Working Principle Of Mixer

A mixer is determined by multiple parameters, and it is impossible to describe a mixer with any single parameter. Shaft power (P), blade discharge (Q), pressure head (H), blade diameter (D) and stirring speed (N) are the five basic parameters to describe a mixer. The discharge of the blade is proportional to the flow rate of the blade itself, the first power of the blade speed and the third power of the blade diameter. The shaft power consumed by stirring is proportional to the specific gravity of the fluid, the power of the blade itself, the third power of the speed and the fifth power of the blade diameter. Under certain power and blade form, the blade discharge (Q) and pressure head (H) can be adjusted by changing the matching of the blade diameter (D) and speed (N), that is, a mixer with a large diameter blade and a low speed (to ensure that the shaft power remains unchanged) produces a higher flow effect and a lower pressure head, while a small diameter blade with a high speed produces a higher pressure head and a lower flow effect. In the stirring tank, the only way to make the micro-groups collide with each other is to provide sufficient shear rate. From the perspective of the mixing mechanism, it is precisely because of the difference in fluid velocity that the various layers of the fluid are mixed with each other. Therefore, any mixing process always involves the fluid shear rate. Shear stress is a force that is the real reason for bubble dispersion and droplet breakage in mixing applications. It must be pointed out that the shear rate of the fluid at each point in the entire mixing tank is not consistent. The study of shear rate distribution shows that there are at least four shear rate values ​​in a mixing tank, which are: Experimental studies have shown that in terms of the blade area, regardless of the type of paddle, when the blade diameter is constant, the maximum shear rate and the average shear rate increase with the increase in speed. However, when the speed is constant, the relationship between the maximum shear rate and the average shear rate and the blade diameter is related to the paddle type. When the speed is constant, the maximum shear rate of the radial blade increases with the increase in the blade diameter, while the average shear rate is independent of the blade diameter. These concepts about the shear rate of the blade area need to be particularly careful in the design of mixer reduction and enlargement. Compared with large tanks, small tank mixers often have the characteristics of high speed (N), small blade diameter (D) and low tip speed (ND), while large tank mixers often have the characteristics of low speed (N), large blade diameter (D) and high tip speed (ND).