Blue Book Flash Card

201. Air in an ideal Diesel cycle is compressed from 3 L to 0.15 L and then it expands during the

constant pressure heat addition process to 0.3 L. Under cold air standard conditions, the

thermal effieciency of this cycle is?

A. 35% B. 44% C. 65% D. 70%

202. Helium gas in an ideal Otto cycle is compressed from 20°C and 2 L to 0.25 L and its

temperature increases by an additional 800°C during the heat addition process. The

temperature of Helium before the expansion process is?

A. 1700°C B. 1440°C C. 1240°C D. 880°C

203. In an ideal Otto cycle, air is compressed from 1.20 kg/m3

and 2.2 L to 0.26 L and the net

work output of the cycle is 440 kJ/kg. The mean effective pressure for the cycle is?

A. 612 kPa B. 599 kPa C. 528 kPa D. 416 kPa

204. An ideal Brayton cycle has a net work output of 150 kJ/kg and backwork ratio of 0.4. if

both the turbine and the compressor had an isentropic efficiency of 80%, the net work output

of the cycle would be?

A. 60 kJ/kg B. 75 kJ/kg

C. 98 kJ/kg D. 120 kJ/kg

205. Air enters a turbojet engine at 200 m/s at a rate of 20 kg/s and exits at 800 m/s relative to

the aircraft. The thrust developed by the engine is?

A. 6 kN B. 12 kN C. 16 kN D. 20 kN

206. A thermal power has a net power of 10 MW. The backwork ratio of the plant is 0.005.

Determine the compressor work.

A. 50.15 kW B. 50.35 kW

C. 50.25 kW D. 50.45 kW

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

wasted heat to a sink at 300 K. If the power output of the engine is 200 kW, the second law

efficiency of this heat engine is?

A. 35% B. 40% C. 53% D. 75%

208. A water reservoir contains 100,000 kg of water at an average elevation of 60 m. The

maximum amount of electric power that can be generated from this water is ?

A. 8 kWh B. 16 kWh

C. 1630 kWh D. 58,800 kWh

209. A house is maintained at 22°C in winter by electric resistance heaters. If the outdoor

temperature is 5°C, the second law efficiency of the resistance heaters is ?

A. 0% B. 5.8% C. 34% D. 77%

210. A thermoelectric refrigerator that resembles a small ice chest is powered by a car battery,

and has a COP of 0.10. If the refrigerator cools a 0.350 L canned drink from 20°C to 4°C in 30

min, determine the average electric power consumed by the thermoelectric refrigerator.

A. 130 watts B. 110 watts C. 120 watts D. 140 watts

211. A Carnot refrigerator operates in a room in which the temperature is 25°C and consumes 2

kW of power when operating. If the food compartment of the refrigerator is to be maintained

at 3°C, determine the rate of heat removal from the food compartment.

A. 1504.8 kJ/min B. 12.86 kJ/min

C. 1625 kJ/min D. 9.57 kJ/min

212. A household refrigerator with EER 8.0 removes heat from the refrigerated space at a rate

of 90 kJ/min. Determine the rate of heat transfer to the kitchen air.

A. 101.25 kJ/min B. 63.05 kJ/min

C. 128.46 kJ/min D. 80 kJ/min

213. An air-conditioning system is used to maintain a house at 75°F when the temperature

outside is 95°F. The house is gaining the heat through the walls and windows at a rate of 1250

Btu/min, and the heat generation rate within the house from people, lights, and appliances

amounts to 350 Btu/min. Determine the minimum power input required for this air-

conditioning system.

A. 10.06 hp B. 1.36 hp C. 1.41 hp D. 7.94 hp

214. A refrigeration system is to cool bread loaves with an average mass of 450 g from 22°C to -

10°C at a rate of 500 loaves per hour by refrigerated air. Taking the average specific and latent

heats of bread to be 2.93 kJ/kg-°C and 109.3 kJ/kg, respectively, determine the product load.

A. 541.7 kJ/min B. 351.6 kJ/min

C. 761.5 kJ/min D. 409.9 kJ/min

215. A house that was heated by electric resistance heaters consumed 1200 kWh of electric

energy in a winter month. If this house were heated instead by a heat pump that has an

average performance factor, PF of 2.4, determine how much money the homeowner would be

saved that month. Assume a price of 0.085 $/kWh for electricity.

A. $42.5 B. $59.50 C. $102 D. $97.75

216. An ammonia simple saturation cycle operates with a suction pressure of 291.6 kPa and a

condenser pressure of 1204 kPa develops 15 tons of refrigeration. Determine the theoretical

horsepower of the compressor. The following enthalpies have been found: condenser entrance

\= 1653 kJ/kg, exit = 346.6 kJ/kg; compressor entrance = 1450.2 kJ/kg, exit = 1653 kJ/kg.

A. 7.23 hp B. 13 hp C. 15 hp D. 8.23 hp

217. An ammonia ice plant operates between a condenser temperature of 35°C and evaporator

of -15°C. It produces 10 metric tons of ice per day from water at 30°C to ice at -5°C. Assuming

simple saturation cycle, determine the horsepower of the motor if the adiabatic efficiency of

the compressor nc = 0.85 and mechanical efficiency nm = 0.95. The specific heat of ice is 2.094

kJ/kg-°C and the latent heat is 335 kJ/kg. From the table for ammonia the following enthalpies

are: condenser entrance = 1703 kJ/kg, exit = 366.1 kJ/kg; compressor entrance = 1443.9 kJ/kg,

exit = 1703 kJ/kg.

A. 17.68 hp B. 18.61 hp C. 15.5 hp D. 21.9 hp

218. A Freon 22 air conditioning under standard operating conditions of 35°C condensing and

5°C evaporating temperatures. The volume flow rate entering the compressor is 23.72 L/s.

Determine the refrigerating capacityif the refrigerating effect is 164 kJ/kg. From the table for

R22 the specific volume at the compressor entrance is 40.46 L/kg.

A. 339.3 TR B. 79.3 TR C. 96.4 TR D. 27.4 TR

219. The refrigerant volume flow rate at the entrance of compressor were obtained from a test

on a twin cylinder, single acting 15 cm x 20 cm, 320 rpm compressor ammonia refrigerating

plant to be 33 L/s. Determine the volumetric efficiency of the compressor.

A. 77.65% B. 87.6% C. 97.6% D. 65.65%

220. A twin cylinder ammonia compressor with volume displacement of 14,726 cm3

operates at

300 rpm. Condenser and evaporator pressure are 1200 kPa and 227 kPa respectively. Specific

volume of refrigerant at the entrance of compressor is 528.26 L/kg. Compression process is

polytropic with n = 1.20 and clearance factor of compressor is 2 percent. Determine the

horsepower required.

A. 60 hp B. 70 hp C. 80 hp D. 90 hp