Emissivity Caracterization in Stainless Steels Alloys for Application in Hidroeletric Turbines

Abstract:

Emissivity is the ratio between the radiant hemispherical power emitted by a real body, at an absolute temperature, and the radiant hemispherical power emitted by a black body at the same temperature. The energy emitted is proportional to the fourth power of the object ́s temperature. Emissivity may vary from 0 (reflected by a mirror) to 1.0 (black body theory). Studies are being carried out at the University of Brasilia to investigate the microstructural behavior of materials used in the repairing of hydroelectric turbines, after several thermal cycles of welding. These studies use thermographic techniques for monitoring the temperature and require that the correct emissivity value for specific materials and surface conditions are used in order to guaranty that the temperatures reported by the radiometric sensors are consistent with the actual temperatures. This study aims to validate an experimental methodology for evaluating the emissivity of the steel ASTM A 743 CA6NM and the AWS 410 NiMo as deposited by a GMAW process at temperatures ranging from 100oC to 1000oC. The experiment consists of heating a small sample of the material with an oxyacetylene torch while a thermocouple, welded on surface of the sample, an infrared sensor and a thermographic camera monitor the surface temperature. During the heating and the cooling process, the sample surface is protected from the air by an argon gas flow directed towards the visualized area. Results consistent with the reported in the literature for similar materials were attained and curves of the emissivity “versus” temperature for the tested materials were produced, providing a basis for proper thermographic temperature monitoring.

• Periodical: Applied Mechanics and Materials (Volumes 719-720)
• Pages: 3-12
• DOI: https://doi.org/10.4028/www.scientific.net/AMM.719-720.3
• Online since: January 2015
• Authors: Matheus Tabata Santos*, Palloma Vieira Muterlle, Guilherme Caribé de Carvalho
• Keywords: ASTM A 743 CA6NM, AWS 410 NiMo, Emissivity, GMAW, Thermographic Monitoring

References

[1] Bramson, M.A. Infrared Radiation, A Handbook For Applications: Plenum Press, N.Y. (1968).

[2] Çengel, Y. Heat Transfer: A Practical Approach. New York: Mcgrall-Hill, 2nd Edition. (2003).

[3] Flir Systems. Thermo Vision A40m Operator's Manual. Sweden. (2004).

[4] Incropera Et Al. Fundamentals Of Heat And Mass Transfer. John Wiley & Sons, 6th Edition. (2007).