The paper describes a mathematical and physical modelling of flow of complex slurries in pipelines, i.e. a flow of slurries composed of solids covering a very broad range of particle sizes that overlaps more than one flow patterns – non-Newtonian, pseudohomogeneous, heterogeneous and fully-stratified. A typical examples are residual products (“tailings”) from mining industry with normal average particle sizes of 20 to 100 μm or more. Experimental results of flows of complex slurries composing of non-Newtonian carrier fluid and three fractions of glass particles in 50 mm pipe are presented. Depending on the particle size, particles show different flow patterns and therefore considerable differences in pressure drops. Fine particles tend behave as a homogeneous matter, while coarser particles exhibit heterogeneous behaviour and even coarser particles form a sliding bed. A mathematical 3-component predictive model for turbulent flow of complex slurries is presented based on well-established semi-empirical formulae developed originally for flows with Newtonian carrier. The predicted values of pressure drops show very reasonable agreement with experimental results and indicate suitability of the model for engineering practice.
Comprehensive knowledge of hydrodynamics inside the feeding channels of spira-lwound membrane modules is recognized as crucial for the efficient operation of such separation equipments. Slits are laboratory models widely used to mimic the fundamentals of hydrodynamics and mass transfer in spiral-wound membrane modules. In this work micro-PIV was the technique chosen to characterize fully developed laminar flows in a slit for both Newtonian and non-Newtonian fluids. Experiments with water, water-glycerol and water-glycerol-xanthan were carried out at different flow rates, ranging from 4.3. to 25.3 L/h. The ternary mixture water-glycerol-xanthan simulates the non-Newtonian rheological behavior of blood. The other fluids are Newtonian and exhibit different viscosities. The fluids rheology was characterized making recourse to a viscometer. Using micro-PIV, velocity maps at several depths of the channel were obtained. As expected, results showed that the Newtonian fluids flows exhibit parabolic profiles typical of laminar developed flows in slits. On the other hand, slightly flattened profiles characterize the non-Newtonian fluid flows. Comparisons with the analytical solutions for laminar developed flows in rectangular slits are very encouraging. and Obsahuje seznam literatury
The unsteady Hartmann flow of a conducting incompressible non-Newtonian viscoelastic fluid between two parallel horizontal insulating porous plates is studied with heat transfer. A uniform pressure gradient which decays exponentially is imposed in the axial direction. An external uniform magnetic field and uniform suction and injection through the surface of the plates are applied in the vertical direction. The two plates are kept at different but constant temperatures while the Joule and viscous dissipations are considered in the energy equation. Numerical solutions for the governing momentum and energy equations are obtained using finite differences. The effect of the magnetic field, the parameter describing the non-Newtonian behavior, and the velocity of suction and injection on both the velocity and temperature distributions is investigated. and Obsahuje seznam literatury