Bedřich Šiška

Fall of non-spherical particles in a Carreau model liquid

Abstract The free fall of short cylinders and rectangular prisms through polymer solutions of different measure of shear-thinning and elasticity has been investigated experimentally in the creeping flow region. The influence of the particle shape and the rheological behaviour of the liquid on the particle terminal velocity have been evaluated. A procedure based on the modification of the Stokes relationship for a Carreau model fluid have been proposed for the prediction of the terminal falling velocity of non-spherical particles. The suitability of the proposed procedure has been documented by good agreement between experimental and calculated terminal falling velocity data.

Terminal falling velocity of spherical particles moving through a Carreau model fluid

Abstract In this paper, the method, which is based on the results of numerical solution of Hills variational principles, is presented for the prediction of the terminal falling velocity of spherical particles moving slowly through a Carreau viscosity model fluid. The suitability of this method is documented by the comparison of calculated data of terminal falling velocity with experimental data measured for the fall of glass, steel, and lead balls through polymer solutions characterised by different measure of shear-thinning and elasticity.

Drag and fall velocity of a spherical particle in generalized newtonian and viscoplastic fluids

Abstract An approach to the calculation of drag and fall velocity of a spherical particle in generalized Newtonian and viscoplastic fluids is suggested. It is based on the application of the modified Rabinowitsch–Mooney equation together with the corresponding relations for consistency variables. The usefulness of this approach has been verified for the Ellis and Bingham fluids. The solution has been used to suggest the corresponding relationships for the calculation of pressure drop in the flow of a viscoplastic fluid through a random fixed bed of particles.

Fluidization of spherical particle beds with non-Newtonian fluids in columns of rectangular cross-section

The results of experimental investigation of expansion of spherical particle beds fluidized with shear-thinning and simultaneously elastic polymer solutions in rectangular (two-dimensional) columns and creeping-flow region are presented.

Creeping flow of viscoelastic fluid through fixed beds of particles

Abstract A method is presented for the pressure drop calculation during the viscoelastic fluid (VEF) flow through fixed beds of particles. It is based on the application of the modified Rabinowitsch–Mooney equation together with the corresponding relations for consistency variables. The course of dependence of dimensionless quantity coming from the momentum balance and expressing the influence of elastic effects on the suitably defined elasticity number is determined experimentally. The satisfactory validity of the approach suggested has been verified for pseudoplastic viscoelastic fluids characterized by the power-law flow model.

Contribution to the rheological testing of pharmaceutical semisolids

Abstract Rheological behaviour of pharmaceutical semisolid preparations significantly affects manufacturing process, administration, stability, homogeneity of incorporated drug, accuracy of dosing, adhesion in the place of application, drug release, and resulting therapeutic effect of the product. We performed test of consistency by penetrometry, rotational, oscillation and creep tests, and squeeze and tack tests of model samples to introduce methods suitable for characterization and comparison of semisolids in practice. Penetrometry is a simple method allowing sorting the semisolids to low and high stress-resistant materials but deficient for rheological characterization of semisolids. Value of yield stress, generally considered to be appropriate feature of semisolids, is significantly influenced by the method of testing and the way of evaluation. The hysteresis loops of model semisolids revealed incomplete thixotropy, therefore, three-step thixotropy test was employed. Semisolids showed nonlinear response in the creep phase of tests and partial recovery of structure by storing energy in the recovery phase. Squeeze and tack tests seem to be convenient ways for comparison of semisolids. Our study can contribute to a better understanding of different flow behaviour of semisolids given by different physicochemical properties of excipients and can bring useful approaches to evaluation and comparison of semisolids in practice.

Dynamic shape and wall correction factors of cylindrical particles falling vertically in a Newtonian liquid

Results of numerical calculations of dynamic shape and wall correction factors for the flow of a Newtonian fluid over a vertically oriented cylindrical particle in a cylindrical tube are reported. Mathematical model of the flow was solved using the finite element method by means of the COMSOL Multiphysics software. Dependences of the shape factor on the cylinder aspect ratio and of the wall correction factor, FW, on the ratio of the cylindrical particle diameter to the tube diameter, and on the aspect ratio were obtained. Numerical dependences were approximated by simple relationships suitable for dynamic shape and wall correction factors prediction.

Flow of viscoplastic fluids through fixed beds of particles : comparison of three approaches

Abstract Three approaches suggested for the purposes of calculation of pressure drop in flow of non-Newtonian fluids through fixed beds representing the capillary concept are compared, i.e. the Blake–Kozeny concept, the Kozeny–Carman concept, and the concept which solves the problem using the integral forms of the momentum balance, the equation of continuity of flow, and the Rabinowitsch–Mooney equation. The comparison with experimental results for viscoplastic fluids (VPF) characterized by the Herschel–Bulkley flow model given in literature leads to a conclusion that the most reliable results are obtained from the approach which used the correct integral forms of governing equations. Also discussed is the possibility of its application for the purposes of calculation of the pressure drop in flow of viscoelastic fluids through fixed beds.

Flow of Viscoelastic Polymer Solutions through Filter Screens

In this contribution, the measurements are presented of the pressure drop in the creeping flow of viscoelastic solution of polyacrylamides through metal wire screens, differing in wire diameter, aperture dimension, and type of weaving. In this flow, a strong elastic pressure drop excess manifest itself. Analysing the extensive set of experimental data, it was verified that for engineering estimation of the pressure drop excess, a simple form of the corrective Deborah number function can be used.