| Hydraulic transport of solid materials is typical application in engineering of solid-liquid two phase flow. As a new type of impurity pump, the screw centrifugal pump has the outstanding advantages, such as high efficiency, wear resistant, anti-clogging, etc. The law of energy conversion and unsteady hydrodynamic characteristics in unique spiral impeller must be greatly different with the traditional centrifugal pump impeller, when transporting solid-liquid two phase medium. The existing research results about the screw centrifugal pump are mainly concentrated on the design method, external characteristic, structure of flow field. The research of energy conversion characteristics in the screw centrifugal pump is relatively less, especially when transporting solid-liquid two phase medium, the current research of the energy transfer, transformation and dissipation process in impeller and casing, is lacking.In this paper, through test and numerical calculation method, the energy conversion ability and the influence factors are mainly studied along different regions in the screw centrifugal pump impeller spiral flow channel and casing, when transporting the water and the solid-liquid two phase medium. The steady and unsteady energy distribution and conversion characteristics of space and time are revealed in impeller spiral channel and casing. And on this basis, the hydraulic design method of the impeller and the casing is put forward based on the theory of two phase flow rate ratio. The main research content is divided into three parts:1. The characteristics of energy conversion in impeller and casing with screw centrifugal pump transporting water.From two aspects of steady and unsteady, the impeller input power, the characteristics of the energy conversion, efficiency and energy loss are studied respectively. The results show that the impeller mainly do power work on fluid through pressure, and the fluid viscous forces work power account for only a small proportion. The method and basis to segment spiral part, transitional part and centrifugal impeller part are given, meanwhile the results show that the spiral part of impeller is critical area of fluid gain energy.As impeller rotating, the instantaneous energy conversion and loss in the impeller continue to change, and has periodic trends. Asymmetry of the blade, the impeller and casing interference effect cause periodic change of the input and output power, impeller surface pressure, also causes instability mutual conversion between the static pressure and dynamic pressure. For flow rate changing, the energy conversion efficiency of impeller spiral part is greater change than the impeller centrifugal part, and the centrifugal part decides the fluctuation characteristics of impeller output power.The main form of energy loss in the impeller is turbulence dissipation loss and wall friction loss. As small flow rate, the loss is given priority to with turbulent dissipation loss, and as large flow rate, the loss is given priority to with friction loss. The main area of the turbulent dissipation loss is in the impeller outlet, and the main area of the friction loss is in the centrifugal part of impeller. The energy loss in casing is mainly impact losses of tongue and turbulent dissipation losses, and its value increase with geometric ratio when flow rate increase.2. The characteristics of unsteady energy conversion in impeller and casing with screw centrifugal pump transporting solid-liquid two phase medium.Using Eulerian solid-liquid two phase flow model, it has carried on the unsteady numerical analysis for impeller shaft power, turbulence intensity of cross section, efficiency, turbulent kinetic energy dissipation rate, dynamic pressure coefficient and the influence of casing energy conversion characteristic when the solid phase concentration and particle size change respectively.The results show that the pump average head will fell, but the fluctuation increased when the solid phase concentration increases. As the increase of particle size and solid phase concentration, the impeller input relative shaft power fluctuations increase, and the efficiency of the pump declines significantly. And the range of high efficient on instantaneous efficiency curve is a little change, its location is made up of impeller, casing shape and relative position of two, but not the physical parameters of the mediumThe impeller efficiency and turbulence intensity on the impeller flow channel section shows strong periodic change rule. Solid phase concentration on the influence of turbulence intensity is greater than the influence of particle size change. As solid phase concentration and particle size increased, each section of turbulent kinetic energy dissipation rate in casing are increasing trend, especially turbulent kinetic energy dissipation rate of sections close to the position of the tongue are dramatic change. The spiral propulsion function of spiral part of impeller flow channel makes effect of the particle diameter and fluid velocity change on turbulence dissipation rate is reduced, the change of the solid phase volume fraction and particle diameter on the influence of the turbulent kinetic energy dissipation are mainly concentrated in the centrifugal impeller part.3. Screw centrifugal pump solid-liquid two phase hydraulic design methods.According to the rule of energy conversion and distribution within the screw centrifugal pump and impeller when transporting solid-liquid two phase medium, and based on the solid liquid two phase flow rate ratio coefficient and the axial velocity matching, the solid liquid two phase flow impeller parameter equation is worked out. And on basis of energy conversion characteristic matching between the casing and impeller, the area of NO.8calculation method is given, Then through numerical analysis, the results show that the pump efficiency increased by8.5%than that of the original model When transporting given volume fraction of solid-liquid two phase flow,therefore proved the design method in this paper to achieve the desired effect. |
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