FT-IR MEASUREMENTS OF EMISSIVITY AND TEMPERATURE DURING HIGH-FLUX SOLAR PROCESSING

The experimental capability to generate and utilize concentrated solar flux has been demonstrated at a number of facilities in the United St ates. To advance this research area the National Renewable Energy Labo ratory (NREL) has designed and constructed a versatile High Flux Solar Furnace (HFSF). Research is ongoing in areas of material processing, high temperature and UV enhanced detoxification, chemical synthesis, h igh flux optics, solar pumped lasers, and high heating rate processes. Surface modifications via concentrated solar flux, however are curren tly performed without the means to accurately monitor the temperature of the surface of interest Thermoelectric and pyrometric devices are n ot accurate due to limitations in surface contact and knowledge of sur face emissivity, respectively, as well as interference contributed by the solar flux. in this article, we present a noncontact optical techn ique that simultaneously measures the directional spectral emissivity, and temperature of the surface during solar processing. A Fourier Tra nsform Infrared (FT-IR) spectrometer is coupled to a processing chambe r at NREL's HFSF with a fiber-optic radiation transfer assembly. The s ystem measures directional emission and hemispherical-directional refl ectance in a spectral region that lacks contribution from solar flux. From these radiative property measurements during solar processing, th e spectral emittance and temperature at the measurement point can be o btained. The methodology, validation measurements, and in-situ measure ments during solar processing of materials are presented. Knowledge of surface temperature during solar processing is an important parameter for process control. Based on validation measurements for spectral em ittance, the temperature error associated with the novel instrument is less than +/-5 percent for surfaces of mid-range emittance. The error decreases for surfaces of higher emittance. This is far better than o ptical methods which are ''lost'' in terms of knowing the appropriate emittance for conversion of measured radiant intensity to temperature.