# Introduction to Thermodynamics Transferring Energy from Here to There Quiz

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## Introduction to Thermodynamics Transferring Energy from Here to There Quiz

## Offered By ”University of Michigan”

**Week 1**

1.

Question 1

Which of the following is an example of a system where the transfer of energy is important?

1 point

- A convection oven
- The computer you are currently using
**All of the other choices are correct**- The air-conditioning unit in your home
- The battery in your phone

2.

Question 2

Energy density is energy per unit mass. Which sector would you expect to have the highest needs for high energy density fuels?

1 point

- Locomotive
**Jet aircraft**- Power Plant
- Scooter (two-wheelers)

3.

Question 3

The Jet Aircraft industry has the highest need for

1 point

- Wind Energy
- Solar Energy
- Low Energy Density Fuels
**High Energy Density Fuels**

4.

Question 4

Why is it important to find new sources of energy?

1 point

- Traditional forms of energy like fossil fuels aren’t as economically viable as they used to be.
- Well-established sources of energy, like gas turbines, solar power, hydroelectric dams and wind turbines, just aren’t popular.
**Energy demands will continue to increase with population growth over the next twenty years.**- It isn’t. At the rate we are consuming today, we will be fine for the foreseeable future.

5.

Question 5

You need to fill a football with air to play with it. You know that your pump expels air at speed of 8.2 ft/s. The needle of your pump has a radius of 4.5 millimeters. What is the volume flow rate of the air being pumped into the football?

1 point

**159 cm^3 / s**- 276 cm^3/s
- 51 cm^3/s
- 634 cm^3/s

6.

Question 6

You need to fill a basketball with air to play with it. You know that your pump expels air at a velocity of 6 cm/s. You know that the volume flow rate of air being pumped into the basketball is 103 cm^3/s. What is the diameter of your needle?

1 point

- 1.1 inches
**1.8 inches**- 5.5 inches
- 2.4 inches

7.

Question 7

Why does the table heat when you set your mug of fresh hot coffee on it?

1 point

- Energy is transferred from the table to the mug.
- Static electricity builds as the mug sits on the table, which causes heat to accumulate.
**Energy is transferred from the hot mug to the table.**- Frictional forces between the mug and table cause heat transfer from the mug to the table.

8.

Question 8

A light-bulb is being used in a lamp. You notice the lamp becomes warm. Which of the following is true?

1 point

- Work is being transferred from the lamp to the light-bulb.
- Heat is being transferred from the lamp to the light-bulb.
**Heat is being transferred from the light-bulb to the lamp.**- Work is being transferred from the light-bulb to the lamp.

9.

Question 9

Which of the following is an extensive property?

1 point

- Density
- Temperature
- Concentration
**Volume**

10.

Question 10

Pressure is an example of an

1 point

- Material Property
- Extensive Property
**Intensive Property**- None of the other options

11.

Question 11

Your car thermometer tells you it is -10 degrees Fahrenheit outside on a brisk day. What is the absolute temperature in Kelvin?

1 point

- -26 K
- -15 K
**250 K**- 450 K

12.

Question 12

You need to set the oven to 450 Kelvin. What temperature do you need to set the oven to in Celsius?

1 point

- 450 degrees Celsius
- 350 degrees Celsius
**177 degrees Celsius**- 0 degrees Celsius

13.

Question 13

Consider a garden hose attached to your home. The system is only the garden hose. Water moves into the hose from your home and leaves the hose to water your plants. The entrance velocity and exit velocity are equal. Is this system an open system or a closed system?

1 point

- A closed system
**An open system**- Need more information

14.

Question 14

Which of the following is not true of a closed system?

1 point

- A closed system has kinetic energy.
**A system is closed if the rate of mass into and out of the system is equal.**- A closed system has potential energy.
- In a closed system, heat and work can cross the boundaries.

15.

Question 15

The following equations represent the temperature of a room. Which room would be considered to be in at a steady-state condition? (T = temperature, t = time)

Room 1: T = 15 + t

Room 2: T = 20

Room 3: T = 30 – 0.5*t

1 point

- Room 1
- Room 1 and Room 3
- Room 3
**Room 2**

16.

Question 16

If the temperature of a hot room with a open window is modeled by T(t) = 72 – 0.25(t). Is this a steady state condition?

1 point

- Yes
**No**- It depends.

17.

Question 17

What is the total energy of a ball the moment it is thrown from a window 5.5 meters from the ground if the velocity of the ball is 10 meters / second when it leaves the window? (Assume the ball has no potential energy when it is on the ground). The mass of the ball is 50 g.

