Jacob McKenzie, Ty Nowotny, Colin Neunuebel The Peltier Effect Jacob 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.

where α is the Seebeck coefficient of the couple 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 of thermoelectric 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

our peltier: Temperature Gradient Carnot Efficiency Nc @ 12v: =1-Tc/Th =1-283.6/342.3 =17.1%

Radioisotopic Thermoelectric Generator (RTG) 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