ASTM E307-72(2002):

Standard Test Method for Normal Spectral Emittance at Elevated Temperatures

Developed by Subcommittee: E21.04

Book of Standards Volume: 15.03
“1. Scope

“1.1 This test method describes a highly accurate technique for measuring the normal spectral emittance of electrically conducting materials or materials with electrically conducting substrates, in the temperature range from 600 to 1400 K, and at wavelengths from 1 to 35 ?m.

“1.2 The test method requires expensive equipment and rather elaborate precautions, but produces data that are accurate to within a few percent. It is suitable for research laboratories where the highest precision and accuracy are desired, but is not recommended for routine production or acceptance testing. However, because of its high accuracy this test method can be used as a referee method to be applied to production and acceptance testing in cases of dispute.

“1.3 The values stated in SI units are to be regarded as the standard. The values in parentheses are for information only.

“1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.”

Title: STANDARDIZATION OF THERMAL EMITTANCE MEASUREMENTS. PART 5. NORMAL SPECTRAL EMITTANCE, 800-1400 K (ABSTRACT BELOW)
DOWNLOAD FULL REPORT IN PDF FORMAT

Corporate Author : NATIONAL BUREAU OF STANDARDS GAITHERSBURG MD

Personal Author(s) : Harrison, William N. ; Richmond, Joseph C. ; Shorten, Frederick J. ; Joseph, Horace M.

Handle / proxy Url : http://handle.dtic.mil/100.2/AD426846

Report Date : NOV 1963

Pagination or Media Count : 99

Abstract: Equipment and procedures were developed to measure normal spectral emittance of specimens that can be heated by passing a current through them, at temperatures in the range of 800 to 1400 K, and over the wavelength range of 1 to 15 microns. A data-processing attachment for the normal spectral emittance equipment was designed to (1) automatically correct the measured emittance for ‘100% line’ and ‘zero line’ errors on the basis of previously-recorded calibration tests; (2) record the corrected spectral emittance values and wavelengths at preselected wavelength intervals on punched paper tape in form suitable for direct entry into an electronic digital computer; and (3) to compute during a spectral emittance test on a specimen the total normal emittance, or absorptance for radiant energy of any known spectral distribution of flux, of the specimen. Working standards of normal spectral emittance having low, intermediate and high emittance values, respectively, were prepared and calibrated for use in other laboratories to check the operation of equipment and procedures used for measuring normal spectral emittance.

For your reference, there are several that deal with emittance that may be of interest to you.

For your convenience, they are on the IRINFO.org web pages at the following links:

www.irinfo.org/tip_of_week_2004.html#t02092004

www.irinfo.org/tip_of_week_2004.html#t04052004

www.irinfo.org/tip_of_week_2003.html#t09292003

www.irinfo.org/tip_of_week_2004.html#t08022004

www.irinfo.org/tip_of_week_2005.html#t09122005

www.irinfo.org/tip_of_week_2005.html#t09192005

www.irinfo.org/tip_of_week_2005.html#t09262005

www.irinfo.org/tip_of_week_2007.html#t05282007

Enjoy!

NASA Portable Infrared Reflectometer Designed and Manufactured

The optical properties of materials play a key role in spacecraft thermal control. In space, radiant heat transfer is the only mode of heat transfer that can reject heat from a spacecraft.

One of the key properties for defining radiant heat transfer is emittance, a measure of how efficiently a surface can reject heat in comparison to a perfect black body emitter.

Heat rejection occurs in the infrared region of the spectrum, nominally in the range of 2 to 25 micrometer.

To calculate emittance, one obtains the reflectance over this spectral range, calculates spectral absorptance by difference, and then uses Kirchhoff’s Law and the Stefan-Boltzmann equation to calculate emittance.

Portable infrared reflectometer for evaluating emittance. Photo from NASA

A portable infrared reflectometer, the SOC–400t, was designed and manufactured to evaluate the emittance of surfaces and coatings in the laboratory or in the field.

It was developed by Surface Optics Corporation under a contract with the NASA Glenn Research Center at Lewis Field to replace the Center’s aging Gier-Dunkle DB–100 infrared reflectometer.

The specifications for the new instrument include a wavelength range of 2 to 25 micrometer; reflectance repeatability of ±1 percent; self-calibrating, near-normal spectral reflectance measurements; a full scan measurement time of 3.5 min, a sample size of 1.27 cm (0.5 in.); a spectral resolution selectable from 4, 8, 16, or 32 cm^–1; and optical property characterization utilizing an automatic integration to calculate total emittance in a selectable temperature range.

The computer specified to drive the software is a laptop with a menu-driven operating system for setup and operation, a full data base manager, and a full data analysis capability through MIDAC Grams/32 software (MIDAC Corporation, Irvine, California).

Spectral scanning is achieved through the use of a Fourier Transform Infrared (FTIR) Michelson interferometer. In addition, the reflectometer’s size and weight make it conducive to portable operation.

