Basic Principals Flashcards
What is the principle that air conditioning relies on?
Several laws of physics
This includes thermodynamics, properties of liquids and gases, behavior of refrigerants, and effects of heat and pressure.
Name the four key areas of physics that air conditioning relies on.
- Thermodynamics
- Properties of liquids and gases
- Behavior of refrigerants
- Effects of heat and pressure on liquids and gases
Each area contributes to the functioning of air conditioning systems.
What is conduction?
Transfer of heat by direct contact
This occurs when two objects at different temperatures touch each other.
What is convection?
Transfer of heat by circulation of a liquid or vapour
This process is commonly observed in fluids where warmer areas rise and cooler areas sink.
What is radiation in the context of heat transfer?
Transfer of heat in all directions, away from a hot object
This does not require a medium and can occur in a vacuum.
Fill in the blank: Heat can be moved from one body to another in one of three ways: conduction, convection, and _______.
radiation
This is a fundamental concept in thermodynamics.
What principles does the process of air conditioning rely on?
The principles of thermal dynamics.
How does thermal energy move?
Thermal energy moves from a region of higher concentration to a region of lower concentration.
What is commonly referred to as the heat content of each region?
Temperature.
What does temperature measure?
Temperature is a measure of the average heat or thermal energy of the particles in a substance.
Does temperature depend on the size or type of object?
No, temperature does not depend on the size or type of object.
What does temperature measure?
Temperature measures the intensity level of the heat, not the actual heat energy within an object.
What is the direction of heat transfer?
Heat energy ALWAYS travels from Hot to Cold.
What affects the speed of heat transfer?
The greater the difference in temperature, the faster heat moves.
When does heat flow stop?
Heat continues to flow until both temperatures are equal.
What is the result of heat reaching equilibrium?
This results in a uniform temperature throughout the mass once the energy is at equilibrium.
What are degrees Fahrenheit and degrees Celsius used for?
Degrees Fahrenheit or degrees Celsius is simply used to state the temperature of a substance or an object.
Example: Room temperature is approx 70° F or 21° C.
What is the term used to state the difference between two temperatures?
The term Fahrenheit or Celsius degrees is used to state the difference between two temperatures, either in the Fahrenheit scale or the Celsius scale.
Example: An AC system should produce a change in temperature of 23.5° F or 13.0° C.
How do tech manuals commonly show temperature changes?
Tech manuals will commonly show temperature changes as 23.5° F or 13.0° C.
What are the boiling and freezing points in Celsius?
Boiling point is 100° C and freezing point is 0° C.
What are the boiling and freezing points in Fahrenheit?
Boiling point is 212° F and freezing point is 32° F.
What is the difference between the boiling and freezing points in Celsius and Fahrenheit?
The difference is 100° C and 180° F.
What is the conversion formula from Celsius to Fahrenheit?
Degrees Celsius to Degrees Fahrenheit: (°C X 1.8) + 32
What is the conversion formula from Fahrenheit to Celsius?
Degrees Fahrenheit to Degrees Celsius: (°F - 32) ÷ 1.8
What is the formula to convert Celsius degrees to Fahrenheit degrees?
Celsius Degrees to Fahrenheit Degrees: °C X 1.8
What is the formula to convert Fahrenheit degrees to Celsius degrees?
Fahrenheit Degrees to Celsius Degrees: °F ÷ 1.8
What is the relationship between Celsius and Fahrenheit degrees?
1 Celsius Degree equals 1.8 Fahrenheit Degrees.
What are degrees Fahrenheit and degrees Celsius used for?
Degrees Fahrenheit or degrees Celsius is simply used to state the temperature of a substance or an object.
Example: Room temperature is approx 70° F or 21° C.
What is the term used to state the difference between two temperatures?
The term Fahrenheit or Celsius degrees is used to state the difference between two temperatures, either in the Fahrenheit scale or the Celsius scale.
Example: An AC system should produce a change in temperature of 23.5° F or 13.0° C.
How do tech manuals commonly show temperature changes?
Tech manuals will commonly show temperature changes as 23.5° F or 13.0° C.
What are the boiling and freezing points in Celsius?
Boiling point is 100° C and freezing point is 0° C.
What are the boiling and freezing points in Fahrenheit?
Boiling point is 212° F and freezing point is 32° F.
