What is a Thermoelectric Cooler?

Abstract: Thermoelectric Cooler(TEC) is found in many applications that require precise temperature control. The small size of the TEC allows precision thermal control of individual components such as fiber optics, laser drivers, precision voltage references, or any other temperature-critical device.

The thermoelectric cooler refers to a component that uses the thermoelectric effect of semiconductors to produce cold energy, also known as a semiconductor cooler. Thermoelectric coolers have many uses. It can be used to make portable cold storage/heat preservation boxes, cold and hot water dispensers, and heat dissipation of electronic devices. The temperature-critical components are integrated with a TEC and a temperature monitor into a single thermally engineered module. An added bonus with TECs is the ability to heat, by reversing the current. At present, the main semiconductor materials used in coolers are bismuth tellurides. The impurity is added to form N or P-type semiconductor temperature difference component after special treatment.  Its work is characterized by cooling while heating.

Catalog

I Working Principle of Thermoelectric Cooler 

If the power supply is reversed, the temperature at the contact will change oppositely. This phenomenon is called Peltier Effect, also known as the thermoelectric effect. In 1821, Thomas Seebeck discovered that when two conductors of different materials were joined together in a loop, and a temperature differential was present between the two junctions, a current flowed through the loop. Twelve years later, J. C. Peltier demonstrated the opposite effect -- that by cutting one of the conductors in the loop and forcing a current through the loop, a temperature differential was observed between the two junctions.

Due to the materials available at the time, the resistive heat generated by the large currents involved dominated the Peltier effect. Today, with material advances, these junctions have become more practical for use as thermoelectric heat pumps performing the same function as fluorocarbon-based vapor compression refrigeration. While they are still not as efficient as vapor-cycle devices, they have no moving parts or working fluid and can be very small in size. The thermoelectric effect of pure metal is very small. If an N-type semiconductor and a P-type semiconductor are used to replace the metal, the effect will be much greater. After the power is turned on, electron-hole pairs are generated near the upper contact, so the internal energy is reduced, the temperature is lowered, and the heat is absorbed to the outside world. In this situation, the upper part is called the cold end. Due to the recombination of electron-hole pairs of the lower contact, the internal energy increases, the temperature rises, and the heat is released to the environment. In this situation, the lower part is called the hot end.

The temperature difference and cooling capacity produced by a pair of semiconductor thermoelectric components are very small. A practical thermoelectric cooler is composed of many pairs of thermoelectric components combined in parallel and in series, which is also called a thermoelectric pile. A single-stage thermoelectric pile can obtain a temperature difference of about 60°C, that is, the temperature of the cold end can reach -10 to -20°C. Increasing the number of thermoelectric pile stages can increase the temperature difference between the two ends. However, the number of stages should not be too many, generally 2 to 3 grades. When these composite thermoelectric components cover the ceramic tiles or other heat-conducting insulating materials, and an endothermic and exothermic effect is formed in the state of electrification. 

working schematic diagram

II Features of Thermoelectric Cooler 

A Thermoelectric cooler has the features of no noise, no vibration, no need for refrigerant, small size, lightweight, etc., and it is reliable in work, easy to operate, and easy to adjust the cooling capacity. However, its refrigeration coefficient is relatively small and power consumption is relatively large, so it is mainly used in occasions with small cold consumption and small footprints, such as the cooling of certain components in electronic equipment and radio communication equipment; some are also used for household refrigerators, but it is not economical. The thermoelectric cooler can also be made into a zero-point meter to ensure the zero-point temperature in the thermocouple temperature measurement.

III Technical Applications of Thermoelectric Cooler 

In the 1950s, with the rapid development of semiconductor materials, thermoelectric coolers gradually moved from laboratory to engineering practice, and they were applied in defense, industry, agriculture, medical and daily life, from a nuclear submarine air conditioning to probe used to cool infrared detectors. As a special cold source, thermoelectric coolers have the following advantages in technical applications: 

1. It does not require any refrigerant, can work continuously, and has no pollution sources, no rotating parts, and no rotation effect. It has no vibration, noise, and has a long life, easy installation.

2. Thermoelectric cooler has two functions: both cooling and heating. The cooling efficiency is generally not high, but the heating efficiency is very high, always greater than 1. Therefore, using one component can replace separate heating and cooling systems.

3. Thermoelectric cooler is a current-exchange component. Through the control of the input current, high-precision temperature control can be achieved. Combined with temperature detection and control means, it is easy to realize remote control, program control, and computer control, which is convenient to form an automatic control system.

4. The thermal inertia of the thermoelectric cooler is very small, and the cooling and heating time is very fast. When the hot end has good heat dissipation and the cold end is empty, the cooler can reach the maximum temperature difference in less than one minute.

5. The reverse use of thermoelectric cooler is temperature difference power generation. Thermoelectric coolers are generally suitable for power generation in medium and low-temperature areas.

6. The power of a single refrigeration element pair of a thermoelectric cooler is very small. However, if they are combined into a stack that is connected in series and parallel to form a refrigeration system, the power can be made so large that the cooling power can range from a few mill watts to tens of thousands of watts.

7. The temperature difference range of thermoelectric cooler can be realized from a positive temperature of 90°C to a negative temperature of 130°C. 

Through the above analysis, the application range of thermoelectric components includes cooling, heating, power generation. And cooling and heating applications are more common. There are the following aspects:

(1)Thermoelectric air conditioner

The semiconductor air conditioner is characterized by no refrigerant, low noise, changing the direction of DC. It can be transferred from refrigeration to heating operation, so it is suitable for air conditioning in a special environment, such as submarine, electronic communication vehicle, and so on, which do not allow refrigerant leakage. 

(2)Thermoelectric thermostat

The thermostat with semiconductor refrigeration is characterized by small capacity and high precision of temperature control and can be used in instruments and experimental instruments with high requirements. For example, the semiconductor zero meter and the semiconductor constant temperature water bath as the measurement datum of the semiconductor thermoelectric pile, their temperature control precision can reach 0.01K.

(3)Semiconductor refrigeration water dispenser

The water dispenser with semiconductor refrigeration is characterized by no refrigerant, compact structure of refrigeration system, and it is suitable for various occasions where to require lightweight and small size of a refrigerator and forbidden refrigerant leakage, such as semiconductor refrigeration water dispenser in Boeing aircraft.

(4)Medical Thermoelectric Cooler

The medical device with semiconductor refrigeration is characterized by compact structure and convenient use, such as frozen slicer, frozen anesthetic mattress, cataract extraction device, and skin disease cold therapy device.

(5)Thermoelectric dehumidifier

The air dehumidifier with semiconductor refrigeration is characterized by no refrigerant, low noise. It is suitable for special environments such as military warehouses, low-noise submarines, and underwater high-pressure tanks that do not allow refrigerant leakage.

(6)Thermoelectric heat pump

The heat pump with semiconductor refrigeration is characterized by low thermal inertia and convenient working condition conversion. General semiconductor air conditioners or semiconductor thermostats can be operated according to heat pump conditions.

Precision thermal control applications will continue to use TEC as a solution. TEC performance can be expected to continue to improve, making them a more attractive solution for a growing range of temperature control applications. TEC may even replace vapor-cycle refrigeration devices used to heat and cool homes. TEC drivers and thermal control loops have only begun to find practical applications.