Maximum Pressure Head Research Articles

Effect of cyclic wave loading on scouring stability of geotube dams

Cyclic wave loading on geotube dams creates a cyclic flow in seams between geotubes regime distinct from the uni-directional flow that has been previously studied. A new laboratory apparatus was used to investigate the effects of hydraulic conditions on the core sand of geotube dams with seams between tubes. With this apparatus, a series of tests was conducted. Various maximum pressure heads (0.25, 0.3, 0.35, and 0.4 m), periods of cyclic wave loading (6, 7, 8, and 10 s) and particle porosities (34%, 35%, 40%, and 45%) were used in this test series. In the test series, the erosion development process of sand was analyzed. The results also indicate that the sand in the dam core can still perform satisfactorily after being scoured into the seam and extending a certain length. This critical length was found to be a function of the sand porosity, cycle period and maximum pressure head.

MATHEMATICAL MODELING FOR WATER HAMMER IN PIPE FLOW

Water hammer phenomenon is a transient flow in pipes that was created by rapid changes of velocity in pipelines. This phenomenon can be caused strong positive and negative pressures in water pipelines. Overall, water hammer creates by suddenly closing valves, shutting off or suddenly restarting pumps. In this study, momentum (Euler) and continuity equations of water hammer is numerically simulated using MATLAB software. Sensitivity analysis has been investigated using several variables such as pipe diameter, wave’s velocity and friction factor. Method of characteristics (MOC) has been implemented in this study. Through the results obtained, it has been shown that when using pipe with diameter (1.2m) instead of (1m), the maximum pressure head decreased by 31.5%, and decreased by 47.7% in the case of using (1.4m) instead of (1m). In case of changing the values of friction factors, it has been shown that the maximum pressure head decreased by 0.86% when using the friction factor value (0.008) instead of (0.007), and decreased by 0.81% when using friction factor value (0.009) instead of (0.007). While for the effect of wave's velocity on the pressure head, it has been shown that the maximum pressure head increased by (10.6%) when using the wave's velocity (300 m/sec) instead of (250 m/sec) and increased by (19.13%) when using (350 m/sec) instead of (250 m/sec) and increased by (26.1%) when using (400 m/sec) instead of (250 m/sec). Also, it has been found that the ending section of pipe is the critical zone for water hammer.

Modelling and experimental investigation of a thermally driven self-oscillating pump

This paper explores the pumping characteristics and behaviour of a thermally driven self-oscillating pump. The pump consists of a single wickless capillary tube with a circular cross-section. The tube is closed at one end and has a T-section with two check valves at the other end to provide for a one directional flow. An experimental setup was built to investigate the output mass flow and pressure head of the pump. During the experiments, the performance of the check valves had a negative influence on the output mass flow. To determine this influence, a video analysis of the fluid oscillation without the check valves was conducted and compared to results with check valves. The average output mass flow with valves was approximately 0.0010kg/s with a maximum measured pump flow of 0.0013kg/s. The maximum pressure head delivered was 0.25bar. A numerical model of the vapour bubble oscillation was developed to get a better understanding of the pump and its working principles. The model is based on the conservation of mass, momentum and energy, and resulted in a non-linear system of coupled differential equations. Overall, the experiments conducted with the thermally driven self-oscillating pump have shown that the pump has good potential to be used in aerospace applications.

Performance enhancement of the synchronous micropump based on experimental and numerical investigations of the magnetic field flux density in planar microcoils

This study presents numerical and experimental investigations targeting enhancing the magnetic field flux magnitudes in electroplated copper microcoils. Improved designs are used in the development of a new generation of the electromagnetic-based synchronous micropump in order to enhance its performance (i.e. the maximum achievable output pressure and flow rate). The synchronous micropump concept is based on managing the movement of two magnets in an annular fluidic channel. The magnets’ rotation is achieved by sequentially activating a set of three-dimensional microcoils to repel or attract one magnet (travelling piston) through the channel, whereas the second one is anchored between the inlet and the outlet ports (valve piston). At the end of each pumping cycle, the magnets exchange their functions. To achieve the maximum achievable output pressure and flow rate, higher magnetic fields without exceeding the material temperature limitation are required. The stronger the magnetic fields that can be generated, the higher the hydraulic power that the pump can deliver. The microcoil conductor width and height were optimized to generate higher magnetic field flux intensity within the pump limitation parameters (i.e. pump footprint and coils’ maximum heat dissipation limit). The new generation of the synchronous pump was run at a rotational speed of up to 800 rpm and provided a maximum flow rate of 3.56 ml/min and a maximum pressure head of 687 Pa.

