Wen-Mei Chen

Effect of structural modification on hydrocyclone performance

The structure of hydrocyclone was designed with a series of modifications, and the comprehensive effects of the structural modifications on operation performance indices of hydrocyclones were investigated experimentally with orthogonal design method. Based on the conventional hydrocyclone, the structural modifications with central insertions named winged core, solid core and inner diffuser could increase all the reduced separation efficiency, separation sharpness, cut size, capacity and flow split, and decrease the energy loss coefficient. The structural modification of 20° cone with spiral has the same function. The parabola type of cone part could increase the separation efficiency, separation sharpness, cut size and capacity, and decrease the energy loss coefficient and flow split. For increasing separation efficiency and reducing energy loss coefficient only, straight vortex finder with siphon and straight underflow pipe with cone are efficient structure designs. From experimental results of this study, useful clues or guidance could be obtained for the structure design of hydrocyclones with different target indices in different applications.

Enhancement of hydrocyclone performance by controlling the inside turbulence structure

Abstract A new hydrocyclone was designed with a winged core fixed below the vortex finder in this study. With the winged core, the turbulence structure characteristics inside the hydrocyclone, including time-averaged pressure, pressure fluctuation, relative pressure fluctuation characteristics, and distribution characteristics of the probability density of the turbulence pressure, were all positively controlled. By controlling the turbulence structure, the performance of the new hydrocyclone was improved effectively. Compared with the common hydrocyclone, the new hydrocyclone was featured with lower energy loss coefficient, higher reduced separation efficiency, higher separation sharpness and larger capacity.

Experimental study of solid–liquid two-phase flow in a hydrocyclone

By using a new type of laser measuring instrument, a particle dynamics analyser (PDA), radial and axial velocity components and the size of solid particles in a hydrocyclone were measured, and the concentration distribution of the solid particles was obtained. In analysing and discussing the separation mechanism of the solid particles, as well as the main causes of the leakage of coarse particles to the overflow and the abrasion on the hydrocyclone wall, some new opinions are put forward.

Numerical prediction of the liquid flow within a hydrocyclone

Abstract The three-dimensional flow fields with a central air core in a hydrocyclone are numerically simulated using a k – e turbulence model. The model constants C 1 , C 2 and C μ are modified because of the anisotropic character of the turbulent viscosity in the hydrocyclone. Experiments show that the predicted velocity profiles agree well with data measured by laser Doppler anemometry (LDA). Based on this prediction, the flow field and the pressure field as well as the distribution of the rate of dissipation of the turbulent energy are discussed. The study shows that an important approach towards reducing energy dissipation in a hydrocyclone is to improve the flow pattern in the cylindrical part.

Effects of internal microstructures of poly(N-isopropylacrylamide) hydrogels on thermo-responsive volume phase-transition and controlled-release characteristics

Poly(N-isopropylacrylamide) (PNIPAM) hydrogels were fabricated with distinctly different internal microstructures. The internal microstructures of the PNIPAM hydrogels were characterized by SEM, and the effects of the internal microstructures of the PNIPAM hydrogels on their thermo-responsive volume phase-transition and controlled-release characteristics were experimentally investigated. The results showed that there were two kinds of microstructures of PNIPAM hydrogels, a homogeneous netlike microstructure and a heterogeneous microstructure with microgel clusters, and the thermo-responsive volume phase-transition behaviors and controlled-release characteristics of the PNIPAM hydrogels were found to be heavily dependent on their internal microstructures. The homogeneous internal microstructure caused a remarkably greater volume change, while the heterogeneous internal microstructure resulted in a more rapid responsiveness and a more ideal thermo-responsive controlled-release property. Consequently, for different applications, PNIPAM hydrogels should be designed and fabricated with different internal microstructures.

