Pipe Slope Research Articles

Preventing Sediment Deposition in Inverted Sewer Siphons

Laboratory experiments were carried out to determine minimum self-cleansing velocities for preventing deposition of sediment in upward sloping and vertical pipes of inverted siphons. Tests were made using sediment sizes of 0.78 and 4.3 mm in a pipe of 150 mm diameter for eight angles of inclination between 0 and 90°. The criterion for self-cleansing conditions was defined as the minimum velocity needed to prevent the formation of deposits on the invert of the pipe. For a given sediment concentration the self-cleansing velocity was found to be a maximum at pipe slopes between about 22.5 and 45°. Analysis of the forces acting on sediment particles in inclined pipes led to the development of a formula for predicting self-cleansing velocities taking account of pipe size, sediment size, sediment concentration, and pipe slope.

Scale model testing and calibration of City of Ottawa sewer weirs

This paper reports the results of a laboratory study of the effects of (i) manhole proximity to installation site, (ii) pipe slope (i.e., approach velocity), (iii) upstream head measurement location, and (iv) submergence on the "hydraulics" of two types of sewer weirs used by the City of Ottawa. The City's streamlined form of broad-crested weir and its compound-shaped sharp-crested weir were initially calibrated for a "pipe straight"-arrangement (no upstream manhole is present) for a wide range of flow conditions at 0.2%, 0.4%, and 1.0% pipe slopes. The calibration tests were then repeated with the weirs positioned immediately downstream of a model manhole structure ("manhole"-arrangement). Corresponding data sets were compared to determine the effects of (i) approach velocity and (ii) manhole proximity (for two different shapes of manhole "benching") on the respective weir discharge coefficients.Key words: sewer weirs, broad-crested weir, compound sharp-crested weir, calibration, sewer benching, discharge coefficients.

ONSET AND HYDRODYNAMIC MECHANISMS ON SLUGGING IN STRATIFIED AIR-WATER TWO-PHASE FLOWS

A theoretical model was proposed in order to determine the transitional flow conditions between separated flows and intermittent flows. Since this model is based on the hydraulic equations for non-uniform flows as well as the theoretical criterion of slug formation, it enables us to take account of the diameter, the length and the slope of the pipe. The validity of the proposed model was confirmed for horizontal and inclined pipes through the comparison with the previous and present experimental results. In addition, fluctuations in the volumetric flow rate of water inflow were examined and the hydrodynamic mechanisms of the fluctuations were clarified.It was also confirmed that the fluctuations decreased less as the pipe slope was steeper.

Two-Fluid Model Approach for Transient Analysis of Free-Surface-Pressurized Flows.

A new computational model is developed here to analyze the influence of entrapped air on free-surface-pressurized flows. A virtual slot with ceiling on the top of the pipe is introduced to treat a separated gas-liquid flow. This model is a modified model of Preissmann's and is applicable not only to open channel flow and closed conduit flow but also pressurized flow with entrapped air. Compared to experimental results using the model of 1/50 scale, the calculation results show that the entrapped air in horizontal pipe advances the time of pressure rising and makes the maximum value of pressure higher. The escape flow of entrapped air at dropshaft is caused by surface waves pushing the air in the horizontal pipe, and then the pipe slope affects the flow rate of air. The air compressibility has less effect on the transient separated air-water flow in the pipe.

Mobile Flume for Pipe Flow

Discharge measurement in partially filled pipes, as occurs in sewage and drainage engineering, is considered with an improved device. The so-called pipe flume is suited for mobile discharge measurement either for a single discharge reading or for the determination of daily or weekly hydrographs. It can easily be mounted in commercially fabricated pipes, and sediment transport does not detract from its accuracy. The device has been extensively tested in a hydraulics lab and the device has an accuracy of ±5% in optimum field conditions. Simplifications compared to the original design include the head determination in the cylindrical container, by which surface fluctuations are practically removed, and effects of pipe slope are eliminated. A discharge-head equation is established for pipe flumes having a diameter larger than 200 mm, where effects of scale are negligible. The discharge-head equation accounts for the pipe filling and the constriction rate, as well as for the position relative to the pipe outle...

Numerical Comparison of Pipe‐Column‐Separation Models

Results comparing six column‐separation numerical models for simulating localized vapor cavities and distributed vaporous cavitation in pipelines are presented. The discrete vapor‐cavity model (DVCM) is shown to be quite sensitive to selected input parameters. For short pipeline systems, the maximum pressure rise following column separation can vary markedly for small changes in wave speed, friction factor, diameter, initial velocity, length of pipe, or pipe slope. Of the six numerical models, three perform consistently over a broad number of reaches. One of them, the discrete gas‐cavity model, is recommended for general use as it is least sensitive to input parameters or to the selected discretization of the pipeline. Three models provide inconsistent estimates of the maximum pressure rise as the number of reaches is increased; however, these models do give consistent results provided the ratio of maximum cavity size to reach volume is kept below 10%.

