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لامپ هالوژن مادون قرمز
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Infrared Radiation (IR) is thermal energy (heat) transported by electromagnetic waves that travel at the speed of light. Infrared energy is the portion of the electromagnetic spectrum between 0.75 to 1,000 microns (see figure below. Energy emitted between 0.1–100 microns is thermal radiation (contains useful heat). Energy emitted between 0.39-0.78 microns contains heat and gives off visible light
IR
IR heat transfer occurs when a temperature difference exists between two bodies. Unlike convection and conduction heat transfer, IR does not require physical contact between the source and the target for heat to flow. Many gases such as air are nearly transparent to the IR. Consequently, IR has little heating effect on the gas, and the heat is transferred directly from the emitter to the product. This results in rapid, efficient heating of the product
Black Body Radiation
Infrared Radiation (IR) is not emitted at a single wavelength, but rather over a spectrum of wavelengths. The wavelength distribution is based upon temperature of the emitting source. In general, the higher the temperature, the shorter the overall wavelength. The graph below shows the difference in peak emission for two emitters at different temperatures
General Infrared (IR) Heating Equation
The amount of heat that is transferred between the heat source and the heated target is defined by the general infrared heating equation, as follows
Q/A = (Vf ) x (Es) x (At) x (K) x (Ts4 – Tt4)
The effect of each of these variables is shown in the table below
Variable | Definition | Comments |
Q/A | Heat flux per unit area | Heat transferred between source and target per unit area |
Vf | View factor | The view factor term is a fraction between 0 and 1 defines how well the the target sees the radiant energy. |
Es | Emissive factor of the source (0–1.0) | Most IR emitters (tungsten, nickel chromium) have emissivity values of 0.9 or greater |
At | Absorption Factor of the Source (0–1.0) | Absorptivity is dependent upon wavelength, color, material, surface condition and temperature affect absorption. |
K | Stefan-Boltzmann Constant | Radiant heating constant |
Ts | Absolute Temperature of the Source | Control variable in radiant heating |
Tt | Absolute Temperature of the Target | Temperature of the heated target |
The view factor and the absorption factor are two important variables for determination of a good infrared application