A two‐wavelength pyrometer for temperature measurements in gas‐solids systems

Abstract

AbstractThe measurement of particle temperature in gas‐solids suspensions by conventional pyrometric methods is complicated by a lack of knowledge of the particle emissivity and the absorption strength of the cloud. Further difficulties may be caused by background re‐radiation, variations in geometrical factors and ‐ if the particles are undergoing chemical reaction ‐ rapid changes in the particle temperature. These difficulties can be eliminated if the radiant energies emitted by the particles at two different wavelengths (close in value) are measured simultaneously.A pyrometer based on this principle was designed and constructed for measuring temperatures both in the infra‐red (500–900 C.) and the visible (800–1200°C.) ranges. The radiation from the particles was passed through suitable pairs of monochromatic filters inserted in diametrical opposition into a metal disk rotating at speeds up to 8,000 r.p.m. The two alternating beams were focused on the cathode of a photoelectric cell, and the resulting voltages measured by means of a cathode‐ray oscilloscope. The instrument was used successfully in an investigation of the rate of reduction of small iron oxide particles in the presence of hydrogen at temperatures ranging from 500 to 1100°C.