What is the difference between the boiling and freezing points in Celsius and Fahrenheit?
The difference is 100° C and 180° F.
What is the conversion formula from Celsius to Fahrenheit?
Degrees Celsius to Degrees Fahrenheit: (°C X 1.8) + 32
What is the conversion formula from Fahrenheit to Celsius?
Degrees Fahrenheit to Degrees Celsius: (°F - 32) ÷ 1.8
What is the formula to convert Celsius degrees to Fahrenheit degrees?
Celsius Degrees to Fahrenheit Degrees: °C X 1.8
What is the formula to convert Fahrenheit degrees to Celsius degrees?
Fahrenheit Degrees to Celsius Degrees: °F ÷ 1.8
What is the relationship between Celsius and Fahrenheit degrees?
1 Celsius Degree equals 1.8 Fahrenheit Degrees.
What are the two units of measure for heat energy?
The BTU (British Thermal Unit) and the Calorie.
What is a BTU?
The BTU is defined as the amount of energy required to raise or lower the temperature of 1 pound of pure water by 1 Fahrenheit degree at sea level.
What is the approximate heat energy released by burning a single wooden match?
It is approximately the amount of heat energy that is released by completely burning a single wooden match.
What is a Calorie?
The Calorie is the amount of energy required to raise the temperature of 1 gram of pure water by 1 Celsius degree (or 1 Kelvin degree).
How many calories are in one BTU?
One BTU equals 252 calories.
What does 1 BTU do to the temperature of water?
1 BTU equals the heat necessary to raise the temperature of 1 lb. of water by 1ºF at sea level.
How many grams are in 1 pound?
1 Pound = 453.5 grams.
What is the relationship between Celsius and Fahrenheit degree changes?
1 Celsius degree change equals 1.8 Fahrenheit degree change.
What is the unit of heat measurement?
Calories
How much heat is required to raise the temperature of 1 gram of water by 1°C at sea level?
1 Calorie
What is the weight of 1 pound in grams?
453.5 grams
How many calories are in 1 BTU?
252 Calories
What is the relationship between Celsius and Fahrenheit degree changes?
1 Celsius degree change equals 1.8 Fahrenheit degree change.
Which contains more heat: 100 BTU’s or 1000 BTU’s?
1000 BTU’s
What is the temperature of a cup of coffee in Celsius and Fahrenheit?
71° C and 160° F
What is the temperature of a pot of coffee in Celsius and Fahrenheit?
71° C and 160° F
What is often stated about an AC system?
An AC system produces cold air, but there is no such thing as ‘cold’.
Cold is described as a lack of heat or the removal of heat.
What is heat?
Heat is the energy in a substance.
How do AC systems operate?
AC systems operate by removing heat from the air entering the cab, resulting in a lower temperature.
Are temperature and heat interchangeable terms?
No, temperature and heat are not interchangeable terms.
Can a substance contain heat at low temperatures?
Yes, a substance can contain heat even at very low temperatures.
Can a substance have a low amount of heat at high temperatures?
Yes, a substance can have a low amount of heat while at a high temperature.
What is an example of heat content at the same temperature?
A cup of coffee at 160°F and a pot of coffee at 160°F are both the same temperature, but the pot contains more heat.
If poured onto separate 1 cu ft blocks of ice, the block that the pot was poured onto will melt the most.
What are the three states of matter?
All matter is in one of three states: Vapour, Liquid, or Solid.
What determines the state of matter?
The amount of heat energy that the matter contains determines the state it is in.
What characterizes a solid state?
Something in a solid state does not contain enough heat energy to make the molecules move in relation to each other.
What characterizes a liquid state?
In a liquid state, the molecules have enough energy to move in relation to each other, and the material will have no shape of its own but will not be compressible.
What characterizes a vapour state?
In a vapour state, the molecules have even more heat energy and can break free from one another, leaving space between them, making them compressible.
What is the relationship between heat and the state of matter during evaporation?
During evaporation, a liquid absorbs heat and changes into a gas.
What happens to heat during condensation?
During condensation, a gas radiates heat and changes into a liquid.
What is sensible heat?
Sensible heat is the heat that changes the temperature of a material.
How can sensible heat be measured?
Sensible heat can be measured with a temperature probe or thermometer.
