Energy Conversion: Power Cycles, Refrigeration, and Heat Pumps

Question 1

In a vapor-compression refrigeration cycle, which component is responsible for condensing the refrigerant vapor?

Accepted Answer

Condenser

Answer

Compressor

Answer

Evaporator

Answer

Expansion valve

Question 2

Which power cycle is commonly employed in coal-fired power plants?

Accepted Answer

Rankine cycle

Answer

Brayton cycle

Answer

Otto cycle

Answer

Diesel cycle

Question 3

In the SI system, what is the standard unit of energy?

Accepted Answer

Joule

Answer

Calorie

Answer

British thermal unit

Answer

Kilowatt-hour

Question 4

How is the efficiency of a heat engine defined?

Accepted Answer

Ratio of work output to heat input

Answer

Ratio of heat input to work output

Answer

Ratio of work input to heat output

Answer

Ratio of heat output to work input

Question 5

What is the commonly used refrigerant in household refrigerators?

Accepted Answer

R-134a

Answer

R-410a

Answer

R-22

Answer

R-32

Question 6

Which of the following describes the ideal Brayton cycle?

Accepted Answer

It comprises two adiabatic and two isentropic processes.

Answer

It operates at constant volume.

Answer

It surpasses the efficiency of the ideal Carnot cycle.

Answer

It is the main cycle used in nuclear power plants.

Question 7

Consider a Carnot heat engine operating between two reservoirs with temperatures T1 and T2. Its ideal efficiency is given by:

Accepted Answer

1 - T2/T1

Answer

T2/(T1 - T2)

Answer

T1/T2

Answer

1 + T2/T1

Question 8

In a heat pump operating in heating mode, which statement accurately describes the relationship between work input and heat transferred to the warm reservoir?

Accepted Answer

Work input is less than heat transferred.

Answer

Work input is equal to heat transferred.

Answer

Work input is greater than heat transferred.

Answer

Work input and heat transferred are unrelated.

Question 9

In a power plant, which type of heat exchanger is commonly used to transfer heat from hot gases produced by fuel combustion to water?

Accepted Answer

Shell-and-tube heat exchanger

Answer

Double-pipe heat exchanger

Answer

Plate-and-frame heat exchanger

Answer

Spiral heat exchanger

Question 10

What is the primary purpose of a condenser in a power plant?

Accepted Answer

To transfer heat from steam to the environment

Answer

To convert steam into water

Answer

To pump water from the condenser to the boiler

Answer

To generate electricity

Question 11

Which parameter is commonly used to assess the performance of a heat pump?

Accepted Answer

Coefficient of performance (COP)

Answer

Specific heat ratio

Answer

Adiabatic efficiency

Answer

Volumetric efficiency

Question 12

What is the primary function of a superheater in a power plant?

Accepted Answer

To increase the temperature of steam entering the turbine

Answer

To decrease the pressure of steam entering the turbine

Answer

To increase the mass flow rate of steam through the turbine

Answer

To improve the efficiency of the condenser

Question 13

What is the primary function of a condenser in a refrigeration cycle?

Accepted Answer

To release heat from the refrigerant to the environment

Answer

To provide cooling for the evaporator

Answer

To increase the pressure of the refrigerant

Answer

To filter out impurities from the refrigerant

Question 14

Which of the following refrigerants is commonly used in refrigeration cycles due to its low environmental impact?

Accepted Answer

Carbon dioxide (CO2)

Answer

Hydrochlorofluorocarbon (HCFC)

Answer

Hydrofluorocarbon (HFC)

Answer

Ammonia (NH3)

Question 15

What is the ideal gas law that describes the relationship between pressure, volume, and temperature of a gas?

Accepted Answer

PV = nRT

Answer

P/V = n/T

Answer

V/T = P/n

Answer

P = nRT/V

Question 16

What is the primary purpose of a diffuser in a gas turbine?

