Solved: A local ventilation system (a hood and duct system) is used to remove air and

Chapter 14, Problem 14-55E

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A local ventilation system (a hood and duct system) is used to remove air and contaminants produced by a welding operation (Fig. P1455E). The inner diameter (ID) of the duct is D 5 9.06 in, its average roughness is 0.0059 in, and its total length is L 5 34.0 ft. There are three elbows along the duct, each with a minor loss coefficient of 0.21. Literature from the hood manufacturer lists the hood entry loss coefficient as 4.6 based on duct velocity. When the damper is fully open, its loss coefficient is 1.8. A squirrel cage centrifugal fan with a 9.0-in inlet is available. Its performance data fit a parabolic curve of the form Havailable 5 H0 2 aV . 2 , where shutoff head H0 5 2.30 inches of water column, coefficient a 5 8.50 3 1026 inches of water column per (SCFM)2 , available head Havailable is in units of inches of water column, and capacity V . is in units of standard cubic feet per minute (SCFM, at 77F). Estimate the volume flow rate in SCFM through this ventilation system.