Why is it called sensible heat?
It is called sensible heat because it can be ‘sensed’ or felt.
What is latent heat?
Latent heat is the heat added to a material to cause a change of state.
Can latent heat be sensed?
Latent heat cannot be ‘sensed’ or felt.
How is latent heat measured?
Latent heat is measured in BTUs or Calories.
What is another term for latent heat?
Latent heat can be referred to as ‘hidden heat’.
What happens to temperature with the addition or removal of latent heat?
With the addition or removal of latent heat, there is no change in temperature.
What is latent heat?
Latent heat is the heat absorbed or released during a change of state without a change in temperature.
What happens when ice reaches 32°F (0°C)?
When ice reaches 32°F (0°C), it begins to melt.
How much heat is required to change one pound of ice to liquid?
Each pound of ice requires 143 BTU to change it to a liquid.
What happens when water reaches 212°F (100°C)?
When water reaches 212°F (100°C), it begins to boil.
How much heat is required to change one pound of water to steam?
Each pound of water requires 970 BTU to change it to steam.
What is the heat added to ice to cause a change of state called?
The heat added to ice to cause a change of state is called latent heat of liquidization.
What is the heat added to water to cause a change of state?
The heat that must be added to water to cause a change of state is called latent heat of vaporization.
What happens when steam at 212°F (100°C) condenses back to a liquid?
Steam will give off 970 BTU per pound as it condenses back to a liquid.
This heat release is called latent heat of condensation.
What occurs when water is cooled down further?
A change of state occurs again and the liquid changes to a solid (ice).
What is the heat given off when water freezes?
The heat given off is 143 BTU per pound, called latent heat of freezing.
What principle is the basis for the operation of an air conditioning system?
The principle of latent heat changes during state transitions.
Why are refrigerants selected?
Refrigerants are selected for their ability to readily change state in order to absorb or give off heat.
What is the latent heat of vaporization for water?
970 BTU per pound at 212°F.
What is the latent heat of vaporization for ammonia?
565 BTU per pound at 5°F.
What is the latent heat of vaporization for propane?
185 BTU per pound at -44°F.
What is the latent heat of vaporization for R-134a?
106 BTU per pound at -15°F.
What is the latent heat of vaporization for R-12?
69 BTU per pound at -22°F.
What is latent heat?
Latent heat is the heat energy that must be added or given up in order for there to be a change of state.
Do different compounds have different latent heat ratings?
Yes, each compound has a different latent heat rating.
How does the amount of heat required for a state change compare to sensible heat?
The amount of heat required to change state is much larger than the sensible heat required to change the temperature on either side of the state change.
What happens to refrigerant in A/C systems at the evaporator?
Refrigerant changes state from a liquid to a vapor inside the A/C systems at the evaporator, absorbing large quantities of heat.
What is the latent heat of liquidization?
The heat that must be added to ice to cause a change of state is called latent heat of liquidization.
What is the latent heat of vaporization?
The heat that must be added to water to cause a change of state is called latent heat of vaporization.
What is the heat release called when steam condenses back to a liquid?
The heat release is called latent heat of condensation.
Steam at 212°F (100°C) gives off 970 BTU per pound as it condenses.
What occurs when water is cooled down further after condensation?
A change of state occurs and the liquid changes to a solid (ice).
The heat given off during this process is 143 BTU per pound.
What is the heat release called when liquid water freezes?
The heat release is called latent heat of freezing.
What principle is the basis for the operation of an air conditioning system?
The principle is based on the ability of refrigerants to readily change state to absorb or give off heat.
What happens to the boiling point of a liquid when pressure is increased?
The boiling point of that liquid will increase.
What happens to the boiling point of a liquid when pressure is decreased?
The boiling point of that liquid will decrease.
Why does coolant in an engine not boil at temperatures above 212°F (100°C)?
Because the cooling system is pressurized, which raises the boiling point.
What occurs if the radiator cap is removed from a hot cooling system?
The liquid may rapidly boil because the pressure on the hot liquid is removed, lowering the boiling point.
What is vapour pressure?
The vapour pressure is the pressure in a closed system that contains a liquid at a specific temperature.
What occurs when a substance reaches its vapour pressure?
There are both vapours and liquids within the same closed system.
What happens if you increase the pressure while keeping the temperature constant?
