Thermal Systems: Principles and Applications in HVAC

Question 1

The first law of thermodynamics states that:

Accepted Answer

Energy cannot be created or destroyed, only transferred or converted from one form to another.

Answer

Heat always flows from a cold object to a hot object.

Answer

The total disorder or randomness (entropy) of a closed system always increases over time.

Answer

The efficiency of a heat engine operating in a cycle can never exceed 100%.

Question 2

In an HVAC system, what is the primary function of a condenser?

Accepted Answer

To remove heat from the refrigerant

Answer

To absorb moisture from the air

Answer

To circulate refrigerant through the system

Answer

To filter the air

Question 3

What is the SI unit for thermal conductivity?

Accepted Answer

Watts per meter-kelvin

Answer

Joules per kilogram-degree Celsius

Answer

British thermal units per hour-foot-Fahrenheit

Answer

Calories per second-centimeter-degree Celsius

Question 4

Which of these is NOT a mode of heat transfer?

Accepted Answer

Condensation

Answer

Convection

Answer

Conduction

Answer

Radiation

Question 5

According to the First Law of Thermodynamics, energy is:

Accepted Answer

Neither created nor destroyed

Answer

Created, but not destroyed

Answer

Destroyed, but not created

Answer

Both created and destroyed

Question 6

What is the SI unit for thermal conductivity?

Accepted Answer

W/mK

Answer

W/m

Answer

J/mC

Answer

J/KgK

Question 7

Which type of heat exchanger is most effective for heat transfer between fluids with a large temperature difference?

Accepted Answer

Shell and tube heat exchanger

Answer

Plate heat exchanger

Answer

Double pipe heat exchanger

Answer

Condenser

Question 8

What is the main function of a thermostat in an HVAC system?

Accepted Answer

Control temperature

Answer

Regulate airflow

Answer

Adjust humidity

Answer

Detect faults

Question 9

Which of the following materials is the most thermally conductive?

Accepted Answer

Steel

Answer

Air

Answer

Water

Answer

Plastic

Question 10

Which of the following is NOT a mode of heat transfer **in engineering applications**?

Accepted Answer

Sublimation

Answer

Conduction

Answer

Convection

Answer

Radiation

Question 11

The first law of thermodynamics states that:

Accepted Answer

Energy cannot be created or destroyed, only transferred or transformed.

Answer

Entropy always increases in a closed system.

Answer

Heat flows spontaneously from a hot reservoir to a cold reservoir.

Answer

The efficiency of a heat engine can never exceed 100%.

Question 12

What is the main purpose of an evaporator in a refrigeration cycle?

Accepted Answer

To absorb heat from the surrounding environment

Answer

To release heat to the surrounding environment

Answer

To compress the refrigerant

Answer

To expand the refrigerant

Question 13

Which of the following factors does NOT affect the overall heat transfer rate of a heat exchanger?

Accepted Answer

Material thickness

Answer

Surface area

Answer

Temperature difference

Answer

Fluid velocity

Question 14

The SI unit of thermal conductivity is:

Accepted Answer

Watts per meter-kelvin

Answer

Joules per kilogram-kelvin

Answer

Calories per gram-degree Celsius

Answer

British thermal units per hour-square foot-degree Fahrenheit

Question 15

What is the primary function of a thermostat in an HVAC system?

Accepted Answer

To maintain a desired temperature setpoint

Answer

To control the flow of refrigerant

Answer

To regulate the fan speed

Answer

To prevent system overheating

Question 16

Which of the following is NOT a type of heat pump system?

Accepted Answer

Solar-powered heat pump

Answer

Air-source heat pump

Answer

Water-source heat pump

Answer

Ground-source heat pump

Question 17

Which law of thermodynamics asserts that the total entropy of an isolated system invariably increases?

Accepted Answer

Second Law

Answer

First Law

Answer

Third Law

Answer

Zeroth Law

Question 18

In a refrigeration system, what is the primary function of the condenser?

Accepted Answer

To dispel heat from the refrigerant

Answer

To compress the refrigerant

Answer

To expand the refrigerant

Answer

To impart heat to the refrigerant

Question 19

In the International System of Units (SI), what is the unit of thermal conductivity?

Accepted Answer

Watts per meter-Kelvin

Answer

Joules per kilogram-Kelvin

Answer

Calories per gram-Celsius

Answer

British thermal units per pound-Fahrenheit

Question 20

How are heat and temperature distinguished?

Accepted Answer

Heat is a type of energy, whereas temperature measures the intensity of heat.

Answer

Temperature is a type of energy, whereas heat measures the intensity of temperature.

Answer

Heat and temperature are synonymous.

Answer

None of the listed options.

Question 21

Identify the greenhouse gas from the list provided.

Accepted Answer

Carbon dioxide

Answer

Oxygen

Answer

Nitrogen

Answer

Hydrogen

Question 22

Which mode of heat transfer involves the movement of a fluid due to density differences?

Accepted Answer

Convection

Answer

Conduction

Answer

Radiation

Answer

Diffusion

Question 23

According to the first law of thermodynamics, the change in internal energy of a system is equal to:

Accepted Answer

Heat transferred to the system minus work done by the system

Answer

Work done on the system minus heat transferred from the system

Answer

Heat transferred into the system plus work done on the system

Answer

Work done by the system plus heat transferred from the system

Question 24

Which of the following is not a type of HVAC system?

