Heating Element
1. Principle of Operation:
- A heating element consists of a heating resistor and associated components.
- When an electric current flows through the resistor, it generates heat.
- This heat production occurs due to the resistance encountered by the electric current as it passes through the material.
- Heating elements are commonly used in household appliances, industrial equipment, and scientific instruments for tasks like cooking, warming, or maintaining specific temperatures.
2. Materials and Resistance:
- The materials used in heating elements have high electrical resistivity.
- Pouillet’s law defines the electrical resistance of a uniform specimen of material based on its resistivity, length, and cross-sectional area.
- The resistance per unit length (Ω/m) of a heating element material is specified in standards.
- For example, ASTM standards dictate that wires greater than 0.127 mm in diameter should be held within a tolerance of ±5% Ω/m.
3. Power Density:
- Heating element performance is often characterized by its power density.
- Power density is the output power divided by the heated surface area.
- It is expressed in watts per square millimeter or watts per square inch.
- Elements with low power density tend to be more expensive but have a longer lifespan.
4. Types of Heating Elements:
Resistance Heater Wire:
- These are long and slender resistors with a circular cross-section.
- The diameter of resistance wire is often measured using systems like American Wire Gauge (AWG).
Ribbon Resistance Heating Elements:
- Made by flattening round resistance wire, resulting in a rectangular cross-section with rounded corners.
- Ribbon widths typically range from 0.3 to 4 mm.
In summary, heating elements play a crucial role in various applications, ensuring warmth, cooking, and precise temperature control.