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This study evaluated the separation of particles suspended in power law fluids by applying a 10 mm hydrocyclone. Al2O3 particles were added to an aqueous polyacrylic acid solution to prepare 0.1 vol% suspensions with different flow behaviors. The effects of operating conditions, such as the inlet velocity, pressure drop, split ratio, and fluid flow behavior, on the fluid velocity distribution, particle trajectory, and particle separation efficiency were studied. The study applied a simulation in which the governing equations were coupled using the SIMPLE algorithm; the Reynolds stress model served as a turbulence model. The distributions of the fluid velocity and pressure were simulated using a segregated, steady-state, three-dimensional implicit numerical solver provided by ANSYS 15.0 software. The tangential velocity increased with the flow behavior index, n, at a fixed inlet velocity and split ratio. This effect was attributed to a lower molecular viscosity. The particle trajectories were simulated using a Lagrangian frame. The particle migration in the cylindrical part of the hydrocyclone dominated the particle separation efficiency. A reduction in the fluid n-value engendered a higher effective viscosity and lower tangential velocity, which caused fewer particle rotations and lower centrifugal effects, consequently lowering the opportunity for particles to collect in the underflow. The separation efficiency increased with the inlet velocity and particle size because of a higher centrifugal effect, but the influence of the inlet velocity was extremely small for a low fluid n-value. The total separation efficiency increased by approximately 40% as the n-value increased from 0.51 to 1.00. The simulated particle separation efficiency was highly consistent with experimental data. This verified the reliability of the simulation method and the validity of this method for understanding the effects of fluid flow behavior on particle separation performance.

Different kinds of Dextran–MnO2 gel particles are prepared in different conditions, depending on variables such as the molecular weight of dextran and formation temperature. Some physical properties and filtration characteristics of these gel particles are measured and discussed. Although the mean sizes of these gel particles are very close to each other, their filtration characteristics are far different due to their mechanical strength and compressibility. A typical filtration curve of gel particles can be divided into three regions, and a retardation cake compression during the filtration can be observed from the curve. The particle formation temperature has a trivial effect on their mechanical strength. An increase in formation temperature leads to only a slight decrease in particle size. On the other hand, gel particles are formed by using dextrans with three different molecular weights – 70,000 (sample A), 500,000 (sample B) and 2,000,000 Da (sample C) – and are used in filtration experiments. The results show that the molecular weight of dextran plays a major role in determining particle mechanical strength; the sequence of particle hardness is sample B > sample A > sample C. The dynamic analysis method proposed by Hwang and Hseuh [K.J. Hwang, C.L. Hseuh, J. Membr. Sci. 214 (2003) 259] is employed to estimate the local cake properties in a filter cake, e.g., solid compressive pressure, porosity and specific filtration resistance. Because sample C has the highest compressibility, it constructs a cake with the lowest porosity and the highest specific filtration resistance; and consequently, the lowest filtration rate. Although the mechanical strength of sample B is higher than that of sample A, its wider particle size distribution results in lower cake porosity and higher filtration resistance, as well as a lower filtration rate. It could be said that the filtration rate decreases with an increase in the molecular weight of dextran.

In order to study the deformation behavior of deformable particles under hydraulic drag and mechanical load such as in filtration, a number of in situ strengths of single calcium-alginate gel particle and inter-particle contact modes among gel particles were explored. A linear viscoelastic contact model based upon the Hertz theory was proposed to describe the deformation behavior of deformable gel particles. The effect of particle deformation due to frictional drag and mass of particles on the reduction of porosity was studied to examine how this variation led to the increase in contact area between particles. Both theoretical and experimental results show that the modified Hertz theory combined with the linear viscoelastic model can be used to predict the mechanical behaviors of gel particle under mechanical compression well. Experimental results also demonstrate that a given mechanical load would result in a higher degree of deformation of particles than under the same amount of hydraulic drag. Based upon the theoretical derivation and the verification of experimental results, a correlated relationship between specific surface area ratio and bed porosity, e, with a validated range of 0.05

Stress distribution in a confined wet cake is analysed by solving the equation of equilibrium of force acting on the system. An integrated equation is derived to estimate the stress distribution within the cake providing the boundary values around the cell are known. The results are applied to estimate the mean stress acting on the confined cake and also to correct the effect of side-wall friction of the compression — permeability (C—P) cell tests. These corrected data are then used to predict the performance of constant-pressure filtrations. From the results of these predictions, it is indicated that the simulated results based on the corrected C—P cell test data may give an average deviation around 5%, while the simulated results based on the CP cell test data without correction give a deviation higher than 10%.

The effect of the size distribution of spheroidal particles on the packing structure at the cake surface is studied in cake filtrations. By analyzing the forces and torques exerted on the depositing particles, the migrations and packing structures of spheroidal particles with various size distributions are simulated. For the packing structures of particles with a normal size distribution, the distribution of the co-ordination number in the cake is asymmetric, and its mean value decreases slightly as the standard deviation increases. When the major to minor axis length ratio of the spheroidal particles, θ, increases, the distribution of the co-ordination number becomes more uniform, but the average value does not change significantly. The packing porosity decreases linearly with increasing standard deviation. For the Rosin-Rammier distribution, the packing porosity and the mean co-ordination number increase with increasing distribution constant. The packing porosity of spheroidal particles increases with the size distribution in the order uniform distribution > Rosin-Rammler distribution > normal distribution. The packing porosity increases with the value of θ for all types of size distribution. The simulated results are compared with the available random-packing data, and the packing densities simulated by this study are closer to the experimental data than those of previous simulations.

The cake formed by uniform-sized spheroidal particles during cake filtration is simulated with the view of force and torque analyses on the particles. Various effects on the structure of the filter cake, such as the filtration rate, concentration of slurry, particle shape, and friction coefficient between particles, are discussed in depth. The simulated results show that the particle shape plays the major role in the packing porosity. As the shape of particles departs from spherical, the structure of the filter cake becomes looser. The simulation results of cake porosity are compared with the available experimental data of random packing under gravity, and good agreement between them exists when the relative sphericity of the particles is larger than 0.7.