Multi-Fluid VoF model assessment to simulate the horizontal air–water intermittent flow

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Numerical simulation of the plug and the slug flow regimes have been performed using the Multi-Fluid VoF and Shear Stress Transport (SST) k–ω models in a horizontal pipe with 44mm diameter. The superficial velocities during the current study were set at 0.16, 1.64 & 3m/s for the gas phase and 1m/s for the liquid one. The pressure and the velocity equations were solved together, utilizing the PIMPLE algorithm in all cases of the present study. The VoF model, as well as the experimental outcomes, were applied to assess the results of Multi-Fluid VoF model. The qualitative comparison of numerical results with the experimental visualization revealed that the Multi-Fluid VoF model simulates precisely the interfacial structure of slug and plug flows, as well as the chronological formation of the slug. The length ratio of the gas slug to the liquid slug goes up with the gas superficial velocity increment; this issue increases the probability at low liquid hold-ups and decreases the higher ones. The Multi-Fluid VoF provided much more matching with the mentioned probability changes in comparison to the VoF model. The pressure drop calculated using Multi-Fluid VoF in the Lockhart–Martinelli framework illustrated a 21.8% improvement averagely in comparison to the VoF model. The obtained transitional slug velocities showed that the Multi-Fluid VoF model presented a maximum error of 8.17% versus the experimental values, while the mentioned error for the VoF model was estimated at 22.01%. Notwithstanding the mentioned advantages, the Multi-Fluid VoF model significantly increased, both the execution time of simulation as well as the associated costs.