Major Assignment onRefrigration & Air conditioning

Thermoelectric effect

Submitted by submitted toSagar Bhardwaj Mr. AdityaK10692 (Asst. prof. ME dept)

History

• In the 1820’s Thomas Seebeck (Germany) discovered that if two metals at different temperatures were touching you could create an electric current

• Jean Peltier discovered that the opposite was also true. By sending a current through two metals you could create differences in temperature

What is it?

• The thermoelectric effect is the direct conversion of temperature differences to electric voltage or vice-versa.

• The direction of heat flow can be controlled by changing polarity of the voltage source

Why does this Effect Occur?

Charge Carrier Diffusion and Phonon Drag

Seebeck Effect Peltier Effect

Thermoelectric Module

The Zeroth Law of Thermodynamics

• Pairs of P and N type conductors are both it contact with a copper plate.

• There will thermo power until the system is at equilibrium. (All three materials are at the same temperature)

Semiconductors

• Semiconductors have an electrical conductivity between materials like copper and glass

• They possess and interesting property where its conductivity increases with added temperature

• P and N type (thermocouples) semiconductors are created by doping.

Applications• Thermoelectric generator• Cooling Computers• Drink Coolers• Recharging Devices• Space Probes• Solar Power• Clothing• Useful, Quiet, no Moving Parts• It is less efficient (10%) and more expensive

Test for Understanding• The USB Coffee cup warmer is an example

of the Seebeck Effect or the Peltier Effect?• Before the P and N type Semiconductors

what material were used instead as thermal couples for thermoelectric modules?

• What are the advantages of using thermoelectric generators over, for example heat engines?

. Principle, construction and working of Thermoelectric power generator

Heat input

Hot junction

Cold junction

P-type N-type

Heat ejection Power output

Thermoelectric power generator based on the principle of Seebeck effect that when the junctions of two different metals are maintained at different temperature, the emf is produced in the circuit

• The figure shows the construction of thermoelectric power generator. • There is a burner in which the propane fuel is used as heating source in one side. • The exhaust is used to transmit a burnt fuel. • On the other side, a cold junction is kept. • The thermoelectric module (TE) (consist of number of

P- type and N-type semiconductor pellets connected in series or parallel depending on the served load)) is kept in

between the hot and cold junction. • The electrical out (load) is taken from the TE module.

WorkingWhen the two sides of semiconductor are maintained with different temperature, the emf is flows across the output

circuit

N-type

V

Cold side Hot side

Heat flow

Electron flow

• As the heat moves from hot side to cold side, the charge carrier moves in the semiconductor materials and hence the potential deference is created.

• The electrons are the charge carriers in the case of N-type semiconductor and Hole are in P-type semiconductors. • In a stack, number of P-type and N-type semiconductors is connected. • A single PN connection can produce a Seebeck voltage

of 40 mV. • The heat source such as natural gas or propane are used for remote power generation

ReferencesRockwood, Alan L. (1984). "Relationship of thermoelectricity to electronic entropy". Phys. Rev. A 30 (5): 2843–4. Bibcode 1984PhRvA..30.2843R. doi:10.1103/PhysRevA.30.2843

G. Jeffrey Snyder and Eric S. Toberer "Complex Thermoelectric Materials" Nature Materials 7, 105-114 (2008).

CRC Handbook of Thermoelectrics, Introduction, Edited by D.M. Rowe, CRC Press, 1995.

G. Jeffrey Snyder, Tristan Ursell. "Thermoelectric efficiency and compatibility" Physical Review Letters, Vol 91 p. 148301 (2003)