CFD study of a rotating gas-liquid separator: Design og bygging av flere mikro-dråpe generatorer
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Extracting Natural Gas from the reservoirs and transporting it to shore requires the gas to be pure from liquids and contaminants. These contaminants can be extracted from the gas by separators. A new separation technology, the Lynx separator, has been developed at NTNU, where a rotating element inside the separator is to capture liquid particles and introduce a centrifugal force for increasing the separation efficiency. The knowledge on how this element influences the flow and performs is limited, and there are no known experiments performed on this system per today. Using CFD tools to construct a suitable model can contribute to increase the knowledge on how this capturing element impacts the flow.The work presented in this thesis has been looking into the structure of metal foams used as the separation mechanism in Lynx separator. A model of a single cell representing a microstructure of the real life foam geometry has been constructed in ANSYS Mechanical APDL and further included in ANSYS FLUENT, where three cells were united as one element with a capturing cylinder around to represent a simple small scale model of the separator. By turbulent k-omega modeling in combination with the Discrete Phase Model, simulations on gas-liquid flow represented by air with inert water particles of different diameters has been calculated upon, where the focus has been set on the interaction between the particles and the metal foam cells. Different cases have been investigated where the capturing element has been set into different angular velocities to quantify the impact on the gas flow and particle behavior. The presented model shows the influence of the different rotating velocities on both gas and particle flow. The capture of particles with a stationary metal foam is mainly limited to larger particles with a diameter of 100 µm and 500 µm. Introducing a centrifugal force results in swirling flow for both gas and larger particles, reducing the interaction of larger particles with the metal foam cells as these particles swirl out towards the walls. The flow of 10 µm particles result in a radial displacement as a result of colliding with the metal foam, separating them from the gas, while capture of 1 µm has showed to be very limited. Introducing a very high rotational velocity has shown to reduce the reliability of the proposed model, and it cannot be verified that this model is reliable as the rotational velocity exceeds 2000 rotations per minute.