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Introduction to Thermodynamics: Transferring Energy from Here to There Quiz Answers

Introduction to Thermodynamics: Transferring Energy from Here to There Week 01 Quiz Answers

Quiz 01: Week 1

Q1. Which of the following is an example of a system where the transfer of energy is important?

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

Q2. Energy density is energy per unit mass. Which sector would you expect to have the highest needs for high energy density fuels?

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

Q3. The Jet Aircraft industry has the highest need for

• Low Energy Density Fuels
• Wind Energy
• High Energy Density Fuels
• Solar Energy

Q4. Why is it important to find new sources of energy?

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

Q5. 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?

• 159 cm^3 / s
• 276 cm^3/s
• 51 cm^3/s
• 634 cm^3/s

Q6. 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?

• 5.5 inches
• 1.1 inches
• 1.8 inches
• 2.4 inche

Q7. Why does the table heat when you set your mug of fresh hot coffee on it?

• Static electricity builds as the mug sits on the table, which causes heat to accumulate.
• Frictional forces between the mug and table cause heat transfer from the mug to the table.
• Energy is transferred from the table to the mug.
• Energy is transferred from the hot mug to the table8

Q8. A light-bulb is being used in a lamp. You notice the lamp becomes warm. Which of the following is true?

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

Q9. Which of the following is an extensive property?

• Temperature
• Density
• Concentration
• Volume

Q10. Pressure is an example of a

• Extensive Property
• Material Property
• None of the other options
• Intensive Property

YQ11. our car thermometer tells you it is -10 degrees Fahrenheit outside on a brisk day. What is the absolute temperature in Kelvin?

Q12. You need to set the oven to 450 Kelvin. What temperature do you need to set the oven to in Celsius

• 0 degrees Celsius
• 450 degrees Celsius
• 177 degrees Celsius
• 350 degrees Celsiu

Q13. 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?

• Need more information
• An open system
• A closed system

Q14. Which of the following is not true of a closed system

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

Q15. 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

• Room 1
• Room 2
• Room 3
• Room 1 and Room 3

Q16. 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?

Q17. 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.

Q18. 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?

• 0.6 m/s
• 1.4 m/s
• 4.4 m/s
• 1000 m/

Q19. 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?

Q20. 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.

• 1.21 g/cm^3
• 2.12 g/cm^3
• 1.65 g/cm^3
• 1.41 g/cm^3

Q21. If the gauge pressure is reported as 6 atm, what is the absolute pressure

Q22. If the absolute pressure is 16 atm, what is the gauge pressure?

• 17 atm
• 16 atm
• 14 atm
• 15 atm

Q23. 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)

• 11.4 cm^2
• 6.0 cm^2
• 0.006 cm^2
• 0.011 cm^2

Q24. 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?

• 177 Pa
• 173 Pa
• 183 Pa
• 169 Pa

Q25. Which of the following is an example of a open system?

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

Q26. Is a water bottle with a cap on it an example of an open system, a closed system, or a different kind of system?

• A closed system
• An open system
• A different kind of system

Q26. 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?

• Nothing needs to change.
• 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!

Q28. You have a rope which is 27.0 cm long. How long is the rope in inches?

• 270.0 mm
• 68.6 in
• 10.6 inches
• 15.3 in

Introduction to Thermodynamics: Transferring Energy from Here to There Week 02 Quiz Answers

Quiz 01: Week 2

Q1. An adiabatic process is

• 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.

Q2. Positive work and positive heat transfer is defined in this class as

• Work done on the system and heat transfer to the system
• Work done by the system and heat transfer to the system
• Work done by the system and heat transfer out of the system
• Work done on the system and heat transfer out of the system

Q3. The Critical Point is

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

Q4. The Triple Point is

• The point above which there is no distinction between liquid and gas phases. 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.
• 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.

Q5. Use the phase diagram of water to identify the state at point 3.

• Vapor Phase
• Solid Phase
• Liquid Phase

Q6. 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.

• -5.3 kJ/kg
• 4.1 kJ/kg
• -4.1 kJ/kg
• 5.3 kJ/kg

Q7. If the specific volume of a substance is greater than the specific volume of saturated vapor then the substance is a

• Compressed Liquid
• Superheated Vapor
• Two-phase

Q8. 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?

