(332j) Static Mixers As Heat Exchangers In Supercritical Fluid Extraction

The performance of a static mixer as a heating device for supercritical carbon dioxide flow is studied and compared with conventional tube-and-tube heat exchangers. Measurements were carried out at pressures ranging from 8.0 to 21.0 MPa, temperatures from 283 to 323K, and mass flow rates from 2 to 15 kg/h. The corresponding Reynolds and Prandtl numbers, at bulk conditions, ranged between 10^3 and 2×10^4 and between 2 and 7, respectively. The temperature increase experienced by the supercritical CO2 flow 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, as well as by buoyancy effects. Computational fluid dynamics have been employed to numerically characterize the velocity field and temperature profile inside the unit-cell elements of the heat exchanger static mixer. The CFD model will be validated by comparing CFD predictions with experimental measurements of pressure drop and temperature profiles.