Question 1

Steam is compressed by an adiabatic compressor from 0.1 MPa and 100°C to 1.0 MPa and 400°C at a rate of 0.85 kg/s. The power input to the compressor is

Accepted Answer

A) 692 kW 
B) 500 kW 
C) 383 kW 
D) 451 kW 
E) 588 kW B

Question 2

Helium gas is to be heated steadily by a 3-kW electric resistance heater as it flows through an insulated duct. If the helium enters at 50°C at a rate of 0.08 kg/s, the exit temperature of helium will be

Accepted Answer

A) 57.2°C 
B) 50.6°C 
C) 62.0°C 
D) 71.9°C 
E) 112.0°C A

Question 3

Saturated liquid water at 1.0 MPa is throttled adiabatically to a pressure of 0.4 MPa. If the change in kinetic energy is negligible, the percentage of water that evaporates during this throttling process will be

Accepted Answer

A) 0.0% 
B) 3.8% 
C) 24.8% 
D) 7.4% 
E) 100% D

Question 4

In a water heating system, cold water at 5°C flowing at a rate of 5 kg/s is mixed adiabatically with hot water at 80°C flowing at a rate of 2 kg/s. The exit temperature of the mixture is

Accepted Answer

A) 26.4°C 
B) 42.5°C 
C) 40.0°C 
D) 64.3°C 
E) 55.2°C

Question 5

fSteam expands in a turbine from 6 MPa and 500°C to 0.2 MPa and 150°C at a rate of 1.2 kg/s. Heat is lost from the turbine at a rate of 34 kJ/s during the process. The power output of the turbine is

Accepted Answer

A) 750 kW 
B) 784 kW 
C) 818 kW 
D) 573 kW 
E) 641 kW

Question 6

Air at 300 K and 200 kPa is throttled by a valve to a pressure of 100 kPa. If the valve is adiabatic and the change in kinetic energy is negligible, the temperature of air after throttling will be

Accepted Answer

A) 150 K 
B) 200 K 
C) 300 K 
D) 450 K 
E) 600 K

Question 7

Steam expands in an adiabatic turbine from 4 MPa and 500°C to 0.5 MPa and 250°C at a rate of 1740 kg/h. The power output of the turbine is

Accepted Answer

A) 1004 kW 
B) 485 kW 
C) 182 kW 
D) 377 kW 
E) 235 kW

Question 8

An adiabatic heat exchanger is used to heat cold water at 12°C entering at a rate of 4 kg/s by hot water entering at 95°C at rate of 2.5 kg/s. If the exit temperature of hot water is 50°C, the exit temperature of cold water is

Accepted Answer

A) 90°C 
B) 50°C 
C) 95°C 
D) 57°C 
E) 40°C

Question 9

Hot combustion gases (assumed to have the properties of air at room temperature) enter a gas turbine at 0.8 MPa and 1500 K at a rate of 2.1 kg/s, and exit at 0.1 MPa and 800 K. If heat is lost from the turbine to the surroundings at a rate of 150 kJ/s, the power output of the gas turbine is

Accepted Answer

A) 1477 kW 
B) 1677 kW 
C) 1327 kW 
D) 1124 kW 
E) 872 kW

Question 10

Steam is accelerated by a nozzle steadily from a low velocity to a velocity of 220 m/s at a rate of 1.2 kg/s. If the steam at the nozzle exit is at 300°C and 2 MPa, the exit area of the nozzle is

Accepted Answer

A) 6.8 cm2  
B) 7.2 cm2 
C) 3.8 cm2 
D) 54.6 cm2 
E) 22.8 cm2

Question 11

Saturated refrigerant 134a vapor at 40°C is condensed as it flows through a tube at a rate of 0.2 kg/s. The condensate leaves the tube as saturated liquid at 40°C. The rate of heat transfer from the tube is

Accepted Answer

A) 21.0 kJ/s 
B) 53.4 kJ/s 
C) 162 kJ/s 
D) 74.4 kJ/s 
E) 32.4 kJ/s

Question 12

An adiabatic heat exchanger is used to heat cold water at 8°C entering at a rate of 3 kg/s by hot air at 150°C entering also at rate of 3 kg/s. If the exit temperature of hot air is 30°C, the exit temperature of cold water is (use constant specific heats at room temperature)

Accepted Answer

A) 150°C 
B) 30°C 
C) 36.9°C 
D) 28.6°C 
E) 128°C

Question 13

In a heating system, cold outdoor air at 10°C flowing at a rate of 6 kg/min is mixed adiabatically with hot air at 50°C flowing at a rate of 1.5 kg/min. Assuming constant specific heats at room temperature, the exit temperature of the mixture is

Accepted Answer

A) 30°C 
B) 18°C 
C) 45°C 
D) 22°C 
E) 38°C

Question 14

Refrigerant 134a enters a diffuser steadily at 0.5 MPa, 50°C, and 120 m/s at a rate of 1.2 kg/s. The inlet area of the diffuser is

Accepted Answer

A) 0.81 cm2 
B) 4.8 cm2  
C) 26 cm2 
D) 5.3 cm2 
E) 100 cm2

Question 15

A heat exchanger is used to heat cold water at 8°C entering at a rate of 1.2 kg/s by hot air at 90°C entering at rate of 2.5 kg/s. The heat exchanger is not insulated, and is loosing heat at a rate of 28 kJ/s. If the exit temperature of hot air is 20°C, the exit temperature of cold water is (use constant specific heats at room temperature)

Accepted Answer

A) 43.1°C 
B) 48.6°C 
C) 78.0°C 
D) 37.5°C 
E) 27.5°C

Question 16

Refrigerant-134a expands in an adiabatic turbine from 1 MPa and 120°C to 0.10 MPa and 50°C at a rate of 0.8 kg/s. The power output of the turbine is

Accepted Answer

A) 72.5 kW 
B) 58.0 kW 
C) 43.5 kW 
D) 46.4 kW 
E) 54.4 kW

Question 17

Refrigerant-134a is compressed steadily from the saturated vapor state at 0.10 MPa to 1.4 MPa and 60°C at a rate of 0.15 kg/s. The refrigerant is cooled at a rate of 1.80 kJ/s during compression. The power input to the compressor is

Accepted Answer

A) 5.74 kW 
B) 7.54 kW 
C) 9.08 kW 
D) 9.34 kW 
E) 46.7 kW

Question 18

Saturated Refrigerant-134a liquid at 0.8 MPa is throttled to a pressure of 0.12 MPa. The temperature of the refrigerant after throttling is

Accepted Answer

A) -14.6°C 
B) -5.6°C 
C) 0°C 
D) 31.3°C 
E) -22.4°C

Question 19

Steam at 4 MPa and 400°C is throttled adiabatically to a pressure of 1 MPa. If the change in kinetic energy is negligible, the specific volume of the steam after throttling will be

Accepted Answer

A) 0.2952 m3/kg 
B) 0.2327 m3/kg 
C) 0.3749 m3/kg 
D) 0.5165 m3/kg 
E) 0.3066 m3/kg

Question 20

Refrigerant-134a is compressed by an adiabatic compressor from the saturated vapor state at 0.12 MPa to 1.2 MPa and 70°C at a rate of 0.108 kg/s. The power input to the compressor is

Accepted Answer

A) 587 kW 
B) 63.4 kW 
C) 6.85 kW 
D) 6.42 kW 
E) 59.4 kW

Exam 5: Mass and Energy Analysis of Control Volumes