Farwise Technology Co.,Ltd. , https://www.farwiselighting.com
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 VR devices more objective and correct understanding , So as to put forward some suggestions for the actual control of such pumps. Second, the front guide vane device on the performance of the pump We use the VR device is circular, guide vane straight leaf type, a total of 17, leaf length 500mm, device diameter 1300mm, 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. KSB company set to VR device guide vane perpendicular to the horizontal plane 90o, when the blade rotation tilt direction and pump impeller rotation direction is the same as the angle (ie, the angle becomes smaller); when the blade tilt direction and pump impeller rotation opposite Increase angle (ie 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 front guide vane and the front guide vane with a blade angle of 90o pump performance comparison According to the information provided by the KSB company and our researchers made relevant tests, the author drawn with the guide vane And the leaves at 90o, with no pre-guide vane pump device characteristics of the two curves, shown in Figure 3. From the figure, we can draw conclusions: 1. Q-H curve of the pump without pre-guide vane and front guide vane is basically two parallel curves, with Q- -H curve slightly lower, which is due to the addition of the front guide vane, the import flow resistance loss caused by the increase of the head down reason. 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 the front 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 o, its pump performance and pre-installed guide vane pump performance is basically similar, then it has little effect on the characteristics of the pump. 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 to be less than 90, the resulting performance curve is significantly leftward and moves substantially parallel to the performance curve at 90 ° angle (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: 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. When the current guide vane is larger than 90o, the direction of the front guide vane flow outlet is opposite to the rotation direction of the impeller, that is, reverse pre-rotation occurs, so that Vlu <0. Also by the Euler equation shows that the pump head HT is greater than the front guide vane at 90o when the 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 guide vanes to the 90o position on both sides of the adjustment 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 speed V1 circumference The component Vlu, therefore, changes the impeller inlet velocity delta, as shown in FIG. 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.From Figure 6 we can clearly see that the front vane angle adjustment on the pump efficiency is obvious.When the guide vane at 90o position, When the guide vane angle increases or decreases step by step, the operating efficiency of the pump is also gradually decreased, and the farther the vane angle deviates from the 90o position, the greater and the more obvious the decrease of the efficiency will make the pump unable to be normal Therefore, we will pump the front guide vane adjustment angle is limited to 75o-110o. Within the range, so that the pump can be more than 75% of the efficiency of safe operation within the range of 75o --- 110o, the pump Of the operating efficiency changes, according to our analysis of the test data, the following rules: When the guide vane in the 75o - 95o within the scope of regulation, the pump operating efficiency changes smaller and more efficient; and once the guide Leaves to more than 95o To adjust, the pump efficiency will significantly accelerate the decline.Table 1 is the same type of pump at different guide vane angle of the operating efficiency of the test data: For the above reasons for the phenomenon, you can use Euler equations and velocity triangles to analyze: From the foregoing we know that when the guide vanes are adjusted to less than 90 ° in the range of 75o-110o, the flow produces a positive pre-rotation of Vlu, which reduces the theoretical head capacity of the pump. However, due to the decrease of the relative speed ω1, The flow loss on the impeller greatly reduced, so the efficiency of the pump did not significantly decreased; on the contrary, when the guide vane angle to more than 90o direction adjustment, although the flow anti-pre-rotation Vlu, to raise the theoretical head HT. However, As the relative speed ω1 increases, so that the liquid flow on the impeller impact loss increases, so the efficiency has a relatively significant decline.If the guide vane angle outside the limit when adjusted, the flow will deviate from the design flow Qd, flow angle .What changes at this time in the impeller blade face will form a swirl zone, causing greater impact loss, the pump efficiency is lower.In summary, we believe that: the guide vane Causing changes in the efficiency of the pump, the pre-rotation of the liquid flow and the impeller impact loss is the main factor.Therefore, the regulation of the front guide vane is limited.Even in the limited use of 75o a 110o should also avoid the pump A long time at the limit of operation .3 on the pump cavitation performance Obviously, when the current guide vane to adjust the direction of more than 90, due to liquid anti-pre-spin, so that the flow in the pump impeller inlet relative speed ω1 Increase, the flow impeller impact, as the guide vane angle increases, the impact is more serious, the pump cavitation performance adversely affected by the pump cavitation basic equation: NPSHr = λ1V20 / 2g Ten λ2ω12 / 2g that, due to the relative speed ω1 increases, making the required NPSHr NPSHr greatly increased, so that the pump cavitation performance degradation. 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 liquid flow