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Research Papers: Forced Convection

Ventilation of Wind-Permeable Clothed Cylinder Subject to Periodic Swinging Motion: Modeling and Experimentation

[+] Author and Article Information
N. Ghaddar1

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

K. Ghali

Department of Mechanical Engineering, Beirut Arab University, Beirut, 1107-2020, Lebanon

B. Jreije

Department of Mechanical Engineering, American University of Beirut, P.O. Box 11-0236, Beirut 1107-2020, Lebanon

1

Corresponding author.

J. Heat Transfer 130(9), 091702 (Jul 10, 2008) (11 pages) doi:10.1115/1.2944245 History: Received May 04, 2007; Revised November 29, 2007; Published July 10, 2008

A theoretical and experimental study has been performed to determine the ventilation induced by swinging motion and external wind for a fabric-covered cylinder of finite length representing a limb. The estimated ventilation rates are important in determining local thermal comfort. A model is developed to estimate the external pressure distribution resulting from the relative wind around the swinging clothed cylinder. A mass balance equation of the microclimate air layer is reduced to a pressure equation assuming laminar flow in axial and angular directions and that the air layer is lumped in the radial direction. The ventilation model predicts the total renewal rate during the swinging cycle. A good agreement was found between the predicted ventilation rates at swinging frequencies between 40rpm and 60rpm and measured values from experiments conducted in a controlled environmental chamber (air velocity is less than 0.05ms) and in a low speed wind tunnel (for air speed between 2ms and 6ms) using the tracer gas method to measure the total ventilation rate induced by the swinging motion of a cylinder covered with a cotton fabric for both closed and open aperture cases. A parametric study using the current model is performed on a cotton fabric to study the effect of wind on ventilation rates for a nonmoving clothed limb at wind speeds ranging from 0.5msto8ms, the effect of a swinging limb in stagnant air at frequencies up to 80rpm, and the combined effect of wind and swinging motion on the ventilation rate. For a nonmoving limb, ventilation rate increases with external wind. In the absence of wind, the ventilation rate increases with increased swinging frequency.

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Copyright © 2008 by American Society of Mechanical Engineers
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Figures

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Figure 1

Representation of the human limb motion inside the clothing cylinder showing (a) front view of the geometry, (b) side view of the geometry, and (c) swinging motion

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Figure 2

A plot of (a) low speed wind tunnel and test section and (b) the swinging limb mechanism and location of measurements in a top view

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Figure 3

A plot of the model predictions and experimentally estimated ventilation rates for closed aperture at different crosswind speeds as a function of the frequency for a domain length of 0.48m, Ym=0.0185m, and ϕmax=20deg

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Figure 4

A plot of the model predictions and experimentally estimated ventilation rates for open aperture at different cross wind speeds as a function of the frequency for a domain length of 0.48m, Ym=0.0185m, and ϕmax=20deg

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Figure 5

A plot of the microclimate (a) dimensionless tangential velocity component and (b) dimensionless pressure difference between the outer surface and inner microclimate pressure as predicted by the current model as a function of θ and the reported results of Sobera (8)

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Figure 6

A plot of ventilation rate as a function of swinging frequency f in rpm at different wind speeds for (a) closed aperture and (b) open aperture at Rs=0.038m, Rf=0.0575m, α=0.05m∕s, ϕmax=20deg, and L=0.48m

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Figure 7

The effect of the ratio of microclimate layer thickness to inner limb radius Ym∕Rs on ventilation rate for closed aperture is shown at Vw=1m∕s for Rs=0.038m, Rf=0.0575m, α=0.05m∕s, L=0.48m, and f=0rpm, 40rpm, and 80rpm

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Figure 8

A plot of ṁa versus ϕmax at Vw=1m∕s for (a) f=40rpm and (b) f=80rpm

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