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

The tubular electric heating tube is protected by a metal shell; The inner spring shaped alloy resistance wire is led out by connecting conductive metal lead rods at both ends, and the thermal insulation medium magnesium oxide is filled between the inner spring shaped alloy resistance wire and the shell armor tube. After densification, its density is equivalent to that of Huagang rock, its thermal conductivity is equivalent to that of steel plate, and its insulation performance is equivalent to that of natural mica.
When the lead rods at both ends are energized, due to the electrical power effect of the resistance wire, the heat from the heating tube manufacturer is transmitted and radiated outward from the resistance wire, magnesium oxide dielectric layer, shell armored tube, air, and shell armored tube contacts. Conduction heat is the main factor, while radiation heat is an auxiliary factor.
When the heat output of the electric heating tube is relatively high under normal temperature and still air working conditions.
However, when the conductive area is relatively small and the surface power density of the heating area of the metal protective sleeve is greater than 2.8 W/cm2, the change from conductivity to radiant heat is more obvious, which is known as the phenomenon of electric heating tubes turning red. At this point, the surface temperature of the sheath tube is above 500 degrees, and the surface color is dark red. As the temperature increases, the color changes to deep red, orange red, orange yellow, torch white, and incandescent white. The electric heating tube configured with Z excellent material can operate stably below orange red, that is, the shell armored tube can withstand a temperature of 800-850 degrees.
Electric heating tubes are power resistors that inevitably have heating effects; When the surface power density of the armor heating area of the electric heating tube shell is too high, it is inevitable that redness will occur. When designing the target thermal positive effect, turning red is normal for optimizing design as long as it helps to meet the requirements of working condition control and satisfies the thread transmission of the entire system. When the design target heat is negative, adjusting the load by designing components with low surface load or installing water cooling, air cooling, or heat dissipation devices. If it is still red, it is not normal. In addition, uneven surface load of tubular electric heating elements can cause local overheating and redness, which is also abnormal.
The theory of whether the redness of the electric heating tube is normal should be included in the entire target design process. Starting from customer needs and based on the definition of goals, establish the functions of the design components, determine the detailed tasks of the components, form design concepts, generate solutions, further analyze and optimize, complete experiments, achieve goals, and meet the market.