Optical depth effects on aluminum oxide spectral emissivity

Joseph Kalman, David Allen, Nick Glumac, Herman Krier

Research output: Contribution to journalArticle

Abstract

Measurements of high-temperature spectral emissivities of aluminum oxide were made within a heterogeneous shock tube over the spectral range of 650-900 nm. The spectral emissivity of optically thin micrometer-scale alumina particles scaled approximately as λ-1.4 from 2800 to 3500 K. Results from optically thin clouds of nanoscale alumina showed that a λ-1.2 dependence, closertothe λ-1 predictedby the Rayleigh limit, is appropriate over the same spectral and temperature ranges. For temperatures below the melting point of alumina, the emissivity of nanoalumina shows a significant temperature dependence. The effect multiple scattering has on the apparent emissivity is studied, and it is determined to contribute to the discrepancy between the current and previous works. A Monte Carlo simulation showed qualitative agreement with the experimental work. It was found that, at small to moderate optical depths, scattering is responsible for a small change in the spectral distribution of particle emissivity. At large optical depths, absorption has a much stronger effect on the apparent spectral emissivity. It was determined that choice of optical depth can strongly affect the results of pyrometry measurements.

Original languageEnglish (US)
Pages (from-to)74-82
Number of pages9
JournalJournal of thermophysics and heat transfer
Volume29
Issue number1
DOIs
StatePublished - Jan 1 2015

ASJC Scopus subject areas

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

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