Static mixers as heat exchangers in supercritical fluid extraction processes

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The performance of a Kenics static mixer as a heat-transfer device for supercriticall carbon dioxide (CO2) flow is studied and compared with conventional tube-in-tube heat exchangers. Measurements were carried out at pressures ranging from 8 to 21 MPa, temperatures from 283 to 323 K, and mass flowrates from 2 to 15 kg/h. The corresponding Reynolds and Prandtl numbers, at bulk conditions, ranged between 10(3) and 2 x 10(4) and between 2 and 7, respectively. The temperature increase experienced by the supercritical CO2 stream varied between 10 and 35 K. The heat fluxes obtained with the static mixer are one order of magnitude higher than the ones observed with a tube-in-tube heat exchanger for the same set of operating conditions. The heat-transfer enhancement is caused by the cross-sectional mixing of the fluid and to a lesser extent by conduction across the metallic mixing elements. Heat-transfer is also affected by temperature-induced variation of physical properties, especially in the pseudocritical region of the fluid. From the experimental data, a correlation was developed for convective heat-transfer to supercritical CO2 in terms of the Nusselt number. (C) 2007 Elsevier B.V. All rights reserved.
Original languageUnknown
Pages (from-to)477-483
JournalJournal of Supercritical Fluids
Issue number3
Publication statusPublished - 1 Jan 2008

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