1. Thermoelectric Power Generation
and Refrigeration Systems
ME 372
Instructor: Jesse Adams
March 1, 2001
By: Ann-Marie Vollstedt

2. Thermoelectric Power Generation and Refrigeration Systems
What are thermoelectric devices used for?
Thermoelectronic devices are used in a variety of applications. They are used by
the military for night vision equipment, electronic equipment cooling, portable
refrigerators, and inertial guidance
systems. Military quality night vision
binoculars 8 (Figure 1) retail at about
$500. These products are useful to the
military during war and training
because they are reliable, small, and
quiet. Another advantage to these
Figure 1: Night vision binoculars.
thermoelectric products is that they
can be run on batteries or out of a car lighter. The medical community uses
thermoelectric applications for hypothermia blankets, blood analyzers, and tissue
preparation and storage4. The main advantage of thermoelectric devices to the medical
community is that the devices allow doctors precise temperature control, which is useful
in handling tissue samples. Hypothermia blankets are pads that patients rest on during
surgery to keep their body at a certain temperature. Many people have thermoelectric
products in their homes such as beer keg coolers, wine cellar chillers, water coolers, and
picnic basket coolers. Water Coolers like Advanced Thermoelectric Product’s “M-5”
7
(Figure 2) retail for about $350. The M-5 holds 0.74 gallons of water and weighs 14.7
pounds without the bottle. Consumers like the M-5 because it constantly keeps water at
an ideal drinking temperature of 39-52 degrees Fahrenheit.

3. Thermoelectric devices are probably most well
known for their contribution to powering spacecrafts like
the Voyager (1980). Radioisotope Thermoelectric
Generators provided all of the on- board electrical power
for NASA’s Voyager. The Thermoelectric devices proved
reliable since they were still performing to specification 14
years after launch. The power system provided the
equivalent of 100-300 watts electrical power and multiples
thereof.9 NASA is now requiring higher efficiency rates
out of smaller units.
Figure 2: M-5 water cooler
What is a Thermoelectric device?
A thermoelectric device is one that operates on a circuit that incorporates both
thermal and electrical effects to convert heat energy into electrical energy or electrical
energy to a temperature gradient. Thermoelectric elements perform the same cooling
function as Freon -based vapor compression or absorption refrigerators. Energy is taken
from a region thereby reducing its temperature. The energy is than rejected to a heat sink
region with a higher temperature. Thermoelectric elements are in a totally solid state,
while vapor cycle devices have moving mechanical parts that require a working fluid.3

4. Thermoelectri
c modules (Figure 3)
are small, sturdy,
quiet heat pumps
operated by a DC
power source. They
usually last about
Figure 3: Thermoelectric module
200,000 hours in
heating mode or about 20 hours if left on cooling mode. When power is supplied, the
surface where heat energy is absorbed becomes cold; the opposite surface where heat
energy is released becomes hot. If the polarity of current flow through the module is
reversed, the cold side will become the hot side and vice-versa. Thermoelectric modules
can also be used as thermocouples for temperature measurement or as generators to
supply power to spacecrafts and electrical equipment.
The History of Thermoelectrics
In 1821, Thomas Seebeck discovered that a continuously flowing current is
created when two wires of different materials are joined together and heated at one end.
This idea is known as the Seebeck Effect1 (Figure 4). The Seebeck effect has two main
applications including temperature measurement and power generation.

5. Thirteen years later Jean Charles Athanase reversed the flow of electrons in
Seebeck’s circuit to create refrigeration. This effect is known as the Peltier Effect.1 This
idea forms the basis for the
thermoelectric refrigerator.
Scottish scientist William
Thomson (later Lord Kelvin)
discovered in 1854 that if a
Figure 4: Seebeck effect: Two wires of different temperature difference exists
metals are connected at both ends to create a closed
circuit. If one end is heated a current will flow between any two points of a current-
continuously.
carrying conductor, heat is either
evolved or absorbed depending upon the material.6 If such a circuit absorbs heat, then
heat may be evolved if the direction of the current or of the temperature gradient is
reversed.
Thermocouples, Generators, and Refrigerators
Thermoelectric modules can also be used as thermocouples for measuring
temperature or providing the temperature-sensing element in a thermostat. To measure
temperature the thermoelectric circuit
is broken so the current quits flowing.
When the current ceases, voltage is
measured by a voltmeter1 (Figure 5).
The voltage generated is a function of
Figure 5: The voltage generated is a function of
the temperature difference and the materials of the temperature difference and the
the two wires used.

6. materials of the two wires used. Two wires used to measure temperature in this manner
form a thermocouple. Thermocouples are the most prevalent device for temperature
measurement.
Thermoelectric modules can also be used as power generators. A thermoelectric
generator (Figure 6) has a power cycle closely related
to a heat engine cycle with electrons serving as the
working fluid. Heat is transferred from a high
temperature heat source to a hot junction and than
rejected to a low temperature sink from the cold
junction. The difference between the two quantities is
the net electrical work produced. The voltage output
has been increased significantly with the use of
Figure 6: A simple
thermoelectric generator semiconductors instead of metal pairs. Some use n-
type and p-type materials connected in series for greater efficiency (Figure 7). N-type
materials are heavily doped to create excess electrons,
while p-type materials are used to create a deficiency of
electrons.
Melcor, the world’s first manufacturer of
thermoelectric coolers, utilizes processed bismuth
telluride to yield semiconductors with thermoelectric
properties3. The couple is connected in series
electrically and in parallel thermally then integrated
into modules. The modules are placed between ceramic
Figure 7: A Thermoelectric
generator using n and p-type
materials.

