Thermoelectric cooling

Thermoelectric cooling uses the Peltier eect to createa heat ux between the junction of two dierent typesof materials. A Peltier cooler, heater, or thermoelectricheat pump is a solid-state active heat pump which trans-fers heat from one side of the device to the other, withconsumption of electrical energy, depending on the di-rection of the current. Such an instrument is also called aPeltier device, Peltier heat pump, solid state refrigerator,or thermoelectric cooler (TEC). It can be used either forheating or for cooling,[1] although in practice the main ap-plication is cooling. It can also be used as a temperaturecontroller that either heats or cools.[2]

This technology is far less commonly applied to refrig-eration than vapor-compression refrigeration is. The pri-mary advantages of a Peltier cooler compared to a vapor-compression refrigerator are its lack of moving parts orcirculating liquid, very long life and invulnerability to po-tential leaks, and its small size and exible shape. Itsmain disadvantage is high cost and poor power eciency.Many researchers and companies are trying to developPeltier coolers that are both cheap and ecient. (SeeThermoelectric materials.)A Peltier cooler can also be used as a thermoelectric gen-erator. When operated as a cooler, a voltage is appliedacross the device, and as a result, a dierence in temper-ature will build up between the two sides.[3] When oper-ated as a generator, one side of the device is heated to atemperature greater than the other side, and as a result, adierence in voltage will build up between the two sides(the Seebeck eect). However, a well-designed Peltiercooler will be a mediocre thermoelectric generator andvice versa, due to dierent design and packaging require-ments.

1 Operating principle

Main article: Peltier eect

Thermoelectric coolers operate by the Peltier eect(which also goes by themore general name thermoelectriceect). The device has two sides, and when DC currentows through the device, it brings heat from one side tothe other, so that one side gets cooler while the other getshotter. The hot side is attached to a heat sink so that itremains at ambient temperature, while the cool side goesbelow room temperature. In some applications, multiplecoolers can be cascaded together for lower temperature.

Peltier element schematic. Thermoelectric legs are thermally inparallel and electrically in series.

Free convection thermoelectric cooler (Peltier cooler) with heatsink surface temperature contours, and rising warmer air andfalling cooler air ow trajectories, predicted using a CFDanalysispackage, courtesy of NCI.

2 Construction

Two unique semiconductors, one n-type and one p-type,are used because they need to have dierent electron den-sities. The semiconductors are placed thermally in paral-lel to each other and electrically in series and then joinedwith a thermally conducting plate on each side. When avoltage is applied to the free ends of the two semicon-ductors there is a ow of DC current across the junctionof the semiconductors causing a temperature dierence.The side with the cooling plate absorbs heat which is thenmoved to the other side of the device where the heat sinkis. TECs are typically connected side by side and sand-wiched between two ceramic plates. The cooling abil-ity of the total unit is then proportional to the number of

1

2 4 USES

TECs in it.Some benets of using a TEC are:

Nomoving parts so maintenance is required less fre-quently

No chlorouorocarbons Temperature control to within fractions of a degreecan be maintained

Flexible shape (form factor); in particular, they canhave a very small size

Can be used in environments that are smaller ormore severe than conventional refrigeration

Has a long life, with mean time between failures(MTBF) exceeding 100,000 hours

Is controllable via changing the input voltage/current

Some disadvantages[4] of using a TEC are:

Only a limited amount of heat ux is able to be dis-sipated

Relegated to applications with low heat ux Not as ecient, in terms of coecient of perfor-mance, as vapor-compression systems (see below)

3 PerformanceA single-stage TEC will typically produce a maximumtemperature dierence of 70 C between its hot and coldsides.[5] The more heat moved using a TEC, the less ef-cient it becomes, because the TEC needs to dissipateboth the heat being moved, as well as the heat it gener-ates itself from its own power consumption. The amountof heat that can be absorbed is proportional to the currentand time.

W = PIt

where P is the Peltier Coecient, I is the current, and tis the time. The Peltier Coecient is dependent on tem-perature and the materials the TEC is made of.Thermoelectric junctions are about 4 times less ef-cient in refrigeration applications than conventionalmeans (they oer around 1015% eciency of theideal Carnot cycle refrigerator, compared with 4060%achieved by conventional compression cycle systems (re-verse Rankine systems using compression/expansion).[6])Due to this lower eciency, thermoelectric cooling isgenerally only used in environments where the solid state

nature (no moving parts, low maintenance, compact size,and orientation insensitivity) outweighs pure eciency.Peltier (thermoelectric) cooler performance is a func-tion of ambient temperature, hot and cold side heat ex-changer (heat sink) performance, thermal load, Peltiermodule (thermopile) geometry, and Peltier electricalparameters.[7]

Requirements for Thermoelectric materials

Narrow band-gap semiconductors because of roomtemperature operation

Heavy elements because of their high mobility andlow thermal conductivity

Large unit cell, complex structure

Highly anisotropic or highly symmetric

Complex compositions

Common thermoelectric materials used as semi-conductors include bismuth telluride, lead telluride,silicon germanium, and bismuth-antimony alloys. Ofthese bismuth telluride is the most commonly used. Newhigh-performance materials for thermoelectric coolingare being actively researched.

