A review on the Investigation of Hydrocyclone Performance by shape optimization

. A hydrocyclone is a centrifugal classifier that separates particles by size using centrifugal force. Applications for hydrocyclones are incredibly varied. It is used to separate solids from liquids, liquids from liquids, and gases from liquids. It is easy to install and use, simple, inexpensive, and low maintenance. It serves as the brain of the mineral processing plant and is used to process water in important sectors of the textile, petroleum, chemical, paper, and agricultural industries. It is made up of a cylindrical and a conical portion. Three holes are present — two outputs and one for the feed intake. The under flow was for pollutant outlet and the vortex finder was for water outlet. Pressure drop, geometrical factors, and feed size distribution all have an impact on the hydrocyclone's efficiency. The present work reviews the shape optimization of vortex finder, spigots, air core and walls of the hydrocyclone for enhancing the desired outcome of the hydrocyclone.


Introduction
Hydrocyclone is a centrifugal classifier, which uses the centrifugal force to create the size separation.Hydrocyclones are extremely versatile in application.It is used to separate solids from liquids, liquids from liquids, and gases from liquids [1,2].It is simple, cheap, less maintenance, easy to install and operate.It forms the heart of mineral processing plant and utilized in major in major industries like textile, petroleum, chemical, paper and agricultural for processing water.[3,4,5] It constitutes two parts namely cylindrical and conical part.It has three openings, one for feed inlet and two for outlets.The vortex finder was for water outlet and under flow was for contaminant outlet.The efficiency of the hydrocyclone is influenced by pressure drop, geometrical parameters and feed size distribution.To increase the output of the hydrocyclone, optimization of the geometry of hydrocyclone plays a vital role.
In general the feed particles were tangentially supplied into the cylindrical portion of the hydrocyclone through the feed inlet.The particle inside the hydrocyclone experiences two types of force, namely centrifugal force and drag force.The former force pushes the particle to the wall while the later one to pulls the particle to the center.Hence two vortex are created, primary vortex and secondary vortex.Higher particles experiences more centrifugal forces and once it strikes the wall it losses the radial momentum and settle down due to gravitational force forming the primary vortex.While the lighter particles along with water experiences drag force and concentrated in the center initially which is thrown out of the hydrocyclone through vortex finder due to pressure difference forming the secondary vortex.
Hydrocyclones were designed based on their application.The optimization of geometrical parameters is essential to reduce energy consumption and improve the performance of the hydrocyclone.This model is not suitable hydro cyclone as turbulence will occur inside the hydro cyclone.Hence RSM (Reynolds Surface Model) need to be implemented for considering curvature and changes in strain rate.The results obtained from the investigation need to be compared with the experimental results of the hydrocyclone.

Optimization in Vortex Finder
Vortex Finder aims to stop the re-entrainment of slurry in the overflow jet.The positioning, the length and shape influence the flow field to a large extend.Lucia Fernandez Martinez et al., [6] investigated by comparing two hydrocyclone of different size with consistent conclusion.By enlarging the vortex finder length, the time taken for the particles to leave through the underflow will be prolonged thereby increasing the separation efficiency.[7] Near to the juncture between the conical and cylindrical part the vortex finder provides an adverse effect due to change of trajectory and turbulence inside the vortex finder.Also when the vortex finder reach near the underflow some coarse particle will enter into the overflow due to short circuit flow [8].Hence depending upon the feed particle size and distribution the optimized length of vortex finder is found to be 0.01 times the total height of the hydrocyclone.
Another way to overcome short circuit flow and increase the classification efficiency is by improving the shape in the form of arc as shown in figure 2. Upon increasing the vortex finder's arc length, the tangential velocity and pressure drop of the hydrocyclone initially increases and then drops down [8].The axial velocity was lowered so as to provide enough time for the coarse particle to leave the hydrocyclone via underflow.The flow field becomes stable as the turbulent intensity was dropped with increase in Arc length.Thus for a 50mm hydrocyclone, the arc length should be 30 mm from the bottom for attaining maximum separation efficiency.

