Influence of geometry and angular velocity on performance of a rotating disk filter

The Effect of the Rotating Disk Geometry on the Flow and Flux Enhancement in a Dynamic Filtration System

A numerical study was conducted to investigate the effect of rotating patterned disks on the flow and permeate flux in a dynamic filtration (DF) system. The DF system consists of a rotating patterned disk and a stationary housing with a circular flat membrane. The feed flow is driven by the rotating disk with the angular velocity ranging from 200 to 1000 rpm and the applied pressure difference between inlet and outlet ports. Wheel-shaped patterns are engraved on the disk surfaces to add perturbation to the flow field and improve the permeate flux in the filtration system. Five disks with varying numbers of patterns were used in numerical simulations to examine the effects of the number of patterns and the angular velocity of the disk on the flow and permeate flux in the DF system. The flow characteristics are studied using the velocity profiles, the cross-sectional velocity vectors, the vortex structures, and the shear stress distribution. The wheel-shaped patterns shift the central core layer in the circumferential velocity profile towards the membrane, leading to higher shear stresses at the membrane and higher flux compared to a plain disk. When the number of patterns on the disk exceeded eight at a fixed Reynolds number, there were significant increases in wall shear stress and permeate flux compared to a plain disk filtration system with no pattern.

Effect of UF Membrane Rotation on Filtration Performance Using High Concentration Latex Emulsion Solution

A high shear rate can be applied to fluid near a membrane surface by rotating the membrane. This shear rate enables higher permeate flux and higher concentration operation when compared with a conventional cross-flow membrane since fouling and/or concentration polarization are reduced. The purpose of this study was to clarify the relationship between the fluid behavior and membrane separation characteristics of a rotating membrane surface when a latex aqueous solution was used. Due to the synergistic effect of particle removal by the centrifugal forces generated by the rotation of the membrane and the reduction in the thickness of the velocity boundary layer, membrane filtration of high-concentration slurry, which is difficult to dewater by the cross-flow method, is possible. The experimental data using an aqueous latex solution with a wide range of slurry concentrations and various membrane diameters are well correlated using a shear rate derived from the boundary layer theory. It is thus confirmed that the shear rate can be used as a design and operating parameter to define the membrane filtration characteristics.

Shear-enhanced membrane filtration of model and real microalgae extracts for lipids recovery in biorefinery context

In this work, the hydrodynamic effects of rotating disk filtration (with maximum shear rates of 16,000 s^-1 and 66,000 s^-1) were evaluated and compared with the crossflow filtration (16,000 s^-1) in the recovery of lipids from a model solution that simulates the characteristics of Parachlorella kessleri aqueous extracts. Four polymeric membranes were tested. The PAN 500 kDa membrane along with the rotating disk filtration presented the best performances for lipid concentration and coalescence. The rotating disk filtration was tested with real microalgae extracts, confirming the total lipid retention and the limited membrane fouling.

Mimic of a large-scale diafiltration process by using ultra scale-down rotating disc filter

Ultra scale-down (USD) approach is a powerful tool to predict large-scale process performance by using very small amounts of material. In this article, we present a method to mimic flux and transmission performance in a labscale crossflow operation by an USD rotating disc filter (RDF). The Pellicon 2 labscale system used for evaluation of the mimic can readily be related to small pilot and industrial scale. Adopted from the pulsed sample injection technique by Ghosh and Cui (J Membr Sci. 2000;175:5-84), the RDF has been modified by building in inserts to allow the flexibility of the chamber volume, so that only 1.5 mL of processing material is required for each diafiltration experiment. The reported method enjoys the simplicity of dead-end mode operation with accurate control of operation conditions that can mimic well the crossflow operation in large scale. Wall shear rate correlations have been established for both the labscale cassette and the USD device, and a mimic has been developed by operating both scales under conditions with equivalent averaged shear rates. The studies using E. coli lysate show that the flux vs. transmembrane pressure profile follows a first-order model, and the transmission of antibody fragment (Fab') is independent of transmembrane pressure. Predicted flux and transmission data agreed well with the experimental results of a labscale diafiltration where the cassette resistance was considered.

Removal of cobalt ions from aqueous solutions by polymer assisted ultrafiltration using experimental design approach: part 2: Optimization of hydrodynamic conditions for a crossflow ultrafiltration module with rotating part

Application of shear-enhanced crossflow ultrafiltration for separation of cobalt ions from synthetic wastewaters by prior complexation with polyethyleneimine has been investigated via experimental design approach. The hydrodynamic conditions in the module with tubular metallic membrane have been planned according to full factorial design in order to figure out the main and interaction effects of process factors upon permeate flux and cumulative flux decline. It has been noticed that the turbulent flow induced by rotation of inner cylinder in the module conducts to growth of permeate flux, normalized flux and membrane permeability as well as to decreasing of permeate flux decline. In addition, the rotation has led to self-cleaning effect as a result of the reduction of estimated polymer layer thickness on the membrane surface. The optimal hydrodynamic conditions in the module have been figured out by response surface methodology and overlap contour plot, being as follows: DeltaP=70 kPa, Q(R)=108 L/h and W=2800 rpm. In such conditions the maximal permeate flux and the minimal flux decline has been observed.