Optimal Sizing of an Air Vessel in a Long-Distance Water-Supply Pumping System Using the SQP Method

AbstractBy optimizing the sizing of air vessels, not only is the damage from water hammer prevented, but also the cost of water hammer protection systems is minimized. This paper presents a numerical simulation of an air vessel in a long-distance transfer main system against water hammer resulting from sudden pump stoppage. An optimal design of air vessel parameters is obtained using sequential quadratic programming (SQP) in this case. Three types of connection configuration (between the air vessel and the main pipeline) are tested in the case study, including a vertical cylindrical vessel with a bypass line (configuration 1), a vertical cylindrical vessel with a bypass line equipped with a throttle valve (configuration 2), and a horizontal cylindrical vessel with separated inflow and outflow lines (configuration 3). The variations of optimal volume of the air vessel, VT, are plotted as a function of the allowable maximum pressure head, Hmax*, with the diameter of the bypass line, db, or the throttle valv...

Optimal closure of system actuators for transient control: an analytical approach

The effect of downstream valve closure scheduling was analyzed to find optimal closure parameters that lead to the minimal maximum pressure head in the water distribution system. Several valve closure strategies were explored, combining the known valve performance curve (change in flow as a function of change in valve's opened area) with unknown valve closure curve (change in valve's opened area as a function of time). Second-order polynomial curve, power function curve, and piece-wise linear curve were implemented and compared. Genetic algorithm and quasi-Newton (QN) optimization methods were applied. The methodology was tested for three networks, including looped gravitational and pressurized networks. The results demonstrate that flexible multi-parametric valve closure curve and QN optimization method are more effective in minimizing the maximum pressure head in the system.

ANALYSIS OF PUMP-PIPE LINE SYSTEM USING ELASTIC THEORY OF FLUID TRANSIENTS

The conditions like pump trip or power failure to pumps can create the extreme pressure fluctuations in pump-pipeline systems which may be the case of increase in maximum pressure head or decrease in minimum pressure head and even reaching to subatmospheric pressure conditions.Simulation of these extreme events could help the designer to take necessary precautions like increasing the thickness of the pipeline orproviding suitablesurge protection devices for the entire pump-pipeline system. Due to complexity nature of hyperbolic partial differential equations involved to describe these extreme events, various numerical methods were available.One such numerical method is called the method of characteristics (MOC) and is widely used to compute the fluid transients which may occur in pump-pipeline system. The objective of the study in the present paper is to analyze hydraulic transient pressuresfor the case of power trip to pumps byusing Elastic theory based on MOCapproach. A case study of J.C.R.Devadula Lift scheme in Telangana State, India is presented. It is observed that water column separation has occurred on downstream of pump delivery and hence transient control device like air vessels and one-way surge tanks are to be planned for this pipeline system.

Analysis of Transient Flow Caused by Fluctuating Consumptions in Pipe Networks: A Many-Objective Genetic Algorithm Approach

Small, but fast fluctuating consumptions in a pipe network can lead to severe transient flows. Such fluctuations are stochastic in nature and, cannot be explicitly identified and analyzed for the systems in operation. This study introduces a mathematical model for taking into account the fluctuating consumptions in analysis and design of pipe networks. For this purpose, the fluctuations are simulated by two successive triangular pulses with adjustable geometry. A many-objective optimization problem is developed to find the worst maximum and minimum pressure heads. A new scheme of genetic algorithms is developed to find the extreme values of all pressure heads in only one single simulation run. The proposed model is applied to two water distribution networks. It is found that, the transient flow caused by fast fluctuating consumptions could seriously affect the system’s performance. For instance, analyzing a real pipe network reveals that, when the fluctuations are critically combined, the nodal pressure heads averagely change by 29 % (13 to 88 %) and −43 % (−16 to −177 %) with respect to the initial steady state.

