Development of Two-Color pyrometry for flame impingement on oxidized metal surfaces

Measuring the temperature on a metal surface exposed to flame impingement is valuable for studying heat transfer. In this study, a non-intrusive two-color pyrometry was developed. It utilized visible light cameras to measure the two-dimensional temperature distribution on different metal surfaces. The experiment involved measuring the temperature distribution of metals (stainless steel, titanium, molybdenum) ranging from 700 °C to 1200 °C under flame impingement conditions. Thermocouple measurements were used as a reference for accuracy and uncertainty assessment. Two monochrome visible-light cameras equipped with optical filters at wavelengths of 750 nm and 905 nm captured different signal intensities corresponding to relative radiation temperatures. Calibration using a black body furnace at multiple temperature points was performed to enhance measurement accuracy. The variation in correction factor was assessed for shutter speeds ranging from 0.01 s to 0.03 s. An uncertainty analysis accounted for factors such as the grey body assumption, monochromatic wavelength assumption, and thermal radiation sources, and the respective uncertainties for these factors were 4.72 %, 2.5 %, and 1.02 %. Despite the presence of severe oxidation layers on the surfaces being measured, the two-color pyrometer successfully detected surface temperatures within an acceptable margin of error; the maximum relative error between the pyrometer and thermocouples was less than 4 %. This paper presents a technique for measuring temperature that produces a two-dimensional temperature distribution. Additionally, this method mitigates the effects of changes in surface emissivity due to temperature or materials.