Thermoelectric Refrigeration

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-:THERMOELECTRIC REFRIGERATION :

What is it? How does it work?

WHAT IS THERMOELECTRIC REFRIGERATION?

Refrigeration is the process of pumping heat energy out of an insulated chamber in order

to reduce the temperature of the chamber below that of the surrounding air.

Thermoelectric refrigeration uses a principle called the "PELTIER" effect to pump heat

electronically. The Peltier effect is named after a French scientist who discovered it in

1834..

HOW DOES IT WORK?

In 1834 Jean Peltier noted that when an electrical current is applied across the junction of

two dissimilar metals, heat is removed from one of the metals and transferred to theother. This is the basis of thermoelectric refrigeration. Thermoelectric modules are

constructed from a series of tiny metal cubes of dissimilar exotic metals which are

physically bonded together and connected electrically. When electrical current passes

through the cube junctions, heat is transferred from one metal to the other. Solid-state

thermoelectric modules are capable of transferring large quantities of heat when

connected to a heat absorbing device on one side and a heat dissipating device on the

other. The Koolatron's internal aluminium cold plate fins absorb heat from the contents,

(food and beverages), and the thermoelectric modules transfer it to heat dissipating fins

under the control panel. Here, a small fan helps to disperse the heat into the air. The

system is totally environmentally friendly and contains no hazardous gases, nor pipes nor

coils and no compressor. The only moving part is the small 12-volt fan. Thermoelectricmodules are too expensive for normal domestic and commercial applications which run

only on regular household current. They are ideally suited to recreational applications

because they are lightweight, compact, insensitive to motion or tilting, have no moving

parts, and can operate directly from 12-volt batteries.

WHY IS IT BETTER THAN AN ICE CHEST?

Food and beverages are kept cold and dry. No space is wasted for ice (unless of course

you want ice, in which case we can help to preserve it 3 or 4 times longer than a plain

cooler)

ADVANTAGES OF THERMOELECTRIC REFRIGERATION

COMPACT SIZE : Very little space is required by the cooling system. The

thermoelectric module is the size of a matchbook.

LIGHTWEIGHT: A 36 qt. capacity unit weighs only 17 lbs. PORTABLE: Carrieswith one hand and is unaffected by motion or tilting.

LOWER PRICED : 20% to 40% less expensive than compressor or absorption units.

LOW BATTERY:Averages approximately 4.5 amps - less than your cars

headlights.
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DRAW:

BATTERY PROTECTION: Used in combination with the Koolatron "Battery Saver"

you can always be assured of having starting power.

PERFORMANCE: Koolatron coolers maintain "cool" temperatures in ambients up to

90 degrees F.HEATING OPTION: Koolatrons can be operated in the heating mode for short periods

of time. Specialty Heater ONLY versions of our insulated boxes are used by Meals on

Wheels, other senior hot meal programs, school hot meal programs and by caterers all

across the country. SAFETY: No open flames, propane, or toxic refrigerants used.

RELIABILITY: Thermoelectrics have a 40 year proven track record in military,

aerospace, laboratory, and now consumer applications.

EASY SERVICE: Most parts are easily replaced by the end-user with a screw driver.

LOW The only maintenance required with any Koolatron unit is periodic.

MAINTENANCE: "dusting" and Vacuuming to ensure good heat dissipation.

COMPARISON OF THERMOELECTRIC REFRIGERATION and OTHER

METHODS OF REFRIGERATION

THERMOELECTRIC: Cooling is achieved electronically using the "Peltier" effect -

heat is pumped with electrical energy.

COMPRESSOR : Cooling is achieved by vaporising a refrigerant (such as freon) inside

the refrigerator - heat is absorbed by the refrigerant through the principle of the "latent

heat of vaporisation" and released outside the refrigerator where the vapour is condensed

and compressed into a liquid again. Uses mechanical energy.

ABSORPTION: Cooling is achieved by vaporising a refrigerant (ammonia gas) inside

the refrigerator by "boiling" it out of a water ammonia solution with a heat source

(electric or propane). Uses the principle of "latent heat of vaporisation". The vapour is

condensed and re-absorbed by the ammonia solution outside the refrigerator. Uses heat

energy. s.

COMPARISON OF THE FEATURES OF ALL THREE SYSTEMS:

COMPACTNESS: Koolatron thermoelectrics are the most compact because of the small

size of the cooling components - cooling module / heat sink / cold sink.

WEIGHT: Koolatron units weigh 1/3 to 1/2 as much as the other units because of the

lightweight cooling system - no heavy compressor.

PORTABILITY: Koolatrons are the most portable because they are light enough to

carry with one hand and are not affected by motion or tilting. Compressor models are

quite heavy and the absorption models must be kept level within 2 - 3 degrees.

PRICE: Koolatron coolers cost 20% - 40% less than the equivalent sized compressor or

absorption units available for recreational use.

BATTERY DRAIN: Koolatron coolers have a maximum current drain on 12 volts of4.5 amps. Compressor portables draw slightly more current when running but may


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average slightly less depending on thermostatic control settings. Absorption portables

draw 6.5 to 7.5 amps when running and may average about 5 amps draw.

BATTERY PROTECTION: Consider the "Battery Saver" option as discussed in the

previous section.

COOLING PERFORMANCE: Compressor systems are potentially the most efficient

in hot weather. Some models will perform as a portable freezer and will refrigerate in

ambient temperatures of up to 110 degrees F. Koolatron units will refrigerate in sustained

ambient temperatures of up to 95 degrees F. If they are kept full, they will refrigerate

satisfactorily even if peak daytime temperatures reach 110 degrees F because the

contents temperature will lag behind the ambient. The food will be just starting to warm

up when the air cools off in the evening which will bring the food temperature back

down to normal. Absorption type refrigerators provide almost the same cooling

performance as Koolatron portables but are less efficient at high ambients.

FREEZING ICE CUBES: Compressor systems will usually make a quantity of small

ice cubes except in very hot weather. Gas absorption systems can do the same except in

hot weather. Koolatron thermoelectric units do not make ice cubes but can preserve them

in a plastic container for 2 - 3 days which is often adequate for most applications.

SAFETY: Koolatron systems are completely safe because they use no gases or open

flames and run on just 12 volts. Compressor systems can leak freon which can be

extremely dangerous especially if heated. Absorption systems may use propane which

can be extremely dangerous in the event of a leak.

RELIABILITY: Koolatrons thermoelectric modules do not wear out or deteriorate withuse. They have been used for military and aerospace applications for years because of

their reliability and other unique features. Compressors and their motors are both subject

to wear and freon-filled coils are subject to leakage and costly repairs. Absorption units

are somewhat temperamental and may require expert servicing from time to time,

especially if jarred when travelling.

EASE OF SERVICING AND MAINTENANCE: Koolatron units have only one

moving part, a small fan (and 12 volt motor) which can easily be replaced with only a

screw driver. Most parts are easily replaced by the end-user. Compressor and absorption

units both require trained (expensive) mechanics and special service equipment to service

them.