1 point

- 2.5 J
- 2.7 J
- 7.0 J
**5.2 J**

18.

Question 18

A ball, with a mass of 0.06 kg, falls off a table (assume it was on the edge and started with no velocity). If the table was 1 meter off the ground, what is the velocity of the ball when it hits the ground?

1 point

- 1000 m/s
- 0.6 m/s
- 1.4 m/s
**4.4 m/s**

19.

Question 19

Consider a brass cylinder used as a hinge in a door. The hinge is 10 cm tall with a diameter of 2 cm. If the density of brass is reported to be 8.5 grams/cubic centimeter, what is the mass of the cylinder?

1 point

- 74 g
- 4 g
- 1068 g
**267 g**

20.

Question 20

Consider a jar of molasses. The empty jar weighs 20 grams and is 6 cm tall with a 3 cm diameter. A jar with molasses weights 90 g. What is the density of the molasses? Assume the molasses fills the entire jar.

1 point

- 1.41 g/cm^3
- 2.12 g/cm^3
**1.65 g/cm^3**- 1.21 g/cm^3

21.

Question 21

If the gauge pressure is reported as 6 atm, what is the absolute pressure?

1 point

**7 atm**- 6 atm
- 5 atm
- 8 atm

22.

Question 22

If the absolute pressure is 16 atm, what is the gauge pressure?

1 point

- 14 atm
- 17 atm
**15 atm**- 16 atm

23.

Question 23

Consider a vertical piston/cylinder system. The piston has a mass of 35 kg and has an unknown radius. There is a pressure gauge to output the pressure inside the cylinder. If the piston is compressed and the pressure gauge reads 300 kPa. What is the area of the piston? ( Assume the piston is compressed as a result of its own weight when in actuality there would probably be an external force)

1 point

- 6.0 cm^2
- 0.011 cm^2
- 0.006 cm^2
**11.4 cm^2**

24.

Question 24

Consider a vertical piston/cylinder system. The piston has 50 g mass and a given radius of 3 cm. What is the pressure due to the piston?

1 point

- 177 Pa
- 169 Pa
- 183 Pa
**173 Pa**

25.

Question 25

Which of the following is an example of a open system?

1 point

- An unopened jar of peanut butter
**A cup of coffee**- An enclosed fish tank.
- A water bottle with a top on.

26.

Question 26

Is a water bottle with a cap on it an example of an open system, a closed system, or a different kind of system?

1 point

- An open system
**A closed system**- A different kind of system

27.

Question 27

You are replicating a lab and want to check your measurements (SI units) with a previous experiment where the measurements were taken in English units. You found the density of water to be 980 kg/m^3, the volume of the water in a tank to be 53.1 cm^3 and the temperature of water to be 20 °C. If the values used in the previous experiment (completed in English units) were 1.93 slugs/ft^3, 5616 in^3, 68 °F, do you need to change any part of the current experiment to match the previous experiment?

1 point

- Everything needs to change. None of the parameters agree.
- The temperature of water needs to change. It is significantly higher than that of the previous experiment.
**The volume of water in your experiment needs to be change. It is much smaller than that of the previous experiment!**- Nothing needs to change.

28.

Question 28

You have a rope which is 27.0 cm long. How long is the rope in inches?

1 point

- 270.0 mm
**10.6 inches**- 68.6 in
- 15.3 in

**Week 2**

1.

Question 1

An adiabatic process is

1 point

A process in which heat transfer occurs across the boundary.

**A process in which no heat transfer occurs across a boundary.**

A process where matter is transferred across a boundary.

A process where matter is not transferred across a boundary.

2.

Question 2

Positive work and positive heat transfer is defined in this class as

1 point

Work done by the system and heat transfer out of the system

**Work done by the system and heat transfer to the system**

Work done on the system and heat transfer to the system

Work done on the system and heat transfer out of the system

3.

Question 3

The Critical Point is

1 point

The point where solid, liquid, and gas phases can occur. It is located at point A.

The point where solid, liquid, and gas phases can occur. It is located at point B.

**The point above which there is no distinction between liquid and gas phases. It is located at point B.**

The point above which there is no distinction between liquid and gas phases. It is located at point A.

4.

Question 4

The Triple Point is

1 point

**The point above which there is no distinction between liquid and gas phases. It is located at point A.**

The point where solid, liquid, and gas phases can occur. It is located at point B.

The point where solid, liquid, and gas phases can occur. It is located at point A.