An Assessment for Hydraulically Efficient Design of Uniformly Sloping Submain Lines

AbstractDetermining the actual pressure head profiles along the submain lines with a uniform slope is very important for proper hydraulic design of water distribution systems. In practice, there are three general pressure head profiles (Type I, Type II, and Type III) along submain lines depending on different uniform line slope situations. Of all types of pressure profiles, the Type IIb profile is considered the optimal (or ideal) pressure profile which can produce the minimum pressure head difference for a given pipe length. This profile occurs when the total energy loss by friction is just balanced by the total energy gain due to uniform downslope. This paper presents a comprehensive analysis based on the energy–gradient ratio (EGR) approach to identify the optimal (or ideal) pressure profile (Type IIb), to achieve the minimal point of the relative maximum pressure variation, ΦH, which can be defined as the ratio of the maximum allowable pressure head difference (∆Hmax) to the total friction drop (hf(L)). This minimal point is regarded as 'the most efficient pressure profile' or 'ideal hydraulic design' in the existing literature. For this purpose, an illustrative figure (Figure 4) was developed to compare values of the relative maximum pressure variation versus the dimensionless EGR (KS = S0/Sf) for all types of pressure profiles. In this figure, the present ϕH curve versus KS values allows the design engineer to make a decision for the best alternative for selecting the KS value, where for a given pipe slope (S0) the KS value can be selected to meet the minimum pressure variation [KS =1, (ϕH)min =0.36] or the range of pressure variation as close to the minimum point as possible. The present design technique may provide a useful decision support tool for achieving a good design solution among hydraulically possible alternatives with minimal pressure head difference, and results in a higher level of water application uniformity along the multi‐outlet pipeline system. Copyright © 2014 John Wiley & Sons, Ltd.

Analytical Approach Determining the Optimal Length of Paired Drip Laterals in Uniformly Sloped Fields

Microirrigation plants, if properly designed, allow for water use efficiency to be optimized and high values of emission uniformity to be obtained in the field. Disposing paired laterals, for which two distribution pipes extend in opposite directions from a common manifold, can contribute to reducing the initial investment cost that represents a limiting factor for small-scale farmers of developing countries where in the last decade, the diffusion of such irrigation systems has been increasing. The objective of this paper is to propose an analytical approach to evaluate the maximum lengths of paired drip laterals for any uniform ground slope, respecting the criteria to maintain emitter flow rates or the corresponding pressure heads within fixed ranges in order to achieve a relatively high field emission uniformity coefficient. The method is developed by considering the motion equations along uphill and downhill sides of the lateral and the hypothesis to neglect the variations of emitters’ flow rate along the lateral as well as the local losses due to emitters’ insertions. If for the uphill pipe, the minimum and the maximum pressure heads occur at the upstream end and at the manifold connection, respectively, on the downhill side, the minimum pressure head is located in a certain section of the lateral, depending on the geometric and hydraulic characteristics of the lateral, as well as on the slope of the field; a second relative maximum pressure head could also exist at the downstream end of the pipe. The proposed methodology allows in particular the number of emitters in uphill and downhill sides of the lateral to be determined separately, and therefore, once fixing emitter’s spacing, the length of the uphill and downhill laterals and the position of the manifold. Applications and validation of the proposed approach, considering different design parameters, are finally presented and discussed.

Test Results of Pressure Head Mitigation of Supercritical Helium Across Cold Circulators at KSTAR for the Justification of the ITER Central Solenoid Cooling Circuit Design

The pressure head necessary for the forced convection of supercritical helium (SHe) across the ITER superconducting (SC) magnet system is generated by centrifugal-compressor type cold circulators. From the viewpoint of the cryogenic system, simulation results indicate that the main challenge of the ITER Central Solenoid (CS) operation is the peaking pressure head of SHe across the cold circulator induced during the rapid ramping of electrical current on the coils. Excess variation in pressure head will push the operation point of the rotating machine beyond the surge line in the compressor map which can trip the circulator and in the worst case result in damages. Therefore, in order to avoid the occurrence of a surge, it has been proposed to open adaptively a cryogenic valve, installed in parallel with the CS cooling channels, during the high pressure head instances. Such an action creates an additional flow channel which consequently suppresses the pressure head peak. The proposed strategy has been numerically benchmarked and tests have been performed in existing cryogenic facilities. In this paper, we will present the test results of pressure head mitigation across the cold circulator dedicated to the KSTAR CS and Poloidal Field (PF) coil cooling circuit with the main purpose of demonstrating the safe operation of the ITER CS circulator as well as cooling circuit during plasma shots. The tests were performed by progressively increasing the coil by-pass valve opening during identical PF/CS current shots and monitoring the tendency of the maximum pressure head variation across the cold circulator. Also, preliminary results of pressure head mitigation during real plasma experiments will be introduced.

