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Experimental study of filling and emptying of a large-scale pipeline
Abstract
This study presents the results from detailed experiments of the two-phase pressurized flow behavior during the rapid filling of a large-scale pipeline. The physical scale of this experiment is close to the practical situation in many industrial plants. Pressure transducers, water-level meters, thermometers, void fraction meters, and flow meters were used to measure the two-phase unsteady flow dynamics. The main focus is on the water–air interface evolution during filling and the overall behavior of the lengthening water column. It is observed that the leading liquid front does not entirely fill the pipe cross section; flow stratification and mixing occurs. Although flow regime transition is a rather complex phenomenon, certain features of the observed transition pattern are explained qualitatively and quantitatively. The water flow during the entire filling behaves as a rigid column as the open empty pipe in front of the water column provides sufficient room for the water column to occupy without invoking air compressibility effects. As a preliminary evaluation of how these large-scale experiments can feed into improving mathematical modeling of rapid pipe filling, a comparison with a typical one-dimensional rigid-column model is made.
... A large-scale complex experimental setup was used in [12] to investigate the pipe filling and emptying processes. The system had a total length of 275 m and was made of a combination of several pipes with different materials (steel, PVC-U, and PMMA), diameters (DN200 and DN250), and elevations. ...
The evaluation of the impact of intermittent water supply on water distribution systems is a complex task. Laboratory tests, in controlled conditions with virtually no constraints on instrument and device location, allow the analysis of the effects of single parameters on pressures and flows. Within the framework of a research consultancy commissioned by the World Bank, the test network at the Water Engineering Laboratory of the University of Perugia, Italy, was modified to analyse pipe filling and emptying phenomena. Herein we describe the characteristics of the set-up, the available instruments and data acquisition system, as well as the installed devices (e.g., air release and in- and off-line ball valves). The set-up was also designed to investigate the effects of the air flow on the overbilling of water meters. The results of a preliminary test allow the typical phases of the phenomenon to be analysed, including the filling of the pipe with water and the discharging of air, the arrival of the water front at the downstream end causing a pressure variation typical of water hammer, and the emptying process and the filling with air. The analysis allows the operational mechanism to be understood and remedial interventions designed and validated.
... Compression effects of air pockets have been analysed in some experimental facilities both storm water systems (Vasconcelos, Klaver, and Lautenbach 2014;Bousso, Daynou, and Fuamba 2013;Vasconcelos and Wright 2008) and water supply networks (Fuertes-Miquel et al. 2018;Zhou, Liu, and Karney 2013a;Hou et al. 2012) knowing the behaviour of the filling procedure, transient effects and head losses associated with hydraulic devices and the consequences of the propagation of entrapped air. However, expansion effects of air pockets, which may occur during the draining water process in water supply networks, have been studied only by a few authors available in the literature. ...
An air pocket’s behaviour inside of a pipeline during transient conditions is of great importance due to its effect on the safety of the hydraulic system and the complexity of modeling its behaviour. The emptying process from water pipelines needs more assessment because the generation of troughs of subatmospheric pressure may lead to serious damage. This research studies the air pocket parameters during an emptying process from a water pipeline. A well-equipped experimental facility was used to measure the pressure and the velocity change throughout the water emptying for different air pocket sizes and valve opening times. The phenomenon was simulated using a one-dimensional (1D) developed model based on the rigid formulation with a non-variable friction factor and a constant pipe diameter. The mathematical model shows good ability in predicting the trough of subatmospheric pressure value as the most important parameter which can affect the safety of hydraulic systems.
... This installation setup consisted of a constant-head water supply tower, a highpressure air tank, a 261-m-long horizontal PVC pipe, a 10.6-mlong steel pipe (divided into a 6.1-m-long horizontal pipe and a 4.5-m-long vertical pipe), PVC and steel joints, steel inlet and outlet parts, various types of valves along the PVC-steel pipeline, and a free-surface basement reservoir. Hydraulic characteristics of the experimental facility have been computed in previous works (Hou et al. 2012;Laanearu and Van't Westende 2010). Tijsseling et al. (2016) and Laanearu et al. (2015) developed a RWCM for analyzing the emptying process using pressurized air. ...
