Fish-hook Effect Research Articles

The effect of seasonal variation of medium viscosity on centrifugal desanding in shaft seal water system of suction dredger: Numerical simulation and mechanism study

As a lubrication medium, the shaft-seal water often carries substantial sand particles in the cutter suction dredger, causing severe wear and tear of the internal components of the slurry pump. It has been proved that the shaft seal water system could be optimized by introducing a hydro cyclone to prolong the service life of the slurry pump. However, it was found that the seasonal variation of water viscosity would produce an obvious effect on the centrifugal separation of sand particles. Therefore, in this study, the influence of seasonal viscosity change on the flow field characteristics and sand particle separation was systematically studied by computational fluid dynamics (CFD). The simulation results showed that the fluid and pressure field in hydro cyclone has good symmetry under different viscosity. While with the increase of viscosity, the fluid resistance coefficient increases, resulting in a downward trend of turbulent kinetic energy and an upward trend of negative pressure zone, which is not conducive to sand particle separation. Moreover, to verify the consistency between simulation and actual industry, the grade efficiency of sand particles was studied and discussed. The average particle size of sand could be reduced from 37.8 μm to 8.1 μm, and the separation efficiency could reach 90% under better suitable dredging conditions (Salinity: 34%, Temperature: 20 °C). Further, the experimental and industrial results showed that the fish hook effect inevitably existed in practice due to the entrainment of coarse particles. This study would provide theoretical support for the subsequent optimization of the shaft seal water system.

Study on the effects of a common liquid hopper on the separation efficiency of parallel hydrocyclones

To improve the separation efficiency of parallel hydrocyclones, a new type of common liquid hopper was designed. The separation efficiency of conventional parallel hydrocyclones and those parallel with liquid hoppers were measured experimentally and the influence of common liquid hopper on the flow field analyzed using FLUENT software. The results showed that the efficiency of the parallel hydrocyclones group with liquid hoppers was higher than that of the conventional group, with the maximum efficiency increased by 2.2% and average efficiency increased by 2.1%. The fishhook effect in the efficiency curves was clearly weakened. The separation efficiency of particles between 3 and 10 μm was clearly improved. Compared with the conventional parallel connection, a liquid hopper made the air core in the parallel hydrocyclone group disappear. Meanwhile. the locus of zero vertical velocities was closer to the inside of the hydrocyclone and the free vortex height higher, which make the separation space larger. In addition, parallel vortices in the liquid hopper possessed an inherent self-stability and restricted each other, which caused the swing amplitude of the vortex system center with liquid hopper to be smaller than that of the single vortex center. Therefore, it was demonstrated here that the common liquid hopper improved the separation efficiency of parallel hydrocyclones.

Numerical simulation and experimental validation for investigating the novel hydraulicbarrier-hydrocyclone in industrial beneficiation process

In the face of the dwindling reserves of high-quality phosphate rock resources in the world, beneficiation and purification of low-grade phosphate ore is a possible solution to alleviate the growing scarcity for strategic phosphorus resources. Hydrocyclone is one of the common equipment for solid–solid separation in liquid medium, which is suitable for mineral beneficiation processing. The study investigated the industrial beneficiation of low-grade phosphate ore by novel hydraulicbarrier-hydrocyclone. The results from computational fluid dynamics (CFD) simulation revealed that Semi-through hydraulicbarrier (S-Hb) hydrocyclone had the optimal performance, making short-circuit flow reduced to 7.17% and eliminating fish hook effect, so that the classification efficiency increased by 5% and separation sharpness reached 0.9516. The reasons leading to performance intensification were elaborated in accordance with the optimization and integration of hydrodynamics multiphase flow field by hydraulicbarrier, including the pressure, velocity, turbulent kinetic energy distribution and air core development, as well as streamline analysis, etc. The results from practical industrial experiment indicated that the P2O5 grade was increased to 23.6wt.% from an initial grade of 17.5wt.%, meeting the medium-grade phosphate ore specifications, and the SiO2 content was decreased from 29.0wt.% to 4.2wt.%, meanwhile, the proportional error was 0.74% about cutting size compared to simulation results, indicating excellent consistency. The investigation offered an economically viable route to beneficiate the low-grade phosphate ore, cogently supporting sustainable development of phosphorus resources in chemical engineering.

