Research Of Liquid-solid Two Phase Flow In Centrifugal Pump With Crystallization Phenomenon And Optimum Design

The liquid-solid two-phase flow with crystallization phenomenon is widespread in modern industry, such as petrochemical industry, pulping process, brine transportation, etc. Precipitated particles will hinder the passageway in the fluid machinery, causing blocking and abrasion in severe conditions. Numerous waste of energy and resources are caused in salt-out process. So it is helpful for energy saving and cutting loss to do further research about the problem.In order to deeply explore the crystallization mechanism, an original model pump is used to conduct numerical calculation and analysis about the flow field in different conditions. Main research work and results are as follows:1. Make a brief introduction of the overseas and domestic research status;conclude the fundamental mechanism of crystallization process comprehensively;make deep explanation of microcosmic behavior of the crystal particles, including nucleation, growth, coalescence, secondary nucleation and break. It is found that particles are mainly produced by second and heterogeneous nucleation, which play a vital role in crystallization. Summarize the transport equations of crystal particle,multiple forms of diffusion are affected by transport processes. In addition, the transport effect limits the subsequent precipitation rate. Fundamental theory of the population balance model is introduced, the purpose of which is to describe the behavior of particles and explain the dynamic evolution process in system.2. Flow field of the model pump is modeled in three-dimension by Pro/E, and unstructured tetrahedral mesh is used in impeller and volute, while structured hexahedron mesh was used in inlet and outlet pipe region. Some part needs mesh encryption in order to get reliable simulation results.3. In order to take various microcosmic behaviors into consideration, the paper imported nucleation and growth model by UDF, and conducted steady and unsteady numerical simulation with CFD-PBM coupling method. After researching of the size distribution principal of crystal particles in different flow rate or volume fraction, it isfound that particles in blade inlet are uniformly distributed, while there exists obvious concentration gradient from the pressure surface to the suction surface in the outlet.Moreover, the relative velocity of crystal phase is slightly larger than that of the fluid phase.4. Taking peak hydraulic efficiency and its head as objective function of optimal design, eight design variables in model pump are analyzed with Plackett-Burman experiment design, orthogonal design and RSM method and correlation equation of objective function and design variables is acquired. By analysis of the correlation equation, optimal parameters are acquired and simulated by CFD. The result is in good agreement with the prediction. Above all, the objective values are improved than before.