Study on Similarity Scale-up Model for Mixing Section of Two-Rotor Continuous Mixer
|School||East China University of Science and Technology|
|Course||Chemical Process Equipment|
|Keywords||similarity scale-up two-rotor continuous mixer mixing section flow field simulation dynamic visualization|
A similarity scale-up model for mixing section of two-rotor continuous mixer was proposed based on characteristics of the mixer, the principle of equivalent average residence time and equivalent shear rate at the top of the rotors, according to the criterion of equivalent energy. The flow field of mixing and discharging sections in two-rotor continuous mixers with 30mm,50mm,75mm and 100mm in diameter was simulated with Polyflow software under the rotational speed of the rotors and feed rate determined by the model. The flow field feature and mixing performance were analyzed under the guideline of equivalent energy in order to validate the similarity scale-up model proposed in the paper. Meanwhile, experiments were carried on two-rotor continuous mixers with 30mm and 75mm in diameter respectively and mixing performance was analyzed. Thus, the similarity scale-up model was validated experimentally. Based on the analysis and experiments, the main conclusions are made as follows:(1) The mean pressure and shear rate of the molten flow in the mixing and discharging sections of the four kinds of two-rotor continuous mixers are almost the same. It means that the kinestate and shear process of the melt in the mixing and discharging sections of the four kinds of two-rotor continuous mixers are similar.(2) The mixing index, disaggregation energy density, instant mixing efficiency, time average mixing efficiency and rate of stretching of the molten flow in the mixing and discharging sections of the four kinds of two-rotor continuous mixers are almost the same, as these parameters characterize the mixing performance, it indicates that the dispersive mixing and distributive mixing capacity in the mixing and discharging sections of the four kinds of two-rotor continuous mixers is similar.(3) In the two two-rotor continuous mixers with different size in diameter, LLDPE melt become ribbons and film because of stretching and mixing, then wrap the titanium white together, titanium white particles were cracked into particles with less than 5μm in diameter after shearing, melting, compressing, kneading, stretching and mixing. The diameter of cracked particles in the two mixers is similar, and the distribution of those particles is similar too. It showed that the degree of mixing of LLDPE and titanium after mixing in the two mixers is similar. As a conclusion, the flow field simulation and analysis conducted for the mixing and discharging sections of the four kinds of two-rotor continuous mixers and the experiment carried on the two different two-rotor continuous mixers have validated the similarity scale-up model proposed in the paper.