thermodynamics

Question 1

Which of the following processes does not typically occur during a topping cycle?

a. High temperature fuel combustion
b. Expansion of working fluid in a turbine
c. Heat recovery
d. Condensation of steam at low pressure

Answer 1

d. Condensation of steam at low pressure

Question 2

A thermodynamic process where the pressure of the system remains constant.

a. Isobaric
b. Isochoric
c. Isothermal
d. Adiabatic

Answer 2

a. Isobaric

Question 3

It is used to get mechanical work from a high energy fluid such as a gas or steam.

a. Condenser
b. Pump
c. Turbine
d. Valve

Answer 3

c. Turbine

Question 4

In a topping cycle, electricity is generated first, and the waste heat created throughout the process is used for heating. This is the most prevalent type of cogeneration.

a. Only the first statement is true.
b. Both statements are true
c. Both statements are false
d. Only the second statement is true

Answer 4

b. Both statements are true

Question 5

Works by using heat transfer to convert a gas or vapor into a liquid, effectively releasing heat in the process.

a. Condenser
b. Valve
c. Pump
d. Turbine

Answer 5

a. Condenser

Question 6

What is the efficiency of a topping cycle?

a. 80% to 90%
b. 60% to 70%
c. 60% to 80%
d. 80% to 95%

Answer 6

c. 60% to 80%

Question 7

Which of the following statements is true about the bottoming cycle?

a. It causes change in internal energy without transfer of heat.
b. The temperature of the cycle remains constant all throughout the process.
c. The waste heat of the process is recovered via heat exchanger.
d. It is where the fuel is combusted to produce electricity to carry out an industrial process.

Answer 7

c. The waste heat of the process is recovered via heat exchanger.

Question 8

Adiabatic processes typically occur very quickly. Some processes are adiabatic.

a. Only the first statement is true
b. Both statements are true
c. Both statements are false
d. Only the second statement is true

Answer 8

a. Only the first statement is true

Question 9

9. Cogeneration is commonly known as ____________?

a. Combined Heat and Pressure
b. Waste Heat to Power
c. Heat and Power Recovery
d. Combined Heat and Power

Answer 9

d. Combined Heat and Power

Question 10

How much heat source does a bottoming cycle system require?

a. 300°C
b. 260°C
c. 200°C
d. 360°C

Answer 10

b. 260°C

Question 11

What does efficiency primarily measure in thermodynamic systems?

a. Total energy input
b. Useful output relative to input
c. Total heat generated
d. Energy lost as heat

Answer 11

b. Useful output relative to input

Question 12

In a power plant, what does overall efficiency account for that simple thermal efficiency does not?

a. Only the turbine output
b. Only the generator losses
c. Auxiliary component losses and total system losses
d. Heat exchanger performance only

Answer 12

c. Auxiliary component losses and total system losses

Question 13

According to Çengel et al. (2015), energy conversion efficiency (η) is defined as:

a. Total energy output divided by total energy input
b. Useful energy output divided by total energy input
c. Total heat lost divided by total heat input
d. Net work divided by net heat input

Answer 13

b. Useful energy output divided by total energy input

Question 14

What property enables us to determine the useful work potential of a given energy amount at a specified state?

a. Enthalpy
b. Internal Energy
c. Exergy
d. Entropy

Answer 14

c. Exergy

Question 15

Gibbs Free Energy is particularly useful for systems at constant:

a. Temperature and volume
b. Pressure and volume
c. Pressure and temperature
d. Temperature and entropy

Answer 15

c. Pressure and temperature

Question 16

What does a negative change in Helmholtz Free Energy (A<0) indicate about a process at constant volume and temperature?

a. Non-spontaneous process
b. Spontaneous process
c. Process at equilibrium
d. Impossible process

Answer 16

b. Spontaneous process

Question 17

What key difference separates exergy from free energy like Gibbs Free Energy?

a. Exergy only applies to heat transfer systems
b. Exergy explicitly accounts for environmental reference states
c. Free energy accounts for irreversibilities
d. Exergy only applies to chemical reactions

