Numerical Simulation of the Effect of Centrifugal Pumping Water Chamber on the Performance of Micro Electric Pumps

【Asian pump network】 Micro pump refers to the input power of less than 1.1kW pump. It has a small flow, high head, light weight, simple structure, versatility, ease of use and other characteristics, widely used in agriculture, petroleum, chemical and other fields. Most of the miniature pumps belong to the low specific rotation centrifugal pump. Due to the smaller blade outlet width, larger impeller diameter, axial flow channel narrow, resulting in large disk losses and hydraulic losses, so the pump efficiency is very low. Numerical Simulation of the Influence of Centrifugal Pumping Water Chamber on the Performance of Micro-Electric Pumps The pressure water chamber is one of the main flow-through components of the pump. Its main forms are spiral pressure water chamber, annular water pressure chamber and space guide vane. In general, the spiral pressure chamber accords with the flow law of the fluid outflow, the flow state is better, the water pump can get better hydraulic performance, and most centrifugal pumps adopt the spiral pressure water chamber. Ring pressure chamber is mainly used for the slurry pump, because the gap between the tongue of this structure is very large, not easy to cause impurities clogging, and the process is convenient; multi-stage pump guide vane also use more annular pressurized water chamber, because Symmetrical structure, easy to arrange through the bar, and to heat deformation uniform. Most of the micro-pump is the use of spiral pressure water chamber, but the spiral section of the small cross-section, the flow channel can not be machined, resulting in its shape and size, surface finish, etc. directly by casting to ensure that, and casting difficulty, flow The roughness of the road surface is large, resulting in a large hydraulic loss in the pump body. For the micro-pump, the pump body hydraulic losses second only to the impeller disc friction loss, the performance of the pump has a pivotal impact. At present, many scholars in this area launched a series of studies. Liu Zailun et al. 1 studied the influence of volute shape on high-speed partial flow pump performance, and pointed out that the use of a rectangular spiral volute can increase the head-off point and improve the pump efficiency. Guo Pengcheng et al studied the different sections of the volute on the performance of the centrifugal pump and found that the rectangular and circular spiral volute in the case of large flow rate slightly higher than the horseshoe-shaped volute, and in the design conditions, slightly lower than the horseshoe some. It has been mentioned that at speeds below 40 rpm, the pump efficiency may be higher than that of a non-machined spiral pressurized chamber due to the ease with which the annular pressurized chamber may be machined and polished. Based on this idea, based on the spiral pressurized water chamber, according to the design theory of annular pressurized water chamber and the difficulty of machining, three kinds of annular pressure water chamber with rectangular section are designed, and these four kinds of pressure Water chamber and the same impeller combination of three-dimensional numerical simulation, compared with the traditional spiral pressurized water chamber micro-pump performance prediction and analysis of the internal flow for the micro-pump performance optimization provides a rational design ideas in this paper selected Zhejiang The XCm158 centrifugal pump produced by the company is used for numerical simulation of the research object. The relevant parameters are: impeller diameter A = 38.5mm, outlet diameter D2 = 162mm, the number of leaves z = 6, the outlet width of the leaves 2 = 2.2mm, , The eighth cross-sectional area Ai = 102.5mm2, the inlet width of the volute chamber 63 = 10.5mm; the rated flow of the pump CL = 4m3 / h, rated head Hi = speed n = 29. It is defined as No. 1 pump. XCm158 micro pump using a spiral pressure chamber, on the basis of which will be changed to a rectangular section of the annular pressure chamber, and to ensure that both sections of the eighth cross-sectional area equal. In addition, based on this annular water pressure chamber, further improvements are made according to the following principles: (1) The diameter of the base circle is unchanged; (2) The inlet width of the water pressure chamber is not changed; (3) The outlet diameter and relative position of the diffuser section are not changed. According to the above principles and the design theory of annular pressurized water chamber, the area of ​​the 8th cross-sectional area of ​​the annular pressurized water chamber can be obtained as 102.5mm2. In the diffusing section, the outlet size adopts the standard nominal diameter of 24mm and is defined as No. 2 pump. The axial height of the eighth section of the chamber was 9.7 mm. Based on this model, the axial height of the annular pressurized water chamber section was increased by 5 and 10 mm respectively as the No. 3 and No. 4 pumps. The main dimensions of the water pressure chamber are shown in Table 1. Model No. Base circle diameter A3 / mm The 8th section height 8 / mm The entrance width The 8th section area The 1st pump The 2nd pump The 3rd pump The 4th pump Table 1 The main geometric parameters of the pressurized water chamber Tab.2 model establishment and algorithm 2.1 Model Building Solid models with PRO / E and then ICEM mesh the model. In modeling, in order to avoid the influence on the flow field and flow in the swirling vortex region Pfi, an inlet pipe at the inlet of the impeller is added, which is 3 times the length of the inlet diameter. Considering the influence of the outlet boundary conditions on the flow field and the convergence Of the impact, in the volute export section plus an outlet pipe, the length of the export diameter of 5 times. Import and export pipe structure using hexahedral mesh; and impeller and volute flow channel complex shape, the use of unstructured tetrahedral body-fitted adaptive grid. 2.2 Numerical calculation method Numerical simulation calculation Reynolds averaged equation is solved by using ANSYSCFX12.0. The Reynolds stress term is solved by the standard e turbulence model and closed the system of equations. In ANSYSCFX12.0, the finite volume method is used to discretize the equations. The convection term in the discretization process is analyzed using high resolution grid, design point conditions and large flow conditions (1.4 times of operating conditions) Static pressure under the conditions of the cloud. Comparing the static pressure of the two pumps, it can be seen that at 0.6 (under the conditions, the static pressure at the outlet of pump No. 1 and No. 3 is basically the same, and the static pressure in the annular pressure water chamber and