• 0.286 m^3/kg
• 0.225 m^3/kg
• 0.188 m^3/kg
• 0.277 m^3/kg

Q9. What is the angular velocity of a shaft if the power is 2.5 kW and the torque is 7 Nm?

• 360 rpm
• 3410 rad/sec
• 3410 rpm
• 170 rad/sec

Q10. 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?

• Both the pressure and the volume decrease.
• Both the pressure and the volume increase.
• The pressure decreases, and the volume increases.
• Both remain constant.

Q11. Where is quality defined on a phase diagram?

• all of the choices
• in the liquid phase
• in the vapor phase
• in the vapor dome

Q12. 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?

• Heat transfer is positive and work transfer is negative.
• Heat transfer is negative and work transfer is positive.
• Heat transfer and work transfer are both positive.
• Heat transfer and work transfer are both negative.

Q13. 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)

• Work transfer only occurs across the system boundary.
• The air in the piston is considered a closed system.
• All of the choices
• Changes in kinetic energy and potential energy are negligible.

Q14. Which of the following is true?

• Heat transfer is a energy transfer process
• You cannot boil water at a constant pressure.
• A system has heat transfer if the system is at a high temperature.
• The units of heat transfer are Kelvin or Celsius.

Introduction to Thermodynamics: Transferring Energy from Here to There Week 03 Quiz Answers

Quiz 01: Week 3

Q1. 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?

• Temperature will increase
• Not enough information to determine the effect on temperature.
• Temperature will decrease.
• Temperature will remain the same.

Q2. 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?

Q3. 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?

• When the change in pressure is small.
• When the change in volume is small.
• When the change in temperature is small.
• When the change in specific heat is small.

Q4. What assumptions must we make to use the continuity equation (mass flow rate = density*velocity*area) ?

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

Q5. 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.

Q6. 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) )?

• -313.5 kJ/kg
• 402.9 kJ/kg
• -402.9 kJ/kg
• 313.5 kJ/kg

Q7. What is the temperature of 5 moles of air at 100 kPa, and with a volume of 0.25 m^3?

• 0.60 °C
• 328 °C
• 12028 °C
• 601 °C

Q8. 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).

• 224°C
• 125°C
• 282°C
• 354°C

Q9. 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?

• 39,275 kg/s
• 28 kg/s
• 78,550 kg/s
• 42,130 kg/s

Q10. 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?

• 234 kg/m^3
• 1052 kg/m^3
• 625 kg/m^3
• 936 kg/m^3

Q11. 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?

• 311.6 °C
• 82.9 °C
• 56.2 °C
• 38.6 °C

Q12. 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)?

• 42.75 kJ/kg
• -42.75 kJ/kg
• -55.75 kJ/kg
• 55.75 kJ/kg

Q13. Which of the following statements is true of a steady state control volume system which experiences no work transfer and no heat transfer?

• No mass is accumulating within the control volume.
• The mass flow rate is zero.
• The energy in the system is changing

Q14. 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?

• 1285 kg
• 710 kg
• 44 kg
• 8400 kg

Q15. 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)?

• Cannot determined without knowing the density of water at the inlet.
• 20 m/s
• 5 m/s
• 80 m/s

Introduction to Thermodynamics: Transferring Energy from Here to There Week 04 Quiz Answers

Quiz 01: Week 4

Q1. What causes heat transfer?

• A difference in specific volume
• A difference in mass flow
• Work transfer
• A difference in temperature

Q2. What is dm_cv / dt for a steady state system?

Q3. Which of the following devices produces work as output?

• Nozzle
• Turbine
• All of the other choices.
• Diffuser

Q4. 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?

• 1317 kJ/kg
• 2726 kJ/kg
• -1409 kJ/kg
• 1409 kJ/kg

Q5. Water flows through a 1000 cm^2 pipe at 200 kg/s. Find the velocity, if the water is at 20 bar and 45 ℃.

• 2.0 m/s
• 0.0002 m/s
• 0.55 m/s
• 5.5 m/s

Q6. 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.

• -1095 kJ/kg
• 1095 kJ/kg
• -219 kJ/kg
• 219 kJ/kg

Q7. 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.

• -67.5 kJ/kg
• -96 kJ/kg
• 67.5 kJ/kg
• 96 kJ/kg

Q8. 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.

