Download - CE 3372 Water Systems Design
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CE 3372 Water S
ystem
s
Design
Lecture
003: Desi
gn guidelines;
hydraulics
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OutlineDistribution Systems Design Guidelines
RG-195 (Texas)Hydraulics of Closed Conduits
Pipelines and NetworksContinuityEnergy Equation
Head Loss Models Hazen-Williams Darcy-Weisbach Chezy-Manning
Fitting Losses
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DESIGN GUIDELINESDesign guidelines are in various manuals, and codes.
In Texas, distribution systems are covered at state level by a document called RG-195. A copy is on the server.
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DESIGN GUIDELINESRG-195 is really a collection of applicable Texas Administrative
Code rules
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DESIGN GUIDELINESRG-195 is really a collection of applicable Texas Administrative
Code rules
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DESIGN GUIDELINESDesign Standards; ANSI; NSF; ASTM; AWWA
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DESIGN GUIDELINESPipe Sizes
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DESIGN GUIDELINESPressure Requirements
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DESIGN GUIDELINESEstimating Demand (several methods)
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Conduit HydraulicsHydraulics is a topic in applied science and engineering dealing
with the mechanical properties of liquids. Fluid mechanics provides the theoretical foundation for hydraulics, which focuses on the engineering uses of fluid properties.
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Water characteristicsWater moves from higher to lower energy (along the path of
least resistance)Gravity flowPumps are used to increase energy to move water to a higher elevation or over a barrier
Flow of water creates friction/resistance; hence there is loss of energy along a flow path.
Flow rate is related to cross sectional flow area and mean section velocity
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CONTINUNITY AT DIFFERENT SECTIONS
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CONTINUNITY AT A JUNCTION
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Energy EquationThe energy equation relates the total dynamic head at two
points in a system, accounting for frictional losses and any added head from a pump.
hL =
hp =ht =
head supplied by a pumphead given to a turbinehead lost to friction
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Energy Equation ASSUMPTIONS
Pressure is hydrostatic in both cross sections
Fluid is incompressibleDensity is constant at the cross sectionFlow is steady
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Energy Equation Assumptions
Pressure is hydrostatic in both cross sections Pressure changes are due only to elevation
Fluid is incompressible Density is constant at the cross section Flow is steady
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Diagram
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Energy Equation
1
2
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Energy grade lineEGL is a line that represents the elevation of energy head of water flowing in a conduit.
It is the sum of the elevation, pressure, and velocity head at a location.
Drawn above HGL at a distance equal to the velocity head
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Hydraulic grade lineHGL is a line that represents the surface/profile of
water flowing in partially full pipe.If pipe is under pressure, flowing full the HGL rises
to where a free surface would exist if there were a piezometer installed in the pipeline
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HGL/EGL
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Head Loss ModelsDarcy-WeisbachHazen-WilliamsChezy-Mannings
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Darcy-WeisbachFrictional loss proportional to Length, Velocity^2Inversely proportional to Cross sectional areaLoss coefficient depends on Reynolds number (fluid and flow properties) Roughness height (pipe material properties)
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Darcy-WeisbachFrictional loss proportional to Length, Velocity^2Inversely proportional to Cross sectional areaLoss coefficient depends on Reynolds number (fluid and flow properties) Roughness height (pipe material properties)
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Darcy-WeisbachDW Head Loss Equation
DW Equation, Discharge Form, CIRCULAR conduits
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Hazen-WilliamsFrictional loss proportional to Length, Velocity^(1.8)Inversely proportional to Cross section area (as hydraulic radius)Loss coefficient (Ch) depends on Pipe material and finish Turbulent flow only (Re>4000)
WATER ONLY!
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Hazen-Williams
HW Head Loss
Discharge Form
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Hydraulic RadiusHW is often presented as a velocity equation using the hydraulic
radius
The hydraulic radius is the ratio of cross section flow area to wetted perimeter
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Hydraulic RadiusFor circular pipe, full flow (no free surface)
AREA PERIMETER
D
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Chezy-ManningFrictional loss proportional to Length, Velocity^2Inversely proportional to Cross section area (as hydraulic radius)Loss coefficient depends on Material, finish
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Fitting (Minor) LossesFittings, joints, elbows, inlets, outlets cause additional head
loss.
Called “minor” loss not because of magnitude, but because they occur over short distances.
Typical loss model is
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Fitting (Minor) LossesThe loss coefficients are tabulated for different kinds of fittings
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Moody Chart
Moody-Stanton chart is a tool to estimate the friction factor in the DW head loss model
Used for the pipe loss component of friction
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ExamplesThree “classical” examples using Moody Char Head loss for given discharge, diameter, material Discharge given head loss, diameter, material Diameter given discharge, head loss, material
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Direct (Jain) EquationsAn alternative to the Moody chart are regression equations
that allow direct computation of discharge, diameter, or friction factor.
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