Fluid Machine Problems

Fluid Machine Problems Centrifugal Pumps 1. When operated at a speed of 1200 rpm, a centrifugal pump gives the following performance: Discharge of water=400 gpm and discharge head=200 feet. If the pump is operated to give a discharge head of 500 feet without change of system characteristics. What must be the speed and volume of water discharged?  Ans. 3000rpm,1000gpm 2.A multi-stage centrifugal pump is to deliver 1000 gpm of water at a total head of 900 ft. Specific speed is is 500 rpm and rotative rpm is 600. a)

Determine the number of stages required. Answer=7

b) If a single stage pump is used, what would be the rotative rpm, Ns = 500rpm.  Answer= 2598 rpm 3. A 3. A double suction pump is required to deliver 2200 gpm against a total dynamic head of 300 ft at a speed of 1750 rpm. Specific gravity is 1.2. a) What horsepower would be required at the pump shaft if the pump is single stage? Answer= 247 HP b)

If the pump were two stage, what should be the horsepower? Answer=232 HP

4. A 4. A 2-stage centrifugal pump delivers 50 gpm of 225°F water against 250 ft. head at 3500 rpm. a)

What is its specific speed? Answer=662 rpm

b) What head could a geometrically similar pump produce if operated at 3000 rpm at 40 gpm flow? Answer=175.4 feet 5. Calculate drive horsepower for pumping 450 gpm cold water to a tank. Suction of 5”Hg vacuum, delivery at 75 psig, both measured close to pump. Assume that np is equal to 0.65. Answer=31.28 HP

6. Determine the specific speeds of the following single-stage pumps and specify the type of pump that would probably be used for each.

PUMP

RPM

CAPACITY, GPM

TOTAL HEAD, FT

A

1150

3500

100

B

885

12000

15

C

675 675

20000

50

D

625

9000

18

 Answer A=2150 and pump type is francis type B,C,D=solve on your own 7.A commercial pump is operating at 2150 rpm and delivers 1800 GPM GPM against a head of 47.03 m. Determine the approximate efficiency based on cengel. 8. A 8. A double suction, single stage centrifugal pump delivers 900 m3/hr of sea water (s.g. = 1.03) from source where water water varies 2 meters from low tide to high tide level. The pump centerline is located 2.6 meters above the surface of the water at high tide level. The pump discharges into a surface condenser 3 meters above pump centerline loss of head due to friction in in suction is 0.8 m and 3 m at discharge. The pump is directly connected to a 1750 rpm, 450 volts, 3 ⵁ, 60 hz source. Required: a.) Sketch the installation b.) Total suction head c.) Total discharge head d.) Ns of the pump e.) BHP if np = 70% f.) Motor hp if em = 80%