This paper presents a mathematical model for analyzing the emptying process in a pipeline using pressurized air. The rigid water column model (RWCM) is used to analyze the transient phenomena that occur during the emptying of the pipeline. The air-water interface is also computed in the proposed model. The proposed model is applied along a 271.6-m-long PVC-steel pipeline with a 232-mm internal diameter. The boundary conditions are given by a high-pressure air tank at the upstream end and a manual butterfly valve at the downstream end. The solution was carried out in a computer modeling program. The results show that comparisons between both the computed and measured water flow oscillations and gauge pressures are very similar; hence, the model can effectively simulate the transient flow in this system. In addition, the results indicate that the proposed model can predict both the water flow and gauge pressure better than previous models.
... Mit dem Eintreffen der Wasserfront entsteht ein schlagartiger Anstieg des Drucks p 2 . Wie Guizani u. a. [22] und Hou u. a. [23,24] ...
Due to the alternate filling and emptying of pipe networks in intermittently operated water distribution systems, present air must exit the pipe network. A part of this air is discharged through house connections and, thus, leads to a use of water meters contrary to their initial conception. In this article, a study is presented in which the measurement error of horizontally mounted single-jet water meters in intermittent supply is investigated experimentally. It has been discovered that the measurement error is mainly caused by the air flow ahead of the arrival of the water front. The study shows an approximately linear correlation of the measurement error and the volume of air in front of the water meter. The impact of the water front itself, the presence of water-air mixtures or unsteady flow processes have only small influences on the measurement result.
... Mit dem Eintreffen der Wasserfront entsteht ein schlagartiger Anstieg des Drucks p 2 . Wie Guizani u. a. [22] und Hou u. a. [23,24] ...
In intermittierend betriebenen Wasserverteilungssystemen muss die durch die alternierende Befüllung und Entleerung des Rohrnetzes in das System eingetragene Luft zwangsläufig auch aus dem System austreten. Ein Teil dieser Luft wird durch Hausanschlussleitungen ausgetragen und führt somit zu einer Verwendung von Wasserzählern entgegen ihrer eigentlichen Konzeption. In diesem Artikel wird eine Studie präsentiert, in der die Messabweichung von horizontal eingebauten Einstrahl-Flügelrad-Wasserzählern bei intermittierender Versorgung experimentell untersucht wurde. Es stellte sich heraus, dass die Messabweichung maßgeblich durch den Luftfluss vor Eintreffen der Wasserfront am Wasserzähler verursacht wird. Der Zusammenhang von Messabweichung und Luftvolumen vor dem Wasserzähler ist näherungsweise linear. Der Einschlag der Wasserfront, das Vorhandensein von Wasser-Luft-Gemischen oder instationäre Fließvorgänge haben dagegen nur einen geringen Einfluss auf das Messergebnis.
... 111.7, 183.7, 206.8, and 252.9 m, respectively; and void fraction (VF1s, VF6s, and VF9s) located at 0.5, 141.9, x = and 251.7 m, respectively. Uncertainties of the measurements are reported in (Hou et al., 2012). A total of 78 steady-state flow measurements were accomplished between the principal filling and emptying experiments. ...
In many industrial applications the liquid trapped inside long pipelines can cause a number of problems. Intrusion of the pressurized air on top of the water column inside the horizontal pipeline can result in a less or more mixed stratified flow. The dynamics of a moving air-water front during the emptying of a PVC pipeline with the diameter-to-length ratio 1: 1100 were experimentally and theoretically studied. In the experiments, the water was driven out of the pipeline with an initial upstream air pressure of 2 barg and a 4.5 m high downstream-end siphon, where the water outflow was restricted by a valve that was closed 11%. The measured discharges and water-level variations are analysed together with Control Volume modelling results. During the 'forced' (not only gravity-driven) emptying process, both the downstream-end drainage and tail leakage behind the moving air water front decreased over the full water-column length. The water-column mass loss due to the tail leakage is referred to as holdup. The Zukoski dimensionless number is used to parameterize the relative shortening of the water column associated with the unidirectional movement of the air-water front along the large-scale horizontal test section of the pipeline, where surface-tension effects and minor losses at joints and turns are negligible.
