thermo fe problems
An apple with an average mass of 0.18 kg and average specific heat of 3.65 kJ / kg- ° C is cooled from 17 ° C to 5 ° C . The amount of heat transferred from the apple is ( a ) 7.9 kJ ( b ) 11.2 kJ ( c ) 14.5 kJ ( d ) 17.6 kJ ( e ) 19.1 kJ
7.9
A rigid tank contains 2 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 2.2 atm , he final temperature in the tank is a ) 71 ° C ( b ) 44 ° C ( c ) -100 ° C d ) 20 ° C ( e ) 172 ° C
71
A room contains 75 kg of air at 100 kPa and 15 ° C . The room has a 250 - W refrigerator ( the refrigerator consumes 250 W of electricity when running ) , a 120 - W TV , a 1.8 - kW electric resistance heater , and a 50 - W fan . During a cold winter day , it is observed that the refrigerator , the TV , the fan , and the electric resistance heater are running continuously but the air temperature in the room remains constant . The rate of heat loss from the room that day is ( a ) 5832 kJ / h ( b ) 6192 kJ / h ( c ) 7560 kJ / h ( d ) 7632 kJ / h ( e ) 7992 kJ / h
7992
A container equipped with a resistance heater and a mixer is initially filled with 3.6 kg of saturated water vapor at 120 ° C . Now the heater and the mixer are turned on ; the steam is compressed , and there is heat loss to thesurrounding air . At the end of the process , the temperature and pressure of steam in the container are measured to be 300 ° C and 0.5 MPa . The net energy transfer to the steam during this process is ( a ) 274 kJ ( b ) 914 kJ ( c ) 1213 kJ ( d ) 988 kJ ( e ) 1291 kJ
988
Water is boiled at 1 atm pressure in a coffeemaker equipped with an immersion - type electric heating element . The coffeemaker initially contains 1 kg of water . Once boiling has begun , it is observed that half of the water in the coffeemaker evaporates in 10 min . If the heat loss from the coffeemaker is negligible , the power rating of the heating element is ( a ) 3.8 kW ( b ) 2.2 kW ( c ) 1.9 kW ( d ) 1.6 kW ( e ) 0.8 kW
1.9
Steam expands in a turbine from 4 MPa and 500 ° C to 0.5 MPa and 250 ° C at a rate of 1350 kg / h . Heat is lost from the turbine at a rate of 25 kJ / s during the process . The power output of the turbine is ( a ) 157 kW ( b ) 207 kW ( c ) 182 kW ( d ) 287 kW ( e ) 246 kW
157
During a heating process , the temperature of an object rises by 10 ° C . This temperature rise is equivalent to a tempera ture rise of ( a ) 10 ° F ( b ) 42 ° F ( c ) 18 K ( d ) 18 R ( e ) 283 K
18 R
Liquid water enters an adiabatic piping system at 15 ° C at a rate of 8 kg / s . If the water temperature rises by 0.2 ° C during flow due to friction , the rate of entropy generation in the pipe is ( a ) 23 W / K ( b ) 55 W / K ( c ) 68 W / K ( d ) 220 W / K ( e ) 443 W / K
23
In a shower , cold water at 10 ° C flowing at a rate of 5 kg / min is mixed with hot water at 60 ° C flowing at a rate of 2 kg / min . The exit temperature of the mixture is ( a ) 24.3 ° C ( b ) 35.0 ° C ( c ) 40.0 ° C ( d ) 44.3 ° C e ) 55.2 ° C
24.3
A frictionless piston - cylinder device and a rigid tank contain 3 kmol of an ideal gas at the same temperature , pres sure , and volume . Now heat is transferred , and the temperature of both systems is raised by 10 ° C . The amount of extra heat that must be supplied to the gas in the cylinder that is main tained at constant pressure is ( a ) 0 kJ ( b ) 27 kJ ( c ) 83 kJ ( d ) 249 kJ ( e ) 300 kJ
249
An adiabatic heat exchanger is used to heat cold water at 15 ° C entering at a rate of 5 kg / s with hot air at 90 ° C enter ing also at a rate of 5 kg / s . If the exit temperature of hot air is 20 ° C , the exit temperature of cold water is ( a ) 27 ° C ( b ) 32 ° C ( c ) 52 ° C ( d ) 85 ° C ( e ) 90 ° ℃
32
A 240 - m³ rigid tank is filled with a saturated liquid vapor mixture of water at 200 kPa . If 25 percent of the mass
361