Accepted Answer

To convert kinetic energy into pressure energy

Answer

To increase the velocity of the gas

Answer

To reduce the temperature of the gas

Answer

To filter out particulate matter from the gas

Question 17

Which of the following is a measure of the resistance of a fluid to flow?

Accepted Answer

Viscosity

Answer

Density

Answer

Specific heat

Answer

Thermal conductivity

Question 18

Which of the following thermodynamic processes is NOT part of the Brayton cycle?

Accepted Answer

Isothermal compression

Answer

Adiabatic expansion

Answer

Constant pressure heat addition

Question 19

In a refrigeration cycle, the purpose of the expansion valve is to:

Accepted Answer

Reduce the pressure and temperature of the refrigerant

Answer

Increase the pressure and temperature of the refrigerant

Answer

Convert the refrigerant from a liquid to a gas

Answer

Convert the refrigerant from a gas to a liquid

Question 20

Which of the following is not a type of heat pump?

Accepted Answer

Gas-powered heat pump

Answer

Air-to-air heat pump

Answer

Water-to-water heat pump

Answer

Ground-source heat pump

Question 21

In an ideal Rankine cycle, the heat addition process takes place at:

Accepted Answer

Constant pressure

Answer

Constant volume

Answer

Constant temperature

Answer

Adiabatic

Question 22

The primary function of a regenerative heat exchanger in a gas turbine engine is to:

Accepted Answer

Enhance the thermal efficiency of the engine

Answer

Reduce the emissions of the engine

Answer

Improve the durability of the engine

Answer

Reduce the noise of the engine

Question 23

The efficiency of a heating-mode heat pump is defined as:

Accepted Answer

The ratio of heat delivered to the work input

Answer

The ratio of work input to heat delivered

Answer

The ratio of work output to heat input

Answer

The ratio of heat input to work output

Question 24

The primary function of a condenser in a refrigeration cycle is to:

Accepted Answer

Remove heat from the refrigerant

Answer

Add heat to the refrigerant

Answer

Compress the refrigerant

Answer

Expand the refrigerant

Question 25

The isentropic efficiency of a compressor is equal to:

Accepted Answer

The ratio of the work required for isentropic compression to the actual compressor work

Answer

The ratio of the actual compressor work to the work required for isentropic compression

Answer

The ratio of the isentropic compressor power to the actual compressor power

Answer

The ratio of the actual compressor power to the isentropic compressor power

Question 26

The purpose of a regenerator in a Brayton cycle is to:

Accepted Answer

Transfer heat from the exhaust gases to the inlet air

Answer

Transfer heat from the inlet air to the exhaust gases

Answer

Cool the air before entering the compressor

Answer

Heat the air before entering the turbine

Question 27

The COP of a refrigeration system in cooling mode is defined as:

Accepted Answer

The ratio of cooling effect to the work required

Answer

The ratio of work required to cooling effect

Answer

The ratio of heat rejected to the work required

Answer

The ratio of work required to heat rejected

Question 28

Which of the following is a significant environmental impact of combustion-based power generation systems?

Accepted Answer

Increased greenhouse gas emissions

Answer

Reduced greenhouse gas emissions

Answer

Enhanced air quality

Answer

Elimination of waste generation

Question 29

Which of the following processes is NOT a form of energy conversion?

Accepted Answer

Energy creation

Answer

Chemical to potential

Answer

Mechanical to electrical

Answer

Electrical to thermal

Question 30

In a power cycle, the thermal energy supplied to the working fluid is converted into:

Accepted Answer

Mechanical work

Answer

Electrical potential

Answer

Chemical energy

Answer

Thermal energy

Question 31

Which of the following determines the maximum theoretical efficiency of a heat engine?

