| Mixing systems are usually installed in crude oil storing equipments to prevent the heavy constituents of crude oil from depositing, which may lead to the wastes of the useful constituents, and to eliminate the cleaning work in oil tanks. The rotary jet mixing system is the safest and most effective method presently. Great progress have been made at abroad in research on this kind of mixing system, while domestic study is still on it's initial step. Especially few documents have been published concerning study on fluid jet working in low pressure, great flow and high viscosity conditions and optimization design of nozzle. The rotary jet mixing system's efficiency greatly depends on nozzle structure and flow field distribution around the nozzle. Based on the structure designed by pioneer in working group, full mathematical simulation of the interior and exterior flow field of the nozzle is carried out using the Computational Fluid Dynamics (CFD) technology. By mathematical method, jet distance of system, influence region and mixing consequence in different working parameters is investigated and the influence of nozzle structure, fluid properties and entry conditions on jet performance is discovered. The main content included in the paper is as followed: flow filed analysis of special nozzle structure, study on single-phase flowing speed, pressure, accompanying flow and mixing consequence of multiphase fluid, optimization design of nozzle structure etc.In this paper, nozzle structure, capable of mixing large flow region, is firstly determined by analyzing actual physical situation and theoretical calculation. Numerical computational grid model is established by creating 3D geometric model and dividing grid using piecemeal grid division method. Reasonable boundary conditions are defined and judgment foundation of convergence condition about the numerical iteration is given. Numerical simulation is finished on the jet and mixing in a certain tank according to single-phase fluid. Flow filed distribution in the tank is obtained. Influence region of jet is forecasted. Comparing results from submerged jet of water, jet characteristics of submerging jet of crud oil is analyzed. Optimization design of nozzle structure is carried out by analyzing flow filed distribution of a series of nozzles, whose media is single-phase fluid.Secondary, according to the nozzle structure with good performance, by changing working parameters (viscosity of crude oil and inlet velocity), influence on the performance of nozzle is analyzed. With mixture model, double-phase mixing flow field of white oil and heavy oil is obtained. Mixing rate of double-phase fluid, especially in the bottom of tank is analyzed. Optimization design of nozzle is verified by the computational results of mixing flow field in many nozzle structures. Mixing uniformity in different oil deposition thickness and different initial jet velocity is compared.As an important procedure in the design of rotary jet mixing system, study results in this paper can provide some important parameters for the nozzle structure design, the choice of oil deposition depth and initial jet velocity. The conclusion gained from the paper is value for the design of mixing system. In the paper, the characteristics of submerging jet with high viscosity and great flow are summarized. The work supplements the current jet theory. |
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