The pressure of an automobile tire is measured to be 190 kPa ( gage ) before a trip and 215 kPa ( gage ) after the trip at a location where the atmospheric pressure is 95 kPa . If the temperature of air in the tire before the trip is 25 ° C , the air temperature after the trip is ( a ) 51.1 ° C ( b ) 64.2 ° C ( c ) 27.2 ° C ( d ) 28.3 ° C ( e ) 25.0 ° C
51.1
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 ( a ) 511 kW ( b ) 393 kW ( c ) 302 kW ( d ) 717 kW ( e ) 901 kW
511
A 900 - kg car cruising at a constant speed of 60 km / h 2-137 is to accelerate to 100 km / h in 4 s . The additional power needed to achieve this acceleration is ( a ) 56 kW ( b ) 222 kW ( c ) 2.5 kW ( d ) 62 kW ( e ) 90 kW
56
A 1 - m³ rigid tank contains 10 kg of water ( in any phase or phases ) at 160 ° C . The pressure in the tank is ( a ) 738 kPa ( b ) 618 kPa ( c ) 370 kPa ( d ) 2000 kPa ( e ) 1618 kPa
618
For specified limits for the maximum and minimum temperatures , the ideal cycle with the lowest thermal efficiency is ( a ) Carnot ( b ) Stirling ( c ) Ericsson ( d ) Otto ( e ) All are the same
( d ) Otto
An apple with a mass of 0.12 kg and average specific heat of 3.65 kJ / kg- ° C is cooled from 25 ° C to 5 ° C . The entropy change of the apple is ( a ) -0.705 kJ / K ( b ) -0.254 kJ / K ( c ) -0.0304 kJ / K d ) 0 kJ / K ( e ) 0.348 kJ / K
-0.0304
Steam is condensed at a constant temperature of 30 ° C as it flows through the condensor of a power plant by rejecting heat at a rate of 55 MW . The rate of entropy change of steam as it flows through the condenser is ( a ) -1.83 MW / K ( b ) -0.18 MW / K ( c ) 0 MW / K ( d ) 0.56 MW / K ( e ) 1.22 MW / K
-0.18
A piston - cylinder device contains 5 kg of saturated water vapor at 3 MPa . Now heat is rejected from the cylinder at constant pressure until the water vapor completely condenses so that the cylinder contains saturated liquid at 3 MPa at the end of the process . The entropy change of the system during this process is ( a ) 0 kJ / K ( b ) -3.5 kJ / K ( c ) -12.5 kJ / K ( d ) -17.7 kJ / K ( e ) -19.5 kJ / K
-17.7
Consider a sealed can that is filled with refrigerant 134a . The contents of the can are at the room temperature of 25 ° C . Now a leak develops , and the pressure in the can drops to the local atmospheric pressure of 90 kPa . The temperature of the refrigerant in the can is expected to drop to ( rounded to the nearest integer ) a ) 0 ° C ( b ) -29 ° C ( c ) 16 ° C ( d ) 5 ° C ( e ) 25 ° C
-29
A 3 - m³ rigid tank contains nitrogen gas at 500 kPa and 300 K. Now heat is transferred to the nitrogen in the tank and the pressure of nitrogen rises to 800 kPa . The work done during this process is a ) 500 KJ ( b ) 1500 kJ ( c ) 0 kJ ( d ) 900 kJ ( e ) 2400 kJ
0
A Carnot cycle operates between the temperature lim ts of 300 and 2000 K and produces 400 kW of net power . The ate of entropy change of the working fluid during the heat addition process is ( a ) 0 kW / K ( b ) 0.200 kW / K ( c ) 0.174 kW / K ( d ) 0.235 kW / K ( e ) 1.33 kW / K
0.235
Heat is lost through a plane wall steadily at a rate of 1500 W. If the inner and outer surface temperatures of the wall are 20 ° C and 5 ° C , respectively , the rate of entropy generation within the wall is ( a ) 0.07 W / K ( b ) 0.15 W / K ( c ) 0.28 W / K ( d ) 1.42 W / K ( e ) 5.21 W / K
0.28
A 2.4 - m - high 200 - m² house is maintained at 22 ° C by an air - conditioning system whose COP is 3.2 . It is estimated that the kitchen , bath , and other ventilating fans of the house discharge a houseful of conditioned air once every hour . If the average outdoor temperature is 32 ° C , the density of air is 1.20 kg / m³ , and the unit cost of electricity is $ 0.10 / kWh , the amount of money " vented out " by the fans in 10 hours is ( a ) $ 0.50 ( b ) $ 1.6 ( c ) $ 5.0 ( d ) $ 11.0 ( e ) $ 16.0
0.50