The point above which there is no distinction between liquid and gas phases. It is located at point B.

5.

Question 5

Use the phase diagram of water to identify the state at point 3.

1 point

Liquid Phase

**Vapor Phase**

Solid Phase

6.

Question 6

Air is cooled in a process with constant pressure of 150 kPa. Before the process begins, air has a specific volume of 0.062 m^3/kg. The final specific volume is 0.027 m^3/kg. Find the specific work in the process.

1 point

5.3 kJ/kg

**-5.3 kJ/kg**

4.1 kJ/kg

-4.1 kJ/kg

7.

Question 7

If the specific volume of a substance is greater than the specific volume of saturated vapor then the substance is a

1 point

**Superheated Vapor**

Two-phase

Compressed Liquid

8.

Question 8

Air is expanded in a polytropic process, i.e. PV^n = constant. The initial specific volume is 0.25 m^3 / kg at a pressure of 127 kPa. If the final pressure is 111 kPa, what is the final specific volume for n = 1.3?

1 point

0.188 m^3/kg

0.286 m^3/kg

0.225 m^3/kg

**0.277 m^3/kg**

9.

Question 9

What is the angular velocity of a shaft if the power is 2.5 kW and the torque is 7 Nm?

1 point

3410 rad/sec

**3410 rpm**

360 rpm

170 rad/sec

10.

Question 10

Consider air in a piston than undergoes a polytropic process where PV^n = constant and n is a positive value. How do the pressure and volume change during expansion?

1 point

**The pressure decreases, and the volume increases.**

Both the pressure and the volume decrease.

Both remain constant.

Both the pressure and the volume increase.

11.

Question 11

Where is quality defined on a phase diagram?

1 point

all of the choices

in the liquid phase

**in the vapor dome**

in the vapor phase

12.

Question 12

Consider a heat engine that inputs 10 kJ of heat and outputs 5 kJ of work. What are the signs on the total heat transfer and total work transfer?

1 point

Heat transfer is negative and work transfer is positive.

Heat transfer and work transfer are both negative.

Heat transfer is positive and work transfer is negative.

**Heat transfer and work transfer are both positive.**

13.

Question 13

In thermodynamics it is very important to state any assumptions at the beginning of your analysis. If you are asked to find the net work transfer out of a cycle of a piston and cylinder, which of the following would you assume? (choose the best answer)

1 point

The air in the piston is considered a closed system.

Changes in kinetic energy and potential energy are negligible.

Work transfer only occurs across the system boundary.

**All of the choices**

14.

Question 14

Which of the following is true?

1 point

A system has heat transfer if the system is at a high temperature.

The units of heat transfer are Kelvin or Celsius.

You cannot boil water at a constant pressure.

**Heat transfer is a energy transfer process**

**Week 3**

1.

Question 1

Saturated water vapor expands in a constant-pressure piston/cylinder system. What must happen to the temperature of the water vapor for this to be true?

1 point

**Temperature will increase**

Temperature will decrease.

Temperature will remain the same.

Not enough information to determine the effect on temperature.

2.

Question 2

If you have a mixture of saturated water vapor and saturated liquid water at a pressure of 6000 kPa and 276°C, and you measure the specific volume to be 0.024 m^3/kg, what is the quality of the mixture?

1 point

0.28

0.37

**0.73**

0.64

3.

Question 3

When is the change in enthalpy (h_2 – h_1) approximately the same as the change in internal energy (u_2 – u_1) for an incompressible fluid?

1 point

When the change in volume is small.

When the change in specific heat is small.

When the change in temperature is small.

**When the change in pressure is small.**

4.

Question 4

What assumptions must we make to use the continuity equation (mass flow rate = density*velocity*area) ?

1 point

**1-D flow, and uniform intensive properties across the inlet and exit**.

1D flow.

Uniform intensive properties across the inlet and exit.

5.

Question 5

Using one of the online data sets for the steam tables, find the ratio of the specific heats for water at 3000 kPa and 1000 °C.

1 point

1.52

1.30

**1.23**

0.88

6.

Question 6

What is the change in specific internal energy for liquid water heated from 25°C to 100 °C (assume the incompressible substance model is valid here, and that the specific heat of water is 4.18 kJ/(kg*K) )?

1 point

-313.5 kJ/kg

**313.5 kJ/kg**

402.9 kJ/kg

-402.9 kJ/kg

7.

Question 7

What is the temperature of 5 moles of air at 100 kPa, and with a volume of 0.25 m^3?

