Reduced Separation Efficiency Research Articles

A numerical study of the effects of lateral flow and retention in open tubular vortex chromatography

Axial dispersion in chromatographic columns is responsible for a reduced separation efficiency. In the present research macrotransport theory is used to predict the phenomenological constants related to axial dispersion. We evaluate the efficacy of lateral flow induced by alternating current (AC) in the presence of retaining walls on the separation resolution. Results show that lateral flows induced by laterally applied potentials as low as 0.3 V reduce C-term dispersion by a factor of 5.0 for unretained conditions (k = 0) and 2.7 for retained (k = 5) conditions, with a diffusion coefficient (Dm) of 10–11m2/s. The present paper further contributes to the understanding of the use of secondary lateral flows for dispersion reduction and offers practical guidance for designing future vortex chromatographic columns. It appears that a maximal performance gain is attained at low aspect ratios (AR=1), with the gain reduced from a factor of 5 to 1.6 for AR=4 for unretained conditions, and from 2.7 to 1.4 for retained conditions (k = 5)

Optimization of Elliptical U-Tube Heat Exchanger (EUTHE) for Spray Cooling Based on the Taguchi and CFD Method

The elliptical U-tube heat exchanger (EUTHE) is widely used in various cooling systems of nuclear engineering for its simple geometrical structure and small space cost. In this paper, a two-phase flow field model of an EUTHE is constructed to analyze the flow characteristics in the elbow zone under different structures with the influence mechanism of droplet motion and liquid film distribution. The Taguchi method is used to investigate the influence of heat transfer performance by structural parameters, and the fitted model is analyzed by regression analysis as well as ANOVA to ensure the accuracy of the prediction results. The results show that thick tubes have a wider liquid film distribution because they are more difficult to trap droplets, achieving high heat transfer capacity while reducing separation efficiency and pressure drop. In addition, the heat transfer capacity and the pressure drop are mostly improved by the increase of the U-tube cross-section long axis length (L2) at the expense of reduced separation efficiency. The optimal cases for each target were obtained by analyzing the influence mechanism of each structural factor, for example, the largest heating tube section (L1) and the U-tube cross-section long axis length (L2), to determine which will lead to the highest heat transfer capacity, which mainly is due to the fact that an increase in these factors leads to the increment of contact area between the fluid and the wall. This work provides a guideline for the design of EUTHE and brings greater benefits to the development of nuclear engineering.

Experimental investigation on flow splitting for the elimination of localized secondary flow in cyclones and enhancement of their performance

The limitation of cyclone performance is attributed to the presence of localized secondary flow, including longitudinal circulation, short circuit flow and eccentric circulation. The present study proposes an enhanced cyclone with split flow (ECSF) to effectively suppress the local secondary flow in cyclones. An experimental setup was constructed to evaluate the performance of ECSF under various operating conditions. The results of the experiment demonstrate that the separation efficiency of ECSF surpasses that of Lapple cyclone due to the synergistic effect of split flows in both the by-pass flow and underflow. When the feed velocity is 13 m/s, the ECSF exhibits a reduced separation efficiency of 89.8% for 10 μm silica particles, which surpasses that of the Lapple cyclone by 10.6%. The ECSF achieves its maximum total and reduced separation efficiencies at a feed velocity of 27 m/s, reaching values of 96.3% and 95.7%, respectively. Compared to the Lapple cyclone, the ECSF demonstrates an extended range of operational capabilities with respect to feed velocity. By maintaining a constant total split ratio in ECSF while increasing the proportion of by-pass flow, it is possible to improve its separation efficiency without augmenting overall energy consumption. The findings of this investigation offer valuable insights for enhancing the dust removal efficiency of cyclones.

