The Peltier EffectJacob McKenzie, Ty Nowotny, Colin Neunuebel

SRJC Engr45 - Fall 2005

History of the Seebeck effect

Discovered by Thomas Johann Seebeck in 1821.

He accidentally found that a voltage existed between two ends of a metal bar when a temperature gradient existed within the bar.

The Seebeck Effect

A temperature difference causes diffusion of electrons from the hot side to the cold side of a conductor.

The motion of electrons creates an electrical current.

The voltage is proportional to the temperature difference as governed by: V=α(Th-Tc)

where α is the Seebeck coefficient of the couple

History of Peltier devices

The Peltier effect is named after Jean Charles Peltier (1785-1845) who first observed it in 1834.

The Peltier effect had no practical use for over 100 years until dissimilar metal devices were replaced with semiconductor Peltiers which could produce much larger thermal gradients.

What is a Peltier Cooler?

Thermoelectric heat pumps that will produce a temperature gradient that is proportional to an applied current.

Peltier Effect With Dissimilar Metals

At the junction of two dissimilar metals the energy level of conducting electrons is forced to increase or decrease.

A decrease in the energy level emits thermal energy, while an increase will absorb thermal energy from its surroundings.

The temperature gradient for dissimilar metals is very small.

The figure of merit is a measure ofthermoelectric efficiency.

Semiconductor Peltier

Bismuth-Telluride n and p blocks

An electric current forces electrons in n type and holes in p type away from each other on the cold side and towards each other on the hot side.

The holes and electrons pull thermal energy from where they are heading away from each other and deliver it to where they meet.

Device Construction

Individual couples are connected in series electrically and in parallel thermally.

Couples are thermally connected by a ceramic that has high electrical resistivity and high thermal conductivity.

Our Peltier:Change in Temperature @ 12v

Temperature and Temperature Difference as a Function of Time

0.00

20.00

40.00

60.00

80.00

100.00

120.00

140.00

160.00

0 200 400 600 800

Time (s)

Temperature (°F)

Hot Side

Cold Side

TempDifference

our peltier:Temperature Gradient

Temperature Gradient as a Function of Voltage

0.00

10.00

20.00

30.00

40.00

50.00

60.00

70.00

0.00 2.00 4.00 6.00 8.00 10.00 12.00

Voltage, V

Temperature, °C

Voltage vsTemp Diff

Cold vs V

Hot vs V

Carnot Efficiency

Nc @ 12v:=1-Tc/Th=1-283.6/342.3=17.1%

Applications

Deep space probes

Microprocessor cooling

Laser diode temperature stabilization

Temperature regulated flight suits

Air conditioning in submarines

Portable DC refrigerators

Automotive seat cooling/heating Radioisotopic Thermoelectric Generator (RTG)

Pros and Cons

Pros

Solid state (no moving parts)

No maintenance

Long service lifetime

Cons

Large electrical power requirements

Inefficient compared to phase change cooling

References

http://www.its.caltech.edu/~jsnyder/thermoelectrics/history_page.htm

http://www.tellurex.com/12most.html

http://www.thermoelectrics.com/introduction.htm, Thermoelectric Materials

http://www.digit-life.com/articles/peltiercoolers/

http://www.heatsink-guide.com/content.php?content=peltierinfo.shtml, THE HEATSINK GUIDE: Peltier Guide, Part 1

http://saturn.jpl.nasa.gov/index.cfm