Pirkovskyi D. Improving the reliability and safety of power plants by preventing water hammers.

Much research has been devoted to improving the reliability and modernization of energy system pumps. However, the issues of the influence of heat-hydrodynamic instability on the reliability of pumping systems are not well understood. The phenomenon of thermo-hydrodynamic instability consists in the emergence of conditions for self-oscillating (self-sustaining) and / or aperiodic (pulsed) processes of changes in the thermo-hydrodynamic parameters of flows (pressure, speed, vapor content, etc.) in the systems of thermal equipment of thermal and nuclear power plants. The emergence of conditions of heat-hydrodynamic instability (HHI) leads to additional hydrodynamic loads on the construction of heat-power equipment and pipelines (water hammer), and also reduces the reliability of their operation in operating, transient and emergency conditions. In cases of critical conditions for the reliability of water hammers (CWH), the design functions of the operation and / or destruction of the designs of heat power equipment and pipelines (HPEaP) are denied. The determining factors for the occurrence of hydrodynamic instability and water hammer in a wide range of regime parameters can be specific features of the flow (network) characteristics of the pumps, that is, the dependence of the hydrodynamic pressure on the speed or flow rate. All this determines the relevance of this work and requires additional study and analysis. The analysis of the well-known approaches to simulating water hammers in heat-power equipment systems determined the need for improvement and development of new methods for modeling the conditions of occurrence and consequences of water hammers due to various types of heat-hydrodynamic instability of single and two-phase flows: oscillatory instability due to the inertia of the pressure-discharge characteristics of pumps and heat mass transfer processes in two-phase flows; aperiodic instability due to a pulsed increase in local hydraulic resistance and transonic flow regimes of single and two-phase flows. When modeling the conditions of occurrence and consequences of water hammer, it is necessary to take into account that the main determining parameter of water hammer is the growth rate of the pressure pulse during the transition of the kinetic energy of deceleration of the flow into the energy of the pulse of water hammer. At the same time, it is also necessary to take into account the possibility of simultaneous or sequential implementation of different types of water hammers. An analysis of the experimental conditions presented in the work on the stands of pumping systems based on the developed similarity criteria determined their inconsistency according to the criteria of hydrodynamic similarity to the real conditions of the main pumping systems of power plants. A method is developed for modeling the conditions of occurrence and consequences of water hammers in open circuits of heat power systems based on the general principles of the theory of heat-hydrodynamic instability. In contrast to the known approaches in the proposed method, the conditions for the occurrence of critical water hammers are determined by the conditions for the transition of vibrational heat-hydrodynamic instability to aperiodic instability. Based on the developed method, the conditions for the occurrence of critical water hammers in open pipeline systems of power plants with a linear approximation of the pressure-flow characteristics of pumps are determined.