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8.2 Thermal Energy Transfer - Coggle Diagram
8.2 Thermal Energy Transfer
Black body radiation
Stefan-Boltzmann law
P e = σ AT 4
P: radiation power emitted
A: surface area
T: temperature
σ: 5.67×10−8W⋅m−2⋅K−4
Emissivity is the ratio of the power per unit area radiated by the object to that of a black body at the same temperature.
e: emissivity
By definition, an object with emissivity e=1 means that it: is a black body, is in equilibrium with its surroundings (emits and absorbs radiant energy at same rate), radiates energy that is characteristic with its temperature
Can be used to evaluate the surface temperature of stars by knowing the luminosity and dimensions of the star
Wien's Law
https://www.youtube.com/watch?v=yCNcbkLFTFs
b = 2.9*10^-3 (given in formula booklet)
Wein's Law, also known as Wien's Displacement Law.
Describes the relationship between the
temperature
of an ideal
blackbody
and the
wavelength
at which the
blackbody emits the most radiation
.
https://www.youtube.com/watch?v=vnFvvkAANhk&list=PL6LH0ngwf3HvwYN633x8UKd1ic35D-aGi&index=4
A blackbody is a hypothetical perfect absorber and radiator of energy, with no reflecing power
The amount of energy emitted by a body is directly proportional to the fourth power of the absolute temperature of that body
confirmed up to temperatures of 1535 K by 1897
Greenhouse effect TLH
IR absorption by greenhouse gases
Carbon dioxide (CO2), water vapor (H2O), methane (CH4), ozone (O3)
Greenhouse gases absorbs infrared radiation, and re-radiates it in all directions
https://www.youtube.com/watch?v=iqXh1EJD1e8
Albedo
Power equation
P=eAT^4
P = radiated power
A = radiating area
σ = Stefan Boltzmann constant = 5.6703x10-8 W/m2 K4
e = emissivity
T = temperature of radiator
The formula for the albedo effect is the power scattered / power incident
albedo = p scattered / p incident
the albedo map for earth
earths mean albedo stands at 30% or 0.3
the Albedo measures the reflectivity of a surface with a lightly coloured surfaces having a high albedo and dark surfaces having a low albedo
Heat transfers FDT
Conduction
Defintition: Is the main method of thermal transfer in solids. Conduction occurs when two solids of different temperatures come in contact with each other. Thermal energy is transferred from the hotter objects to the colder object
Metals are best conduction - non-metals are usually poor conductors - Liquids and gases are even poorer conductors
Conduction can occur through two mechanisms
Atomic vibrations
Free electron condition
Process of Conduction
When a substance is heated, the atoms, or ions, start to move around (vibrate) more. The atoms at the hotter end of the solid will vibrate more than the atoms at the cooler end. These collisions transfer internal energy until thermal equilibrium is achieved throughout the substance. As they do so they bump into each other, transferring energy from atom to atom. This occurs in all solids, metals and non-metals alike
As they do so they bump into each other, transferring energy from atom to atom
These collisions transfer internal energy until thermal equilibrium is achieved throughout the substance
This occurs in all solids, metals and non-metals alike
Convection
imagine a container with a fluid and a bunsen burner at the bottom. as the fluid at the bottom gains energy, the partciles gain kinetic energy and move further appart, causing the same mass of particles to occupy a bigger volume, causing the density to decrease. This less dense warmer fluid will now rise to the top and replace the colder fluid, which will begin warming up at the bottom, then rising to the top as the fluid on the top cools down. this repeats over and over and creates a convection current
for examples winds are huge convection currents which have energy sources at the top and bottom (sun and earth). Blankets keep us warm because they slow down the convection current created in our rooms by us being energy sources
Radiation
Only thermal radiation can transfer heat without any physical medium such as a solid, liquid or gas.
thermal radiation is photons carrying infrared energy
All physical substances in solid, liquid, or gaseous states can emit energy via a process of electromagnetic radiation because of vibrational and rotational movement of their molecules and atoms.
When thermal radiation as electromagnetic waves strike a surface, their energy is converted into heat energy.
Infrared radiation visualized in colors
