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Research Papers: Natural and Mixed Convection

Natural Convection From Interrupted Vertical Walls

[+] Author and Article Information
Mehran Ahmadi, Golnoosh Mostafavi

Laboratory for Alternative Energy
Conversion (LAEC),
Mechatronic Systems Engineering,
Simon Fraser University (SFU),
Surrey, BC V3T 0A3, Canada

Majid Bahrami

Laboratory for Alternative Energy
Conversion (LAEC),
Mechatronic Systems Engineering,
Simon Fraser University (SFU),
Surrey, BC V3T 0A3, Canada
e-mail: mbahrami@sfu.ca

Data acquisition system.

1Corresponding author.

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF HEAT TRANSFER. Manuscript received October 16, 2013; final manuscript received August 18, 2014; published online September 16, 2014. Assoc. Editor: Sujoy Kumar Saha.

J. Heat Transfer 136(11), 112501 (Sep 16, 2014) (8 pages) Paper No: HT-13-1539; doi: 10.1115/1.4028369 History: Received October 16, 2013; Revised August 18, 2014

Steady-state external natural convection heat transfer from interrupted rectangular vertical walls is investigated. A systematic numerical, experimental, and analytical study is conducted on the effect of adding interruptions to a vertical plate. Comsol multiphysics is used to develop a two-dimensional numerical model for investigation of fin interruption effects on natural convection. A custom-designed testbed is built and six interrupted wall samples are machined from aluminum. An effective length is introduced for calculating the natural convection heat transfer from interrupted vertical walls. Performing an asymptotic analysis and using a blending technique, a new compact relationship is proposed for the Nusselt number. Our results show that adding interruptions to a vertical wall can enhance heat transfer rate up to 16% and reduce the weight of the fins, which in turn, lead to lower manufacturing and material costs.

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References

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Figures

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Fig. 1

Effect of interruptions on boundary layer growth in natural heat transfer from a vertical wall

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Fig. 2

(a) Schematic of the numerical domain and boundary conditions for vertical interrupted wall and (b) grid used in the model for interrupted wall

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Fig. 3

Grid independency study; walls average heat flux versus number of elements for the benchmark case (see Table 1)

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Fig. 4

(a) velocity domain and (b) temperature domain for the benchmarks case; the diffusion of velocity and temperature in the gap causes the air to reach the top wall with higher velocity and lower temperature

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Fig. 5

(a) A schematic and photo of the testbed and (b) back side of the samples; positioning of the thermocouples and heater

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Fig. 6

Heat transfer versus γ = G/l for different ζ = l/t values. The figure also shows the comparison between the numerical data (symbols) and introduced asymptotes (lines) for natural convection heat transfer from interrupted vertical walls.

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Fig. 7

Effective length versus γ = G/l for different ζ = l/t values. The figure also shows the comparison between the numerical data (symbols) and the proposed relationship (lines) for the effective length (Leff).

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Fig. 8

Nusselt number versus γ = G/l for different ζ = l/t values. The figure also shows the comparison between the numerical data (hollow symbols), experimental data (solid symbols), and the proposed compact relationship (lines).

Tables

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