الكهرباء الحرارية - الطاقة الكهربائية .. الفيزياء

Thermoelectricity - Electrical Energy .. Physics

Thermoelectricity

When two different metals are connected to each other, a voltage appears on both ends of the connection, the value of which changes with the change in temperature and the nature of the two metals used. If we connect several wires of two different types of metals, so that we form two connections, and keep them at two different temperatures, a difference in potential appears between them, which generates an electric current flowing between them. This phenomenon is known as the Seebach phenomenon (named after Thomas Seebach), and it allows us to know the difference in the temperature of the two connections based on knowing the voltage between them. This structure is called a thermocouple, known for its extreme sensitivity to rapid fluctuations in temperature, which increases as the number of connections used in succession increases.

(To the left) A radiation meter to measure the difference between the sun's rays and the rays reflected by the ground. (To the right) A Peltier element that gives a difference in temperature.

(The heat resulting from the decay of a radioactive isotope provides the electrical power needed for an automatic weather station.)

As for the Peltier effect, which was discovered by Jean Peltier, it is the reverse phenomenon of the Seebach effect. If the current passes through a circuit containing several connections made of two different types of metals, it leads to an increase in the temperature of one of them and a decrease in the temperature of the other. If we reverse the direction of the current, the hot connection cools and the cold connection heats up. For this reason, the Peltier effect is characterized as a reversible phenomenon.

The Peltier effect, which appears on a connection between two different metals, is characterized by its very small value, and its use in practical aspects is very difficult. However, there are types of thermocouples made of semiconductors that are characterized by their high efficiency, which is approximately two hundred times more than the efficiency of metallic couples, and they can generate a temperature difference of up to 75 degrees Celsius. In addition, a diode made of a metal and a semiconductor of class M (positive) can generate a voltage opposite to that generated by another diode made of the same metal and a semiconductor of class C (negative). This construction is called a Peltier element, and when current passes through the diode, it is able to absorb heat on one side and release it on the other. If the current is reversed, the direction of heat flow is also reversed. If the goal is to maintain a certain temperature in the body, it is possible in this case to use a diode that acts as a thermal switch, raising or lowering the temperature as needed. Conversely, electric current passes through the Peltier element if the temperature of one end rises and the temperature of the other end decreases.