| Slug flow crystallization is an efficient crystallization method developed in recent years.It has the advantages of high controllability,easy operation and little amplification effect on the scale-up process.Meanwhile,narrow crystal size distribution and high product quality can be obtained.However,one of the major problems existing in the slug flow crystallization is the unsteady flow of gas-liquid along the channel,according to experimental experience.Therefore,it is necessary to study gas-liquid two-phase flow in a channel.The VOF model is chosen to simulate the flow of gas-liquid two-phase in a channel(d=3.2mm).The validity of the simulation parameters and model selection is verified under the conditions of previous experiments to simulate a similar gas-liquid flow pattern.The slug flow can be formed when the velocity ratio of gas and liquid is 1:1 or so,and the length of the gas and liquid slug increases with the increase of superficial velocity.It can be seen from the velocity vector inside the liquid slug that the internal circulation is formed when the superficial velocities of gas and liquid are 0.01m/s respectively,while no internal circulation is formed when the magnitude of superficial velocity is 10-1m/s,only a wake vortex at the gas-liquid interface can be found.In addition,we analyzed the problem about unsteady flow in slugs through the results of simulation studies.It is found that the main cause of the instability of the slug flow in the experiment is the effect of pulse of peristaltic pump.For this purpose,dual pump heads can be used to reduce this pulse effect to improve the experiment condition.Based on the CFD simulation results,a slug flow crystallization experiment is conducted.The crystallization experimental results show that the slug flow crystal has great advantages over the tank crystallization.Higher quality crystal products can be obtained when internal circulation existing in the liquid slug. |
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