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topic 4576

What is Emissivity?


(2000)

I am looking for any information on "emissivity" or heat radiation properties of anodized aluminum. What is it and how can it be kept constant from load to load. A potential customer has told me that a difference of 0.2 can occur from load to load and this is to much of a difference. She needs assurance that this will not happen, but I can't do this if I'm not even familiar with the term.

Erin Lewis
anodizing - Calgary, Alberta, Canada


(2000)

Emissivity, generally indicated by Greek letter epsilon, and ranging from 0 to 1, is the ability of a body to receive or transmit heat power as infrared radiant energy.

The radiant power emitted by a body is proportional to its temperature to the fourth. An ideal "black" body has an emissivity = 1. For the real bodies the emissivity depends to a large extent on the surface finishing. For specular surfaces, emissivity can be as low as 0.03, for rough surfaces over 0.8.

Typically, emissivity of black anodised aluminum is 0.85.

Emissivity can be measured by means of suitable instrumentation.

Basics on the topic of power radiation can be found in every book of heat transmission; a lot of data can be found in many handbooks, e.g.edited from NASA or ESA.

pasquale cirese
- campi bisenzio - Italy

Infrared Thermometer


(2000)

Just a correction in the term "transmit" used by Pasquale. Transmit means a wave, e.g., IR, passing through without absorption, like in light transmitting through a glass. Then there is reflectivity. Most relatively smooth metal surfaces tend to reflect a substantial portion of the IR radiation. The ideal Black Body with emissivity of 1 absorbs all heat received and emits all of it. No transmission and no reflection (unless my fundamentals are questionable).

Mandar Sunthankar
- Fort Collins, Colorado


(2005)

Given a blackbody radiant cure zone for a paint finishing oven, if there is an area with clear metal (i.e., high "e" coating has been removed) will the (heated) surface / skin temperature be greater than surrounding area?

Cindy Dilworth
industrial / process air handling - Detroit, Michigan


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

Practical Temperature Measurement



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