Upload
sreedhar-reddy-sajjala
View
16
Download
0
Embed Size (px)
DESCRIPTION
Fluid Mech
Citation preview
5/21/2018 Presentation FM(Fall 2013)
1/208
Dr.S.Sreedhar Reddy
Assistant Professor
5/21/2018 Presentation FM(Fall 2013)
2/208
Fluid Mechanics in everyday life
In this way, the air and the water of rivers and seas are alwaysmoving.
Such a movement of gas or liquid (collectively called fluid) iscalled the flow,and the study of this is fluidmechanics.
5/21/2018 Presentation FM(Fall 2013)
3/208
5/21/2018 Presentation FM(Fall 2013)
4/208
5/21/2018 Presentation FM(Fall 2013)
5/208
Units and Dimensions
Allphysical quantities are given by a few fundamental quantities or their combinations.
The units of such fundamental quantities are called base units, combinations of thembeing called derived units.
The system in which lengths, mass and time are adopted as the basic quantities, and
from which the units of other quantities are derived, is called the absolute system of
units.
5/21/2018 Presentation FM(Fall 2013)
6/208
System of Units
MKS system of units
This is the system of units where the meter (m) is used for the unit of length, kilogram
(kg) for the unit of mass, and second (s) for the unit of time as the base units.
CGS system of units
This is the system of units where the centimeter (cm) is used for length, gram (g) for
mass, and second (s) for time as the base units.
International system of units (SI)SI, the abbreviation of La System International dUnites, is the system developed from
the MKS system of units.
It is a consistent and reasonable system of units which makes it a rule to adopt only one
unit for each of the various quantities used in such fields as science, education and
industry.
There are seven fundamental SI units, namely: meter (m) for length, kilogram (kg) for
mass, second (s) for time, ampere (A) for electric current, Kelvin (K) for thermodynamic
temperature, mole (mol) for mass quantity and candela (cd) for intensity of light.
5/21/2018 Presentation FM(Fall 2013)
7/208
Density, Specific gravity and Specific Volume
Density
The mass per unit volume of material is called the density, which
is generally expressed by the symbol p.
The density of a gas changes according to the pressure, but that
of a liquid may be considered unchangeable in general.
The units of density are kg/m3 (SI). The density of water at 4C
and 1 atm is 1000 kg/m3.
SPECIFIC GRAVITY
The ratio of the density of a material p to the density of water pw
iscalled the specific gravity, which is expressed by the symbol s:
5/21/2018 Presentation FM(Fall 2013)
8/208
The reciprocal of density, i.e. the volume per unit mass, is called the specific volume,
which is generally expressed by the symbol u :
5/21/2018 Presentation FM(Fall 2013)
9/208
Specific Weight
Specific weight of a fluid, Definition:weight of the fluid per unit volume Arising from the existence of a gravitational force The relationshipand g can be found using the following:
Since = m/therefore = g (1.3)
Units:N/m3
Typical values:Water = 9814 N/m3; Air = 12.07 N/m3
5/21/2018 Presentation FM(Fall 2013)
10/208
Example 1.2A reservoir of oil has a mass of 825 kg. The
reservoir has a volume of 0.917 m3
. Computethe density, specific weight, and specificgravity of the oil.
Solution:
3/900917.0
825mkg
m
volume
massoil
3
oil m/N882981.9x900g
mg
volume
weight
9.0998
900
@
STPw
oil
oilSG
5/21/2018 Presentation FM(Fall 2013)
11/208
5/21/2018 Presentation FM(Fall 2013)
12/208
1.6 ViscosityViscosity, , is a measure of resistance to
fluid flow as a result of intermolecularcohesion. In other words, viscosity can beseen as internal friction to fluid motionwhich can then lead to energy loss.
Fluid with a high viscosity such as syrupdeforms more slowly than fluid with a lowviscosity such as water. The viscosity is
also known as dynamic viscosity. Units: N.s/m2or kg/m/s
Typical values:Water = 1.14x10-3 kg/m/s; Air = 1.78x10-5 kg/m/s
5/21/2018 Presentation FM(Fall 2013)
13/208
Example:
AirWaterOilGasolineAlcoholKeroseneBenzene
Glycerine
Fluid Newtons lawof viscosity
Newtonian fluidsobey refer
Newtons law of viscosity is given by;
dy
du (1.1)
The viscosity is a function only of the condition of the fluid, particularly itstemperature.
