A transient heat transfer model is formulated for a shrinking packed-bed of reacting ZnO particles exposed to concentrated solar irradiation. The model combines conduction, convection, and radiation heat transfer with simultaneous sintering and reaction kinetics. Validation is accomplished in terms of temperatures and dissociation rates experimentally measured using a solar-driven thermogravimeter with ZnO packed-bed samples subjected to solar flux concentration ratios ill the range 1225-2133 suns and surface temperatures in the range 1834-2109 K. Operating conditions are typical of an ablation regime controlled I v the rate of radiative heat transfer to the first layers of ZnO undergoing endothermic dissociation. (C) 2009 American Institute of Chemical Engineers AIChE J, 55: 1659-1666, 2009