Although most of the planned uses for the instrument are expected to be in the laboratory, some field operations are anticipated. The only requirement for field operation is a source of power (115 V alternating current).

NASA Glenn took delivery of this world-unique, portable infrared reflectometer in January 1999. It is a resounding success, and an evaluation of thermal control materials for NASA and aerospace customers is currently underway.

Find out more about this research.

Glenn contact: Dr. Donald A. Jaworske, (216) 433–2312, Donald.A.Jaworske@grc.nasa.gov

Author: Dr. Donald A. Jaworske

Headquarters program office: OSS (ATMS)

Programs/Projects: Space Power, ISS, Aerospace Industry

Emissivity & other infrared-optical properties FAQs at the evitherm website,
evitherm is the European Virtual Institute for Thermal Metrology

Click on the number below for an answer on the evitherm website…

C1. What is the emissivity of a surface?
C2. Why is emissivity important?
C3. How is emissivity used?
C4. Is it easy to measure emissivity?
C5. Is it possible to predict or calculate emissivity?
C6. What type of emissivity should I use for my application: total emissivity or spectral emissivity?
C7. What is the emissivity of painted metal surfaces and how does it depend on layer thickness?
C8. Which surfaces behave like a grey body?
C9. What is the emissivity of a layer of gas?
C10. Where can I find information on the emissivity of a given surface?
C11.How can I measure the emissivity of a surface using an IR-thermometer?
C12. What is the difference between emissivity and emittance?
C13. What is a radiant barrier?
C14. What is a low-e coating?
C15. What is low-e glass?
C16. What is a selective absorber?
C17. Is a knowledge of emissivity important for contactless temperature measurements?
C18. What is infrared thermography?

Effects of Preoxidation Treatments on Spectral Normal and Total Normal Emittance of Inconel, Inconel-X and Type 347 Stainless Steel

Authors: Wayne S. Slemp; NATIONAL AERONAUTICS AND SPACE ADMINISTRATION HAMPTON VA LANGLEY RESEARCH CENTER

Abstract:

The spectral/normal-emittance values of several oxidized surfaces prepared by varying the preoxidation treatments or oxidation time for inconel, Inconel-X, and type 347 stainless steel were determined at temperatures of 900, 1,200, l,500, and 1,800 F over a wavelength range of 1 to l5 microns. Polishing, grit blasting, etching, or combinations of these preparations were used as preoxidation treatments. These values were compared for 900 and 1,800 F to determine the effects of these treatments on the spectral-normal-emittance values. Significant effects of preoxidation treatments and oxidation times on the spectral normal emittances of oxidized inconel, Inconel-X, and type 3k7 stainless steel are presented. In general, if a grit-blasted surface is etched before being oxidized, the final oxidized surface will have a lower emittance but will be more adherent and uniform. Of the two types of grit used in this study, the coarser grit provided the higher emittance. Polishing provided the lowest emittance of all specimens tested. In the one set of tests in which oxidation time was varied (on the inconel specimens), increasing oxidation time increased the emittance; however, increasing the time beyond 2 hours produced no further effect.

The Optical Properties measurements laboratory at The USA National Institute of Standards & Technology (NIST), a part of the Optical Technology Division of the PHYSICS Laboratory has been developing a full spectral emissivity (emittance) measurement capability.

The laboratory has established high accuracy infrared reflectance and transmittance capabilities for wavelengths between 1 µm and 18 µm. Near normal absolute spectral reflectance and transmittance of both specular and diffuse samples can be measured from near ambient to 200 °C using a custom integrating sphere and Fourier transform (FT) spectrometer. Additional capabilities for specular samples include transmittance down to 10 K using an optical cryostat, as well as variable angle transmittance and reflectance using a custom goniometer and polarizers.

_{Layout of the NIST Setup for Direct and Indirect Infrared Spectral Emittance Measurements}

Spectral directional emittance can be determined indirectly form reflectance and transmittance measurements described on the NIST Page: Infrared Spectrophotometry. These capabilities have limits of temperature, measurement geometry and sample type.

To expand the spectral emittance capabilities, a separate facility has been developed for its measurement at NIST using the direct method of radiance comparison of the sample with a blackbody(BB) reference source.

The facility consists of a set of reference blackbody sources mounted on a motorized stage for selection; interchangeable sample heater/mounts on motorized translation and rotation stages; a removable visible/near-infrared integrating sphere for measuring the sample temperature above 500 K; and low scatter interface optics to image the 3 mm to 5 mm central region of the sample or BB source onto a water cooled field stop.

Each BB contains calibrated platinum resistance thermometer (PRT) or thermocouple (TC) temperature sensors.

The spectral emissivities of the BBs have been calculated using a Monte Carlo ray tracing algorithm with input of the measured spectral reflectance of the cavity wall materials or coatings.

_{Integrating sphere for non-contact temperature measurement with sample heater in place}

_{Heaters for Transparent (Left) and Opaque (Center) Samples; Heater (up to 600 °C) and Set of Samples for Emittance Measurements (Right)}

The sample emittance is determined through a series of measurement steps.