1 point

12028 °C

**328 °C**

0.60 °C

601 °C

8.

Question 8

If a process begins with saturated water vapor at a pressure of 25 bar and a temperature of 225 °C and the pressure is increased to 50 bar through a polytropic process with n = 1.5, what is the final temperature of the water vapor (use the ideal gas model, despite the fact that we begin with a saturated vapor).

1 point

125°C

**354°C**

224°C

282°C

9.

Question 9

You’re examining a large pipe that has a circular cross-section with a radius of 2.5 meters. The pipe is uniform, and doesn’t allow the water that flows through it to pool or collect anywhere (that is, the water flows uniformly and edge effects of the flow can be ignored). If the water has a density of 1000 kg/m^3 and flows at a constant speed of 4 m/s, what is the mass flow rate of the water inside the pipe?

1 point

28 kg/s

42,130 kg/s

39,275 kg/s

**78,550 kg/s**

10.

Question 10

Water enters a turbine at a pressure of 50 bar and a temperature of 180 °C. The turbine can use either liquid phase water or steam (water vapor). The inlet diameter is 2 meters, and the speed of the water at the inlet is 30 m/s. The outlet diameter is 5.34 meters, and the speed of the water at the exit is 4 m/s. What is the density of the water at the exit state?

1 point

**936 kg/m^3**

234 kg/m^3

625 kg/m^3

1052 kg/m^3

11.

Question 11

Consider air at two states. The first state is at a pressure of 200 kPa and a temperature of 60°C. The second state is at a pressure of 1.5 bar. Given n = 1.3, what is the temperature at the second state?

1 point

311.6 °C

56.2 °C

82.9 °C

**38.6 °C**

12.

Question 12

What is the change in internal energy for water starting at 25 bar and 500°C and ending at 30 bar and 525°C (take c_v to be 1.71 kJ/(kgK) and c_p to be 2.23 kJ/(kgK)?

1 point

-42.75 kJ/kg

55.75 kJ/kg

**42.75 kJ/kg**

-55.75 kJ/kg

13.

Question 13

Which of the following statements is true of a steady state control volume system which experiences no work transfer and no heat transfer?

1 point

The mass flow rate is zero.

**No mass is accumulating within the control volume.**

The energy in the system is changing

14.

Question 14

Consider a room of 15m x 15m x 5 m. If the pressure in the room is 101 kPa and the temperature is 35°C, what is the mass of the air in the room?

1 point

44 kg

710 kg

8400 kg

**1285 kg**

15.

Question 15

Consider water moving through a pipe. The diameter of the inlet is 10 cm and the diameter at the outlet is 7 cm. What is the velocity at the outlet, if the velocity at the inlet is 10 m/s (assume the pressure and temperature remain the same)?

1 point

**20 m/s**

Cannot determined without knowing the density of water at the inlet.

5 m/s

80 m/s

**Week 4**

1.

Question 1

What causes heat transfer?

1 point

**A difference in temperature**

A difference in mass flow

A difference in specific volume

Work transfer

2.

Question 2

What is dm_cv / dt for a steady state system?

1 point

2

0.5

1

**0**

3.

Question 3

Which of the following devices produces work as output?

1 point

Nozzle

**Turbine**

Diffuser

All of the other choices.

4.

Question 4

What is the change in specific enthalpy if water vapor at 80 bar and a quality of 0 is expanded to a saturated vapor at 100 bar?

1 point

-1409 kJ/kg

**1409 kJ/kg**

2726 kJ/kg

1317 kJ/kg

5.

Question 5

Water flows through a 1000 cm^2 pipe at 200 kg/s. Find the velocity, if the water is at 20 bar and 45 ℃.

1 point

0.0002 m/s

**2.0 m/s**

5.5 m/s

0.55 m/s

6.

Question 6

Consider a pump with a mass flow rate of water of 5 kg/s. The water enters at 99 °C and 9999 kPa and leaves at 150 °C and 15000 kPa. What is the specific work of the pump? Assume the process is adiabatic.

1 point

219 kJ/kg

**-219 kJ/kg**

-1095 kJ/kg

1095 kJ/kg

7.

Question 7

A rigid container holds an ideal gas with c_v = 0.75 kJ/(kgK). The container is cooled from 110 ℃ to 20 ℃. Find the specific heat transfer (kJ/kg) for the process.

1 point

-96 kJ/kg

**-67.5 kJ/kg**

96 kJ/kg

67.5 kJ/kg

8.

