Field Studies of Discoloration in Water Distribution Systems: Model Verification and Practical Implications

Discoloration in water distribution systems has been studied in partnership with a number of U.K. water companies by measuring the turbidity response to changes in hydraulic conditions induced by systematic flushing. The resulting data was used to verify a predictive empirical model and hence the underlying assumptions made in its development. Model simulations, made using previously established parameters defined solely by pipe diameter and pipe material, are presented alongside measured data to demonstrate this verification. The primary cause of discoloration observed is the mobilization of material from cohesive layers bonded to pipe walls. These layers demonstrate a profile of increasing shear strength with increasing degree of discoloration. Differences are demonstrated in the layer and ultimate shear strength characteristics of the discoloration layers formed in iron and plastic pipes, with a modeled shear stress of 1.2?N/m2 shown to exhaust material layers in plastic pipes. Based on the observed data it is theorized that accumulation of material to the pipe walls is primarily dependent on two mechanisms; ubiquitous background concentrations in the bulk water, and if present corrosion by-products from iron pipes and fittings. A consequence of this is that all pipes within a water distribution system are susceptible to the development of material layers. In the formulation of operation and maintenance strategies it is suggested that iron and plastic pipes should be treated differently to obtain optimum operational effectiveness and minimize discoloration risk.     

Timescale Behavior of the Wall Shear Stress in Unsteady Laminar Pipe Flows

Based on two-dimensional (2D) flow model simulations, the effects of the radial structure of the flow (e.g., the nonuniformity of the velocity profile) on the pipe wall shear stress, τw, are determined in terms of bulk parameters such as to allow improved 1D modeling of unsteady contribution of τw. An unsteady generalization, for both laminar and turbulent flows, of the quasi-stationary relationship between τw and the friction slope, J, decomposes the additional unsteady contribution into an instantaneous energy dissipation term and an inertial term (that is, based on the local average acceleration-deceleration effects). The relative importance of these two effects is investigated in a transient laminar flow and an analysis of the range of applicability of this kind of approach of representing unsteady friction is presented. Finally, the relation between the additional inertial term and Boussinesq momentum coefficient, is clarified. Although laminar pipe flows are a special case in engineering practice, solutions in this flow regime can provide some insight into the behavior of the transient wall shear stress, and serve as a preliminary step to the solutions of unsteady turbulent pipe flows.     

Nonconservative Formulation of Unsteady Pipe Flow Model

A new approach to numerical modeling of water hammer is proposed. An unsteady pipe flow model incorporating Brunone’s unsteady friction model is used, but in contrast to the standard treatment of the unsteady friction term as a source term, the writers propose a nonconservative formulation of source term. Second-order flux limited and high order weighted essentially nonoscillating numerical schemes were applied to the proposed formulation, and results are in better agreement with measurements when compared with results obtained with standard form.     

海水绕流扬矿管边界层分析

介绍不同雷诺数下海水绕流深海扬矿管的流动情况,分析管面形成层流及湍流边界层的分离过程,比较二者分离点的位置及压差阻力情况,分析绕流阻力和举力的形成过程、计算方法、影响因素及相应的减阻措施。     

Feasibility of Amending Slurry Walls with Zero-Valent Iron

Rapid degradation of aqueous trichloroethylene (TCE) was observed in batch experiments conducted with soil∕bentonite slurry wall materials amended with the addition of zero-valent iron. The first-order TCE decay constants for soil∕bentonite∕iron mixtures, when normalized to the available iron surface area, were approximately 1–2 orders of magnitude higher than observed in batch experiments with pure iron systems. Permeability tests indicated an increase in SB hydraulic conductivity roughly proportional to the amount of iron added. Based on the observed reaction rates and the assumption of sustained long-term performance, significantly less than one percent added iron would be required to reduce the diffusive flux of TCE across an installed slurry wall by over 10 orders of magnitude. However, the release of hydrogen gas was noted as a potential problem for low permeability systems containing zero-valent iron.     

热轧厂层流冷却设备的布局及计算

通过对热轧厂层流冷却水循环系统的初步设计,提出了层流冷却高位水箱容量和泵站供水能力的计算方法。对层流冷却系统采用独立的水循环系统,保证了水质和水压的稳定,同时计算出生产最恶劣钢板时高位水箱容量和水泵供水能力,并对层流冷却进行水力学计算,推导出了层流冷却集管出水口水流速度和容量。不仅使层流冷却设备布局更加紧凑,节约了用水,还为层流冷却设备的深度设计和布局提供了参考。     

Experimental Study of a Right-Angled End Junction between a Pipe and an Open Channel

This paper presents an experimental study of a junction between a closed conduit and an open channel. This study was undertaken to explore hydraulic properties of outlets of subsurface drainage or sewage networks into an open air stream during flood events. Experiments were conducted in a laboratory flume, with a main rectangular channel joined at right angle to a lateral circular pipe. Both branches were supplied with independent flow rates and downstream water level was controlled by an adjustable weir. Several flow patterns were identified, combining free-surface and pressurized flows. Transitions between these flow patterns, as well as changes in water level or energy, in response to the modifications of experimental variables, were studied and could be linked to known properties of single channels, single pipes, and homogeneous junctions. Transitions between free-surface and pressurized pipe flow appeared to be strongly dependent on the whole set of experimental variables and the pipe longitudinal slope. This work contributes to a better knowledge of hydraulic and hydrologic key processes for point source discharging.     

