Water diversion used 12 sets of large vertical mixed flow pump, the impeller is equipped with a German company KSB front guide vane device (Inlet Vane Conttrol Device VR), the purpose is to achieve a wide range of pump performance . 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 VR devices more objective and correct understanding , So as to put forward some suggestions for the actual control of such pumps. T Toothed Pu Timing Belt,Cargo Conveyor Belt,Heat Resistant Rubber Conveyor Belt,Synchronous Belts Jiangsu Bailite Transmission Technology Co., Ltd , https://www.nbzsindustrialbelt.com
We use the VR device is circular, guide vane straight leaf type, a total of 17, leaf length 500mm, device diameter 1300mm, the device is driven by a motor, through the multi-section transmission with universal joints will be The torque is transmitted to the input shaft of the device, and then the blades of the device are rotated synchronously through the gear system in the device, so as to adjust the angle of the guide vanes.
KSB company set to VR device guide vane perpendicular to the horizontal plane 90 º, when the blade rotation tilt direction and pump impeller rotation direction for the same angle (ie, the angle becomes smaller); when the blade tilt direction and pump impeller rotation direction opposite Increase angle (ie angle becomes larger). First of all, the first pump installed and not installed before the guide vane, the performance of the pump for some analysis.
(A) Comparison of pump performance without front guide vane and front guide vane with blade angle of 90 ° According to the information provided by KSB Company and the relevant tests conducted by our researchers, And when the blade is at 90º, it is compared with the characteristic curve of the pump without front vane device, as shown in Fig.3. From the figure, we can draw to conclude that the Q-H curve of the pump with the front guide vane and the front guide vane at 90º is basically two parallel curves with Q --- H of the front guide vane The curve is slightly lower due to the drop in head due to the increased resistance of the incoming flow resistance after the pre-guide vane is added. As can be seen from the Q-η curve, the two curves are basically close and have a coincidence point. On the left side of this point, the Q-η curve of the front guide vane is slightly higher than the Q-η curve of the front guide vane 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. It can be seen that when the vane position is at 90 º, the performance of the pump is basically similar to that of the pre-vane pump without any effect on the pump characteristics. Second, take a look at changes in performance of the pump at different angles. Effect of VR Guide Vane on Pump Performance at Different Angles. Performance curve of the VR unit pump at various vane angles. As can be seen in Figure 4, when the current guide vane is adjusted to less than 90, the resulting performance curve is clearly to the left and is substantially parallel to the performance curve at 90 degrees (in the continuous operating limit range Inside). 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 90º. When, Vlu = 0). From the Euler equation:
HT = (u2v2u-ulvlu) / g
That, when the guide vane angle to less than 90º. 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 adjusted to be greater than 90 °, 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. The same Euler equation shows that at this time the pump head HT is greater than the front guide vane at 90º head. 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.
Because the front guide vanes are adjusted to both sides of the 90º position, the liquid flow produces a positive pre-rotation and a reverse pre-rotation respectively before entering the pump impeller, and a circumferential component Vlu of the absolute velocity V1 is generated at the impeller blade inlet so that the impeller inlet Speed ​​triangle changes, 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 with the increase of the vane angle value.We can clearly see that the effect of the vane angle adjustment on the pump efficiency is obvious.When the guide vane is at 90 o, , The efficiency is the highest.When the guide vane angle increases or decreases gradually, the pump operating efficiency also gradually decreases.Moreover, the guide vane angle deviates from the 90 ° position, the bigger and the more obvious the efficiency decline, the pump can not work normally.Therefore, We limit the pump's front guide vane adjustment from 75º-110º to allow the pump to operate safely over 75% efficiency.
In the range of 75º - 110º, the operating efficiency of the pump varies. According to our analysis of the test data, there are the following rules: When the guide vane is adjusted within the range of 75º - 95º, the operating efficiency of the pump changes Smaller, and more efficient; and once the guide vanes are tuned to more than 95º, the pump efficiency will be significantly reduced. Table 1 shows the running data of three pumps of the same type at different guide vane angles. Table 1 Test data of pump operating efficiency at different guide vane angles Guide vane angle 75º 80º 85º 90º 95º 100º 105º 110º
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
For the above reasons, we can use the Euler equation and velocity triangle to analyze: From the above we know, 75º-110º. When the guide vanes are adjusted to less than 90º, the flow produces a positive pre-rotation of Vlu, which lowers the theoretical head of the pump. However, the efficiency of the pump did not decrease significantly due to the decrease of the relative velocity ω1, which greatly reduced the impact loss of the impeller on the liquid flow. On the contrary, when the guide vane angle was adjusted to more than 90 °, 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 limited 75º-110º range, avoid running the pump for a long time at extreme angles. Obviously, when the current guide vane is adjusted to a value greater than 90, due to the anti-pre-rotation of the liquid flow, the relative velocity ω1 of the liquid flow at the inlet of the pump impeller increases and the flow impinges on the impeller. As the guide vane angle Increasingly, this impact is also more serious, the pump cavitation performance adversely affected.
Cavitation from 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 impact of the flow on the impeller, the vibration value at the pump impeller becomes larger as the vane angle increases. Table 2 is a pump at a certain water level, the angle of the front guide vane and the value of the vibration value at the impeller. Table 2 Variations of guide vane angle and vibration value at impeller Value Guide vane angle 75º 80º 85º 90º 95º 100º 105º 110º
Vibration value (mm / s) 1.87 1.90 1.93 2.01 2.08 2.19 2.24 2.55
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 guide vane adjustment range limited to the appropriate area, then its negative effects will not be too large.