Accepted Answer

Temperatures of the heat source and sink

Answer

Efficiency of the turbine

Answer

Type of working fluid

Answer

Rate of heat transfer

Question 32

In a heat pump, the refrigerant absorbs thermal energy from the:

Accepted Answer

Cold reservoir

Answer

Condenser

Answer

Expansion valve

Answer

Hot reservoir

Question 33

Compared to the Carnot cycle, the efficiency of an Otto cycle is:

Accepted Answer

Lower

Answer

Dependent on the fuel used

Answer

Equal

Answer

Higher

Question 34

The main function of a turbine in an energy conversion system is to:

Accepted Answer

Convert thermal energy to mechanical energy

Answer

Generate electricity

Answer

Transfer heat

Answer

Provide cooling

Question 35

What is the primary working fluid used in most Rankine cycles?

Accepted Answer

Water

Answer

Air

Answer

Ammonia

Answer

R-134a

Question 36

Which of the following components increases the pressure of the working fluid in a Brayton cycle?

Accepted Answer

Compressor

Answer

Evaporator

Answer

Condenser

Answer

Turbine

Question 37

Which of the following is an irreversible process?

Accepted Answer

Friction

Answer

Heat transfer

Answer

Work done

Question 38

What is the primary purpose of a heat exchanger?

Accepted Answer

To transfer heat between fluids

Answer

To evaporate a fluid

Answer

To increase the pressure of a fluid

Answer

To condense a fluid

Question 39

What is the purpose of a condenser in a refrigeration cycle?

Accepted Answer

To reject heat to the surroundings

Answer

To increase the pressure of the refrigerant

Answer

To decrease the temperature of the refrigerant

Answer

To absorb heat from the surroundings

Question 40

What is the primary purpose of a regenerator in a gas turbine engine?

Accepted Answer

To transfer heat from the exhaust gases to the compressed air

Answer

To increase the pressure of the compressed air

Answer

To cool the compressed air

Question 41

How are closed and open systems differentiated in thermodynamics?

Accepted Answer

In a closed system, there is no mass exchange with the surroundings, unlike an open system.

Answer

Closed systems are always reversible, while open systems are not.

Answer

Closed systems do not exchange heat with the surroundings, while open systems do.

Question 42

Identify the energy conversion device that transforms mechanical energy into electrical energy.

Accepted Answer

Generator

Answer

Motor

Answer

Transformer

Question 43

A power plant operates with a thermal efficiency of 35%. If the heat input to the plant is 1000 MW, what is the power output?

Accepted Answer

350 MW

Answer

1428 MW

Answer

700 MW

Answer

1000 MW

Question 44

A refrigerator operates with a coefficient of performance (COP) of 3. If the refrigerator removes 500 J of heat from the cold reservoir, how much work is required?

Accepted Answer

166.67 J

Answer

500 J

Answer

250 J

Answer

1500 J

Question 45

In a Carnot cycle, which process is responsible for transferring heat from the high-temperature reservoir to the working fluid?

Accepted Answer

Isothermal heat addition

Answer

Adiabatic compression

Answer

Isothermal heat rejection

Answer

Adiabatic expansion

Question 46

What is the primary function of a condenser in a refrigeration cycle?

Accepted Answer

To reject heat from the refrigerant to the surroundings.

Answer

To evaporate the refrigerant liquid.

Answer

To compress the refrigerant vapor.

Question 47

A heat pump is used to heat a house in winter. If the heat pump has a COP of 4, and it consumes 5 kW of electrical power, what is the heating capacity of the heat pump?

Accepted Answer

20 kW

Answer

5 kW

Answer

1 kW

Answer

15 kW

Question 48

Which of the following statements is TRUE regarding the efficiency of a reversible heat engine?

Accepted Answer

It is the maximum possible efficiency for any heat engine operating between the same temperature limits.

Answer

It is always less than 100%.

Question 49

A Brayton cycle is primarily used in which type of power generation system?

Accepted Answer

Gas turbine power plants

Answer

Hydroelectric power plants

Answer

Solar thermal power plants

Answer

Nuclear power plants

Question 50

A heat pump is essentially a reversed ________.

Accepted Answer

Refrigeration cycle

Answer

Carnot cycle

Answer

Brayton cycle

Answer

Rankine cycle