Question

1.Steam is accelerated by a nozzle steadily from a low velocity to a velocity of 210 m/s at a rate of 3.2 kg/s. If the temperature and pressure of the steam at the nozzle exit are 400 °C and 2 MPa, the exit area of the nozzle is:

Select one:

a. 8.4  cm2

b. 10.2 cm2

c. 23.0 cm2

d. 152 cm2

e. 24.0 cm2

2.An adiabatic heat exchanger is used to heat cold water at 15 °C entering at a rate of 5 kg/s by hot water at 90 °Centering at a rate of 4 kg/s. If the exit temperature of hot water is 50 °C, the exit temperature of cold water is

Select one:

a. 47 °C

b. 55 °C

c. 78 °C

d. 42 °C

e. 90 °C

3.Steam is compressed by an adiabatic compressor from 0.2 MPa and 150 °C to 0.8 MPa and 350 °C at a rate of 1.30 kg/s. The power input to the compressor is:

Select one:

a. 302 kW

b. 717 kW

c. 901 kW

d. 511 kW

e. 393 kW

4.Hot combustion gases (assumed to have the properties of air at room temperature) enter a gas turbine at 1 MPa and 1500 K at a rate of 0.1 kg/s, and exit at 0.2 MPa and 900 K. If heat is lost from the turbine to the surroundings at a rate of 15 kJ/s, the power output of the gas turbine is:

Select one:

a. 45 kW

b. 15 kW

c. 60 kW

d. 75 kW

e. 30 kW

5.Refrigerant -134a expands in an adiabatic turbine from 1.2 MPa and 100 °C to 0.18 MPa and 50 °C at a rate of 1.25 kg/s. The power output of the turbine is:

Select one:

a. 46.3 kW

b. 72.7 kW

c. 66.4 kW

d. 89.2 kW

e. 112.0 kW

6.Refrigerant -134a at 1.4 MPa abd 90°C is throttled to a pressure of 0.6 MPa. The temperature of the refrigerant after throttling is:

Select one:

a. 82 °C

b. 80 °C

c. 22 °C

d. 90 °C

e. 56 °C

7.Air is to be heated steadily by an 8 kW electric resistance heater as it flows through an insulated duct. If the air enters at 50°C at a rate of 2 kg/s, the exit temperature of air is:

Select one:

a. 46.0 °C

b. 54.0 °C

c. 50.0 °C

d. 55.4 °C

e. 58.0 °C

Answer 1