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Research Papers: Natural and Mixed Convection

Measurement of Time-Averaged Turbulent Free Convection in a Tall Enclosure Using Interferometry

[+] Author and Article Information
M. E. Poulad

Department of Mechanical and Industrial Engineering, Ryerson University, 350 Victoria Street, Toronto, M5B 2K3, ON, Canadampoulad@ryerson.ca

D. Naylor1

Department of Mechanical and Industrial Engineering, Ryerson University, 350 Victoria Street, Toronto, M5B 2K3, ON, Canadadnaylor@ryerson.ca

P. H. Oosthuizen

Department of Mechanical and Materials Engineering, Queen’s University, Kingston, K7L 3N6, ON, Canadaoosthuiz@me.queensu.ca

1

Corresponding author.

J. Heat Transfer 133(4), 042501 (Jan 19, 2011) (8 pages) doi:10.1115/1.4003081 History: Received June 28, 2010; Revised November 17, 2010; Published January 19, 2011; Online January 19, 2011

Laser interferometry is combined with high-speed digital cinematography to measure time-averaged transient and turbulent convective heat transfer rates. The method is applied to study free convection in a tall vertical air-filled enclosure. Measurements are made at three wall spacings in the turbulent flow regime (5.2×104RaW2.8×105). An automated image processing algorithm is used to calculate the instantaneous local heat flux from a sequence of interferograms that is captured by a high-speed camera. The local Nusselt number distributions on the hot and cold walls are obtained by time-averaging the fluctuations in local heat flux. The effects of key experimental parameters, such as the camera frame rate and the total image capture time, are investigated. For the current problem, it is shown that a total capture interval of about 10 s is required to accurately measure the time-average local Nusselt number. Within the measurement uncertainty, the average Nusselt number results are in agreement with a widely used empirical correlation from the literature.

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Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 1

Experimental geometry and coordinate system

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Figure 2

Sequence of infinite fringe interferograms near the cold wall at a time interval of Δt=0.3 s(0.355≤y/H≤0.372, H/W=24, RaW=1.02×105)

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Figure 3

A typical near-wall pixel intensity profile and the best fit sine wave over one period used to obtain the fringe shift gradient. The inset image shows the horizontal scan location on the infinite fringe interferogram of the near-wall region.

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Figure 4

Instantaneous and running time-averaged local heat flux on the cold wall of a tall vertical enclosure (y/H=0.27, H/W=17.1, RaW=2.8×105, frame rate=100 Hz)

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Figure 5

Running time-averaged local heat flux on the cold wall of the enclosure calculated from three independent time series of images (y/H=0.27, RaW=2.8×105, H/W=17.1, frame rate=100 Hz)

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Figure 6

Time-average local Nusselt number distribution on the hot and cold walls of a tall vertical air-filled enclosure: (a) RaW=5.19×104, H/W=30; (b) RaW=1.02×105, H/W=24; and (c) RaW=2.79×105, H/W=17

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Figure 7

Comparison of the measured average Nusselt number with the experimental data of ElSherbiny (21) and the empirical correlation of ElSherbiny (22)

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