Influence of initial nozzle opening on the maximum pressure head at the impulse turbine inlet and set of needle closing law

The maximum pressure head at the impulse turbine inlet is one of the most important parameters for operation of the impulse turbine. In order to determine the most critical operating condition for the maximum pressure head rise at the impulse turbine inlet, the formula which demonstrates the relation between relative pressure head and the initial opening is obtained through theoretical derivation. It shows a good agreement with the numerical results by the method of characteristics. A parabolic shaped flow characteristic of the nozzle is utilized in the derivation. Besides, the fact that the maximum pressure often occurs in the moment of the first wave reflection for the hydropower plants with impulse turbines is considered. The formula indicates that the maximum of pressure head rise increases monotonously with the initial opening decreasing. Therefore, the most critical condition for the maximum pressure head at the impulse turbine inlet is the condition of load rejection from small opening rather than the load rejection condition from full opening in the rated or maximum head. When adopting linear or two-speed closing law, the derived formula can be used to calculate the closing speed and the opening of break point, realizing the optimization of closure.

Bi-level Optimization of Closed Surge Tanks Placement and Sizing in Water Distribution System Subjected to Transient Events

Abstract This paper presents a bi-level optimization approach for placement and sizing of closed surge tanks in the water distribution system subjected to transient events. This study considers minimizing the maximum pressure head under various transient conditions given a budget constraint. Bi-level optimization utilizes the hierarchical structure between decision variables. In the upper level, optimal set of devices are assigned locations, while in the lower level the optimal sizing parameters are attained. The two problems are iteratively updated and solved until convergence. The suggested method is demonstrated and tested on a small case study, demonstrating the potential of the suggested approach.

ANALYSIS OF DIFFERENT PROTECTION METHODS AGAINST WATER HAMMER ON WATER SUPPLY NETWORK (CASE STUDY-ASSIUT CITY NETWORK)

The effect of using different protection devices on water hammer phenomenon to provide an acceptable level of protection against system failure due to pipe collapse or bursting is presented. Water Hammer and Mass Oscillation (WHAMO) software is used in the analysis which uses the implicit finite difference scheme for solving the momentum and continuity equations at unsteady state case. Assiut city water supply network is used. The network is supplied from two points at pump No. 36 and pump No. 37. Flow of pipe network is studied under steady normal case, without any protection case against water hammer phenomenon, and the model under different operation cases; with a transient protection device(s) such as non-return valve, open surge tank, air chamber and pressure relief valve (PRV). The results are performed for three scenarios; the first is the normal operation of pump 36 and failure of pump 37, the second is the normal operation of pump 37 and failure of pump 36, and finally failure of pumps 36 and 37 together. The results showed that using of open surge tank or air chamber with non-return valve protects the pipe network effectively from the harm of water hammer. Also, using PRV with non-return valve protects the pipe network from extreme pressures. Although using non-return valve only doesn’t have a great effect on the maximum pressure head than the normal case, it protects the network from the more low pressures than without protection one. All protection cases safeguard the pipe network from the extremes of water hammer, but increase the water hammer wave period. Finally, the sudden shut down of the pumps 36 and 37 together has the large effect on the pressure heads than the shut down of any of them only.

Analysis of transient signals in simple pipeline systems with an extended blockage

This paper investigates the effect that an extended blockage has on a transient signal by examining numerical and experimental results in the time and frequency domains. Extended blockages can develop in pipelines via the processes of tuberculation, scaling, bio film growth, sediment deposition or through designed reductions in pipe diameter. It is identified that consideration of the gradual formation of these faults is important in pipeline design as they can significantly change the fundamental period of a pipelines transient response, maximum and minimum transient pressure heads and the evolution of the transient signal, thus potentially increasing a systems susceptibility to failure. Analysis of transient signals affected by a blockage provides information on the property and location of the extended blockage. In this paper, comparisons between discrete and extended blockage models are made and the effects of changes in blockage diameter, length and wave speed on the transient response are investigated. Furthermore, the ability of existing models to represent extended pipeline faults under transient conditions is evaluated through comparisons of numerical transient responses with new experimental results from the laboratory. Results show that the transient behaviour is modelled with a good level of accuracy over the first few periods of oscillation and that the level of accuracy decays with time. A periodic Fourier analysis of the data demonstrates that the damping rates of the experimental response are higher than the numerical predictions. Applying this new method of signal analysis has shown that the transient signal exhibits larger damping rates in the higher frequency components of the response.

