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 designed 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 difficulties in manufacturing and using heaters of various power levels.
An important parameter of the heating wire is surface power. If the resistivity is too high, after passing a certain current, the surface power will also be high. Therefore, small-power appliances use small-diameter wires with small currents, but the current depends on the resistance, 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 ensure 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, multiple factors related to power must be considered for the heating wire (or strip) used.
The power required by this type of heater
The allowable surface power of this material, the cross-sectional area of the heating wire (strip), the length of the heating wire, and the shape of the heating wire (straight, spiral, zigzag, winding, 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, the wire diameter would need to be extremely thin, making it impossible to manufacture. Therefore, electric blankets use manganese-copper wire, which has a much lower resistivity than iron-chromium-aluminum, allowing sufficient length.
In fact, the resistance required by this type of heater and the thickness and length of the heating wire become clear when compared to the size of light bulbs.
