Experimental and regression-based correction for velocity and temperature effects on friction head loss in polyethylene pipes: case study

Considering the importance of sufficient pressure in supplying demand in water distribution networks, it is necessary to study the factors affecting pressure variation, that the roughness of pipes directly affects the pressure of nodes. Therefore, the study of factors affecting the change in roughness coefficient (Hasen-Williams) in water distribution networks is important. Pipes diameter, age and corrosion are among factors affecting the change in the roughness coefficient of pipes that are evaluated in this paper. The roughness coefficients were plotted against each of the above mentioned factors, and the approximate relations of the roughness coefficient was obtained by fitting to the obtained graphs. Finally, by combining the relations obtained, a general relation is obtained for the roughness coefficient. Also, in this paper, the cast iron pipes, for which laboratory data is available, were used to obtain a mathematical relationship.Then again, instead of using the roughness coefficient of new pipes in analysis and design, the roughness coefficient for the end of the design period was used, taking into account the effective factors mentioned.To evaluate the results of the proposed method, a two-loop network was investigated in two common and real situations. The results showed that if the roughness coefficient of new pipes at the end of design period is used for designing, there will be a save of about 50% in cost of pipes, but then the network pressure at the end of design period will be reduced by more than 25%. Therefore, in order to ensure that there is sufficient pressure and demand satisfaction throughout the design period, it is necessary to accept an increase in the cost of network implementation at the beginning of the project.

Future water demands and pipe roughness coefficients used in the design of water distribution networks (WDNs) have a high degree of uncertainty. Fuzzy analysis of WDNs provide how the uncertainties in independent or basic parameters (such as nodal demands and pipe roughness coefficients) are propagated to dependent or derived parameters (such as pipe flows, pipe velocities, and available pressure heads). Usually demand dependent analysis is used for such analysis. A WDN may be pressure deficient or may become pressure deficient because of high pipe roughness or inadequate pump pressure and may not be able to meet desired demands at all nodes. Thus, it is desirable to consider the nodal outflows as unknown and as a function of available pressure heads under pressure-deficient conditions. An approach for fuzzy analysis of a WDN that takes into account pressure-deficient condition using node flow analysis is presented in this paper. The proposed methodology is illustrated with an example network taken from literature. The methodology is useful in identifying vulnerable zones in WDNs and can be extended for reliability analysis under uncertainty of nodal demands and pipe roughness coefficients. Comparison of results with usual demand-dependent analysis shows that proposed method is better for identifying vulnerable zones.

The analysis of hydraulic behavior of the water distribution network (WDN) is forefront part of the planning and augmentation of any water supply projects. The analysis of WDN determines the estimation of discharges, hydraulic gradient levels (HGL), nodal concentrations, etc., to fulfill the requirements of population. In the conventional approach of analysis, unique value of pipe discharges and hydraulic heads are obtained. The results so obtained may not give satisfactory performance in practice due to many uncertainties in nodal demands, pipe roughness, lengths, diameters of pipes, water levels in reservoirs, head-discharge characteristics of pumps, etc. In this study, the uncertainty in discharges and hydraulic heads are evaluated using two different pipe networks, the data for which is obtained from literature. Further, the membership function of pipe roughness has been used to calculate the membership function of discharges and hydraulic heads by incorporating EPANET with vertex method of fuzzy approach. The uncertainties in discharges and hydraulic heads at different α-cuts are evaluated considering the uncertainties in pipe roughness. The results of pipe discharges are found to vary between 15 and 30 % whereas the hydraulic heads at nodes vary between 0.3 and 3 m when the uncertainty is about 8 % in Hazen–Williams coefficient of pipe roughness in selected four- and five-pipe networks, respectively. Moreover, when the uncertainty of pipe roughness is combined with other kind of uncertainties as discussed above, would further aggravate the uncertainty in pipe discharges and nodal heads. As a result, the reliability of network would decrease in terms of either meeting the required discharges or the nodal heads to the consumers. This study would help to design the pipe network under the conditions of uncertainty in input parameters.

