Stainless steel material samples with different surface roughness values were investigated to determine their spectral directional emissivity at elevated temperatures up to 1200 K in the visible to near-infrared wavelength range and in the infrared around 4 μm. The emissivity measurements were accomplished by measuring the radiation from an appropriately designed test specimen in a furnace heating facility with optical access. Blackbody radiation, needed to determine the emissivity, was generated through a cavity in the specimen itself. During the time of measurement, the sample was shielded from the furnace radiation through a retractable cold radiation shield. In the visible to near-infrared wavelength range, the specimen was imaged on the entrance slit of a 500 mm focal length spectrometer, enabling simultaneous measurement of a sample normal to the viewing direction, the blackbody cavity, and a tilted sample. In the infrared, a FLIR camera was used to image filtered radiation around 4 μm. Surface roughness increased emissivity significantly in comparison to polished samples. The actual roughness values only had minor effects. Preoxidation of the samples caused a significant increase in emissivity for polished surfaces but had only minor effects for rough samples. The measured emissivities show only a weak variation with temperature.
|Number of pages
|Journal of Thermophysics and Heat Transfer
|Published - 2019
Bibliographical noteFunding Information:
This work was supported by an award from NASA Kentucky under NASA award number NNX10AL96H. Two authors were funded in part through U.S. National Science Foundation Grant CBET 1235759 for the year 2015. The authors would like to thank NASA Ames Research Center for providing test samples and technical guidance, Frank Hui from NASA Ames Research Center for lending the pyrometer, and Kozo Saito and Ahmad Salaimeh of the Institute of Research for Technology Development at the University of Kentucky for lending their FLIR infrared camera for this research. The authors would also like to thank Floyd Taylor and Herb Mefford, University of Kentucky, for their assistance in designing and machining many of the components necessary for this project and to Gregory Walden and Ricky Green, University of Kentucky, for their help in preparing, taking, and analyzing the data. Finally, the authors would like to thank Jay Grinstead and Megan Macdonald for their valuable comments and suggestions during the NASA review.
© 2019 American Institute of Aeronautics and Astronautics Inc. All rights reserved.
ASJC Scopus subject areas
- Condensed Matter Physics
- Aerospace Engineering
- Mechanical Engineering
- Fluid Flow and Transfer Processes
- Space and Planetary Science