and i also need examples of each.
thanks ((:
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Answers (2)
Convection (The movement of heat in a liquid or gas through currents in the liquid or gas that fluctuate up and down) - The swirling of water in a pot over a flame is heat energy being transported in the water through convection.
Conduction (The movement of heat energy through a solid as the energy passes from particle to particle through vibrations created by the closely packed solid particles.) - Metals get hot when put into contact with a heat source, because heat is conducted through the metal to your skin.
Radiation (The transfer of heat energy in the form of rays, including light rays, coming from a heat source. This kind of transfer, unlike the other two, can happen through a vacuum.) - Heat is produced when a material is put into contact with sunlight, a form of radiation.
They aren't so much different types, the word modes is preferred. There are three modes of heat transfer.
Mode 1: conduction. Direct heat transfer through molecular/atomic collisions. The only mode of heat transfer which works through solids.
Mode 2: convection. Heat transfer by conduction in a fluid, enhanced by the flow of the fluid.
This flow can either be pre-existing and it is called forced convection, or it can be a buoyantly driven flow in a gravitational field and is called natural convection.
Mode 3: radiation. Heat transferred by electromagnetic waves, emitted by bodies based on their individual temperature and emissivity (how black the body is). Also absorbed and converted to heat by bodies if there is incident radiation on their surface (also dependent on the property emissivity).
A hot object has a net emission of radiation, a colder object has a net absorption of radiation.
Radiation heat transfer typically uses infrared rays to carry the energy, which is why you don't see it. Objects which are hot enough will emit visible light.
Emissivity can be thought of as a participation in radiation fraction. Black bodies fully participate, "white" bodies do not participate should they exist. Gray bodies partially participate, and the same fraction of participation at each "color".
Examples:
Mode 1: your frying pan conducts heat through its iron body from the source of heat to the food.
Mode 2 forced: a computer fan is used to remove heat dissipated by the computer chips.
Mode 2 natural: during the daytime, air above hotter land rises, and is displaced by cold air over the nearby lake. The hot air eventually cools and falls over the lake. You notice this because of the daytime wind direction, inland.
When night falls, the water is warmer than the land, and the opposite wind pattern occurs, out to the lake.
Mode 3: when you are on the beach on a hot day in the tropical regions, the air is comfortable, but the sand burns your feet. This is because the sand absorbs the sun's incident light and converts it to heat. The ambient air cools it off by convection, but it still stabilizes at a temperature uncomfortable to your feet.