Existence of Critical Recovery and Impacts of Operational Mode on Potable Water Microfiltration

Results from a potable water microfiltration (MF) pilot study employing untreated surface water are reported. The effects of filtrate flux and recovery on direct flow, outside-inside, hollow fiber MF fouling rates, and backwash effectiveness are presented. Constant flux experiments suggested the existence of a critical recovery below which MF fouling rates were low and effectiveness of backwashes was high and relatively independent of the recovery. However, in the range of experimental conditions investigated, fouling rates increased dramatically and backwash effectiveness decreased steeply when this critical recovery was exceeded regardless of the flux. In general, for a fixed recovery, specific flux profiles analyzed on the basis of volume filtered per unit membrane area were insensitive to filtrate flux. Fouling was accelerated by operating membranes at constant flux rather than at constant pressure, in part, because of membrane compaction and cake compression. Changing the mode of filtration between constant flux and constant pressure is shown to have no effect on MF filtrate water quality. For any given capacity, membrane area requirements are decreased, and power requirements are increased when membranes are operated at constant flux rather than at constant pressure.     

Optimal Design of Pressurized Irrigation Subunit

A linear programming (LP) model is presented for optimal design of the pressurized irrigation system subunit. The objective function of the LP is to minimize the equivalent annual fixed cost of pipe network of the irrigation system and its annual operating energy cost. The hydraulic characteristics in the irrigation subunit are ensured by using the length, energy conservation, and pressure head constraints. The input data are the system layout, segment-wise cost and hydraulic gradients in all the alternative pipe diameters, and energy cost per unit head of pumping water through the pipeline network. The output data are: segment-wise lengths of different diameters, operating inlet pressure head, and equivalent annual cost of the pipeline network. The explicit optimal design is demonstrated with design examples on lateral and submain or manifold of pressurized irrigation systems. The effect of the equations for friction head loss calculation on optimization procedure is investigated through the design example for microirrigation manifold. The performance evaluation of the proposed model in comparison with the analytical methods, graphical methods, numerical solutions, and dynamic programming optimization model reveals the good performance of the proposed model. The verification of operating inlet pressure head obtained by the proposed model with accurate numerical step-by-step method suggested that it is mostly accurate.     

深井矿山充填满管输送理论及应用

为了提高深井矿山充填管道的满管状态,提出以满管率作为系统满管状态定量描述指标,基于水力学输送理论推导了满管率的数学模型,并对其影响因素作了理论分析,明确减小管道直径及增大系统流量是提高满管率的最佳途径.基于管道两相流理论,建立了管径、流速以及满管率关系的数学表达式,为系统最佳输送参数的选取提供了理论依据.对某深井矿山充填系统进行的局部改造结果显示:将系统原φ150 mm水平管道替换为φ85 mm管道,同时增大流量至80 m³·h^-1,系统满管率为原来的6倍,有效减轻了管道磨损.     

Physically Based Coupled Model for Simulating 1D Surface–2D Subsurface Flow and Plant Water Uptake in Irrigation Furrows. I: Model Development

Physically based modeling of the interacting water flow during a furrow irrigation season can contribute to both a sustainable irrigation management and an improvement of the furrow irrigation efficiency. This paper presents a process based seasonal furrow irrigation model which describes the interacting one-dimensional surface–two-dimensional subsurface flow and crop growth during a whole growing period. The irrigation advance model presented in a previous study is extended to all hydraulic phases of an irrigation event. It is based on an analytical solution of the zero-inertia surface flow equations and is iteratively coupled with the two-dimensional subsurface flow model HYDRUS-2. A conceptual crop growth model calculates daily evaporation, transpiration and leaf area index. The crop model and HYDRUS-2 are coupled via its common boundaries, namely (1) by the flux across the soil-atmosphere interface; and (2) by the flux from the root zone, which is associated with the plant water uptake. We assume the water stress is the only environmental factor reducing crop development and hence final crop yield. The model performance is evaluated with field experimental data in the companion paper, Part II: Model Test and Evaluation (W?hling and Mailhol 2007).     