This research presents the analytical relationship between the frictional head loss obtained by two of the most common equations; Darcy-Weisbach and Hazen-Williams, considering plastic and metallic pipe materials as major categories. A wide range of hydraulic situations have been covered for water supply systems for buildings through five models for each pipe material category, based on water temperatures ranging from 20°C to 60°C, pipe diameters from 15 mm to50 mm and volume flow rates of 0.25 lps to 2 lps. The head loss values obtained by both equations were used to establish the correlation between them by using statistical techniques. The analyses show reliable results with combined correlation coefficient of 0.981 between both equations for plastic and metallic pipes, while the R2 value for the trend line of head loss values obtained by these equations was found to be 0.9978. This relationship should prove to be very useful for the water supply pipe manufacturers and designers for the mutual conversion of frictional head loss values obtained by these equations.

When designing large diameter water transmission pipelines, some engineers rely on design rules-of-thumb or a previous project as a template, without recognizing the inherent differences of each project. For large-scale water supply projects, mistakes in hydraulic design, especially underestimating friction headlosses, can be magnified resulting in reduced system capacities, catastrophic failures, or potential litigation. One of the most common mistakes in hydraulic design of large-diameter pipelines is underestimating pipe resistance and friction headlosses. The Hazen-Williams equation is the most widely used method for calculating headlosses in pipelines because it is simple and easy to use. However, the Hazen-Williams equation is empirical and, for large-diameter pipelines, has a limited range of applicability. Conversely, the Darcy-Weisbach equation provides a better approximation of friction headlosses since it takes into account the pipe roughness and Reynolds Number for different pipe materials, and is valid for all pipe sizes and turbulent flow ranges. Although there is an abundance of evidence of the limitations of the Hazen-Williams equation, it is continually misused in the engineering industry. There are many other design issues that can cause serious performance problems with large-diameter pipeline projects if not taken into consideration during design. Additional common hydraulic design pitfalls include: underestimating effects of sediment and biological material in raw water sources, not accounting for aging of pipeline materials, inadequate pipe pressure class design, improper placement and sizing of air valves, lack of accurate transient and surge analysis, inadequate flow and pressure field measurement, and potential need for pipeline maintenance and cleaning. There have been numerous publications on the topic of hydraulic design and proper calculation of pipeline friction headlosses. However, the focus of this paper is to provide analysis through case studies of several major water supply systems that reaffirms the importance of utilizing proper hydraulic considerations. Common hydraulic design oversights and short-cuts can often result in capacity and maintenance problems for large water supply systems.

Development of Prediction Models for Friction Losses in Drip Irrigation Laterals equipped with Integrated In-line and On-line Emitters using Dimensional Analysis

The scope of Reynolds number in the model experiment and the serviceability on Blasius friction factor equation were analyzed. The exponent of prototype–model scale and the proper distribution of the friction and vortex head loss in Moody’s formula were studied. It was consider that the friction head loss could not be reduced with the accession of vortex head loss. New conversion method of hydraulic efficiency for prototype pump performance using model based on Prandtl-Colebrook formula with a wide Reynolds number range and Nikuradse’s experiments to be consistent with was proposed The conversion results was compared with IEC 60995:1991, JIS B 8327:2002 methods. It is indicated that Prandtl-Colebrook formula has advantage of the strongly theoretical elements, the simply computational method and the high computation precision. It can be becoming to confirm of the prototype hydraulic efficiency from model acceptance tests of hydraulic machines with consideration of scale effects.

