•Condensation induced water hammer (CIWH) regime maps under different pipe lengths were obtained.•Transition criterion of periodic CIWH considering pipe length was developed.•Frequency correlation of ...periodic CIWH considering pipe length was developed.•Correlation of the occurrence position of periodic CIWH was developed.
Condensation induced water hammer (hereafter, CIWH) phenomenon is widely observed in various industrial operations, causing severe damage to related equipment and personal safety. This study investigated the CIWH regime map and the oscillation characteristics of periodic CIWH under different pipe lengths when the steam was discharged into a water tank through a horizontal pipe. First, the CIWH regime maps were obtained under different pipe lengths, with distinct regimes of periodic CIWH and non-periodic CIWH. A criterion was proposed to predict the transitions from periodic to non-periodic CIWH. It was found that the occurrence frequency of periodic CIWH decreased with the increase in the pipe length. An empirical correlation of Strouhal number, non-dimensionalized occurrence frequency, was developed to predict the occurrence frequency. The correlation could reproduce more than 95 % of the experimental data with the error of -20.2 % to 23.7 %. The pressure oscillation intensity of periodic CIWH was analyzed. The oscillation intensity increased when the pipe length and steam mass flux increased, whereas it increased first and then decreased when pool temperature increased. Finally, the occurrence position of periodic CIWH was found to be nearly constant under the same test condition. The position moved downstream of the steam when the pipe length and Froude number increased, and Jakob number decreased. The average occurrence position was correlated with the error of -17.1 % to 18.4 %.
•The research conducted experiments on Condensation-Induced Water Hammer in WASIF.•In experiments, subcooled water injected radially into steam filled horizontal pipe.•Experimental results enhance ...CIWH triggering understanding in horizontal pipes.•A correlation predicts the necessary minimum feed water flow for CIWH initiation.•The study presents a regime map as a reference to prevent CIWH.
Condensation-Induced Water Hammer (CIWH) phenomenon involves dynamic pressure changes caused by rapid condensation of steam in subcooled water. The magnitude of pressure spike is often large and can cause damage to the pipes and components in steam-water systems. Understanding the phenomena is vital for obtaining a safe and reliable design. This paper describes experimental investigations carried out in a specially designed facility called Water and Steam Interaction Facility (WASIF-I), that offers control over water and steam flow rates, can operate in co–, cross-, or counter-current flow mode and contains multiple injection locations. The occurrence of CIWH in horizontally oriented pipes filled with saturated steam is studied for the case where subcooled water is injected in cross-flow mode. The effect of geometrical and operating variables on the initiation of CIWH as well as peak pressure are brought out in this experimental work. A correlation to predict the critical minimum feed water flowrate necessary for triggering CIWH is developed based on multiple, nonlinear regression analysis of data from around 150 experiments. A regime map is presented that can be used as a guideline to preclude occurrence of CIWH.
Whether the superposition of pressure pulsation and water hammer pressure caused by the fast closing of guide vanes causes water column separation in draft tube inlets is a hot topic in engineering ...and academic fields. It is also not known whether the bridging of water column separation endangers the operation of the units. This study uses a model pumped storage power station platform with two units to perform water column separation. Data on the pressure pulsation at different measurement points, discharges, and speeds are collected by an acquisition system, whereas the development process of water column separation is characterized by a high-speed camera. The measured pressure is decomposed into the water hammer pressure, which migrates with the unit operation point and pressure pulsation. The test results reveal that the pressure in the inlet section of the draft tube below the vaporization pressure that lasts for several seconds is a sufficient and necessary condition for water column separation to occur. The water hammer pressure has a significant influence on the water column separation, while low-frequency pressure pulsation has less influence. Water column separation is divided into four stages: starting, improvement, separation, and bridging. The main frequency of the pressure pulsation in the water column separation process is the frequency of the water hammer caused by load rejection and has a value of 0.47f/fn. Cavity bridging generates a frequency of 0.30f/fn. The flow-speed curve remains in the braking condition of turbine for 1.25 s. The separation and part of the bridging stage occur under the braking condition of turbine.
•The development stages of water column separation are proposed.•The frequency and amplitude of pressure pulsation in different stages are proposed.•The migration trajectory of water column separation is analyzed.•The occurrence criterion of water column separation is discussed.
•A new Matched-Field Processing (MFP) technique for leak detection is developed.•The new method can localize leaks by domain enumeration.•The new method is more robust to noisy measurements than the ...conventional one.•The conventional and the proposed MFP model are closely investigated.•Several leak detection problems including two laboratory tests are discussed.