The magnitude of the velocity gradient (du/dy) has no effect on the magnitude of .
= shear stress
= viscosity of fluid
du/dy= shear rate, rate of strain or velocity gradient
Newtonian and Non-Newtonian
Fluid
5/21/2018 Presentation FM(Fall 2013)
14/208
Fluid Newtons lawof viscosity
Non- Newtonianfluids
Do not obey
The viscosity of the non-Newtonian fluid is dependent on thevelocity gradientas well as the condition of the fluid.
Newtonian Fluids a linear relationship between shear stress and the velocity gradient (rate
of shear), the slope is constant the viscosity is constant
non-Newtonian fluids slope of the curves for non-Newtonian fluids varies
Newtonian and Non-Newtonian
Fluid
5/21/2018 Presentation FM(Fall 2013)
15/208
If the gradient mis constant, the fluid is termed as Newtonian fluid.Otherwise, it is known as non-Newtonian fluid. Fig. 1.5 showsseveral Newtonian and non-Newtonian fluids.
UNITS OF VISCOCITY
5/21/2018 Presentation FM(Fall 2013)
16/208
UNITS OF VISCOCITY
5/21/2018 Presentation FM(Fall 2013)
17/208
5/21/2018 Presentation FM(Fall 2013)
18/208
5/21/2018 Presentation FM(Fall 2013)
19/208
5/21/2018 Presentation FM(Fall 2013)
20/208
5/21/2018 Presentation FM(Fall 2013)
21/208
5/21/2018 Presentation FM(Fall 2013)
22/208
5/21/2018 Presentation FM(Fall 2013)
23/208
5/21/2018 Presentation FM(Fall 2013)
24/208
5/21/2018 Presentation FM(Fall 2013)
25/208
5/21/2018 Presentation FM(Fall 2013)
26/208
5/21/2018 Presentation FM(Fall 2013)
27/208
5/21/2018 Presentation FM(Fall 2013)
28/208
5/21/2018 Presentation FM(Fall 2013)
29/208
Pressure
When fluid is at rest, at any point of a supporting surface , the force exerted by a fluid is
normal to the surface.
This normal force exerted by a fluid at a point per unit area of the surface is calledPressure IntensityorUnit Pressureor Specific Pressureor Hydrostatic Pressure.
In this case, p is the pressure and P is the pressure force.
5/21/2018 Presentation FM(Fall 2013)
30/208
The unit of pressure is the Pascal (Pa), but it is also expressed in bars or meters of
water column (mH2O).
5/21/2018 Presentation FM(Fall 2013)
31/208
Pressure of fluid at rest
In general, in a fluid at rest the pressure varies according to the depth.
When the base point is set at Zo below the upper surface of liquid as
shown in figure, and Pois the pressure acting on that surface, then P = Po
when Z = Zo, so
5/21/2018 Presentation FM(Fall 2013)
32/208
Thus it is found that the pressure inside a liquid increases in proportion
to the depth.
Example:01
What is the water pressure on the sea bottom at a depth of 6500m? The specific
gravity of sea water is assumed to be 1.03.
Example :02
What depth of oil of specific gravity 0.9 will produce a pressure intensity of 9
Kg/cm2?
Example :03
Convert a pressure head of 40 m 0f oil to corresponding head of water if the
specific gravity of oil is 0.8?
5/21/2018 Presentation FM(Fall 2013)
33/208
5/21/2018 Presentation FM(Fall 2013)
34/208
5/21/2018 Presentation FM(Fall 2013)
35/208
Absolute pressure and gauge pressure
5/21/2018 Presentation FM(Fall 2013)
36/208
Absolute pressure and gauge pressureThere are two methods used to express the pressure: one is based on the perfect
vacuum and the other on the atmospheric pressure. The former is called the absolute
pressureand the latter is called the gauge pressure. Then,
5/21/2018 Presentation FM(Fall 2013)
37/208
5/21/2018 Presentation FM(Fall 2013)
38/208
5/21/2018 Presentation FM(Fall 2013)
39/208
F l i th f i th f li id fl i i id i th
5/21/2018 Presentation FM(Fall 2013)
40/208
For example, in the case of measuring the pressure of liquid flowing inside a pipe, the
pressure p can be obtained by measuring the height of liquid H coming upwards into a
manometer made to stand upright as shown in figure.
