Emissivity of aluminum-oxide particle clouds: Application to pyrometry of explosive fireballs

Patrick Lynch, Herman Krier, Nick Glumac

Research output: Contribution to journalArticle

Abstract

Pyrometry measurements of clouds of high-temperature particles require an estimate of the spectral dependence of the particle emissivity. Common assumptions for this dependence range from ελ ∼ λ-2 to ελ ∼ constant. Depending upon the assumption used, there is uncertainty in the temperature of 100 s to a 1000 K in hightemperature clouds. Such errors are not apparent in goodness of fit of spectral data.A heterogeneous shock tube was used to measure the emissivity of aluminum oxide in an inert environment as a function of temperature (2000-3500 K), wavelength (0:55-0:95 μm), and particle diameter (50 nm-10 μm). In micro-sized alumina particles, the spectral dependence upon temperature transitions from decreasing with wavelength to increasing with wavelength with the dependence being roughly gray at about 3000 K. Because of local minima in the ελ vs λ curve, a power-law (λn) dependence is insufficient to describe the emissivity. However, if such a dependence is assumed, n transitions from -1.4 to 0.5 as temperature increases from 2500-3500 K. Nano-sized alumina particles exhibit an even stronger spectral dependence. At 2678 K, n is approximately -1:2 but reaches as high as 2.1 at 3052 K. Considering optical depth issues, there is merit in gray emissivity approximations for high-temperature (∼3000-3300 K) particles typical of aluminum particle combustion

Original languageEnglish (US)
Pages (from-to)301-308
Number of pages8
JournalJournal of thermophysics and heat transfer
Volume24
Issue number2
DOIs
StatePublished - Apr 1 2010

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ASJC Scopus subject areas

  • Condensed Matter Physics
  • Aerospace Engineering
  • Mechanical Engineering
  • Fluid Flow and Transfer Processes
  • Space and Planetary Science

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