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Research Papers: Natural and Mixed Convection

Free Convection in Asymmetrically Heated Vertical Channels With Opposing Buoyancy Forces

[+] Author and Article Information
D. Roeleveld

Department of Mechanical &
Industrial Engineering,
Ryerson University,
350 Victoria Street,
Toronto, ON M5B 2K3, Canada
e-mail: droeleve@ryerson.ca

D. Naylor, W. H. Leong

Department of Mechanical &
Industrial Engineering,
Ryerson University,
350 Victoria Street,
Toronto, ON M5B 2K3, Canada

1Corresponding author.

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF HEAT TRANSFER. Manuscript received September 11, 2013; final manuscript received November 28, 2013; published online March 7, 2014. Assoc. Editor: Zhixiong Guo.

J. Heat Transfer 136(6), 062502 (Mar 07, 2014) (11 pages) Paper No: HT-13-1472; doi: 10.1115/1.4026218 History: Received September 11, 2013; Revised November 28, 2013

Laser interferometry and flow visualization were used to study free convective heat transfer inside a vertical channel. Most studies in the literature have investigated buoyancy forces in a single direction. The study presented here investigated opposing buoyancy forces, where one wall is warmer than the ambient and the other wall is cooler than the ambient. An experimental model of an isothermally, asymmetrically heated vertical channel was constructed. Interferometry provided temperature field visualization and flow visualization was used to obtain the streamlines. Experiments were carried out over a range of aspect ratios between 8.8 and 26.4, using temperature ratios of 0, −0.5, and −0.75. These conditions provide a modified Rayleigh number range of approximately 5 to 1100. In addition, the measured local and average Nusselt number data were compared to numerical solutions obtained using ANSYS FLUENT. Air was the fluid of interest. So the Prandtl number was fixed at 0.71. Numerical solutions were obtained for modified Rayleigh numbers ranging from the laminar fully developed flow regime to the turbulent isolated boundary layer regime. A semi-empirical correlation of the average Nusselt number was developed based on the experimental data.

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Figures

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Fig. 1

Schematic of the problem geometry

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Fig. 2

Schematic of two equivalent vertical channel cases with different temperature ratios; one with negative buoyancy forces and one with positive buoyancy forces relative to the gravity vector

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Fig. 3

Boundary conditions and computational domain

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Fig. 4

Comparison of dimensionless velocity profiles at various temperature ratios for fully developed flow at y/L = 0.5 and Ra(b/L) = 0.5 obtained from the numerical model and the analytical solution by Aung [1]

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Fig. 5

(a) Flow visualization, (b) sketch of the observed flow patterns, and (c) numerical solution streamlines for RT = −0.5, A = 17.6 and Ra(b/L) = 67.5

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Fig. 6

(a) Flow visualization, (b) sketch of the observed flow patterns, and (c) numerical solution streamlines for RT = −0.75, A = 17.6 and Ra(b/L) = 23.1

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Fig. 7

Infinite fringe interferograms at A = 17.6 for different temperature ratios

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Fig. 8

Infinite fringe interferograms and numerically predicted isotherms at RT = −0.5 for different aspect ratios

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Fig. 9

Graph of local Nusselt number versus nondimensional vertical distance for RT = −0.5, A = 26.4, and Ra(b/L) = 12.3

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Fig. 10

Instantaneous and running time-averaged local heat fluxes for RT = −0.5 with A = 8.8 at y/L = 0.5

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Fig. 11

Graph of local Nusselt number versus nondimensional vertical distance for RT = −0.5, A = 8.8, and Ra(b/L) = 1084

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Fig. 12

Overall channel average Nusselt number variation with modified Rayleigh number for RT = −0.5

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Fig. 13

Overall channel average Nusselt number variation with modified Rayleigh number for RT = −0.75

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Fig. 14

Comparison of the semi-empirical correlation for RT = −0.5 and RT = −0.75 with the experimental and numerical data

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