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Qairo University
Fhculty of Engineering
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Mechanical Power Dept./prog.
Turbomachinery I (MEP 405 A)
Midterm Exam
Nov. 9, 2015
Question 1(15 points):
(.$) a. Define: (i) Polytropic efficiency (ii) Total-tototal efficiency (iii) Totatto-static efficiency
(Use the h-s chart for a compressor to demonstrate your answer)
:
( tO)O. An.8 stages axial flow air compressor operates at 15000 rpm and produces a pressure
ratio of 4. The compressor has an efficiency of 0,86, and equal pressure ratio per stage.
\-/
i. Find the polytropic efficiency and specific work for both first stage and compressor.
ii.
27 "C, Poo = 1.0 baQ.
lf compressor speed was changed to 20000 rpm, find the specific work required for
the compressor.
(Too =
_Question 2 (15 pointsl:
\-./
@
Y-/
lsignificanceofspecificspeed?SupportyouranSwerwithrelations
for both axial and radial turbomachines.
b. A c.entrifugal
pump with an impeller of 20 cm diameter gives at maximum efficiency point
a discharge of 3 m3/min of water at 1500 rpm againsl a head of 5 m. The maximum
overallefficiency is 80 %.
i. What should be the percentage increase in pump speed of rotation if a similar
impeller is used, with 50 7o increase in size, to give 20 m3/min of water?
ii. calculate the head and pumping power for the second pump.
iii. Calculate the pumping power of the second pump when running at the same speed.
Assume 2 points drop in pump efficiency. comment on your result.
Good Luck
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