The basic principle of TEC (II)

The cooling principle of TEC is shown in figure 1. P and N type semiconductors are sandwiched between metal plates, which can form a pathway. Under the action of external electric field, the hole of P type in the point(a) needs to absorb certain energy to improve its own potential energy and then goes into P type semiconductor, so the temperature of the junction can be decreased and the cold contact point is formed. But the hole in the point(b) needs to release the excess energy to enter thesheet metal, and then the junction temperature will rise to form a hot contact.

The free electrons flow in the N type semiconductor and its direction is contrary to the direction of holes. At the point of c, they absorb heat and then enter the N type semiconductor.At the point of d, they release heat and then enter the sheet metal. So at a and c, the external heat can be absorbed and at the b and d, the extra heat can be released, which is cooling principle of TEC. Obviously, by changing the current direction, the cooling and heating can be switched. 

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