Peltier’s effect

information about peltier effect

1. Muhammad Umair (15261509-048) Sana Nazir (15261509-077) Maryam Butt (15261509-080) Saba Mazhar (16341509-003) Presented by:

2. Peltier’s Effect

3. History: In 1834, a French watchmaker and part time physicist, Jean Charles Athanase Peltier found that an electrical current would produce heating or cooling at the junction of two dissimilar metals. In 1838 Lenz showed that depending on the direction of current flow, heat could be either removed from a junction to freeze water into ice, or by reversing the current, heat can be generated to melt ice.

4. What is Peltier’s Effect? The Peltier effect is the presence of heating or cooling at an electrified junction of two different conductors. The Peltier effect is a temperature difference created by applying a voltage between two electrodes connected to a sample of semiconductor material. Electrodes (a conductor through which electricity enters or leaves an object, substance, or region ). Semiconductor material(a solid substance that has a conductivity between that of an insulator and that of most metals, either due to the addition of an impurity or because of temperature effects).

5. This phenomenon can be useful when it is necessary to transfer heat from one medium to another on a small scale

6. Peltier’s Effect Process:

7. Equation: When a current is made to flow through a junction between two conductors, A and B, heat may be generated or removed at the junction. The Peltier heat generated at the junction per unit time, Q ˙ Q˙ = ( Π A − Π B ) I where Π A, Π B is the Peltier coefficient of conductor A and B, and I is the electric current (from A to B).

8. Cont … The total heat generated is not determined by the Peltier effect alone, as it may also be influenced by Joule heating.

9. Explanation of peltier’s effect Consider a Cu-Fe thermocuple having both the junction at the same temperature. If current is passed through this thermocouple in the direction as shown, heat is evolved at the junction A and absorbed at the junction B. Therefore , junction A is heated while the junction B is cooled.

10. Cont … If current in the circuit is reversed, thermoelectric effect is also reversed i.e., junction B is heated and junction A is cooled. When two dissimilar metal are joined, contact potential difference is established at the junction i.e. potential of the one metal becomes above that of the other. In the case Cu-Fe thermocouple, the potential of Fe is above that of Cu.

11. Cont … At the junction B, current flows from Cu to Fe i.e. from lower potential to higher potential. Hence, energy is required for this purpose. As a result, energy is absorbed from the junction and it is cooled. At the junction A , current flows from Fe to Cu i.e. from higher potential to lower potential. Hence, energy is given out at this junction. Consequently, junction A becomes hot.

12. Cont … Peltier effect is reversible. If the direction of current through the thermocouple is reversed, the heat is evolved and absorbed at the junction are also interchanged.

13. The Peltier effect can be used to create a Refrigerator that is compact and has no circulating fluid or moving parts. Such refrigerators are useful in applications where their advantages outweigh the disadvantage of their very low efficiency Refrigerator

14. Dehumidifiers: The cooling effect of Peltier heat pumps can be used to extract water from the air in dehumidifiers. A camping/car type electric cooler can typically reduce the temperature by up to 20 °C (36 °F) below the ambient temperature. Climate-controlled jackets are beginning to use Peltier elements.

15. The effect is used in satellite and spacecraft to counter the effect of direct sunlight on one side of a craft by dissipating the heat over the cold shaded side, whereupon the heat is dissipated by thermal radiation into space. satellite

16. In fiber optic applications, where the wavelength of a laser or a component is highly dependent on temperature, Peltier coolers are used along with a thermistor in a feedback loop to maintain a constant temperature and thereby stabilize the wavelength of the device. fiber optic applications

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