5/21/2018 Presentation FM(Fall 2013)
41/208
Differential Manometer or U-tube manometer
When the pressure P is large, this is inconvenient because H is too high.
So a U-tube manometer, as shown in following figure, containing a high-density
liquid such as mercury is used.
In this case, when the density isp,
5/21/2018 Presentation FM(Fall 2013)
42/208
5/21/2018 Presentation FM(Fall 2013)
43/208
In the case of measuring the pressure difference between two pipes in both of
which a liquid of density p flows, a differential manometer as shown in figure is
used.
Fig. Differential manometer
I th f Fi h th diff ti l f th li id i ll t
5/21/2018 Presentation FM(Fall 2013)
44/208
In the case of Fig. a, where the differential pressure of the liquid is small, measurements
are made by filling the upper section of the meter with a liquid whose density is less than
that of the liquid to be measured, or with a gas. Thus
Figure (b) shows the case when the differential pressure is large. This time, a liquid
column of a larger density than the measuring fluid is used.
5/21/2018 Presentation FM(Fall 2013)
45/208
E l
5/21/2018 Presentation FM(Fall 2013)
46/208
Example:
Obtain the pressure p at point A in Figs (a), (b) and (c).
Example:
5/21/2018 Presentation FM(Fall 2013)
47/208
Example:
Obtain the pressure difference P1- P2in Figs (a) and (b).
5/21/2018 Presentation FM(Fall 2013)
48/208
5/21/2018 Presentation FM(Fall 2013)
49/208
5/21/2018 Presentation FM(Fall 2013)
50/208
5/21/2018 Presentation FM(Fall 2013)
51/208
5/21/2018 Presentation FM(Fall 2013)
52/208
5/21/2018 Presentation FM(Fall 2013)
53/208
5/21/2018 Presentation FM(Fall 2013)
54/208
5/21/2018 Presentation FM(Fall 2013)
55/208
5/21/2018 Presentation FM(Fall 2013)
56/208
5/21/2018 Presentation FM(Fall 2013)
57/208
5/21/2018 Presentation FM(Fall 2013)
58/208
5/21/2018 Presentation FM(Fall 2013)
59/208
5/21/2018 Presentation FM(Fall 2013)
60/208
5/21/2018 Presentation FM(Fall 2013)
61/208
5/21/2018 Presentation FM(Fall 2013)
62/208
5/21/2018 Presentation FM(Fall 2013)
63/208
5/21/2018 Presentation FM(Fall 2013)
64/208
5/21/2018 Presentation FM(Fall 2013)
65/208
5/21/2018 Presentation FM(Fall 2013)
66/208
5/21/2018 Presentation FM(Fall 2013)
67/208
5/21/2018 Presentation FM(Fall 2013)
68/208
5/21/2018 Presentation FM(Fall 2013)
69/208
5/21/2018 Presentation FM(Fall 2013)
70/208
5/21/2018 Presentation FM(Fall 2013)
71/208
5/21/2018 Presentation FM(Fall 2013)
72/208
5/21/2018 Presentation FM(Fall 2013)
73/208
5/21/2018 Presentation FM(Fall 2013)
74/208
Buoyancy
http://en.wikipedia.org/wiki/Image:Submerged-and-Displacing.png5/21/2018 Presentation FM(Fall 2013)
75/208
1. Fluid pressure acts all over the wetted surface of a body floating in a fluid, and the
resultant pressure acts in a vertical upward direction. This force is called buoyancy.
2. The buoyancy of air is small compared with the gravitational force of the immersed
body, so it is normally ignored.
Cube in liquid
Suppose that a cube is located in a liquid of density p as shown in figure.
5/21/2018 Presentation FM(Fall 2013)
76/208
The pressure acting on the cube due to the liquid in the horizontal direction is balanced
right and left.
