Sriram Kiran Annapragada, Department of Chemical & Petroleum Engineering, University of Wyoming, Laramie, WY 82072, M. P. Sharma, Chemical and Petroleum Engineering, University of Wyoming, Laramie, WY 82071, and William Lindberg, Mechanical Engineering, University of Wyoming, Laramie, WY 82071.
Fine solid materials at the nano and micro level are used in wide applications like catalysts, coatings, electronics, ceramics, superconductors, dyestuff, pigments, pharmaceuticals, food, etc. The properties of these fine scale materials are related to their particle size. A class of the current technologies to produce these fine scale materials employs many organic solvents as the process fluids which pollute the environment and could be potential contaminants. The biggest challenge in all these technologies is to obtain a narrow distribution of particle sizes. The development of a single scalable process that removes many of the constraints and limitations of the current methods is very essential. The Supercritical Fluid Assisted Atomization (SCFA) techniques are ‘Green Technologies' which do not pollute the extracts, residues, and also the environment in most cases. Several of these methods are known to produce particle size in the range of nano and micro meters with narrow particle size distributions.
An experimental examination of the influence of operating conditions in production of micronized powders using the Supercritical Fluid Atomization (SCFA) technology along with an investigation of the atomization processes in these sprays is presented in this work. A theoretical model to predict the choked flow conditions across the nozzle and the size of the particles produced is also discussed. The experimental investigation involved supercritical carbon dioxide system to produce spray dried powders and concurrently examine the atomization processes using a high speed high magnification photography technique. High speed photography techniques revealed a dominant atomization mechanisms in the decompressive supercritical sprays. Various operating conditions were used to produce spray-dried powders and the effect of each of them on particle size was investigated. Under certain conditions, bimodal particle size distribution in sprays were observed and investigated. The shape and morphology of the powders produced were also investigated. Trends comparable to the experimental results were predicted using a proposed theoretical model.