Fabrication and characterization of dual-layer hollow fiber membranes incorporating poly(citric acid) grafted GO with enhanced antifouling property for water treatment

ABSTRACT Membrane fouling which occurs during filtration process is a perennial issue and could lead to reduced separation efficiency. In this work, poly(citric acid) grafted graphene oxide (PGO) was respectively incorporated into matrix of single-layer hollow fiber (SLHF) and duallayer hollow fiber (DLHF) membranes, aiming to improve membrane antifouling properties during water treatment. Different loading of PGO ranging from 0 to 1 wt% was first introduced into the SLHF in order to identify the best PGO loading for the DLHF preparation with its outer layer modified by nanomaterials. The findings showed that at the optimized PGO loading of 0.7 wt%, the resultant SLHF membrane could achieve both higher water permeability and bovine serum albumin rejection compared to the neat SLHF membrane. This is owing to the improved surface hydrophilicity and increased structural porosity upon the incorporation of optimized PGO loading. When 0.7 wt% PGO was introduced only to the outer layer of DLHF, the cross-sectional matrix of the membrane was altered, forming microvoids and spongy-like structure (more porous). Nevertheless, the BSA rejection of the membrane was improved to 97.7% owing to the presence of inner selectivity layer that was produced from different dope solution (without PGO addition). The DLHF membrane also demonstrated significantly higher antifouling properties compared to the neat SLHF membrane. Its flux recovery rate is 85%, i.e., 37% better than that of neat membrane. By incorporating hydrophilic PGO into the membrane, the interaction of the hydrophobic foulants with the membrane surface is greatly reduced.

Polyacrylonitrile nanofibrous membrane composited with zeolite imidazole skeleton-8 and silver nanoclusters for efficient antibacterial and emulsion separation

Oily wastewater discharged by industrial development is an important factor causing water pollution. Membrane separation technology has the advantages of low cost, simple operation, and high efficiency in the treatment of oily wastewater. However, membrane materials are easily eroded by microorganisms during long-term storage or use, thereby resulting in reduced separation efficiency. Herein, a zeolite imidazole skeleton-8@silver nanocluster composite polyacrylonitrile (ZIF-8@AgNCs/PAN) nanofibrous membrane was fabricated by electrospinning and in situ growth technology. The surface chemistry, morphology, and wettability of the composite membranes were characterized. The carboxyl groups on the surface of hydrolyzed PAN nanofibers, which can be complexed with zinc ions (Zn2+), are utilized as growth sites for porous metal organic frameworks (ZIF-8). Meanwhile, AgNCs are loaded into ZIF-8 to achieve stable hybridization of ZIF-8@AgNCs and nanofibers. The loading quantity of ZIF-8@AgNCs, which can dominantly affect the surface roughness and the porosity of the membranes, is regulated by the feeding amount of AgNCs. The ZIF-8@AgNCs/PAN membrane achieves effective oil-water separation with high separation efficiency toward petroleum ether-in-water emulsion (98.6%) and permeability (62 456 ± 1343 Lm-2 h-1 bar-1). Furthermore, the ZIF-8@AgNCs/PAN membrane possesses high antibacterial activity against Gram-negative Escherichia coli (E. coli) and Gram-positive Staphylococcus aureus (S. aureus), which is beneficial for the long-term storage and use of the membrane.

Tuning the electrophoretic separations on a surface-accessible and flexible fibre-based microfluidic devices.

Electrophoresis on textile fiber substrates provides a unique surface-accessible platform for the movement, separation and concentration of charged analytes. The method employs the inherently inbuilt capillary channels existing within textile structures, which can support electroosmotic and electrophoretic transport processes upon applying an electric field. Unlike confined microchannels in classical chip-based electrofluidic devices, the capillaries formed by the roughly oriented fibers within textile substrates can impact the reproducibility of the separation process. Here, we report an approach for precise experimental conditions affecting the electrophoretic separation of two tracer solutes, fluorescein (FL) and rhodamine B (Rh-B) on textile-based substrates. A Box-Behnken response surface design methodology has been used to optimise the experimental conditions and predict the separation resolution of a solute mixture using polyester braided structures. The magnitude of the electric field, sample concentration and sample volume are of primary importance to the separation performance of the electrophoretic devices. Here, we use a statistical approach to optimise these parameters to achieve rapid and efficient separation. While a higher potential was shown to be required to separate solute mixtures of increasing concentration and sample volume, this was counteracted by a reduced separation efficiency due to joule heating, which caused electrolyte evaporation on the unenclosed textile structure at electric fields above 175 V cm-1. Using the approach presented here, optimal experimental conditions can be predicted to limit joule heating and attain effective separation resolution without compromising the analysis time on simple and low-cost textile substrates.

