Study On Particle Image Velocimetry And Inverse Analysis In Aeration Tank

Gas-liquid two-phase flows are widely applied in engineering and environmental processes. However, there have been many problems for human beings to known clearly so far, such as overfall, nonsteady flow, mechanism of interaction, heat and mass transfer between the two phases and so on. Those problems must be settled imminently in many engineering applications, so it is especially essential to measure and get detailed information about the full field velocity.In the paper, particle image velocimetry technique and inverse analysis method were used to study gas-liquid two-phase flows. The work accomplished are as follows: First, the particle image velocimetry arithmetic based on Fast Fourier Transformation was studied on the basis of particle image velocimetry principle; Second, five traditional phase-separation methods were summarized and its advantages and disadvantages were discussed elementarily; Third, not only the principle of inverse analysis and its equation calculation but also the drag coefficient and the lift coefficient involved in the equation were studied; Fourth, applying the computer language Visual C++, the particle image velocimetry program and inverse analysis program were developed on the operation system Windows and verified separately by the particle images synthesized by mathematic method and Taylor-Green vortex flow; Finally, the gas-liquid two-phase flows in aeration tank were experimented and analyzed by the program.The main conclusions can be draw from paper as follows:(1) By analyzing serial particle images, particle image velocimetry based on Fast Fourier Transformation can detect velocity of flow and get other parameters efficiently and quickly. The correlative coefficient will reach to 0.8. However, using this arithmetic, the false vectors will appear and centralize with high frequency in the area, where velocity is large and velocity gradient is strong.(2)The more number of gas velocity we known, the higher effect of inverse analysis we will get. However, when the number of gas velocity increase to some extent, the effect will not be evident. If we want to make the correlative coefficient of velocity more than 0.9, we must know more than 1/6 number of gas full- field velocities.(3)In the aeration tank equipment, gas-liquid two-phase flows will behave three flowing cases. When flows are in case 3, the bubbles in the equipment will have longest rest time and stronger turbulent intensity, so oxygen transferring speed and efficiency will be advanced greatly. When we design aeration tank, we must make gas-liquid two-phase flows in case 3.