The thermo-optical properties of some solar absorbers

Abstract

The solar absorbers in the utilization of solar energy are selected according to their thermooptical properties, environmental stability and fabrication costs. At low temperature applications, a suitable black dye may be used. We measured the dye used in Turkey and found that ithad an ?s value of 0.88 and ?{lunate}80 of 0.80, and graphite powder, which was more stable to environmental condition and temperature, had ?s value of 0.95 and ?{lunate}80 of 0.93. At medium temperature application low cost black nickel coating may be preferable and their ?s values were varied between 0.080 and 0.92 and ?{lunate}100 values between 0.08 and 0.50 depending on the coating variables. Black chromium coating may be also used for this purpose and they are stable up to 400°C depending on the preparation processes. Their ?s values varied between 0.88 and 0.96 and ?{lunate}100 between 0.080 and 0.22. For high temperature applications, textured chromium surfaces prepared by PVD technique have a promising future and have ?s values of 0.80-0.90 and ?{lunate}100 values of 0.10-0.30 depending on the coating variable. The dependence of thermo-optical properties of the above surfaces to temperature were discussed. As we know ?s values do not depend upon temperature. The variation of ?{lunate} with temperature were calculated from near normal hemispherical reflectance data which has some effect on the design of solar collectors. © 1987.