A Precise Calibration Technique for Measuring High Gas Temperatures

Abstract

A technique was developed for direct measurements of gas temperatures in the range of 2050K-2700K with improved accuracy and reproducibility. The technique utilized the low-emittance of certain pure, metal-oxide fibers whose diameters varied from 60 – 400μm in the experiments. The uncertainty of the technique was limited by the uncertainty in the melting points of the materials, i.e. ±15K. The abrupt increase in the emittance of the fibers upon melting was utilized as indication of reaching a known gas temperature. The accuracy of the technique was confirmed by both the fiber-diameter independence of the results and by the calculated low emittance values of transparent fibers, of order 0.01 al a few degrees below their melting point. This melting-point temperature was approached by increments smaller than 4K, accomplished by controlled increases of reactant flow rates in H²/air or H²/O² flames. As applications, the technique was used (a) for assessing the uncertainty in thermocouple measurements for inferring gas temperatures, and (b) for calibrating an IR camera to measure gas temperatures, thereby demonstrating its capability as an excellent calibration reference.

Keywords:

• Diagnostics
• Measurement techniques
• Optical measurement
• Thermocouple measurement
• Flames
• Heat transfer and radiation