Fig. 2. Hydrocyclone [8]
Hyung wook Yi et al. [24] described hydrocyclone as a constant and effective filtering device used to eliminate particles flowing through pipelines.Researches were made in optimizing the outlet flow ratio of mini hydrocyclone.It separates particles in the size range for classifying bacterial and algae from the flow.The mini hydrocyclone was fabricated using 3D printer for SWAS thermal power plant application for replacing strainer filter.Using gravimetric method separation efficiency was measured and compared with the sludge discharged from the underflow and overflow outlets.The optimization of the outlet flow ratio has been obtained by adjusting the overflow and underflow diameter of the mini hydrocyclone.The results obtained through the Full Factorial Design and optimization were compared with the experimental results.
Liu P et al, [25] A hydrocyclone, centrifugal sedimentation device used to separate extremely large size particle with two products.This research consists of two stage hydrocyclone with four products.In the first stage, fine particles exit through the internal overflow of a coaxial double pipe and medium sized particles exit through the outer overflow pipe.Through a study of the fluid flow dispersion in multi-product hydro cyclones using numerical simulations, the impacts of geometrical parameters and operating parameters in hydro cyclones were investigated.This fourproduct separation hydrocyclone finds its application in the iron concentration recovery.This research offers resources for comprehending the theoretical and practical applications of the multi-product grading instrument development and flow field distribution in hydro cyclones.

Optimization in Spigots
The performance of the hydrocyclone is impacted by three spigots.They are the feed intake, underflow, and overflow diameters.S. Venkatesh et al. [9] investigation into the aforementioned geometrical parameter's change to improve hydrocyclone performance.The head will increase and the pressure drop will increase as the feed inlet dimension increases [10].It causes the inlet height and width to be reduced by 63 and 53 mm respectively.The capacity to load particles is reduced when the amount decreases further.Similar to this, if overflow dimensions are increased, the head will decrease and the pressure drop will do the same.Thus, the hydrocyclone delivers the anticipated pressure drop when the feed dimensions are decreased together with the underflow dimension and increased.
The optimized spigots of the hydrocyclone have a drastic influence over the flow characteristics.M. Quteishat [11] investigated the flow field characteristic for understanding the relation among the different geometrical parameters within the hydrocyclonefor improving the flow pattern.The velocity component is shown in the figure 3. [11] Among the three components, tangential velocity is the essential component for the better working of hydrocyclone.Higher the VƟ, larger the centrifugal force acted upon the particle.Whereas the axial velocity should be smaller so that fine particles alone would leave through the overflow.Using numerical solution though the velocity components are predicted it should be experimentally validated.In order to validate it scholars usually deploy LDA (Laser Doppler Anemometer) for measuring the mean velocity of the flow field.The hydrocyclone which need to be validated by LDA should be made of Plexiglas [11], which allows total optical access for measurement.In the absence of flat plane box covering the hydrocyclone, the mean velocity was determined by using LDA.Thus LDA permits a nonintrusive coupling of the flow field within hydrocyclone.PIV (Particle Imaging Velocimetry) is being used conventionally to measure the flow field.

Fig. 3. Illustration of hydrocyclone velocity components
Gregori Ullmann et al. [22] made an optimization study of thickener hydrocyclone by investigating 56 geometry of the separating device.Thickener hydrocyclone used to create a liquid free solid subsequent for extraction of dissolved metals.Differential Evolution (DE) algorithm was adapted for obtaining 3 different optimized hydrocyclone.The optimized hydrocyclone were numerically and experimentally compared to acquire lower Eu Number with maximum total efficiency.Table 1 shows the underflow to through put ratio of the 3 optimized hydrocyclone were 35%, 30% and 87% smaller than the conventional hydrocyclone.