For the vertical direction, where the atmospheric pressure is Po,
The force Flacting on the upper surface A is expressed by the following equation:
The force F2acting on the lower surface is:
When the volume of the body in the liquid is V, the resultant force F from the pressure
5/21/2018 Presentation FM(Fall 2013)
77/208
acting on the whole surface of the body is
From this equation, the body in the liquid experiences a buoyancy equal
to the weight of the liquid displaced by the body. This result is known as
Archimedesprinciple.
The centre of gravity of the displaced liquid is called centreof buoyancy
and is the point of action of the buoyancy force.
5/21/2018 Presentation FM(Fall 2013)
78/208
5/21/2018 Presentation FM(Fall 2013)
79/208
5/21/2018 Presentation FM(Fall 2013)
80/208
5/21/2018 Presentation FM(Fall 2013)
81/208
5/21/2018 Presentation FM(Fall 2013)
82/208
5/21/2018 Presentation FM(Fall 2013)
83/208
5/21/2018 Presentation FM(Fall 2013)
84/208
5/21/2018 Presentation FM(Fall 2013)
85/208
5/21/2018 Presentation FM(Fall 2013)
86/208
5/21/2018 Presentation FM(Fall 2013)
87/208
5/21/2018 Presentation FM(Fall 2013)
88/208
5/21/2018 Presentation FM(Fall 2013)
89/208
Example:01
5/21/2018 Presentation FM(Fall 2013)
90/208
An ice berg of specific weight 900 Kg/m3 floats in sea water of specific weight 1025
Kg/m3.Find the ratio of the volume of the iceberg above the sea water level to its total
volume?
Example :02
A cubical body of side 0.25 m and specific gravity 2.5 is immersed in water. Find the
least force required to lift the body?
5/21/2018 Presentation FM(Fall 2013)
91/208
Archimedes's Principle
5/21/2018 Presentation FM(Fall 2013)
92/208
1. An object is subject to an upward force when it is immersed in liquid. The force is
equal to the weight of the liquid displaced.
2. The apparent weight of a block of aluminum (1) immersed in water is reduced by an
amount equal to the weight of water displaced.
3. If a block of wood (2) is completely immersed in water, the upward force is greater
than the weight of the wood. (Wood is less dense than water, so the weight of the
block of wood is less than that of the same volume of water.)
4. So the block rises and partly emerges to displace less water until the upward force
exactly equals the weight of the block.
5/21/2018 Presentation FM(Fall 2013)
93/208
5/21/2018 Presentation FM(Fall 2013)
94/208
Fig. Stability of a ship
Figure shows a ship of weight W floating in the water with an inclination of small angle .
The location of the centroid G does not change with the inclination of the ship.
But since the centre of buoyancy C moves to the new point C,a couple of forces Ws =
5/21/2018 Presentation FM(Fall 2013)
95/208
Fs is produced and this couple restores the shipsposition to stability.
The intersecting point M on the vertical line passing through the centre of buoyancy C
(action line of the buoyancy F) and the centre line of the ship is called the metacentre,
and GM is called the metacentric height.
If M is located higher than G, the restoring force acts to stabilize the ship, but if M is
located lower than G, the couple of forces acts to increase the roll of the ship and so
make the ship unstable.
5/21/2018 Presentation FM(Fall 2013)
96/208
Fundamentals of flow
5/21/2018 Presentation FM(Fall 2013)
97/208
5/21/2018 Presentation FM(Fall 2013)
98/208
5/21/2018 Presentation FM(Fall 2013)
99/208
1. A flow whose flow state expressed by velocity, pressure, density, etc., at any
position, does not change with time, is called a steady flow.
2. On the other hand, a flow whose flow state does change with time is called an
unsteady flow.
5/21/2018 Presentation FM(Fall 2013)
100/208
5/21/2018 Presentation FM(Fall 2013)
101/208
Smoke from a chimney
On a calm day with no wind, smoke ascending from a chimney looks like a single line as
shown in figure (a).
However, when the wind is strong, the smoke is disturbed and swirls as shown in figure
(b) or diffuses into the peripheral air.