On a hot summer day , the air in a well - sealed room is circulated by a 0.50 - hp fan driven by a 65 percent efficient motor . ( Note that the motor delivers 0.50 hp of net shaft power to the fan . ) The rate of energy supply from the fan - motor assembly to the room is ( a ) 0.769 kJ / s ( b ) 0.325 kJ / s ( c ) 0.574 kJ / s ( d ) 0.373 kJ / s ( e ) 0.242 kJ / s
0.574
Steam at 1 MPa and 300 ° C is throttled adiabati cally to a pressure of 0.4 MPa . If the change in kinetic energy is negligible , the specific volume of the steam after throttling is ( a ) 0.358 m³ / kg ( b ) 0.233 m³ / kg ( c ) 0.375 m³ / kg ( d ) 0.646 m³ / kg ( e ) 0.655 m³ / kg
0.646
A refrigerator is removing heat from a cold medium at 3 ° C at a rate of 5400 kJ / h and a medium at 30 ° C . If the coefficient of performance of the rejecting the waste heat to refrigerator is 2 , the power consumed by the refrigerator is ( a ) 0.5 kW ( b ) 0.75 kW ( c ) 1.0 kW ( d ) 1.5 kW ( e ) 3.0 kW
0.75
A piston - cylinder device contains an ideal gas . The gas undergoes two successive cooling processes by rejecting heat to the surroundings . First the gas is cooled at constant pressure until T₂ = 3/4T₁ . Then the piston is held stationary while the gas is further cooled to T3 = 1/2T₁ , where all tempera tures are in K. odak 1. The ratio of the final volume to the initial volume of the gas is ( a ) 0.25 ( b ) 0.50 ( c ) 0.67 ( d ) 0.75 ( e ) 1.0 2. The work done on the gas by the piston is ( a ) RT 14 ( b ) c , T , / 2lan ( c ) c , T₁ / 2 ( d ) ( c + cp ) T , / 4 ( e ) c ( T₁ + T₂ ) / 2 agoulin to 3. The total heat transferred from the gas is ( a ) RT , / 4 ( b ) c , T , / 2 ( c ) c , T₁ / 2 ( d ) ( c + cp ) T , / 4 ( e ) c ( T₁ + T3 ) / 2
0.75, RT1/4, (cp+cv)T1/4
Air is compressed steadily and adiabatically from 17 ° C and 90 kPa to 200 ° C and 400 kPa . Assuming constant specific heats for air at room temperature , the isentropic effi ciency of the compressor is ( a ) 0.76 ( b ) 0.94 ( c ) 0.86 ( d ) 0.84 ( e ) 1
0.84
At sea level , the weight of 1 kg mass in SI units is 9.81 N. The weight of 1 lbm mass in English units is ( a ) 1 lbf ( b ) 9.81 lbf ( c ) 32.2 lbf ( d ) 0.1 lbf ( e ) 0.031 lbf
1
A window air conditioner that consumes 1 kW of 6-169 electricity when running and has a coefficient of performance saturation of 3 is placed in the middle of a room and is plugged in . The rate of cooling or heating this air conditioner will provide to the air in the room when running is ( a ) 3 kJ / s , cooling ( b ) 1 kJ / s , cooling ( c ) 0.33 kJ / s , heating ( d ) 1 kJ / s , heating ( e ) 3 kJ / s , heating
1 heating
Water is boiling at 1 atm pressure in a stainless steel pan on an electric range . It is observed that 1.25 kg of liquid water evaporates in 30 min . The rate of heat transfer to the water is ( a ) 1.57 kW ( b ) 1.86 kW ( c ) 2.09 kW ( d ) 2.43 kW ( e ) 2.51 kW
1.57
Argon gas expands in an adiabatic turbine from 3 MPa and 750 ° C to 0.3 MPa at a rate of 5 kg / s . The maximum power output of the turbine is ( a ) 0.64 MW ( b ) 1.12 MW ( c ) 1.60 MW ( d ) 1.95 MW ( e ) 2.40 MW
1.60
An air - conditioning system operating on the reversed Carnot cycle is required to remove heat from the house at a rateof 32 kJ / s to keep its temperature perature of the outdoors is 35 ° C , the power required to operate constant at 20 ° C . If the tem this air - conditioning system is ( a ) 0.58 kW ( b ) 3.20 kW ( c ) 1.56 kW ( d ) 2.26 kW ( e ) 1.64 kW
1.64
1.5 kg of liquid water initially at 12 ° C is to be heated to 95 ° C in a teapot equipped with an 800 - W electric heating element inside . The specific heat of water can be taken to be 4.18 kJ / kg- ° C , and the heat loss from the water during heating can be neglected . The time it takes to heat water to the desired temperature is ( a ) 5.9 min ( b ) 7.3 mino ( c ) 10.8 min ( d ) 14.0 min ( e ) 17.0 min
10.8