A new method for simulating lateral hydraulics in laminar or turbulent flow has been developed. The outflow is considered as a discrete variable and the friction head losses are calculated using the Darcy–Weisbach equation with an equivalent friction factor. Local head losses are also computed by applying equivalent coefficients that can be dependent on Reynolds number. Considering these premises, a compact expression that is valid for any type of regime has been deduced for calculating global head losses along any lateral stretch. The proposed method is useful to workout the hydraulic computation of laterals with the inlet segment at full or fractional outlet spacing, and complex laterals when a different pipeline diameter, slope, flow regime or emitter gap have to be considered.

Pipe material and natural organic matter impact drinking water biofilm microbial community, pathogen profiles and antibiotic resistome deciphered by metagenomics assembly

Leakages in water distribution networks (WDNs), in addition to water loss, causes more problems such as water pollution and land subsidence. In this paper, a new method is proposed to determine the leaky areas in WDNs. At first, a WDN is divided into several virtual areas. Then, while leakage is considered as an additional demand of nodes, the simultaneous calibration of the demands and the roughness coefficient of pipes is carried out by the imperialist competitive algorithm (ICA). Finally, the leakage probability of each area is estimated. The proposed method was implemented in a model water network with three scenarios (one, two and six simultaneous leakages, respectively) and a real water network, with two different leaky scenarios. The results showed that the proposed algorithm can correctly predict the location of multi simultaneous leakages considering their values priority. However, with increasing the number of simultaneous leakages, the ability of the used optimization algorithm (ICA) was reduced as for the studied model network, the average errors of the roughness coefficient of pipes for the three scenarios were approximate 2.3, 3.2, and 4.5%, respectively. The proposed method can be utilized by water utilities for locating leaky areas.

Friction head loss equations and friction correction factors were evaluated and compared to field observations collected from thirty center pivots with laterals made of PVCs. The friction head loss equations include Darcy-Weisbach (D-W), Hazen-Williams (H-W), and Scobey, in addition to a proposed equation valid for smooth and rough pipe types and for all turbulent flow types. The proposed equation was developed by combining the equations of D-W and H-W, along with the multiple nonlinear regression technique. The friction correction factors were computed by using the typical Christiansen, modified Christiansen, Anwar, and Alazba formulae. The evaluation has been based on statistical error techniques with observed values as a reference. With the combination of modified Christiansen, Anwar, and Alazba formulae, the results revealed that the magnitudes of friction head loss calculated by using the D-W, H-W, and proposed equations were in agreement with field observations. The root mean square deviation (RMSD) values ranged from 1.6 to 1.7 m. As expected, and when the typical Christiansen friction correction factor was used with the D-W, H-W, and proposed equations, the results showed poor agreement between observed and computed friction head loss values. This was clearly reflected by the high RMSD values that ranged from 5.4 to 5.9 m. On the other hand, agreement occurred between observed friction head loss values and those calculated by using the Scobey equation, invalid for PVC pipe type, when combined with the typical Christiansen formula. This interesting finding led to improved results of the Scobey equation through a developed Cs coefficient suitably valid for PVC pipe type through analytically mathematical derivation; accordingly, the RMSD value dropped from approximately 8.6 to 1.6 m.

With the increasing worry over water supplies, there is much interest worldwide in measures to be taken to retain the integrity of water distribution networks. This paper reports on a study of the integrity of polyethylene water distribution pipes related to the effect of chlorine in the water. Pipes used in water distribution networks are subject to demanding environmental, functional, and other stresses. Their working lifespan depends much on retention by the material of its antioxidant. In dry air, polyethylene can retain its properties for many decades. However, when polyethylene pipes are used in water distribution networks, the diffusion and loss of antioxidant from the material is increased from the inner pipe surface. When chlorine is present in the water, it can enter and spread through the material to increase the depletion rate of the antioxidant population. In this research, samples of pipe materials and sections of manufactured pipes have been subjected to accelerated life assessments. Also, modelling techniques have been devised to simulate the depletion of antioxidants in the pipe materials and used to research different possibilities including varying the concentrations of aggressive agents.

