Factors that determine the outer diameter of the resistance wire coil in the electric heating tube

What factors determine the outer diameter of the resistance wire coil in a heating tube? Below, we'll explain the factors that determine the outer diameter of the resistance wire coil in heating tubes:

1. Uneven Resistance Drop Rate in Heating Tubes

In heating tubes, the resistance wire is surrounded by magnesium oxide powder. The compression process after filling it with magnesium oxide powder reduces the porosity of the magnesium oxide, resulting in a 15-25% reduction in resistance. The influence of the coil's outer diameter on the resistance drop rate should be considered. Generally, a larger coil's outer diameter increases the resistance drop rate, which can also lead to unevenness. This unevenness needs to be reduced, as it directly affects the rated power.

2. Insulation Distance and Insulation Resistance in Heating Tubes

The insulation resistance between the resistance wire and the sheath at high temperatures is different from that at low temperatures. However, considering the insulation distance from the perspective of insulation resistance itself, the larger the distance, the higher the insulation resistance between the resistance wire and the sheath. From a heat conduction perspective, there is a certain limit. The insulation distance varies depending on the required insulation resistance and operating temperature, but if using high-quality magnesium oxide powder as insulation, a typical value of 1.5-3mm is appropriate.

III. Thermal Conductivity in Heating Tubes

The heat from the resistance wire in a heating tube is transferred to the sheath through the magnesium oxide powder, and then to the heated object. Generally, a coiled resistance wire is considered to have an outer diameter d. When wrapped with an insulating material of a certain thermal conductivity, the thickness of the material is determined to achieve optimal heat dissipation.