Research on the Motion of Solid Particles in a Hydrocyclone

Abstract By using a new type of laser surveying instrument named the particle dynamics analyzer, the radial and axial velocity components and the size and concentration of solid particles at selected positions within a transparent hydrocyclone were measured directly, and profiles of the solid particle flow field were obtained. Some new observations were made, such as that the maximum concentration was at the loci of zero vertical velocity, and there was separation of some particles in the inner helical flow.

Fouling-resistant Composite Membranes for Separation of Oil-in-water Microemulsions *

Abstract Fouling-resistant ceramic-supported polymer composite membranes were developed for removal of oil-in-water (O/W) microemulsions. The composite membranes were featured with an asymmetric three-layer structure, i.e., a porous ceramic membrane substrate, a polyvinylidene fluoride (PVDF) ultrafiltration sub-layer, and a polyamide/polyvinyl alcohol (PVA) composite thin top-layer. The PVDF polymer was cast onto the tubular porous ceramic membranes with an immersion precipitation method, and the polyamide/PVA composite thin top-layer was fabricated with an interfacial polymerization method. The effects of the sub-layer composition and the recipe in the interfacial polymerization for fabricating the top-layer on the structure and performance of composite membranes were systematically investigated. The prepared composite membranes showed a good performance for treating the O/W microemulsions with a mean diameter of about 2.4μm. At the operating pressure of 0.4MPa, the hydraulic permeability remained steadily about 190L·m −2 ·h −1 , the oil concentration in the permeate was less than 1.6mg·L −1 , and the oil rejection coefficient was always higher than 98.5% throughout the operation from the beginning.

Effects of geometric and operating parameters and feed characters on the motion of solid particles in hydrocyclones

The effects of geometric and operating parameters and feed characters on the motion of solid particles in hydrocyclones were experimentally investigated by using a new type of laser surveying instrument named particle dynamics analyzer. The absolute radial velocity of solid particles decreases with increasing the positional radius, and the axial distribution curves of the particle radial velocity are parabolic. The particle radial velocity increases with increasing the inlet pressure or with increasing the diameter of the underflow pipe. When the particle density or the particle size increases, the absolute radial velocity of the solid particles decreases. The particle radial velocity also decreases with increasing the feed particle concentration. The axial distribution curves of the particle axial velocity are also parabolic. The axial velocity in the inner helical flow increases with the increase of the flow rate of overflow; while that in the lower positions in the outer helical flow increases with increasing the flow rate of underflow.

Long-term prediction of nonlinear hydrodynamics in bubble columns by using artificial neural networks

Abstract An artificial neural network (ANN) model was proposed for the long-term prediction of nonlinear dynamics underlying holdup fluctuations in bubble columns with three different diameters of 200, 400 and 800 mm. Local holdup fluctuations were measured with an optical probe in the bubble columns. The superficial gas velocity was varied in the range of 33–90 mm/s. The time intervals between successive bubbles were extracted from the time series of holdup fluctuations to represent hydrodynamic behaviors in the system and used as training and validation data sets. The effect of data preprocessing as well as the numbers of nodes in input and hidden layers on the ANN training behavior was systematically investigated. The prediction capability of the ANN was evaluated in terms of time-averaged characteristics, power spectra and Lyapunov exponents. It was observed that: the ANN model, which was trained with experimental time series and gas velocity, can be used for the long-term prediction of dynamic characteristics in bubble columns by using random data as the initial input. The results indicate that the trained ANN models have the potential of modeling nonlinear hydrodynamic behaviors in bubble columns.

Enhanced performance for crossflow microfiltration processes with tubular ceramic membrane

The fluid flow pattern, the regeneration method and the regeneration cycle of crossflow microfiltration processes were optimised experimentally using tubular ceramic membranes to provide guidance for the design of an efficient membrane holder structure and technology for crossflow microfiltration. The results show that the outer helical flow pattern, combined with the regeneration method of backshock with compressed gas, can enhance the performance of crossflow microfiltration, i.e. the concentration polarisation and the membrane fouling in the crossflow microfiltration can be controlled effectively. Furthermore, the permeate flux remains stable for a long period of time with a short backshock cycle.