Study Set Content:
141. Steam flows through a nozzle at 400°C and 1 MPa (h = 3263.9 kJ/kg) with velocity of 300
m/s. Find the stagnation enthalpy.
A. 3300 kJ/kg B. 3290 kJ/kg
C. 3320 kJ/kg D. 3309 kJ/kg
D. 3309 kJ/kg
142. Air flows through a nozzle at a speed of 350 m/s. Find the stagnation temperature if the
entrance temperature is 200°C.
A. 241.25°C B. 251.25°C
C. 261.25°C D. 271.25°C
C. 261.25°
143. Carbon dioxide flows through a nozzle with a speed of 400 m/s. Compute the dynamic
temperature.
A. 92.56 K B. 94.56 K
C. 96.56 K D. 98.56 K
B. 94.56 K
144. Carbon dioxide flows through a nozzle with speed of 380 m/s. The entrance condition of
nozzle is 250°C and 1200 kPa. Find the stagnation pressure.
A. 2,136.34 kPa B. 2,146.34 kPa
C. 2,156.34 kPa D. 2,166.34 kPa
A. 2,136.34 kPa
145. Air enters a diffuser with a velocity of 200 m/s. Determine the velocity of sound if air
temperature is 30°C.
A. 349 m/s B. 359 m/s
C. 369 m/s D. 379 m/s
A. 349 m/s
146. Air flows through a nozzle with temperature of entrance of 420 K stagnation temperature
of 468 K. Find the Mach number.
A. 0.744 B. 0.754
C. 0.764 D. 0.774
B. 0.754
147. Air at 300 K and 200 kPa is heated at constant pressure to 600 K. Determine the change of
internal energy.
A. 245.58 kJ/kg B. 235.58 kJ/kg
C. 225.58 kJ/kg D. 215.58 kJ/kg
215.58 kJ/kg
148. An insulated rigid tank initially contains 1.5 lb of helium at 80°F and 50 psia. A paddle
wheel with power rating of 0.02 hp is operated within the tank for 30 min. Determine the final
temperature.
A. 159.22°F B. 169.22°F
C. 179.22°F D. 189.22°F
C. 179.22°F
149. A 4 m2
asphalt pavement with emissivity of 0.85 has a surface temperature of 50°C. Find
the maximum rate of radiation that can be emitted from the surface.
A. 2,068 .32 watts B. 2,078.32 watts
C. 2,088.32 watts D. 2,098.32 watts
D. 2,098.32 watts
150. Air at 10°C and 80 kPa enters a diffuser of a jet engine steadily with a velocity of 200 m/s.
The inlet area of diffuser is 0.40 m2
. Determine the mass flow rate of air.
A. 72.79 kg/s B. 74.79 kg/s
C. 76.79 kg/s D. 78.79 kg/s
D. 78.79 kg/s
151. Consider a refrigerator whose 40 watts light bulb remains on continuously as a result of a
malfunction of the switch. If the refrigerator has a COP of 1.3 and the cost of electricity is 8
cents per kW-hr, determine the increase in the energy consumption of the refrigerator and its
cost per year if the switch is not fixed.
A. P 49.59 B. P 47.59
C. P 45.59 D. P 43.59
A. P 49.59
152. A 75 hp motor that has an efficiency of 91% is worn out and is replaced by a high-efficiency
motor that has an efficiency of 95.4%. Determine the reduction in heat gain of the room due to
higher efficiency under full-load conditions.
A. 2.24 kW B. 2.44 kW
C. 2.64 kW D. 2.84 kW
B. 2.44 kW
153. A household refrigerator that has a power input of 450 watts and a COP of 2.5 is to cool
five large watermelons, 10 kg each, to 8°C. If the watermelons are initially at 20°C, determine
how long it will take for the refrigerator to cool them. The watermelons can be treated as water
whose specific heat is 4.2 kJ/kg-K.
A. 2220 seconds B. 2230 seconds
C. 2240 seconds D. 2250 seconds
C. 2240 seconds
154. When a man returns to his wall-sealed house on a summer day, he finds that the house is
at 32°C. He returns on the air conditioner which cools the entire house to 20°C in 15 minutes. If
COP is 2.5, determine the power drawn by the air conditioner. Assume the entire mass within
the house is 800 kg of air for which cv = 0.72 kJ/kg-K, cp = 1.0 kJ/kg-K.
A. 1.072 kW B. 2.072 kW
C. 3.072 kW D. 4.072 kW
B. 2.072 kW
155. A heat source at 800 K losses 2000 kJ of heat to a sink at 500 K. Determine the entropy
generated during this process.
A. 1.5 kJ/K B. 2.5 kJ/K
C. -2.5 kJ/K D. 4 kJ/K
A. 1.5 kJ/K
156. Helium gas is compressed in an adiabatic compressor from an initial state of 14 psia and
50°F to a final temperature of 320°F in a reversible manner. Determine the exit pressure of
Helium.
A. 38.5 psia B. 40.5 psia
C. 42.5 psia D. 44.5 psia
B. 40.5 psia
157. Air passes thru a nozzle with efficiency of 90%. The velocity of air at the exit is 600 m/s.
Find the actual velocity at the exit.
A. 382 m/s B. 540 m/s
C. 458 m/s D. 568 m/s
. 568 m/s
158. A 50 kg block of iron casting at 500 K is thrown into a large lake that is at a temperature of
285 K. The iron block eventually reaches thermal equilibrium with the lake water. Assuming
average specific heat of 0.45 kJ/kg-K for the iron, determine the entropy generated during this
process.
A. -12.65 kJ/K B. 16.97 kJ/K
C. 4.32 kJ/K D. 6.32 kJ/K
C. 4.32 kJ/K
159. A windmill with a 12 m diameter rotor is to be installed at a location where the wind is
blowing at an average velocity of 10 m/s. Using standard condition of air (1 atm, 25°C),
determine the maximum power that can be generated by the windmill.
A. 68 kW B. 70 kW
C. 72 kW D. 74 kW
B. 70 kW
160. Consider a large furnace that can supply heat at a temperature of 2000°R at a steady rate
of 3000 Btu/s. Determine the exergy of this energy. Assume an environment temperature of
77°F.
A. 2305.19 kW B. 2315.19 kW
C. 2325.19 kW D. 2335.19 kW
. 2315.19 kW
