The Peltier Effect.
The Peltier effect is that when the passage of electric current through the contact (junction) of two conductors made of different (heterogeneous) materials, in addition to the traditional Joule heat, is absorbed or secreted (depending on the direction of the current) for extra warmth.
Direct conversion of electrical energy into thermal energy (heating, cooling) and Vice versa – the thermoelectric effect was discovered in 1821 by Thomas Johann Seabeam in 1834 by Jean-Charles Peltier, in 1858, William Thomson (or Kelvin). Respectively, and are called thermoelectric effects (phenomena) by the name of its discoverers: the Seebeck effect, the Peltier effect, the Thomson effect.
The Peltier effect is that when the passage of electric current through the contact (junction) of two conductors made of different (heterogeneous) materials, in addition to traditional Joule heat, is absorbed or secreted (depending on the direction of the current) for extra warmth. Additional heat (released or absorbed) is called the Peltier heat.
The amount of emitted or absorbed additional heat is proportional to current density and also depends on the materials selected conductors.
Peltier heat is given by:
Q = PAV·I·t,
Q is the amount absorbed or the heat
I – current,
t – time of current flow,
P is the Peltier coefficient.
In turn, the Peltier coefficient is using the equation:
P = α·T,
α – Thomson coefficient,
T is the absolute temperature, expressed in K.
As can be seen from the formula, the Peltier coefficient is significant dependence on temperature. Some values of Peltier coefficient for various pairs of metals are presented in the table.
|The values of Peltier coefficient for various pairs of metals|
|T, TO||P, mV||T, TO||P, mV||T, TO||P, mV|
The Peltier effect is more noticeable in semiconductors than in metals. For metals, the Peltier coefficient is 10-2 to 10-3 for semiconductors – from 3·10-1 to 10-3 V.
The Peltier effect is essentially the opposite of a previously opened Seebeck effect (thermoelectric effect). The essence of the Seebeck effect is that in a closed circuit, consisting of connected dissimilar conductors, between which in the contact area, there is a temperature gradient, there is an electric current.
The Peltier effect has a rather low efficiency. Despite it was created device operating on the Peltier effect – thermoelectric elements, which have found wide application in measuring, computing, and household appliances (mobile refrigeration installation, small generators for generating electricity, cooling systems in household appliances, dehumidifiers, etc.).
Note: © Photo ,