GB/T 39986-2021Pumps - Testing - Submersible mixers for wastewater and similar applications (English PDF)

2.1 Thrust-to-power ratio

The ratio of the thrust of the stirrer to the power of the stirrer.

Note 1. The ratio of the minimum necessary mixing system power dissipation to the agitator power consumption refers to the (end-user-oriented) system efficiency. In order to understand the weight of the thrust-to-power ratio It is important to consider the situation where the agitator produces a longitudinal flow velocity u in the recirculation channel such as the sewage oxidation ditch. This is actually a common application of agitator Use, and the following argument may be extended to other applications in principle.

The flow momentum loss in a cycle is equal to the momentum rate provided by the agitator in a quasi-steady state. This is given by the agitator thrust F. Momentum loss caused The power consumption P=Fu, which is the minimum stirring system power necessary to maintain the speed u. Therefore, the system efficiency P/P1=Fu/P1.

In this expression, the characteristics of the agitator can be separated from the system requirements, and it can be concluded that the thrust power ratio RFP is an important parameter related to the efficiency of the agitator. It should be noted The point is that it depends on the diameter and speed of the impeller, not just the geometry of the impeller. In addition to considering the generation of vertical flow energy efficiency, it is also necessary to consider the actual Various factors such as the diameter and speed of the impeller available in the application.

Note 2. The efficiency of the impeller can be defined as the ratio of the power produced by the axial movement of the impeller flow to the electric power absorbed by the agitator. In this definition, it is assumed that the approach speed u is sufficient It is small enough and has negligible influence on the characteristics of the agitator impeller. The relationship between hydraulic discharge power Ph=pQ and thrust is. p=F/A and F =2rhoQ2/A It can be applied to the agitator test specified in this standard. Because the exit section best meets the requirements of the plane velocity distribution, A/2 is usually used. by A=piD2/4, we get.

Ph = F/AAF/2rho 1 /2 =F3/2/D pirho/2 1 /2 Therefore, the impeller efficiency can be obtained.

/2/pirho/2 1 /2D P1 It is worth noting that usually the correction is in the range of 1%, and the efficiency is usually given as (assuming SI unit [F]. Newton, [P1]. Watt, [D]. meter, and such as Clean cold water as defined in 5.4.5.2).

/2/40DP1 Although the derivation given here is not based on completely correct assumptions, more rigorous methods can be used to derive approximate expressions of efficiency.

Since the efficiency of the stirring system is determined according to the diameter and speed of the impeller, the efficiency of the impeller itself is not important.

2.2 Advance ratio

The ratio of the speed of the propeller or the average environmental speed of the liquid to the (essential) blade tip speed.

2.3 Impeller Reynolds number

The ratio of the inertial force and the viscous force at the impeller.