An ideal gas has a gas constant R = 0.3 kJ / kg - K and a constant - volume specific heat c , = 0.7 kJ / kg - K . If the gas has a temperature change of 100 ° C , choose the correct answer for each of the following : 1. The change in enthalpy is , in kJ / kg , ( a ) 30 ( b ) 70 ( c ) 100 ( d ) insufficient information to determine 2. The change in internal energy is , in kJ / kg , ( a ) 30 ( b ) 70 ( 100 ( d ) insufficient information to determine 3. The work done is , in kJ / kg , ( a ) 30 ( b ) 70 ( c ) 100 ( d ) insufficient information to determine 4. The heat transfer is , in kJ / kg , ( a ) 30 ( b ) 70 boobin ( c ) 100 ( d ) insufficient information to determine. 5. The change in the pressure - volume product is , in kJ / kg , ( a ) 30 ( b ) 70 ( c ) 100 ( d ) insufficient information to determine
100, 70, 30
A refrigeration cycle is executed with R - 134a under the saturation dome between the pressure limits of 1.6 and 0.2 MPa If the power consumption of the refrigerator is 3 kW , the maxi mum rate of heat removal from the cooled space of this refrig erator is ( a ) 0.45 kJ / s ( b ) 0.78 kJ / s ( c ) 3.0 kJ / s ( d ) 11.6 kJ / s ( e ) 14.6 kJ / s
11.6
The drinking water needs of an office are met by cool ing tap water in a refrigerated water fountain from 23 to 6 ° C at an average rate of 18 kg / h . If the COP of this refrigerator is 3.1 , the required power input to this refrigerator is ( a ) 1100 W ( b ) 355 W ( c ) 195 W ( d ) 115 W ( e ) 35 W
115
A piston - cylinder device contains 5 kg of air at 400 kPa and 30 ° C . During a quasi - equilibium isothermal expansion process , 15 kJ of boundary work is done by the sys tem , and 3 kJ of paddle - wheel work is done on the system . The heat transfer during this process is 1.21 ( 6 ) a ) 12 kJ ( b ) 18 kJ ( c ) 2.4 kJ d ) 3.5 kJ ( e ) 60 kJ
12
A 3 - m³ rigid vessel contains steam at 2 MPa and 500 ° C . The mass of the steam is ( a ) 13 kg ( b ) 17 kg ( c ) 22 kg ( d ) 28 kg ( e ) 35 kg
17
Steam enters an adiabatic turbine steadily at 400 ° C and 5 MPa and leaves at 20 kPa . The highest possible percent age of mass of steam that condenses at the turbine exit and leaves the turbine as a liquid is ( a ) 4 % ( b ) 8 % ( c ) 12 % ( d ) 18 % ( e ) 0 %
18 %
The label on a washing machine indicates that the washer will use $ 85 worth of hot water if the water is heatedby a 90 percent efficient electric heater at an electricity rate of $ 0.125 / kWh . If the water is heated from 18 to 45 ° C , the amount of hot water an average family uses per year is ( a ) 19.5 tons ( b ) 21.7 tons ( c ) 24.1 tons ( d ) 27.2 tons ( e ) 30.4 tons
19.5
A heat engine cycle is executed with steam in the saturation dome between the pressure limits of 7 and 2 MPa . If heat is supplied to the heat engine at a rate of 150 kJ / s , the maximum power output of this heat engine is ( a ) 8.1 kW ( b ) 19.7 kW ( c ) 38.6 kW ( d ) 107 kW ( e ) 130 kW
19.7
Consider a fish swimming 5 m below the free surface of water . The increase in the pressure exerted on the fish when it dives to a depth of 25 m below the free surface is ( a ) 196 Pa ( b ) 5400 Pa ( c ) 30,000 Pa ( d ) 196,000 Pa ( e ) 294,000 Pa
196000
An apple loses 3.6 kJ of heat as it cools per ° C drop in its temperature . The amount of heat loss from the apple per ° F drop in its temperature is ( a ) 0.5 kJ ( b ) 1.8 kJ ( c ) 2.0 kJ ( d ) 3.6 kJ ( e ) 6.5 kJ
2.0
A heat pump is absorbing heat from the cold out doors at 5 ° C and supplying heat to a house at 25 ° C at a rate of 18,000 kJ / h . If the power consumed by the heat pump is 1.9 kW , the coefficient of performance of the heat pump is ( a ) 1.3 ( b ) 2.6 ( c ) 3.0 ( d ) 3.8 ( e ) 13.9
2.6
Steam enters a diffuser steadily at 0.5 MPa , 300 ° C , and 90 m / s at a rate of 3.5 kg / s . The inlet area of the diffuser is ( a ) 22 cm² ( b ) 53 cm² ( c ) 126 cm² ( d ) 175 cm² ( e ) 203 cm²
203
The atmospheric pressures at the top and the bottom of a building are read by a barometer to be 96.0 and 98.0 kPa . If the density of air is 1.0 kg / m³ , the height of the building is ( a ) 17 m ( b ) 20 m ( c ) 170 m ( d ) 204 m ( e ) 252 m
