Efficient Thermal Measuring Method for the Determination of Solar Absorptance and Thermal Emittance of Thermal Control Surfaces

Abstract

For the determination of the solar absorptance as and the thermal emittance e optical methods are preferably utilized. These methods include both spectral reflectance as measurements and/or emission (e) measurements. as must be measured in the common range 0,3 m to 2,5 m and e in the range 5 m to 35 m with a better resolution than 10 nm. Additionaly in the above spectral ranges integrated reflectance measurements are know, for which special detectors are used. These optical measuring procedures are quite exact. They also yield information about a possible spectral selective behavior of surfaces.However, special measuring equipment is required. The known thermal (or calorimetrical) methods (1) require, that the test surfaces are in the thermal balance with their environment. For the as determination a suitable solar simulator with high constant ofthe entire measuring phase. Since these measurement intervals for reaching thermal equilibrium are very long, this is a fundamental disadvantage of the thermal method. The work presented in this paper demonstrates possibilities, to neglect the solar simulation for the determination of e completely and to shorten the irradiation times for the as determination drastically. Thus the requirement of the long term stability of the solar irradiation intensity no longer plays a dominant role.