Study of the Fluid Passing through the Screen in the Three Products Hydrocyclone Screen (TPHS): A Theoretical Analysis and Numerical Simulation

The three products hydrocyclone screen (TPHS), a branch of the hydrocyclone, effectively removes the fish-hook effect, which has been used in the industrial field. The current cylindrical screen in the TPHS generates the characteristic flow known as the screen underflow, which has a significant impact on device performance. To investigate the flow behaviour of the fluid passing through the screen, a combination of a dynamic analysis and a numerical simulation was used. The permeating process in the TPHS was abstracted by a simple fan mode in this work to generate the flow-rate equations and the driving-force models. The pressure difference was the driving force for the screen penetration in the ideal fluid, but it also included a viscous force in the viscous fluid. Furthermore, at the same inlet velocity, the viscous fluid had a higher flow rate than the ideal, indicating that the viscosity promoted the fluid penetration. Meanwhile, as the inlet velocity increased, the mass flow of the screen backflow increased, while the corresponding proportion first rose to a peak then dropped and then gradually stabilised. Furthermore, a flow equation for the screen underflow in the TPHS was developed, which is related to the structural parameters (the rotation radius, the length of the cylindrical screen, the aperture size, and the open-area percentage) and the process parameters (the dynamic viscosity of the fluid and the pressure difference between the feed inlet and the screen outlet).

CFD-Based Structural Optimization of Rotor Cage for High-Efficiency Rotor Classifier

Due to the uneven materials dispersion and high dust concentration in industrial applications of turbo air classifiers, a high-efficiency rotor classifier was designed. Numerical simulations by ANSYS-Fluent 19.0, the effects of rotor cage shape, the number of blades, and the blade profile on the inner flow field, as well as classification performance, were investigated. The simulation results indicated a significant improvement in flow field distribution near the classification surface with the conical rotor cage. Furthermore, there was an average reduction of 10.1% in cut size, as well as a 23.6% increase in classification accuracy. When the number of blades was 36, the flow field distribution between the blades was relatively uniform and a smaller cut size was obtained at a higher classification accuracy. A streamline blade with 52° as the inlet installation angle effectively reduced the impact of the airflow on the blade and eliminated the inertia anti-vortex between blades. The cut size reduction was 4.7–6.3%, with a basically unchanged classification accuracy. The material classification experimental results were in agreement with the simulated results. The discrete phase model (DPM) could well-predict the cut sizes and classification accuracy, but it could not present the fishhook effect. The present study provides theoretical guidance for the structural optimization of an air classifier with a rotor cage.

Development of a New Solver to Model the Fish-Hook Effect in a Centrifugal Classifier

Centrifugal air classifiers are often used for classification of particle gas flows in the mineral industry and various other sectors. In this paper, a new solver based on the multiphase particle-in-cell (MP-PIC) method, which takes into account an interaction between particles, is presented. This makes it possible to investigate the flow process in the classifier in more detail, especially the influence of solid load on the flow profile and the fish-hook effect that sometimes occurs. Depending on the operating conditions, the fish-hook sometimes occurs in such apparatus and lead to a reduction in classification efficiency. Therefore, a better understanding and a representation of the fish-hook in numerical simulations is of great interest. The results of the simulation method are compared with results of previous simulation method, where particle–particle interactions are neglected. Moreover, a validation of the numerical simulations is carried out by comparing experimental data from a laboratory plant based on characteristic values such as pressure loss and classification efficiency. The comparison with experimental data shows that both methods provide similar good values for the classification efficiency d50; however, the fish-hook effect is only reproduced when particle-particle interaction is taken into account. The particle movement prove that the fish-hook effect is due to a strong concentration accumulation in the outer area of the classifier. These particle accumulations block the radial transport of fine particles into the classifier, which are then entrained by coarser particles into the coarse material.

Structural optimization of vortex finder for a centrifugal air classifier

To further improve the centrifugal air classifier performance, effects of the fully-inserted vortex finders with slots are investigated. Experimental results show that the classifier with the non-uniform slotted vortex finder has the higher particle selectivity, smaller cut size and narrower product particle size distribution than the classifier with the uniform slotted vortex finder and the base partly-inserted vortex finder. The classifier obtains the particle classifying sharpness of 1.72 when the primary and secondary gas velocities are 12 m/s and 2.4 m/s. The experimental curves present a same distorted S-shape with the fish-hook dip at about 4 μm. Simulation results indicate that the non-uniform slotted vortex finder could accelerate the swirling flow with the gas tangential velocity averagely increased by 3 m/s. The static pressure varies from −350 Pa to 1700 Pa. Meanwhile, the slotted vortex finder can reduce the influence of the short circuit flow on coarse particles. The DPM model can well predict the cut size with a maximum error of 4.9%, but not the fish-hook effect. The obtained results can provide a guideline for the vortex finder design of the centrifugal air classifier.