Impulse Response Method for Pipeline Systems Equipped with Water Hammer Protection Devices

Surge protection devices, such as surge tanks and air chambers, have been modeled with the impulse response method for transient analysis of water distribution systems. The lumped inertia model and continuity equation are used to represent nonpipe hydraulic elements. Results of pressure or discharge variations obtained by using the impulse response method and the method of characteristics are in good agreement. The impulse response method provides total pressure and discharge along any pipeline segment by direct integration of the ratio of complex head or complex discharge to a complex downstream discharge, respectively. A modification is proposed so that transition between turbulent and laminar flows can be considered. The representation of hydraulic devices has been incorporated into the impedance matrix method, which was developed for heterogeneous and multilooped pipe network systems. The potential advantages of the proposed method over other conventional approaches were investigated by applying the proposed method to hypothetical pipe network systems.     

液压比例流量控制技术在步进式加热炉上的应用

通过对步进式加热炉的工艺特点和液压比例流量控制技术的工作原理进行分析,莱钢轧钢厂在步进式加热炉上成功地应用了液压比例液量控制技术,保障了重载下活动梁的平稳运行,并解决了系统运行中易出现的故障问题。     

Extended Thermodynamics Derivation of Energy Dissipation in Unsteady Pipe Flow

Extended irreversible thermodynamics (EIT) provides a framework for deriving extensions to phenomenological equations (e.g., Newton's law of viscosity, Fick's law of mass transport, and Darcy's law for porous media flow) for problems involving high frequencies (i.e., rapid transients). In this paper, a phenomenological equation is derived for energy loss in 1D unsteady pipe flow using an EIT formalism. The resulting wall shear stress is equal to the sum of (1) the steady-state shear stress; (2) a term that is proportional to the local (i.e., temporal) acceleration; and (3) a term that is proportional to the product of the velocity and the convective (i.e., spatial) acceleration. The form of this EIT-based wall shear stress formula shows that EIT provides a physical basis for instantaneous acceleration based unsteady friction formulas. It also illustrates the limitations and underlying assumptions of these models. For example, instantaneous acceleration based unsteady friction formulas are limited to fast transients (i.e., transients in which the water hammer timescale is significantly smaller than the diffusion timescale). A characteristics solution for unsteady pipe flow is proposed in which the phenomenological equation is used to model energy dissipation. Comparison of numerical test results with measured data from upstream and downstream valve closure laboratory experiments shows excellent agreement.     

Prefabricated Vertical Drains Flow Resistance under Vacuum Conditions

The results of experimental research are presented and discussed with focus on the internal well resistance of prefabricated vertical drains (PVD) under vacuum-induced water flow. Measured results included fluid flow rates for two different cross-sectional hydraulic profiles (Types I and II PVDs). Experimental results indicated linear relationships, independent of the PVD widths, between extracted fluid velocity and the applied hydraulic gradient. Data showed a laminar flow regime to predominate for test velocities corresponding to hydraulic gradients <0.5. The larger nominal hydraulic radius of the Type II PVD is credited with providing a flow rate equal to approximately 3.2 times that of the Type I PVD at approximately the same operating total head. There was no apparent dependency of the transmissivity θ on the width or lengths (3, 4, and 5 m) of the PVDs tested. In the case of the 100-mm-wide Type I PVD, θ = 618 mm2∕s was estimated from the measured data versus θ = 1,996 mm2∕s for Type II PVD with the same dimensions.     

基于固液两相流模拟的选矿循环水深度澄清装置优化

部分选矿循环水中含一定量的高分散性悬浮颗粒,仅依靠简单浓缩沉降难以澄清,无法达到回用要求。针对这一难题,提出了一种选矿循环水固体悬浮物澄清装置。为优化装置的结构参数与运行参数,建立了选矿循环水深度澄清装置的二维物理模型,基于计算流体力学（CFD）的方法,选用Mixture和RNG k?ε 模型对装置主要的结构参数与运行参数展开了数值模拟研究。研究发现适当降低水力循环区喷嘴长度,增加喉管与喷嘴管径比、颗粒沉降区开口尺寸、装置直径等结构,能够降低颗粒沉降区平均湍动能,由于湍动能为单位质量流体由于紊流脉动所具有的动能,故降低了颗粒沉降区流场的紊流程度,增加了水流的稳定性,提高了装置对悬浮颗粒的去除效果;同时发现降低入口流速、增加悬浮颗粒粒径有助于提高悬浮物的去除率,当进水流速为0.1 m·s?1、经过混凝的悬浮颗粒形成粒径大于100 μm时,装置对选矿循环水中的悬浮颗粒去除效果显著。      

