Quote:
|
Originally Posted by CBFryman
all heat felt by us is infared radiation.
|
No, there are several ways to transfer heat.
There are:
1. Heat transport through kinetic energy in the molecules. This is heat is transfered in for example a piece of copper. The copper can also transfer the kinetic energy better than for example iron. Typically measured in W/(m*K), for example copper 380 and iron 71 W(m*K). If you put your hand on a hot piece of metal I can guarantee you that you will feel that it's hot!
2. Convection is the heat transfer between a fluid and a solid wall. If the wall is warmer than the fluid the wall will heat the fluid through transfer of kinectic energy like in 1, however when the fluid is heated it density drop and the particles will flow upwards. This is how the cylinderwalls in an piston engine transfer heat to the coolant. And once again I can guarantee you that if you toch the hot coolant you will feel how hot it is.
3. Heat transfer through radiation. Radiation through electromagnetic waves can occur even in vacuum, which isn't the case with the two above. All objects at a temperature above 0 K emitts heat radiation, how much it emitts depends on a coefficient for the material and surface, and when the radiation hits and object some of it is taken up, the other is reflected. Some materials are very good to reflect, gold is one of them, and that is why whe can find gold in the engine bay of McLaren F1 as well as on some satellites. On the other hand, if the object is "black" it will emitt all radiation that fells on it, but note that "black" isn't the colour black, snow is for example excellent in absorbing infrared radiation. The frequency of radiation depends on the temperature of the emitting object, the sun does for example emitt at such high temperature that the heat radiation is on the visible spectrum, this is why a black car exposed to sunlight gets hotter than a white one, black is here "black".
Just some thermodynamics 101...
Show Printable Version | 
Subscribe to this Thread
10-05-2004, 01:13 PM