Accepted Answer

Irrigation system

Answer

Refrigeration system

Answer

Ventilation system

Answer

Heating system

Question 25

What is the standard international unit (SI unit) of thermal conductivity?

Accepted Answer

W/mK

Answer

kJ/kgK

Answer

J/sK

Answer

kcal/hmK

Question 26

What is the primary purpose of a pressure relief valve in an HVAC system?

Accepted Answer

To prevent excessive pressure buildup

Answer

To release air from the system

Answer

To avoid freezing

Answer

To control the flow of refrigerant

Question 27

Which type of heat exchanger commonly appears in HVAC systems for exchanging heat between fluids?

Accepted Answer

Any of the above

Answer

Shell and tube heat exchanger

Answer

Plate heat exchanger

Answer

Double pipe heat exchanger

Question 28

Which of the following is not a mode of heat transfer?

Accepted Answer

Diffusion

Answer

Convection

Answer

Conduction

Answer

Radiation

Question 29

The first law of thermodynamics states that?

Accepted Answer

Energy cannot be created or destroyed.

Answer

Heat always flows from hot to cold.

Answer

Entropy always increases.

Answer

Work is always converted to heat.

Question 30

What is the primary purpose of a heat exchanger?

Accepted Answer

To transfer heat from one fluid to another.

Answer

To cool down a fluid.

Answer

To heat up a fluid.

Answer

To separate two fluids.

Question 31

What is the SI unit of thermal energy?

Accepted Answer

Joule

Answer

Calorie

Answer

British Thermal Unit

Answer

Watt

Question 32

What is the distinction between sensible and latent heat?

Accepted Answer

Sensible heat is associated with a change in temperature, while latent heat is associated with a change in phase.

Answer

Sensible heat is transferred by conduction, while latent heat is transferred by radiation.

Answer

Sensible heat is always greater than latent heat.

Answer

There is no difference between sensible and latent heat.

Question 33

What is the primary purpose of a pressure relief valve in an HVAC system?

Accepted Answer

To prevent excessive pressure build-up.

Answer

To regulate airflow.

Answer

To control temperature.

Answer

To filter out contaminants.

Question 34

Which of the following is NOT a mode of heat transfer?

Accepted Answer

Plastic deformation

Answer

Radiation

Answer

Conduction

Answer

Convection

Question 35

The first law of thermodynamics states that energy:

Accepted Answer

Cannot be created or destroyed, only transferred or transformed

Answer

Flows from hot to cold

Answer

Increases in an isolated system

Question 36

An adiabatic process occurs when:

Accepted Answer

There is no heat transfer to or from the system

Answer

Temperature remains constant

Answer

Volume remains constant

Answer

Pressure remains constant

Question 37

Which of the following is NOT a component of a typical HVAC system?

Accepted Answer

Transmission line

Answer

Ductwork

Answer

Air conditioner

Answer

Furnace

Question 38

The primary function of a condenser in an HVAC system is to:

Accepted Answer

Release heat from the refrigerant

Answer

Filter the air in the space

Answer

Increase the pressure of the refrigerant

Answer

Cool the air in the space

Question 39

A psychrometric chart is primarily used to determine:

Accepted Answer

The state of moist air

Answer

The efficiency of an HVAC system

Answer

The thermal comfort of occupants

Answer

The load on an HVAC system

Question 40

Which of the following is the INCORRECT mode of heat transfer?

Accepted Answer

Magnetic

Answer

Radiation

Answer

Convection

Answer

Conduction

Question 41

The first law of thermodynamics states that:

Accepted Answer

Energy cannot be created or destroyed, only transferred or transformed.

Answer

Entropy of an isolated system always increases.

Answer

Heat always flows from a cool object to a warm object.

Question 42

The main purpose of a condenser in an HVAC system is to:

Accepted Answer

Release heat from the refrigerant.

Answer

Vaporize the refrigerant.

Answer

Filter the refrigerant.

Answer

Compress the refrigerant.

Question 43

What is the primary function of a thermostatic expansion valve (TXV) in a refrigeration system?

Accepted Answer

Control the refrigerant flow into the evaporator.

Answer

Prevent excessive cooling of the evaporator.

Answer

Protect the compressor from overheating.

Question 44

Which property of air is the most crucial factor in determining its ability to transfer heat?

Accepted Answer

Thermal conductivity

Answer

Specific heat capacity

Answer

Viscosity

Answer

Density

Question 45

How are sensible and latent heat distinguished?

Accepted Answer

Sensible heat changes a substance's temperature, while latent heat changes its phase.

Answer

Sensible heat is measured in joules, while latent heat is measured in calories.

Answer

Sensible heat is transferred through conduction, while latent heat is transferred through evaporation.

Question 46

In mechanical engineering, a common application of thermodynamics is:

Accepted Answer

Engine design

Answer

Electrical system design

Answer

Construction engineering

Answer

Medical technology

Question 47

What is the role of an air filter in an HVAC system?

Accepted Answer

Remove particles from the air.

Answer

Add moisture to the air.

Answer

Increase the air temperature.

Answer

Circulate the air.

Question 48

How are temperature and heat capacity related?

Accepted Answer

Heat capacity represents the amount of heat needed to raise the temperature of a substance by one degree.

Answer

Heat capacity is only significant at extreme temperatures.

Answer

Heat capacity decreases as temperature increases.