BACK
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FAQ & Technical Info

FAQ & Technical

Information

Click on the section of interest:

Frequently Asked Questions1. How does a thermoelectric module work?

2. What is the mathematical equation for describing the operation of a thermoelectric mod

3. What are the advantages of a thermoelectric unit over a compressor?

4. What industries does thermoelectrics serve?

5. What is the efficiency of a thermoelectric module?

6. I want to make my own cooling assembly. How do I select the right module for my syst

7. How reliable are thermoelectric systems?

8. Will TE Technology do contract manufacturing?

9. Can I use a thermoelectric cooler as a heater?

10. How big or small can a thermoelectric cooler be?

11. What is the best way to power a thermoelectric cooler?12. How precisely can a thermoelectric cooler maintain temperature?

13. What temperature ranges can a thermoelectric cooler achieve?

14. What ambient temperature environments do thermoelectric coolers withstand?

15. How do I determine if thermoelectric cooling is best for my application?

16. Why should I have TE Technology manufacture a system for my application?

17. What type of testing does TE Technology recommend?

18. What kind of over temperature protection do I need?

19. How do Pulse-Width Modulated (PWM) controllers operate?

20. What are some considerations for using a liquid chiller?

21. What is the manufacturing test process for all cooling assemblies at TE Technology?

22. How does the TE Technology module part number system work?
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23. What is the best way to attach a temperature sensor when making temperature measur

or when using a temperature controller?

Terms and Definitions Technical Information on Cooling Assemblies Technical Information on TE Modules Technical Papers and Company Literature

Frequently Asked Questions on Thermoelectrics

1. How does a thermoelectric module work?

Thermoelectric modules are solid-state heat pumps that operate on the Peltier effect (see definitio

thermoelectric module consists of an array of p- and n-type semiconductor elements that are heav

doped with electrical carriers. The elements are arranged into array that is electrically connected i

series but thermally connected in parallel. This array is then affixed to two ceramic substrates, on

each side of the elements (see figure below). Let's examine how the heat transfer occurs as electr

flow through one pair of p- and n-type elements (often referred to as a "couple") within the

thermoelectric module:
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The p-type semiconductor is doped with certain atoms that have fewer electrons than necessary t

complete the atomic bonds within the crystal lattice. When a voltage is applied, there is a tendenc

conduction electrons to complete the atomic bonds. When conduction electrons do this, they leav

holes which essentially are atoms within the crystal lattice that now have local positive charges

Electrons are then continually dropping in and being bumped out of the holes and moving on to t

available hole. In effect, it is the holes that are acting as the electrical carriers.

Now, electrons move much more easily in the copper conductors but not so easily in the

semiconductors. When electrons leave the p-type and enter into the copper on the cold-side, holes

created in the p-type as the electrons jump out to a higher energy level to match the energy level

electrons already moving in the copper. The extra energy to create these holes comes by absorbin

Meanwhile, the newly created holes travel downwards to the copper on the hot side. Electrons fro

hot-side copper move into the p-type and drop into the holes, releasing the excess energy in the f

heat.


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The n-type semiconductor is doped with atoms that provide more electrons than necessary to com

the atomic bonds within the crystal lattice. When a voltage is applied, these extra electrons are ea

moved into the conduction band. However, additional energy is required to get the n-type electro

match the energy level of the incoming electrons from the cold-side copper. The extra energy co

absorbing heat. Finally, when the electrons leave the hot-side of the n-type, they once again can

freely in the copper. They drop down to a lower energy level, and release heat in the process.

The above explanation is imprecise as it does not cover all the details, but it serves to explain in

what are otherwise very complex physical interactions. The main point is that heat is always abso

the cold side of the n- and p- type elements, and heat is always released at the hot side of thermoe

element. The heat pumping capacity of a module is proportional to the current and is dependent o

element geometry, number of couples, and material properties.

Back to the top

2. What is the mathematical equation for describing the operation of a thermoelectric modu

The figure above represents a thermoelectric couple. It shows some terms used in the mathemati

equation:

L = element height A = cross-sectional area Qc = heat load

Tc = cold-side temperature Th = hot-side temperature I = applied current

Additionally, there is the following:

S = Seebeck coefficient R = electrical resistivity K = thermal conductivity

V = voltage N = number of couples

Here are the basic equations:
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Qc = 2 * N* [S * I * Tc -1/2 * I^2 * R * L/AK * A/L * (ThTc)]

V = 2 * N * [S * (ThTc) + I * R * L/A]

The first Qc term, S*I*Tc, is the peltier cooling effect. The second term,1/2*I^2*R*L/A, represeJoule heating effect associated with passing an electrical current through a resistance. The Joule h

distributed throughout the element, so 1/2 the heat goes towards the cold side, and 1/2 the heat go

towards the hot side. The last term, K*A/L*(Th-Tc), represents the Fourier effect in which heat

conducts from a higher temperature to a lower temperature. So, the peltier cooling is reduced by t

losses associated with electrical resistance and thermal conductance.

For the voltage, the first term, S*(Th-Tc) represents the Seebeck voltage. The second term, I*R*

represents the voltage related by Ohms law.

These equations are very simplified and are meant to show the basic idea behind the calculations

are involved. The actual differential equations do not have a closed-form solution because S, R, a

are temperature dependent. Unfortunately, assuming constant properties can lead to significant er

TE Technology uses special, proprietary modeling software which takes into account the tempera

dependency of the thermoelectric material properties as well as all the relevant design aspects of t

overall system. The software uses material property data from actual test results on thermoelectri

modules, so it yields highly accurate results. When we build a custom cooler for your application,

high accuracy means you generally only need one prototype to verify cooling performance.

Back to the top

3. What are the advantages of a thermoelectric unit over a compressor?

Thermoelectric modules have no moving parts and do not require the use of chlorofluorocarbons.

Therefore they are safe for the environment, inherently reliable, and virtually maintenance free. T

can be operated in any orientation and are ideal for cooling devices that might be sensitive to

mechanical vibration. Their compact size also makes them ideal for applications that are size or

limited where even the smallest compressor would have excess capacity. Their ability to heat and

by a simple reversal of current flow is useful for applications where both heating and cooling is

necessary or where precise temperature control is critical.

Back to the top

4. What industries does thermoelectrics serve?Thermoelectric coolers are used for the most demanding industries such as medical, laboratory,

aerospace, semiconductor, telecom, industrial, and consumer. Uses range from simple food and

beverage coolers for an afternoon picnic to extremely sophisticated temperature control systems i

missiles and space vehicles.

A thermoelectric cooler permits lowering the temperature of an object below ambient as well as

stabilizing the temperature of objects above ambient temperatures. A thermoelectric cooler is diff

from a heat sink because it provides active cooling unlike a heat sink which provides only passiv

cooling.

