Thermoelectric cooling uses the Peltier effect to create a heat flux between the intersections of two different types of materials. Peltier cooling, heating, or thermoelectric heat pumps are solid state heat pumps that transfer heat from one side of the device to another, with electrical energy consumption, depending on the direction of the current. Such instruments are also called Peltier devices , Peltier heat pumps , solid state coolers , or thermoelectric coolers ( TEC ). It can be used either for heating or cooling, although in practice the main application is cooling. It can also be used as a temperature control that heats or cools.
This technology is much less applied to cooling than vapor compression refrigeration. The main advantage of Peltier coolant compared to a vapor compression refrigerator is the lack of moving parts or circulating fluid, very long life, immunity to leakage, small size, and flexible form. The main disadvantage is the high cost and poor power efficiency. Many researchers and companies are trying to develop a cheap and efficient Peltier cooler. (See Thermocoupled materials.)
Peltier coolers can also be used as thermoelectric generators. When operated as a coolant, the voltage is applied across the device, and as a result, the temperature difference will increase between the two sides. When operated as a generator, one side of the device is heated to a greater temperature than the other side, and as a result, the voltage difference will build between both sides (Seebeck effect). However, a well designed Peltier cooler would be a mediocre thermoelectric generator and vice versa, due to the different designs and packaging requirements.
Video Thermoelectric cooling
Principle of operation
The thermoelectric cooler operates with a Peltier effect (which also uses a more general thermoelectric effect). This device has two sides, and when DC current flows through the device, it brings heat from one side to the other, so one side becomes colder while the other becomes hotter. The "hot" side is attached to the heat sink so that it stays at room temperature, while the cold side enters below room temperature. In some applications, some coolants can be combined into one for lower temperatures.
Maps Thermoelectric cooling
Construction
Two unique semiconductors, one n-type and one p-type, are used because they need to have different electron densities. Semiconductors are placed thermally in parallel with each other and electrically in series and then joined with thermal conduction plates on each side. When a voltage is applied to the free end of two semiconductors there is a DC current flow at the junction of the semiconductor junction which causes a temperature difference. The side with the cooling plate absorbs heat which is then transferred to the other side of the device where the heat sink is located. Thermoelectric Cooling, also abbreviated as TEC is usually connected side by side and flanked between two ceramic plates. Total unit cooling capability is then proportional to the number of TECs in it.
Some of the benefits of using TEC are:
- No moving parts so less care needed
- No chlorofluorocarbons (CFC)
- Temperature control in degree fractions can be maintained
- Flexible form (form factor); in particular, they can have a very small size
- Can be used in environments smaller or heavier than conventional cooling
- Long life, with mean time between failures (MTBF) exceeding 100,000 hours
- Can be controlled via input/current voltage changes
Some of the disadvantages of using TEC are:
- Only a limited amount of heat flux can be removed
- Relegated to an application with low heat flux
- Not as efficient, in terms of performance coefficients, as a vapor compression system (see below)
Performance
Single stage TEC will usually produce a maximum temperature difference of 70 ° C between the heat and the cold side. The more heat it moves using the TEC, the more inefficient, since TEC needs to remove the heat removed and the heat it generates from its own consumption power. The amount of heat that can be absorbed is proportional to current and time.
where P is the Peltier coefficient, I is the current, and t is the time. The Peltier coefficient depends on the temperature and materials produced by TEC.
In cooling applications, thermoelectric connections have about 1/4 efficiency compared to conventional means (they offer an efficiency of about 10-15% of the ideal Carnot fridge cycle, compared to the 40-60% achieved by conventional compression cycle systems (reverse Rankine systems using compression/expansion).) Due to this lower efficiency, thermoelectric cooling is generally used only in environments where solid-state properties (no moving parts, low maintenance, compact size, and insensitive orientation) exceed pure efficiency.
Peltier cooling performance (thermoelectric) is a function of ambient temperature, heat sink and heat sink performance, thermal load, thermopent geometry, and Peltier electrical parameters.
