Under what circumstances is it normal for electric heating tubes to turn red

Under what circumstances is it normal for electric heating tubes to turn red

Metal tubular electric heating elements are armored with metal tube shells; The internal spring shaped alloy resistance wire is led out through a conductive metal lead out rod connected at both ends. It is filled with thermal conductivity and insulation medium magnesium oxide between the outer shell armor tube. After densification treatment, its density is equivalent to that of granite, its thermal conductivity is equivalent to that of steel plate, and its insulation performance is equivalent to that of natural mica.

When the two ends of the guide rod are electrified, due to the electrical work effect of the resistance wire, heat is conducted and radiated outward from the resistance wire, magnesium oxide dielectric layer, shell armor tube, air, and shell armor tube contacts. Mainly focused on heat conduction, supplemented by radiant heat.

Under normal temperature and static air conditions, when the heat generation of the electric heating tube is relatively large and the conductive area is relatively small, and the surface power density of the heating area of the metal shell armored tube is>2.8W/cm2, the transition from conductive to radiative heat is more obvious, also known as the redness phenomenon of the electric heating tube. At this time, the surface temperature of the shell armored tube is>500 degrees, and the surface color is dark red. With the increase of temperature, the color changes to dark red, orange red, orange yellow, torch white, and incandescent white directions. The electric heating tube with the optimal material configuration can operate stably below orange red, which is the temperature resistance of the shell armor tube at 800-850 degrees.

Electric heating tubes are power type resistors, which inevitably have heating effects; When the surface power density of the heating area of the armored tube of the electric heating tube shell is too high, it is inevitable to have a phenomenon of redness. When designing the target heat positive effect, as long as redness helps to control the working conditions and meets the overall system thread transfer requirements, it is considered an optimized design, and redness is normal. When the design target heat has a negative effect, the load is generally adjusted by designing low surface load components or installing water-cooled, air-cooled, or heat dissipation devices. If it still turns red, it is abnormal. In addition, the uneven surface load of tubular electric heating elements and the occurrence of local overheating and redness are also abnormal.

The question of whether the redness of the electric heating tube is normal should be placed throughout the entire target design process. Starting from customer needs and defining goals as criteria, based on this, establish the functions of design components, determine component details and tasks, form design concepts, generate solutions, further analyze and optimize, complete experiments, achieve goals, and meet market demands.

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