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Wavy Films Flow: Linear Stability and Evolution
Wein, Ondřej ; Tihon, Jaroslav
The Orr-Sommerfeld (OS)problem is analyzed in terms of the relation between complex-valued wavenumber alfa and celerity c. For the long-wave regular branch, Taylor series to c(alfa) is found to be of limited use, as its convergence radius pi is to small. Wave characteristics of the conception region, including besides c(alfa) also the wall shear rate impendance q , are obtained for the maximum spatial growth rate scenarioo by solving the OS problem numerically.
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Supercritical Fluid Extraction and Characterisation of Urtica Dioica L. Leaves Pigments
Sajfrtová, Marie ; Sovová, Helena ; Bártlová, Milena ; Opletal, L.
Extraction and fractionation of green and yellow pigments from stinging nettle leaves was studied using ethanol-modified carbon dioxide as a solvent. The extracts were analysed by means of HPLC and RP-HPLC systems. The effect of operation conditions was analysed in a series of experiments at pressures from 20 MPa to 28 MPa, temperatures between 25 °C and 60 °C, and ethanol concentration in CO2 between 0 and 7.4 wt.%. The main result was that the best conditions for the supercritical fluid extraction of pigments were ethanol concentration in CO2 4.5 - 7.4 wt.%, temperature 40°C and pressure 28MPa and that degradation of pigments was eliminated with decrease of temperature of micrometer valve and addition of small amount of antioxidant to ethanol.
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Evaluation of Extraction Curves Obtained by Supercritical Fluid Extraction from Plant Materials
Sovová, Helena
Evaluation of extraction curves is based on modelling the extraction process. Various models have been published and used to evaluate experimental data in the last years. A combined model, closely related to the results of ReverchonŽs research group, is presented in this study. Dimensionless form of the model is solved by numerical integration and also analytical approximative solutions are presented. Experimental extraction curves from the literature were analysed using the model for supercritical fluid extraction of both essential oils and fatty oils.
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