Optimization in Air Core
A low pressure, partially air-filled axial core is generated inside the hydrocyclone as a result of the fluid rotating spirally.This core is directly connected to the atmosphere from the underflow to the overflow.Because of the ongoing disruption from progressive waves, the surface of the air core will not be regular.The development of an air core suggests that vortex stability is crucial for preserving feed rate and enough pressure.Air core development is crucial for the removal of dense particles.Investigation by Rajendran Sripriya et al., [12] shows that reducing the air core improves the separation efficiency of the hydrocyclone.By quantifying the appearance of the air core inside the hydrocyclone its efficiency can be improved.A dense medium hydrocyclone in the industrial scale was developed in the investigator work which removes particles of size within the range 40mm to 0.5 mm.Using mathematical models in dynamic simulation the air core development, its size and shape can be predicted [13,14].Figure 4 describes the air core representation picture obtained by adjusting the flow splitting the air core type can be determined.Among the different methods of suppressing the air core, the familiar and most accepted one was by introducing a rod within the hydrocyclone by fixing it along the central axis and supported outside the overflow and underflow.Thus it acts like a fixed beam with negligible vibration.This method was introduced by Liang-Yin Chu et al. [15] additionally evaluated the features involved with solid core like maximum separation sharpness, maximum total separation efficiency and minimal corrected cut size.Figure 5 shows the new types of hydrocyclone by changes in cone shape to parabola and hyperbola type with and without solid core.
To replace the air core inside the hydrocyclone, a solid rod has to be introduced, the tangential velocity increases causing the centrifugal force of the particle to be improved and thereby separation progress.Consequentially the radial and axial velocity components near the vortex finder were all diminished by the air core removal.The investigation revealed that the enhancement of hydrocyclone cone, the separation becomes remarkable.The test is validated using tracer of different specific gravity in the transparent setup.

Optimization in the Wall
Fernanda Falqueto Salvador et al. [16] replaced the walls of the hydrocyclone with filtering walls made of Bronze particle (Dp= 150 µm) and 2.5 mm thickness and compared its performance with that of the conventional hydrocyclone.The figure 6 shows the different types of hydrocyclone in comparision with the conventional hydrocyclone.The Computational Flud Dynamic studies reported that the filtration would reduce the rotational flow and pressure drop as the pores leads to excess liquid into the device.In addition it reduces the radial velocity and thereby reducing the pumping energy cost [17].The optimization was done for two cases, one is for identifying the configuration with minimum Euler Number and another was to find the configuration with maximum total efficiency.After the simulation using CFD with RSM, Response Surface Methodology turbulence model the optimized ratios had been obtained for the two cases as shown in the table 1.Luiz G.M. Vieira et al., [18] after evaluating through experimental and CFD simulation of 25 different configuration stated that the filtered hydrocyclone has significant influence over the separation performance and capacity over the conventional hydrocyclone.[20,21] At constant pressure the Euler number has a reduction of 13% for filtered hydrocyclone over the conventional hydrocyclone.With connection to it at constant flow rate the pressure drop in the filtered hydrocyclone was less because the pores involves an excess liquid into filtering device.

Conclusion
Accordingly, the desired outcome of the hydrocyclone can be improved by adopting the following shape optimization in the hydrocyclone for the particular process requirement based on the thorough analysis received from various scholars.i) The optimal length of the vortex finder is discovered to be 0.01 times the overall length of the cyclone, depending on the feed particle size and distribution.
ii) The hydrocyclone provides the anticipated pressure drop when the feed dimensions are decreased together with the underflow diameter and increased.iii) The hydrocyclone performs better at separating lighter particles when adding a solid core parallel to central axis.iv) The separation performance would be improved and the cost of pumping energy would decrease if the walls of the hydrocyclone were replaced with filtering walls, which would result in a reduction in Euler Number and pressure drop.

Table 1 .
2023 https://doi.org/10.1051/e3sconf/202340504047 E3S Web of Conferences 405, 04047 (2023) D.O.Silva et al. [23] studied 25 hydrocyclone using central composite design in order to obtain an empirical correlation.The empirical correlation has been used to predict the overall efficiency and Euler Number.Upon using the DE algorithm the maximum overall efficiency and minimum Euler Number were obtained.The obtained values have been fitted to experimental data.The optimized hydrocyclone has an overall efficiency of 85.5% and Euler number as 2150.The cut off size is 4.3 µm.The scale ratio of the geometry for maximum overall efficiency has been described in table 1. Optimized scale for different ratios of the best thickener

Table 2 .
Optimized scale for different ratios of the geometries of hydrocyclone with filtered walls