It is demonstrated that the air-water interface in a large-scale pipeline during its filling and emptying reveals different kinematical conditions. In addition to shear at the pipe wall, there is also shear produced by air intrusion inside the water column. The experimental findings of unidirectionally moving water fronts along the horizontal test section of a PVC pipeline with diameter-to-length ratio 1:1100 are analysed. A simple Control Volume model is used for modelling of the waterfront splitting in the pipeline, where free-surface and mixed stratified flows are present. The Froude-number criterion is used to figure out the hydraulic regimes (sub-and supercritical) of the stratified flows in the pipeline. The Zukoski dimensionless number, which characterizes the relative shortening of the water column due to air intrusion on top of the moving water column, is also estimated.
This study presents the results from detailed experiments of the two-phase pressurized flow behavior during the rapid filling of a large-scale pipeline. The physical scale of this experiment is close to the practical situation in many industrial plants. Pressure transducers, water-level meters, thermometers, void fraction meters, and flow meters were used to measure the two-phase unsteady flow dynamics. The main focus is on the water-air interface evolution during filling and the overall behavior of the lengthening water column. It is observed that the leading liquid front does not entirely fill the pipe cross section; flow stratification and mixing occurs. Although flow regime transition is a rather complex phenomenon, certain features of the observed transition pattern are explained qualitatively and quantitatively. The water flow during the entire filling behaves as a rigid column as the open empty pipe in front of the water column provides sufficient room for the water column to occupy without invoking air compressibility effects. As a preliminary evaluation of how these large-scale experiments can feed into improving mathematical modeling of rapid pipe filling, a comparison with a typical one-dimensional rigid-column model is made. (C) 2014 American Society of Civil Engineers.
The high frequency (0.1 kHz) pressure and velocity measurements of two-phase unsteady flow are used to determine the hydraulic-grade-line (HGL) along the pipeline with a complex layout. The semi-empirical method is applied to estimate the pressure drop for the outflow, and thus determine the pipe downstream-end conditions for the modeling purposes. A Control Volume (CV) model coefficient beta, representing residual motion due to the pressurized water-column stratification is specified. Pressurized two-phase unsteady flow phases in a 250 mm diameter and 275 meters long PVC pipeline with steel inlet and outlet counterparts are considered for the evaluation of this method. (C) 2013 The Authors. Published by Elsevier Ltd.
Fluid-structure interaction in piping systems ~FSI! consists of the transfer of momentum and
forces between piping and the contained liquid during unsteady flow. Excitation mechanisms
may be caused by rapid changes in flow and pressure or may be initiated by mechanical action
of the piping. The interaction is manifested in pipe vibration and perturbations in velocity
and pressure of the liquid. The resulting loads imparted on the piping are transferred to the
support mechanisms such as hangers, thrust blocks, etc. The phenomenon has recently received
increased attention because of safety and reliability concerns in power generation stations,
environmental issues in pipeline delivery systems, and questions related to stringent industrial
piping design performance guidelines. Furthermore, numerical advances have allowed
practitioners to revisit the manner in which the interaction between piping and contained liquid
is modeled, resulting in improved techniques that are now readily available to predict FSI.
This review attempts to succinctly summarize the essential mechanisms that cause FSI, and
present relevant data that describe the phenomenon. In addition, the various numerical and
analytical methods that have been developed to successfully predict FSI will be described.
Several earlier reviews regarding FSI in piping have been published; this review is intended to
update the reader on developments that have taken place over the last approximately ten
years, and to enhance the understanding of various aspects of FSI.