Numerical investigation on particles separation using an enhanced cyclone with shunt device: Effect of vortex finder lengths

To improve the performance of the enhanced cyclone with shunt device (ECSD), the vortex finder lengths optimization for the ECSD is carried out by numerical investigation. Reynolds stress model and discrete phase model are adopted. The results show that the separation ability of the ECSD can be improved by longer vortex finder, which is contrary to the generally accepted conclusion that the vortex finder length of the traditional cyclone should not be longer than cylindrical section length. When the ratio of vortex finder length to cylindrical section length reaches 1.5 (225 mm vortex finder), the total separation efficiency, reduced separation efficiency and comprehensive separation efficiency are 90.7%, 89.7%, and 80.6%, respectively, which are the highest. The tangential velocity distribution is one of the most important reasons that the separation efficiency increases with the increase of the vortex finder length in general. The tangential velocity in the conical section of the ECSD increased with the increase of vortex finder length. When the length of vortex finder is the same as that of cylindrical section, the overall energy consumption and split ratio of the ECSD are the largest of 1.88 kPa and 12.4%, respectively, which is detrimental to the overall performance of ECSD.

Experimental study on the separation performance of an enhanced cyclone with shunt device

To expand the application field of the cyclone, an enhanced cyclone with shunt device (ECSD) is proposed to continuously remove coarse particles from the air. To study the performance of the ECSD, an experimental bench was set up, and a series of analyses were carried out using silica particles, talc powder and light calcium powder to simulate particles in air. The effects of the split flow rate, particles (feed concentration and physical properties), feed flow rate and feed static pressure on the separation performance were investigated. The experimental results show that the separation efficiency of the ECSD is higher than that of a traditional cyclone, and continuous particle separation can be realized. With the split flow rate increasing from 0 m3/h to 5.2 m3/h, the total separation efficiency and reduced separation efficiency increase by 53% and 37%, respectively. However, the split flow rate of this model should be controlled within 5.2 m3/h (split ratio 45%); otherwise, the separation efficiency could not be effectively improved and the energy consumption would increase. The cut-off sizes for talc powder, light calcium powder and silica particle are approximately 3.6 μm, 3.8 μm and 5 μm, respectively. For particles with sizes less than 1 μm, the separation efficiency of the ECSD can still exceed 25%. Note that the ECSD has great potential to apply to the field where particulate matter needs to be removed.

Antibacterial nanocellulose membranes coated with silver nanoparticles for oil/water emulsions separation

The superhydrophilic/underwater superoleophobic nanocellulose-based membranes show great potential in oil/water emulsion separation. However, nanocellulose composed of polysaccharides inevitably suffered from bacterial erosion during use or storage, resulting in structural damage or reduced separation efficiency. In this work, silver nanoparticles (AgNPs) as effective bactericidal materials are uniformly deposited on tunicate cellulose nanocrystals (TCNCs) by in situ hydrothermal reduction of silver nitrate. TCNCs not only act as reducing agents for silver ions, but also work as dispersant and stabilizers of AgNPs. Nanocomposite membranes are fabricated by vacuum-assisted filtrating of AgNPs@TCNC suspension, which exhibit nanoporous structure, superhydrophilicity, and underwater superoleophobicity. These membranes could efficiently separate oil/water microemulsion with water flux (>324 L m−2 h−1 bar−1) and oil rejection (>99%). Importantly, these membranes show excellent antibacterial efficacy against E. coli and S. aureus, benefiting to their long-term use and storage.

Cellulose Nanofiber Nanocomposite Pervaporation Membranes for Ethanol Recovery

In spite of the growing interest to exploit nanocellulose in membranes for water purification, reverse osmosis, packaging, and other applications, examples of nanocellulose-containing membranes for pervaporation are rather limited. We here report the preparation of dense nanocomposite pervaporation membranes consisting of a polystyrene-block-polybutadiene-block-polystyrene (SBS) matrix and high-aspect-ratio cellulose nanofibers (CNFs). The membranes were produced by a solvent casting evaporation process, and the CNF concentration was systematically varied. At the highest CNF concentration (15 wt %), a 5-fold increase in Young’s modulus (271 MPa) and a 10-fold increase in the yield strength (18 MPa) were observed, while the elongation at break (37%) remained appreciable, suggesting that the CNFs form a reinforcing network in the SBS matrix. At the same time, the water permeability and sorption doubled and increased ten times (at relative humidity = 100%). Pervaporation experiments were carried out with a 10 wt % ethanol/water mixture at 40 °C. A 3-fold increase in mass fluxes was observed at a CNF content of 15 wt %, which was accompanied by a 40% decrease in the separation factor. This resulted in an increase of the pervaporation separation index from 66.5 g m–2 h–1 (neat SBS) to 89.4 g m–2 h–1 (15 wt % CNF nanocomposite), indicating that the relative increase in fluxes more than compensates the reduced separation efficiency.

