Spatially resolved solid-phase temperature characterization in a sillimanite tube furnace using a broadband two-color ratio pyrometry.

Tube furnaces are heating devices used for the synthesis of inorganic and organic compounds. It is essential to predict the spatially resolved temperature of solid substances placed inside tube furnaces in contact with its walls for a fixed steady temperature of the furnace walls. This enables efficient study of transport phenomena and control of the fabrication process in the furnace. In this work, the two-color ratio pyrometry (TCRP) using a digital single lens reflex camera has been used for the temperature characterization of a stainless steel metal sheet placed at the center of a 1000 mm long tube furnace. Temperature was measured for furnace walls set between 1000 K and 1426 K. The TCRP technique accounted for intensity from the heated target over the broadband visible region. The camera was calibrated and tested for signal linearity in its color channels for a fixed source illumination. The technique yields a mean sheet temperature of 979.5 K ± ∼24% (attributed to camera noise and uncertainties in gray level intensity, calibration lamp output, and monochromator and photodetector efficiency) and 1391 K ± 6.7% for a furnace wall temperature of 1000 K and 1426 K, respectively. Experiments showed that the effect of distance between the target and the camera on temperature measurement was negligible. Emission spectroscopy in the vis-near-infrared region (650-1100 nm) was also performed to predict sheet temperature. It yields results within 4.5% of TCRP at low furnace temperature but deviates by about 8.6% for temperatures above 1150 K, most likely due to experimental errors in spectroscopy. Analytical heat balance on the sheet, IR imaging, and numerical simulations yield temperatures within 5% of TCRP. This work shows that the TCRP technique can be used for spatially resolved temperature measurements of metals in tube furnaces and can readily be extended to ceramics or other class of solid materials whose emissivity can be shown to be invariant with wavelength in the visible region.