Thermoelectric coolers can be used for applications that require heat removal ranging from milli-up to several thousand watts. However, there is a general axiom in thermoelectrics: the smaller th
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better. A thermoelectric cooler makes the most sense when used in applications where even the s

vapor compressor system would provide much more cooling than necessary. In these situations, a

thermoelectric cooler can provide a solution that is smaller, weighs less, and is more reliable than

comparatively small compressor system.

However, the trend in recent years has been for larger and larger thermoelectric systems. As pow

supplies become less expensive this has driven the cost of a complete thermoelectric system (cool

power supply, and temperature controller) lower, so higher power systems are now more marketa

Systems with capacities in the 200-400 watt range are becoming more common, although they ar

not nearly as common as smaller systems where the cooling capacity is below 100 watts.

Large thermoelectric systems in the kilo-watt range have been built for specialized applications s

cooling within submarines and railroad cars or cooling process baths in specialized areas such as

semiconductor manufacturing. In cases where thermoelectric coolers are used for such large

applications there generally has been a good reason why a vapor compressor system has not been

(for example, vibration needs to be minimized or precision temperature control is required). In wcase, the extra cost and higher power consumption of the thermoelectric cooler can be justified.

Typical applications for thermoelectric coolers include:

Laser diodes

Laboratory instruments

Temperature baths

Electronic enclosures

Refrigerators

Telecommunications equipment

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5. What is the efficiency of a thermoelectric module?

Technically, the word efficiency relates to the ratio of the amount of work one gets out of a mach

the amount of power input. In heat pumping applications, this term is rarely used because it is pos

to remove more heat than the amount of power input it takes to move that heat. For thermoelectri

modules, it is standard to use the term "coefficient of performance" rather than "efficiency." The

coefficient of performance (COP) is the amount of heat pumped divided by the amount of supplie

electrical power.

The COP depends on the heat load, input power, and the required temperature differential. Typic

the COP is between 0.3 and 0.7 for single-stage applications. However, COPs greater than 1.0 ca

achieved especially when the module is pumping against a positive temperature difference (that i

when the module is removing heat from an object that is warmer than the ambient). The figure

below shows a normalized graph of COP versus I/Imax (the ratio of input current to the module's

specification). Each line corresponds with a constant DT/DTmax (the ratio of the required temper

difference to the module's DTmax specification).


10/30

Back to the top

6. I want to make my own cooling assembly. How do I select the right module for my system

You can use our module selector program atwww.tetech.com/Peltier-Thermoelectric-Cooler-Mo

Selector.html. Detailed instructions on how to use the program in conjunction with your thermal

can be downloaded from there. Other module software programs we have seen base performance

recommendations on certain assumptions that otherwise can lead to significant errors. Our modul

selector program does not make any assumptions about your system designrecommendations a

based on the module's operating temperatures, heat load, and DTmax. This makes for a more acc

selection process since you know what assumptions are being made. Be aware that proper modul

selection is an iterative process that does take time and research. If you do not want to spend the t

and expense of selecting your own module, designing your own system, having the necessary skil

labor to assemble it, etc., then we have a highly recommended alternative: standard (or custom) c

assemblies. All of the hard work has already been done by us when you purchase an assembly fro

Technology.

However, if you are certain that you want to make your own cooling assembly, here is a brief

description of what's involved:

First you must define your operating temperatures and how much heat you need to remove. Base

these parameters the Module Selector program will help you select a module for lowest power

consumption, for smallest size, or a combination of the two. (Again, see www.tetech.com/module

further information.)

Next, you analyze your thermal system based on the size and operating voltage and current for th

selected module. In this step, you are making sure the operating temperatures and heat load you u

select the module are realistic. If the analysis shows that your numbers were realistic, then you ar

finished. Otherwise, you must enter a new heat load and operating temperatures and iterate the pr

until the module you select meets your final requirements.
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Back to the top

7. How reliable are thermoelectric systems?Thermoelectric systems are highly reliable provided they are installed and used in an appropriate

manner. The specific reliability of thermoelectric coolers tends to be difficult to define though be

failure rates are highly dependent upon the particular application. Thermoelectric modules that ar

steady state (constant power, heat load, temperature, etc.) can have mean time between failures

(MTBFs) in excess of 200,000 hours. However, applications involving thermal cycling show

significantly worse MTBFs, especially when TE coolers are cycled up to a high temperature. Wit

thermal cycling, a more appropriate measure of reliability is not time but rather number of cycles.

All materials expand or contract as they are heated or cooled. Different materials will expand at

different rates. The rate of expansion is given by the material property called the coefficient of th

expansion (CTE). Generally, as the cold side of a module gets colder, it will shrink, and as the ho

gets hotter, it will expand. This flexes the thermoelectric elements and their solder junctions.

Furthermore, because the module is constructed of several different materials, there is added stressimply because the materials themselves are expanding/contracting at different rates. After repeat

thermal cycling, the solder junctions within the module fatigue, and the electrical resistance incre

Cooling performance is reduced, and eventually the module becomes inoperable. The "failure poi

thus a function of operating temperature, the amount of temperature cycling, and how much degr

the particular system can tolerate before performance becomes unacceptable. All thermoelectric

modules (regardless of manufacturer) experience the same stresses of operation, but how they tol

these stresses is a question of build qualityselecting a manufacturer with good, strong solder ju

is a must! (Of course, we take special care in ensuring that our modules have the highest quality s

junctions.)

A similar phenomenon occurs when a module is soldered or adhered with epoxy to a heat sink. T"zero-tension" point (that is, the point where there is no internal stress resulting from mismatches

CTE) will freeze between the ceramic substrate and the heat sink when the solder or epoxy beco

rigid at some temperature which is typically different from the operating temperature. In other wo

the module is pre-stressed when the module and solder cool back down to room temperature (ass

the module is soldered to a heat sink).

As the assembly is thermally cycled, not only does the module itself undergo fatigue stress, the b

line between the module and heat sink is also stressed. Again, different materials will expand at

different rates. The heat sink, the solder (or epoxy), and the module will expand differently. This

particularly troublesome because the bond could potentially fail at local spots. The module could

overheat at these local spots which would exacerbate the problem. This is why we do not recomsoldering (or epoxy-ing) the module to its heat sink. If you do solder (or epoxy) the modules, we

recommend that you thermal cycle the compete assembly to make sure you get adequate lifetimes

TE Technology does not publish thermoelectric cooler reliability data for general use. Reliability

only valid for the conditions under which a test was conducted, and it is not necessarily applicabl

other configurations. There are numerous application parameters and conditions that will affect

reliability. Cooler assembly, mounting methods, power supply, temperature control systems and

techniques, and temperature profiles are just a few factors that can combine to produce failure rat

ranging from extremely low to very high. Again, the "failure point" is specific to each application

There can also be tradeoffs between a cooler's thermal performance, the cost to manufacture the c


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pulse-width-modulated (frequency at least 300 Hz) control should always be chosen over ON/OF

control to ensure better reliability. The ON/OFF type of controller basically causes thermal cyclin

so should be avoided.

e) Exposure to high temperatures should be minimized as much as possible to extend reliability.