Question 8

Water is compressed in a piston/cylinder system with specific heat transfer into the system of 150 kJ/kg. Determine the specific work that occurs if the water is initially a superheated vapor at 2000 kPa and 300°C and the final state is 2500 kPa and 350°C.

1 point

208 kJ/kg

185 kJ/kg

**71 kJ/kg**

53 kJ/kg

9.

Question 9

Consider a problem where you need to find the change in enthalpy. The initial state and the final state have the same pressure, but the pressure changes throughout the process. Which of the following list of variables is needed to solve the problem?

1 point

**c_p, T_2, T_1**

c_v, T_2, T_1

T_2, T_1

c_p, c_v, T_2, T_1

10.

Question 10

Consider a dropping a ball from a height of 5 m into a pool of warm water. Which of the following is true?

1 point

There is significant work transfer.

**There is a change in internal energy in the process.**

The potential energy can be ignored.

Energy is not conserved.

11.

Question 11

In this course, we commonly assume which of the following for flow devices like pumps, heat exchanges, turbines and compressors?

1 point

Steady State, Steady Flow, Constant Temperature

**Steady State and Steady Flow**

Steady State

Steady Flow

12.

Question 12

Which of the following is true about a nozzle?

1 point

The area at the exit is greater than the area at the entrance of a nozzle.

**There is a change in pressure from the inlet to the outlet of the nozzle.**

The velocity of the fluid at the entrance is larger than the velocity of the fluid at the exit of a nozzle.

Nozzles are not adiabatic.

13.

Question 13

Consider a car at a chilly temperature of 44 °F. If the pressure is 101 kPa, what is the density of air in the car? How would increasing the temperature to 77°F change the density of air in the car?

1 point

1257 g/m^3, increase by 77 g/m^3

1124 g/m^3, decrease by 98 g/m^3

1124 g/m^3, increase by 98 g/m^3

**1257 g/m^3, decrease by 77 g/m^3**

14.

Question 14

Air is flowing in a 0.2 meter diameter pipe at a uniform velocity of 0.5 m/s. The temperature is 49 °C and pressure is 99 kPa. Determine the mass flow rate in kg/s.

1 point

**0.017 kg/s**

0.066 kg/s

0.007 kg/s

0.021 kg/s

15.

Question 15

A piston/cylinder system has an initial volume of 0.1 m^3 and contains nitrogen initially at 150 kPa, 25 °C. The piston compresses the nitrogen until the pressure reaches 1 MPa and the temperature is 150°C. During the compression process, heat is transferred from the nitrogen, and the work done on the nitrogen is 20 kJ. Determine the heat transfer of the process. The gas constant R for nitrogen is 0.2968 kJ/(kgK) and the specific heat c_v is 0.745 kJ/(kgK).

1 point

-8.4 kJ

8.4 kJ

**-4.2 kJ**

-3.7 kJ

**Week 5**

1.

Question 1

If you have air at a temperature of 418 K and a pressure of 3 atm, what is its density if you assume that the ideal gas equation holds true?

1 point

0.0025 kg/m^3

49 kg/m^3

0.000049 kg/m^3

**2.5 kg/m^3**

2.

Question 2

*ANSWERS A LITTLE OFF. You have air flowing through a 0.5 m x 1.0 m vent. The air flows into the vent at a temperature of 300 K and a speed of 1.0 m/s. If the air leaves the vent at a temperature of 250 K, what is the rate of heat transfer that occurs in the vent? Assume that the ideal gas equation holds true for the air in this situation, and the pressure of the air is constant at 1 atm, and that this occurs over a short period of time.

1 point

34 kW

-40 kW

**-34 kW**

-53 kW

3.

Question 3

You need to fill up a basketball that’s low on air pressure. It’s initially at a gauge pressure of 6 psi, and you want to inflate it to 7 psi so that it is properly inflated. The volume of the ball is 7000 cubic centimeters, and you can assume that the volume of the ball remains constant as you pump air into it. What is the initial mass of air in the ball, if you assume that the air in the ball is at the ambient temperature of 298 K and that the ideal gas relations hold true for the air in the ball? (Please use the absolute pressure in the ideal gas formula)

1 point

1.9 g

0.12 g

**11.7 g**

0.96 g

4.

Question 4

Now that you’ve filled the ball, you know that it’s at a gauge pressure of 7 psi and the air inside is again at the ambient temperature of 298 K (so you filled it quickly and allowed it to reach equilibrium, as discussed in lecture). What is the new mass of air inside the ball? (Please use the absolute pressure in the ideal gas formula)

1 point

**12.2 g**

2.1 g

11700 g

13.2 g

5.

