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Chapter 14: Fans, Blowers, Compressors Text, Questions and Answers

By John Constance
From Mechanical Engineering License Review, Fifth Edition

14-1 General

With the exception of the fact that gases are compressible the theory of design for equipment to move gases and vapors is similar to that of pumps for liquids. Heads developed in terms of feet of fluid being pumped are almost identical for equivalent circumferential speeds as for centrifugal pump designs. Axial flow impellers impart similar heads to both liquids and gases and valve actions in positive displacement compressors are quite similar to those of piston water pumps.

When considering the compression of gases, the machines are usually referred to as fans (centrifugal and propeller), blowers (centrifugal and lobular), and compressors (multistage centrifugal, lobular, and piston).

FANS AND BLOWERS

Q14-1

Find the motor size needed to provide the forced-draft service to a boiler that burns coal at the rate of 10 tons per hr. The air requirements are 59,000 cfm, air is being provided under 6 in. water gauge (WG) by the fan which has a mechanical efficiency of 60 per cent. Assume fan to deliver at a total pressure of 6 in. WG.

Q14-2

A blower with the inlet open to the atmosphere delivers 3,000 cfm of air at a pressure of 2 in. WG through a duct 11 in. in diameter, the manometer being attached to the discharge duct at the blower. Air temperature is 70 F, and the barometer pressure is 30.2 in. Hg. Calculate the air horsepower.

Answers

Q14-1

The horsepower is determined by the basic formula given as

We must convert the 6 in.

Copyright Engineering Press 2000 under license agreement with Books24x7
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