• 53 kJ/kg
• 185 kJ/kg
• 208 kJ/kg
• 71 kJ/kg

Q9. 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?

• c_p, T_2, T_1
• c_v, T_2, T_1
• T_2, T_1
• c_p, c_v, T_2, T_1

Q10. Consider a dropping a ball from a height of 5 m into a pool of warm water. Which of the following is true?

• There is a change in internal energy in the process.
• The potential energy can be ignored.
• There is significant work transfer.
• Energy is not conserved.

Q11. In this course, we commonly assume which of the following for flow devices like pumps, heat exchanges, turbines and compressors?

• Steady State, Steady Flow, Constant Temperature
• Steady State
• Steady State and Steady Flow
• Steady Flow

Q12. Which of the following is true about a nozzle?

• Nozzles are not adiabatic.
• 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.
• The area at the exit is greater than the area at the entrance of a nozzle.

Q13. 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?

• 1257 g/m^3, decrease by 77 g/m^3
• 1257 g/m^3, increase by 77 g/m^3
• 1124 g/m^3, increase by 98 g/m^3
• 1124 g/m^3, decrease by 98 g/m^3

Q14. 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.

• 0.066 kg/s
• 0.021 kg/s
• 0.017 kg/s
• 0.007 kg/s

Q15. 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).

• -8.4 kJ
• 8.4 kJ
• -4.2 kJ
• -3.7 kJ

Introduction to Thermodynamics: Transferring Energy from Here to There Week 05 Quiz Answers

Quiz 01: Week 5

Q1. 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?

• 49 kg/m^3
• 2.5 kg/m^3
• 0.000049 kg/m^3
• 0.0025 kg/m^3

Q2. *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.

• 34 kW
• -53 kW
• -34 kW
• -40 kW

Q3. 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)

• 0.12 g
• 1.9 g
• 0.96 g
• 11.7 g

Q4. 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)

• 12.2 g
• 13.2 g
• 2.1 g
• 11700 g

Q5. 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?

• 377 kW
• 249 kW
• 577 kW
• 229 kW

Q6. What is the efficiency of the heat engine in the previous problem (express your answer as a percentage)?

Q7. 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)?

Q8. 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)?

Q9. Heat naturally flows from

• Regions of lower temperature to regions of higher temperature.
• Heat does not move.
• Regions of higher temperature to regions of lower temperature.

Q10. An engine takes in 493 kW of heat and rejects 128 kW of heat. What is the power generated (assuming there are no losses)?

• 365 kW
• 128 kW
• 621 kW
• 493 kW

Q11. 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)?

*Q12. Define fridge… Which of the following are true for a large home refrigerator or heat pump?

• Operates in a cycle
• All of the other choices.
• Requires work
• Transfers heat.

Q13. Which of the following causes a system to be irreversible?

• Unrestrained expansion
• Friction
• Mixing two different substances
• All of the other choices.

*Q14. 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?

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

Q15. Which one of the following conditions is necessary for a process to be considered a cycle?

• A process in which the final pressure is different from the initial pressure.
• A process in which heat transfer does not occur.
• A process in which work transfer does not occur.
• A process during which the initial state and the final states are the same.

Introduction to Thermodynamics: Transferring Energy from Here to There Week 06 Quiz Answers

Quiz 01: Week 6

Q1. A wall air conditioner releases heat

• outside the room
• into the room
• as cold air

Q2. Why can you cool a room with an air conditioner and not a refrigerator?

• 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.

Q3. 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%?

• Yes. The Carnot Efficiency is 91%
• Yes. The Carnot Efficiency is 52%
• No. The Carnot efficiency is 52%
• No. The Carnot Efficiency is 91%

Q4. 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

Q5. 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?

Q6. 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?

• Q_cold = 162.7 W and Work = 79.7 W
• Q_cold = 115 W and Work = 23 W
• Q_cold = 73.6 W and Work = 18.4 W
• Q_cold = 18.4 W and Work = 73.6 W

Q7. 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.

Q8. If we wanted to increase the efficiency in the Carnot cycle in the previous question we could…

• Increase the temperature of the cold reservoir.
• Increase the temperature of the hot reservoir.
• Both increase the temperature of the hot reservoir and decrease the temperature of the cold reservoir.
• Both increase the temperature of the cold reservoir and decrease the temperature of the hot reservoir.
• Decrease the temperature of the cold reservoir.
• Decrease the temperature of the hot reservoir.