Question 5

If you run a heat engine that takes in 413 kW of heat and rejects 164 kW of heat, what is the power generated by the engine?

1 point

377 kW

229 kW

**249 kW**

577 kW

6.

Question 6

What is the efficiency of the heat engine in the previous problem (express your answer as a percentage)?

1 point

**60%**

32%

40%

18%

7.

Question 7

You have a refrigeration system that takes in 397 kW of heat and puts out 599 kW of heat. What is the coefficient of performance (C.O.P.) of the system (do NOT express this value as a percentage)?

1 point

0.64

1.51

0.34

**1.97**

8.

Question 8

You have a heat pump that takes in 397 kW of heat and puts out 599 kW of heat. What is the coefficient of performance (C.O.P.) of the system (do NOT express this value as a percentage)?

1 point

1.97

2.61

**2.97**

0.63

9.

Question 9

Heat naturally flows from

1 point

**Regions of higher temperature to regions of lower temperature.**

Heat does not move.

Regions of lower temperature to regions of higher temperature.

10.

Question 10

An engine takes in 493 kW of heat and rejects 128 kW of heat. What is the power generated (assuming there are no losses)?

1 point

493 kW

**365 kW**

621 kW

128 kW

11.

Question 11

An engine takes in 493 kW of heat and rejects 128 kW of heat. What could be the power generated assuming the engine is not ideal (assuming there are losses beyond what is measured)?

1 point

**334 kW**

394 kW

365 kW

12.

Question 12

*Define fridge… Which of the following are true for a large home refrigerator or heat pump?

1 point

Transfers heat.

Operates in a cycle

Requires work

**All of the other choices.**

13.

Question 13

Which of the following causes a system to be irreversible?

1 point

**All of the other choices.**

Mixing two different substances

Friction

Unrestrained expansion

14.

Question 14

*DEFINE REFRIDGE. Think about how a refrigerator works and the system of the refrigerator and the area outside of the refrigerator at ambient temperature. Is the high temperature body the refrigerator or the ambient air around the refrigerator?

1 point

Provided the refrigerator is working, the bodies are of the same temperature.

**Provided the refrigerator is working, the area around the refrigerator is the higher temperature body.**

Not enough information to answer.

Provided the refrigerator is working, the refrigerator is the higher temperature body.

15.

Question 15

Which one of the following conditions is necessary for a process to be considered a cycle?

1 point

**A process during which the initial state and the final states are the same.**

A process in which the final pressure is different from the initial pressure.

A process in which work transfer does not occur.

A process in which heat transfer does not occur.

**Week 6**

1.

Question 1

A wall air conditioner releases heat

1 point

as cold air

**outside the room**

into the room

2.

Question 2

Why can you cool a room with an air conditioner and not a refrigerator?

1 point

They both can cool a room.

**An air conditioner releases the heat outside while a fridge releases heat out of the back.**

An air conditioner uses more energy and therefore is more effective in cooling a room.

3.

Question 3

Consider an engine that operates at a low temperature of 33°C and a higher temperature of 367 °C. Would it be possible to have an efficiency of 65%?

1 point

Yes. The Carnot Efficiency is 91%

Yes. The Carnot Efficiency is 52%

**No. The Carnot efficiency is 52%**

No. The Carnot Efficiency is 91%

4.

Question 4

You are designing an engine with a hot reservoir of 555°C and a cold reservoir of 22°C. What is the maximum efficiency of the engine?

1 point

0.602

0.040

0.960

**0.644**

5.

Question 5

Consider a refrigerator. What is the coefficient of performance if the heat released is 6.75 Watts and the heat added is 3.75 Watts?

1 point

0.55

1.75

0.80

**1.25**

6.

Question 6

Given the coefficient of performance of a heat pump is 1.25 and the heat released into the hot reservoir is 92 W, what is the heat required from the cold reservoir and what is the work required for this output?

1 point

Q_cold = 162.7 W and Work = 79.7 W

Q_cold = 115 W and Work = 23 W

**Q_cold = 18.4 W and Work = 73.6 W**

Q_cold = 73.6 W and Work = 18.4 W

7.

Question 7

What is the efficiency of a Carnot cycle with the temperature at state 1 of 300 °C and a temperature at state 2 and 3 of 33 °C and the temperature at state 4 of 275°C.

1 point

93.0%

35.5%

**45.4%**

89.0%

8.

