| The research investigated the mechanical emulsification approach to make micron-dimethyl silicone oil emulsion with narrow particle size distribution; the flow field within the emulsification device was also simulated through CFD (computational fluid dynamics).Silicone oil emulsion is made under ambient temperature; 500,000mm~2/s of the dimethyl silicone oil is used as raw material, AEO3, AEO7, OP are used to form mixed mulsifier, thickener CJ is used as stabilizer. Single-factor experimental method is used to investigate the influence of different emulsifiers on the emulsion particle size distribution.The test shows that the compound emulsifier from AEO3, AEO7, OP is very effect; its good stability is proved through freeze-thaw, sedimentation and dispersion experiments. Orthogonal test was deployed to find the optimal ratio of raw materials to achieve the good narrow distribution for small particles, the optimum concentrations of the dimethyl silicone oil, AEO3, AEO7, OP are respectively 50%, 2%, 2% and 1%. Also the influence of each variable to latex particle size distribution was studied with single factor analysis.The parameters for the optimal narrow molecular weight distribution are 5% mass of emulsifiers 1200 rpm(round per minute) stirring speed, 80min emulsification time. It is also identified that the latex particle size distribution becomes narrower because of an extended emulsification within certain period of time and as well as an increased stirring speed within certain speed range.With today's high-speed computer is able to perform very sophisticated computation. CFD provides alternative other than relying on either pure theory or physical experimental study as in the past; it is a powerful tool with integration of both mathematical equations and physical properties. The research is focused on silicone oil emulsion system which is in micron range. It is white opaque in appearance and it is not practical to investigate the internal fluid flow status only through the convention experimental method. In view of the significant impact about uniformity of particle size, the study used CFD further to simulate the mixing process of the emulsion system to obtain mixing flow pattern, velocity vector distribution, concentration field, pressure field, and etc. These information are very important for the proper selection of emulsification equipment and the stirring speed, they are also helpful in the future for the real industrial production.The 3D model for the fluid flow within a blender was created using commercial solfware FLUENT which is based onκ-εturbulence model and the multiple reference frame (MRF) method. The flow field within the blender was simulated for three different types of paddle in order to identify the velocity distribution and concentration for the each paddle type. It is found that the velocity field and turbulence field are correlated closely with the flow pattern caused by paddle stirring. In the area with paddle stirring, the flow velocity and the turbulent kinetic energy are higher and the turbulence is more intensified.Of all the three types of paddle, the double helical ribbon impeller creates the biggest high-velocity flow region, needs the shortest mixing time and consumes the greatest electric power.In order to find the change of power consumption along with the mixing speed, tests for four (4) mixing speeds were performed for each of three types of paddle. It is found that the power consumption on the double helical ribbon impeller increases most significantly with elevated the stirring speed hence the mixing effect is enhanced very much. |
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