Standard modules are rated for a maximum of 80 C. High-temperature modules are rated for 200

modules. However, these temperature limits are somewhat arbitrary. All modules, regardless of

manufacturer, will be affected by operation at high temperatures. Some, of course, are more resist

changes than others though.

The module is constructed with nickel-plated copper conductors to electrically connect the

thermoelectric pellets to each other. The copper has a tendency to diffuse into the thermoelectric

material, and this would then degrade the performance. So the nickel plating is added to serve as

diffusion barrier to the copper. Unfortunately, the nickel is not a perfect barrier, and copper atom

still diffuse albeit at a much slower rate than if there were no nickel barrier at all. The rate of diff

typically increases exponentially with temperature: the higher the operating temperature, the morquickly will diffusion occur along with the corresponding degradation in performance. However,

particular with the 80 C module, at 85 C, solder constituents can begin migrating along cleavag

plains of the thermoelectric material due to a theorized minor eutectic reaction. This leads to a

mechanically weak solder joint and physical expansion of the pellet.

The temperature ratings for the modules are derived from their construction technique. The 80 C

module uses solder that melts at 140 C. It has excellent electrical contacts. The 200 C module a

two nickel barriers: a layer of nickel on the copper tab and a layer of nickel on the ends of the pel

The solder melts at 232 C.

f) Additional information can be found by downloading publications concerning reliability atwww.tetech.com/Downloadable-Publications.html#reliability.

g) Not all thermoelectric modules are made with the same quality! Different manufacturers have

different techniques, and we have seen widely varying quality when comparing modules of equiv

size and capacity from a variety of manufacturers. Improper soldering, improper metallization of

ceramics, and improper nickel plating are just a few of the potential problems that can reduce reli

Be careful when selecting your module vendor!

Back to the top

8. Will TE Technology do contract manufacturing?

TE Technology does contract manufacturing for companies who have an existing thermoelectric

and would like to find a company to manufacture their part. We have in house state of the art mac

capabilities along with a complete environmental control test department. When companies add u

costs of the thermoelectric engineers, assembly workers, inventory, and manufacturing floor spac

along with the costs of designing, maintaining, and calibrating the required thermoelectric test

equipment, they find this is more expensive than the raw materials themselves. Through outsourc

these customers reduce their overhead expenses while benefiting from our consistently excellent

quality. No matter how small or big your production levels are, if you would like to explore this o

please send us the specifications of your thermoelectric cooling assembly with the quantities you

require, and we will be happy to quote.
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Back to the top

9. Can I use a thermoelectric cooler as a heater? Thermoelectric coolers can indeed be used for very effective and efficient heating. Since thermoe

coolers are solid-state heat pumps, they can actively pump heat from the ambient in addition to th

heating effect that comes from the electrical resistance of the cooler itself. So, the thermoelectric

can be more efficient than a resistive heater (within limits). The heating can be so effective that y

could very easily cause the module to reach the melting point of the solder! Care must be taken to

ensure that the module does not overheat.

If you are interested in using one of our standard cooling assemblies for a cooling and/or heating

application, please consult with us to determine which assembly would work best.

If you are interested in building your own assembly, you can use the cooling performance graphs

thermoelectric module to estimate how much heating can be done. The total heating load is calculby first estimating a temperature difference across the module and assuming an input current for

particular module. This defines the active amount of heat that the module can pump from the amb

Combining this with the total power input determines how much total heating the module can do.

would then iterate the temperature difference guess based on the thermal resistances to and from t

module and the corresponding heat loads being transferred.

It is possible for the module to provide heating in which the temperature difference across the mo

greater than its DTmax. However, in such cases, the module cannot pump any active heat, and th

module would then be acting essentially as a resistive heater.

If you plan to do temperature cycling, you can use one of our bipolartemperature controllers. Thcontrollers determine whether heating or cooling is required automatically based only on the set p

(Please also review FAQ#7 for questions on module reliability.) If you only need to do heating or

cooling above or below the ambient, a heat-only/cool-only controller can work.

Back to the top

10. How big or small can a thermoelectric cooler be?There are practical limits to the individual sizes of a module or cooling assembly.Micro-modules

example, are more expensive to produce because they are less suitable for automated processing.

larger modules, coefficients of thermal expansion and costs tend to limit thermoelectric modules t

within a certain physical footprint.

For cooling assemblies, the minimum size might be limited by the minimum requirements neede

provide sufficient heat sinking. The maximum size is limited by the requirements of the mountin

plates. If the plates get too large, then it becomes too difficult to maintain sufficient surface flatne

Generally, when more cooling capacity is required than what the typically largest size cooler can

provide, multiple coolers are used rather than using one giant cooler. Approximately speaking, th

largest individual cooler has a footprint of approximately 254 mm x 177 mm, such as our standar

200. There are always exceptions though; these are just general guidelines.

Back to the top
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11. What is the best way to power a thermoelectric cooler? a) Ideally, thermoelectric coolers should operate on purely direct current for the best performance

However, a ripple factor of 10% will only result in 1% degradation in temperature difference. Mo

power supplies have better filtering than that, so ripple is not likely to be a concern.

b) Care should be taken not to overpower the cooler. Overpowering the cooler could lead to

inadvertently exceeding the temperature ratings and causing damage to the cooler.

c) The input power for maximum efficiency of a cooler does not correspond to its maximum oper

voltage and current. When maximum efficiency is desired, the applied power should be typically

2/3 of the Vmax and Imax specifications of the module(s) used in the assembly.

d) If a temperature controller is used, it should be of the linear type or the pulse-width-modulated

(PWM) type to minimize any detrimental effects of temperature cycling. Care should be taken to

PWM frequency that is fast enough so that no thermal cycling is induced within the device. TE

Technology's controllers use a frequency range from approximately 300 Hz to 3,000 Hz.

Back to the top

12. How precisely can a thermoelectric cooler maintain temperature?

There are many factors that contribute to or detract from the overall system stability. However, a

thermoelectric cooler can provide a very high degree of temperature stability because the amount

cooling it provides is proportional to the applied current. One of our customers has reported stabil

within +/-0.0003 C. Achieving that level of stability requires considerable effort though. Ultimat

the answer to this question is a function of the controller and its resolution, the response time of t

specific cooling assembly, and the response time of the object being cooled.

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13. What temperature ranges can a thermoelectric cooler achieve?

