Deck 5: Mass and Energy Analysis of Control Volumes

Question 1

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

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

Answer 1

6.8 cm²

Question 2

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

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

Answer 2

4.8 cm²

Question 3

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)

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

Answer 3

36.9°C

Question 4

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)

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

Question 5

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

A)90°C
B)50°C
C)95°C
D)57°C
E)40°C

Question 6

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

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

Question 7

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

A)30°C
B)18°C
C)45°C
D)22°C
E)38°C

Question 8

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

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

Question 9

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

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

Question 10

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

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

Question 11

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

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

Question 12

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

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

Question 13

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

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

Question 14

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

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

Question 15

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

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 16

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

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

Question 17

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

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

Question 18

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

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

Question 19

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

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

Question 20

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

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