When the existing conditions have determined that the thermal resistance of the PTC heater is difficult to overcome significantly, the thermal resistance is inversely proportional to the heat conduction area of the component and proportional to the heat transfer thickness of the component-when the component is PTC material or other heat-generating material, if it is The heat source is presented in a thin layer, which can be regarded as an isothermal heating element with low thermal resistance. In other words, the method of surface heating makes the PTc heating element and other surface heaters low in thermal resistance, high-efficiency high-power or high-temperature heaters are mainly formed by the components or media between the surface heating element and the heated thermal load Overcoming thermal resistance.
However, after the same electrical strength material is made into a thin PTC sheet, the breakdown voltage of the element may be reduced very low. When the electrode is coated in the traditional manner, the applied operating voltage will be limited. The interdigital electrode gap can be determined by factors such as the volume resistivity of the material, the applied working voltage and the final thermal effect. To enhance the electrical strength of the surface, the interdigital electrode can be covered with a layer of high insulation and high temperature protection membrane. In any case, the entire heater from the heat source component to the surface of the heating plate is expected to have high thermal conductivity. A heater with an area of about 50cm2 has a total Q value of 0.3C / W. However, the value of the general heat transfer heater with similar structure is usually about 2.5 ℃ / W. The degree of obvious difference indicates that the temperature difference between the heat source PTC element and the heater heat transfer plate is high, but the heating power is small. In this case, if other factors (curie point of PTC element, electric strength, material of heater components, etc.) are not properly coordinated, the failure rate of the heater increases. Use PTC heating element surface to generate heat, dissipate heat, fast heat, small heat capacity, its temperature rising characteristic is good, and save electricity.
Experiments show that the heating power of the sheet surface heating heater can be considered from the following aspects:
(1) Curie point of PTC material
(2) Volume resistivity of PI'C material
(3) Heat load of heater.