This set of Thermodynamics Multiple Choice Questions & Answers (MCQs) focuses on “Volumetric Efficiency”.
1. The temperature and pressure conditions at free air delivery are
a) 27 degree Celsius, 100 bar
b) 15 degree Celsius, 101.325 bar
c) 27 degree Celsius, 101.325 bar
d) 15 degree Celsius, 100 bar
View Answer
Explanation: This is known as FAD(free air delivery).
2. The volumetric efficiency is defined as the ratio of
a) total volume / piston displacement volume
b) total volume / gas volume taken during suction
c) gas volume taken during suction / swept volume
d) swept volume / gas volume taken during suction
View Answer
Explanation: The swept volume is also called piston displacement volume.
3. Clearance is given by
a) total volume / swept volume
b) total volume / clearance volume
c) swept volume / clearance volume
d) clearance volume / swept volume
View Answer
Explanation: Here C=Vc/Vs.
4. The clearance volumetric efficiency is equal to
a) 1 + C + C(p2/p1)^(1/n)
b) 1 – C – C(p2/p1)^(1/n)
c) 1 – C + C(p2/p1)^(1/n)
d) 1 + C – C(p2/p1)^(1/n)
View Answer
Explanation: Here C is the clearance and p1,p2 are pressures.
5. As clearance and pressure ratio increases, volumetric efficiency ____
a) decreases
b) increases
c) remains constant
d) none of the mentioned
View Answer
Explanation: This comes from the equation of volumetric efficiency.
6. To get maximum flow capacity, compressors are built with maximum practical clearance.
a) true
b) false
View Answer
Explanation: To get maximum flow capacity, compressors are built with minimum practical clearance.
7. When the clearance volume is at minimum level,
a) volumetric efficiency is maximum
b) flow through machine is maximum
c) both of the mentioned
d) none of the mentioned
View Answer
Explanation: We can get this from volumetric efficiency equation.
8. For a given pressure ratio, volumetric efficiency is zero when maximum clearance is
a) 1 / ((p2/p1)^(1/n) +1)
b) 1 / ((p2/p1)^(1/n) -1)
c) 1 / ((p1/p2)^(1/n) -1)
d) 1 / ((p1/p2)^(1/n) +1)
View Answer
Explanation: This comes from the equation of volumetric efficiency when we put volumetric efficiency equal to zero.
9. Increasing the pressure ratio, increases the volumetric efficiency.
a) true
b) false
View Answer
Explanation: For a fixed clearance, increasing the pressure ratio decreases the volumetric efficiency.
10. Which of the following is correct?
a) p2max/p1 = (1 + 1/C)n
b) p2max/p1 = (1 – 1/C)n
c) p2max/p1 = (1 – C)n
d) p2max/p1 = (1 + C)n
View Answer
Explanation: the maximum pressure ratio which can be attained by a reciprocating compressor cylinder is limited by the clearance.
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