Stormwater drainage systems are designed to operate in a free surface flow regime, however, transition into a pressurized flow regime may occur during intense rain events as the inflow exceeds the transport capacity of the system in free surface flow mode. The air phase within the sewers may then become pressurized, significantly altering the dynamics of the flow. Flow regime transitions have been linked to the occurrence of serious operational problems in stormwater systems, such as geysering and structural damage of sewers. While such flow conditions have been investigated previously, the current knowledge on this problem is still limited and fragmented, particularly regarding the role of the air phase in the filling process. The investigation presented in this thesis included experiments performed in reduced scale models representing stormwater storage tunnels, sewers and ventilation towers of stormwater systems. Numerical investigation was also performed to cre ate models to simulate flow regime transition caused by rapid filling of stormwater systems. The results of these investigations indicate that: (1) the magnitude of the surges caused by inflow bores in storage tunnels increase with the pressure head behind the pipe-filling bore front; (2) different new flow features caused by the air phase pressurization have been detected, which depend mainly on the ventilation degree provided in the system; (3) numerical models for the flow regime transition problem can be successfully modified to incorporate some the of newly identified air/water interactions in the predictions; (4) a new model concept for the flow regime transition was proposed, which overcomes the inability of Preissmann slot-based models to simulate sub-atmospheric, full pipe flows; (5) the numerical oscillations that contaminate the numerical predications of pipe-filling bores from shock-capturing models can be attenuated with judicious introduction of numerical diffusion; (6) new mechanisms for air pocket entrapment in stormwater storage tunnels undergoing rapid filling have been identified, and air pocket entrapment may relatively common; (7) the geysering caused by the release of large air pocket through water-filled ventilation towers can be minimized by appropriate selection of the ventilation tower diameter; (8) air phase pressurization caused by flow regime transition is also an important issue when the sewers are initially in steady flow conditions.
In this paper analytical and experimental results are presented for pressurizing isolated pockets of air at the end of a water column in a horizontal pipeline. The analytical phase addresses issues such as (1) effect of elasticity of water column, (2) variation of length of water column during the transient, and (3) thermodynamic processes during compression and expansion of gas pockets. The analysis shows that many entrapped air problems in liquid systems are principally governed by the liquid inertia and the gas elasticity, with the latter considered as a lumped quantity. However, laboratory experiments coupled with both inelastic and elastic liquid behavior have shown that, for severe cases of pressurization, wave propagation in the liquid medium needs to be considered. Analytical results are presented demonstrating the range of application of inelastic liquid (rigid column) and lumped gas behavior.
The effect of the presence of entrapped air in liquid pipelines has been analytically demonstrated for several configurations. The numerical solution to the differential equations of continuity, momentum and thermodynamic gas response clearly shows that entrapped air may prove to be either detrimental or beneficial, depending upon the amount and location of the air as well as the pipeline configuration and the nature and cause of the treatment. The most severe case of entrapped air occurs during the rapid acceleration of a liquid column toward a volume of air that is completely confined. The resulting pressure peak can be many times the initial imposed pressure if the transient is applied rapidly. Design information in the form of dimensionless parametric curves is included to size an air-release valve to limit the peak pressure to the necessary desired value. Results also illustrate the effect of the initial location of an unconfined air pocket on the magnitude of the maximum air pressure. The presence of the air causes peak pressures that are either greater or less than those that would occur without any air. (A)
Analytical and experimental laboratory studies were conducted for rapid pressurizing of entrapped gas at the end of a horizontal liquid pipeline, for which there is an orifice at the exit. The analytical model was developed to define the physics behind the gas venting case. Experiments were conducted for a range of orifice sizes from 1.59 mm to 12.70 mm in a 26.0 mm pipe with reservoir pressure two, three and four times that of ambient pressure for five different pipe configurations. Experimental results confirm that the assumption of the rigid column entrapped air model is valid for a range of conditions. Comparison of analytical and experimental model results indicated the analytical model predicted pressures quite well for the first peak. Both results of experimental and analytical model show that pressure can be increased or reduced depending on the liquid acceleration.
In the transition from free-surface flow to pressurized flow of underground drainage systems, air is frequently entrapped which makes it difficult to predict the transient phenomena by usual computational models. In this paper, a modified lumped parameter model is introduced to examine the behavior of entrapped air during transitional flows in a long horizontal circular pipe. By using the model, the volume changes of entrapped air in the pressure flows can be evaluated from the measured pressures at the upstream and downstream ends. It is confirmed that the calculation considering the volume changes of the air reproduces exactly the measured pressure at any point of the pipe. The presence of entrapped air causes earlier transition and higher rise in pressure in the mixed free-surface-pressure flow. In addition, it turns out to suppress the pressure oscillation of a U-tube type.