Optical Measurement Techniques Applied to Solar Selective Coatings.

摘要

Optical measurement techniques have been developed for determining the solar absorptance,alpha /sub s/,and emittance,epsilon,of solar coatings. The optical equipment includes a Beckman DK-2 Spectroreflectometer and a Gier Dunkle Solar Reflectometer (Model MS-251) for alpha /sub s/measurements and a Gier Dunkle Infrared Reflectometer (Model DB-100) for epsilon measurements. Because all this equipment is designed to accommodate flat samples,special calibration and measurement procedures were developed for the determination of the optical properties of coatings deposited on cylindrical surfaces. In addition, a small zero offset associated with the MS-251is discussed,and its incorporation in the measurement procedure for this instrument is presented. The accuracy of the MS-251for measurements of the alpha /sub s/properties of black chrome coatings was determined to be better than +- 0.03absorptance units. Although the Gier Dunkle Infrared Reflectometer is designed to measure the room temperature emittance,two modifications of the instrument's capability are discussed. The first modification involves removal of an internally mounted polyethylene filter so that the measurement spectrum shifts to approximately a 100exp 0 C blackbody. The accuracy of the emittance values determined in this mode of operation is better than +- 0.02emittance units for the black chrome coating. The second modification replaces the polyethylene filter with a sapphire filter. In this operating condition,and when properly calibrated,the reflectometer can be used to determine the 300exp 0 C emittance of the black chrome coating. (ERA citation 02:058756)