In this study, characteristics of sever slugging was investigated in a two-phase flowloop which is composed of downwardly inclined pipe and vertical riser. A globe type valve was installed at the upper part of the vertical riser to control the flow rate and the gas was injected through the injection points in the horizontal section. When changing the gas-liquid ratio at the gas injection point, different type of slugging was observed, such as severe slugging, oscillation, and combination of both, were observed at the boundary between slugging and stable condition. Based on the observation, the stability map for the flowloop was developed to provide flow patterns under different ranges of superficial velocity of liquid and gas. Moreover, it was observed that when injecting gas at the point downstream of the liquid pump, the pressure of the flowloop showed a flow regime of dual frequency severe slugging, which is a combination of high frequency fluctuation and low frequency oscillation. When injecting gas through the other two points, only severe slugging fluctuation was observed, however the slug growth pattern was different depending on the superficial liquid velocity. OLGA, a multiphase flow simulation software, was used to model the obtained experimental results. The simulation results showed the deviation for the amplitude of gas tank pressure was within 5% and the deviation for the period was within 10% under severe slugging formation. The model was further developed to predict the pressure changes under different severe slugging types including the dual frequency severe slugging.
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