One man who systematically studied such states of flow was Osborne Reynolds.
5/21/2018 Presentation FM(Fall 2013)
102/208
Reynolds used the device shown in figure.
5/21/2018 Presentation FM(Fall 2013)
103/208
Colored liquid was led to the entrance of a glass tube.
Figure: Reynolds' experiment
As the valve was gradually opened by the handle, the colored liquid flowed, as shown in
fi lik i f th d ith t i i ith i h l t
5/21/2018 Presentation FM(Fall 2013)
104/208
figure, like a piece of thread without mixing with peripheral water.
When the flow velocity of water in the tube reached a certain value, as shown in figure
that the line of colored liquid suddenly became turbulent on mingling with the peripheral
water.
The former flow is called the laminar flow, the latter flow the turbulent flow, and the flow
velocity at the time when the laminar flow had turned to turbulent flow the critical
velocity.
Laminar Flow
5/21/2018 Presentation FM(Fall 2013)
105/208
1. Laminar flow is a type of flow in which the fluid particles move in layers.
2. There is no transportation of fluid particles from one layer to another.
3. The fluid particles in any layer move along well defined paths or stream lines.
Turbulent Flow
1. Turbulent flow is the most common type of flow that occurs in nature.
2. There is a general mixing up of the fluid particles in motion.
3. There is continuous collision between fluid particles involving transference of
momentum between them
Whenever water is allowed to flow at a low velocity by opening the tap a little,
the water flows out smoothly with its surface in the laminar state.
5/21/2018 Presentation FM(Fall 2013)
106/208
the water flows out smoothly with its surface in the laminar state.
But as the tap is gradually opened to let the water velocity increase, the flow
becomes turbulent and opaque with a rough surface.
Compressible and Incompressible Flow
5/21/2018 Presentation FM(Fall 2013)
107/208
1. In general, liquid is called an incompressible fluid, and gas a compressible fluid.
Nevertheless, even in the case of a liquid it becomes necessary to take
compressibility into account whenever the liquid is highly pressurized, such as oil in a
hydraulic machine.
2. Similarly, even in the case of a gas, the compressibility may be disregarded
whenever the change in pressure is small.
Rotational and Irrotational flows
5/21/2018 Presentation FM(Fall 2013)
108/208
1. As fluids moves the fluid particles may be subjected to a rotatory displacements.
Suppose a particle which is moving along a stream line rotates about its own axis
also then the particle is said to have a rotational motion.
2. If the particles as it moves along the stream lines does not rotate about its own axis
the particle is said to have irrotational motion.
Irrotational flow Rotational flow
5/21/2018 Presentation FM(Fall 2013)
109/208
5/21/2018 Presentation FM(Fall 2013)
110/208
5/21/2018 Presentation FM(Fall 2013)
111/208
5/21/2018 Presentation FM(Fall 2013)
112/208
5/21/2018 Presentation FM(Fall 2013)
113/208
5/21/2018 Presentation FM(Fall 2013)
114/208
5/21/2018 Presentation FM(Fall 2013)
115/208
5/21/2018 Presentation FM(Fall 2013)
116/208
5/21/2018 Presentation FM(Fall 2013)
117/208
5/21/2018 Presentation FM(Fall 2013)
118/208
5/21/2018 Presentation FM(Fall 2013)
119/208
5/21/2018 Presentation FM(Fall 2013)
120/208
5/21/2018 Presentation FM(Fall 2013)
121/208
5/21/2018 Presentation FM(Fall 2013)
122/208
5/21/2018 Presentation FM(Fall 2013)
123/208
5/21/2018 Presentation FM(Fall 2013)
124/208
5/21/2018 Presentation FM(Fall 2013)
125/208
5/21/2018 Presentation FM(Fall 2013)
126/208
5/21/2018 Presentation FM(Fall 2013)
127/208
5/21/2018 Presentation FM(Fall 2013)
128/208
5/21/2018 Presentation FM(Fall 2013)
129/208
5/21/2018 Presentation FM(Fall 2013)
130/208
5/21/2018 Presentation FM(Fall 2013)
131/208
5/21/2018 Presentation FM(Fall 2013)
132/208
5/21/2018 Presentation FM(Fall 2013)
133/208
5/21/2018 Presentation FM(Fall 2013)
134/208
5/21/2018 Presentation FM(Fall 2013)
135/208
5/21/2018 Presentation FM(Fall 2013)
136/208
5/21/2018 Presentation FM(Fall 2013)
137/208
5/21/2018 Presentation FM(Fall 2013)
138/208
5/21/2018 Presentation FM(Fall 2013)
139/208
5/21/2018 Presentation FM(Fall 2013)
140/208
5/21/2018 Presentation FM(Fall 2013)
141/208
5/21/2018 Presentation FM(Fall 2013)
142/208
5/21/2018 Presentation FM(Fall 2013)
143/208
5/21/2018 Presentation FM(Fall 2013)
144/208
Calculate Reynolds' Number and
decide what type of flow is this?
