Active millimeter-wave pyrometer

Abstract

A 135 GHz heterodyne receiver with a rotatable graphite waveguide/mirror system has been implemented on a waste remediation DC arc furnace for internal surface temperature measurements. The linear temperature measurement range extends from <10 to approximately 15,000*C relative to ambient with a simultaneous capability to monitor surface reflectivity with the local oscillator leakage. Reliable and robust operation on a continuous 24 hour basis in a smoky, dirty furnace environment is demonstrated for a total of 5 furnace runs reaching a maximum temperature of 2200*C. Complete temperature profile measurements with approximately 5 cm spatial resolution clearly documented thermal gradients on the slag melt surface and refractory walls and ceiling for all operating regimes of the furnace. The unique active probing capability of this instrument provided additional real time information on melt surface turbulence, changing furnace wall emissivity, and millimeter-wave optic losses inside the furnace.1

Thermal return reflection method for resolving emissivity and temperature in radiometric measurements

“…The alumina brick is of a more porous nature than the laboratory grade alumina and therefore consistent with having a lower reflectivity (0.17) and lower refractive index (2.4). This is also consistent with earlier reflectivity measurements of 0.13 for this same brick material [2].…”

“…A hot lossy waveguide will partially compensate for viewed signal losses by its own emission. Consequently, a pyrometer measurement with a waveguide that degrades with temperature does not necessarily fall out of calibration [2].…”

“…An active millimeter-wave pyrometer has been demonstrated that can measure emissivity along with temperature [2] and was used to improve the accuracy of temperature profile measurements inside an arc furnace [3]. The main limitation of this work was that the leaked local oscillator signal used to probe the viewed emissivity was coherent.…”

Molten salt dynamics in glass melts using millimeter-wave emissivity measurements

“…Four probe electrode techniques requiring glass contact for conductivity measurements [6] are not reliable in a plant environment. In this report, we demonstrate the novel adaptation of active millimeterwave radiometry [7] to non-contact detection and monitoring of salt pool formation and its dynamics in a pilot scale joule-heated test melter.…”

Millimeter‐Wave Monitoring of Nuclear Waste Glass Melts ‐ An Overview

“…Another important advantage is the ability to fabricate efficient MMW melter viewing components from refractory materials. Application of MMW pyrometry to a dc arc furnace melter has been previously demonstrated [1].…”