Modeling Discoloration in Potable Water Distribution Systems

Discoloration of potable water supplied to customer taps is one of the biggest causes of water quality related customer complaints. At present, understanding of the fundamental processes that cause discoloration is limited and the modeling of events unfeasible. This paper describes the development, verification, and validation of a novel cohesive transport modeling approach to simulate discoloration within distribution systems. The model is based on the principal that strength characteristics of fine particulate material accumulated at the pipe walls are conditioned by the shear stress of the usual daily hydraulics. Discoloration occurs when the flow through the systems changes, exceeding the peak daily value. Fieldwork results from two sites are presented in detail: Site 1 demonstrates model application including sensitivity and parameter dependence, while data from Site 2 is used to investigate the hypothesis that daily hydraulic forces condition the material layers within the pipes. Model simulations are also presented for a selection of other field sites to demonstrate the wider applicability of the model.     

In Situ Characterization of Resuspended-Sediment Oxygen Demand in Bubbly Creek, Chicago, Illinois

Sediment oxygen demand (SOD) can be a significant oxygen sink in various types of water bodies, particularly slow-moving waters with substantial organic sediment accumulation. In most settings in which SOD is a concern, the prevailing hydraulic conditions are such that the impact of sediment resuspension on SOD is not considered. However, in the case of Bubbly Creek in Chicago, the prevailing slack water conditions are interrupted by infrequent intervals of very high flow rates associated with pumped combined sewer overflow (CSO) during intense hydrologic events. These events can cause resuspension of the highly organic, nutrient-rich bottom sediments, resulting in precipitous drawdown of dissolved oxygen (DO) in the water column. To address this issue, a new in situ experimental apparatus designed to achieve high flow velocities was implemented to characterize SOD, both with and without sediment resuspension. In the case of resuspension, the suspended sediment concentration was analyzed as a function of bed shear stress, and a formulation was developed to characterize resuspended-sediment oxygen demand (SODR) as a function of suspended sediment concentration in a form similar to first-order biochemical oxygen demand (BOD) kinetics with the DO term in the form of Monod kinetics. The results obtained can be implemented into a model containing hydrodynamic, sediment transport, and water-quality components to yield oxygen demand varying in both space and time for specific flow events. The results are used to evaluate water quality improvement alternatives that take into account the impact of SOD under various flow conditions.     

Rapid melting and solidification of a surface layer

A one-dimensional computer heat flow model is used to investigate the effect of high intensity heat fluxes,e.g. those achieved via continuous CO2 laser radiation, on the important surface layer melting and subsequent solidification variables of three substrate materials: aluminum, iron, and nickel. Temperature profilesvs time, melting, and solidification interface velocities, heating, and cooling rates in the surface layers of the three metals are calculated. Results are presented in a general form to permit determination of these variables for large ranges of absorbed heat fluxes and times. General trends established show that temperature gradients in the liquid and solid phases and interface velocities are directly proportional to the absorbed heat flux, whereas melt depth is inversely proportional to the absorbed heat flux. Average cooling rates comparable to splat cooling can be achieved by increasing the heat flux and reducing the dwell time of the incident radiation. An order of magnitude increase in the absorbed heat flux results in a corresponding two orders of magnitude increase in average cooling rates in the liquid during solidification of crystalline and noncrystalline structures. Formerly Research Associate, Formerly Research Associate, Formerly Research Associate,     

Efficient Quasi-Two-Dimensional Model for Water Hammer Problems

Quasi-two-dimensional models for turbulent flows in water hammer are necessary for advancing the understanding of flow behavior in pipe transient; conducting detailed investigation of the fate of transient-induced contamination; and validating one-dimensional water hammer models. An existing quasi-two dimensional numerical model for turbulent water hammer flows has the attributes of being robust, consistent with the physics of wave motion and turbulent diffusion, and free from the inconsistency associated with the enforcement of the no slip condition while neglecting the radial velocity at boundary elements, such as valves and reservoirs. However, this scheme is computationally intensive making it unsuitable for practical pipe systems or for conducting numerical experiments. This paper addresses the efficiency and stability of this existing scheme. In particular, algebraic manipulations show that the original scheme can be decoupled into two tridiagonal systems, one for piezometric head and radial flux and another for axial velocity. This decoupling is the reason for the high efficiency of the modified scheme. The original and proposed schemes are applied to a pipe–reservoir–valve system. It is found that, for the same spatial and temporal discretization, both schemes are of equal accuracy. However, significant saving in computer execution time is achieved by using the modified scheme. Application of the modified scheme to pipes of realistic dimensions and wavespeeds (length 35.2 km, diameter 200 mm, and wave speed 1000 m/s) takes only a few minutes to execute. This small execution time requirement makes the current quasi-two-dimensional model suitable for application to practical water hammer problems. The stability domain of the proposed scheme is established using the Von Neumann method.