The best circumferential speed of water ring vacuum pump impeller

1 Circular speed expression The water ring pump is a collective term for water ring vacuum pumps and water ring compressors. Speaking from the working principle, it is a rotary vane volumetric pump. However, from the analysis of its energy conversion process, it belongs to the impact type machine, that is, it converts the kinetic energy of the working medium water into pressure energy for compressing the gas to be transported, thereby achieving the purpose of pumping gas.

Its energy transfer process can be decomposed into: The motor drives the impeller to rotate, and the impeller drives water to form a water ring. In the first half of the week, the water buried in the impeller is accelerated by the impeller and its circumferential velocity increases with increasing radius. When the water is thrown from the tip of the blade, it reaches the peripheral speed of the impeller (abbreviated as the peripheral speed), making the water sufficient. Kinetic energy. In the latter half of the week, the water re-enters the impeller, the speed drops, and the kinetic energy is converted into pressure energy for the compression of the gas. It is not difficult to see from the above process that the impeller peripheral speed u2 represents the energy delivered by the impeller to the water loop. Specifically, the milk characterizes the amount of energy delivered by the impeller to the unit mass of water, which is the basis for determining the overall pump structural parameters. Here we focus on the establishment of the best circumferential speed of the water ring vacuum pump impeller.

The impeller circumferential speed to determine the degree of gas compression, in order to obtain the required compression ratio inner / p impeller minimum circumferential speed required: P. - suction absolute pressure, Pa small - impeller head correction factor, y The working medium is heavy, N/m3 102Pa, obtained: U2min=1.35~17.5m/s is obtained, it needs to be optimized. At this time, many factors should be considered.

Effect of temperature efficiency is The pump isothermal efficiency can be expressed by the following equation: Inconsistent energy loss.

7 - Mechanical efficiency. The friction loss of bearings, packings and shafts is measured to slightly increase with decreasing speed. 7/m=0.985~0.99 VV volumetric efficiency. Measure the fullness of inhaled gas, leakage loss, and clearance loss.

The actual gas volume was measured by the test device.

Water pump technology 2000.3 (Theoretical gas volume can be calculated by formula.

Gas hydraulic loss, 7h = 0500.70 Here, we mainly analyze the above-mentioned changes in efficiency in the high-efficiency zone 102Pa), and use the following test to verify.

Test verification is to make the test results universally meaningful. The design principle of the test plan is to ensure that the pump peripheral speed covers the normal working range of the vacuum pump, which can be adjusted between 13.517.5 m/s. Changing the peripheral speed can be achieved by changing the pump shaft speed or the impeller outer diameter. However, it is difficult to change the outer diameter of the impeller to meet the requirements of the speed range, and the test results are also doped with the influence of changes in the geometric dimensions, resulting in analysis difficulties. However, there is no such problem as changing the rotational speed, and it is easy to implement. Therefore, a scheme for changing the rotational speed is adopted. At the same time, taking into account the increase in pump power after the increase in the original pump shaft caused by overload and gas volume caused by the discomfort of the original window, decided to use a weekly speed of about 17.5m / s pump speed test. , Third gear speed, see test results.

With the change is very small, for the sake of simple analysis, take = 0.99, 7 = 0.94, so only analyze the rj, rj, and 17h changes can be, Table 1 is the test 杲 at A = 450hPa, the three efficiency changes.

Table 1 + with "2 changes in the law of inhalation of gas filled with the degree of gas flow into the space of the impeller, how much, and the suction window speed, the ratio of the length and diameter of the impeller and its peripheral speed. Corresponding to the determined pump and working conditions, only with the change, with the reduction, the time it takes for the impeller to turn over the same angle becomes longer, and the fullness of the inhaled gas is increased.

Leakage loss refers to the loss of gas caused by the gas in the compression chamber through the axial (radial) gap between the impeller and the distribution plate (return) to the suction chamber, and the pressure in the compression chamber and suction chamber. Poor, gap size and impeller speed. After the pump and working conditions are determined, it is only related to the peripheral speed. It can be divided into two items: along the direction, back through the gap from the compression chamber to the suction chamber, so there is a water ring between the compression chamber and the suction chamber to supplement the flow of water, so this gap is also filled with water, blocking the gas Back to the string of channels, so as long as the supplemental water is normal, the leak can be ignored here.

With the opposite direction, back through the gap from the compression chamber to the suction chamber. With the reduction of U2, the impediment to leakage becomes weak, and the leakage loss increases.

Loss of clearance means that the residual gas that is not discharged in the discharge chamber pushes open the water ring that is in contact with the impeller hub, and the amount of air loss caused by the return of the water ring back to the suction chamber with the impeller. It mainly occurs in the high vacuum area (A. The results of the above comprehensive, at higher to, TJv decreases sharply with the mountain, when the milk is low, little change, see Table 1 2.4 with "2 changes in the law of water ring hydraulic The loss consists of two parts: a) The length and local loss of the water ring as it flows along the wall of the pump body and the impeller, and its size can be expressed as, where the drag coefficient is related to the roughness, shape and size of the overflow wall surface. When the pump structure is fixed, the Fan Qi Dan persimmon decreases with the help of reduction.

b) Loss of momentum exchange at the outer diameter of the water ring inside and outside the impeller. According to the consistency of the size and direction of the water ring velocity and the water ring velocity at the impeller exit, the greater the deviation between the two, the greater the water ring impact loss. It is related to the impeller outlet angle and the matching degree of the pump body, and has little to do with the large suction water pump technology 2000.3.

Gas hydraulic loss also includes local loss caused by two parts of gas passing through the suction and exhaust windows at a certain speed. The higher the speed, the greater the loss. For a certain pump, the suction and exhaust window area is constant. As the assist decreases, the gas volume decreases, and the window speed becomes lower, and the loss becomes smaller.

Energy loss due to over-compression and under-compression For a pump, the start of the exhaust window is based on a suction pressure (see ). In actual use, inhalation pressure changes. When the actual suction pressure is higher than the design suction pressure (low vacuum), the gas pressure in the chamber at the discharge port is greater than the external pressure ft, which results in overcompression, and the corpse 2 is reduced to ft by expansion, causing energy loss (see). When the actual suction pressure is lower than the design suction pressure (high vacuum), the water ring hydraulic loss and the gas window loss play a major role in the above items. Therefore, the hydraulic efficiency 77 - decreases the compression ratio/Pl abnormality with milk. Elevated, see Table 1. In conjunction with the changes in the efficiency of various efficiency, the isothermal efficiency of the pump 7U increases with the reduction of the impeller peripheral speed U2, see Table 1. 2 and the impact of the pump on the stability of the work of the experimental pump and the All the impellers are provided by Lanzhou Shuili General Factory. I would like to express my sincere thanks to this factory.

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