Influence of flow velocity and pipeline characteristics on water hammer Li Zhiqin (School of Architecture and Environmental Engineering, Taiyuan University of Technology) The effect of the thickness of the pipe wall on the magnitude of the water hammer pressure in the pipeline, the growth process of the water hammer pressure and its phase 1: A In the pipe diversion system, the water hammer phenomenon often occurs in the pipeline due to the rapid adjustment of the valve. Therefore, in the engineering design of the pressure pipe diversion system, the water hammer must be calculated to determine the maximum and minimum water hammer that may occur Pressure, study the appropriate measures to prevent and weaken the effect of water hammer. The methods of water hammer calculation include analytical method, graphic method and characteristic line method. Among them, the characteristic line method can calculate the more complicated water hammer problem considering the influence of resistance by computer. The method is rigorous and has high accuracy. Therefore, in this paper, the characteristic line method is used to calculate the water hammer in steel pipes and PVC pipes, and the effects of water flow velocity, pipe material, and pipe wall thickness on the magnitude of the water hammer pressure, the long process of water hammer pressure, and the phase length of water hammer are analyzed. Provide certain h-one calculation node pressure head of the pressure-measuring tube when taking measures to prevent and weaken the water hammer effect in the project, m; v calculation node flow rate, m 9-angle between the pipe and the horizontal plane, degree; c determined by the following formula , E-one pipe material elastic coefficient; W-pipe wall thickness; C1 one-one parameter, determined by embedding method.
When there is no axial movement of the pipeline, C1 is determined by the following formula. When the characteristic line equation and its discrete bookmark2 are calculated using the characteristic line method to calculate the water hammer, the equation used is: where the Poisson's ratio of the pipe material is discrete to the above formula, Find the pressure and flow velocity at the non-boundary nodes as follows: Li Zhiqin, male, born in March 1965, master, lecturer, research direction: hydraulics and river dynamics, Taiyuan, 030024 where Ax and At are distance and time step respectively 2 Calculation of initial conditions and boundary conditions bookmark5 Table 1 Correspondence between the maximum water hammer pressure at the valve and the flow velocity in the pipe No. Flow velocity in the pipe Direct water hammer pressure / MPa Indirect water hammer pressure / MPa PVC pipe steel pipe PVC pipe steel pipe 11. Table 2 110mm Number of maximum water hammer pressure at W / D W / D flow rate in pipe / (ms-1) Maximum water hammer pressure / MPa Phase growth into the table 3200mm PVC pipe Maximum water hammer pressure number at different W / D W / D pipe flow rate) Maximum The initial condition of the schematic diagram of water hammer pressure / MPa phase calculation. The initial flow rate in the pipe is calculated according to the flow rate during normal water diversion, the initial pressure at each node is calculated as follows, and the upstream boundary conditions. The head of the pressure pipe at this location h = H = downstream boundary condition. When the valve is suddenly closed, the water flow velocity v = 0; when the valve is gradually closed according to the straight line rule, the water flow velocity and head are determined according to the following formula, 3 The calculation result and analysis coefficient are 3.X 1Cf; The resistance coefficient is 0.025 and the elasticity coefficient is 2K 1010. From the calculation results, it can be seen that the maximum water hammer pressure at the valve will increase with the increase of the water flow velocity in the pipe. Table 1 is the corresponding relationship between the maximum water hammer pressure at the valve and the flow velocity in the pipe when direct water hammer and indirect water hammer occur in the steel pipe and PVC pipe. In addition to the influence of the water flow velocity in the pipe, the maximum water hammer pressure at the valve is also relative to the wall thickness of the pipe The size of the W / D value is related to Table 2 and Table 3 are 110mm and 200mm two pipe diameters, the maximum water hammer pressure value in PVC pipes of different W / D. Although the flow rate value gradually increases from top to bottom, the maximum water hammer pressure does not gradually increase, and 3) the flow rate in the pipe is different, and the increase in the maximum water hammer pressure at the valve is also different from that at the valve at different water flow rates in PVC pipes. The change process of the water hammer pressure is the same as the change process of the maximum water hammer pressure at the valve at different water flow rates in the steel pipe. The growth rate of the water hammer pressure in the first phase is equal to the equivalent value from the figure and Table 1. It can be seen that the difference in pipeline materials will affect the propagation speed of the water hammer wave and thus the time for the valve to withstand the maximum water hammer pressure. The greater the material elastic coefficient of the pipe, the faster the water hammer wave propagates in it, so that the valve will bear the maximum water hammer pressure for a shorter time; at the same time, the difference in pipe material also affects the magnitude of the maximum water hammer pressure , The greater the elastic coefficient of the pipeline, the higher the maximum water hammer pressure. When the flow rate is the same, the maximum water hammer pressure in the steel pipe is higher than the maximum water hammer pressure in the PVC pipe. As can be seen from Table 2 and Table 3, the pipeline The size of the W / D value will also affect the propagation speed of the water hammer wave, thereby affecting the phase length of the water hammer. The larger the W / D value, the shorter the phase length of the water hammer. The valve will withstand the maximum. 4 Conclusion The maximum water hammer pressure at the valve The size depends not only on the flow rate of the water flow in the pipe, but also on the size of the pipe's W / D value. In the same pipeline, the maximum water hammer pressure increases with the increase of flow rate; in different pipelines, the maximum water hammer pressure increases with the increase of W / D value.
The size of the water flow velocity in the pipe also affects the maximum water hammer pressure. The maximum flow velocity in the pipe: 1.00m / s; the water hammer pressure growth rate: 9. (%; the phase length: 2.709s The growth rate of the maximum water hammer pressure change process at the valve in the steel pipe The greater the mid-water flow velocity, the greater the increase in the water hammer pressure in one phase. The length of time the valve withstands the maximum water hammer pressure depends on the material of the pipe and the W / D value of the pipe. The greater the elastic coefficient of the material, the valve The shorter the time to withstand the maximum water hammer pressure, the greater the W / D value of the pipeline, and the shorter the time for the valve to withstand the maximum water hammer pressure
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