Introduction to the Principle of Semiconductor Refrigeration
Abstract: This article introduces the principle of semiconductor refrigeration. Semiconductor refrigeration utilizes the Peltier effect of semiconductor materials to achieve the purpose of refrigeration. It has no rotating parts, high reliability, and can not only cool but also heat, which is applied in many fields.
Semiconductor refrigeration is also known as thermoelectric refrigeration, electronic refrigeration, or thermoelectric cooling. It uses P-N junctions composed of special semiconductor materials to form thermocouple pairs, generating the Peltier effect, and forming a refrigeration effect through direct current.
The Peltier Effect
When an electric current passes through a loop composed of different conductors, the phenomena of heat absorption and heat release will respectively occur at the joints of different conductors according to the different directions of the current. This was discovered by J.C.A. Peltier in 1834 and is called the “Peltier effect”.
When an electric current passes through a loop composed of different conductors, the phenomena of heat absorption and heat release will respectively occur at the joints of different conductors according to the different directions of the current. This was discovered by J.C.A. Peltier in 1834 and is called the “Peltier effect”.
The reason for the formation of the Peltier effect lies in that charge carriers move in the conductor to form an electric current. Since the charge carriers are at different energy levels in different materials, when they move from a high energy level to a low energy level, they release the excess energy. On the contrary, when they move from a low energy level to a high energy level, they will absorb energy from the outside (manifested as refrigeration).
The refrigeration effect of the Peltier effect mainly depends on the energy level difference of the two materials in which the charge carriers move, that is, the thermoelectric potential difference.
Pure metals have good electrical and thermal conductivity, but their refrigeration efficiency is extremely low, and the refrigeration effect is not obvious.
Semiconductor materials have extremely high thermoelectric potential, which can produce a good refrigeration effect, and the refrigeration efficiency is also acceptable, so they can be used to make thermoelectric coolers.
Thermoelectric Cooler
A thermoelectric cooler is composed of an N-type semiconductor and a P-type semiconductor, and the N and P are connected by conductors such as copper and aluminum.
After a direct current is connected in this circuit, energy transfer occurs.
The junction where the current flows from the N-type element to the P-type element absorbs heat and becomes the cold end, while the junction where the current flows from the P-type element to the N-type element releases heat and becomes the hot end.
The above process is reversible. If the direction of the current is reversed, the heat-absorbing end will be transformed into the heat-releasing end, and the heat-releasing end will be transformed into the heat-absorbing end.
Therefore, the thermoelectric cooler can easily complete the conversion between the functions of a refrigerator and a heat pump.
The heat absorption and heat release effects of semiconductor refrigeration are determined by the magnitude of the current and the number of pairs of N and P elements of the semiconductor materials.
Common semiconductor refrigeration sheets are usually composed of hundreds of pairs of NP element pairs to enhance the refrigeration and heating effects.
Generally, semiconductor refrigeration sheets use ceramic substrates, which have good thermal conductivity, insulation and withstand voltage, and their coefficient of thermal expansion matches that of the chip, thus improving the performance of the semiconductor refrigeration sheets.
Semiconductor refrigeration sheets are standardized industrial products.
Further improvements on this basis will contribute to the promotion and application of the refrigeration sheets.
By installing a heat dissipation plate and a cooling fan on one side of the semiconductor refrigeration sheet, the refrigeration and heating effects can be enhanced.
By changing the direction of the direct current, the switching between the refrigeration and heating functions can be easily achieved.
In this way, semiconductor refrigeration has been applied in many fields.
Compared with compression refrigeration, absorption refrigeration and other methods, semiconductor refrigeration has a relatively low efficiency, but its advantages are also quite obvious:
First, semiconductor refrigeration does not require refrigerants, has no pollution sources, no rotating parts, and there is no vibration or noise during operation.
It has a long service life and is simple to install.
Second, semiconductor refrigeration can not only cool but also heat, and the switching is convenient.
Third, through the control of the input current, semiconductor refrigeration can achieve high-precision temperature control.
Fourth, the thermal inertia of semiconductor refrigeration is very small, and the refrigeration and heating are rapid, with a short time to reach the rated effect.
Fifth, the power of a single refrigeration element pair in semiconductor refrigeration is very small, but they can be combined, and the capacity range of refrigeration equipment is very wide. Sixth, the temperature difference range of semiconductor refrigeration sheets is large, which can be realized from -130°C to 90°C. Based on the above advantages, semiconductor refrigeration is widely applied in the temperature control fields of electrical components, medical devices, experimental devices and other equipment.
In terms of civil applications, semiconductor refrigeration is widely used in refrigerated water dispensers, car refrigerators, tram air conditioners and other scenarios.
In addition, the reverse application of semiconductor refrigeration is thermoelectric power generation, which can also be used in medium and low-temperature power generation scenarios.