Comprehensive investigation of startup regimes for a frozen heat pipe

The authors describe results of an experimental investigation of startup of an ammonia heat pipe made of aluminum with longitudinal channels and radiative heat rejection. They determine the influence of the startup dynamics of the location of the frozen heat transfer agent and the slope of the heat pipe to the horizontal. They propose a simplified method of determining the startup characteristics when the main mass of heat transfer agent is frozen in the heater zone.

A computer model to calculate varied flow functions for circular channels

A computer model is developed to calculate the gradually varied flow profiles based on the Keifer and Chu approach. Numerical integration using Simpson's rule is adopted. The model can handle positive, horizontal and adverse pipe slopes. The computer model can provide total G.V.F. length or a detailed x-y calculation. Lotus 1-2-3 print-graph capabilities are used to plot the G.V.F. profiles.

Field measurements of the hydraulic resistance of sanitary sewers

Measurements of the in-service hydraulic roughness of some 33 lengths of small suburban sanitary sewers are reported. The test results indicate that the hydraulic roughness used in design should vary with pipe slope, material, and the proportion of the design flow that is dry-weather flow. In particular, the typical design roughness currently recommended seems low for low slope sewers, but high for those with slopes greater than about 1%. The tests revealed that sewers installed below the usual recommended minimum slope were operating as successfully as those of steeper slope, which implies that the current minimum-slope recommendations may be too conservative. An alternate approach to minimum-slope specification is suggested. Several augmented-flow tests were also carried out. These confirmed that the variation in effective roughness with depth is much stronger than is usually assumed. They also showed that there is a significant hysteresis in the roughness variation on the rising and falling limbs of a hydrograph. Key words: sewers, pipeflow, coefficients, roughness, resistance, hydraulics, wastewater, sanitary.

A laboratory study of primary saline intrusion in a circular pipe

Results are presented from a series of laboratory experiments in which the intrusion and arrest of a salt wedge in a smooth circular pipe have been investigated over a range of densimetric Reynolds (Re Δ) and Froude (F Δ) numbers. Horizontal and inclined pipes have been considered, in order to model intrusion in the outlet ports and tunnels of long sea outfalls. An empirical estimator expression has been derived to represent the functional dependence of wedge length upon densimetric Reynolds and Froude numbers respectively, and pipe slope. The agreement between the predicted wedge lengths and the measured values is generally good for a wide parameter range (Re Δ: 7,300-13,200; F Δ: 0.25-0.68) typical of prototype operation. Comparisons between the pipe data and measurements of salt wedges in open channels reveal the pitfalls of applying two dimensional results to a three dimensional configuration.

Designing Sanitary Sewers with Microcomputers

A program titled Sanitary Sewer Design (SSD) has been developed for the Apple II microcomputer. SSD is a heuristic program that attempts to find the least costly design of a sanitary sewer network or pipeline. The program computes velocities, water depths, pipe slopes, and inverts corresponding to inputted diameters, flows, pipe lengths, ground elevations, and design criteria. SSD was used to find the least costly design of a 3.25 mile sewer trunk line in Chapel Hill, N.C., for the Orange Water and Sewer Authority (OWASA). It was also used to perform a sensitivity analysis, which evaluated the effect that design criteria, uncertainty in flows, and alteration of pipe diameters have on the cost of a sewer system. The sensitivity analysis indicated that: (1) Costs can be reduced 20‐25% by relaxing the pipe size progression criterion; and (2) sewer design was relatively sensitive to flow uncertainty.

Pipes and pipe flow process in an upland catchment, Wales

The results of observations on the spatial localisation, origin and function of soil pipes in an upland catchment are discussed. The pipes occur in distinct zones in the brown earth soils of the lower slopes, and form a hydrological link conducting water between an upslope zone of highly permeable skeletal soils and the stream channel. It is proposed that in this catchment, pipes develop from an initial network of mole burrows, modified by hydraulic activity to produce an efficient downslope transmission network. A conceptual model for the pipe slope segment is proposed which recognises the importance of this transmission role. Slope discharge controls switching between saturated throughflow, pipe flow and overland flow, each of which has a specific threshold value for operation. Attempts to investigate the significance of pipe flow at the catchment scale met with limited success, but it appears to be important in increasing both contributing area and duration of storm flow.

Cablegation: V. Dimensionless Design Relationships

ABSTRACT Asimplified design method using dimensionless relationships was developed for the cablegation automated surface irrigation system. The method consists of two parts: the pipe flow distribution and the infiltration-runoff distribution. The maximum outlet head, maximum stream size and number of flowing outlets are calculated using a set of dimensionless equations, given the pipe size, pipe slope, outlet size and spacing and total inflow rate. These equations enable a direct determination of the design variables without calculating the entire distribution of outlet flows. If the desired maximum stream size is known, the required outlet size can be calculated directly without trial and error. The infiltration-runoff analysis is presented as a series of dimensionless relationships in graphical form. These curves are used mainly for determining the required maximum stream size given a time-based furrow intake curve, furrow length and spacing, gross water application and percent runoff. Curves are also presented for the case of constant stream size for comparison with cablegation and for use in designing constant-inflow irrigation systems..

