Compressor - Problem Solving UPDATED
ACTUAL Exam Questions and CORRECT
Answers
negative - CORRECT ANSWER - Positive work is based on an engine when man dreamed of
some machine that replaces the horse. A compressor and a pump for that matter are the reverse of
an engine in the sense that they consume mechanical energy rather than produce it. Therefore the
work of a compressor is always
-145 - CORRECT ANSWER - An ideal single stage air compressor without clearance takes in
air at 100 kPa with a temperature of 16 deg. C and delivered at 413 kPa after isentropic
compression. What is the discharge work done by the compressor in kJ/kg.
0.287 - CORRECT ANSWER - Value for Gas Constant of Air in kJ/kg-K
5.6 - CORRECT ANSWER - An air compressor is to compress 8.5 m^3/min from 98.56 kPa
to 985.6 kPa. Assuming ideal conditions, and with n = 1.3, what will be the saving in work due
to two staging?
Answer in kW.
0.746 - CORRECT ANSWER - 1 horsepower = how many kW?
77.68 - CORRECT ANSWER - A two stage compresor with first stage piston displacement of
94,390 cm^3/s is driven by a motor. Motor output is 35 HP, suction temperature is 22 deg. C,
volumetric efficiency 85%, mechanical efficiency 95%, the intercooler pressure is 30 psi gage.
Air temperature in and out of the intercooler are 105 deg. C and 44 deg. C. Final discharge
pressure is 100 psi gage, suction estimated 14.5 psi. Find the compression efficiency.
Answer in %.
112.02 - CORRECT ANSWER - A single stage air compressor handles 0.454 m^3/s of
atmospheric pressure, 27 deg. C air, and delivers it to a receiver at 652.75 kPa. Its volumetric
, efficiency is 0.72, its compression efficiency on an isothermal basis is 0.85 and its mechanical
efficiency is 0.90. If it rotates at 350 rpm, what power in kW is required to drive it?
Answer in kW.
-32.02 - CORRECT ANSWER - A rotary compressor receives 8 m^3/min. of a gas (R = 0.410
kJ/kg-K, Cp = 1.03 kJ/kg-K) at 108 kPa, 27 deg. C and delivers it at 650 kPa. Find the work if
compression is polytropic with PV^1.3 = C.
Answer in kW.
water jacket - CORRECT ANSWER - water-filled casing surrounding a device, typically a
metal sheath having intake and outlet vents to allow water to be pumped through and circulated.
The flow of water to an external heating or cooling device allows precise temperature control of
the device.
34.94 - CORRECT ANSWER - Air taken from the atmosphere at 100 kPa and 21 deg. C is
delivered to the air receiver at 690 kPa and 150 deg. C by means of a water jacketed
reciprocating compressor. The compressor has rated capacity of 0.15 m^3/s free air. Determine
the power required to compress the air.
Answer in kW.
100 - CORRECT ANSWER - 1 bar = how many kPa?
70.15 - CORRECT ANSWER - The stroke of the piston of an air compressor is 250 mm and
the clearance volume is equal to 6% of the stroke volume. The pressure of the air at the
beginning of the compression of 0.98 bar and it is discharged at 3.8 bar. Assuming compression
to follow the law PV^n = C, where n = 1.25, calculate the distance moved by the piston from the
beginning of its pressure stroke before the discharge valves opens. Express this as a percentage
of the stroke.
157.54 - CORRECT ANSWER - A double acting compressor with piston displacement of
0.05 m^3 per stroke operates at 500 rpm. The clearance factor is 5% and it receives air at 100
kPa and discharges it at 600 kPa. The compression and re-expansion curve is polytropic with n =
1.3. Determine the power required to compress the air.
Answer in kW.
ACTUAL Exam Questions and CORRECT
Answers
negative - CORRECT ANSWER - Positive work is based on an engine when man dreamed of
some machine that replaces the horse. A compressor and a pump for that matter are the reverse of
an engine in the sense that they consume mechanical energy rather than produce it. Therefore the
work of a compressor is always
-145 - CORRECT ANSWER - An ideal single stage air compressor without clearance takes in
air at 100 kPa with a temperature of 16 deg. C and delivered at 413 kPa after isentropic
compression. What is the discharge work done by the compressor in kJ/kg.
0.287 - CORRECT ANSWER - Value for Gas Constant of Air in kJ/kg-K
5.6 - CORRECT ANSWER - An air compressor is to compress 8.5 m^3/min from 98.56 kPa
to 985.6 kPa. Assuming ideal conditions, and with n = 1.3, what will be the saving in work due
to two staging?
Answer in kW.
0.746 - CORRECT ANSWER - 1 horsepower = how many kW?
77.68 - CORRECT ANSWER - A two stage compresor with first stage piston displacement of
94,390 cm^3/s is driven by a motor. Motor output is 35 HP, suction temperature is 22 deg. C,
volumetric efficiency 85%, mechanical efficiency 95%, the intercooler pressure is 30 psi gage.
Air temperature in and out of the intercooler are 105 deg. C and 44 deg. C. Final discharge
pressure is 100 psi gage, suction estimated 14.5 psi. Find the compression efficiency.
Answer in %.
112.02 - CORRECT ANSWER - A single stage air compressor handles 0.454 m^3/s of
atmospheric pressure, 27 deg. C air, and delivers it to a receiver at 652.75 kPa. Its volumetric
, efficiency is 0.72, its compression efficiency on an isothermal basis is 0.85 and its mechanical
efficiency is 0.90. If it rotates at 350 rpm, what power in kW is required to drive it?
Answer in kW.
-32.02 - CORRECT ANSWER - A rotary compressor receives 8 m^3/min. of a gas (R = 0.410
kJ/kg-K, Cp = 1.03 kJ/kg-K) at 108 kPa, 27 deg. C and delivers it at 650 kPa. Find the work if
compression is polytropic with PV^1.3 = C.
Answer in kW.
water jacket - CORRECT ANSWER - water-filled casing surrounding a device, typically a
metal sheath having intake and outlet vents to allow water to be pumped through and circulated.
The flow of water to an external heating or cooling device allows precise temperature control of
the device.
34.94 - CORRECT ANSWER - Air taken from the atmosphere at 100 kPa and 21 deg. C is
delivered to the air receiver at 690 kPa and 150 deg. C by means of a water jacketed
reciprocating compressor. The compressor has rated capacity of 0.15 m^3/s free air. Determine
the power required to compress the air.
Answer in kW.
100 - CORRECT ANSWER - 1 bar = how many kPa?
70.15 - CORRECT ANSWER - The stroke of the piston of an air compressor is 250 mm and
the clearance volume is equal to 6% of the stroke volume. The pressure of the air at the
beginning of the compression of 0.98 bar and it is discharged at 3.8 bar. Assuming compression
to follow the law PV^n = C, where n = 1.25, calculate the distance moved by the piston from the
beginning of its pressure stroke before the discharge valves opens. Express this as a percentage
of the stroke.
157.54 - CORRECT ANSWER - A double acting compressor with piston displacement of
0.05 m^3 per stroke operates at 500 rpm. The clearance factor is 5% and it receives air at 100
kPa and discharges it at 600 kPa. The compression and re-expansion curve is polytropic with n =
1.3. Determine the power required to compress the air.
Answer in kW.