Experimental study on fine particle separation in a wet electrostatic classifier

Fine particles were separated by applying an electrostatic field in a designed wet classifier to improve the classification performance. Separation experiments were performed using fine silica particles with a size range from 0.21 to 8.71 μm based on the zeta potential of the suspended particles in the water. The effects of feed flow rate, electrode voltage, and feed particle concentration on separation performance were discussed. The results show that partial separation efficiency increased with feed flow rate and feed particle concentration, but decreased with electrode voltage. Maximum total separation efficiency was achieved at a given feed flow rate, a given electrode voltage, and a given feed particle concentration. The total separation efficiency reached 61.9 % when the nozzle diameter was 1.0 mm, the feed flow rate was 46.2 mL/min, and the electrode voltage was 150 V, which was higher by approximately 11.1 % compared to gravity settling. The separation factor for electrostatic wet classification reached 44,000 for 0.5 μm particles. The 50 % cut size decreased linearly with the increase in electrode voltage and a minimum 50 % cut size of 1.033 μm was obtained. Particle agglomeration effect, fishhook effect, and strong reverse flow should be considered when wet classification technology is employed in engineering applications.

Optimization of the powder state to enhance the enrichment of functional mung bean protein concentrates obtained by dry separation

To increase the purity and yield of mung bean protein concentrates obtained by dry separation, the state of the powder was optimized from the milling to air classification processes. Relatively coarse milling (rotator frequency 40 Hz) by a full-scale airflow impact mill generated sufficient detached protein bodies while not overly damaging the starch granules. Subsequently, a higher classifier wheel frequency (50–70 Hz), an induced-draft fan frequency (50–70 Hz), and a lower feed rate (1.0–6.0 kg/h) reduced the cut point and fish-hook effect, thereby contributing to the improvement of protein separation efficiency. Under optimal conditions designed by response surface methodology (RSM), the protein concentrates with separation efficiency 84.0 ± 4.4% and superior free radical scavenging capacity when compared with original flour and protein isolate (wet) was obtained. These results provide insight into the critical parameters affecting powder state, thus facilitating the development of a dry separation method to fractionate mung bean protein.

Fish-hook effect in granulometric efficiency curves of hydrocyclones: A misuse of laser diffraction particle size analysers

Numerous studies have reported the so-called fish-hook effect on granulometric efficiency curves of hydrocyclones. This effect has been reported since laser diffraction particle size analysers started to be used. In this work a 15-mm-diameter Bradley hydrocyclone has been used to separate a suspension of calcium carbonate 1,2% in volume to analyse the fish-hook effect. The Malvern Mastersizer 2000 particle size analyser has been used and both Fraunhofer's and Mie's light scattering theories have been assessed. It has been concluded that the fish-hook effect is a result of using Fraunhofer's correlation to determine the size of particles which are knowingly out of its range of validity (diameters smaller than 50 μm) or using Mie's correlation with inappropriate particles' imaginary refraction indexes (IRI). A method to determine the appropriate IRI in the Malvern Mastersizer 2000 is also presented. The fish-hook effect is therefore a misuse of laser diffraction particle size analysers.

Classifier performance during dynamic fine grinding in fluidized bed opposed jet mills

Dry grinding of particles to sizes below 10 µm can be realized in fluidized bed opposed jet mills. In these mills the energy for comminution is supplied by pressurized gas, which is introduced through focused nozzles. The gas transports the material towards an internal classifier, which separates the fines from the coarse material. The fines are discharged whereas the coarse material is recycled. Within this study special attention is paid to separation at the classifying wheel. Limestone batch grinding experiments were performed in a fluidized bed opposed jet mill equipped with on-line and in-line probes: The particle size distributions (PSDs) of the product flow and the solid concentration below the classifier were determined on-line. The flow field around the classifier was recorded by a high-speed camera and off-line measurements of the mill inventory and its PSD were performed. Our measurements reveal that the solid transport from the milling zone to the classifier and the classifier performance strongly depend on solid concentration. Increasing the solid feed concentration or the classifier wheel speed leads to unwanted accumulation of product-sized particles inside the mill. In particular, we find high solid loadings of up to 1.05 g⋅g−1 and strong cluster formation (local zones of high solid concentration) in the vicinity of the classifier blades. Estimated separation efficiency curves of the classifier show a strong “fish-hook effect” which increases with the solid concentration. Our findings are relevant for future process optimization by careful tuning of grinding performance, holdup and classifier speed.

