Download CE 3372 Water Systems Design

CE 3372 Water Systems Design
CLOSED CONDUIT HYDRAULICS
Review!
 Difference between an Easement and ROW
 What is a plat?
 Explain MUD
 Explain Bond
 3 resources for design
Outline
 Hydraulics/Characteristics
 Energy Equation
 Diagram
 EGL and HGL
 Head Loss Models
 Moody Chart
 Direct Method
Hydraulics Definition
 Hydraulics 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.
-Wikipedia
Water Characteristics
 Water moves from higher to lower energy
(Path of least resistance)
Gravity flow
 Pumps can be used to increase the energy to move water
to a higher level or over a barrier

 Flow of water has resistance
 The flow rate (Q) of water moving past a cross
section is equal to the area (A) of the cross section
multiplied by the velocity (v)
Mean Section Velocity
 In most engineering contexts, the mean section
velocity is the ratio of the volumetric discharge and
cross sectional area.
Q
V
A
 The velocity distribution in a section is important in
determining frictional losses in a conduit.

Flows
 1-Dimensional Flow
 The change of fluid variables (velocity, temp, etc.) in one
direction dominates over the change in the other two
directions.
 2-D and 3-D
 Change in fluid variables is significant in multiple directions
 Water is almost always a 3-dimensional flow
 However, 3D is difficult to quantify and model
 Most analysis simplifies water to 1-D or 2-D flow
 Coefficients, model calibration and experience
are used to account for simplifying assumptions
z
y
x
CONTINUITY
CONTINUITY
Energy Equation
 The energy equation relates the total dynamic head
at two points in a system, accounting for frictional
losses and any added head from a pump.
hp = head supplied by a pump
ht = head given to a turbine
h = mechanical energy converted to thermal
L
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
Diagram
Diagram
Lift Station
Suction Side
Discharge Side
Energy Equation
2
1
Energy Grade Line
 EGL 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
Hydraulic Grade Line
 HGL 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
HGL/EGL
Head Loss
 Darcy-Weisbach
 Hazen-Williams
 Chezy-Mannings
Darcy-Weisbach
 Frictional loss (hf) is proportional to
 Length and Velocity^2
 hf is inversely proportional to
 Cross-sectional area
 Loss coefficient depends on
 Reynolds number (fluid and flow properties)
 Roughness height (pipe material properties)
Darcy-Weisbach
 DW Head Loss Equation
 DW Equation - Discharge Form for
CIRCULAR conduits
Hazen-Williams
 Frictional loss (hf) proportional to
 Length, Velocity^(1.85)
 Loss is 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!
Hazen-Williams
 HW Head Loss
 Discharge Form
Hydraulic Radius
 HW 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
Hydraulic Radius
 For circular pipe, full flow (no free surface)
AREA
D
PERIMET
ER
Chezy-Manning
 Frictional loss proportional to
 Length, Velocity^2
 Inversely proportional to
 Cross section area (as hydraulic radius)
 Loss coefficient depends on
 Material, finish
Chezy-Manning
 CM Head Loss
 Discharge form replaces V with Q/A
Head Loss
 Major Friction Losses - pipe walls.
 Occur in all pipes
 Dependent on pipe and fluid properties
 Minor Losses - outlets, inlets, expansions,
contractions, valves and any other geometrical
obstructions in the fluid flow.

Mostly caused by disturbances in flow that result in increased
turbulence and motion in directions other than the general
direction of flow
Fitting (Minor) Losses
 Fittings, 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
Fitting (Minor) Losses
 The loss coefficients are tabulated for different kinds
of fittings
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
Examples
 Three “classical” examples using Moody Chart
 Head loss for given discharge, diameter, material
 Discharge given head loss, diameter, material
 Diameter given discharge, head loss, material
Direct (Swamee-Jain) Equations
 An alternative to the Moody chart are regression
equations that allow direct computation of discharge,
diameter, or friction factor.
Head
 Head – Energy per unit weight of water!!
 Energy = KE + PE
=[ velocity + (elevation + pressure) ]
Piezometer