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Research Papers

Experimental and Theoretical Study of Ventilation and Heat Loss From Isothermally Heated Clothed Vertical Cylinder in Uniform Flow Field

[+] Author and Article Information
Nesreen Ghaddar1

 American University of Beirut, P.O. Box 11-0236, Beirut 1107-2020, Lebanonfarah@aub.edu.lb

Kamel Ghali

 American University of Beirut, Beirut 1107-2020, Lebanonka04@aub.edu.lb

Mohamad Al-Othmani

 American University of Beirut, P.O. Box 11-0236, Beirut 1107-2020, Lebanonmha41@aub.edu.lb

Ingvar Holmer

Ergonomics and Aerosol Technology, Lund University, Box 118, SE 211 00 Lund, Swedeningvar.holmer@design.lth.se

Kalev Kuklane

Ergonomics and Aerosol Technology, Lund University, Box 118, SE 211 00 Lund, Swedenkalev.kuklane@design.lth.se

1

Corresponding author.

J. Appl. Mech 77(3), 031011 (Feb 23, 2010) (8 pages) doi:10.1115/1.4000429 History: Received March 23, 2009; Revised July 31, 2009; Published February 23, 2010; Online February 23, 2010

The flow characteristics and heat transfer are studied in a vertical annulus of a heated cylinder surrounded by a permeable cylinder, subject to cross uniform wind with open end to the environment and in the presence of natural convection. The objective here is to develop a computationally efficient model capable of capturing the physics of the flow and heat transport to predict air renewal rates in the vertical annulus. The small quantities of air infiltrating/exfiltrating through the porous cylinder over its upstream/downstream regions do not substantially affect the external flow pattern around the clothed cylinder. The air annulus flow and heat transport model predicted the radial and vertical mass fluxes and the mass flow rate at the opening as a function of environment conditions, porous cylinder thermal properties, wind speed, and annulus geometry. Experiments were performed in a low speed wind tunnel (0.5–5 m/s), in which an isothermally heated vertical cylinder surrounded by a clothed outer cylinder was placed in uniform cross wind. The tracer gas method is used to predict total ventilation flow rates through the fabric and the opening. Good agreement was found between the model and experimental measurements of air renewal rate and predicted heat loss from the inner cylinder at steady conditions. A parametric study is performed to study the effect of wind speed and temperature difference between the wind and skin temperature on induced ventilation through the clothing and the opening. It is found that natural convection enhances ventilation of the annulus air at wind speed, less than 3 m/s, while at higher speeds, natural convection effect is negligible. As the temperature difference between external wind and inner cylinder surface increases, the vertical air temperature gradient and total upward airflow through the opening increase.

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Copyright © 2010 by American Society of Mechanical Engineers
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Figures

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Figure 1

The physical configuration of the clothed vertical cylinders of radii Rs and Rf and height L

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Figure 2

The computational domain and grid distribution

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Figure 3

Schematic of (a) the clothed heated vertical cylinder setup in the low speed wind tunnel and (b) the location of the N2 injection, N2 suction holes, and the mounted thermocouples

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Figure 4

A plot of the model predictions and experimentally obtained opening and normal ventilation rates cross wind speed of 0.5 m/s, 1, 2 m/s, and 4 m/s with and without heating at for environmental conditions of T∞=22°C and inner cylinder surface temperature of Ts=33.5°C

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Figure 5

Plots of the predicted and experimentally measured values of (a) angular-averaged air annulus temperature as a function of height at wind speed of 2 m/s and (b) the total power input to the heated surface as a function of wind velocity at surface temperature of 33.5°C and environment temperature of 22°C

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Figure 6

Plots of (a) the normal ventilation rate through outer fabric and (b) the air annulus angular-averaged temperature as a function of cylinder height for both models with and without natural convection effect at fabric permeability of 0.05 m/s and ambient temperature of 25°C

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Figure 7

Plot of the air annulus angular-averaged temperature as a function of cylinder height at different ambient conditions for both models with and without natural convection effect at fabric permeability of 0.05 m/s and wind speed of 0.5 m/s

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Figure 8

A plot of the angular-averaged air temperature at the opening as a function of wind velocity at ambient condition of 25°C with and without natural convection effect for a fabric of permeability of 0.05 m/s

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Figure 9

Plot (a) the total ventilation rate through the fabric as predicted by the mixed convection model as a function of wind velocity at various fabric permeabilities and (b) the corresponding % increase in ventilation when natural convection is incorporated

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Figure 10

Plots of the total heat loss through the fabric as predicted by the mixed convection model as a function of wind velocity at various fabric permeabilities

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