Blue Book Flash Card

161. A heat engine receives heat from a source at 1200 K at a rate of 500 kJ/s and rejects the

waste heat to a medium at 300 K. The power output of the engine is 180 kW. Determine the

irreversibility rate for this process.

A. 190 kW B. 195 kW

C. 200 kW D. 205 kW

162. A dealer advertises that he has just received a shipment of electric resistance heaters for

residential buildings that have an efficiency of 100 percent. Assuming an indoor temperature of

21°C and outdoor temperature of 10°C, determine the second law efficiency of these heaters.

A. 8.74% B. 6.74%

C. 3.74% D. 4.74%

163. A thermal power plant has a heat rate of 11,363 Btu/kW-hr. Find the thermal efficiency of

the plant.

A. 34% B. 24%

C. 26% D. 30%

164. A rigid tank contains 2 kmol of N2 and 6 kmol of CO2 gases at 300 K and 115 MPa. Find the

tank volume using the ideal gas equation.

A. 7.33 m3

B. 5.33 m3

C. 3.33 m3

D. 1.33 m3

165. A spherical balloon with a diameter of 6 m is filled with helium at 20°C and 200 kPa.

Determine the mole number.

A. 9.28 kmol B. 10.28 kmol

C. 11.28 kmol D. 13.28 kmol

166. The air in an automobile tire with a volume of 0.53 ft3

is at 90°F and 20 psig. Determine the

amount of air that must be added to raise the pressure to the recommended value of 30 psig.

Assume the atmospheric pressure to be 14.7 psia and the temperature and the volume to

remain constant.

A. 0.026 lb B. 0.046 lb

C. 0.066 lb D. 0.086 lb

167. A rigid tank contains 20 lbm of air at 20 psia and 70°F. More air is added to the tank until

the pressure and temperature rise to 35 psia and 90°F, respectively. Determine the amount of

air added to the tank.

A. 11.73 lb B. 13.73 lb

C. 15.73 lb D. 17.73 lb

168. A rigid tank contains 5 kg of an ideal gas at 4 atm and 40°C. Now a valve is opened, and

half of mass of the gas is allowed to escape. If the final pressure in the tank is 1.5 atm, the final

temperature in the tank is?

A. -38°C B. -30°C

C. 40°C D. 53°C

169. The pressure of an automobile tire is measured to be 200 kPa (gage) before the trip end

220 kPa (gage) after the trip at a location where the atmospheric pressure is 90 kPa. If the

temperature of the air in the tire before the trip is 25°C, the air temperature after the trip is?

A. 45.6°C B. 54.8°C

C. 27.5°C D. 26.7°C

170. Water is boiling at 1 atm pressure in a stainless steel pan on an electric range. It is

observed that 2 kg of liquid water evaporates in 30 min. The rate of heat transfer to the water

is?

A. 2.07 kW B. 0.47 kW

C. 2.51 kW D. 3.12 kW

171. Consider a person standing in a breezy room at 20°C. Determine the total rate of heat

transfer from this person if the exposed surface area and the average outer surface

temperature of the person are 1.6 m2

and 29°C, respectively, and the convection heat transfer

coefficient is 6 W/m2 with emissivity factor of 0.95.

A. 86.40 watts B. 81.70 watts

C. 198.1 watts D. 168.1 watts

172. Water is boiler in a pan on a stove at sea level. During 10 minutes of boiling, it is observed

that 200 grams of water has evaporated. Then the rate of heat transfer to the water is:

A. 0.84 kJ/min B. 45.1 kJ/min

C. 41.8 kJ/min D. 53.5 kJ/min

173. An aluminum pan whose thermal conductivity is 237 W/m-°C has a flat bottom whose

diameter is 20 cm and thickness of 0.4 cm. Heat is transferred steadily to boiling water in the

pan through its bottom at a rate of 500 watts. If the inner surface of the bottom of the pan is

105°C, determine the temperature of the surface of the bottom of the pan.

A. 95.27°C B. 105.27°C

C. 115.27°C D. 125.27°C

174. For heat transfer purposes, a standing man can be modeled as a 30 cm diameter, 170 cm

long vertical cylinder with both the top and bottom surfaces insulated and with the side surface

at an average temperature of 34°C. For a convection heat transfer coefficient of 15 W/m2

-°C,

determine the rate of heat loss from this man by convection in an environment at 20°C.

A. 316.46 watts B. 326.46 watts

C. 336.46 watts D. 346.46 watts

175. A 5 cm diameter spherical ball whose surface is maintained at a temperature of 70°C is

suspended in the middle of a room at 20°C. If the convection heat transfer coefficient is 15

W/m2

-°C and the emissivity of the surface is 0.8, determine the total heat transfer from the

ball.

A. 23.56 watts B. 32.77 watts

C. 9.22 watts D. 43.45 watts

176. A frictionless piston-cylinder device and a rigid tank contain 1.2 kmol of an ideal gas at the

same temperature, pressure and volume. Now heat is transferred, and the temperature of both

systems is raised by 15°C. The amount of extra heat that must be supplied to the gas in the

cylinder that is maintained at constant pressure is?

A. 0 B. 50 kJ

C. 100 kJ D. 150 kJ

177. A supply of 50 kg of chicken at 6°C contained in a box is to be frozen to -18°C in a freezer.

Determine the amount of heat that needs to be removed. The latent heat of the chicken is 247

kJ/kg, and its specific heat is 3.32 kJ/kg-°C above freezing and 1.77 kJ/kg-°C below freezing. Thecontainer box is 1.5 kg, and the specific heat of the box material is 1.4 kJ/kg-°C. Also the

freezing temperature of chicken is -2.8°C.

A. 15,206.4 kJ B. 50.4 kJ

C. 15,156 kJ D. 1,863 kJ

178. Water is being heated in a closed pan on top of a range while being stirred by a paddle

wheel. During the process, 30 kJ of heat is transferred to the water, and 5 kJ of heat is lost to

the surrounding air. The paddle wheel work amounts to 500 N-m. Determine the final energy of

the system if its initial energy is 10 kJ.

A. 35.5 kJ B. 40.5 kJ

C. 25.5 kJ D. 14.5 kJ

179. A classroom that normally contains 40 people is to be air-conditioned with window air-

conditioning units of 5 kW cooling capacity. A person at rest may be assumed to dissipate heat

at a rate about 360 kJ/hr. There are 10 light bulbs in the room, each with a rating of 100 watts.

The rate of heat transfer to the classroom through the walls and the windows is estimated to

be 15,000 kJ/hr. If the room is to be maintained at a constant temperature of 21°C, determine

the number of window air-conditioning units required.

A. 1 units B. 2 units

C. 3 units D. 4 units

180. A 4 m x 5 m x 6 m room is to be heated by a baseboard resistance heater. It is desired that

the resistance heater be able to raise the air temperature in the room from 7 to 23°C within 15

minutes. Assuming no heat losses from the room and an atmospheric pressure of 100 kPa,

determine the required power of the resistance heater. Assume constant specific heats at room

temperature.

A. 2.34 kW B. 1.91 kW

C. 4.56 kW D. 6.34 kW