Optical properties of single particles for solar heated fluidized beds

Abstract

Experimental investigations on the optical absorption properties of solid-gas solar receivers by Sandia National Laboratories in 1986 have shown some particles (e.g. Masterr Beads) as good candidates for failing curtain receivers or fluidized beds. Their experiments have shown the necessity for detailed investigations of single particles and ensembles since the optical properties play a vital role for effective absorption in the solar spectrum and as well as low heat losses in the infra-red. So far little has been done to investigate selective properties of candidate particles for solar applications since these involve tedious measurements of particles which in most cases have to be heated simultaneously to account for temperature-dependent optical properties. At the DLR in Stuttgart an optical laboratory has been installed with the aim to develop further instrumentation and measurement techniques for determining optical scattering and absorption properties of particulates of interest in fluidized beds. An electrodynamic levitator used to "electrically suspend" single charged particles in order to measure light scattering is presented. This technique allows the determination of optical constants from a spherical, chemically inert particle of unknown chemical composition. First measurements on an oil droplet and on a spherocarb are presented. © 1991.