The Mechanism Of Water Hammer Caused By Variable Frequency Flow Regulation Systems

The application of highly-efficient energy saving variable frequency flow regulation technique is becoming more and more widespread, and the phenomenon of water hammer caused by variable frequency flow regulation has become the key technical problem of its application. Internationally, at present, there is still a lack of reports on research findings of the generation mechanism of water hammer caused by variable frequency flow regulation and the control strategy of advanced intelligent control on water hammer pressure, the generation mechanism of water hammer is still unclear. So how to accurately predict the water hammer pressure of variable frequency flow regulation delivery system of complex process industry, as well as precise control of water hammer pressure, is still a technical challenge of the process industry. Therefore, it has very important theoretical research and engineering application value in ensuring the safe operation of process equipment system to study the theoretical predicting method of the water hammer caused by establishing variable frequency flow regulation and the advanced intelligent control strategy of precise control on water hammer pressure. Based on the characteristics of water hammer caused by variable frequency flow regulation, the full 3-D transient isothermal viscoelastic theoretical model and its corresponding high efficient steady finite element numerical algorithm was established to describe its generating process in this article. With numerical simulation, the regulation of the influence of process parameters, rheological properties parameters and system structure on water hammer process caused by variable frequency flow regulation was studied, the generation mechanism was revealed, the correlating control model of the process parameters and rheological properties parameters which avoid water hammer caused by variable frequency flow regulation was established, and the scientific theoretical foundation of precise control on water hammer pressure was laid. Main achievements are as follows:(1)Based on the rheology and fluid dynamics theory, in accordance with the characteristics of water hammer caused by variable frequency flow regulation of viscoelasticity and pure viscosity fluid, with reasonable hypothesis, the full 3-D transient isothermal viscoelastic theoretical model and its corresponding high efficient steady finite element numerical algorithm was established to describe its generating process of water hammer.(2) The water hammer intensity factor caused by variable frequency flow regulation is mainly decided by the density, viscosity and relaxation time of fluid. The water hammer intensity factor caused by variable frequency flow regulation increases with the increasing density and relaxation time of fluid, and decreases with the increasing viscosity. Increasing viscosity or decreasing the density and relaxation time of fluid is beneficial to control water hammer.(3) Increasing the value of viscosity will lead to enhance the effects of viscous dissipation damping. So it can effectively reduce the propagation of pressure wave, which can weaken the degree of water hammer. Increasing the value of relaxation time will lead to enhance the elasticity of fluid, which can increase the propagation of pressure wave, and strengthen the degree of water hammer.(4) The water hammer intensity factor caused by variable frequency flow regulation is mainly decided by system flow rate, frequency control time and frequency range. The water hammer intensity factor caused by variable frequency flow regulation increases with system flow rate and frequency range, but decreases with increasing frequency control time. Decreasing flow rate and frequency range or increasing frequency control time is beneficial to control water hammer.(5) With numerical simulation, the correlating control model of the process parameters and rheological properties parameters which avoid water hammer caused by variable frequency flow regulation was established, and the scientific theoretical foundation of precise control on water hammer pressure was laid.