Question 8

If we wanted to increase the efficiency in the Carnot cycle in the previous question we could…

1 point

Increase the temperature of the hot reservoir.

Increase the temperature of the cold reservoir.

Both increase the temperature of the hot reservoir and decrease the temperature of the cold reservoir.

Decrease the temperature of the hot reservoir.

Decrease the temperature of the cold reservoir.

**Both increase the temperature of the cold reservoir and decrease the temperature of the hot reservoir.**

9.

Question 9

A refrigerator uses 1000W to keep your food cold. How much power is saved if a different refrigerator with a coefficient of performance of 3 is used? (Assume that Q_L is 1000 W)

1 point

4000 W

**666.67 W**

2000 W

333.33 W

10.

Question 10

In ideal Rankine cycle the pump and turbine are

1 point

**Adiabatic and Reversible**

None of the others

Reversible

Adiabatic

11.

Question 11

In an Ideal Rankine cycle, the Boiler and Condenser are

1 point

Reversible

Adiabatic

**Constant Pressure**

All of the other options

12.

Question 12

Calculate the thermal efficiency of a Carnot cycle heat engine operating between reservoirs at 325°C and 35°C.

1 point

**0.48**

0.67

0.33

0.89

**Week 7**

1.

Question 1

Which of the following statements about the property entropy is not true?

1 point

Entropy is an extensive property

**It measures the amount of heat of a substance.**

The units of specific entropy are kJ/kg K.

2.

Question 2

Consider a Rankine power plant that has uses no reheat with water as the working fluid. The steam generator operates at 100 bar and the condenser operates at 10 bar (absolute). The water enters the turbine at a temperature of 775 degrees Celsius. Assume no losses in the system. What is the specific enthalpy and the specific entropy of the water as it enters the turbine?

1 point

enthalpy- 3930 kJ/kg, entropy- 7.18 kJ/(kg*K)

enthalpy- 3930 kJ/kg, entropy- 7.35 kJ/(kg*K)

**enthalpy- 4053 kJ/kg, entropy- 7.35 kJ/(kg*K)**

entropy- 4053 kJ/kg, enthalpy- 7.18 kJ/(kg*K)

3.

Question 3

Assume the turbine is ideal and adiabatic. What is the specific entropy of the steam as it exits the turbine and enters the condenser? Hint: you need to use the results from the previous problem.

1 point

4053 kJ/kg

2.503 kJ/kg

**specific entropy = 7.35 kJ/(kg*K)**

Cannot be determined.

4.

Question 4

What is the specific enthalpy at the exit state of the condenser? Assume the steam leaves the condenser as a saturated liquid at 10 bar (absolute).

1 point

**763 kJ/kg**

1500 kJ/kg

2700 kJ/kg

405 kJ/kg

5.

Question 5

What is the specific entropy of the water as it exits the condenser?

1 point

1.8 kJ(kg*K)

1.2 kJ/(kg*K)

**2.1 kJ/(kg*K)**

1.3 kJ/(kg*K)

6.

Question 6

As you move from the inlet state to the exit state of the pump, which of the following is true?

1 point

The entropy will be the same as it was at the inlet state to the turbine.

**The pump is isentropic.**

The change in specific enthalpy will be the same as the turbine.

The specific enthalpy will remain the same.

7.

Question 7

If the specific enthalpy at the exit of the turbine is 2700 kJ/kg, what is the heat rejected from this Rankine Cycle in units of kJ/kg?

1 point

2750 kJ/kg

3219 kJ/kg

**1940 kJ/kg**

1335 kJ/kg

8.

Question 8

Using the heat output in the previous problem and the heat input is 3630, what is the efficiency?

1 point

60.8 %

64.4 %

24.5 %

**46.6 %**

9.

Question 9

Which of the following statements about cycle efficiency is false?

1 point

Real turbines and real pumps are not isentropic.

Real boilers and real condensers are not isobaric.

**Superheaters do not affect cycle efficiency.**

10.

Question 10

Determine the q_h and q_l of a Rankine cycle using steam as the working fluid in which the condenser pressure is 10 kPa. The boiler pressure is 2000 kPa and the steam leaving the boiler is a saturated vapor.

Given: State 1 is the state of the fluid entering the pump, state 2 is state of the fluid entering the boiler, state 3 is state of the fluid entering the turbine and state 4 is the state entering the condenser, and h1 = 191.8 kJ/kg, h2 = 193.8 kJ/kg, h3 = 2799.5 kJ/kg, h4 = 2007.5 kJ/kg

1 point

q_h=1813.7 kJ/kg, q_l=2.0 kJ/kg

q_h=1915.7 kJ/kg, q_l=598.2 kJ/kg

**q_h=2605.7 kJ/kg, q_l=1815.7 kJ/kg**

11.