Pipes and pipe flow process in an upland catchment, Wales

The results of observations on the spatial localisation, origin and function of soil pipes in an upland catchment are discussed. The pipes occur in distinct zones in the brown earth soils of the lower slopes, and form a hydrological link conducting water between an upslope zone of highly permeable skeletal soils and the stream channel. It is proposed that in this catchment, pipes develop from an initial network of mole burrows, modified by hydraulic activity to produce an efficient downslope transmission network. A conceptual model for the pipe slope segment is proposed which recognises the importance of this transmission role. Slope discharge controls switching between saturated throughflow, pipe flow and overland flow, each of which has a specific threshold value for operation. Attempts to investigate the significance of pipe flow at the catchment scale met with limited success, but it appears to be important in increasing both contributing area and duration of storm flow.

Cablegation: 11. Simulation and Design of the Moving-Plug Gated Pipe Irrigation System

ABSTRACT THE hydraulics of a moving-plug gated pipe irrigation system are analyzed. A relationship was developed for predicting orifice discharge coefficients for a range of typical pipe flow velocity and head conditions. A simula-tion model was developed to predict the time distribution of orifice flows, the distribution of infiltrated water across a field, and runoff rates. The model can be used to design cablegation systems for fields having variable pipe slopes and variable furrow lengths. Orifice sizes are varied along the pipe line and the plug travel speed is varied in order to obtain optimum net water application for all furrows and to keep the furrow stream sizes within acceptable limits.

Models of Quasi-Steady and Unsteady Discharge from Plumbing Fixtures.

Modeling methods are developed to predict the discharge characteristics of simulated simplified configurations for plumbing fixtures connected to horizontal drain branch piping. Computations are carried out to illustrate several methods of determining the effect of various loss coefficients of the drain connection, pipe length, pipe diameter, and friction factor. Solutions are obtained for the case of a fixture with a constant head (continuous refill) and a falling head (emptying of a sink). Numerical solution of the non-linear differential equation for the falling head case was obtained by the Runge-Kutta method. Discharge characteristics are presented for a range of flows and pipe diameter-to-length ratios representative of plumbing installations. The feasibility of developing predictive models for hydraulic characteristics of interconnected plumbing fixture and drainage piping systems is shown. The variations of efflux rate with the drain pipe diameter, length, and slope obtained from the assumed models are similar in trend to the available experimental data.

Performance study of horizontal branch in building drainage system

Self-siphonage of traps of sanitary appliances caused by full-bore water discharge affects the performance of horizontal branches in building drainage sustems. Relationships have been established correlating flow, diameter and slope of branch pipes connected to main drainage stack for permissible loss of water seal with recourse to an experimental investigation in the laboratory on a range of wash-basins, as is usual in office buildings, with a view to developing a performance oriented design procedure. A measure has also been suggested to control development of negative pressure caused by self-siphonage.

OPTIMAL DESIGN OF STORMWATER DRAINAGE NETWORKS FOR ROADS.

Keywords LIVERPOOL UNIVERSITY OPTIMAL, DESIGN, STORMWATER, DRAINAGE, NETWORKS, ROADS, METHODS, SYSTEMS, HIGHWAYS, OPTIMISATION, PIPES, SIZE, SLOPES, FIXED, LAYOUT, INTERMEDIATE, MANHOLES, GEOMETRY, SAVINGS, CAPITAL, COSTS, COMPUTERS, PROGRAMS, PRACTICAL, DYNAMICS, PROGRAMMING, SERIAL, SYSTEMS, MULTIPIPE, POSITIONING... Show All

Performance of Model Storm Sewer Junctions

The design of an effective storm water junction structure requires calculation of the energy losses, and associated backwater effects, in the vicinity of the junction under anticipated maximum flows in the incoming sewers. In the case of hydraulically inefficient junctions, energy losses due to stream mixing and from drag can lead to surcharged conditions in the conduits. Under these conditions Sangster suggests appropriate energy loss coefficients based on extensive tests on small-scale junction structures in which the inflow and outflow pipes were surcharged. However, efficient storm sewer systems normally operate under free surface conditions. Consequently the experimental program, described in this note, had the following main objectives: 1. To provide data on the relative efficiency of different-shaped junction structures operating under free surface conditions; 2. to investigate junctions having large inlet pipe diameters and small incoming pipe slopes; and 3. determination of suitable modifications to junction geometry in light of recent attempts to improve the performance of some inefficient junctions in an existing sewer system.

MATHEMATICAL PROGRAMMING IN SEWER NETWORK DESIGN

This paper addresses itself to the question of obtaining the minimum cost design for a wastewater collection network. It first presents an empirical cost function for a single sewer line. The concept of optimization is then explored with respect lo sewer networks. The design problems of selecting an optimal mix of pipe diameters and slopes, given a set of economic and technological inputs as well as a network layout is then presented in three alternative mathematical programming formulations: separable convex, dynamic and geometric programming. These formulations guarantee the generation of global optimal solutions. Numerical solutions can be obtained using presently available computer capabilities. The paper concludes with an evaluation of the proposed formulations and their implications for both design practice and overall cost reduction in the area of wastewater collection.