Case 13: Water - Net Positive Suction Head Available - Example 1 & 2
Reference: Cameron Hydraulic Data , 18th Edition, 1994, Ingersoll-Dresser Pumps. Page 1-13, Example No 1 and Example No 2
Pipe Flow Expert File: Case_13_Water_Net_Positive_Suction_Head_Available.pfe
Problem Description:
A pump is used to deliver water to a distribution system.
The friction loss through the suction line is assumed as 2.92 ft head in all cases.
Example No 1:
The water source is 10 ft below the pump.
The pressure on the surface of the fluid is atmospheric, 14.696 psia.
Find the NPSHa and the suction lift required.
Example No 2:
The water source is 10 ft above the pump.
The pressure on the surface of the fluid is atmospheric, 14.696 psia.
Find the NPSHa and the suction head available.
Fluid Data: Water at 68°F at sea level.
Result Comparison:
|
Data Item Example 1 |
Published data |
Pipe Flow Expert |
|
NPSH available () |
20.26 |
20.26 |
|
Suction Lift () |
12.92 |
-12.90 HGL at pump |
|
Data Item Example 2 |
Published data |
Pipe Flow Expert |
|
NPSH available () |
40.26 |
40.26 |
|
Suction Head () |
7.08 (positive) |
7.07 HGL at pump |
Commentary:
The published data and the calculated results compare well.
These are very simple examples where the friction loss through the pipes is assumed, not calculated.
To model these situations in Pipe Flow Expert a pipe diameter and flow rate was chosen and then the pipe length was varied until the frictional loss through the pipes of 2.92 ft hd was obtained.
The discharge pipework was modeled with a similar pipe size and a 10 ft lift on the discharge side of the pump.
This allows the HGL at the node where the pump has been located to be used for comparison with the published suction head available.