Question 11

Calculate the efficiency of Rankine cycle for previous problem.

1 point

**30.3%**

25.7%

43.5%

12.

Question 12

Consider a heat engine with the heat input of 900 kJ at a temperature of 500 °C. The heat engines rejects heat to the the surroundings at a temperature of 25 °C. The engine produces 375 kJ of work. How much heat is rejected to the surroundings?

1 point

150 kJ

**525 kJ**

850 kJ

1250 kJ

13.

Question 13

Consider a heat engine with heat input of 900 kJ at a temperature of 500 °C. The heat engines rejects heat to the the surroundings at a temperature of 25 °C, and produces 375 kJ of work. What is the engine efficiency?

1 point

**42%**

61%

58%

33 %

14.

Question 14

Consider a heat engine with the heat input of 900 kJ at a temperature of 500 °C. The heat engines rejects heat to the the surroundings at a temperature of 25 °C, and produces 375 kJ of work. What is the Carnot efficiency?

1 point

33%

**61%**

95%

41%

**Week 8**

1.

Question 1

Which statement is false?

1 point

The Rankine Cycle uses water as its working fluid while the Brayton Cycle uses air.

**Both the Brayton Cycle and the Rankine Cycle have phase change.**

Both Brayton cycle efficiency and Rankine cycle efficiency increase with a increase in burner operating pressure.

The compressor in the Brayton Cycle is comparable to the pump in the Rankine Cycle

2.

Question 2

What is the efficiency of a Brayton Cycle if the specific work into the compressor is 330 kJ/kg and the specific work out of the turbine is 675 kJ/kg and the specific heat transfered into the heat exchanger is 580 kJ/kg?

1 point

37%

170%

**59%**

41%

3.

Question 3

Determine the efficiency given the following fictional specific enthalpies: h_1 = 300 kJ/kg, h_2 = 580 kJ/kg, h_3 = 1460 kJ/kg, h_4 =750 kJ/kg. (Assume that state 1 is the entrance to the compressor, state two is between the compressor and the burner, state 3 is between the burner and the turbine and state 4 is the exit of the turbine)

1 point

**49%**

80%

53%

32%

4.

Question 4

Determine the back work ratio given the following fictional specific enthalpies used in the previous problem: h_1 = 300 kJ/kg, h_2 = 580 kJ/kg, h_3 = 1460 kJ/kg, h_4 =750 kJ/kg. (Assume that state 1 is the entrance to the compressor, state two is between the compressor and the burner, state 3 is between the burner and the turbine and state 4 is the exit of the turbine)

1 point

**39%**

67%

55%

2.5%

5.

Question 5

Find the approximate efficiency of a combined cycle with 40% electricity out of both the Rankine and Brayton cycles.

1 point

40%

16%

**64%**

24%

6.

Question 6

Which of the following is not a renewable resource?

1 point

Wind, sun, and natural gas are renewable resources.

Wind

**Natural Gas**

Sunlight

7.

Question 7

Which of the following has the largest energy density on a per volume basis?

1 point

Hydrogen

**Diesel**

Coal

Oil

8.

Question 8

Which of the following has the largest energy density on a per mass basis?

1 point

**Hydrogen**

Oil

Liquid Fuels

Coal

9.

Question 9

What is the mass flow rate of a refrigeration fluid with a density of 1136 kg/m^3, a volume flow rate of 0.015 cm^3 / s?

1 point

**0.017 g/s**

17 kg/s

0.013 g/s

13 kg/s

10.

Question 10

*COP > 1…. If the heat transfer into a refrigeration system is 278 kJ/s and the work of the cycle is 325 kJ/s, then what is the efficiency of the refrigeration system?

1 point

17%

14%

**86%**

55%

11.

Question 11

An Ideal Brayton cycle has:

1 point

2 isentropic processes and 2 isochoric processes

**2 isentropic processes and 2 isobaric processes**

2 isentropic processes and 2 isothermal processes

12.

Question 12

The Brayton cycle has the same 4 processes as the Rankine cycle, but the T-S and P-V diagrams look very different; why is that?

1 point

Brayton cycle crosses in over the two-phase region

Rankine Cycle have all the processes in saturated liquid region

**Brayton cycle have all the processes in superheated region**