A Study On Air-liquid Two-phase Flow In The Upwelling Pipe

Air-lift artificial upwelling in big vertical pipe is a very important technology,which uses artificial way to inject the high pressure gas into the big vertical pipe under deep sea water and lift nutrient-rich deep water up to euphotic zone to feed phytoplankton using the drag force produced by bubbles rising to enhance the marine primary productivity by increasing fishing output.As to the relatively fragmented and simple existing theory on this field,the air-lift artificial upwelling system research work has not been effectively carried out.So it is very important to study the core parameters,such as pipe and gas injection parameters and so on,to analyze the transition of flow pattern and influence of upwelling in upwelling pipe.The main contents of this thesis are:In chapter 1,the purposes and meanings of this thesis are presented.The air-lift artificial upwelling and the research status of gas-liquid two-phase flow inside the pipe are summarized respectively.Finally,the development of two-phase flow pattern and the classification of gas-liquid two-phase flow pattern in vertical tube are briefly reviewed in this thesis.In chapter 2,theoretical model of air-lift artificial system in upwelling pipe is established and perfected.Taking the pipe diameter into consideration in the current energy conservation equation,it's the first time for this thesis to research the theory of air-liquid two-phase flow in large upwelling pipe,which indicates that efficiency in the open-cycle air-lift system is higher than the close-cycle air-lift system in large upwelling pipe,however,the close-cycle air-lift system in upwelling pipe copes with the problems effectively of air-injecting pressure and surrounding field influence.In chapter 3,the upwelling pipe structure parameter is studied to explore the influence upon the liquid flow rate.With the help of numerical simulation by the FLUENT software,it is concluded that the water lifting volume increases when increasing the upwelling pipe diameter,the air injecting depth and air injecting rate,which decreases with the increase of pipe length.In addition,the lifting efficiency decreases when increasing the air injecting rate.Finally,the impact of adding obstacle in the upwelling pipe is inquired.Although the apparent turbulence dissipation relates to the energy loss,the water lifting rate is increased obviously.In chapter 4,the relationship between the void fraction with air-liquid two-phase flow pattern is studied.On the basis of the assumption that the void fraction in the grid is more than half area,it is concluded that void fraction under different flow pattern corresponds to the different peak value.In chapter 5,air lifting experiments underwater in the upwelling pipe is carried out.Experiments employing the transparent organic glass pipe as the upwelling pipe,observe and measure successfully the form and change of air-liquid two-phase flow pattern,the liquid flow rate in upwelling pipe based on the different pipes,air injecting rates and air injecting depths.In chapter 6,some conclusions in this thesis are summarized and the future research proposals are suggested.