4 Uses

A USB-powered beverage cooler

Thermoelectric coolers are used for applications that re-quire heat removal ranging from milliwatts to severalthousand watts. They can be made for applications assmall as a beverage cooler or as large as a submarine orrailroad car. TECs have limited life time. Their healthstrength can be measured by the change of their AC re-sistance. When a TEC gets old or worn out, the ACresistance (ACR) will increase.[8]

34.1 Consumer products

Peltier elements are commonly used in consumer prod-ucts. For example, Peltier elements are used in camping,portable coolers, cooling electronic components andsmall instruments. The cooling eect of Peltier heatpumps can also be used to extract water from the air indehumidiers. A camping/car type electric cooler cantypically reduce the temperature by up to 20 C (36F) below the ambient temperature. Climate-controlledjackets are beginning to use Peltier elements.[9][10] Ther-moelectric coolers are used to replace heat sinks for mi-croprocessors. They are also used for wine coolers.

4.2 Science and imaging

Peltier elements are used in scientic devices. They are acommon component in thermal cyclers, used for the syn-thesis of DNA by polymerase chain reaction (PCR), acommon molecular biological technique which requiresthe rapid heating and cooling of the reaction mixture fordenaturation primer annealing and enzymatic synthesiscycles.With feedback circuitry, peltiers can be used to imple-ment highly stable temperature controllers that keep de-sired temperature within +/0.01 Celsius. Such stabilitymay be used in precise laser applications to avoid laserwavelength drifting as environment temperature changes.The eect is used in satellites and spacecraft to counterthe eect of direct sunlight on one side of a craft by dis-sipating the heat over the cold shaded side, whereuponthe heat is dissipated by thermal radiation into space.[11]Since 1961, some unmanned spacecraft (including theCuriosity Mars rover) utilize radioisotope thermoelec-tric generators (RTGs) that convert thermal energy intoelectrical energy using the Seebeck eect, lasting severaldecades, fueled by the decay of high energy radioactivematerials.Photon detectors such as CCDs in astronomicaltelescopes, spectrometers, or very high-end digital cam-eras are often cooled down with Peltier elements. Thisreduces dark counts due to thermal noise. A dark countoccurs when a pixel registers an electron because of athermal uctuation rather than because it has received aphoton. On digital photos taken at low light these occuras speckles (or pixel noise.)[12]

Thermoelectric coolers can be used to cool computercomponents to keep temperatures within design limits,or to maintain stable functioning when overclocking. APeltier cooler with a heat sink or waterblock can cool achip to well below ambient temperature.In ber optic applications, where the wavelength of alaser or a component is highly dependent on temperature,Peltier coolers are used along with a thermistor in a feed-back loop to maintain a constant temperature and thereby

stabilize the wavelength of the device.Some electronic equipment intended for military use inthe eld is thermoelectrically cooled.

5 Identication

TE -C=standard

S=small

Size

Typically 1# of stages

(P-N couples) Highlydoped=more conductive

# of couples

Typically 6 to 9 ampsCurrent rating

Peltier elements all conform to a universal identication speci-cation

The vast majority of TECs have an ID printed on theirheated side.[7]

These universal IDs clearly indicate the size, number ofstages, number of couples, and current rating in amps, asseen in the adjacent diagram.[13]

6 See also Thermotunnel cooling Thermoacoustics

7 References[1] Taylor, R.A., Solbrekken, G., Comprehensive system-level

optimization of thermoelectric devices for electronic cool-ing applications, Components and Packaging Technolo-gies, IEEE Transactions on (Volume:31 , Issue: 1 )

[2] Thermoelectric Coolers Basics. TECMicrosystems. Re-trieved 16 March 2013.

[3] Frequently asked questions about our product. Tellurex.Retrieved 16 March 2013.

[4] http://www.engr.sjsu.edu/ndejong/ME_146.htm - Pow-erPoint under the Thermoelectric Coolers link

[5] The Heatsink Guide. Retrieved 3 May 2013.

