A computational fluid dynamics model of supercritical fluid extraction of a solute (caffeine) from a fixed bed of porous solid matrix (coffee beans) using a supercritical solvent (carbon dioxide) is developed. The mathematical model is developed considering diffusion-controlled transport in the particle and film mass transfer resistance around the particle. Accurate representations of the transport properties of supercritical carbon dioxide are considered. The conservation equations are numerically solved using an implicit finite volume method. Supercritical fluid extraction of a solute from a solid matrix has a slow dynamics even when solute free solvent is re-circulated and therefore improvements in the mass transfer process are required. The effect of acoustically excited flows on supercritical fluid extraction in a fixed bed extractor is investigated. Harmonically oscillating inlet wall boundary condition is used to model a piezoelectric transducer. The use of acoustic excitation represents a potential efficient way of enhancing mass transfer processes. Application of acoustic excitations at the fundamental frequency of the extractor (f = 996 Hz) increased the overall yield by about 15%. The effects produced by compressions and decompressions, as well as by radiation pressure and streaming contribute to the enhancements.

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