This study offers a vast improvement to the established Matched Field Processing (MFP) method for leak identification in terms of its versatility to pinpoint leaks with a single spatial measurement. All the previous schemes require at least two measurement signals of pressure head as well as transient signal of the upstream flow rate so as to render a solution to the leak identification problem. This study reformulates the one-dimensional identification procedure so that localization can be accomplished using a single spatial measurement. The numerical results convincingly demonstrate that the new method outweighs the conventional one as it provides a smoother objective function and hence robust to identify leaks using observations of greater noise levels. Checked against two recent laboratory experiments, the proposed method gave satisfactory localization to both of which. The new scheme can provide an improved (both in terms of efficiency and accuracy) initial estimate to the multidimensional optimizations required to localize multiple leaks.
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•The dynamics of bubble from initial expansion to collapse stages were simulated.•A typical double-peak structure of shock wave was detected by a hydrophone.•The jet speed and water ...hammer pressure under different conditions were compared.•CSF experiments were carried out and acquire specimens with good quality.
This paper aims at introducing a novel forming technology named Cavitation Shotless Forming (CSF) and simulating the dynamics of cavitation bubble from initial expansion to collapse stages. The plasma shock wave and bubble collapse shock wave were detected under different laser energies. A wall reflection shock wave was detected by a hydrophone, which is consistent with the simulation result. The trajectory of the bubble was captured by Matlab software. The bubble moves towards the solid wall due to the Bjerknes force. The bubble shape, pressure field and velocity field distributions under different standoff distances were compared. The impinging time of micro-jet was prolonged when the standoff distance was small, and the jet speed and maximum pressure increases with the increasing of standoff distances. In addition, the water hammer pressure under different standoff distances and initial bubble pressures were analyzed. It increases with the increase of initial bubble pressure but decreases with the standoff distance. Finally, the experiments of CSF were carried out, and the specimens show typical morphologies under different standoff distances and the forming depth of specimen decreases with the increase in standoff distances.
•An alternative transient modelling and leakage detection approach is proposed.•The time domain impedance function is introduced for the transient response.•PSO is integrated into impedance ...calibration scheme addressing wide range of surge amplitudes.•The leakage-identified impedance function substantially improves leakage detection.•Numerical and experimental verifications demonstrate the superiority of the method.
An alternative approach to modeling the hydraulic transient response and leakage detection is proposed for reservoir pipeline valve systems. Exponential-function-based impedance formulations are derived in the frequency domain, which are useful for identifying the pressure response of different pipeline elements and abnormalities. The time-domain impedance function (TIF) is introduced to address the transient response for a specific pipeline system. The TIF comprehensively simulates various valve maneuvers or flowrates in either the laminar or turbulent flow regimes. The delineated TIF from the measured pressure head in the pipeline system with leakage exhibits potential for leak location prediction. The integration of the particle swarm optimization scheme into the inverse TIF algorithm provides a robust evaluation capability under a wide range of surge amplitudes. The developed leakage-identified impedance function substantially improves the leakage detection ability through transient impact isolation. Both the numerical and experimental verifications demonstrate the potential of the proposed method for leak detection as well as water hammer simulation for pipeline systems.
The water hammer, resulting from sudden valve closures or similar operations, is a primary cause of leakage and damage in fluid-conveying pipe systems. This work aims to investigate the reliability ...sensitivity of fluid-conveying pipes under the water hammer. A reliability model for the fluid-conveying straight pipe, involving uncertainty and fluid-structure interaction, is developed based on the stress-strength interference theory. Then the method of characteristics is employed to analyze the nonlinear behaviors of the pipe. To avoid excessive model evaluations, the Kriging surrogate strategy is used to evaluate rapidly the statistics of nonlinear responses. Furthermore, the Kriging model coupled with the single-loop Monte Carlo simulation is presented for estimating reliability sensitivity indices. The accuracy of results is verified by the Monte Carlo simulation. The results reveal that the proposed method is feasible for the reliability sensitivity analysis of fluid-conveying pipe under the water hammer. Moreover, the wall thickness has the most obvious influence on stress failure, followed by the inner radius, while the pipe length, Young's modulus, density of the pipe material, and Poisson ratio show a low effect. This work can not only guide the safety design of pipe but also enrich the theory and application of statistical analysis and reliability sensitivity evaluation for liquid-conveying pipe systems.
•A reliability model for water hammer-induced failure of fluid-conveying pipe is developed.•The reliability model is proposed, incorporating uncertainty and fluid-structure interaction.•The Kriging-based strategy is employed to estimate the response and reliability sensitivity of the pipe.•Different input variables have diverse effects on the nonlinear behavior and reliability of the pipe.
Hydraulic transient is an unavoidable phenomenon which occurs in any piping system during a sudden change in operating conditions, and it sometimes leads to cavitation; subsequently generates very ...high pressure in the system. The intensity of pressure developed from sudden or gradual closure of the valves at the downstream side primarily depends on the closure time of the valve. This paper is an experimental investigation into the effect of valve closure time on transient flow characteristics in a piping system. The experiments with different flow rates of fluid and valve closure times in the piping system proved that the occurrence of cavitation in a pipe links very much with the closure time of valve and the characteristics of water hammer pressure wave.