Performance of Single and Double Shaft Disk Separators

Rotating disks separators, mounted on single and double hollow shafts, are investigated experimentally. The shaft and disks were enclosed in stainless steel housing. Many parameters were measured to study their influence on the performance of single and double shaft disk filters at various rotation speeds. These parameters are pressure inside the housing, permeate flux, and electrical power consumption. The average velocity coefficient k˜ for single and double shaft disk separators was estimated and was found to be a good criterion of module performance as well. The comparison of measured and calculated filtration flow rate at various rotation speeds was in a good agreement. The estimated average shear stress is found to be about twice in double shaft filter disk. The feasibility of double shaft disk separator in treating filtration without filter cake is highly appreciated.

CFD-aided design of a dynamic filter for mammalian cell separation

In the present work, a rotating disk filter was designed for mammalian cell separation with the aim of avoiding both cell damage and membrane fouling. Different geometric and operational variables of the rotating disk filter were studied using computational fluid dynamics (CFD) by varying rotor radius, rotor angle, membrane-rotor distance, and angular velocity. The combinations of these variables followed a statistical design, so that an analysis of the CFD results provided correlations describing the average shear stress on the membrane surface and the maximum shear stress in the whole module as a function of the variables studied. Based on these correlations, and on the shear resistance levels of Chinese hamster ovary (CHO) and baby hamster kidney (BHK) cell lines, which were investigated using a cone-and-plate viscosimeter, it was possible to determine the geometry and angular velocity that would minimize both cell damage and membrane fouling. After construction, the filter was tested in filtration experiments at increasing permeate fluxes. Cell viability remained >90% for the duration of the experiments (2.5 h), and no indication of fouling was observed. It was shown that the designed dynamic filter is able to effectively avoid both cell damage and membrane fouling, and thus can be used for mammalian cell harvesting and perfusion.

Microfiltration and ultrafiltration of polysaccharides produced by fermentation using a rotating disk dynamic filtration system

The recovery of exopolysaccharides (EPS) produced by Sinorhizobium meliloti bacteria by dynamic microfiltration was investigated using a rotating disk device designed in our laboratory, equipped with a 0.2 microm nylon membrane. This system differs from commercially available systems by the presence of vanes on the disk which produce a very important increase in permeate flux while yielding excellent EPS transmission. For polymers produced under standard fermentation conditions (70 h at 30 degrees C), the mass flux rose to 650 g h(-1) m(-2) using a disk equipped with 2 mm vanes rotating at 2000 rpm against 380 g h(-1) m(-2) with a smooth disk at the same speed. The maximum flux observed was 1560 g h(-1) m(-2) with a 6-mm vanes disk rotating at 3000 rpm and a 36 degrees C broth. An interesting finding was that the permeate flux J(f) for various disks can be correlated by the same function of the mean shear stress at the membrane tau(wm) according to J(f) = 4.6 tau(wm) (0.717) for a 30 degrees C broth, showing that the effect of vanes is merely to increase the shear stress by raising the fluid core velocity between the membrane and the disk. With 6-mm vanes the core angular velocity was found to be 84% of disk velocity vs. 45% for a smooth disk. When the fermentation temperature was increased to 36 degrees C to produce a lower molecular weight polymer, the permeate flux rose by about 250%, much more than what could be expected from the reduction in permeate viscosity and followed the same power law with membrane shear stress as for 30 degrees C. The same device was equipped with a PES 50 kDa membrane to concentrate EPS by ultrafiltration. Permeate fluxes were of the order of 160 L h(-1) m(-2) at 2000 rpm and 30 degrees C with nearly complete EPS rejection. Finally, the net electrical power consumed by the disk was measured by subtracting the power consumed without fluid from the power during filtration at the same speed. This power increases with speed and with the presence of vanes, but since the gain provided by the vanes is very high, the specific energy per m(3) of permeate is minimal with the highest vanes tested (6 mm) and maximal for smooth disks.

Cell retention devices for suspended-cell perfusion cultures

Perfusion cultures of animal cells have several advantages over batch or fed-batch cultures. They give, for instance, higher productivities and a consistent product quality, and allow steady state operation and better cell physiology control. However, one of the main aspects limiting performance and scale-up of perfusion processes is the need for an adequate cell retention device. The devices currently in use for stirred perfusion bioreactors are continuous centrifuges, tangential flow membrane filters, dynamic filters, spin-filters, ultrasonic and dielectrophoretic separators, gravity settlers and, more recently, hydrocyclones. The advantages and disadvantages of each of these methods will be discussed.