Study On Solid-liquid Separation Characteristics And Fatigue Performance Of Air-Sparged Hydrocyclone

Hydrocyclone is a separation equipment based on the different centrifugal forces due to the difference density of separated mediums.It has many advantages on simple structure,convenient operation,high separation efficiency,large production capacity and so on.Therefore,the hydrocyclone is widely used in mineral processing,chemical industry,biology and some other industrial fields.The air-sparged hydrocyclone technology has been gradually developed in recent years.However,the technology is only used in liquid-liquid separation or particle flotation.Taking into consideration the improved internal flow structure of hydrocyclone due to sparged air,we taked a new approach by sparging air to enhance the solid-liquid separation of hydrocyclone in this paper.Numerical simulation and experimental system are performed to research the enhanced solid-liquid separation by filling air.The main contents and conclusions are as follows:To simulate the flow field structure of the air-sparged hydrocyclone,the RSM turbulence model was used to calculate the turbulent flow field,the free surface VOF multiphase flow model was selected to calculate the air-liquid interface.Comparing with the traditional swirling flow technology,the air sparged hydrocyclone can effectively eliminate the circulating flow and improve the tangential and axial velocities to enhance the separation effect.The PIV was used to measure the flow field in the hydrocyclone,and experimental data were compared with the results obtained by the CFD simulations to verify the correctness and accuracy.The separation performance test platform was established to study the effects of inlet velocity,distribution of air-sparged positions?A,B,C,D?and pressure Pair on the enhanced separation characteristics of the air-sparged hydrocyclone.Results show that the separation efficiency E increases with the increase of inlet velocity,and it can be divided into I,II and III regions by the growth rate.The growth rate in II region is larger than that in the other two regions;The separation efficiencies under different air sparged positions are different obviously.Specifically,E decreases when the air-sparged hole is at A and D,while increases at B and C ports.The pressure drop decreases with A,B,C and D in order.In addition,the separation efficiency E has a normal distribution with the increase of Pair,and E approaches to the maxim?m value when P_air=0.3⁰.5,while the pressure drop is unchanged with the increase of Pair.Hence,the recommended operating conditions is:C point inflation and P_air=0.4MPa,v=2.5m/s.Under this condition,the air-sparged hydrocyclone technology can effectively improve the separation efficiency up to almost 14%of medi?m sand particles?10?27?d_s?80um?,and the d50 can be reduced from 52?m to 41?m.A high-speed camera was used to set up the test platform to research the air core.The whole process from the formation of air core was observed systematically,and the influence rule of air core is studied.After sparging the air,the diameter of air core increases rapidly from top to bottom and then becomes steady.The stabilization time T decreases with the increase of the air pressure.The diameter of air core increases rapidly with the filling of pressurized gas,reaching the maxim?m value at the location.With the further increase,the diameter of air core keeps unchanged,and fluctuates and decreases slightly.In addition,the change of air inlet?A,B,C,D?had little effect on the diameter of air core.Comparing with the theoretical formula of the diameter air core of conventional hydrocyclone,the empirical formula of the air core diameter in the air-sparged hydrocyclone under the condition of small gas-liquid ratio?<2%?is obtained.The formulae of air core diameter of air sparged hydrocyclone is proposed byd_air?28?d_c1[?10?(0.66-0.57P_air?10?0.73P²_air)?d_cd_o?²]^-.0625.It is found that the diameter of the air col?mn is unsteadily,the diameter of the air core fluctuates at all times,and the fluctuation rate of the air core n_airincreases gradually with the axial direction of the cyclone,reaching 18%at Y=-330.The hydrocyclone is in the risk of fatigue failure.Therefore,it is necessary to study the safety performance.In this paper,the ratcheting behavior of bolt and gasket were studied according to the working characteristics of the hydrocyclone.Results show that the stress amplitude,stress rate and different loading sequences have great influences on the ratcheting strain of the PTFE gasket.Based the experimental data,A modified VP model to predict the ratcheting behavior of the 35CrMo bolt was establisded considering the combined effects of stress rate and stress amplitude and a very good prediction accuracy has been verified.