Q9. 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)

• 4000 W
• 2000 W
• 333.33 W
• 666.67 W

Q10. In ideal Rankine cycle the pump and turbine are

• None of the others
• Adiabatic and Reversible
• Adiabatic
• Reversible

Q11. In an Ideal Rankine cycle, the Boiler and Condenser are

• Adiabatic
• Reversible
• Constant Pressure
• All of the other options

Q12. Calculate the thermal efficiency of a Carnot cycle heat engine operating between reservoirs at 325°C and 35°C.

Introduction to Thermodynamics: Transferring Energy from Here to There Week 07 Quiz Answers

Quiz 01: Week 7

Q1. Which of the following statements about the property entropy is not true?

• It measures the amount of heat of a substance.
• Entropy is an extensive property
• The units of specific entropy are kJ/kg K

Q2. 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?

• enthalpy- 4053 kJ/kg, entropy- 7.35 kJ/(kg*K)
• enthalpy- 3930 kJ/kg, entropy- 7.35 kJ/(kg*K)
• entropy- 4053 kJ/kg, enthalpy- 7.18 kJ/(kg*K)
• enthalpy- 3930 kJ/kg, entropy- 7.18 kJ/(kg*K)

Q3. 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

• specific entropy = 7.35 kJ/(kg*K)
• 4053 kJ/kg
• 2.503 kJ/kg
• Cannot be determined.

Q4. 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).

• 2700 kJ/kg
• 763 kJ/kg
• 405 kJ/kg
• 1500 kJ/kg

Q5. What is the specific entropy of the water as it exits the condenser?

• 1.8 kJ(kg*K)
• 1.3 kJ/(kg*K)
• 2.1 kJ/(kg*K)
• 1.2 kJ/(kg*K)

Q6. As you move from the inlet state to the exit state of the pump, which of the following is true?

• The pump is isentropic.
• The specific enthalpy will remain the same.
• The change in specific enthalpy will be the same as the turbine.
• The entropy will be the same as it was at the inlet state to the turbine.

Q7. 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?

• 1940 kJ/kg
• 1335 kJ/kg
• 3219 kJ/kg
• 2750 kJ/kg

Q8. Using the heat output in the previous problem and the heat input is 3630, what is the efficiency?

• 60.8 %
• 46.6 %
• 64.4 %
• 24.5 %

Q9. Which of the following statements about cycle efficiency is false?

• Real turbines and real pumps are not isentropic.
• Real boilers and real condensers are not isobaric.
• Superheaters do not affect cycle efficiency.

Q10. 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

• q_h=1915.7 kJ/kg, q_l=598.2 kJ/kg
• q_h=2605.7 kJ/kg, q_l=1815.7 kJ/kg
• q_h=1813.7 kJ/kg, q_l=2.0 kJ/kg

Q11. Calculate the efficiency of Rankine cycle for previous problem.

Q12. 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?

• 150 kJ
• 525 kJ
• 1250 kJ
• 850 kJ

Q13 .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?

Q14. 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?

Introduction to Thermodynamics: Transferring Energy from Here to There Week 08 Quiz Answers

Quiz 01: Week 8

Q1. Which statement is false?

• 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

Q2. 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?

Q3. 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)

Q4. 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)

Q5. Find the approximate efficiency of a combined cycle with 40% electricity out of both the Rankine and Brayton cycles.

Q6. Which of the following is not a renewable resource?

• Sunlight
• Natural Gas
• Wind
• Wind, sun, and natural gas are renewable resources.

Q7. Which of the following has the largest energy density on a per volume basis?

Q8. Which of the following has the largest energy density on a per mass basis?

• Oil
• Liquid Fuels
• Hydrogen
• Coal

Q9. 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?

• 0.013 g/s
• 17 kg/s
• 0.017 g/s
• 13 kg/s

Q10. *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?

Q11. An Ideal Brayton cycle has:

• 2 isentropic processes and 2 isochoric processes
• 2 isentropic processes and 2 isobaric processes
• 2 isentropic processes and 2 isothermal processes

Q12. 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?

• Brayton cycle have all the processes in superheated region
• Brayton cycle crosses in over the two-phase region
• Rankine Cycle have all the processes in saturated liquid region

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