The first step is a measurement of the sample’s hemispherical-directional reflectance at the measurement temperature and at a single wavelength matched to the filter radiometer.

The second step is a relative radiance measurement of the sample to a BB at the same wavelength.

The third step is to compare the sample spectral radiance to that of the reference blackbody source as a ratio with the FTIR .

_{Three Steps of Spectral Directional Emittance Scale Realization}

Finally, here’s a few results:

_{Spectral emittance of SiC and Pt10Rh samples}.

References

• Infrared spectral emissivity characterization facility at NIST,
  L.M. Hanssen, S.N. Mekhontsev, and V.B. Khromchenko,Proc. SPIE 5405, 112 (2004).
• Temperature- and angle-resolved infrared spectral directional emissivity of SiC, Alumina, and Pt for temperatures up to 1000 °C, C.P. Cagran, L.M. Hanssen, M. Noorma, and S.N. Mekhontsev,Intl. J. Thermophysical Prop. (submitted 2006).
• Use of a high temperature reflectometer for surface temperature measurements,
  L.M. Hanssen, M. Noorma, A.V. Prokhorov, S.N. Mekhontsev, and C.P. Cagran, Intl. J. Thermophysical Prop. (submitted 2006).

Introductory Guide to Emissivity

This is an introductory page on the National Physical Laboratory (NPL) website in the UK.

It has several such sketches as on the left showing the concept of the “radiometric method” of emissivity measurement and discusses both the concepts and measurement methods used to quantify spectral and total emissivity values.

The page also features links to other resource materials on the subject and a list of reference books.

It is not an oxymoron, nor a quote from Yogi Berra.

Real Blackbodies do not exist, at least on Earth. Only approximations or simulations are real. We use them to calibrate IR Thermometers, Radiation Pyrometers and Thermal Imagers.

Technically they should have a spectral emissivity very close to 1.0. How close, you might ask? Read on.
Max Planck needed the concept of a perfect absorber of electromagnetic, thermal radiation to develop his theory of Thermal Emission of Radiation in 1899. Fortunately, Gustav Kirchhoff had already develped the foundation for them forty years earlier.

A perfect blackbody is perfectly absorbing to all the thermal radiation incident upon it. For that reason it had, necessarily, to be opaque and non-reflecting.

By logical reasoning, it was also clear that the same device had to be a perfect emitter of thermal radiation related to its absolute temperature, that is, temperature on the Absolute or Kelvin Temperature Scale.

There are several radiation equations or “Laws” that have been developed to describe the physics of thermal emission properties. They are well explained in a number of texts and shown in some detail in the online Hyper Physics website.

In an online Java applet, one can see visually also the three main radiation laws in graphic action; the temperature on the screen is shown on a column in a thermometer on the right side, and you can change it by clicking and/or dragging on it with your mouse.

If someone asks about the color of a blackbody, you can always refer them to this great set of webpages by Mitchell Charity at MIT.
They show both the temperature from 1000 K to 29,800 K (of course below about 700 K blackbodies actually look black to the human eye) . As can be seen on this page, red, white and blue blackbodies are possible!

There aren’t many 29,800 K blackbodies on Earth, but astronomers & AstroPhysicists see them all the time. How do you think they measure the temperatures of stars?

So, now you know, there can be both Red and Blue Blackbodies!

The devices used by calibration laboratories to calibrate and check the calibration of IR Thermometers, Radiation Thermometers and Infrared Thermal Imagers are not perfect (and seldom Blue, but often appearing Black, Red, Orange, Yellow and even White), but they can be very close to perfect.

The closer to perfection, the higher the cost of them also.

A blackbody having a spectral emissivity of 0.99 would have, at best, an error of about ± 1% in emitted thermal radiation or radiance, at a stable operating temperature and could be used to calibrate Infrared Thermometers.

The thermometers would be limited in their calibration uncertainty, since the radiance they emit would be uncertain to at least ± 1%.

Depending upon the radiance to temperature relationship for the temperature in question, that could mean a bigger or smaller effective temperature calibration uncertainty that could be assigned to a thermometer being calibrated.

That’s another issue for another time, but , if you can’t wait, one of the best explanations (and a lot more) that we have seen on that subject is in a 547 KB, downloadable PDF file from Land Instruments.

A NASA report by R. Kumar, dated Sep 1, 1977, available online and downloadable as a PDF document.

ABSTRACT:

The effects of temperature and emittance on the relative magnitude of reflected energy and emitter energy from a target including atmospheric effects was studied. From the calculations of energy reflected and emitted from a target including atmospheric effects using LOWTRAN 3 programs for midlatitude summer model, the following conclusions were obtained (1) At 3.5 micrometers q is considerably less than 1 except at high temperatures and for high emittance (2) at 4 micrometers q is of the order of magnitude equal to 1 for most targets and (3) at 4.6 micrometers, q is considerably greater than 1 at high temperatures and high emittance. In addition, incident atmospheric emission reflected from the target was found to be negligible except for targets having low temperature and low emittance.