Far infrared heaters have a high radiation from the surface, so the surface temperature tends to be lower.
When receiving heat (electromagnetic waves), there are materials that reflect (reflectivity α), absorb (absorption rate β), and transmit (transmission rate γ), and the following calculation formula applies:
α + β + γ = 1
An ideal object that reflects nothing (0) and transmits nothing (0) while absorbing everything is called a black body.
In other words, 0 + 1 + 0 = 1
Since the reciprocal of absorption is radiation, an object with a radiation rate of 1 is called a black body.
The radiation rate is expressed in comparison to a black body, so the radiation rates of other materials are less than or equal to 1.
The closer the radiation rate is to 1, the closer it is to a black body, making it easier to emit thermal radiation.
To simply observe the differences in radiation rates among heating elements, one can measure the surface temperature of heating elements with the same shape and watt density (W/cm²).
The red line represents the surface temperature rise curve of a far-infrared heater with a radiation rate of 0.9, while the blue line represents that of a stainless steel heater with a radiation rate of 0.2.
【Trivia: Radiation Rate】
- Heating elements with a low radiation rate emit less radiation from their surface, and heat transfer occurs only to the air in contact with the surface.
→ They tend to store heat easily, causing the internal temperature to rise and the surface temperature to be high.
- In contrast, far-infrared heaters have a large amount of radiation from their surface.
→ They store less heat, resulting in a lower surface temperature.
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