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topic 1705

Emissivity Control or Coatings for Thermal Management


(1998)

I am looking for an inexpensive, portable emissivity measurement device. The only emissivity measurement device I have found to date costs over $25,000. I wish to spend less than 10% of that for a simple, portable multi frequency or infrared wavelength device.

... and suggestions for rapidly removing oxidation from a metal surface that has been exposed to high temperatures in order to reduce the emissivity of that surface. I am using Haynes 188 which I believe can easily be polished to a 0.2-0.3 emissivity, but when my hardware is installed in the test stand, it is difficult to access and maintenance is costly. I currently have only one reasonable suggestion, which is to use Scotch-Brite or similar product manually or with a cloth backing wheel on a grinder.

Another option open to me is to coat the surface with Zirconium Oxide for thermal insulation.

Mark Fitzsimmons
- Canoga Park, California
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Practical Temperature Measurement

(1998)

You are posing a fairly complex set of conditions that cover basics of both physics and material science. Let me ask you a simple question first. Why do you want emissivity lowered? Also, wouldn't zirconium oxide increase emissivity, I wonder.

There are several companies that provide nitride coating services. Check with www.svg.org or some of the vacuum coating/sputtering shops.

Mandar Sunthankar
- Fort Collins, Colorado


(1998)

A simple way of measuring the emissivity would be to heat the surface and a surface with a known emissivity to the same temperature as determined by a thermocouple. Then read the temperature of the two surfaces with a standard infrared pyrometer. The difference in the two infrared temperature measurements would be due to the difference in the emissivities of the surfaces.

Donald M. Mattox
Society of Vacuum Coaters
Albuquerque, New Mexico

Ed. note:
            Mr. Mattox is
            the author of -->



(1998)

What do you mean by emissivity and What will you accomplish by checking emissivity? I was reading the problem and answers. Why do you want to check the emissivity?.

Maroof Qurashi
- Crane, Indiana


(1999)

i would like to know what is emissivity value of cordierite. And, What measure equipment is for emissivity of cordierate and ceramic glass. I will appreciate your kind.

T.G. LIM
- South KOREA


Infrared Thermometer

(1999)

if you find a response to how to measure the emissivity of a surface, let me know please.

I have another question, is there a material (natural in preference) with a very known emissivity?

said dhimdi
university of Gent Gent, Belgium


(2001)

Low cost solution for the emissivity measurement is by reading the temperature of the surface by using the infrared thermometer and thermocouple. By applying emissivity correction, when the IR thermometer shows temperature equivalent to that of thermometer, the emissivity is known.

Please let me know how to measure the emissivity using FTIR.

J.P.Mangalhara
- Jodhpur, Rajasthan, India


(2001)

When measuring the emissivity of a surface, it is important to take into account the waveband of observation. Most commercial non-contact temperature measurement devices operate in either the 3 to 5 micrometer waveband, or the 8 to 12. Emissivity will vary with angle and temperature, as well. The method of setting the emissivity of an instrument so that its temperature agrees with that of a thermocouple works as long as the background source of infrared radiation (also called T ambient or T surroundings) is accounted for. It is possible to get false readings when using this method. For example, if you were observing a hot reflection off of steel, the total radiation from the surface would be more than you would expect to get from the same piece of steel when reflecting ambient or cooler radiation. In general, clean, specular, polished metals have very low emissivities. The emissivities tend to be slightly higher in the shorter wavebands.

A few references may help: Common Sense Approach to Thermal Imaging, by Gerald C. Holst., JCD publishing 2000, ISBN 0-8194-3722-0 ISBN 0-9640000-7-5, Winter Park FL 32789; Theory and Practice of Radiation Thermometry, edited by D.P. Dewitt and Gene D. Nutter, John Wiley & Sons 1988, ISBN 0-471-61018-6; Nondestructive Testing Handbook Third Edition, Volume 3, Infrared and Thermal Testing, Technical Editor Xavier P.V. Maldague, Editor Patrick O. Moore, American Society for Nondestructive Testing 2001, ISBN 1-57117-044-8.

Bernard R. Lyon Jr.
- Billerica, Massachusetts


(2003)

The only technology I am aware of for measuring emissivity directly was developed by Quantum Logic. Theirs is a patented method for determining absolute temperature by first determining the emissivity of a target surface and correcting for reflected radiance. Mikron manufactures a hand held instrument based on this technology that costs about $7000. Quantum Logic gives a good explanation of emissivity and their method of measuring it. If you will explain why you need to measure the emissivity of Haynes 188 I may have some other sources of information to recommend including ceramic coatings to prevent the oxidation, maintain a high or low emissivity, or a thermal barrier coating (usually zirconia) to lower the metal temperature.

Mack Hounsel
refractory materials - Houston, Texas


January 22, 2010

You can measure emissivity to a fairly high level of accuracy with an infrared camera such as those manufactured by FLIR. Search for the term "emissivity" on Youtube to learn more.

David Brown
infrared training - Billerica, Massachusetts



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