A water pump design method based on the area ratio principle is proposed. That is, under the condition of keeping the area ratio constant unchanged, matching different impellers on the same deflector to obtain the efficient pump with different parameters.
Submersible pump is the most widely used general machinery, not only for industrial use, but also for the vast rural areas. With the development of rural electrification, from domestic water to farmland irrigation, submersible pumps have become indispensable tools. It is widely used, in order to expand the scope of use, this paper presents a method based on the principle of area ratio pump design. Submersible pump performance is mainly determined by both impeller and deflector, high efficiency pump not only requires efficient impeller, but also with the impeller well-matched deflector, if the deflector does not fit, not only reduce the pump Efficiency, but also to a certain extent, affect the stability of pump performance. HHAnderson proposed the centrifugal pump area ratio principle, pointed out that the impeller outlet flow area and the throat area ratio is the pump head, flow, shaft power and other parameters of the main determinants. For the first time, RC Worster proved mathematically that the principle of area ratio proposed by HHAnderson was scientific.
In our country, the area ratio principle has been introduced since the early 1980s. Some people have used the area ratio principle to analyze the existing pumps, but the research work is still not deep enough. Therefore, this paper presents a design method based on the area ratio principle Under the condition of keeping the area ratio constant unchanged, different impellers are selected for the same deflector to obtain efficient pumps with different parameters. The method is validated through experimental research and numerical simulation.
1, the theory of area ratio principle
In the pump impeller design, the general assumption that the impeller inlet without pre-rotation, vu, 1 = 0, then the basic equation of the pump:
Equation 1
Where HT --- pump theoretical lift, m
u2 --- impeller outlet circumferential speed, m / s
vu, 2 --- impeller outlet flow absolute velocity of the circumferential component, m / s
According to the impeller exit speed triangle we can see:
Equation 2,3
Assuming that there is no hydraulic loss in the transition region between the exit of the impeller and the throat of the deflector, v2 = vt, substituting (2) into (3) yields:
Equation 4
The impeller transmits energy to the liquid, the deflector collects the liquid flowing out of the impeller and discharges the liquid. The deflector does not add any energy to the liquid but affects the pump operating point and maximum efficiency point. The impeller and deflector coupling should follow the liquid flow continuity equation, then:
Equation 5
Where vt --- flow throat flow velocity, m / s
Fth --- deflector throat area, mm2
ω2 --- impeller outlet blades relative speed, m / s
F2 --- impeller outlet blade area, mm2
Will type (5) rewritten as:
Equation 6
Where Y --- area ratio coefficient
Substituting Eqs. (4) and (6) into Eq. (1), the relation between the theoretical lift of the pump and the area ratio is:
Equation 7
Visible, to get a higher pump head, should make the area ratio coefficient Y ≤ 1.
Zhang Junda on the 166 kinds of pump hydraulic model area ratio coefficient statistics and regression, and plotted the area ratio coefficient and pump specific rotation curve, obtained most of the pump area ratio coefficient Y ≤ 1, further evidence of The above conclusion is correct. Guo Zijie derived the approximate expression of the area ratio coefficient and the specific rotation number, and counted the area ratio coefficients of a large number of centrifugal pumps, and the data showed that their area ratio coefficients Y≤1. Accordingly, this paper proposes to obtain an efficient water pump through the matching impeller on the same deflector under the condition of keeping the area ratio constant unchanged.
2, test equipment and experimental research
In order to study the effect of area ratio on the performance of submersible pumps, submersible pumps were used for testing. On the same deflector were optional 2 kinds of impeller, open test bench in Lanzhou University of Science and Technology test, the same motor test only change the pump. In order to ensure that cavitation and swirl do not occur in the suction zone, the impeller has a sufficient submergence depth under water. The input power of the motor is measured by electric method, and the motor efficiency is estimated according to the efficiency on the nameplate. Take 250QJ125 submersible pump test, while maintaining the area of ​​the throat and the impeller vane blade outlet area ratio of the area ratio factor Y = 0.87 constant under the premise of redesign of an impeller Ⅱ, the impeller installed in the Submersible pump pilot on the test. Optional 2 different impeller submersible pumps, their best operating point of the measured data shown in Table 1.
Table 1 best condition point measured value
Table 1 best condition point measured value
Fig. 1 Schematic diagram of area between impeller exit vanes
Fig.1 Schematic diagram of area between impeller exit vanes
Table 2 Impeller exit vane area and deflector throat
Table 2 Impeller exit vane area and deflector throat
Table 2 Impeller exit vane area and deflector throat
In order to ensure the reliability of the test data, the author measured the area between the blades of the impeller and the area of ​​the throat of the deflector. Figures 1 and 2 are the method for determining the area between the outlet blades of the impeller and the throat area of ​​the flow deflector, and Table 2 shows the measured results. As can be seen from Table 2: The two pump area than the coefficient of a slight deviation, which is caused by part machining error. In the case of the same deflector optional impeller, as long as the ratio of the same area to maintain the same, you can get a high efficiency submersible pump.
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