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Model Fluids (model + fluid)
Selected AbstractsDetermination of membrane areas for ultrafiltration processesJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 10 2001Changsheng Liu Abstract For batch mode ultrafiltration processes a numerical method for calculating membrane area has been devised with flux predicted from Flemmer's model. Erythromycin broth filtrate was used as a model fluid. Experiments at a 20,dm3 scale were used to estimate the parameters involved in Flemmer's equation, from which membrane areas appropriate for operations of 80 metric tons were calculated. Factors such as rejection, concentration ratio, etc, which affect the membrane size for batch operation, are discussed. The calculated results were consistent with experimental data at the 100,dm3 scale. For continuous operation equations for calculating membrane areas have also been established. The minimum membrane area was calculated at the optimum concentration ratios of each stage, usually their values were different at each stages. Comparison between batch and continuous mode in the context of the membrane area required is also discussed. The method could be applicable to other ultrafiltration operations. © 2001 Society of Chemical Industry [source] Development of an optimal hybrid finite volume/element method for viscoelastic flowsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 11 2003M. Aboubacar Abstract A cell-vertex hybrid finite volume/element method is investigated that is implemented on triangles and applied to the numerical solution of Oldroyd model fluids in contraction flows. Particular attention is paid to establishing high-order accuracy, whilst retaining favourable stability properties. Elevated levels of elasticity are sought. The main impact of this study reveals that switching from quadratic to linear finite volume stress representation with discontinuous stress gradients, and incorporating local reduced quadrature at the re-entrant corner, provide enhance stability properties. Solution smoothness is achieved by adopting the non-conservative flux form with area integration, by appealing to quadratic recovered velocity-gradients, and through consistency considerations in the treatment of the time term in the constitutive equation. In this manner, high-order accuracy is maintained, stability is ensured, and the finer features of the flow are confirmed via mesh refinement. Lip vortices are observed for We>1, and a trailing-edge vortex is also apparent. Loss of evolution and solution asymptotic behaviour towards the re-entrant corner are also discussed. Copyright © 2003 John Wiley & Sons, Ltd. [source] INFLUENCE OF FLOW REGIMES ON TEMPERATURE HETEROGENEITIES WITHIN A SCRAPED SURFACE HEAT EXCHANGERJOURNAL OF FOOD PROCESS ENGINEERING, Issue 3 2000ERIC DUMONT ABSTRACT In industrial applications, fluids processed in scraped surface heat exchangers often show large temperature heterogeneities at the exchanger outlet. Our study deals with the thermal evolution of model fluids, Newtonian and non-Newtonian in heating or cooling conditions and allows us to link the phenomena of appearance and disappearance of temperature heterogeneities with the changes in the flow pattern within the exchanger. Based on literature data dedicated to scraped surface heat exchangers as well as to annular spaces without blades, we have shown that thermally homogeneous products can be obtained when Taylor vortices appear in the exchanger. Studies done on the exchanger with and without blades show that the thermal behavior is basically the same for both geometries but with a difference in critical Taylor numbers value for change in heat transfer regime. The presence of blades promotes the appearance of instabilities at lower values of generalized Taylor number (Tag= 10 with blades; Tag= 39 without blades). It shows as well, that the value of critical Taylor number in scraped surface heat exchanger closely depends upon the flow-rate even for very low values for Reaxg (Reaxg < <1). [source] Flow and mass transfer of fully resolved bubbles in non-Newtonian fluidsAICHE JOURNAL, Issue 7 2007Stefan Radl Abstract In this work, high-resolution 2-D numerical simulations were performed on the motion of deformable bubbles in non-Newtonian fluids and the associated mass transfer. For that purpose, we have implemented a semi-Lagrangian advection scheme and improved the fluid dynamic calculation by the usage of implicit algorithms. Non-Newtonian fluids are described by generalized Newtonian as well as viscoelastic model fluids. As shear-thinning model we use a Power-Law and a Carreau-Yasuda model, the viscoelastic fluid simulations are based on an Upper-Convected Maxwell model combined with a recently introduced model for the evolution of the effective shear rate. The mathematical challenges arising from the hyperbolic nature of the resulting set of equations are addressed by inclusion of artificial diffusion in the stress equation. In our work, it was found that shear thinning effects have impact on collision rates, and therefore, may influence coalescence of bubbles in non-Newtonian liquids. Furthermore, for the first time, concentration fields of dissolved gas in viscoelastic fluids are presented. The study shows that the fluid elasticity plays a major role for bubble rise velocity, and therefore, mass transfer. As the wake dynamics differ significantly from that in Newtonian liquids, abnormal mixing characteristics can be expected in the bubbly flow of viscoelastic fluids. © 2007 American Institute of Chemical Engineers AIChE J, 2007 [source] |