Answer 17

b. Exergy explicitly accounts for environmental reference states

Question 18

In exergy analysis for power generation, what is primarily identified in each component like turbines and pumps?

a. Maximum pressure
b. Irreversibilities and energy quality losses
c. Maximum temperature
d. Total input energy

Answer 18

b. Irreversibilities and energy quality losses

Question 19

The Carnot efficiency formula for an ideal heat engine operating between two reservoirs is:

a. η = Qout / Qin
b. η = Wout / Win
c. η = 1 - TL/TH
d. η = TH/TL

Answer 19

c. η = 1 - TL/TH

Question 20

What performance term is used instead of “efficiency” for refrigerators and heat pumps?

a. Energy Ratio
b. Heat Utilization Factor
c. Coefficient of Performance (COP)
d. Thermal Work Output

Answer 20

c. Coefficient of Performance (COP)

Question 21

Which of the following best describes the First Law of Thermodynamics?

a. Energy can be created and destroyed, but it can also be transformed between forms.
b. Energy cannot be transformed from one form to another, it can only be created.
c. Energy cannot be created or destroyed, it can only be transformed from one form to another.
d. Energy is created during physical and chemical processes and cannot be destroyed.

Answer 21

c. Energy cannot be created or destroyed, it can only be transformed from one form to another.

Question 22

According to the Kelvin-Planck statement, which of the following is true?

a. A device can receive heat from a single reservoir and produce a net amount of work if it operates on a cycle.
b. It is impossible for any device to receive heat from a single reservoir and produce a net amount of work.
c. A heat engine can only produce work if it receives heat from multiple reservoirs.
d. A device can produce a net amount of work if it absorbs heat from one reservoir and releases it to another.

Answer 22

b. It is impossible for any device to receive heat from a single reservoir and produce a net amount of work.

Question 23

Which of the following best describes the Second Law of Thermodynamics?

a. Energy is conserved, but it can be created or destroyed depending on the process.
b. The Second Law states that energy can only be transferred, not transformed, between different forms.
c. Energy has no inherent quality, and all processes occur equally in both directions.
d. The Second Law sets limits on the efficiency of energy conversion systems and asserts that energy has both quality and quantity.

Answer 23

d. The Second Law sets limits on the efficiency of energy conversion systems and asserts that energy has both quality and quantity.

Question 24

Which of the following statements about entropy is true?

a. Entropy measures the amount of heat in a system, with higher entropy indicating more heat.
b. Entropy is a measure of the disorder or randomness of a system, with higher entropy indicating less useful energy for doing work.
c. Entropy decreases as the system becomes more disordered and less random.
d. Lower entropy corresponds to more possible microscopic arrangements of a system.

Answer 24

b. Entropy is a measure of the disorder or randomness of a system, with higher entropy indicating less useful energy for doing work.

Question 25

Which of the following statements best describes the irreversibility of the unrestrained expansion of a gas separated from a vacuum by a membrane? a. The unrestrained expansion of the gas can be reversed by simply compressing the gas and adding heat. b. Restoring the system requires compressing the gas and removing heat, but fully converting heat back into work would violate the second law of thermodynamics. c. The expansion of the gas does not violate the second law of thermodynamics because the process is reversible. d. The unrestrained expansion of a gas can occur without any change in heat or work.

Answer 25

b. Restoring the system requires compressing the gas and removing heat, but fully converting heat back into work would violate the second law of thermodynamics.

Question 26

Which of the following statements best describes a closed feedwater heater in steam power plants? a. A closed feedwater heater transfers heat from the extracted steam to the feedwater without mixing the two streams, allowing them to operate at different pressures. b. In a closed feedwater heater, the extracted steam and feedwater mix directly, allowing the system to operate at the same pressure. c. The feedwater in a closed feedwater heater is heated by burning fuel, not by extracted steam. d. A closed feedwater heater operates at lower pressures than open feedwater heaters due to the direct mixing of steam and feedwater.

Answer 26

a. A closed feedwater heater transfers heat from the extracted steam to the feedwater without mixing the two streams, allowing them to operate at different pressures.

