The Peltier Effect by MJJKZn

VIEWS: 114 PAGES: 13

									   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.
    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
                                 Temperature and Temperature Difference
                                         as a Function of Time
                    160.00


                    140.00


                    120.00
 Temperature (¡F)




                    100.00
                                                                      Hot Side
                     80.00
                                                                      Cold Side
                     60.00
                                                                      Temp
                                                                      Difference
                     40.00


                     20.00


                      0.00
                             0       200      400       600   800
                                             Time (s)
                                      our peltier:
                                  Temperature Gradient
                             Temperature Gradient as a Function of Voltage
                                                                                               Carnot Efficiency
                  70.00


                  60.00
                                                                                               Nc @ 12v:
                  50.00                                                                        =1-Tc/Th
                                                                                  Voltage vs
                                                                                               =1-283.6/342.3
Temperature, ¡C




                                                                                  Temp Diff
                  40.00
                                                                                  Cold vs V    =17.1%
                  30.00                                                           Hot vs V

                  20.00


                  10.00


                   0.00
                      0.00      2.00   4.00     6.00       8.00   10.00   12.00
                                              Voltage, V
             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

								
To top