The vast majority of applications involve temperature differences of less than 60 C across the T

module, and less than 45C from the cooled object to ambient. One custom application we built

involved cooling down to 145 K. However, that required very special efforts to achieve a miniscu

amount of heat pumping. In any case, the temperature range will depend on a variety of factors,

principally on the number of stages. By stacking modules one on top of another, each module, or

acts like an electronic heat sink for the module above it. As the number of stages increases, theachievable temperature difference also increases. Unfortunately, the heat pumping capacity decre

Back to the top

14. What ambient temperature environments do thermoelectric coolers withstand?

The maximum ambient temperature will depend on the desired reliability, the heat sink, how muc

is being dissipated, and the temperature rating for the module or other system components (such

and insulating materials). Typically the maximum ambient temperature is limited to approximatel

C for standard coolers that use fan-cooled heat sinks. Coolers that use high-temperature modules

able to operate at higher ambient temperatures though. However, most commercially available fa
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have a maximum operating temperature of -10 C to +70 C. Be sure to consult with us to verify

whether operating in higher ambient temperatures is possible.

Back to the top

15. How do I determine if thermoelectric cooling is best for my application?

Thermoelectric cooling is ideal for very small cooling systems. Thermoelectrics are also ideal wh

both heating and cooling is needed and when precision temperature control is required. Thermoel

systems are also ideal for aerospace applications because the cooler can be mounted in any orient

and still function properly. However, as the heat load increases, the advantages that thermoelectri

cooling offer in comparison to compressor systems diminishes. When evaluating on the basis of

load alone, a compressor system will likely be more cost effective when the heat load is greater t

approximately 200 W.

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16. Why should I have TE Technology manufacture a system for my application?

TE Technology has technical expertise in all relevant disciplines applicable to thermoelectrics. O

forty years of thermoelectric experience go into every product. In addition, we have specialized t

equipment unique to the thermoelectric industry that enables quick (inexpensive) and accurate tes

results on 100% of our products (clickherefor more information). We provide reliable, durable,

effective systems, and we provide them on-time. Our large inventory, state of art machining and

global resources provide added versatility from prototype to production manufacturing.

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17. What type of testing does TE Technology recommend?

TE Technology recommends that all products be tested under "worst-case" conditions in their act

simulated application. We want our customers to feel comfortable that the cooling system will m

of their suitability and reliability requirements. While we cannot tell our customers whether certai

products may be suitable or reliable for their specific requirements, we can and do test products a

collect data so customers can make informed decisions. TE Technology possesses extensive testi

equipment including: temperature-controlled chambers; high humidity enclosures; thermal cyclin

equipment; temperature measurement equipment; and, thermoelectric testers. TE Technology off

valuable testing services so your company does not have to "reinvent the wheel". Further, we canour customers in designing customized testing experiments for the products. Just give us a call, a

will be happy to discuss our various testing services and costs.

Back to the top

18. What kind of over temperature protection do I need?

If a cooling assembly is being purchased, we also recommend that over/under-temperature protec

utilized to minimize potential damage to the coolers during operation. This can happen if the liqu

liquid cooler) is allowed to freeze, or if the cooling medium (air, liquid, etc.) is reduced and the c

becomes overheated. Some customers use our standard temperature controllers, such as the TC-4
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which have over-temperature protection circuitry that may reduce the likelihood of such situation

occurring. Other customers choose to incorporate this protective circuitry into the power supply.

course, we at TE Technology are happy to assist our customers in choosing the type of protection

may be most effective for their systems. Please note that standard coolers are not equipped with

over/under temperature protection, unless otherwise specified. If it is not specified, it is the custo

responsibility to provide this protection, or to request that over/under temperature protection be

included. We have designed and integrated many of these safeguards into the products at our faci

Simply contact us to discuss your options.

Back to the top

19. How do Pulse-Width Modulated (PWM) controllers operate?

With PWM, power to the TE device is switched quickly "ON" and "OFF" at a constant frequency

creates a square wave "pulse" of power with a constant time period. The "ON" time, or pulse wid

be varied to create an average output voltage (Vaverage) that is required by the TE device to maithe set temperature (Figure 19.1)

Figure 19.1

The "ON" and "OFF" pulses occur so rapidly that the module does not have enough time to chantemperature in response to each electrical pulse. Instead, the module assumes a temperature differ

relative to Vaverage. When the controller is properly tuned thermal cycling is eliminated. Thus, t

controllers do not degrade the reliability of a module from thermal cycling in the same way that a

thermostatic or slow "ON-OFF" controller would.

All of TE Technology's controllers require some minimum voltage to operate the on-board

microprocessor. The minimum voltage can be anywhere from 9 VDC up to 50 VDC, depending o

controller. If the thermoelectric load can also be driven with this input voltage then only one pow

supply is needed for the application. All of TE Technology's standard thermoelectric cooling asse

are designed so that the assembly and a controller can operate from one power supply.


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When operating from one power supply the input voltage to the temperature controller will defin

output voltage during the "ON" portion of the waveform, and Vaverage will range anywhere fro

to V+ depending on the ratio of "ON" time to "OFF" time. In the waveforms shown above V+ is

to the input voltage from the power supply, and during the "ON" cycle of the waveform V+ will

applied across the thermoelectric load. Therefore, when using a single power supply you should c

an input voltage that is no greater than the Vmax of the cooling assembly or thermoelectric modu

If you are making your own cooling system from thermoelectric modules, the maximum operatin

voltage (the controller's input voltage) is usually no more than 75% of module's Vmax. Of course

you wire multiple modules in series or in a series-parallel combination, Vmax of the module syst

will be the Vmax of each module multiplied by the number of modules in series. In this case, the

voltage is generally no more than 75% of the module system.

What happens if you want to operate a thermoelectric module at a voltage that is less than what is

required to operate the controller's microprocessor? In this case you should use a temperature con

that allows the microprocessor and thermoelectric load to be powered by two independent power

supplies. In this configuration the microprocessor can be powered by a small, higher voltage suppthe thermoelectric load can be powered with a supply that, in theory, is as low as 0 V. Referring a

to the waveforms above this allows the user to select a V+ that is suitable for a low-voltage

thermoelectric load while still giving the microprocessor enough voltage to operate. All of TE

Technologys temperature controllers can be set up with two power supplies.

PWM controllers come in two basic varieties, and the difference between the two determines if th

controller can automatically reverse power to achieve both heating and cooling, or if it must be se

either for only cooling or only heating. In the basic cool only/heat only controller, there is a singl

transistor in series with the thermoelectric module and power supply (Figure 19.2). This transisto

as a switch, S, that either closes or opens to turn power on or off to the thermoelectric module. Th

needs to tell the controller if applying more power to the thermoelectric module will cause thetemperature sensor to get warmer or cooler. If the user wants to change the configuration of the

controller from cooling to heating, the wires going from the controller to the thermoelectric modu

must be physically reversed, and the controller needs to be reconfigured so that it knows that appl

more power now has the reverse affect on the sensor temperature. The benefit to this type of cont

that it is simple and less expensive.


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Figure 19.2

The second variety of controller is the bipolar controller. A bipolar controller has 4 transistors act

switches that can automatically reverse the direction of current flow to the thermoelectric module

circuit is known as an H-bridge, because the thermoelectric module and transistors form an "H" i

schematic.

