The hydrodynamics of multiphase flow in a Liquid-Liquid Cylindrical Cyclone (LLCC) compact separator have been studied experimentally and theoretically for evaluation of its performance as a free water knockout device. In the LLCC, no complete oil-water separation occurs. Rather, it performs as a free water knockout, delivering a clean water stream in the underflow and an oil rich stream in the overflow. A total of 260 runs have been conducted for the LLCC for water-dominated flow conditions. Four different flow patterns in the inlet have been identified, namely, Stratified flow, Oil-in-Water Dispersion and Water Layer flow, Double Oil-in-Water Dispersion flow, and Oil-in-Water Dispersion flow. For all runs, an optimal split ratio (underflow to inlet flow rate ratio) exists, where the flow rate in the water stream is maximum with 100% water cut. The value of the optimal split ratio depends upon the existing inlet flow pattern, varying between 60% (for Stratified and Oil-in-Water Dispersion and Water Layer flow patterns) to 20% for the other inlet flow patterns. For split ratios higher than the optimal one, the water cut in the underflow stream decreases as the split ratio increases. A novel mechanistic model has been developed for the prediction of the complex flow behavior and the separation efficiency in the LLCC. The model consists of several sub-models, including inlet analysis, nozzle analysis, droplet size distribution model, and separation model based on droplet trajectories in swirling flow. Comparisons between the experimental data and the LLCC model predictions show excellent agreement. The model is capable of predicting both the trend of the experimental data as well as the absolute measured values. The developed model can be utilized for the design and performance analysis of the LLCC.

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