impeller of No. 3 pump changes more evenly , While the pressure pump No. 1 pump spiral pressure chamber near the diaphragm at a greater pressure gradient at the same time the impeller blade near the diaphragm pressure side of the outlet there is a clear high pressure zone, which is due to the pump No. 1 flow in small flow does not Uniform, the direction of the speed vector chaos, resulting in the return flow in the 1.0Qi conditions, annular pressure distribution chamber pressure distribution increases first and then decrease and then increase, probably because of the annular structure of the pressure chamber and tongue The gap between the impeller is too large, inevitably there will be a phenomenon under different operating conditions point two kinds of pump static pressure cloud backflow phenomenon, at the tongue at the part of the fluid to re-enter the pressurized water chamber.But it is due to the backflow from the shunt, So that the outlet section of the pressure chamber greatly reduce the flow velocity, to achieve the kinetic energy of the pump outlet to the conversion of pressure, and the results of spiral pressure chamber is different at 1.4 (3, operating conditions, both the outlet static pressure Obvious difference, annular pressure chamber outlet static pressure significantly In the spiral pressure water chamber, the reason may be that the larger the flow rate, the larger the proportion of friction loss along the pressure chamber, the more prominent the inner wall smoothness of the annular water pressure chamber is more prominent.In addition, the two pump outlet static pressure The difference between the pressure difference and the lift curve is concordant.It can be concluded that the pressure and velocity of the helical pressure chamber are uniformly distributed only at the maximum efficiency point of the pump and the pressure and velocity distribution are not uniform under the pump partial pressure operation.The annular pressure On the contrary, the pressure and speed distribution of the pump are evenly distributed at the dead point, once the flow is generated, the balance is destroyed, and the hydraulic loss of the annular pressure water chamber at the maximum efficiency point is larger than that of the spiral pressure water chamber, In the electric pump, due to the machinability of the surface of the annular pressure chamber flow channel, better hydraulic performance can be obtained, which exceeds the effect of the unstable pressure distribution caused by the annular pressure chamber on the performance of the pump. 4 Radial Force Analysis Pump In operation, the fluid will be subjected to the radial force along the radial direction of the impeller, and the radial force will cause the pump shaft to be subjected to the alternating stress to produce the directional deflection. The size directly affects the stability of the pump shaft. In addition, Of the shaft seal will make the gap becomes uneven, and the shaft seal clearance is too large is the leading cause of some pump leaks, so in the design of the pump radial force due to the need for appropriate consideration for the numerical simulation of the No. 1 pump And the radial force of pump 3. The radial force distribution of the two pumps can be seen from the radial force of pump No. 1 with the flow rate increases and then decreases and then increases to reach the minimum near the design conditions, But not zero because of the asymmetric structure of the pump impeller flow path leading to the flow velocity and impeller outlet pressure distribution asymmetry; and No. 3 pump radial force at the smallest flow when the smallest, With the increase of flow rate.The radial pressure distribution law of these two kinds of water pressure chamber is consistent with.In addition, from the small flow to the pump near the rated flow, the radial force of pump No. 3 is less than pump No. 1; in the large flow area , The radial force of pump No. 3 is slightly larger than that of pump No. 1. In this way, pump No. 3 with an annular pressure chamber can operate safely and stably in the full flow range compared to pump No. 1. 5 Test Verification No. 1 pump And pump No. 3 according to the rotary pump hydraulic (on page 88) Centrifugal pump impeller The internal turbulent kinetic energy and dissipation rate analysis Ye Daoxing Wang Yang will be compared with the turbulent dissipation rate and turbulent kinetic energy distribution can be seen is very similar to the law: in different conditions, the turbulent dissipation rate increases with increasing radius , Reaches a maximum value and begins to decrease, then begins to increase after a minimum value until the impeller exit (except. 6 (operating conditions), the turbulence dissipation rate reaches the maximum value in the region of only = 60mm; under the design conditions, the turbulent dissipation rate is the smallest, except for the region of 55mm to 65mm only, the turbulent dissipation Rates are below 400m2 / s3; Under the condition of 6Qd, the distribution of the turbulent dissipation rate appears opposite to that under other conditions, and the distribution of the small central and small ends is large. In other conditions, the distribution of the large and small middle ends is small. At the same time, = 85mm, the turbulent dissipation rate increases very rapidly. This may be due to the fact that in the low flow regime, axial eddies are generated in the impeller flowpath in this region, resulting in a sharp increase in the turbulence dissipation rate. Although the turbulence dissipation rate is higher than the design condition, it can be seen that the turbulence dissipation rate is still far below 0.6 (condition; overall, under the design conditions, the turbulence dissipation rate is the smallest, and the turbulent flow rate Scattered energy rate slightly higher than the design conditions, the small flow, the turbulent dissipation maximum 4. Conclusion In this paper, the two-equation turbulence model e, the experimental verification, analysis of the numerical calculation and experiment measured XST standard centrifugal pump head , Efficiency, shaft power and other data to verify the reliability of the numerical calculation.) Turbulent kinetic energy and turbulence dissipation rate distribution along the radius of a very similar law, that is, the turbulent flow of large area turbulent dissipation rate Big, and vice versa. ) In addition to the low flow rate of 0.6, the distribution of turbulent kinetic energy and turbulence dissipation rate first increases along the radius and then decreases, finally increasing this phenomenon. Under 6Qd low flow conditions, the turbulent kinetic energy and turbulence dissipation rate is the largest and the fluid energy loss is the most serious. In terms of efficiency, the pump should be operated under low flow conditions. (Editor: Huang Nengwen QQ:)