In this type of controller, when all of the switches (labeled S1 through S4) are open no current flothrough the module (Figure 19.3). Closing switches S1 and S4 causes current to flow in one direc

(Figure 19.4). Alternately, closing switches S2 and S3 (S1 and S4 are now open) allows the curre

flow to be reversed (Figure 19.5). This type of control circuit is more complex and thus more

expensive, but it is the only practical solution when the application could require both heating an

cooling to maintain the desired temperature.


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Figure 19.3

Figure 19.4


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Figure 19.5

Back to the top

20. What are some considerations for using a liquid chiller?TE Technology's standard liquid coolers have been designed for cooling water and inert gasses. T

style of exchanger is ideal for low cost and high performance. It allows for a larger number of flo

passages than could otherwise be obtained with exchangers that use a single serpentine tube pressinto a plate.

There are some special considerations when using this style of exchanger. Any fluid you use in th

coolers will be in contact with anodized aluminum, copper, and the epoxy that is used to bond in

copper tubes. Certain fluids, additives, and corrosion inhibitors will erode the epoxy and corrode

metal surfaces. Therefore, if you plan to use any other fluids and/or additives, you should thoroug

test the unit under actual operating conditions and temperatures before designing it into your prod

make sure it will not be damaged. It should be noted that corrosion of the metal surfaces can be

detrimental not only to heat transfer but also to other components in the system. For example, co

saltwater in a marine aquarium may cause copper to be introduced into the water. This might har

even kill the fish, so this type of liquid cooler is not recommended for this application. In any cas

should test the cooler to verify its suitability for the application.

On a related note, the standard liquid coolers are pressure tested to 410 kPa (60 psi). However, it

recommended that operating pressures not exceed 205 kPa (30 psi). This should be kept in mind s

you inadvertently cool to below the freeze point of the water since water will expand as it freezes

this can potentially break epoxy joints or burst the copper tubing itself. You might also need to co

shipping and storage temperatures. If the cooler is not drained prior to storage or shipping, freezi

could occur and damage could result. Again though, if you use an additive to depress the standar

freeze point of water (or some other liquid), the additive should be tested for compatibility.

Thermal cycling can also potentially cause problems with the exchanger (as well as with the


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thermoelectric modules, which is addressed in a separate FAQ). The aluminum, epoxy, and copp

have different coefficients of thermal expansion. Consequently, rapid changes in temperature can

induce a thermal fatigue stress that can result in leaks.

TE Technology can replace the standard liquid exchanger in the cooling assembly with a liquid

exchanger in which the liquid would be in contact with only one material. We can offer exchange

have a single-piece stainless steel serpentine tube pressed into an aluminum plate. These exchang

be attached to some of our standard cold plates, effectively turning them into a liquid chiller. Als

custom device, the epoxy-bonded copper tubes in our standard liquid exchanger can be replaced

welded-on aluminum end caps and thread-in fittings for the fluid inlet and outlet. This technique

removes epoxy compatibility issues and thermal cycling issues from the exchanger consideration

Technology has also manufactured folded-fin liquid exchangers and liquid exchangers machined

solid block of material such as stainless steel or copper. If you are interested in custom devices pl

contact the factory.

Lastly, the standard performance rating for the liquid chillers is based on the assumption that watflowing at 1.6 L/min (25 gph). Performance will change if a different fluid is used and/or a differ

flow rate is used. Consult with TE Technology, and we can determine the performance under diff

operating conditions for you.

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21. What is the manufacturing test process for all cooling assemblies at TE Technology? TE Technology performs numerous tests at the component and system level to ensure the quality

consistency of the thermoelectric cooling systems we manufacture. Each step is a link in a chain

quality that has been developed from years of experience in making tens of thousands of cooling

assemblies.

The process starts by testing 100% of the thermoelectric (TE) modules for their thermoelectric

properties. Each module is tested on our own, custom-made thermoelectric testing system. This s

measures the thermoelectric material properties: electrical resistivity, thermal conductivity, Seebe

coefficient, and figure of merit. These measurements ensure that the semiconductors used in the

modules provide consistent thermal and electrical properties when used in a cooling assembly. T

system also checks the AC-resistance of the entire module. This check is important as it confirms

the solder connections within a module are not damaged. For example, a typical 127 couple mod

contains 254 thermoelectric elements and 508 solder junctions. If any one of these solder junction

breaks then the entire module will be useless. Furthermore, if more than one module is wired in s

then all of the modules wired in that series will be useless, too. It is important to remember that ha "dead" module in the system is much worse than if it were not there at all. Not only will the dea

modules fail to provide any useful cooling, they will also provide a path for heat leakage from the

side of the cooling assembly back to the cold side.

Next, the components of the cooling assembly are checked to make sure they have the physical

characteristics necessary to effectively transfer heat from the cold sink, through the TE module, a

then into the heat sink. To accomplish this, the physical parameters of the heat exchangers and th

modules are inspected. The surfaces of the heat exchangers are measured for flatness and surface

in the areas that contact the TE modules. If more than one module will be used in a cooling asse

the module heights are matched so no more than 0.025mm of height variation exists between the

modules are also checked to ensure the ceramic substrates are flat and parallel within specificatio


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Thus far in the process, the components have been inspected to ensure all of the components are

sufficient quality to be used in the assembly. However, this alone does not guarantee that a good

cooling assembly will result. There are still many problems that can arise during the assembly pr

The three main concerns and their test solutions are as follows:

1) One or more of the TE modules is inadvertently placed upside down in the cooler: TE modules

invariably have the wires connected to the hot side of the module. Without powering the module

the only way you can tell the hot side from the cold side of a module. When modules are being w

into a harness it is possible to inadvertently flip a module so that it heats instead of cools. This be

easier to do if the module is sealed with an epoxy, and the module is only slightly thicker than its

wires. Therefore, as the assembly is made the modules are placed on the heat sink and briefly po

with a low current. The assembler then verifies that the cooling sides of the modules are all in the

correct orientation by touching each module and making sure it is operating in the cooling mode

in the heating mode.

2) A TE module's wire has shorted to the heat sink or cold sink: If an excess ball of solder or a str

wire contacts the heat sink or cold sink, the voltage supplied to the thermoelectrics can be shorted

metal surfaces of the cooler thus causing a potentially dangerous condition for anyone touching t

device while it is powered. TE Technology verifies there are no electrical short circuits by measu

the high-potential resistance between the module's wiring and the exposed metal surfaces.

