Under what circumstances is it normal for the electric heating tube to become red

Under what circumstances is it normal for the electric heating tube to become red

The metal tubular electric heating element is protected by a metal tube shell; the inner spring-shaped alloy resistance wire is led out through the conductive metal lead rods connected at both ends, and the heat conduction and insulating medium magnesium oxide is filled between it and the shell armor tube, and is compacted , Its density is equivalent to that of granite, its thermal conductivity is equivalent to that of steel, and its insulation performance is equivalent to that of natural mica. When the lead rods at both ends are energized, due to the electrical function of the resistance wire, the heat is conducted and radiated outwards by the resistance wire-magnesium oxide dielectric layer-shell armor tube-air and shell armor tube contacts. Mainly conduct heat, supplemented by radiant heat. Under normal temperature and still air conditions, when the heat generation of the electric heating tube is relatively large and the conduction area is relatively small, when the surface power density of the heating zone of the metal shell armor tube is >2.8W/cm2, the conduction will be converted to radiant heat. It is more obvious, that is, the redness phenomenon commonly known as the electric heating tube. At this time, the surface temperature of the shell armor tube is> 500 degrees, and the surface color is dark red, and with the increase of temperature, the color becomes dark red, orange red, orange yellow, torch The direction of white and incandescent changed. The electric heating tube configured with the best material can run stably below orange-red, that is, the temperature resistance of the shell armor tube of 800-850 degrees. The electric heating tube is a power-type resistor, and heating effect is inevitable; when the surface power density of the heating area of the electric heating tube shell armor tube is too large, redness is inevitable. When the design target heat is positive effect, as long as the redness is helpful to the working condition control requirements and meets the overall system thread transfer, it is an optimized design, and redness is normal. When the design target heat is a negative effect, the load is generally adjusted by designing low surface load components or accompanied by water-cooled, air-cooled, and heat-dissipating devices. If this is the case, it is abnormal if the heat is still red. In addition, the surface load of the tubular heating element is uneven, and it is also abnormal to produce local overheating and redness.

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