204
Helium gas enters an adiabatic nozzle steadily at 500 ° C and 600 kPa with a low velocity and exits at a pressure of 90 kPa . The highest possible velocity of helium gas at the nozzle exit is ( a ) 1475 m / s ( b ) 1662 m / s ( c ) 1839 m / s ( d ) 2066 m / s ( e ) 3040 m / s
2066
Steam enters an adiabatic turbine at 8 MPa and 500 ° C at a rate of 18 kg / s , and exits at 0.2 MPa and 300 ° C . The rate of entropy generation in the turbine is ( a ) 0 kW / K ( b ) 7.2 kW / K ( c ) 21 kW / K ( d ) 15 kW / K ( e ) 17 kW / K
21
Consider a 2.5 - m - deep swimming pool . The pressure difference between the top and bottom of the pool is ( a ) 2.5 kPa ( b ) 12.0 kPa ( c ) 19.6 kPa ( d ) 24.5 kPa ( e ) 250 kPa
24.5
Air at 27 ° C and 5 atm is throttled by a valve to 1 atm . If the valve is adiabatic and the change in kinetic energy is negligible , the exit temperature of air will be ( a ) 10 ° C ( b ) 15 ° C ( c ) 20 ° C ( d ) 23 ° C ( e ) 27 ° C
27
Water enters a pump steadily at 100 kPa at a rate of 35 L / s and leaves at 800 kPa . The flow velocities at the inlet and the exit are the same , but the pump exit where the dis charge pressure is measured is 6.1 m above the inlet section . The minimum power input to the pump is ( a ) 34 kW ( b ) 22 kW ( c ) 27 kW ( d ) 52 kW ( e ) 44 kW
27
A 0.5 - m³ rigid tank contains nitrogen gas at 600 kPa and 300 K. Now the gas is compressed isothermally to a volume of 0.2 m³ . The work done on the gas during this compression process is ( a ) 82 kJ ( b ) 180 kJ ( c ) 240 kJ ( d ) 275 kJ ( e ) 315 kJ
275
A room is filled with saturated steam at 100 ° C . Now a 5 - kg bowling ball at 25 ° C is brought to the room . Heat is transferred to the ball from the steam , and the temperature of the ball rises to 100 ° C while some steam condenses on the ball as it loses heat ( but it still remains at 100 ° C ) . The specific heat of the ball can be taken to be 1.8 kJ / kg . ° C . The mass of steam that condensed during this process is ( a ) 80 g ( b ) 128 g ( c ) 299 g ( d ) 351 g ( e ) 405 g
299
An ordinary egg with a mass of 0.1 kg and a specific heat of 3.32 kJ / kg- ° C is dropped into boiling water at 95 ° C . If the initial temperature of the egg is 5 ° C , the maximum amount of heat transfer to the egg is ( a ) 12 kJ ( b ) 30 kJ ( c ) 24 kJ ( d ) 18 kJ ( e ) infinity
30
A 2 - kW baseboard electric resistance heater in a vacant room is turned on and kept on for 15 min . The mass of the air in the room is 75 kg , and the room is tightly sealed so that no air can leak in or out . The temperature rise of air at the end of 15 min is ( a ) 8.5 ° C ( b ) 12.4 ° C ( c ) 24.0 ° C ( d ) 33.4 ° C ( e ) 54.8 ° C
33.4
A typical new household refrigerator consumes about 680 kWh of electricity per year and has a coefficient of perfor mance of 1.4 . The amount of heat removed by this refrigerator from the refrigerated space per year is ( a ) 952 MJ / yr ( b ) 1749 MJ / yr ( c ) 2448 MJ / yr d ) 3427 MJ / yr ( e ) 4048 MJ / yr
3427
A heat exchanger is used to heat cold water at 15 ° C entering at a rate of 2 kg / s with hot air at 85 ° C entering at a rate of 3 kg / s . The heat exchanger is not insulated and is los ing heat at a rate of 25 kJ / s . If the exit temperature of hot air is 20 ° C , the exit temperature of cold water is ( a ) 28 ° C ( b ) 35 ° C ( c ) 38 ° C ( d ) 41 ° C ( e ) 80 ° C
35
Combustion gases with a specific heat ratio of 1.3 enter an adiabatic nozzle steadily at 800 ° C and 800 kPa with a low velocity and exit at a pressure of 85 kPa . The lowest pos sible temperature of combustion gases at the nozzle exit is ( a ) 43 ° C ( b ) 237 ° C ( c ) 367 ° C ( d ) 477 ° C ( e ) 640 ° C
367
Steam is compressed from 6 MPa and 300 ° C to 10 MPa isentropically . The final temperature of the steam is ( a ) 290 ° ℃ ( b ) 300 ° C ( c ) 311 ° C ( d ) 371 ° C ( e ) 422 ° C
