Effect of front guide vane adjustment on pump performance and usage control
Abstract: In the second phase project of water diversion from the upper reaches of Huangpu River in Shanghai, 12 large-scale vertical mixed flow pumps were used. Inlet Vane Conttrol Device VR manufactured by German KSB company was installed in front of the impeller in order to realize In a wide range of regulating pump performance. Keywords: guide vane pump performance guide vane angle I. INTRODUCTION Shanghai Huangpu River upstream water diversion project of the second phase, the use of 12 large vertical mixed flow pump, the impeller are equipped with German front KSB company manufactured guide vane device (Inlet Vane Conttrol Device VR), the purpose is to achieve a wide range of pump performance adjustment. Pump structure as shown in Figure 1, the parameters are: flow Q = 6.5M3 / S, head H = 15.5M, speed n = 297rpm, the number of comparison ns = 353, efficiency η = 0.80, shaft power P = 1400KW. Pre-guide vane device (referred to as VR device) is currently not much use on the pump at home and abroad, in this regard, few technical information and reports. To this end, the author based on the past three years on the pump operating conditions and the relevant experimental data and technical information on the use of VR devices to adjust the performance of the pump to do some analysis and analysis of the reasons in order to have a more objective and correct understanding of VR devices , So as to put forward some suggestions for the actual control of such pumps. The set of VR devices we use is circular in shape. The guide vanes are straight leaves with a total of 17 blades with a length of 500 mm and a device diameter of 1300 mm. See Figure 2. The device is driven by a motor and transmits the torque to the input shaft of the device through a multi-section transmission rod with a universal joint. Then, the blades of the device are rotated synchronously through the gear system in the device to adjust the angle of the guide vanes. China leading manufacturers and suppliers of Level 2 Charger ,Ev Charging Stations, and we are specialize in Charging Station,Flexible Group Charging Station, etc. Level 2 Charger,Ev Charging Stations,Charging Station,Flexible Group Charging Station Shenzhen Hongjiali New Energy Co., Ltd. , https://www.hjlcharger.com
Effect of two front guide vanes on pump performance
KSB company set to VR device guide vane perpendicular to the horizontal plane 90 & ordm ;, when the blade rotation tilt direction and the pump impeller rotation direction for the same angle (ie, the angle becomes smaller); when the blade tilt direction and pump impeller rotation opposite To increase the angle (that is, the angle becomes larger). Below the first installment of the pump installed with no guide vane, the performance of the pump for some analysis.
(A) without the pre-guide vane and the front guide vane equipped with a blade angle of 90 ° pump performance comparison According to the information provided by the KSB company and our researchers make relevant tests, the author draws with pre-guide Leaves and leaves at 90 ord m, with no pre-guide vane pump device compared with the characteristics of both curves, shown in Figure 3. From the figure, we can draw to conclude:
1. Without front guide vane and guide vane before 90? Q-H curve of the pump is basically two parallel curves, front guide vane Q --- H curve slightly lower, which is due to plus After the front guide vane, the import flow resistance loss caused by the rise of the decline of sake.
2. From the Q-η curve shows that the two curves are basically close, and there is a coincidence point on the left of this point, there is a front guide vane Q-η curve than before the guide vane Q-η curve slightly higher 3 On the right side of this point, the Q-η curve of the front guide vane is slightly lower than the Q-η curve of the front guide vane, which coincides with the optimal operating point. This shows that in the best conditions, the front guide vane resistance loss is minimal for the pump, does not cause any impact; and in the small flow, due to influent pipe less flow, uneven flow, plus the front After the guide vane, since the diversion effect, so that the liquid flow inlet uniformity of enhancement, the resulting efficiency has improved than the original; and in the large flow, the role of diversion disappeared, on the contrary due to the increase of the guide vane, the resistance loss increases, Resulting in lower efficiency.
Visible, when the guide vane position at 90 ord m, the performance of its pump is not installed before the guide vane pump performance is basically similar, then it has little effect on the pump characteristics.
Second, take a look at the guide vane at different angles when the pump performance changes.
(B) of the VR device guide vane at different angles on the performance of the pump 1 on the Q-H performance curve Figure 4 is a VR device pump in a variety of guide vane angle performance curve. It can be seen from Fig. 4 that when the current guide vane is adjusted in a direction less than 90, the resulting performance curve is clearly to the left and is substantially parallel to the performance curve at 90 ° angle (at continuous operating limits Range). This is because at this time, the flow direction of the front guide vane exit is consistent with the rotation direction of the impeller. The flow has a forward pre-rotation Vlu in front of the pump impeller inlet (Vlu flow at the impeller inlet at the circumferential speed of the absolute velocity ), So Vlu> 0 (front guide vane is 90 ord., Vlu = 0). From the Euler equation:
HT = (u2v2u-ulvlu) / g
Know that when the guide vane angle to less than 90 ㎡. When the direction is adjusted, because Vlu> 0, the theoretical lift of the pump HT is less than that of the guide vane. When the pump head HT. And, the smaller the value of the front vane angle, Vlu value is larger, the greater head lift, so Q-H characteristic curve to the left. In actual use, it is the use of this feature, while keeping the head is basically constant, the flow becomes smaller with the VR angle becomes smaller, so as to achieve the purpose of reducing the flow. However, when the current guide vane is greater than 90 mm, the direction of the front guide vane flow outlet is opposite to that of the impeller, that is, reverse pre-rotation occurs, so that Vlu <0. Also by the Euler equation shows, when the pump head HT is greater than the front guide vane in 90  head lift. Furthermore, the larger the leading vane angle, the smaller the Vlu, the greater the lift of the pump, and the Q-H characteristic shifts to the right. Therefore, it is possible to increase the pump flow rate with the increase of the vane angle under a certain lift. Practice shows that the above effect is obvious.