Question 27

In gas-turbine power plants, the ratio of the compressor work to the turbine work is called the __? a. Back work ratio b. Compression ratio c. Specific heat ratio d. Front work ratio

Answer 27

a. Back work ratio

Question 28

The Otto Cycle is named after who? a. Beau de Otto b. Nikolaus A. Otto c. Rudolph Otto d. Jean Francois Otto

Answer 28

b. Nikolaus A. Otto

Question 29

Which of the following statements about diesel engines is TRUE? a. Diesel engines compress both air and fuel during the compression stroke, leading to autoignition. b. Diesel engines compress only air during the compression stroke, allowing them to operate at higher compression ratios. c. Diesel engines operate at lower compression ratios than gasoline engines to prevent autoignition. d. Diesel engines rely on spark plugs to ignite the fuel-air mixture at higher compression ratios.

Answer 29

b. Diesel engines compress only air during the compression stroke, allowing them to operate at higher compression ratios.

Question 30

What is the primary application of the Brayton cycle today? a. It is used in steam engines for power generation. b. It is used in gas turbines, where both compression and expansion occur in rotating machinery. c. It is used in internal combustion engines, where air is compressed and ignited by spark plugs. d. It is used in diesel engines for powering large vehicles.

Answer 30

b. It is used in gas turbines, where both compression and expansion occur in rotating machinery.

Question 31

Which of the following best describes the purpose of a refrigerator? a. To add heat to a system. b. To convert heat into work. c. To transfer heat from a low-temperature medium to a high-temperature medium. d. To maintain a constant temperature.

Answer 31

c. To transfer heat from a low-temperature medium to a high-temperature medium.

Question 32

What is the working fluid used in a refrigeration cycle called? a. Air b. Water c. Refrigerant d. Oil

Answer 32

c. Refrigerant

Question 33

In a vapor-compression refrigeration cycle, where does the refrigerant undergo a throttling process, causing a significant drop in pressure and temperature? a. Compressor b. Condenser c. Expansion valve (capillary tube) d. Evaporator

Answer 33

c. Expansion valve (capillary tube)

Question 34

34.During which process in the vapor-compression refrigeration cycle does the refrigerant absorb heat from the refrigerated space? a. Compression b. Condensation c. Expansion d. Evaporation

Answer 34

d. Evaporation

Question 35

What happens to the refrigerant as it flows through the condenser? a. It evaporates. b. It is compressed. c. It cools down and condenses by rejecting heat. d. Its pressure and temperature drop drastically.

Answer 35

c. It cools down and condenses by rejecting heat.

Question 36

What is a common heat source for most existing heat pumps during winter? a. The ground b. Water sources c. Cold outside air d. Geothermal energy

Answer 36

c. Cold outside air

Question 37

According to the text, why are air-source heat pumps not ideal for very cold climates? a. They become too efficient and overheat the space. b. Their efficiency drops considerably when temperatures are below freezing. c. They start to produce cold air instead of heat. d. They require a different type of refrigerant in cold temperatures.

Answer 37

b. Their efficiency drops considerably when temperatures are below freezing.

Question 38

How can a window air-conditioning unit be used as a heat pump in winter, according to the text? a. By increasing the fan speed. b. By adjusting the thermostat to a higher setting. c. By installing it backwards. d. By adding a separate heating element.

Answer 38

c. By installing it backwards.

Question 39

What does SEER (Seasonal Energy Efficiency Ratio) measure for air conditioners and heat pumps? a. The instantaneous energy efficiency. b. The rate of heat removal at a specific point in time. c. The ratio of the total heat removed during a normal cooling season to the total electricity consumed. d. The maximum cooling capacity of the unit.

Answer 39

c. The ratio of the total heat removed during a normal cooling season to the total electricity consumed.

Question 40

40. What does EER (Energy Efficiency Ratio) measure for cooling equipment? a. The total amount of heat removed over a season. b. The total electricity consumed over a season. c. The ratio of the rate of heat removal to the rate of electricity consumption in steady operation. d. The average energy efficiency over a period of time

Answer 40

c. The ratio of the rate of heat removal to the rate of electricity consumption in steady operation.