3) Inadequate thermal interfaces: Consider a typical cooling assembly where the cold sink, TE m

and heat sink are all clamped together using screws. The screws are torqued to a specific level tha

turn, translates to a specific compressive force on the module allowing intimate thermal contact

between the TE modules and heat-sink and cold-sink plate surfaces. However, if there is a burr in

of the tapped holes, if there is a deformed thread on the screw, if the screw is too long or the tapphole too short, the torque will not translate into the proper compression force. If there is a spec of

piece of hair hidden by the thermal grease the thermal interface will be ruined. Visual inspection

problem is nearly impossible; especially since usually a vapor-sealing gasket surrounds the perim

the modules. TE Technology has developed a unique thermal junction quality test to combat this

problem. Using the aforementioned thermoelectric test equipment, a small current is applied to th

thermoelectric modules and a temperature difference between the heat sink and the cold sink is cr

Then, the current is switched off and the temperature difference is allowed to decay. The TE mod

act as small power generators during the decay, so by monitoring the corresponding rate of voltag

decay the quality of the thermal interfaces within the assembly can be measured. The AC resistan

the cooler is also checked to make sure the solder junctions within the modules have not been da

during the assembly process.

These tests take only minutes to complete and are done on 100% of the assemblies made at TE

Technology. Because the thermal interface test is so fast it costs much less then a full performanc

which is the only other way to verify the thermal junctions in an assembly.

In summary, the following tests are performed for every assembly:

The thermoelectric properties are checked for every module.

The AC resistance is checked on every module to make sure the solder connections within th

module are not damaged.

The physical dimensions and finishes are checked for all components. The modules are checked for proper wiring polarity/orientation during assembly.


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The high-potential resistance between the module's wiring and the exposed metal surfaces is

to verify there are no electrical short circuits.

The thermal interfaces are verified so proper heat transfer is guaranteed.

The AC resistance of each completed assembly is checked to verify the solder connections w

the modules have not been damaged during assembly.Thus, by following this chain of steps TE Technology can ensure consistent performance for ever

cooling assembly we make. To read more about these test methods view the technical papers in t

downloadable publications section atdownloadable publications section.

Back to the top

22. How does the TE Technology module part number system work? TE Technology module part numbers consist of three different componentsthe category code, t

element configuration and the potting suffix.

There are five different two-letter category codes. The following is the list of the different modulcategories:

TE = Standard, Micro, & Multi-Stage

HP = High Performance

CH = Center Hole

VT = High Temperature

SP = Series/Parallel

The module category is followed by the element configuration. The element configuration is mad

of different numbers that are separated by a hyphen. The configuration can contain up to six diffe

numbers depending on the module category.

Generally, the first number specifies the number of couples per stage (see exception below), follo

by the width of the element (in mm) and the height of the element (in mm). For instance, the CH-

1.0-1.3 is a center-hole module that has 19 couples, with 1.0 mm wide and 1.3 mm tall elements.

example the 1.3 mm element height does NOT include the thickness of the copper conducting ba

soldered on each side of the element. The 1.0 mm and 1.3 mm dimensions are for the semicondu

element itself.

To help you keep the terminology understandable remember that an "element" is one of the

semiconductor blocks within the thermoelectric module. Elements are always used in pairs withi

module--one N-type and one P-type element. A "couple" is then formed from one N-type and on

type element connected in series (electrically). Thus, for every couple within the module there w

be two elements. Sometimes, for physical strength where the wires enter a module, a redundant

or P-type element will be added in the corner of the module, but these are not counted to increase

number of couples.

Additionally, some High Performance or High Temperature module might have a fourth number

to the element configuration, for instance the HP-127-1.4-1.5-72. This last number indicates the

of the material if it is greater than that which is used for the standard modules. Therefore, the DT

this case is 72C.

Exception: The element configuration is a little different for Multi-Stage
http://www.tetech.com/Downloadable-Publications.htmlhttp://www.tetech.com/Downloadable-Publications.htmlhttp://www.tetech.com/Downloadable-Publications.htmlhttp://www.tetech.com/FAQ-Technical-Information.html#tophttp://www.tetech.com/FAQ-Technical-Information.html#tophttp://www.tetech.com/FAQ-Technical-Information.html#tophttp://www.tetech.com/Downloadable-Publications.html


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modules. Here, the first number is the number of stages which is followed by the

number of couples per stage. The number of couples per stage is in parentheses.

The last numeral is the height of the element. For instance, the TE-2-(127-127)-

1.15 is a 2-stage module consisting of two 127 couple stages with an element

height of 1.15 mm.

The last component of the module part number is the potting suffix. A module can either have no

which indicates that this module is unpotted (TE-63-1.4-1.15) or it can have a capital "P" (TE-63-

1.15P) which signifies that this module is potted. This means that the module has a sealing comp

(http://www.tetech.com/Moisture-Protection-Ruggedizing.html) applied around the perimeter of t

module.

Back to the top

23. What is the best way to attach a temperature sensor when making temperature

measurements or when using a temperature controller?

Properly attaching a temperature sensor to any particular part is more complicated than it looks. P

review our technical guide:sensor attachment[Adobe PDF document].

Back to the top

Terms and Definitions

Ambient Temperature: Temperature of the air or environment surrounding a thermoel

cooling system; sometimes called room temperature.

Active Heat Load: The amount of heat being generated by something regardless

whether a temperature difference exists. For example, this cou

the waste heat from a powered electronic device. Typically, th

the input power of the device (voltage * current) minus any o

power. Another example is the heat produced by an exothermi

chemical reaction. See also "Passive Heat Load."

AC-Resistance (ACR): The electrical resistance of a thermoelectric module. The "AC

refers to alternating current and serves as a reminder that mea

with a typical ohm-meter (which uses a DC signal) will yield

erroneous results. Actually, even an AC ohm-meter can also yerroneous results (although not as severe errors compared wit

typical ohm-meters). Therefore, TE Technology uses speciall

designed test equipment to accurately measure this parameter.

BTU (British Thermal Unit): The amount of heat required to raise one pound of water by o

degree Fahrenheit at a standard temperature of 39.2 F and at

atmosphere pressure. 1 Btu = 1055 J.

CFM (Cubic Feet per Minute): The volumetric flow rate of a gas, typically air, expressed in t

English system of units. This generally refers to the amount o

passing through the fins of a forced convection heat sink.
http://www.tetech.com/Moisture-Protection-Ruggedizing.htmlhttp://www.tetech.com/Moisture-Protection-Ruggedizing.htmlhttp://www.tetech.com/Moisture-Protection-Ruggedizing.htmlhttp://www.tetech.com/FAQ-Technical-Information.html#tophttp://www.tetech.com/FAQ-Technical-Information.html#tophttp://www.tetech.com/docs/thermoelectric_temperature_controller_sensor_attachment_with_notes_on_thermocouples.pdfhttp://www.tetech.com/docs/thermoelectric_temperature_controller_sensor_attachment_with_notes_on_thermocouples.pdfhttp://www.tetech.com/docs/thermoelectric_temperature_controller_sensor_attachment_with_notes_on_thermocouples.pdfhttp://www.tetech.com/FAQ-Technical-Information.html#tophttp://www.tetech.com/FAQ-Technical-Information.html#tophttp://www.tetech.com/FAQ-Technical-Information.html#tophttp://www.tetech.com/docs/thermoelectric_temperature_controller_sensor_attachment_with_notes_on_thermocouples.pdfhttp://www.tetech.com/FAQ-Technical-Information.html#tophttp://www.tetech.com/Moisture-Protection-Ruggedizing.html


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COP (Coefficient of

Performance):

COP is the ratio of the heat removed (or added, in the case of

heating) divided by the input power.

