Research On Gas Solid Flow And Solid Particle Erosion In Gate Valve

The dissertation dwells on dilute pneumatic conveying system of double disk flat gate valves. The internal two phase flow properties and solid particle erosions are systematically studied with experimental and numerical simulation methods. By analyzing the erosion of gate valves, some valuable results are obtained, which are helpful for the erosion prediction and optimal design of double disk flat gate valves.Based on physical analysis of gas phase and particles, simulation models of two phases and solid particle erosion for double disk flat gate valves are established, and the simulation procedure is designed. This simulation method is validated by the experimental data from previous literatures. Then, two phase flow properties, solid particle erosion in valves are studied, and the optimal design of valve is also investigated. In the process of erosion study, the structure of gate valve is simplified as the cavity of an annular pipe. Based on the erosion analysis of cavity structure, the a erosion formula is proposed for the erosion prediction on sealing surface of gate valve, and an improving design scheme for the erosion prevention of gate valves is presented. Finally, an test platform of valves is builded, and experimental studies are carried out. The results further verify the effectiveness of the improving design scheme.The main contents of this dissertation are briefly stated as the followings:1. Simulation modeling of dilute gas solid flow and erosion prediction in gate valves. According to the requirement of present study, the Eulerian-Lagrangian Finite element modeling method is used for the simulation of gas phase and discrete phase. In order to save computation time, modeling assumptions on the compressibility of gas phase and particle parameters are proposed. The conservation equations for continuous phase are built by the comparative analysis of turbulence modeling methods; Based on the analyzation of forces acting on the particles, influence of turbulence on particles and the interaction between particle and wall, the kinetic model of particle motion is established; The model of particle erosion for simulation is got by the Taylor expansion of suitable erosion model for sigle particle.2. Research on the internal dilute two phase flow propties of double disk flat gate valve. Three-dimensional simulation method is used to investigate internal two phase flow properties and interactions between phases in the double disk flat gate valve. The influences of particles and their diameter on gas flow are studied for different valve placement and valve opening degree. Meanwhile, particle trajectories are extracted and analyzed, showing the effect of direction difference between gravity force and flow on the motion of particles. 3. Research on the particle of double disk flat gate valve. Since a gate valve usually operates fully open to let fluid pass through, the geometry is simplified as a cavity of an annular pipe based on structure analysis. Then three-dimensional CFD method is used to investigate solid particle erosions in the cavity structure. For convenience, the total erosion ratio is introduced to characterize the degree of erosion. The influences of cavity placement on erosion distribution of the aft wall are investigated firsly, indicating that the erosion is more severe for horizontal placed. Then the effects of geometric and flowing parameters on the erosion of sealing surface (surface T) of the horizontal placed gate valve are studied. According to the fitted results, a simple formula was proposed for the calculation of the total erosion ratio on surface T of the gate valve. This formula was validated by comparing its results with those of the CFD in another16orthogonal experiments. Furthermore, the formula was improved by combining with the existed erosion mode.4. Research on design improvent of valve structure. Height difference with the leading wall higher than the aft is introduced into cavity structure. Two-dimensional simulation method is used to investigate internal two phase flow properties and particle erosion in the horizontal placed cavities with hight differences. The influences of height difference on gas flow, particle distribution and solid particle erosion are studied, the results indicating that lower the aft wall of ideal cavity even to a small extent will significantly reduce particle erosion on it. Based on this result, an improving design scheme for the erosion prevention of gate valves is presented, indicating that pipe diameter upstream should be smaller than that downstream.5. Experiment research on the eroion in cavity structures. An test platform of valves is builded, and experimental studies are carried out based on highspeed CCD camera and surface profile testing system. The influence of height difference on distribution of particles is investigated, and the distributions of erosion on the aft wall are tested. Meanwhile, the influences of height difference on the maximum erosion degree of aft wall are analyzed, The results indicate once again the intention of the introduction of height difference, and the resits further verify the correctness of simulation procedure.