| Due to its simple structure,no moving parts,convenient operation and maintenance,high separation efficiency and fast separation,hydrocyclones have been widely used in the separation of heterogeneous media in petrochemical,environmental,mineral processing,medicine and many other fields over the past century.For fine discrete phases(particles or droplets)in the mixture to be separated,the separation efficiency is lower when using conventional hydrocyclone(CHC).In response to this problem,in the early 1990 s,researchers carried out related research by reducing the size of CHC and designing the mini hydrocyclone(MHC,the main diameter was less than 35 mm).It is found that the centrifugal acceleration of the liquid flow in MHC can reach 10 to 50 times that of CHC under the same feed velocity,which makes MHC show a better separation efficiency for the fine discrete phase.However,compared with CHC,the research on the separation performance of MHC for discrete phases of different types and particle size ranges has not been systematically studied,and the enhancement mechanism of MHC to the separation efficiency of fine discrete phases mainly stays at the level of theoretical analysis.Additionally,the current optimization and prediction methods for the separation performance of MHCs are relatively cumbersome and have low accuracy.Therefore,revealing the separation mechanism of the MHCs and establishing the accurate and high efficiency optimization and prediction methods are of great significance for shortening its research period and expanding the application field of the MHCs.In the current study,the separation performance of hydrocyclones with different main diameters under the same feed velocity is firstly studied,for different discrete phase types and particle size distribution ranges.It was found that although the pressure loss of the MHC is higher than that of CHC,the separation efficiency of the MHC is higher than that of CHC under the same feed velocity.For both cases where the density is less and greater than that of water,the optimal particle size ranges in which the separation efficiency of the discrete phase is significantly enhanced by MHC were respectively clarified.At the same time,exampled by microplastic particles that have not yet formed a standard separation method,the experimental study on the separation performance of two MHCs with different main diameters was carried out,and keep the feed pressure of two MHCs the same during experiment.The results show that the separation efficiency of the MHC with a smaller main diameter is higher,especially for fine particles by 10-40 μm,the efficiency enhancement effect is more obvious.To study the feasibility of further improving the separation efficiency of the MHC,these above two MHCs with different main diameters were connected in series to form a two-stage MHC series separation system.Through the research on the separation performance under the same feed pressure,it was found that the total separation efficiency of microplastics is higher than that of any single-stage MHC operating independently.Using theoretical analysis,the efficiency enhancement mechanism of MHC was analyzed from the perspectives of the radial force of discrete phase both in the MHC and CHC,the Reynolds number,the wake entrainment effect of large particles and the empirical formula.And the influence of the main diameter of hydrocyclone on particle migration is obtained through the migration trajectories and migration time of the particles in hydrocyclone with different main diameters.It was found that the larger the main diameter and the larger the particle size,the easier it is for particles with a density greater than water to escape from the overflow outlet.With the help of high-speed video technology,the gas core morphology of CHC and MHC was studied under different operating parameters.Results show the ratio of gas-core diameter of the CHC to the that of MHC is much larger than the ratio of the main diameters of the two hydrocyclones.The reason for the enhanced efficiency of the MHC is explained from the perspective of gas-core morphology.By using Particle Image Velocimetry(PIV)technology,the axial velocity distribution trends of MHC and CHC was studied,and combined with the analysis of LZVV,the advantages of MHC for the separation of discrete phases with density greater and less than that of water were respectively investigated.By summarizing the optimization methods of the current MHC geometric parameters,taking the vortex finder length of MHC as an example,a fast optimization method of geometric parameters based on CFD-dynamic mesh(DUOM)was proposed.By comparing the conventional single factor optimization method(SFOM)and DUOM under the same conditions,the results of the two optimization methods have a high degree of agreement.while the two optimization results have a high degree of agreement,and DUOM saves 49.76%time than SFOM.The relationship models between the main diameter of hydrocyclone and the operating parameters on the separation performance,and the relationship model between the main diameter and the physical parameters of the medium on the separation performance were established,respectively.Taking into account MHC’s different flow field characteristics to CHC,1656 experimental sample data of MHC’s separation performance from different researchers were obtained,and further,a BP neural network prediction model of the separation efficiency of MHC was established based on the machine learning.The established prediction model is effectively verified by the test data set.The research on the prediction performance of the model with different number of hidden layers,number of neurons and initial learning rate was carried out,and the optimal number of hidden layers,neurons and initial learning rate were obtained.The error of the prediction model is only 7.26e-4,which realizes the accurate prediction of the separation efficiency of MHC.In practical applications,additionally,for the given physical parameters of the medium to be separated and the separation efficiency metric,the BP model can obtain the combination relationship of the corresponding geometric parameters and operating parameters,which provides guidance for the structural design and the regulation of operating parameters of MHC.Aiming at the risk of blockage at the inlet and outlet of MHC in the application of complex working conditions,a particle size rearrangement separator was designed through combining with the high efficiency of MHC and the larger space characteristics of CHC,and the rearrangement effect of the rearrangement inlet was effectively verified.The separation performance of the anti-blocking separator and CHC with the equivalent main diameter was compared and found that although the pressure loss of the anti-blocking separator was higher than that of CHC,it can reduce the risk of blockage of the outlet of MHC,and the separation efficiency is higher than that of CHC,especially for small particle size particles. |
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