Requirements for thermoelectric materials:
- Narrow band-gap semiconductor due to room-temperature operation
- Heavy elements due to their high mobility and low thermal conductivity
- Large unit cell, complex structure
- Very anisotropic or very symmetrical
- Complex composition
Common thermoelectric materials used as semiconductors include bismuth telluride, lead telluride, germanium silicon, and bismuth antimony alloys. From bismuth telluride this is the most commonly used. New high performance materials for thermoelectric cooling are being actively researched.
Usage
Thermoelectric coolers are used for applications requiring heat removal from milliwatts up to several thousand watts. They can be made for applications as small as a beverage cooler or as large as a submarine or train car. TEC has a limited life time. Their health strength can be measured by the change in their AC resistance (ACR). When TEC becomes "old" or outdated, the ACR will increase.
Consumer products
Peltier elements are commonly used in consumer products. For example, Peltier elements are used in camping, portable cooling, cooling of electronic components and small instruments. The cooling effect of the Peltier heat pump can also be used to extract water from the air in the dehumidifiers. Camping type electric coolers/cars can usually reduce temperatures up to 20 ° C (36 ° F) below ambient temperature. The climate-controlled jacket starts using the Peltier element. Thermoelectric coolers are used to add heat sinks to microprocessors. They are also used for wine coolers.
Industrial
Thermoelectric coolers are used in many areas of industrial manufacturing and require a thorough performance analysis as they face tests running thousands of cycles before the industry's products are launched into the market. Some applications include laser equipment, thermoelectric or cooling air conditioners, industrial electronics and telecommunications, automotive, mini-refrigerators or incubators, military cabinets, IT enclosures, and more.
Science and images
Peltier elements are used in scientific devices. They are common components in the thermal cycle, which are used for DNA synthesis with polymerase chain reaction (PCR), a common molecular biology technique, requiring rapid heating and cooling of the reaction mixture for the primary annealing cycle of denaturation and enzymatic synthesis.
With feedback circuits, the Peltier element can be used to apply a very stable temperature controller that maintains the desired temperature in Ã, Â ± 0.01 Ã, Â ° C. The stability can be used in appropriate laser applications to avoid the laser wavelength drift when the temperature changes environment.
This effect is used in satellites and spacecraft to reduce the temperature difference caused by direct sunlight on one side of the plane by scattering heat on the cool side of the shade, where it is dissipated as thermal radiation into space. Since 1961, several unmanned spacecraft (including the Curiosity Mars rover) used radioisotope thermoelectric generators (RTGs) that convert heat energy into electrical energy using the Seebeck effect. These devices can survive for decades, as they are triggered by the decay of high-energy radioactive materials.
Photon detectors like CCDs in astronomical telescopes, spectrometers, or high-end digital cameras are often cooled by Peltier elements. This reduces the amount of darkness due to thermal noise. The dark count occurs when the pixel registers electrons caused by thermal fluctuations rather than photons. In digital photos taken at low light this happens as speckles (or "noise pixels").
The thermoelectric cooler can be used to cool the computer components to keep the temperature within the design limit or to keep the function stable during overclocking. Peltier coolers with heat sink or waterblock can cool the chips well below room temperature.
In fiber optic applications, where the wavelength of a laser or component is heavily dependent on temperature, the Peltier cooler is used in conjunction with the thermistor in the feedback loop to maintain a constant temperature and thereby stabilize the device wavelength.
Some electronic equipment intended for military use in the field is thermoelectrically cooled.
Identify
Most TECs have IDs printed on the cooled side.
This universal ID clearly shows the size, number of stages, number of pairs, and current rating in amps, as seen in the adjacent diagram.
See also
- Thermoacoustics
- Thermotunnel cooling
References
External links
- Thermoelectric in Curlie (based on DMOZ)
- tec-microsystems.com, Termoelektrik Cooler Basics - answers to the most common questions
- TEC FAQs in pictures, Cooling Thermoelectric FAQ - simple and quick answers in images
Source of the article : Wikipedia
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