Numerical Simulation Of Non-Newtonian Fluid-Particle Two-Phase Flow In Centrifugal Pumps

Centrifugal pumps are commonly used in the engineering field and the flow field characteristics inside them have received a lot of attention.The fluids inside centrifugal pumps in practice are more complex and are usually not purely aqueous media.In contrast,non-Newtonian fluids such as mud,concrete and drilling fluids are the more common transport fluids.Drilling fluids are typically non-Newtonian fluids,of which the powerlaw fluid model is one of the more common rheological models,with shear viscosity varying with the applied shear rate.In contrast,for engineering non-Newtonian fluids there are also large particles within the fluid.This solid-liquid two-phase flow situation can lead to a more complex flow field inside the centrifugal pump,affecting the hydraulic characteristics of the pump.In practical applications such as deep-sea mining,the centrifugal pump has a long outlet vertical pipeline,and the hydraulic characteristics and particle flow patterns associated with the coupling of non-Newtonian fluids and particles in the vertical pipeline are also a subject for study.Therefore,it is important to study the flow characteristics of the two-phase flow of non-Newtonian fluids and particles inside the centrifugal pump and in the vertical pipeline.In order to have a better and more extensive analyses of the rheological characteristics of non-Newtonian fluids inside centrifugal pumps,this thesis take a conventional centrifugal pump as the experimental object,and select a 10 m long vertical pipe,employing a combination of numerical calculations,simulations and theoretical analyses to analyze the flow field characteristics of single-phase non-Newtonian fluids inside centrifugal pumps,the flows field characteristics of non-Newtonian fluid-particle coupling inside vertical pipes and the flows field characteristics of non-Newtonian fluidparticle coupling between centrifugal pumps and vertical pipes,respectively.The flow field characteristics of the combined non-Newtonian fluid-particle coupling of the centrifugal pump and the vertical pipe are analyzed.The flow field characteristics of the non-Newtonian fluid-particle two-phase flow in a centrifugal pump are summarized and analyzed by studying the effect on the internal pressure of the worm casing and the vane pressure and the particle flow law.The main research contents are as follows:(1)The current status of research on non-Newtonian fluid flow,non-Newtonian fluid-particle two-phase flow and solid-liquid two-phase flow in vertical pipelines inside centrifugal pumps are collated respectively,establishing fluid calculation models,nonNewtonian fluid models and coupled CFD-DEM models.And the suitable power-law fluid parameters are selected as the main research fluid in this thesis.The model construction and meshing of the centrifugal pump and the vertical pipe are performed,with the verification of the mesh irrelevance and the relevant experimental test results.It proves the accuracy of the chosen numerical analysis method.(2)The flow field characteristics of the non-Newtonian fluid in the centrifugal pump were analyzed under changing flow rates and it was found that as the pump drew different viscosity fluids,the non-Newtonian fluid flowed away from the back pressure side of the vanes as the flow rate increased,so that the flow rate was smaller than the front side of the vanes.At the same time,the shear collision between the fluid at the impeller outlet and the fluid in the snail casing area,as well as the static and dynamic interference,result in the non-Newtonian fluid consuming more mechanical energy than the water.(3)The analysis of the flow characteristics of coarse particles inside a vertical pipe at different diameters shows that the particles in the pipe all produce a retention effect when they reach the middle section of the pipe.Comparing the transport under different working conditions it can be found that the non-Newtonian fluid,due to its viscosity,makes the particles more evenly distributed in the pipe cross section and the losses along the pipe are more stable.In order to balance the stability and economy of hydraulic lifting in deep sea mining,it is considered that the particle size should be controlled at about0.01 m.(4)Through the analysis of the non-Newtonian fluid-particle two-phase flow characteristics inside the system combining centrifugal pump and vertical pipeline at the design flow rate,it is found that the number of particles inside the impeller is small and there is no accumulation in the working condition of water-particle coupling,and the particles are mainly concentrated in the worm shell,which means that the particle overflow situation is good.However,as the drilling fluid is both viscous and denser than water,the particles cannot flow out of the blade area as easily as when they are transported by water,so the accumulation is more serious.The retention effect was still seen in the vertical pipe.Areas of particle concentration alternate along the vertical of the pipe from the bottom to the top of the pipe.The interaction between the particles and the interaction between the particles and the pipe wall increases,thus increasing energy consumption and dynamic resistance.