EVALUATION OF PORTABLE OPTICAL PROPERTY MEASUREMENT EQUIPMENT FOR SOLAR SELECTIVE SURFACES

The operation and accuracy of portable optical measurement equipment for determining the solar absorptance, αs, and emittance, ϵ, of solar selective surfaces are presented. The optical equipment includes a Gier Dunkle Solar Reflectometer (Model MS-251) and a Willey Alpha Meter (Model 2150) for αs measurements and a Gier Dunkle Infrared Reflectometer (Model DB-100) and a Willey Ambient Emissometer (Model 2158) for ϵ measurements. The accuracy of the MS-251 for measurements of as for electrodeposited black chrome coatings was determined to be better than ±0.03 absorptance units. For the same coatings, the Willey Alpha Meter accuracy was limited by deviations up to 0.11 absorptance units. The accuracy of the Gier Dunkle Infrared Reflectometer for ϵ(100°C) measurements is better than ±0.02 emittance units. Values for ϵ(100°C) determined with the Willey Emissometer using black chrome coatings are higher than the actual 100°C emittance. However, since the relationship is linear, the correct emittance can be calculated by multiplication by a constant factor. © 1978 by ASME.