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& Heat Transfer Mechanisms
Veritasium: Misconceptions About Heat
Veritasium: Misconceptions About Heat
When we touch something that is hot or cold, what are we actually sensing? Is it the temperature of the object, or the rate at which heat flows between the object and our hand?
When we touch something that is hot or cold, what are we actually sensing? Is it the temperature of the object, or the rate at which heat flows between the object and our hand?
Heat, Q
Heat, Q
Heat is simply the net transfer of energy between objects that have different temperatures. The direction of heat flow depends on temperature. Heat energy (or just heat) always flows from hot objects (higher average KE) to cold objects (lower average KE).
Heat is simply the net transfer of energy between objects that have different temperatures. The direction of heat flow depends on temperature. Heat energy (or just heat) always flows from hot objects (higher average KE) to cold objects (lower average KE).
Thermodynamic System
Thermodynamic System
A thermodynamic system is a quantity of matter of fixed identity, around which we can draw a boundary. The boundaries may be fixed or movable. Energy can be transferred across the system boundary. Everything outside the boundary is the surroundings.
A thermodynamic system is a quantity of matter of fixed identity, around which we can draw a boundary. The boundaries may be fixed or movable. Energy can be transferred across the system boundary. Everything outside the boundary is the surroundings.
Energy into and out of the system is typically by heat energy transfer.
Energy into and out of the system is typically by heat energy transfer.
Heat transfer mechanisms
Heat transfer mechanisms
Heat transfer is an exchange of thermal energy (heat) between systems. Heat transfer is classified into various mechanisms, such as thermal conduction, thermal convection, thermal radiation, and transfer of energy by phase changes.
Heat transfer is an exchange of thermal energy (heat) between systems. Heat transfer is classified into various mechanisms, such as thermal conduction, thermal convection, thermal radiation, and transfer of energy by phase changes.
Heat Transfer by Conduction
Heat Transfer by Conduction
Conduction is heat transfer by means of molecular agitation within a material without any motion of the material as a whole.
Conduction is heat transfer by means of molecular agitation within a material without any motion of the material as a whole.
If two systems are each in thermal equilibrium with a third system, they are in thermal equilibrium with each other. This law helps define the concept of temperature.
If two systems are each in thermal equilibrium with a third system, they are in thermal equilibrium with each other. This law helps define the concept of temperature.
Energy conduction rate
Energy conduction rate
A = area of contact (m^2)
A = area of contact (m^2)
L = thickness of material (m)
L = thickness of material (m)
Heat transfer
Heat transfer
Thermal conduction is the transfer of heat internal energy by microscopic collisions of particles and movement of electrons within a body.
Thermal conduction is the transfer of heat internal energy by microscopic collisions of particles and movement of electrons within a body.
Practice Problems for heat transfer by conduction
Practice Problems for heat transfer by conduction
Problem #1: CALCULATING HEAT TRANSFER THROUGH CONDUCTION: CONDUCTION RATE THROUGH AN ICE BOX
Problem #1: CALCULATING HEAT TRANSFER THROUGH CONDUCTION: CONDUCTION RATE THROUGH AN ICE BOX
A Styrofoam ice box has a total area of 0.950 m^2 and walls with an average thickness of 2.50 cm. The box contains ice, water, and canned beverages at 0ºC. The inside of the box is kept cold by melting ice. How much ice melts in one day if the ice box is kept in the trunk of a car at 35.0ºC ?
A Styrofoam ice box has a total area of 0.950 m^2 and walls with an average thickness of 2.50 cm. The box contains ice, water, and canned beverages at 0ºC. The inside of the box is kept cold by melting ice. How much ice melts in one day if the ice box is kept in the trunk of a car at 35.0ºC ?
k (styrofoam): 0.010 J/s⋅m⋅ºC
Problem #2: CALCULATING THE TEMPERATURE DIFFERENCE MAINTAINED BY A HEAT TRANSFER: CONDUCTION THROUGH AN ALUMINUM PAN
Problem #2: CALCULATING THE TEMPERATURE DIFFERENCE MAINTAINED BY A HEAT TRANSFER: CONDUCTION THROUGH AN ALUMINUM PAN
Water is boiling in an aluminum pan placed on an electrical element on a stove top. The sauce pan has a bottom that is 0.800 cm thick and 14.0 cm in diameter. The boiling water is evaporating at the rate of 1.00 g/s. What is the temperature difference across (through) the bottom of the pan?
Water is boiling in an aluminum pan placed on an electrical element on a stove top. The sauce pan has a bottom that is 0.800 cm thick and 14.0 cm in diameter. The boiling water is evaporating at the rate of 1.00 g/s. What is the temperature difference across (through) the bottom of the pan?
Newton's law of cooling
Newton's law of cooling
Newton's law of cooling states that the rate of heat loss of a body is directly proportional to the difference in the temperatures between the body and its surroundings.
Newton's law of cooling states that the rate of heat loss of a body is directly proportional to the difference in the temperatures between the body and its surroundings.
Coffee Cooling experiment
Coffee Cooling experiment
Suppose you get a cup of coffee at a coffee shop. You get a phone call and know that the call is going to take a few minutes. You have a decision to make, do you mix the cream into the coffee right away or do you wait several minutes and put the cream in after the call, right before you drink it? The goal, we assume, is to have the coffee as hot as possible. So, the main question is how the coffee is going to cool as you wait until after your call.
Heat Transfer by Convection
Heat Transfer by Convection
Convection is heat transfer by mass motion of a fluid such as air or water when the heated fluid is caused to move away from the source of heat, carrying energy with it.
Convection is heat transfer by mass motion of a fluid such as air or water when the heated fluid is caused to move away from the source of heat, carrying energy with it.
Applications
Applications
Air in a room / atmosphere
Air in a room / atmosphere
Applications
Applications
Fluids in a pot
Fluids in a pot
Magma in the Earth's Sun's mantle
Magma in the Earth's Sun's mantle
Ocean currents
Ocean currents
Heat Transfer by Radiation
Heat Transfer by Radiation
Thermal radiation is energy transfer by the emission of electromagnetic waves which carry energy away from the emitting object. For ordinary temperatures (less than red hot"), the radiation is in the infrared region of the electromagnetic spectrum.
Thermal radiation is energy transfer by the emission of electromagnetic waves which carry energy away from the emitting object. For ordinary temperatures (less than red hot"), the radiation is in the infrared region of the electromagnetic spectrum.
The Electromagnetic Spectrum
The Electromagnetic Spectrum
Video (Veritasium): Why Are 96,000,000 Black Balls on This Reservoir?
Video (Veritasium): Why Are 96,000,000 Black Balls on This Reservoir?
I took a boat through 96 million black plastic balls on the Los Angeles reservoir to find out why they're there. The first time I heard about shade balls the claim was they reduce evaporation. But it turns out this isn't the reason they were introduced.
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