Search results for "Fluid Dynamics"
showing 10 items of 1005 documents
Stability of melt flow due to a traveling magnetic field in a closed ampoule
2004
The linear three-dimensional instability of the flow due to a low frequency traveling magnetic field in a regular cylinder is studied numerically for height-to-diameter ratios in the range [0.5:2.5]. The first instability has the form of an azimuthal wave with wave numbers between 1 and 6 depending on the aspect ratio. It is shown that the flow is stable if the Reynolds number is below 290. Even stronger stationary flows may be obtained in a flattened cylinder.
Calculation of shear influences on the phase separation of polymer blends exhibiting upper critical solution temperatures
1994
Calculations were performed on the basis of a generalized Gibbs energy of mixing G γ, which is the sum of the Gibbs energy of mixing of the stagnant system and E s, the energy stored in the system during stationary flow. With increasing shear rate γ, the demixing temperatures shift to lower values (shear-induced mixing; diminution of the heterogeneous area), then to higher values (shear-induced demixing), and finally to lower values again before the effects fade out. The details of the rather complex phase diagrams resulting for a given shear rate are primarily determined by a band in the T/χ plane (χ = mole fraction) within which (∂2 E s/∂χ2) T UCST where they submerge. Bound to a suitable…
On the measurement of bubble size distribution in gas–liquid contactors via light sheet and image analysis
2010
Abstract Particle image velocimetry techniques coupled with advanced image processing tools are receiving an increasing interest for measuring flow quantities and local bubble-size distributions in gas–liquid mechanically agitated vessels. When trying to analyze image information the problem arises that bubble sizes are generally underestimated, due to the fact that the laser sheet used for lighting the system randomly cuts bubbles over non-diametrical planes, leading to an apparent bubble size distribution even in the ideal case of single sized bubbles. Clearly in the case of bubbles with a size distribution the experimental information obtained is affected by the superposition of effects.…
Channel flow at an immobilised liquid|liquid interface
2000
A novel rectangular channel flow electrochemical cell for the study of liquid | liquid interfaces is presented. The organic phase is immobilised by the use of a gelling agent, while the aqueous phase flows past the interface. This creates an asymmetric setup that allows us to establish diagnostic criteria to determine, for example, the direction of the ion transfer. The effects of varying flow rate and sweep rate have been considered both theoretically and experimentally. By comparison with two-dimensional simulations, it is demonstrated that a simple one-dimensional theory can be used to describe the cyclic voltammetry response of the channel flow cell.
Novel general expressions that describe the behavior of the height equivalent of a theoretical plate in chromatographic systems involving electricall…
2002
Novel general expressions are constructed and presented that describe the behavior of the height equivalent of a theoretical plate (plate height), H, as a function of the linear velocity, Vx, along the axis, x, of the column and the kinetic parameters that characterize the mass transfer and adsorption mechanisms in chromatographic columns. Open tube capillaries as well as columns packed with either non-porous or porous particles are studied. The porous particles could have unimodal or bimodal pore-size distributions and intraparticle convective fluid flow and pore diffusion are considered. The expressions for the plate height, H, presented in this work could be applicable to high-performanc…
Experimental and fluid dynamic study of continuous supercritical water gasification of glucose
2016
Abstract The supercritical water gasification (SCWG) of glucose as a model compound for H 2 production is studied in term of process development at 25 MPa and 650 °C. Gasification has been investigated using a laboratory scale continuous plant comprising a continuous down flow reactor with a volume of 200 cm 3 , a heat recovery section and pre-heat of the biomass to simulate more closely an industrial design. Feed streams (pure water and glucose solution) are introduced at the top of the vessel and products are extracted from the bottom. The reactor is equipped with various inlet points that allow to modify the inlet position of reacting streams in order to study the effect of stream mixing…
Densities, Viscosities, and Refractive Indices of Some Binary Liquid Systems of Methanol + Isomers of Hexanol at 298.15 K
1996
Viscosities, densities, and refractive indices of eight binary liquid systems containing ethanol + some isomers of hexanol have been determined at 298.15 K. The excess property values were fitted to the Redlich-Kister equation to estimate the binary coefficients and the standard deviations.
Circulating fluidized bed reactors – part 01: analyzing the effect of particle modelling parameters in computational particle fluid dynamic (CPFD) si…
2019
A CPFD hydrodynamic model was developed for a circulating fluidized bed system and the simulation results were validated against experimental data based on particle circulation rate. Sensitivity of the computational mesh was primarily tested and extended grid refinement was needed at the loopseal to match the particle circulation rate with experimental data. The particle circulation rate was independent of the range of number of computational particles used in this study. A 10% reduction of the particle circulation rate was observed as the particle-wall interaction parameter was changed from 0.85 to 0.55 and 17% increment when the close-packed volume fraction was changed from 0.56 to 0.62. …
Results of Numerical Modeling of Blood Flow in the Internal Jugular Vein Exhibiting Different Types of Strictures
2022
The clinical relevance of nozzle-like strictures in upper parts of the internal jugular veins remains unclear. This study was aimed at understanding flow disturbances caused by such stenoses. Computational fluid dynamics software, COMSOL Multiphysics, was used. Two-dimensional computational domain involved stenosis at the beginning of modeled veins, and a flexible valve downstream. The material of the venous valve was considered to be hyperelastic. In the vein models with symmetric 2-leaflets valve without upstream stenosis or with minor 30% stenosis, the flow was undisturbed. In the case of major 60% and 75% upstream stenosis, centerline velocity was positioned asymmetrically, and areas of…
Complex miscibility behaviour for polymer blends in flow
1995
Abstract Experimental observations of the effect of shear flow on the miscibility of binary polymer blends are compared to calculations based on a generalized Gibbs energy of mixing Gγ˙. This mixing free energy characterizes the steady state established at shear rateγ˙, as the sum of G z , the equilibrium Gibbs energy and E s , the energy the system stores while flowing.