Mixing mechanism of high viscosity fluid
Source: internal company
Fluid mixing mechanism can be divided into three types: convective mixing, shear mixing and diffusion mixing. Different from the low-viscosity fluid, the mixing mechanism of high-viscosity fluid is mainly shear mixing and convective mixing, and diffusion plays little role. The shearing action produced by the agitator blade will tear the material to be mixed into thinner and thinner layers (shear), and finally achieve uniform mixing with the main body as a continuous phase. For the mixing process with high viscosity fluid in the stirred tank, only the shear action with mixing impetus is not enough. Due to the uneven distribution of shear rate in the tank, the mixing efficiency varies from fast to slow. Therefore, there must be a circulation (convection) that transmits the driving force to the whole tank, that is, the fluid elements in the high shear zone and the low shear zone are continuously exchanged. For the full tank, the mixing rate depends on the exchange rate between the fast and slow mixing zone. Generally speaking, the exchange rate in laminar mixing region depends on the axial circulating capacity of the agitator, the stronger the axial circulating capacity, the faster the mixing rate.
For the mixing of a single fluid, a circulating flow pattern is produced after the agitator is started. As for the mixing of a variety of fluids with different viscosity (referred to as heteroviscous fluid), the circulation flow is inhibited due to the difference in viscosity, density and possible elasticity of different fluids. In the early mixing stage, a good circulation flow pattern cannot be formed, but it takes a long time, that is, the mixing time of various viscous fluids is much longer than that of a single fluid.