Podcast
Questions and Answers
If the distance to a radiant heat source is doubled, how does the intensity of the radiant heat change?
If the distance to a radiant heat source is doubled, how does the intensity of the radiant heat change?
- The intensity decreases by a factor of four. (correct)
- The intensity increases by a factor of four.
- The intensity remains the same.
- The intensity decreases by a factor of two.
In thermodynamics, the movement of molecules ceases at what temperature?
In thermodynamics, the movement of molecules ceases at what temperature?
- $-273 \degree C$ (correct)
- $-40 \degree C$
- $0 \degree C$
- $0 \degree F$
Which of the following best describes the concept of sensible heat?
Which of the following best describes the concept of sensible heat?
- The heat required to change the state of a substance without changing its temperature.
- The heat required to change the temperature of a substance without changing its state. (correct)
- The heat that is invisible and cannot be measured by a thermometer.
- The total heat energy stored within a substance.
What is the relationship between the specific heat and the amount of energy needed to change the temperature of a substance?
What is the relationship between the specific heat and the amount of energy needed to change the temperature of a substance?
In the context of heat transfer, what characterizes natural convection?
In the context of heat transfer, what characterizes natural convection?
Why does the HVAC/R industry utilize Fahrenheit scale?
Why does the HVAC/R industry utilize Fahrenheit scale?
Which of the following scenarios exemplifies heat transfer primarily through conduction?
Which of the following scenarios exemplifies heat transfer primarily through conduction?
Considering two identical objects at different temperatures, what factor, when increased, will decrease the time it takes for heat transfer to take place?
Considering two identical objects at different temperatures, what factor, when increased, will decrease the time it takes for heat transfer to take place?
What distinguishes heat from temperature?
What distinguishes heat from temperature?
If 5 lbs of water decreases in temperature from 80°F to 60°F, how much heat is released?
If 5 lbs of water decreases in temperature from 80°F to 60°F, how much heat is released?
When water condenses, changing from vapor to liquid, what type of heat transfer occurs?
When water condenses, changing from vapor to liquid, what type of heat transfer occurs?
What is the significance of turbulence in the context of heat transfer involving fluids?
What is the significance of turbulence in the context of heat transfer involving fluids?
How many BTU's are required to change 5 lbs of water at 60°F to steam at 212°F?
How many BTU's are required to change 5 lbs of water at 60°F to steam at 212°F?
Identify the INCORRECT statement about latent heat.
Identify the INCORRECT statement about latent heat.
How does the specific heat factor of ice/steam compare to liquid water?
How does the specific heat factor of ice/steam compare to liquid water?
Flashcards
What is temperature?
What is temperature?
How fast molecules are moving.
What is heat?
What is heat?
A quantity of energy.
What is a BTU?
What is a BTU?
Heat energy to raise 1 lb. of water 1 F.
How does heat transfer?
How does heat transfer?
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What is Sensible Heat?
What is Sensible Heat?
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What is Specific Heat?
What is Specific Heat?
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What is 1 btu/lb?
What is 1 btu/lb?
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What is 0.5 btu/lb?
What is 0.5 btu/lb?
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What is Latent Heat?
What is Latent Heat?
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What is Latent heat of vaporization?
What is Latent heat of vaporization?
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What is Latent heat of condensation?
What is Latent heat of condensation?
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What is Latent heat of fusion?
What is Latent heat of fusion?
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What is 970 btu/lb?
What is 970 btu/lb?
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What is 144 btu/lb?
What is 144 btu/lb?
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How is heat transferred?
How is heat transferred?
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Study Notes
Temperature
- Temperature measures how fast molecules are moving.
- The faster the molecules move, the higher the temperature.
- Molecular movement stops at absolute zero which is -273°C or -460°F.
- Temperature is expressed in Fahrenheit or Celsius.
- The HVAC/R industry uses Fahrenheit.
Heat
- Heat refers to the quantity of energy, not the temperature of an object.
- The HVAC/R industry denotes heat quantity in British Thermal Units (BTU).
- One BTU raises the temperature of 1 lb of water by 1°F.
- Heat moves from higher to a lower temperature to achieve equilibrium.
Specific Heat
- Sensible heat changes the temperature of a substance.
- Specific heat is the amount of heat needed to raise 1 lb. of a substance by 1°F.
- Water: 1 btu/lb
- Ice/Steam: 0.5 btu/lb
Latent Heat
- Latent heat changes the state of a substance, otherwise known as ‘invisible heat’.
- Water boils at 212°F, and adding more heat increases the rate of boiling, not the temperature.
- Vaporization: liquid transforms into a vapor.
- Condensation: vapor transforms into a liquid.
- Fusion: solid transforms into a liquid, or vice versa.
- Condensation/Vaporization factor of water: 970 btu/lb.
- Fusion factor: 144 btu/lb.
Heat Transfer
- Heat transfers from a higher temperature to a lower temperature.
- Time, temperature, and turbulence drive heat transfer.
- The longer heat transfers, the more heat is transferred.
- The greater the temperature difference, the faster the transfer.
- Greater turbulance creates faster mixing of fluids for transfer.
Types of Heat Transfer
- Conduction transfers heat through a material without moving the material itself
- Natural Convection transfers heat through a fluid by the fluid's natural movement.
- Forced Convection transfers heat through a fluid using the fluid's movement driven by mechanical means.
- Radiation transfers heat through electromagnetic waves, not needing a medium.
- Radiant heat intensity decreases by the square of the distance.
Heat Transfer Formulas
- Specific heat formula: Q(btu)= m x sh x ∆T
- Q = Quantity of heat
- M = Mass in lbs.
- SH = specific heat factor
- ∆T = temperature difference.
- Water's specific heat factor: 1btu per Ib
- Ice/Steam's specific heat factor: .5 btu per Ib
- Latent heat formula: Q= m x Lf
- Q= Quantity of heat in BTUs
- M= Mass in lbs.
- Lf = Latent heat factor
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