Why the Heating Wire of an Electric Heater Needs High Resistance
The resistance of the heating wire in an electric heater is selected based on the set power. The higher the power, the lower the total resistance.
The resistivity of the heating wire has an appropriate range. If the resistivity is too high or too low, the heating wire would need to be very short or very long, very thin or very thick, which poses manufacturing and usage difficulties for heaters of various power levels.
An important parameter of the heating wire is surface power. If the resistivity is too high, when a certain current is applied, the surface power will also be high. Therefore, for low-power appliances, small diameter and small current are used, but the current magnitude depends on the resistance value, and the length and diameter of the heating wire are calculated accordingly.
Large industrial electric furnaces use heating strips to increase the surface area and ensure that the surface power does not exceed the limit. At the same time, to achieve high power, a sufficiently large current is required. Thus, the length, cross-sectional area, and shape of each heating strip are comprehensively considered.
Therefore, when designing an electric heater, the heating wire (or strip) used must take into account multiple factors related to power.
The power required by this heater
The allowable surface power of this material, the cross-sectional area of the heating wire (or strip), the length of the heating wire, and the shape of the heating wire (straight, spiral, zigzag, wound, etc.).
Some special heaters, such as electric blankets, require a large heat dissipation area and low unit power. If conventional nickel-chromium and iron-chromium-aluminum heating wires are used, extremely thin wires would be needed, making them impossible to manufacture. Therefore, electric blankets use manganese-copper wire, which has a much lower resistivity than iron-chromium-aluminum, thus providing sufficient length.
In fact, the required resistance and the thickness and length of the heating wire for such heaters become clear when compared with light bulbs of different sizes.
