Heat transfer
As a rule, materials that conduct electricity well be good thermal conductors. Metals are good conductors. Silver and gold perfectly, but not very practical for use in heating and refrigeration equipment. Copper is almost as good as the conductor of silver and has the advantage of being much cheaper. Aluminum, among other common metals, is also an excellent conductor and is relatively inexpensive. This is one of reasons, the most heat-exchange coils made of copper tubes with aluminium fins. This arrangement speed transfer of heat from the air in the refrigerant inside the cooling coil, or of fluid within the heating heat exchanger in the air passing over it.
As copper and aluminum, as a rule, melt under the heat, steel or cast iron is often used for heat exchangers at the nut straight equipment, such as furnaces shown here. Good conductor speed transfer of heat from the flame of the air flowing through the external heat exchanger.
Air bubbles is one of the best insulators are available.
Examples include polystyrene foam Board, fiberglass and cellulose insulation, and dead air spaces such as those between the glass double glass. Cork and articles of wood, especially soft wood, also are good insulators.
As insulators slow heat transfer by conduction, they are used in buildings with both above and below ground, as shown by the arrows in the illustration. The Cabinet cooling coil often insulated to prevent housing becomes so cold that the water in the air condenses on the street, what "sweating." Housing furnaces often isolated to prevent outside becomes so hot that it is dangerous for people or buildings...
|
Refrigeration 
