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Infrared Heating Basics

        This section of the technical manual is a summary of the physics involved in all infrared heating systems. The information can be used as an aid in calculating system power requirements as well as determining the feasibility of a given infrared heating application.

Infrared Energy:

        When infrared energy strikes an object it may be absorbed, transmitted, or reflected from the surface. The sum of the amount of energy absorbed, transmitted, and reflected must equal 100% of the total incident energy. An object is called a "blackbody" if it absorbs (or emits) 100% of incident infrared radiation.

1 = ρ + α + t

Where:
    ρ = reflectivity
    α = absorptivity
    t = transmissivity

Example: Infrared energy strikes an object that is 30% reflective, and 20% transparent, how much infrared energy is absorbed by the object?

1 = .30 + α + .20
α = 1 - .30 -.20 = .50 (or 50% )

        The term "blackbody radiation" was derived from an experiment in cavity radiation. A small hole was drilled into an object and light was focused into the hole. The hole (cavity) appeared to be black. Light that entered the cavity is trapped and absorbed into the object allowing no light to escape. Radiant energy emitted from a "blackbody" source is dependent only on the temperature of the cavity walls and is not at all dependent on any other characteristic of the source such as color.

Emissivity:

        A true "blackbody" source for industrial applications has not yet been developed. However, various radiant heating elements are available with a wide range of radiant efficiencies. The efficiency of a radiant heater is given by its emissivity value. Emissivity is defined as the ratio of the radiant energy emitted by an object at a given temperature and the radiant energy emitted by a "blackbody" at the same temperature.

                 W_s
e =     ^{_____________}
                W_bb

Where:
    e = emissivity of source
    W_s = Total radiant energy emitted from a source at temperature T₁
    W_bb = Total radiant energy emitted from a blackbody at temperature T₁

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