo viscous fluid

2006 ◽  
Vol 4 ◽  
pp. 166-173
Author(s):  
K.V. Moiseyev
Keyword(s):  
Heat Transfer ◽  
Free Convection ◽  
Viscous Fluid ◽  
Two Dimensional ◽  
Quadratic Dependence ◽  
Rayleigh Numbers

In this paper, two-dimensional free convection of a liquid with a quadratic dependence of viscosity on the temperature in square is simulated numerically at different angles of inclination to the horizon. The integral coefficients of heat transfer on isothermal boundaries and the minimum critical Rayleigh numbers are calculated.

Effect of Surface Radiation on Free Convection in Vertical Cylinders Partially Annular

2018 ◽  
Vol 389 ◽  
pp. 36-49
Author(s):  
Belkacem Ould Said ◽  
Mohamed Amine Medebber ◽  
Nourddine Retiel
Keyword(s):  
Heat Transfer ◽  
Free Convection ◽  
Radiation Heat Transfer ◽  
Surface Radiation ◽  
Navier Stokes ◽  
Discrete Ordinates ◽  
Energy Equations ◽  
Vertical Cylinders ◽  
Rayleigh Numbers ◽  
Emissivity Coefficient

The coupled of free convection with surface radiation in an annular region of two concentric vertical cylinders filled with air has been numerically investigated. The steady-state continuity, Navier–Stokes and energy equations were carried out by the finite volume method, and the Discrete Ordinates Method (DOM) was used to solve the radiative heat transfer equation (RTE). The computations have been performed for 103 ≤Ra≤ 106, with the emissivity coefficient of all the walls varying between 0 and 1. The influence of the both, Rayleigh numbers and emissivity coefficient of the wall for fixed height ratio X=0.5 on natural convection and radiation heat transfer in enclosure have been solved. The result shows that surface radiation significantly altered the temperature distribution and the flow patterns, especially at higher Rayleigh numbers. The average Nusselt number has also been discussed for different emissivity through the enclosure.

On free convection experiments in inclined air layers heated from below

1980 ◽  
Vol 96 (3) ◽  
pp. 461-479 ◽  
Author(s):  
Douglas W. Ruth ◽  
K. G. T. Hollands ◽  
G. D. Raithby
Keyword(s):  
Heat Transfer ◽  
Free Convection ◽  
Convective Motion ◽  
Secondary Transition ◽  
Transfer Data ◽  
Experimental Heat ◽  
Experimental Heat Transfer ◽  
Air Layers ◽  
Rayleigh Numbers ◽  
Theory And Experiment

The heat transfer and free convective motion, in inclined air layers heated from below, for angles of incidence 0 [les ] ϕ [les ] 30°, and Rayleigh numbers 100 < Ra cos ϕ < 10000, are studied experimentally. Results of both heat-transfer measurements and flow-visualization studies are reported. The purpose of the study was to investigate the fact, first noted by Hollands et al. (1976), that the experimental heat-transfer data, for ϕ > 20°, is not a function of the product Ra cos ϕ only, as expected from theoretical consideration. This discrepancy between theory and experiment is here attributed to a hypothesized secondary transition in the convective motion, due primarily to perturbation velocities in the upslope direction. This secondary transition appears to be the same as that predicted theoretically by Clever & Busse (1977); qualitative agreement with their theory is observed.

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