2 on the efficiency of the pump η As the leading guide vane to adjust both sides of the 90 ° position so that the flow before entering the pump impeller, respectively, had a positive pre-rotation and reverse pre-rotation, the impeller blade inlet to produce absolute velocity V1 The circumferential component, Vlu, therefore changes the impeller inlet velocity delta, as shown in Figure 5. The solid line is the velocity triangle without pre-rotation, and the dotted lines are the velocity triangles with positive pre-rotation and reverse pre-rotation, respectively. It can be seen from the figure that the relative velocities ω1 are not the same in the three conditions, ω'1 is the relative velocity when the liquid flow is positively pre-rotated, and ω1 is the relative velocity when the liquid flow is reversely pre-rotated. ω1 increases as the vane angle increases.
From Figure 6 we can clearly see that the front guide vane angle adjustment of the pump efficiency is obvious. When the guide vane is in the 90 ° position, the pump operates in the most efficient area with the highest efficiency. When the guide vane angle is gradually increased or gradually reduced, the pump operating efficiency is also gradually decreased. And, the guide vane angle deviates from the 90 ° position, the greater the decline in efficiency and the more obvious, so that the pump can not be normal operation. Therefore, we will pump the guide vane adjustment angle is limited to 75 ~ -110 *. Range, so that the pump can be more than 75% efficiency in the safe operation.
Within the 75 --- --- 110 ~ ordin range, the pump operating efficiency changes, according to our analysis of the test data, the following rules:
When the guide vane is adjusted within the range of 75 ÷ ---- 95 ㎡, the operating efficiency of the pump changes less and is more efficient; and once the guide vane is adjusted to more than 95 degrees, the efficiency of the pump will be accelerated obviously . Table 1 is the same type of three pumps at different guide vane angle running efficiency of the test data: Table 1 under different guide vane pump operating efficiency of the test data Guide vane angle 75 ord 80 ord 85 ord 90 ord 95 ord 100 ord 105 ord 105 ord & 110 & ordm;
A Pump Efficiency% 81.82 82.22 82.51 82.70 81.76 80.25 77.89 76.10
B Pump Efficiency% 85.62 85.73 85.73 85.01 84.08 82.26 79.83 77.43
C Pump Efficiency% 88.50 87.36 87.40 86.92 85.80 84.47 8107 79.25
The reason for the above phenomenon can be analyzed by the Euler equation and the velocity triangle: From the foregoing we know that 75? -110 ?. When the guide vane is adjusted to a direction less than 90 °, the flow produces a positive pre-rotation Vlu, which lowers the theoretical head of the pump. However, since the relative velocity ω1 is decreased, the impact loss of the flow impeller is greatly reduced, so the pump efficiency is not significantly reduced; on the contrary, when the vane angle is adjusted to more than 90 °, Rotate Vlu, raised the theoretical head HT. However, as the relative velocity ω1 increases, the impact loss from the flow to the impeller increases, so that the efficiency is significantly reduced. If the guide vane angle to the outside of the regulation, will deviate from the design flow Qd, flow angle. Changes occur, this time in the impeller blade face will form a vortex area, causing greater impact loss, pump efficiency is lower.
In summary, we believe that: pre-guide vane adjustment caused by changes in pump efficiency, pre-flow of liquid and the impeller impact loss is the main factor. Therefore, the front guide vane adjustment is limited. Even within the limits of the use of 75 ~ a 110 *, should also avoid long-term operation of the pump at the limit angle.
3 on the pump cavitation performance Obviously, when the current guide vane to adjust the direction of more than 90, due to anti-spin flow generated, so that the liquid flow in the pump impeller inlet relative speed ω1 increased flow on the impeller Impact, as the guide vane angle increases, the impact is more serious, adversely affect the cavitation performance of the pump.
Cavitation by the pump basic equations:
NPSHr = λ1V20 / 2g ten λ2ω12 / 2g
It is known that due to the increase of the relative speed ω1, the required NPSHr greatly increases, so that the cavitation performance of the pump is reduced. Therefore, in operation, according to the pump cavitation characteristic curve and the water level and head changes, adjust the guide vane angle to ensure that the effective NPSHa NPSHa greater than the required NPSHr. In addition, due to the fluid impact on the impeller, the vibration value at the pump impeller also increases with the increase of the vane angle. Table 2 is a pump at a certain water level, the angle of the front guide vane and the value of the vibration value of the impeller. Table 2 Vane angle and the vane at the vibration value of the corresponding changes in the value of the guide vane angle 75 ord 80 ord 85 ord 90 ord 95 ord 100 ord 105 ord 110 ord 110 ㎡
Vibration value (mm / s) 1.87 1.90 1.93 2.01 2.08 2.19 2.24 2.55
Three Conclusion Pump guide vane adjustment can effectively change the pump operating conditions, to a large extent, meet the requirements of production and use. At the same time, due to the guide vane adjustment, the flow direction changes, so that the liquid flow on the impeller impact and head loss increases, resulting in reduced pump operating efficiency, and affect the pump cavitation performance. However, as long as the vane adjustment range is limited to the appropriate area, then its negative effect