371
Electric power is to be generated in a hydroelectric power plant that receives water at a rate of 70 m³ / s from an elevation of 65 m using a turbine - generator with an efficiency of 85 percent . When frictional losses in piping are disregarded , the electric power output of this plant is ( a ) 3.9 MW ( b ) 38 MW ( c ) 45 MW ( d ) 53 MW ( e ) 65 MW
38
Air is to be compressed steadily and isentropically from 1 atm to 16 atm by a two - stage compressor . To minimize the total compression work , the intermediate pressure between the two stages must be ( a ) 3 atm ( b ) 4 atm ( c ) 8.5 atm ( d ) 9 atm ( e ) 12 atm
4
Consider a Carnot refrigerator and a Carnot heat pump operating between the same two thermal energy reser voirs . If the COP of the refrigerator is 3.4 , the COP of the heat pump is ( a ) 1.7 ( b ) 2.4 ( c ) 3.4 ( d ) 4.4 ( e ) 5.0
4.4
In a heating system , cold outdoor air at 7 ° C flowing at a rate of 4 kg / min is mixed adiabatically with heated air at 70 ° C flowing at a rate of 5 kg / min . The exit temperature of the mixture is ( a ) 34 ° C ( b ) 39 ° C ( c ) 42 ° C ( d ) 57 ° C ( e ) 70 ° C
42
A 2 - kW electric resistance heater submerged in 5 kg of water is turned on and kept on for 10 min . During the pro cess , 300 kJ of heat is lost from the water . The temperature rise of the water is ( a ) 0.4 ° C ( b ) 43.1 ° C ( c ) 57.4 ° C ( d ) 71.8 ° C ( e ) 180 ° C
43.1
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 ( a ) 44.7 kW ( b ) 66.4 kW ( c ) 72.7 kW ( d ) 89.2 kW ( e ) 112.0 kW
44.7
Hot combustion gases ( assumed to have the properties 1500 K at a rate of 0.1 kg / s , and exit at 0.2 MPa and 900 K. of air at room temperature ) enter a gas turbine at 1 MPa and 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 ( a ) 15 kW ( b ) 30 kW ( c ) 45 kW ( d ) 60 kW ( e ) 75 kW
45
Water is boiled in a pan on a stove at sea level . During 10 min of boiling , it is observed that 200 g of water has evapo rated . 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 ( e ) 225.7 kJ / min
45.1
An adiabatic heat exchanger is used to heat cold water at 15 ° C entering at a rate of 5 kg / s with hot water at 90 ° C entering at a rate of 4 kg / s . If the exit temperature of hot water is 50 ° C , the exit temperature of cold water is ( a ) 42 ° C ( b ) 47 ° C ( c ) 55 ° C ( d ) 78 ° C ( e ) 90 ° C
47
Helium gas is compressed from 1 atm and 25 ° C to a pressure of 10 atm adiabatically . The lowest temperature of helium after compression is ( a ) 25 ° C ( b ) 63 ° C ( c ) 250 ° C ( d ) 384 ° C ( e ) 476 ° C
476
Saturated water vapor at 40 ° C is to be condensed as it flows through a tube at a rate of 0.20 kg / s . The condensate leaves the tube as a saturated liquid at 40 ° C . The rate of heat transfer from the tube is ( a ) 34 kJ / s ( b ) 481 kJ / s ( c ) 2406 kJ / s ( d ) 514 kJ / s ( e ) 548 kJ / s
481
A heat pump cycle is executed with R - 134a under the saturation dome between the pressure limits of 1.2 and 0.16 MPa . The maximum coefficient of performance of this heat pump is ( a ) 5.7 ( b ) 5.2 ( c ) 4.8 ( d ) 4.5 ( e ) 4.1
5.2
Saturated steam vapor is contained in a piston - cylinder device . While heat is added to the steam , the piston is held stationary , and the pressure and temperature become 1.2 MPa and 700 ° C , respectively . Additional heat is added to the steam until the temperature rises to 1200 ° C , and the piston moves to maintain a constant pressure . 1. The initial pressure of the steam is most nearly ( a ) 250 kPa ( b ) 500 kPa ( c ) 750 kPa ( d ) 1000 kPa ( e ) 1250 kPa 2. The work done by the steam on the piston is most nearly ( a ) 230 kJ / kg ( b ) 1100 kJ / kg ( c ) 2140 kJ / kg ( d ) 2340 kJ / kg ( e ) 840 kJ / kg 3. The total heat transferred to the steam is most nearly ( a ) 230 kJ / kg ( b ) 1100 kJ / kg ( c ) 2140 kJ / kg d ) 2340 kJ / kg ( e ) 840 kJ / kg
500, 230, 2140