Reuse of wastewater has been widespread in this era to support the water sustainability process. Therefore, treated wastewater should be conveyed to suitable places and adopted for different uses. This study presents an empirical relationship between the Darcy-Weisbach and Hazen-Williams equations for four types of pipe material (ductile iron, GRP, concrete, and plastic) by using WaterCAD Version 8i. Two hydraulic models were developed to estimate the head loss in pipes by using different diameters: first, using pipe diameters from 800 mm to 1,200 mm for a flow rate of 1.16 m3/s, second, adopting pipe diameter from 1,600 mm to 2,000 mm for a flow rate of 4.63 m3/s. The study results are the head loss values obtained from the Darcy-Weisbach and Hazen-Williams equations, which were used to correlate them using IBM SPSS Statistics. The correlation coefficient between both equations turned out to be 0.991, 0.990, 0.990, and 0.990 for ductile iron, GRP, concrete, and plastic pipe materials. Additionally, the relationship between head loss and pipe diameter is negatively proportioned for both equations. Also, both head loss equation results are the same. The head loss values in the Darcy’s equation were higher for ductile iron and GRP materials, while being lower for concrete and plastic materials for both models. Selecting concrete or plastic pipes to convey treated wastewater is better than other pipe materials. Another conclusion is that the pipe diameter affects the head loss magnitude irrespective of the kind of equation whether Darcy-Weisbach or Hazen-William equation. Finally, this relationship is very useful for designers in converting the head loss values obtained using these equations.

The increasing share of renewable energy sources in the energy mix is posing new challenges for operating the power system. As a result, system operators must use the available flexibility more effectively to accommodate the surge in renewable energy. There are different ways to source flexibility including demand–response measures and sector integration. This paper investigates the utilization of flexibility from an integrated water and power network. A novel, augmented, distribution robust chance-constrained market clearing problem is proposed, assuming a centralized and fully competitive market set-up. Power generators and water pumps are modelled as flexible assets to procure flexibility from the integrated water and power network. Affine response policies and availability costs are defined to regulate the flexibility dispatch mechanism. The resulting coordination mechanism is nonlinear and non-convex. To make the problem feasible, different approximation and relaxation techniques are applied. A novel, hybrid, convex hull-based relaxation technique is proposed to convexify the friction head losses and pump energy consumption. The resulting problem is a second-order cone program which enables the power system operator to properly estimate and utilize the demand-side flexibility available in the water network. The results show that the electricity market benefits from grid flexibility obtained through the coordinated operation of controllable power generators and water pump loads. Under studied conditions, it was found that water pumps, when functioning as demand–response providers, can effectively compensate for power system imbalances, covering up to 25% of the total wind power mismatch. The sensitivity analysis emphasized the substantial impact of varying availability costs on the responses of flexible generators and water pumps. The error analysis identified the convex approximation of friction head losses as the primary source of inaccuracy in our model.

Potable water distribution networks (WDNs) and wastewater collection networks (WWCNs) are the two fundamental constituents of the complex urban water infrastructure. Such water networks require adapted design interventions as part of retrofitting, extension, and maintenance activities. Consequently, proper optimization methodologies are required to reduce the associated capital cost while also meeting the demands of acquiring clean water and releasing wastewater by consumers. In this paper, a systematic review of the optimization of both WDNs and WWCNs, from the preliminary stages of development through to the state-of-the-art, is jointly presented. First, both WDNs and WWCNs are conceptually and functionally described along with illustrative benchmarks. The optimization of water networks across both clean and waste domains is then systematically reviewed and organized, covering all levels of complexity from the formulation of cost functions and constraints, through to traditional and advanced optimization methodologies. The rationales behind employing these methodologies as well as their advantages and disadvantages are investigated. This paper then critically discusses current trends and identifies directions for future research by comparing the existing optimization paradigms within WDNs and WWCNs and proposing common research directions for optimizing water networks. Optimization of urban water networks is a multidisciplinary domain, within which this paper is anticipated to be of great benefit to researchers and practitioners.