Finite element analysis experiments on landfill cover drainage with geosynthetic drainage layer

Landfill cover systems invariably include a drainage layer which is most often a drainage geocomposite. Finite element analysis of seepage in landfill covers with a drainage geocomposite was performed to determine the effect of rainfall rate, slope length, slope angle, anisotropy, multiple materials and three-dimensional slopes on the pressure head above the liner. Simple methods, based on published equations, were found to provide similar maximum pressure head on the liner as the steady state finite element analysis when only the geocomposite was involved in the drainage. Pressure heads for transient, more-than-one-material, three-dimensional and anisotropic cases were found to be very different from simple solutions. The finite element analysis showed the variation of pressure head along the liner to be highly non-linear with the geocomposite and cover soil saturation occurring simultaneously. The seepage analysis was combined with a limit-equilibrium slope stability analysis to determine factors of safety against slope failure and compare the results with simple methods.

Filling dynamics and phase change of molten salt in cold receiver pipe during initial pumping process

The filling dynamics and phase change performances of molten salt in cold receiver pipe during initial pumping process are numerically analyzed with variable inlet velocity due to pump characteristic curve. In general, cold receiver pipe during initial pumping process will be frozen for molten salt solidification as the inlet temperature is lower than critical temperature, or else it will be unobstructed with melting process at higher inlet temperature. During pumping process with melting, the flow velocity will first decrease by solidification and then increase by melting effect, and the melting time decreases with inlet temperature. As the freezing phenomena appears during pumping process, the flow velocity will decrease to zero, while the pressure loss reaches the maximum pressure head, and the freezing time increases with inlet temperature. Since a solid layer exists adjacent to the pipe wall in phase change region, the flow velocity and pressure loss remarkably increases along flow direction, and the phase change region will dominate the pressure loss. As the inlet temperature decreases, the phase change region remarkably enlarges, and the filling time rises.

Construction and initial operation of MHD PbLi facility at UCLA

A magnetohydrodynamic flow facility MaPLE (Magnetohydrodynamic PbLi Experiment) that utilizes molten eutectic alloy lead–lithium (PbLi) as working fluid has been constructed and tested at University of California, Los Angeles. The loop operation parameters are: maximum magnetic field 1.8T, PbLi temperature up to 350°C, maximum PbLi flow rate with/without a magnetic field 15/50l/min, maximum pressure head 0.15MPa. The paper describes the loop itself and its major components, basic operation procedures, experience of handling PbLi, initial loop testing, flow diagnostics and current and near-future experiments. The obtained test results of the loop and its components have demonstrated that the new facility is fully functioning and ready for experimental studies of magnetohydrodynamic, heat and mass transfer phenomena in PbLi flows and also can be used in mock up testing in conditions relevant to fusion applications.

Computational modeling and simulation of electro-hydrodynamic (EHD) ion-drag micropump with planar emitter and micropillar collector electrodes

Computational models can be used to simulate a prototype of electrohydrodynamic (EHD) ion-drag micropump with planar emitter and micropillar collector electrodes. In this study, a simple and inexpensive design of an ion-drag micropump was modeled and numerically simulated. A three-dimensional segment of the microchannel was simulated by using periodic boundary conditions at the inlet and outlet. The pressure and velocity distribution at the outlet and in the entire domain of the micropump was obtained numerically. The effect of the gap between the emitter and the collector electrode, width and the height of micropillar and flow channel height was analyzed for optimum pressure and output flow rate. The enhanced performance of micropump was compared with existing designs. It was found that the performance of micropump could be improved by decreasing the height of micropillar and the gap between both electrodes. The numerical results also show that a maximum pressure head of about 2350 Pa and maximum mass flow rate 0.4 g min−1 at an applied voltage 1000 V is achievable with the proposed design of micropump. These values of pressure and flow rate can meet the cryogenic cooling requirements for some specific electronic devices.

Experimental study of a novel Magneto Mercury Reciprocating (MMR) micropump, fabrication and operation

Today, MEMS have wide applications in modern technologies. Magneto hydro dynamic (MHD) micropumps play an important role in the MEMS industry and have been thoroughly studied in the recent years. In this study, the idea of classic reciprocating micropumps was combined with magneto hydro dynamics (MHD) to develop a novel Magneto Mercury Reciprocating (MMR) micropump. To attain this goal, the Lorentz force, as the actuation mechanism, was used to move a conductive liquid (mercury) slug in a reciprocating manner in order to suck the working fluid (air) from the inlet and pump it to the outlet. The performance of the fabricated MMR micropump was examined in terms of parameters such as pressure difference, pumping frequency, and magnetic flux density. The maximum flow rate was achieved at a minimum backpressure of 9.5mL/min. The maximum pressure head achieved in the experiments was 245Pa. Furthermore, the results of these experiments were compared with other micropumps, which showed an improvement of 153% over the next best MHD micropump presented to date.