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 ( a ) 46.0 ° C ( b ) 50.0 ° C ( c ) 54.0 ° C d ) 55.4 ° C ( e ) 58.0 ° C
54.0
Refrigerant - 134a at 1.4 MPa and 70 ° C is throttled to a pressure of 0.6 MPa . The temperature of the refrigerant after throttling is ( a ) 70 ° C ( b ) 66 ° ℃ ( c ) 57 ° C ( d ) 49 ° C ( e ) 22 ° C
57
Air in an ideal Diesel cycle is compressed from 2 to 0.13 L , and then it expands during the constant - pressure heat addition process to 0.30 L. Under cold - air - standard conditions the thermal efficiency of this cycle is ou - ar ( a ) 41 percent ( b ) 59 percent ( c ) 66 percent Sidistava 21 ( d ) 70 percent ( e ) 78 percent
59
A 2 - kW electric resistance heater in a room is turned on and kept on for 50 min . The amount of energy transferred to the room by the heater is ( a ) 2 kJ ( b ) 100 kJ ( c ) 3000 kJ ( d ) 6000 kJ ( e ) 12,000 kJ
6000
Argon gas expands in an adiabatic turbine steadily from 600 ° C and 800 kPa to 80 kPa at a rate of 2.5 kg / s . For isentropic efficiency of 88 percent , the power produced by the turbine is ( a ) 240 kW ( b ) 361 kW ( c ) 414 kW ( d ) 602 kW ( e ) 777 kW
602
An Otto cycle with air as the working fluid has a com pression ratio of 10.4 . Under cold - air - standard conditions , the thermal efficiency of this cycle is ngelli consumat ( a ) 10 percent ( b ) 39 percent ( c ) 61 percent ( d ) 79 percent ( e ) 82 percent
61
Two Carnot heat engines are operating in series such that the heat sink of the first engine serves as the heat source of the second one . If the source temperature of the first engine is 1300 K and the sink temperature of the second engine is 300 K and the thermal efficiencies of both engines are the same , the temperature of the intermediate reservoir is ( a ) 625 K ( b ) 800 K ( c ) 860 K ( d ) 453 K ( e ) 758 K
625
A well - sealed room contains 60 kg of air at 200 kPa and 25 ° C . Now solar energy enters the room at an average rate of 0.8 kJ / s while a 120 - W fan is turned on to circulate the air in the room . If heat transfer through the walls is negligible , the air temperature in the room in 30 min will be ( a ) 25.6 ° C ( b ) 49.8 ° C ( c ) 53.4 ° C d ) 52.5 ° C ( e ) 63.4 ° C
63.4 ° C
The elevator of a large building is to raise a net mass of 550 kg at a constant speed of 12 m / s using an electric motor . The minimum power rating of the motor should be ( a ) 0 kW ( b ) 4.8 kW ( c ) 12 kW ( d ) 45 kW ( e ) 65 kW
65
Refrigerant - 134a is compressed by a compressor from the saturated vapor state at 0.14 MPa to 0.9 MPa and 60 ° C at a rate of 0.108 kg / s . The refrigerant is cooled at a rate of 1.10 kJ / s during compression . The power input to the compressor is ( a ) 4.94 kW ( b ) 6.04 kW ( c ) 7.14 kW d ) 7.50 kW ( e ) 8.13 kW
7.14
Consider a refrigerator that consumes 320 W of elec tric power when it is running . If the refrigerator runs only one - quarter of the time and the unit cost of electricity is $ 0.13 / kWh , the electricity cost of this refrigerator per month ( 30 days ) is ( a ) $ 4.9 ( b ) $ 5.8 ( c ) $ 7.5 ( d ) $ 8.3 ( e ) $ 9.7
7.5
A heat engine receives heat from a source at 1000 ° C and rejects the waste heat to a sink at 50 ° C . If heat is supplied to this engine at a rate of 100 kJ / s , the maximum power this heat engine can produce is ( a ) 25.4 kW ( b ) 55.4 kW ( c ) 74.6 kW ( d ) 95.0 kW ( e ) 100 kW
74.6
A glycerin pump is powered by a 5 - kW electric motor . The pressure differential between the outlet and the inlet of the pump at full load is measured to be 211 kPa . If the flow rate through the pump is 18 L / s and the changes in elevation and the flow velocity across the pump are negligible , the overall efficiency of the pump is ( a ) 69 percent ( b ) 72 percent ( c ) 76 percent ( d ) 79 percent ( e ) 82 percent
76
