Question 5 [12 Marks] The pump whose performance data is plotted in Figure 4 was operating at a rotational speed of 1950 rpm and had an impeller diameter of 15 m. First, state the affinity law for centrifugal pumps when the impeller varies, then use the equations of the affinity laws to determine the head that would result in a capacity of 4000 L/min. Then, compute the performance of the pump impeller diameter changes to 35 m. Efficiency (%) 30 100 Total Head (m) 200 r 150 Head 100 Efficiency Power 8 500 1000 1500 Pump capacity (gal/min) 0 2000 4000 6000 Pump capacity (L/min) 2000 2500 8000 10000 40 Power (w)
(exam prep fluids 3) The head developed by the 250mm impeller diameter pump (from annexure A) rotating at 2900rev/min in the system below at its operating point was found to be 72m of water (p=1000kg/m²; 4=1.14x10-3Pa.s; y=9.81kN/m²; Pvapor-1.7kPa abs). The total length of the 77.9mm diameter pipe (e=0.000046m) is 20m. The elbows are 90° standard (Le/D=30). Take atmospheric pressure as 100kPa (abs) and the gauge pressure above the fluid surface in the sealed tank is 25kPa below atmospheric. 3.1 Obtain an expression for the NPSH, to the pump in the system from the energy equation. 3.2 Obtain the pipe friction factor 3.3 Suggest a suitable position for the pump if a 10% tolerance between NPSH and NPSHr is to be achieved to avoid cavitations. 3.4 Calculate the output power of the pump. 3.5 Obtain the power required to drive the pump.
![Question 5
[12 Marks]
The pump whose performance data is plotted in Figure 4 was operating at a
rotational speed of 1950 rpm and had an impeller diameter of 15 m. First, state the
affinity law for centrifugal pumps when the impeller varies, then use the equations of
the affinity laws to determine the head that would result in a capacity of 4000 L/min.
Then, compute the performance of the pump impeller diameter changes to 35 m.
Efficiency (%)
30
100
Total Head (m)
200 r
150
Head
100
Efficiency
Power
8
500
1000
1500
Pump capacity (gal/min)
0
2000
4000
6000
Pump capacity (L/min)
2000
2500
8000
10000
40
Power (w)](/v2/_next/image?url=https%3A%2F%2Fcontent.bartleby.com%2Fqna-images%2Fquestion%2F4815a2f9-f91a-4047-aa70-6e46a60dfdea%2F81497150-8a8f-4508-8fab-7f8514be12c6%2Fn2hkcwr_processed.jpeg&w=3840&q=75)
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