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Study on the Numerical Simulation and Test of Two-phase Flow in the Entrainment Jet Clean-up System

Author: BaiTingHe
Tutor: LiRenNian
School: Lanzhou University of Technology
Course: Fluid Machinery and Engineering
Keywords: entrainment jet clean-up system two-phase flow fluid dynamics model theejector PIV industrial test
CLC: O359
Type: PhD thesis
Year: 2012
Downloads: 83
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Abstract


Jet technology has a long history, but the emergence of Reynolds stress makes the basic mathematical model equations to describe the operation of the turbulence flow field not closed. At present, it is still unable to solve the turbulence problem with the Reynolds equation and the mechanism of turbulence has not been thoroughly studied, not to mention the fact that one or more general turbulence theories can be accurately and effectively used to solve practical engineering problems. Though there are many methods and tools for the design and test of the jet fluid dynamics, these tools and methods are all semi-empirical theoretical methods based on empirical methods experimental data. Comparative studies in engineering application show that there are great differences between results derived from these methods and tools and those from theoretical calculation. Therefore, it is necessary to carry out extensive and in-depth fundamental theoretical research on three-dimensional turbulent jet fluid dynamics. The purpose of this research is to study the flow field structure and jet turbulence dynamic properties of the ejectors with special structures through the three-dimensional mathematical model of the turbulent jet established by the ejector, the necessary device to clean up the suspended solids in the circulating water system and then calculate the distribution of the turbulence flow field of the ejector with the mathematical model to master the mechanism of fluid dynamics of its turbulence flow field, so as to get the description method closest to the actual state of its turbulence flow field.The major content of this paper are as follows:1. Review of the origin and development of techniques to clean up the suspended solids in the circulating water system, discussion on the performance characteristics and influencing factors of ejectors with special structures adopted by new and highly-efficient cleaning technologies and elaboration on the purpose and structure of the paper. 2. Description of the fluid dynamics model of the traditional classical jet flow field and the fluid dynamics model and the algorithm of the currently advanced three-dimensional turbulent jet flow field.3. Study on the structure algorithm of the ejector based on the analysis of the lateral flow field structure of the projected jet plane and the vertical flow field structure perpendicular to the jet plane.4. Analysis on the theoretical algorithm of mathematical models for the three-dimensional turbulent jet flow field. On the premise of effectiveness, analysis is made on the boundary conditions of the tank sidewalls of the system and the disturbing effect of the main process flow field on the jet flow field so as to make the mathematical model algorithm for the fluid dynamics of the clean-up system of suspended solids more accurate from the perspective of the affecting factors of the overall system flow field.5. Analysis on PIV flow field trial tests and CFD simulation for the three-dimensional turbulent jet flow field. Analysis is made on the process and mechanism of jet vortex generation, development, diffusion and annihilation based on the test results. At the same time, verification is performed on the calculation results from the mathematical model theory as well as on the CFD simulation results to see if they are accurately in accordance with the structure and performance of the real flow field.6. Verification of the accuracy and applicability of the technology to clean up suspended solids for the industrial circulating water system through industrial tests on the basis of results from the PIV flow field trial tests and CFD simulation for the three-dimensional turbulent jet flow field. This technology is developed on the basis of two-phase flow and theoretical research with the ejector as its key element which is designed and developed according to the calculation results from the mathematical model theory.This research project is innovative in the following aspects:1. Although many scholars have studied underwater free submerged jets problems and derived relatively complete experimental and theoretical formulas, nearly all the research in literature is about underwater free submerged jets without hybrid tubes, but for little research of ejectors with. Based on the discussion of multi-phase flow model seen frequently in engineering research, this project converted mathematical model of into that of underwater free submerged jets with hybrid tubes and established Mixture mathematical model of hybrid tubes by amendment.This rearch project established the control equation and unsteady turbulence model algorithm between the nozzles and the inlets of suction tubes, and achieved the relatively complete and accurate Mixture model for multi-phase flow, which made the Mixture model of hybrid tubes more consistent with the actual conditions in the flow field.2. According to the model algorithm of Mixture mathematical model of hybrid tubes which has already been established, and CFD simulation of jet devices can achieve regional coverage of basin-wide level regardless of jet-burners positive jet flow or reverse direction side of the jet flow, this rearch project designed injector model which met the requirements for covering the basin-wide of sludge cleaning system.3. According to the model algorithm between the nozzles and the inlets of suction tubes and CFD simulation basin-wide flow of sludge cleaning system, this rearch project designed a height restriction ejector which impacts on the system is vertical plane.4. According to the study of PIV flow field measurement technology on the flow field in the large area,1:1scale test model has beed achieved.From analysis of the real flow field, we can see the designed ejector’s simulation results are consistent with CFD whether vertical or horizontal flow. Namely, ejector’s horizontal flow can realize regional coverage of basin-wide level and height restriction within the extent of the vertical plane. The research result checks of theoretical research accurately on the Mixture mathematical model of the ejector and provides reliable scientific theory for scientific and and optimization of the Mixture mathematical model.5. According to the study of PIV flow field measurement technology on the flow field in the large area, large-scale test results which is in line with the true state of the jet flow field can be achieved. This provides an effective way to study and explore large-size and even large size model’s methodology of the PIV flow field measurement test. Besides, it also can avoid experimental error caused by large-size physical model using a small model during the process of PIV flow field measurement test.

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CLC: > Mathematical sciences and chemical > Mechanics > Fluid Mechanics > Multiphase flow
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