Mini-hydrocyclones application in the reduction of the total oil-grease (TOG) in a prepared sample of produced water

The process of de-oiling produced water from offshore oil fields was evaluated using hydrocyclones. An experimental design was employed and the results were used to create an empirical model that describes the reduced separation efficiency as a function of different concentrations of infeed and the pressure drop. A study was made of the procedure for preparing the oil-water emulsions used here in order to reproduce the TOG of the produced water generated in oil field. A procedure to verify the operation of these devices demonstrated that six hydrocyclones operating in tandem can attain the legally acceptable concentration of oil in the treated effluent.

Separation of Saccharomyces cerevisiae from alcoholic fermentation broth by two commercial hydrocyclones

Two different commercial hydrocyclones, Doxie® type-A and AKW® type RWK 21, were employed to separate yeast from alcoholic fermentation broth and their performances were compared. The independent variables selected for this study were the pressure at the inlet of both hydrocyclones, the pressure on the underflow of the Doxie hydrocyclone and the underflow diameter of the AKW hydrocyclone. It was found that the AKW hydrocyclone showed better separation performance than the Doxie hydrocyclone, providing a separation efficiency of up to 89.13% and a processing capacity of more than 239.25kg/h. Mathematical models were generated to predict the performance of the hydrocyclones (mass flow inlet, separation efficiency, flow ratio and reduced separation efficiency) under different experimental conditions. To evaluate the flow field of the hydrocyclones, a three-dimensional simulation was performed using the Large Eddy Simulation (LES) approach, providing detailed information about the flow and turbulence inside these devices, which was essential to understand the separation performance exhibited by them.

Effects of Operating Variables on the Yeast Separation Process in a Hydrocyclone

This work involved the use of a hydrocyclone to separate yeast from alcoholic fermentation suspensions. The performance of the hydrocyclone was quantified using empirical models that describe the capacity, total separation efficiency, flow ratio, and reduced separation efficiency as a function of the concentration of the suspension and the operating pressure drop. The results showed capacities of 0.1283 to 0.1820 m3/h, total separation efficiencies of 81.96% to 92.19%, reduced separation efficiencies of 0.63% to 58.44%, and flow ratios ranging from 81.05% to 84.85%.

Study of Biological Material Separation in Hydrocyclones

Hydrocyclones use the same principle of separation of centrifuges, but with no moving parts and no mechanical complexity. For these reasons as well as its versatility in applications, low cost, simple operation, small size, high production efficiencies with short residence times, these devices have been widely found in industry, and even suggested as a practical alternative to solid-liquid separations involving biological material. In the process of fermentation to produce ethanol, the yeastSaccharomyces cerevisiaeare recovered and recycled to a new stage of fermentation. This separation process is a major challenge, because the yeasts are small and low density. In this sense, the objective of this work was to investigate the use of hydrocyclones for the separation of yeast from alcoholic fermentation. A factorial experimental design (24) was applied and the results were used to determine empirical mathematical model that describes the reduced separation efficiency as a function of different geometrical and operating variables.

Separation Performance of a Low-pressure Hydrocyclone for Suspended Solids in a Recirculating Aquaculture System

The separation performance of a low-pressure hydrocyclone (LPH) was evaluated for suspendedsolids removal in a recirculating aquaculture system (RAS). The dimensions of the LPH were 335 mm cylinder diameter, 575 mm cylinder height, 60 mm overflow diameter, 50 mm underflow diameter, and 68° cone angle. The inflow rate varied (400, 600, 800, and 1,000 mL s -1 ) with 25%, 25%, 20%, and 10% of bypass (Rf), respectively. The maximum total separation efficiency (Et) and reduced separation efficiency (E't) for suspended solids from the effluent of the second settlement tank (before biofiltration) were 58.9% and 45.2%, respectively, at an inflow rate of 600 mL s -1 and 25% of Rf. The maximum Et and E't for suspended solids from the water supply channel (after biofiltration) were 24.4% and 16%, respectively, at an inflow rate of 1,000 mL s -1 and 10% of Rf. The maximum grade efficiency (Ei) was 51.6% for a 300 µm particle size at an inflow rate of 600 mL s -1 with 23% of Rf. The maximum reduced grade efficiency (E'i) was 37.6% for a 300 µm particle size at an inflow rate of 1,000 mL s -1 with 11% of Rf. The results indicate that the separation performance of the LPH for suspended solids removal was size selective and that maximum removal occurred at particle sizes ranging from 300 to 500 µm.

