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Apparatus for Measuring Total Emissivity of Small, Low-Emissivity SamplesAn apparatus was developed for measuring total emissivity of small, lightweight, low-emissivity samples at low temperatures. The entire apparatus fits inside a small laboratory cryostat. Sample installation and removal are relatively quick, allowing for faster testing. The small chamber surrounding the sample is lined with black-painted aluminum honeycomb, which simplifies data analysis. This results in the sample viewing a very high-emissivity surface on all sides, an effect which would normally require a much larger chamber volume. The sample and chamber temperatures are individually controlled using off-the-shelf PID (proportional integral derivative) controllers, allowing flexibility in the test conditions. The chamber can be controlled at a higher temperature than the sample, allowing a direct absorptivity measurement. The lightweight sample is suspended by its heater and thermometer leads from an isothermal bar external to the chamber. The wires run out of the chamber through small holes in its corners, and the wires do not contact the chamber itself. During a steady-state measurement, the thermometer and bar are individually controlled at the same temperature, so there is zero heat flow through the wires. Thus, all of sample-temperature-control heater power is radiated to the chamber. Double-aluminized Kapton (DAK) emissivity was studied down to 10 K, which was about 25 K colder than any previously reported measurements. This verified a minimum in the emissivity at about 35 K and a rise as the temperature dropped to lower values.
Document ID
20110002985
Acquisition Source
Goddard Space Flight Center
Document Type
Other - NASA Tech Brief
Authors
Tuttle, James
(NASA Goddard Space Flight Center Greenbelt, MD, United States)
DiPirro, Michael J.
(NASA Goddard Space Flight Center Greenbelt, MD, United States)
Date Acquired
August 25, 2013
Publication Date
January 1, 2011
Publication Information
Publication: NASA Tech Briefs, January 2011
Subject Category
Man/System Technology And Life Support
Report/Patent Number
GSC-15697-1
Report Number: GSC-15697-1
Distribution Limits
Public
Copyright
Public Use Permitted.
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