Peltier coolers/heaters(From Chris Webster)
A typical peltier device consists of a number of series-connected N- and P-type semiconductors sandwiched between two ceramic plates, such that the flow of majority carriers (electrons or holes) in each semiconductor occurs in a single direction, as shown below:
(hot side) ============================== <-- ceramic /|\ __________ __________ | majority | | | | | | | | | carrier | N | | P | | N | | P | | flow (-) _____|___| |___|__|___| |___|_____ (+) =============================== <-- ceramic (cold side)
The device works by depleting the cold side of thermally-generated carriers and moving them to the hot side; in essence, the device is a heat pump. When a fixed potential is placed across the device's terminals, a fixed temperature difference will be maintained between the hot and cold sides. If the hot side has a sufficiently "beefy" heat sink, this temperature difference can be several tens of degrees C.
The process is reversible -- placing a temperature difference across the device will cause a voltage to develop across its terminals.