Emissivity of a material is a measure of its ability to radiate thermal energy in comparison to a perfect black body. The three main techniques for measuring infrared emissivity are calorimetric, radiometric, and reflection methods. The most common application of emissivity is in non-contact temperature measurements using Infrared thermometers and pyrometers and for thermal imaging. The laboratory network of Infinita Lab, USA, offers this test to clients based in the USA and across the world.
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The emissivity of a material is a measure of its ability to radiate thermal energy in comparison to a perfect black body. Emissivity is computed, using the Stefan Boltzmann law, as the ratio of thermal radiation from the surface to thermal radiation from a perfect blackbody at the same absolute temperature and wavelengths, under the same viewing conditions. It is a dimensionless number, ranging from 0 (for a perfect reflector or white body) to 1 (for a black body). The emissivity value depends on the material and nature of the surface, as well as the wavelength.
The three main methods for measuring infrared emissivity are calorimetric, radiometric, and reflection methods. The calorimetric method is based on heating the sample and analyzing the dissipated Stefan–Boltzmann power. Radiometry measures the surface temperature using an infra-red thermometer. In reflective emissivity measurements, the intensity of the radiation reflected from a surface is measured by infrared (FTIR) and Diffuse Reflectance Infrared Fourier Transform (DRIFT) spectroscopy or by Attenuated Total Reflection (ATR).
The most common application of emissivity is in non-contact temperature measurements using Infrared thermometers and pyrometers and for thermal imaging. It is essential for thermal engineering of furnaces, heat transfer equipment, and building and equipment insulation calculations. Emissivity has been used to determine planetary temperatures and for space vehicle material and insulation design. Earth surface emissivity is important for thermal remote sensing used in climatology, meteorology, and oceanography.
Common Uses of Emissivity
Non-contact temperature measurement
Thermal engineering of radiative equipment such as furnaces
Insulation systems engineering
Design and quality control of coated glass, low emission flat glass and architectural glass.
Design of low emissivity coatings for glass including polymer composite coatings and liquid coatings with nanocomposites
Rapid thermal processing (RTP) is a technique of importance in the semiconductor industry that requires the measurement of emissivities
Radiometric Emissivity Imaging (REI) is a technique to detect open cracks on static and moving surfaces
Advantages of Emissivity
Allows non-contact temperature estimation
Enables precise thermal modeling and design
Wavelength and temperature correlation
Spot measurements are possible
Limitations of Emissivity
Interference from background radiation and transmitted radiation
Dependence on the nature and finish of the surface