Some of the vapour will condense back to liquid.
What describes a system where pressure and temperature have stabilized?
The system is described as being at ‘equilibrium’.
Can you provide an example of vapour pressure?
An example is the ‘static pressure’ inside a container of refrigerant, or an air conditioning system that has been sitting.
What are the three methods of heat transfer?
Conduction, Convection, Radiation
What is conduction?
The flow of heat through a solid.
How is conduction illustrated in an engine cooling system?
The heat created by combustion is transferred through the ‘cooler’ cylinder liners to the lower temperature coolant.
What is convection?
The movement of hot engine coolant from one place to another.
How does convection occur in an engine cooling system?
Hot coolant rises and moves to the top of the radiator, transferring heat from combustion with it, assisted by the water pump.
What role does the water pump play in convection?
It assists in the movement of hot coolant to the top of the radiator.
How is heat transferred from the coolant to the radiator?
Heat is transferred to the cooler radiator tubes and fins by conduction.
How is heat transferred from the radiator to the atmospheric air?
The heat from the radiator is transferred to the cooler atmospheric air by the process of radiation.
What role does the engine fan play in heat transfer?
The engine fan speeds up the transfer of heat by moving cooler air across the radiator tubes and fins.
How does an AC system function similarly to a cooling system?
An AC system removes heat from the cab and moves it to the atmosphere.
Is it possible to pump cold into an area?
It is not possible to pump cold into an area.
What must be done to reduce temperature?
To reduce the temperature, we must remove heat energy.
What is the purpose of the air-conditioning system?
The purpose of the air-conditioning system is to move heat energy from one area to another.
What needs to happen at the evaporator in the cab?
The equipment needs to remove the heat energy at the evaporator in the cab and move it to the condenser in the cooling fan air stream.
What is necessary to understand the heat transfer process in AC systems?
We need to know what the refrigerant cycle is.
What is the first component of the refrigerant cycle?
Compressor - refrigerant enters as a low pressure vapour.
What happens to the refrigerant in the compressor?
The vapour is compressed and exits the compressor as a high pressure vapour.
What is the second component of the refrigerant cycle?
Condenser - refrigerant enters as a high pressure vapour.
What occurs in the condenser?
Heat contained in the refrigerant is transferred to the cooler air of the atmosphere.
What is the result of the heat transfer in the condenser?
Refrigerant changes state to a high pressure liquid and exits the condenser.
What is the state of refrigerant when it enters the expansion valve?
Refrigerant enters as a high pressure liquid.
What happens to the pressure of the refrigerant as it moves through the orifice?
The pressure drops.
What occurs to the boiling point of the refrigerant in the expansion valve?
The boiling point is reduced.
What is the state of refrigerant when it exits the expansion valve?
Refrigerant exits as a low pressure liquid.
What is the state of refrigerant when it enters the evaporator?
Refrigerant enters as a low pressure liquid.
What happens to the refrigerant in the evaporator?
Heat is absorbed from the air in the cab.
What change occurs to the refrigerant in the evaporator?
Liquid refrigerant is changed to a vapour.
What is the state of refrigerant when it exits the evaporator?
Refrigerant exits as a low pressure vapour.
What happens to the refrigerant after it exits the evaporator?
Refrigerant returns to the compressor and the cycle repeats.
What are various sources of heat?
Field or road heat, engine/transmission/hydraulic heat sources, solar heat, atmospheric heat.
What is necessary for an air conditioning system to operate successfully?
It must be capable of removing heat from the cab at a faster rate than it can enter.
What does an air conditioning system do?
It removes heat, moisture, dust, and pollen from the air entering the operator’s cab.
What happens to liquids when they change from a liquid to vapor?
Liquids absorb heat.
What happens to gases when they change from vapor to liquid?
Gases give off heat.
How does heat move?
Heat always moves from the hotter to the colder.
What affects the temperature at which a liquid changes to vapor?
It varies with the pressure on it.
What characteristics must refrigerant liquids have for best heat exchanges?
They must have a low boiling point and heat and cool readily.
What are the four processes involved in refrigeration?
- Compression - heats up the vapor
- Condensation - changes vapor to liquid and releases heat
- Expansion - reduces pressure
- Evaporation - changes liquid to vapor and absorbs heat.