7. plates to offer optimum stability, electrical insulation, and thermal conductivity. The
modules can be either mounted in parallel to increase the heat transfer effect or stacked to
achieve high differential temperatures.
Global makes a thermoelectric generator5 (Figure 8). In the center of the
generator is a thermoelectric module, which
contains lead-tin-telluride semiconductor elements.
On one side of the module there is a gas burner.
The other side has aluminum cooling fins or a heat
pipe to keep it cool. The hot side maintains a
temperature of 540 degrees Celsius, while the cold
Figure 8: Global's thermoelectric
side stays at about 140 degrees Celsius. generator
Thermoelectric devices can also be used as refrigerators on the bases of the Peltier
effect.1 To create a thermoelectric refrigerator
(Figure 9), heat is absorbed from a refrigerated
space and than rejected to a warmer environment.
The difference between these two quantities is the
net electrical work that needs to be supplied.
These refrigerators are not overly popular because
they have a low coefficient of performance. The
coefficient of performance for thermoelectric
refrigerators can be calculated by dividing the
Figure 9: A Thermoelectric
cooling effect by the work input as shown in the refrigerator based on the Peltier
effect.

8. example on page 10.
Temperature Range
It is theoretically possible to get a temperature range of about 75 degrees Celsius working
against the hot side at a temperature of 35 degrees Celsius.2 This will only happen if there
is no thermal load, which will not happen in a real system. Typical applications yield
about half of the theoretical temperature difference. More extreme temperatures can be
reached by using multiple thermoelectric modules. Since thermoelectric modules will not
perform as well in colder temperatures, their temperature range becomes much smaller.
Advantages
Thermoelectric devices are advantageous because they are reliable, light in weight, small,
quiet, and inexpensive.2 They will function in environments that are too severe, too
sensitive, or too small for conventional refrigeration. These environmentally friendly
devices offer precise temperature control, while requiring minimal maintenance because
they have no moving parts. Thermoelectric devices are most useful for small cooling
jobs where a compressor based system would be impractical. These devices are also
useful because they can heat as well as cool depending on the polarity of the power
source.
Assembly
Thermoelectric modules are installed2 through mechanical clamping, epoxy
bonding, and solder bonding (Figure 10). While the modules are strong in compression,

9. they are weak in shear so excess loading
should be avoided. Maximum
recommended compression loading is
350 lbs. per sq. inch of module surface.
Future Research
Researchers are working on
Figure 10: Thermoelectric Installation guide
improving the efficiency of
thermoelectric devices, reducing the cost of producing them and increasing their
applications. Researchers are trying to maximize the electricity output for a given heat
source by changing the materials used in construction. They are also studying materials
so they can predict their reliability and long-term behavior. The Japanese government is
funding thermoelectric research in the fields of space technology, and domestic and
industrial uses. Professor Michael Rowe proved that the amount of heat contained in the
water leftover from a bath would provide enough electricity to power a color television
for an hour.9 Electric power was produced through a series of thermocouples squeezed in
between a few hot and cold-water channels. The power produced was about 100 watts.
Research in the field of thermoelectrics is bound to continue because it offers a
convenient, earth friendly alternative to normal power systems.

10. Example Problem
Problem 10.73 from Thermodynamics, An Engineering Approach.
Question: A thermoelectric refrigerator removes heat from a refrigerated space at –5
degrees Celsius at a rate of 130 Watts and rejects it to an environment at 20 degrees
Celsius. Determine the maximum coefficient of performance this thermoelectric
refrigerator can have and the minimum required power input?
Solution:
Recall: The standard comparison for refrigeration cycles is the reversed Carnot cycle.
The performance of refrigerators is expressed in terms of the coefficient of performance
(COP).
CoolingEffect QH
COP= =
WorkInput Wnet −in
1
The COP for Carnot refrigerators is:
TH
( − 1)
TL
a. Maximum coefficient of refrigeration:
1 1
COP max = COP r = = = 10.72
TH 293K
( − 1) ( − 1)
TL 268K
b. Minimum required power input:
.
. QL 130W
W in = = = 12.1W
COPmax 10.72

11. Works Cited
1. Cengal,Yunus, and Michael Boles. Thermodynamics: An Engineering Approach.
Hightstown: McGraw Hill, 1998.
2. “An Introduction to Thermoelectrics.” Tellurex Corporation. February 8, 2001. <
http://www.tellurex.com/> (1 February 2001).
3. “Thermoelectric History/General Information.” Melcor, Thermoelectric
Engineering Handbook. < http://www.melcor.com/handbook.htm> (1 February
2001).
4. “Thermoelectric Applications.” Melcor, Thermoelectric Engineering Handbook. <
http://www.melcor.com/handbook.htm> (1 February 2001).
5. “About Generators.” Global Thermoelectrics.<
http://www.globalte.com/genabout-frames.htm > (1 February 2001).
6. “Thermoelectrics.” The Columbia Encyclopedia. <
http://www.bartleby.com/65/th/thermoel.html > (1 February 2001).
7. “The M-5 Water Cooler.” Advanced Thermoelectric Products. <
http://www.electracool.com/products.htm> (27 February 2001).
8. “Night Vision Binocular.” Night Vision Optics. <
http://www.nightvisionoptics.com/> (27 February 2001).
9. “Thermoelectric Generators: Seebeck effect used for conversion of heat energy
into electric power.” Global Techno Scan.
http://www.globaltechnoscan.com/31jan-6feb/generators.htm (1 February 2001).