Experimental and theoretical analysis of the classification of Sn0.3Ag0.7Cu lead-free solders powder

Classification experiments using Sn0.3Ag0.7Cu lead-free solder powder prepared by supersonic gas atomization were conducted by turbo air classifier. The effects of rotor cage rotary speed on the cut size and partial classification efficiency of Sn0.3Ag0.7Cu solder powder were investigated. The relationship between cut size and rotor cage rotary speed was calculated through curve fitting. Results showed that cut size and median diameter of fine powders decreases exponentially with an increasing of the rotor rotary speed. The “fish-hook effect” existed in the turbo air classification process of Sn0.3Ag0.7Cu solder powder. The “fish-hook effect” weakens and classification efficiency increases with the rotor cage rotary speed decreasing. The efficiency of classifier was evaluated with the classification size ratio (CSR) index. It shows that higher rotor cage rotary speed is beneficial to the separation of coarse and fine powders adequately, and the classification is difficult when the size distribution of material fed is narrow.

Inclusion of screening to remove fish-hook effect in the three products hydro-cyclone screen (TPHS)

A novel three product hydro-cyclone screen (TPHS) has been developed at the Key Laboratory of Coal Processing and Efficient Utilization, China University of Mining and Technology, China for particle separation. The new hydro-cyclone consists of a cylindrical screen embedded in a conventional hydro-cyclone (CH), which combined both centrifugal classification and screening. The present study aimed to remove the fish-hook effect and demonstrate the performance of TPHS based on pilot-scale and industrial-scale experiments. In pilot scale, the screen aperture size varied in the range ∼0.50–0.70 mm, while the aperture size was 0.60 mm in case of industrial-scale. It found that the performance of hydro-cyclone significantly influenced by the aperture size. In contrast to the pilot-scale CH, the fines and the water recovery of TPHS in underflow were reduced and became less with the increase of aperture size, while the contrary trends of fines obtained in overflow. Furthermore, TPHS generated a new outgoing stream namely screen underflow due to the presence of a cylindrical screen, wherein the dominant size distribution was close to overflow. Note that the fish-hook effect was disappeared entirely in TPHS because the trapped and entrained fines in underflow reduced significantly. Also, the performance of both TPHS and CH was discussed based on the Hancock classification efficiency (HE), imperfection (I) and cut size (d50c) using the data obtained from the pilot-scale and industrial-scale experiments which indicate that TPHS represented a better performance than CH. A successful industrial-scale application of TPHS instead of CH in coal preparation plant demonstrated its advantage and application potential.

Effect of inlet particle arrangement on separating property of a cyclone separator

Different arrangements of particles on the inlet section exert different effects on the separation property of a cyclone separator. Sorting classifier with different heights was connected in series with a conventional cyclone, positive rotation cyclone, and reverse rotation cyclone respectively, to investigate the effect of particle arrangement on the separation property and inner flow field. Results indicate that the implementation of a sorting classifier increases the pressure drop and energy consumption of a cyclone separator. The taller the sorting classifier, the larger the flow is. The energy consumption in positive rotation cyclone is closer to that in reverse rotation cyclone. Meanwhile, the tangential velocity in inner flow field is higher and the separating property is enhanced. The reverse rotation cyclone relieves the fishhook effect, whereas the positive rotation cyclone eliminates such effect. The reverse and positive rotation cyclones demonstrate an improved separating property for particles smaller and greater than 1 μm, respectively. Moreover, the reverse rotation cyclone demonstrates superior overall separation, but the positive rotation cyclone demonstrates a greater classification effect than the reverse rotation cyclone.

A Comparative Study on the Separation of Different‐Shape Particles Using a Mini‐Hydrocyclone

AbstractThe separation efficiency from water of different‐shape particles was studied experimentally using a mini‐hydrocyclone. Spherical and flaky (plate‐like) aluminum particles with the same particle size distributions were employed. Also, the effects of the feed flow rate and the temperature on the separation performance were studied. The results were investigated in terms of slurry recovery, total efficiency, and partition curves. The separation efficiency of the spherical particles increased with increasing particle size, temperature, and feed flow rate, as expected. The fishhook effect, as a noticeable phenomenon, was observed for the spherical particles. In case of the flaky particles, the separation showed an unusual behavior: The separation efficiency decreased with increasing particle size in the largest particle fraction, which has so far not been reported and addressed in this way.