On‐column detection of multiphoton‐excited fluorescence in CE using hyphenated cylindrical‐square capillaries

Multiphoton-excited fluorescence (MPEF) is a complementary and useful mode of LIF detection in CE with advantages of ultra-low mass detectability and spectral excitability, but it is currently quite limited by its end-column configuration. In this article, we demonstrate a novel strategy of on-column schemes that can greatly facilitate MPEF detection in CE. FITC-labeled amine species were used as the model samples for the evaluation and comparison of those detection scenarios. By using the square capillary instead of the conventional cylindrical one, the on-column MPEF could be readily achieved, with detection sensitivity of 0.72 microM that was comparable with the end-column mode. However, this strategy unfavorably reduced separation efficiency. The theoretical plate number on averaging all the sample peaks was significantly decreased from 283,000 to 19,000/m. To minimize such an influence, a short square capillary acting as an on-column MPEF detection cell was then mounted to a long cylindrical capillary responsible for the CE separation. Results indicated that both high separation efficiency (240,000/m) and better detectability (0.42 microM) were realized simultaneously by using this binary-capillary configuration. Quantitative analysis was performed under the optimized detector configuration and revealed a linear dynamic range of 2 orders of magnitude, with mass detection limit down to the mid-yottomole level.

Enhancement of hydrocyclone separation performance by eliminating the air core

A new hydrocyclone was designed with a solid core fixed along the central axis in this study. By introducing the solid core, the air core inside the hydrocyclone could be eliminated effectively. Comprehensive effects of eliminating the air core by the solid core on the hydrocyclone performance indices were experimentally investigated. To examine the influence mechanism of air core on the separation performance, a Laser Doppler Anemometer (LDA) was used to investigate the turbulent flow field inside hydrocyclones with and without air cores. The results showed that the radial and axial velocity components in the area near the entrance of the vortex finder, and the radial and axial turbulence components were all reduced by eliminating the air core, i.e. the flow field characteristics inside the hydrocyclone with solid core became more suitable for the separation process. By replacing the air core with solid core, the hydrocyclone separation performance was improved effectively. Comparing the hydrocyclones with air core and solid core, it was proved to be featured with higher total separation efficiency, larger reduced separation efficiency, smaller corrected cut size and higher separation sharpness, although the hydrocyclone cone shape changed from common type, to parabola type, and to hyperbola type. By increasing the inner space of the hydrocyclone cone, the improvement of separation performance became more remarkable.

Enhancement of hydrocyclone performance by controlling the inside turbulence structure

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.

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.

Solid–liquid separation of livestock slurry: efficiency and cost

Environmental problems may arise on specialized livestock farms, which produce a surplus of nutrients in relation to crop requirements. Separation of this slurry into a liquid fraction and a dry-matter and nutrient-rich fraction, followed by transporting the nutrient-rich fraction to farms with fewer animals, may alleviate the problem. This study showed that the most informative index of separation is the reduced separation efficiency index; where an index value of 0 indicates that the nutrients are distributed equally between the solid fraction and the liquid fraction, and a value of 1 indicates that the nutrients are concentrated in the solid fraction. The reduced separation efficiency values obtained when using simple mechanical screen separators were 0.07–0.5 for dry matter (DM), 0.01–0.1 for total N (TN) and 0–0.2 for total phosphorus (TP). In comparison, decanting centrifuges were very efficient in removing DM (index: 0.36–0.74) and TP (index: 0.4–0.82), but not in separating TN (index: 0.11–0.19). The costs of a treating 4000 tonnes of slurry with a mechanical screen separator or with a decanting centrifuge are £0.44 and £2.21/tonne p.a., respectively.