Preliminary Study On The Air-lift Artificial Upwelling

Upwelling is an oceanographic phenomenon that brings colder, nutrient-rich deep sea water to the ocean surface. If artificial upwelling can be produced in the nutrient-poor sea surface regions, primary production in these regions would increase as it does in regions with natural upwellings. However, owing to the abominable condition of marine environment, there’s no effective way to lift the nutrient-rich deep sea water. It is meaningful to find an artificial upwelling method which is simple, insensitive and needs less maintain. In this paper, the technology of underwater air injection is employed to solve the problem. The whole thesis consists of6chapters as follow:In chapter1, the background and significance of the research subject is presented. The traditional artificial upwelling methods, underwater air injection technology as well as its application in lifting the liquids are reviewed. At the same time the outline and the main research contents of the thesis are also presented.In chapter2and3, the numerical experiments about the line source and point source models are performed using the commercial CFD software FLUENT. The perceptual cognition of air lift upwelling is obtained by the simulations, In order to give a basis for the next steps of choosing the model of air-liquid two-phase flow simulation, finding the best parameter setting for the experiments, we compare the single-point source and multi-point source air lift upwellings in some aspects like the velocity field distribution and lifting efficiency. It is found that the rising of air-bubbles in water will lead to the upwelling. In addition, though the upwelling flow rate increases as the number of the air inlets increases in one upwelling pipe, the lifting efficiency decreases because of the total air flow rate increases.In chapter4, using a plexiglass pipe as the upwelling-pipe, laboratory experiments are performed in a4.5m deep tank to obtain the flow rate ratio of water to gas under the different air injection conditions. On one hand, the air flow rate is controlled to different values. The results show that the upwelling flow rate increases as the injection air flow rate increases, and there is a good lineal relationship between them in a certain range. On the other hand, the direction of the air inlet is changed to find the relationship between the vertical height of air inlet and lifting efficiency.In chapter5, a numerical simulation is adopted to investigate the performance of the deep sea water after it is lifted to the ocean surface. The effects of upwelling flow rate, velocity radio and density difference at the level of pipe exit on the flow behavior are respectively studied. According to the results, the maximum lifting height increases as the upwelling flow rate increases and there is no significant relationship between the location of separate point and the upwelling flow rate. As the crossflow rate increases, the depth of separate point decreases, the horizontal displacement of separate point increases, and the change of maximum lifting height is unconspicuous. As the density difference increases, the maximum lifting height decreases, the depth of separate point increases, and the distance between separate point and pipe decreases.Finally, the work is summarized and the conclusion remarks are presented in chapter6.