Packing Efficiency Characterization of SiC Abrasive Machining Particles for Photovoltaic Silicon Wafer Slicing

Silicon Carbide (SiC) abrasive machining solid particulates is one of the key engineering materials in the continuous development of wafer technology. Analysis of its packing behaviour is important to ensure the highest quality in the ingot cutting process to produce silicon PV wafers. One of the parameters that is monitored is the amount of fine particles present during the cutting operation and the subsequent separation technologies to recycle the material to reduce cost and allow environmental sustainability. This study presents results showing that with increasing circularity, less fines remain in the slurry suspension which is expressed as the percentage of total volume of particles in the slurry mixture. Furthermore, the work has gathered that there is a strong relationship between the % fines removed and the average diameter of the particles. An analysis of the relationship between the actual % fines remaining as a function of particle diameter reveals that the % fines remaining decreases as the particle diameter increases and this behavior correlates well with a power law equation. This agrees with a model of the fishhook effect during particle separation in a mini-hydrocyclone expressed as an equation raised to the fourth power.

Effects of the geometry of fine powder outlet on pressure drop and separation performances for dynamic separators

The performance of a dynamic separator installed in the cement industry with different conceptions of fine collection outlets, was evaluated using the FLUENT software. One cylinder shaped and four tangential shaped fine exit tubes were designed to compare the behavior of the flow field of various geometries of air classifiers. Turbulence closure is affected by employing the Reynolds Stress Model which takes into consideration the effects of swirl, rotation and high complex three-dimensional flows. The discrete phase model was used to predict the effect of the geometry of the outlet on the collection efficiency and the fish-hook effect. It is found that the modified structure have a great impact on the velocity and pressure fields. The simulation results indicate that the tangential and the axial velocities are hardly influenced by the modified structure of the fine powder geometry. The findings also suggest that the large radial velocity gradients in the axial region as well as in the areas between the rotor blades would cause the return of the fine particles to the annular region to be mixed again with the coarse powder. This phenomenon is more marked for the A type of the separator and leads to a higher fish-hook effect in the selectivity curve. But in simulation, reducing the number of the fine powder exits can decrease greatly the computing memory and time.

Comments on ‘fish hook effect in classifier efficiency curves’ in recent publications in Powder Technology

This note deals with reports of fish hook effect in classifier efficiency curves in recent publications in Powder Technology. Particle size characterisation methods followed in all of them are critically examined. It is shown that where the particle size distributions are determined by laser diffractometry, there is a distinct possibility that correct optical parameters of the test materials may not have been used. In one occurrence, where sieving is the method for measurement of particle size, sufficient details are not available. In another study, the method of size analysis is not disclosed. That is, in all the cases, the accuracy in estimating the efficiency and hence the quality of the data cannot be assessed. Consequentially, the results of all these reports on fish hook should be treated with caution.

Study of particle's shape factor, inlet velocity and feed concentration on mini-hydrocyclone classification and fishhook effect

This research aims to study the influence of particle's shape factor, inlet velocity and feed volume concentration on the particle classification and fishhook effect in a mini-hydrocyclone. To develop study of innovation, three particles with extensive range of sphericities (0.05, 0.34, and 0.82) were chosen. The maximum separation efficiency was determined at three conditions: the highest inlet velocity, most sphericity and lowest particle concentration. The high particle sphericity offers less drag for an equivalent particle diameter. The results revealed that fishhook effect is more explicit for spherical particles. The presence of fishhook effect was described based on available theories.

Fish hook effect in centrifugal classifiers – a further analysis

Two distinctly different types of fish hooks are reported in literature, of which, the most common shape shows a decrease in efficiency to a minimum followed by a monotonic increase with size. The other shape exhibits an increase in efficiency with size till a critical point is reached; the efficiency then decreases till a minimum is reached, followed by a monotonic increase with size.Early theories to explain fish hook phenomenon through variable bypass are shown to be simple mathematical transformations. The ‘mechanistic model’ attributes occurrence of fish hook to a sharp fall in settling velocities in a centrifugal field with change in flow from Stokesian to transient regime. This explanation is shown to be dubious and not in conformity with known principles of physics. Also, the boundary layer model and the entrainment model require considerable refinement as mechanics of fluid flow around irregular particles is not well developed. It is shown that CFD simulations show efficiency curves with or without fish hook effect depending upon the assumptions for simulation.The method of sizing analyses in detection of fish hook effect is critically discussed. Most of the occurrences of fish hook are reported when sizing analyses are carried out by laser diffractometry using Fraunhofer approximation for data interpretation. When alternate sizing techniques, such as Andreasen pipette, disc centrifuge, Coulter counter, Dynamic Light Scattering etc. are used or when Mie theory is applied in Laser techniques, fish hook is not reported.Fish hook effect appears to be repeatable where it was studied. However, the conditions of reproducibility are to be specified by the proponents, if the phenomenon is to find general acceptance. It is likely that fish hook would continue to be regarded as a placebo. Its exclusion in simulation models does not appear to affect cyclone performance prediction.