The Research On Solid-liquid Two-phase Flow Characteristics Of Screw Centrifugal Pump Based On Particle-trajectory Model

The screw centrifugal pump is a new type of slurry pump integrated with screw pump and centrifugal pump. Its main structure is a screw centrifugal impeller, the inlet of impeller is a screw type blade, and its outlet is similar as a mixed-flow blade. The screw part of impeller has a function like volumetric, the centrifugal part put the pumped medium which have acquired energy in impeller into volute, and convert it into pressure energy. It is a good trash pump-no clogging, less damage-all good qualities rolled up into one.In this paper, the solid-liquid two-phase flow characteristics of screw centrifugal pump have been simulated by using CFD technology based on Particle-trajectory Model. The trajectory, energy change of different solid phase particle and under the different work condition was analyzed, also the wear of flow passage components and laws of performance change was discovered. The main contents include:On the one hand, analyzed the flow condition in the screw centrifugal pump, under the basic assumptions, using the continuous equation and the particle control equation analyzed the particle force and the flow condition in impeller, also the feasibility and range of application of Particle-trajectory Model was analyzed. It can offer a theory foundation for characteristics and performance change of two phase flow.On the other hand, the velocity, pressure and surface streamline distribution was analyzed by numerical simulation under water condition. Also the test and numerical results was compared. Under the two-phase flow condition, the trajectory of particle, mass concentration on the flow passage components surface, also the wear and influence of external characteristic of different volume fraction in the computational domain was analyzed. It follows that the relations between good no clogging, less damage and flow characteristics when the transmission medium is solid-liquid two-phase flow.By using the theoretical analysis and numerical simulation, the qualitative and quantitative of results was analyzed in the whole computational domain, acquired results as follows:1、The main work region of impeller is screw part, and there is a "unloading" phenomenon at centrifugal part. Also backflow and secondary flow in the computational domain, the flow condition are unsteady and generate secondary flow at more position at mini-flow condition, which can lead more hydraulic loss.2、The different inject position and physical property of particle can lead different wear mode and wear degree, and the trajectory also can be influenced, the change of diameter and volume fraction of particle is proportional to flow interference caused by solid particle.3、At the same volume fraction of solid phase, the velocity fluctuate wildly at inlet part are when transport the micro particle d=0.05mm and d=0.2mm, after entering the impeller domain, the carrying capacity of liquid phase are becoming weak, and the retardant capacity becoming strong, it can lead velocity-slip and flow turbulence.4、When the particle enter the impeller domain at a certain speed, it will impact with impeller head, leading the mass concentration of solid phase distribute concentrated in this domain, and the main wear mode is erosion, as the increase of wrap angle, the wear position more generated at the shroud of impeller outlet, the wear appears as abrasive mode.5、As the diameter and volume fraction increasing of solid phase particle, the carrying capacity of liquid phase to solid phase becoming more weak, the sedimentation leaded by gravity can lead the pump hydraulic head and efficiency decreased. And there is an optimal diameter and volume fraction range, which can improve the transport capacity of screw centrifugal pump when transport solid-liquid two-phase flow.There is some innovations in this paper,1、Present the model based on Euler-Lagrange coordinate, investigate the motion of continuous phase under Euler coordinate, and the particle phase analyzed under Lagrange coordinate.2、predicted the particle motion laws and wear regularity in the computational domain by studying the trajectory and volume fraction distribution. Also divided the flow channel into3parts, and carried out the quantitative analysis of particle trajectory and energy change with relevant position. It has a guiding significance for performance improvement and optimization design theory.