Technical improvement of mixer
The mixer is determined by multiple parameters. It is impossible to describe a mixer with any single parameter.
Shaft power (P), blade discharge (q), head (H), blade diameter (d) and mixing speed (n) are five basic parameters to describe a mixer. The experts of Baoshen machinery explained that the discharge volume of the blade is directly proportional to the flow standard of the blade itself, the first power of the blade speed and the third power of the blade diameter. The shaft power consumed by mixing is directly proportional to the specific gravity of the fluid, the power standard of the blade itself, the third power of the rotating speed and the fifth power of the blade diameter.
Under the condition of certain power and blade form, the discharge volume (q) and pressure head (H) of the blade can be adjusted by changing the matching of the diameter (d) and speed (n) of the blade, that is, the large-diameter blade with a mixer with low speed (ensuring constant shaft power) will produce higher flow effect and lower pressure head, while the small-diameter blade with high speed will produce higher pressure head and lower flow effect. In the stirred tank, the only way to make the micro clusters collide with each other is to provide sufficient shear rate.
From the mixing mechanism, it is the existence of fluid velocity difference that makes the fluid layers mix with each other. Therefore, the mixing process always involves the fluid shear rate. Shear stress is a kind of stress, which is the real reason for bubble dispersion and droplet breakage in stirring application. It must be pointed out that the shear rate at each point of the fluid in the whole stirred tank is not the same. Through the research on the distribution of shear rate, the employees of Baoshen machinery show that there are at least four shear rate values in a mixing tank. They are: the experimental research shows that in terms of blade area, no matter what slurry type, when the blade diameter is constant, the maximum shear rate and average shear rate increase with the increase of rotating speed. However, when the rotating speed is constant, the relationship between the maximum shear rate and the average shear rate and the blade diameter is related to the pulp type. When the rotating speed is constant, the maximum shear rate of radial blade increases with the increase of blade diameter, while the average shear rate is independent of blade diameter.
The above concepts about the shear rate in the blade area need special attention in the design of mixer reduction and amplification. Compared with the large tank, the small tank mixer often has the characteristics of high speed (n), small blade diameter (d) and low tip speed (nd), while the large tank mixer often has the characteristics of low speed (n), large blade diameter (d) and high tip speed (nd).
