N-1

The characteristic and horsepower curves shown in Fig. N-1 indicate the performance of a double-inlet forced-draft fan operating at sea level with a speed of 1,180 rpm when handling air at 40 F. Determine the static pressure developed by the fan and the power required to drive it when it handles 514,000 lb per hr of 80 F air at an altitude of 5,000 ft, where the barometric pressure is approximately 24.9 in. Hg abs.

Figure N-1

N-2

1. Draw an approximate head vs. capacity curve for a fanhandling flue gas of any standard type for a design pressure of 10 in. water and 150,000 cfm at 300 F.

2. Assuming the fan to be driven by a constant-speed motor, explain how to determine the head curve with gas at 400 F.

3. If a 30 per cent pressure drop is added to the system resistance, what will be the output of the fan in cfm with the gas at 300 F?

N-3

Characteristic curves in Fig. N-4 are for a forced-draft fan operated at speeds of 1,200 and 900 rpm. Also shown is the efficiency curve obtained at an operating speed of 1,200 rpm. Estimate the horsepower required to drive the fan when operated at a speed of 900 rpm and at a flow rate of 300,000 cfm at 15 in. water static pressure.

Figure N-4

N-4

The performance characteristics of a centrifugal compressor are shown in Fig. N-5; symbols are defined as follows: