Authors: K. EI Moueddeb. S.F. Barrington and B.G. Newman
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Published in: CBE Journal » CBE Journal Volume 38 (1996)

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Description: To determine the most accurate procedure to monitor the air distribution pattern of perforated ventilation ducts, methods were compared for the experimental measurement of duct static air pressure and outlet air flow. Static air pressure readings, using a pitot static tube and piezometric wall taps, were compared for a rectangular perforated wooden ventilation duct with a length to hydraulic diameter ratio (LID,,) of 21.85 and 14 outlets giving an aperture ratio of 0.5. All readings were identical except for those measured over 25% of the duct length near the fan end, as they were exposed to air swirling and showed a coefficient of variation as high as 5.2%. Thus, the pitot static tube and piezometer wall taps will give the same air static pressure readings if, between the fan and the perforated duct, a non perforated section is added and its length is 10 times the duct's hydraulic diameter. The air flow at each outlet was measured using the grid method applied to both the outlet surface itself and the inside duct cross section, upstream and downstream from each outlet. Because the true outlet air flow equals the product of the air jet velocity component perpendicular to the surface and the flow area, a new instrument was developed to simultaneously measure the outlet air jet discharge angle and velocity. The outlet air flow measurements were performed using 4 rectangular perforated ducts with LID" of 18.8 and 12 outlets giving, respectively, aperture ratios of 0.5, I, 1.5, and 2. As compared to measurements taken inside the perforated duct, those obtained at the outlet surface predicted the outlet air flow with an error of 3 to 28%, for aperture ratios of 0.5 to 2, respectively. This error was due to the contraction of the outlet air jet which was too small to be measured accurately.

Citation: K. EI Moueddeb. S.F. Barrington and B.G. Newman 1996. EVALUATION OF METHODS TO MEAS RE THE PERFORMANCE OF PERFORATED VENTILATION DUCTS. Canadian Agricultural Engineering 38(3):207-213.
Volume: 38
Issue: 3
Pages -
Date: 1996
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Type: Text.Article
Format: PDF
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Coverage: Canada
Language 1: en
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Rights: Canadian Society for Bioengineering
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