DTmax: The maximum obtainable temperature difference between the

and hot side of the thermoelectric elements within the module

Imax is applied and there is no heat load applied to the modulThis parameter is based on the hot-side of the elements within

module being at 300 K. In reality, it is virtually impossible to

remove all sources of heat in order to achieve the true DTmax

Therefore, the number only serves as a standardized indicator

cooling capability of a thermoelectric module.

Electrical Resistivity: Electrical resistivity relates the amount of current an object wi

transmit through its volume caused by a voltage difference acr

that volume. Typical unit is ohm * m. Electrical resistivity is a

intrinsic property of a material. When multiplied by the length

object and divided by the cross sectional area of an object it yithe electrical resistance of the object.

Heat Pumping: The amount of heat that a thermoelectric device is capable of

removing, or "pumping", at a given set of operating parameter

Heat Sink/Cold Sink: A heat sink is a device that is attached to the hot side of

thermoelectric module. It is used to facilitate the transfer of he

from the hot side of the module to the ambient. A cold sink is

attached to the cold of the module. It is used to facilitate heat

transfer from whatever is being cooled (liquid, gas, solid obje

the cold side of the module. The most common heat sink (or c

sink) is an aluminum plate that has fins attached to it. A fan isto move ambient air through the heat sink to pick up heat fro

module. Another style uses a plate with tubing embedded in it

liquid is sent through the tubing to pick up heat from the mod

Imax: The current that produces DTmax when the hot-side of the

elements within the thermoelectric module are held at 300 K.

Material Specifications: Material Specifications, in the context of thermoelectrics, are

thermal and electrical properties of the semiconductors that he

define how the semiconductor will behave. These typically in

parameters such as Seebeck coefficient, electrical resistivity, a

thermal conductivity when specified for the N-type or P-typesemiconductor material. Once a thermoelectric (Peltier) modu

been assembled the material properties of the module can be t

as a whole.

When specified for a thermoelectric module the average prop

of all the elements within a module can be measured (using a

power test method) and used to project parameters such as DT

Imax, Vmax, and Qmax. Testing a module with a full power

thermal test would not be practical, since it would involve pla

the thermoelectric module in a cooling assembly and testing t

thermal performance of that assembly (time consuming,


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expensive). The material specifications for the module do not

completely define how the module itself will behave within th

assembly, since these material properties predict the thermal

performance of the semiconductor elements exclusive of the (

parasitic losses due to perimeter sealing (potting) and (2) thetemperature rises and drops across the substrates. For this reas

the predicted cooling curves will show a slightly lower values

maximum V, I, Q, and DT.

Passive Heat Load: The heat transferred by virtue of a temperature difference. For

example, this is the heat that enters through insulated cabinet

when the cabinet is colder than the ambient temperature. Anot

example is the heat from solar radiation.

Peltier Effect: The phenomenon whereby the passage of an electrical current

through a junction consisting of two dissimilar metals results i

cooling effect. When the direction of current flow is reversedheating will occur.

Qmax: The amount of heat that a TE elements can remove when ther

zero degree temperature difference across the elements within

module, the hot-side temperature of the elements are at 300 K,

the module is being powered with a current of Imax.

Seebeck Coefficient: The Seebeck Coefficient is a measure of the electrical voltage

potential that exists in an electrical conductor whose ends are

maintained at two different temperatures and current is not flo

It is an intrinsic property and has units of V/K. Thermocouple

for temperature measurement utilize this principle.

Specific Heat: The amount of thermal energy required to raise the temperatur

particular substance by one temperature degree. Typical units

J/kg/K.

Thermal Coefficient of

Expansion:

A measure of the dimensional change of a material due to a c

in its temperature. Common measurement units include centi

per centimeter per degree Celsius and inch per inch per degre

Fahrenheit.

Thermal Conductivity: Thermal conductivity relates the amount of heat an object will

transmit through its volume when a temperature difference isimposed across that volume. It is an intrinsic property and typ

units include W/m/K and Btu/h/ft/F. When multiplied by the

sectional area of an object and divided by the length of an obj

yields the thermal conductance of the object.

Thermal Interface: A physical interface between two objects through which heat i

conducted. In the case of thermoelectrics, this refers to the ph

connection the module has with the heat sink/cold sink. Usual

thermal grease is used between the module and heat sink.

Sometimes it might be solder. Other times, it might be a ther

conductive pad.


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Thermal Resistance: A measure relating a temperature rise per unit of applied heat.

mediums through which heat is conducted have an associated

thermal resistance. Common thermal resistances are heat sink

resistance and thermal interface resistance. Thermoelectric co

perform better with heat sinks having a low thermal resistanceThermoelectric Module: A semiconductor-based electronic component that functions a

small heat pump. By applying a low voltage DC power source

TE module, heat will be moved through the module from one

to the other. Therefore, one side will be cooled while the oppo

side will be heated. Consequently, a TE module can be used f

both heating and cooling.

Thomson Coefficient: If the ends of an electrical conductor are held at two different

temperatures, a voltage potential is created because there will

tendency for electrons at the hot end of the conductor to drift

towards the cold end of the conductor. When an external curreapplied, so that electrical carriers flow from cold end to the ho

the electrical carriers must absorb heat to maintain equilibriu

the temperature. If the external current was applied from hot t

cold, the carriers would release heat to maintain temperature

equilibrium. The Thomson Coefficient is a measure of the vol

per difference in temperature, and with the application of an

external current is a measure of the heat generated or absorbe

unit temperature difference per unit current.

Usually, the Thomson effect is intrinsic to the material. How

the Thomson effect can also be extrinsically applied to a cond

by varying the material properties along the length of theconductor. This can actually improve the cooling performance

compared to the usual isotropic material. The Thomson effect

really more complex than that described above. It is difficult t

into words what the mathematics accurately describe. For furt

details clickhere.

Vmax: The voltage that is produced at DTmax when Imax is applied

the hot-side temperature of the elements within the thermoele

module are at 300 K.

Figure-of-Merit (Z) The Z is a direct measure of the cooling performance of a

thermoelectric module. Z = S^2/R/K where S is the SeebeckCoefficient, R is electrical resistivity and K is the thermal

conductivity of the thermoelectric material. Z is temperature

dependent though, so, when comparing one module to another

must be based on the same hot-side temperatures.

Back to the top

Technical Information on Cooling Assemblies
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Instructions below are in Adobe PDF Documents. Most computers have Acrobat Reader already

installed. If yours does not you can get Adobe's free Acrobat