5. A duct of 0.45 m diameter and 90 m long leads from a fan discharge chamber where the pressure is15 mm of water to a plenum chamber where the pressure is 10 mm of water.In order to increase the flow, two alternatives are considered. One is to lay a duct of 0.3 m diameterand 90 m long in parallel with the duct of 0.45 m diameter. The other is to increase the diameter of0.45 m diameter duct for the last 60 m length. Calculate the increased diameter so that this methodgives the same flow as the 0.45 m and 0.3 m ducts in parallel. Assume that the pressures in the fanchamber and plenum chamber are unaffected by changes in the flow and consider duct friction lossesonly. The friction factor may be taken as 0.0o55.6. A 0.3 m diameter circular duct carries standard air at a velocity of 360 m/min. It is replaced by arectangular duct having the same pressure loss per unit length due to friction. Determine thedimensions of the rectangular duct if the aspect ratio is to be 1.5 for (a) the same volume flowthrough the two ducts, and (b) the same velocity in the two ducts.[Ans. 0.567 m1[Ans, 0.336 m, 0.224 m: 0.375 m, 0.25 m 17. A fan delivers air at 8 m/s to the main line of air conditioning duct. After a straight run of10 m, a branch of 4 m length delivers air to a room with 2 m'/s. Another branch after a 5 m furtherrun is taken from the main branch. This branch is 5 m in length and delivers 3 m'/s. The main branchruns straight for another 5 m and then turns by 90° and runs for another 5 m length and delivers 3 m/s of air. The losses are given asFor elbow : 0.25 p, where p,mm of water.4.04For branch : 0.2 p, + Elbow lossFor straight through section : 0.25 x Difference of velocity pressureFitting losses where change in area occurs.Find the size of all the ducts and determine the static pressure requirement. Use the following formulafor friction rate :0.002 268 (0)RS2(D)4973where Q is in m'/s and D is in m.PrFind the friction rate in main line and then assume same friction rate for whole of duct work.(Ans. 1.128 m, 1.01 m : 0.783 m ; 0,905 mm of water; 0.0586 mm of water / m length ]+ Main duct8. A main air duct of constant rectangularcross-section 2 m by 0.6 m has severalbranch pieces leading off it. One of these 0.6 mbranches is shown in Fig. 20.28. Thebranch leaves the main at right anglesand has a 90° bend in it of radius 0.6 m,as well as a damper for flow regulationand an exit grill. The branch is 0.6 m by0.3 m and 3 m long. The flow throughthe main duct before this off take is 750m'/min and the flow required in thebranch is 90 m'/min. Čalculate the-BranchF-2m-0.6 mDamper -GrllAir outletFig. 20.28

Answered: Image /qna-images/answer/048d8a44-9b5d-4e03-a7ab-60eec8b1a28a.jpg

6. A 0.3 m diameter circular duct carries standard air at a velocity of 360 m/min. It is replaced by a rectangular duct having the same pressure loss per unit length due to friction. Determine the dimensions of the rectangular duct if the aspect ratio is to be 1.5 for (a) the same volume flow through the two ducts, and (b) the same velocity in the two ducts. (Ans. 0.336 m. 0.224 m: 0.375 m, 0.25 m

6. A 0.3 m diameter circular duct carries standard air at a velocity of 360 m/min. It is replaced by a rectangular duct having the same pressure loss per unit length due to friction. Determine the dimensions of the rectangular duct if the aspect ratio is to be 1.5 for (a) the same volume flow through the two ducts, and (b) the same velocity in the two ducts. (Ans. 0.336 m. 0.224 m: 0.375 m, 0.25 m

Elements Of Electromagnetics

7th Edition

ISBN:9780190698614

Author:Sadiku, Matthew N. O.

Publisher:Sadiku, Matthew N. O.

ChapterMA: Math Assessment

Section: Chapter Questions

Problem 1.1MA

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6. A 0.3 m diameter circular duct carries standard air at a velocity of 360 m/min. It is replaced by a rectangular duct having the same pressure loss per unit length due to friction. Determine the dimensions of the rectangular duct if the aspect ratio is to be 1.5 for (a) the same volume flow through the two ducts, and (b) the same velocity in the two ducts. [Ans. 0.336 m, 0.224 m ; 0.375 m, 0.25 m]