[6] Brown, D.R.; N. Fernandez, J.A. Dirks, T.B. Stout(March 2010). The Prospects of Alternatives to Va-por Compression Technology for Space Cooling and FoodRefrigeration Applications. Pacic Northwest NationalLaboratory (PNL). U.S. Department of Energy. Retrieved16 March 2013.

4 8 EXTERNAL LINKS

[7] PCB Heaven - Peltier Elements Explained. PCBHeaven. PCB Heaven. Retrieved 1 May 2013.

[8] "- Usage Guide of Tec-Modules..

[9] Hsu, Jeremy (2011-06-14). Cold? Put this jacket on.Hot? Put this jacket on Climate-controlled coat goes fromzero to 100 degrees C 'in the ip of a button'". NBC News.NBC. Retrieved 16 March 2013.

[10] Ferro, Shaunacy (2013-03-15). How Winter Woes In-spired A Nanotech Fix For Everything From Cold NecksTo Knee Pain. Popular Mechanics. Bonnier Corp. Re-trieved 16 March 2013.

[11] Kotlyarov, Evgeny; Peter de Crom; Raoul Voeten (2006).Some Aspects of Peltier-Cooler Optimization Appliedfor the Glove Box Air Temperature Control.. SAE In-ternational: 1.

[12] Low Temperature Cooled Multi-Channel CCD DetectorSystem. ScienceTech. Retrieved 14 October 2013.

[13] Versteeg, Owen. Peltier Element Identication. Re-trieved 14 October 2013.

Thermoelectric Coolers FAQ in pictures - simple andclear answers for the most common questions

8 External links Thermoelectrics at DMOZ

59 Text and image sources, contributors, and licenses9.1 Text

Thermoelectric cooling Source: http://en.wikipedia.org/wiki/Thermoelectric%20cooling?oldid=653198465 Contributors: Rjstott,Rmhermen, Ahoerstemeier, Docu, Samw, Dfeuer, Robbot, Sanders muc, Sterlingda, Buster2058, BenFrantzDale, Tom k&e, Gadum, Be-land, NathanHurst, Discospinster, Nigelj, Kjkolb, Atlant, BRW, Stephan Leeds, SteveLetwin, Robbit, Feezo, Uncle G, Pol098, Bluemoose,Nanite, Seidenstud, Allen Moore, Karelj, Spincycle, Tone, Jasonwert, David R. Ingham, Klazuka, Dhollm, Fleet Pete, Elkman, Kkmurray,2over0, Morcheeba, Shawnc, Sbyrnes321, SmackBot, Telestylo, Thorseth, KVDP, Mdd4696, Gilliam, Michbich, Thumperward, Foogod,Snowmanradio, Lostart, CyrilB, Arkrishna, Peter R Hastings, JohnCD, Headbomb, Tchannon, Grandonia, Gkhan, JAnDbot, Adjwil-ley, Magioladitis, VoABot II, Damien Shiest, Ronchristie, Atropos235, Squids and Chips, Xenonice, Almazi, Mercurywoodrose, Hqb,Wcaswell, Sloggerbum, Isolm, Spinningspark, SieBot, Hustvedt, The Thing That Should Not Be, Mild Bill Hiccup, Thermomaster, Pixel-Bot, NFLDolphinsGuy, Kvongunten, Addbot, Mortense, Cantaloupe2, H92Bot, Glane23, DennisDallas, Brufnus, Yobot, AnomieBOT,Ma-terialscientist, Spike-from-NH, Sennaya, AtxApril, Idyllic press, TobeBot, Oivindhr, TigraXXX, Obsidian Soul, EmausBot, John of Read-ing, Bobkart, ZroBot, Sailmastersteve, DASHBotAV, ClueBot NG, Ynsark Navi, BG19bot, DeathMetalParrot, Piguy101, Loriendrew,Khjbxgx, Cibico9, Kobrapromotions, OwenVersteeg, Wellentech1981, Neacor1, Heatlord, Fluous, Prokaryotes, Ratdz70095, Monkbot,Eladhaber, Fang.liu761 and Anonymous: 96

9.2 Images File:CFD_Free_Convection_Peltier_Cooler.gif Source: http://upload.wikimedia.org/wikipedia/en/1/10/CFD_Free_Convection_

Peltier_Cooler.gif License: CC-BY-SA-3.0 Contributors:I created this model and CFD analysis for WikipediaPreviously published: http://www.novelconceptsinc.com Original artist:Heatlord

File:Peltier_IDs_explained.svg Source: http://upload.wikimedia.org/wikipedia/commons/4/47/Peltier_IDs_explained.svg License: CCBY 3.0 Contributors: Own work Original artist: Owen Versteeg

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Operating principle Construction Performance Uses Consumer productsScience and imaging

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