Fluid Mechanics

It is desired to design a pump-piping system to keep a 1-million-gallon capacity water tank filled.

The plan is to use a modified (in size and speed) version of the model A centrifugal pump. Provided

is the test data for a small model of this pump: D = 5:45 in, ω = 1760 rpm, tested with water at

20C:

Q, gal/min

0

5

10

15

20

25

30

35

40

45

50

55

60

H, ft

28

28

29

29

28

28

27

26

25

23

21

18

15

Efficiency, %

0

13

25

35

44

48

51

53

54

55

53

50

45

 

where Q is the volumetric flow rate and h = Δp/ρg is the centrifugal pump “head.”

The tank is to be filled daily with groundwater at 10C from an aquifer, which is 0.8 mi from the

tank and 150 ft lower than the tank. Estimated daily water use is 1.5 million gal/day. Filling time

should not exceed 8 h per day. The piping system should have four “butterfly” valves with variable

openings, 10 90degree elbows, and galvanized-iron pipe of a size to be selected in the design. The design

should be economical both in capital costs and operating expense. Use the following cost estimates

for system components:

 

Pump and motor $3500 plus $1500 per inch of impeller size

Pump speed Between 900 and 1800 rpm

Valves $300 + $200 per inch of pipe size

Elbows $50 plus $50 per inch of pipe size

Pipes $1 per inch of diameter per foot of length

Electricity cost 10¢ per kilowatt-hour

 

Select the combination of pipe size, pump impeller size, and speed for this task (using the data

provided), that yields the lowest cost after 20 years of operation.

 

1. Introduction

2. Problem description – Describe the proposed problem and design objectives.

3. Design process – Present the logical steps and equations used to perform your analysis.

4. Design description – Give a detailed cost analysis of your design. Show what the effect of

impeller diameter, flow rate, and speed is on both overhead cost and operational costs.

5. Summary