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In a rotating-disk dynamic filter, the effects of the rotating-disk structure, including the shape and number of vanes, on the distribution of fluid velocity and shear stress acting on the membrane surface were examined using computational fluid dynamics (CFD). Six types of rotating disk were designed and installed above the filter membrane in a filter chamber to study their performance. Three-dimensional fluid flow fields in the filter chamber were simulated for various rotating disks, disk rotation speeds, and feed flow rates by using FLUENT software. The equations of continuity and momentum balance were solved numerically using a finite volume scheme along with the renormalization-group k-ε model. The simulated results indicated that the disk structure and rotation speed were the most crucial factors affecting the filtration performance. An optimal disk design for higher permeate fluxes and less membrane cake fouling can be achieved by increasing the shear stress on the membrane surface. A rotating disk equipped with more vanes can generate higher shear stress on the membrane surface for a given rotation speed. However, more power should be supplied to drive the rotating disk. Although the B2 rotating disk showed the highest filtration flux, Type-A2 and Type-C disks had the optimal designs, which were achieved by considering the filtration flux and power consumption simultaneously. [ABSTRACT FROM AUTHOR]

Effects of geometric structure parameters of 10 mm-diameter hydrocyclones on the particle separation efficiency are studied using computational fluid dynamics (CFD). The fluid velocity profiles and particle trajectories are simulated using RFLOW software with a standard isotropic k-ε turbulent model. The JIS standard CaCO3-17 particles are adopted as a particulate sample in simulations and experiments. Comparing the simulated results with experimental data, a maximum deviation about 20% in partition curves occurs for 5-10 µm particles. However, fairly good agreements for the cut-size predictions and the fish-hook phenomenon are obtained. The simulated cut-size d50 is only 2 µm larger than that measured in experiments, while the value of d100 can be accurately predicted. An increase in overflow diameter or a decrease in underflow diameter leads to a lower separation efficiency but a clearer separation sharpness due to lower fluid underflow rate. A short-and-wide rectangular inlet is more efficient for particle separation than a tall-and-narrow one. An inclined inlet conduit plays an inessential role on the efficiency improvement but gains a 2 µm reduction in d100. Comparing the simulated results, the hydrocyclone used in the experiments of this study exhibits a higher separation sharpness than the Rietema type and a higher efficiency than the Bradley type based on the same operation capacity and hydrocyclone size. [ABSTRACT FROM AUTHOR]

The models of particle fouling and membrane blocking in a submerged membrane filtration are developed in this study. The effects of operating conditions, such as aeration intensity (air flow rate) and filtration pressure, on the filtration flux, membrane blocking, and cake formation are discussed thoroughly. The experimental results show that the filtration resistances due to cake formation and membrane blocking play significant roles in determining the overall filtration resistance, but the latter one is more dominant. An increase in aeration intensity leads the filtration flux to increase due to the reduction of cake formation on the membrane surface. However, a higher filtration pressure causes more severe membrane internal blocking and then to lower filtration flux. The cake properties and the filtration resistance due to membrane blocking are analyzed and can be regressed to empirical functions of filtration pressure. A force balance model for particle deposition on the membrane surface is also derived. In order to estimate the shear stress acting on the membrane surface, the diameter, shape, and rising velocity of air bubbles are analyzed based on hydrodynamics. Once the model coefficients are obtained, the pseudo-steady filtration flux under various conditions can be estimated by the proposed model and the basic filtration equation. The calculated results agree fairly well with the available experimental data. [ABSTRACT FROM AUTHOR]

The filtration characteristics of cross‐flow microfiltration of fine particles suspended in polymeric aqueous solution are studied. Polymethylmethacrylate (PMMA) submicron particles are suspended in polyacrylamide (PAA) aqueous solution to prepare the suspensions used in experiments. Effects of operating conditions, such as cross‐flow velocity, filtration pressure, and PAA concentration, on the filtration flux and the cake properties are discussed. The results show that an increase in cross‐flow velocity or filtration pressure causes the filtration flux to be higher, but the filtration flux decreases with an increase in PAA concentration. Since the flow behavior indices of three prepared suspensions are almost the same, the average specific filtration resistance of cakes under various cross‐flow velocities and PAA concentrations remain almost constant; and then the cake mass plays a major role in determining the filtration resistance and the filtration flux. A force balance model is derived for particle deposition on the membrane surface. Once the empirical coefficients are obtained from experimental data, the filtration flux at pseudo‐steady state can be predicted accurately. [ABSTRACT FROM AUTHOR]

The effects of particle size on the cake properties and the performance of cross-flow microfiltration are studied. A particulate sample with a wide size distribution range from submicron to micron is used in experiments. The probabilities of particle deposition are analyzed based on a force analysis. Since the major forces in determining the particle deposition and packing in the filter cake are different for submicron and micron particles, the particle size plays an important role in the filtration performance. Cake properties, such as mass, porosity and average specific filtration resistance of the cake, are calculated theoretically and compared with experimental data. Except for the overestimation of the mean particle size for about 1 μm, the calculated results of the pseudo-steady filtration rate and cake properties under various operating conditions agree fairly well with the experimental data. [ABSTRACT FROM AUTHOR]

The use of cross-flow microfiltration for purification of liposome vesicles is studied. The liposomes are concentrated while the phospholipid monomers are rejected or permeated through the filter membrane during filtration. Effects of operating conditions, such as cross-flow velocity and filtration pressure, on the filtration rate, the cake properties, the rejection coefficient of phospholipid, and the separation efficiency are discussed. The experimental results show that the filter cake formed by liposome vesicles exhibits a very high compressibility and specific filtration resistance. Cake resistance plays a major role on the overall filtration resistance. The filtration rate attenuates quickly at the beginning of filtration, due to the deposition and the compression of liposome vesicles. After a period of time, the filtration rate gradually approaches a pseudo-steady value. An increase in applied filtration pressure causes an increase in the filtration rate at the pseudo-steady state, the membrane and the cake resistances, and the separation efficiency. On the other hand, the filtration rate at a pseudo-steady state increases, whereas the cake resistance decreases with the increase in cross-flow velocity. However, the effects of operating conditions on internal membrane fouling are negligible. A theory based on the basic filtration equation and the force balance model of particle deposition is proposed for estimating the filtration rate at a pseudo-steady state. The experimental data agree very well with the model calculations. A lower cross-flow velocity or filtration pressure gives the phospholipid monomers more opportunities to penetrate the cake and the membrane into filtrate. Therefore, the rejection coefficient increases with the increase in filtration pressure or cross-flow velocity. Compared with the conventional “dead-end” cake filtration, the use of cross-flow microfiltration in the purification of liposomes is an efficient method. [ABSTRACT FROM AUTHOR]

Two polymeric membranes, PTFE and PVDF, were employed in a direct contact membrane distillation system to investigate the effects of NaCl concentration, feed temperature, and flow rate on distillate flux and NaCl rejection. The distillate flux increases with increasing the feed flow rate or temperature, PTFE membrane has a higher distillate flux than that of PVDF, and PTFE membrane also has a larger solute rejection than that of PVDF membrane. The decrease of solute rejection by PVDF membrane is owing to the membrane pore wetting, especially at high feed temperature and flow rate. The membrane fouling tests under various feed compositions show that increasing NaCl concentration from 4.5 wt% to 10 wt% or the addition of CaSO4 or BSA into NaCl solution does not cause severe fouling on the PTFE membrane. The distilled water flux recovery (FR) is about 0.96-0.97. The addition of MgCl2 or MgSO4 has a little significant fouling tendency, the distilled water FR is about 0.87-0.88. [ABSTRACT FROM AUTHOR]