Mechanism of thermoelectric characteristics of the

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The mechanism of the thermoelectric characteristics of PTC electric heating elements

PTC electric heating elements have similar performance with general thermistors in the range below the to Curie point temperature, that is, the resistance value decreases with the increase of temperature. In general, for thermistors, the more the number of moving charges increases at high temperature, and they are mostly in a "hibernating state" at low temperature. Therefore, the higher the temperature is, the more energetic they are, and the more moving charges are, that is, the resistance decreases

The characteristics of PTC electric heating elements are displayed near the Curie point. This characteristic was initially speculated to be related to the phase shift of strong inductors. Later, in the test, the Curie point was transferred due to the mixing of trace impurities, followed by the abnormal impedance, and the corresponding temperature transfer began. From these phenomena, it is considered that PTC characteristics are fundamentally generated by the particle field, which is due to the phase shift from strong induction to constant induction. The special manifestation of strong induced electricity is the existence of spontaneous polarization. Polarization is based on the reversal of electric field, the hysteresis between polarization and electric field, and the high induced electric power in general. These particularities disappear when they reach the Curie point, and the induced electric power gradually disappears according to Curie Weiss law. For impedance anomalies, according to the particle field theory, there is a potential "mountain" (barrier) that hinders the movement of electrons on the crystalline particle field. When electrons want to cross this potential "mountain" and enter another crystal field from one crystal field, a visual explanation is used here, that is, in the strong induction region, this potential "mountain" is not too high, and electrons can easily cross it, However, when reaching the Curie point, the potential "mountain" immediately increases, and it is very difficult to cross it. At the same time, this explanation is the theory of sudden increase in resistance. As for the theory that the "mountain" increases when it reaches the Curie point, it is because the Curie point is used as the dividing line, and the induced electric power decreases sharply after it reaches the Curie point. At the same time, the spontaneous polarization effect has also disappeared. It is not difficult to cross the "mountain" of particle field in the strong induced electric area. The "mountain" near the Curie point rises sharply, and the "mountain" in the constant induction area is quite high, so it is difficult to overcome. Close to the Curie point, the slope is very large, and the "mountain" road is steep. As the temperature rises, the "mountain" gets higher and higher, and only one tenth of the load charge crosses the "mountain"

structural form of PTC electric heating element

① disc type PTC electric heating element. The appearance of disc PTC electric heating element is disc-shaped, which means that the surface of the element is heated and the object is heated by conduction. At first, this kind of element was only suitable for small and low-power electric heating appliances. Later, a high calorific element with heat sink was developed. At present, there are three types of disc PTC electric heating elements in common use: one is that the frequency of workers using the pressure tester is different, which is two of the elements; The surface is equipped with electrodes, which are connected with leads and supported by resin film; The other is that the two surfaces of the element are equipped with alumina ceramic sheets, surrounded by silicone rubber insulation, and equipped with lead terminals; Another kind is equipped with comb electrodes on both sides, and the thickness of the element is relatively thin

disc PTC electric heating element is the earliest type, which is suitable for foot warmers, heat preservation pots, mosquito repellents and other products

② honeycomb PTC electric heating element. The honeycomb PTC electric heating element is a kind of heating body with large calorific value and air heat transfer. There are two kinds of heating elements: round and square. Generally, the diameter of the round is 30~60mm and the thickness is 3 Mm, whose structure is equivalent to that a large number of hexagonal or other shaped through holes are opened on the disc type electric heating element. PCI indicates that the through hole density is 40~80 holes/c ㎡, and the grid wall thickness is 0.2~0.3m. The edge of the element is equipped with one or several aluminum spraying electrodes. When heating, forced ventilation is used for heat exchange, and the heat output can be adjusted by controlling the ventilation. In actual use, 2-5 electric heating elements are often assembled into a component, so that the heating power can reach 300-1200w. The honeycomb PTC electric heating element is suitable for large capacity air heating devices with large air volume and small volume, such as electric heaters, bedding dryers, electric combs, hair dryers, etc

③ harmonica PTC electric heating element. Harmonica electric heating element is also a kind of heating element for air heating device, which has many kinds, shapes and sizes. The basic structure is to assemble 20~40 thin and long heating elements side by side in the shape of harmonica, which are fixed and electrically connected by metal electrode plates to form a harmonica shaped heater. Its characteristic is that it does not need to change the overall size to adjust the calorific value, and different calorific values can be obtained by changing the number of pieces of the assembled components. When air passes through the gap of the sheet element, it can exchange heat with the element to obtain greater heat

this kind of electric heating element has the advantages of low pressure loss, voltage resistance, simple installation and adjustment, and is widely used, such as in four season air-conditioning greenhouses, various dryers, dehumidifiers and other products

④ belt PTC electric heating element. Two busbars (electrodes) are arranged in parallel in the center of the strip, and the core material made of PTC material is around the two busbars. The core material is coated with a layer of polyurethane and a layer of polyolefin as electrical insulator, which has good thermal radiation performance. The outermost part is coated with metal armor materials, such as steel wire, copper or stainless steel, to increase strength

the PTC material in such components and the polymer in the outer layer can be drawn together. This material can also be used to make sheet elements

In addition to the above-mentioned types, PTC electric heating elements also include foil type, round cable type, etc

main advantages of PTC electric heating element

the reason why PTC electric heating element can be rapidly developed and widely used as a new type of electric heating element [mainly because it has the following unique advantages.

① PTC element is a kind of solid element with two ends. It can be made into different shapes, structures and external dimensions by using ceramic technology, and the number of elements used can be determined according to different needs. It can be reasonably arranged in the limited space of the working system, which is easy to overcome the technical difficulties in assembly and insulation.

② constant temperature heating. The whole working system (including heating element, heat dissipation mechanism, working voltage and ambient temperature) after determination, the working temperature is close to constant

③ temperature limiting fever. When the whole working system is started, the maximum heating temperature of the system will be limited, because it has certain safety

④ automatic temperature compensation. When the system temperature fluctuates greatly due to external factors, PTC heater can quickly adjust the heating power, automatically compensate the positive and negative temperature and maintain constant temperature depending on the physical property change of the material itself

⑤ it can adapt to wide voltage fluctuations. If 220V voltage is used, the constant temperature can still be maintained when the voltage fluctuates by ± 20%

⑥ good safety. At present, the maximum surface temperature of various PTC components is lower than 400 ℃, and there is no open fire when heating, which is not easy to cause combustion

⑦ no oxidation, long service life. PTC components have been widely used because of the above advantages; It is especially suitable for some occasions with low temperature and low power. By selecting different PTC materials and components and designing different thermal systems, the working temperature can range from tens of degrees Celsius to more than 300 degrees Celsius, and the power can range from several watts to several kilowatts. (end will reach the kiloton level in the next 5 to 10 years)

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