The stirring of high-viscosity fluids generally refers to the mixing of mutually soluble high-viscosity liquids. The application of high-viscosity fluids in industrial production is increasing. Many high molecular polymers are high-viscosity fluids, and many of them are non-Newtonian fluids. The viscosity will change during the stirring process, so the requirements on the stirrer are even higher, and the stirrer is required to be able to adapt to the change in viscosity to complete the stirring operation. However, high-viscosity fluid stirring also has various heterogeneous operations in industry, such as dispersion, solid dissolution, and chemical reactions.
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During the stirring operation, it is not difficult to use a stirrer to cause turbulence in the low-viscosity mutual solution. However, after the viscosity reaches a higher level, due to the effect of the viscous force, a laminar flow state can only appear. It is especially difficult that this laminar flow can only occur near the agitator, and the high-viscosity liquid a little farther away from the blade is still static. In this way, it is difficult to cause the liquid to circulate in the stirring equipment, that is, there will be dead zones in the equipment, which is very unfavorable to various stirring processes such as mixing, dispersion, heat transfer, and reaction. Therefore, the primary problem of mixing high-viscosity liquids is to solve the problems of fluid flow and circulation.
In this case, the circulation flow rate of the agitator cannot be increased by increasing the stirring speed, because when the fluid viscosity is high, the flow rate discharged by the agitator is very small. If the rotation speed is too high, channeling will be formed in the high-viscosity solution. The surrounding liquid is still a dead zone. A more effective solution is to try to make the agitator push a larger range of fluid.
Therefore, the ratio of the agitator diameter to the inner diameter of the device and the ratio of the width of the paddle to the inner diameter of the device for high-viscosity liquids are required to be relatively large. Sometimes it is also required to increase the number of layers of the agitator to increase the stirring range.
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From the perspective of the stirring mechanism, when mixing high-viscosity liquids in the laminar flow zone, the liquid units are stretched, thinned or divided under the action of shearing and subdivision. As the shearing time increases, the mixing is gradually achieved.
At the same time, because the shear field in the mixing equipment is not uniform, for example, the anchor agitator has a strong shear zone in the gap between the anchor and the wall of the kettle, and the mixing rate of the liquid is faster, while the middle area of the kettle is a low shear zone. , The mixing rate is slow. Therefore, the liquid exchange rate between the high-shear zone and the low-shear zone or the circulation capacity of the liquid in the kettle is also an important factor affecting the mixing.
In addition, fluctuations in the velocity of the fluid in the equipment can also promote mixing. In other words, the mixing rate of the high-viscosity liquid mainly depends on the relative movement rate between the stirrer and the surface of the kettle wall and the distance between each other. For this reason, a stirrer for the high-viscosity fluid is also required. The ratio of the diameter of the stirrer to the inner diameter of the equipment Both are quite large. In the actual production process, commonly used viscous fluid stirrers include anchor stirrers, ribbon stirrers, frame stirrers, etc.