A heat engine cycle is executed with steam in the saturation dome . The pressure of steam is 1 MPa during heat addition , and 0.4 MPa during heat rejection . The highest pos sible efficiency of this heat engine is ( a ) 8.0 % ( b ) 15.6 % ( c ) 20.2 % ( d ) 79.8 % ( e ) 100 % 021
8.0 %
A 2 - kW pump is used to pump kerosene ( p = 0.820 kg / L ) from a tank on the ground to a tank at a higher elevation . Both tanks are open to the atmosphere , and the elevation difference
8.3
A glass of water with a mass of 0.32 kg at 20 ° C is to be cooled to 0 ° C by dropping ice cubes at 0 ° C into it . The latent heat of fusion of ice is 334 kJ / kg , and the specific heat of water is 4.18 kJ / kg- ° C . The amount of ice that needs to be added is ( a ) 32 g ( b ) 40 g ( c ) 80 g ( d ) 93 g ( e ) 110 g
80
Helium gas is compressed steadily from 90 kPa and 25 ° C to 800 kPa at a rate of 2 kg / min by an adiabatic compres sor . If the compressor consumes 80 kW of power while operat ing , the isentropic efficiency of this compressor is ( a ) 54.0 % ( b ) 80.5 % ( c ) 75.8 % ( d ) 90.1 % ( e ) 100 %
90.1 %
A unit mass of an ideal gas at temperature T under goes a reversible isothermal process from pressure P₁ to pres sure P , while losing heat to the surroundings at temperature T in the amount of q . If the gas constant of the gas is R , the entropy change of the gas As during this process is ( a ) As = R In ( P₂ / P₁ ) ( b ) As = R ln ( P₂ / P₁ ) -q / T ( c ) As = R In ( P₁ / P₂2 ) ( d ) As = R ln ( P₁ / P₂ ) -q / T ( e ) As = 0
As = R In ( P₁ / P₂2 )
A unit mass of a substance undergoes an irreversible process from state 1 to state 2 while gaining heat from the sur roundings at temperature T in the amount of q . If the entropy of the substance is s , at state 1 and s₂ at state 2 , the entropy change of the substance As during this process is ( a ) As < S₂ - S₁ ( b ) As > S₂ - S1 ( c ) As = S₂ - S₁ ( d ) As = S₂ - S₁ + q / T ( e ) As > S₂ - S₁ + q / T
As = S₂ - S₁
A 75 - hp compressor in a facility that operates at full load for 2500 h a year is powered by an electric motor that has an efficiency of 93 percent . If the unit cost of electricity is $ 0.11 / kWh , the annual electricity cost of this compressor is ( a ) $ 14,300 ( b ) $ 15,380 ( c ) $ 16,540 ( d ) $ 19,180 ( e ) $ 22,180
14300
A heat pump with a COP of 3.2 is used to heat a per fectly sealed house ( no air leaks ) . The entire mass within the house ( air , furniture , etc. ) is equivalent to 1200 kg of air . When running , the heat pump consumes electric power at a rate of 5 kW The temperature of the house was 7 ° C when the heat pump was turned on . If heat transfer through the envelope of the house ( walls , roof , etc. ) is negligible , the length of time the heat pump must run to raise the temperature of the entire contents of the house to 22 ° C is ( a ) 13.5 min ( b ) 43.1 min ( c ) 138 min ( d ) 18.8 min ( e ) 808 min
13.5
Steam is accelerated by a nozzle steadily from a low velocity to a velocity of 280 m / s at a rate of 2.5 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 ( a ) 8.4 cm² ( b ) 10.7 cm² ( c ) 13.5 cm² ( d ) 19.6 cm² ( e ) 23.0 cm²
13.5
A 6 - pack of canned drinks is to be cooled from 18 ° C to 3 ° C . The mass of each canned drink is 0.355 kg . The drinks can be treated as water , and the energy stored in the aluminum can itself is negligible . The amount of heat transfer from the six canned drinks is ( a ) 22 kJ ( b ) 32 kJ ( c ) 134 kJ ( d ) 187 kJ ( e ) 223 kJ
134
Liquid water is to be compressed by a pump whose isentropic efficiency is 85 percent from 0.2 MPa to 5 MPa at a rate of 0.15 m³ / min . The required power input to this pump is ( a ) 8.5 kW ( b ) 10.2 kW ( c ) 12.0 kW ( d ) 14.1 kW ( e ) 15.3 kW
14.1
A fan is to accelerate quiescent air to a velocity of 9 m / s at a rate of 3 m³ / s . If the density of air is 1.15 kg / m³ , the minimum power that must be supplied to the fan is ( a ) 41 W ( b ) 122 W ( c ) 140 W ( d ) 206 W ( e ) 280 W
140