Example: Lubricating Oil at a velocity of
1 m/s (average) flows through a pipe of
100 mm ID. Determine whether the f low
is laminar or turbu lent.
5/21/2018 Presentation FM(Fall 2013)
145/208
5/21/2018 Presentation FM(Fall 2013)
146/208
5/21/2018 Presentation FM(Fall 2013)
147/208
5/21/2018 Presentation FM(Fall 2013)
148/208
5/21/2018 Presentation FM(Fall 2013)
149/208
5/21/2018 Presentation FM(Fall 2013)
150/208
5/21/2018 Presentation FM(Fall 2013)
151/208
5/21/2018 Presentation FM(Fall 2013)
152/208
5/21/2018 Presentation FM(Fall 2013)
153/208
5/21/2018 Presentation FM(Fall 2013)
154/208
5/21/2018 Presentation FM(Fall 2013)
155/208
5/21/2018 Presentation FM(Fall 2013)
156/208
5/21/2018 Presentation FM(Fall 2013)
157/208
5/21/2018 Presentation FM(Fall 2013)
158/208
5/21/2018 Presentation FM(Fall 2013)
159/208
5/21/2018 Presentation FM(Fall 2013)
160/208
5/21/2018 Presentation FM(Fall 2013)
161/208
5/21/2018 Presentation FM(Fall 2013)
162/208
5/21/2018 Presentation FM(Fall 2013)
163/208
5/21/2018 Presentation FM(Fall 2013)
164/208
5/21/2018 Presentation FM(Fall 2013)
165/208
5/21/2018 Presentation FM(Fall 2013)
166/208
5/21/2018 Presentation FM(Fall 2013)
167/208
5/21/2018 Presentation FM(Fall 2013)
168/208
5/21/2018 Presentation FM(Fall 2013)
169/208
Introduction
5/21/2018 Presentation FM(Fall 2013)
170/208
20% of worlds electrical energy
demand
25-50% of energy usage in someindustries
Used for
Domestic, commercial, industrial and
agricultural services
Municipal water and wastewater services
What are Pumping Systems
Introduction
5/21/2018 Presentation FM(Fall 2013)
171/208
UNEP 2006
Objective of pumping system
What are Pumping Systems
(US DOE, 2001)
Transfer liquid
from source to
destination
Circulate liquidaround a system
Introduction
5/21/2018 Presentation FM(Fall 2013)
172/208
UNEP 2006
Main pump components
Pumps
Prime movers: electric motors, diesel engines,air system
Piping to carry fluid
Valves to control flow in system
Other fittings, control, instrumentation
End-use equipment
Heat exchangers, tanks, hydraulic machines
What are Pumping Systems
Introduction
5/21/2018 Presentation FM(Fall 2013)
173/208
UNEP 2006
Head
Resistance of the system
Two types: static and friction
Static head
Difference in height between
source and destination
Independent of flow
Pumping System Characteristics
destination
source
Stati
c
head
Statichead
Flow
Introduction
5/21/2018 Presentation FM(Fall 2013)
174/208
UNEP 2006
Static head consists of
Static suction head (hS): lifting liquid relative to
pump center line Static discharge head (hD) vertical distance
between centerline and liquid surface in
destination tank
Static head at certain pressure
Pumping System Characteristics
Head (in feet) = Pressure (psi) X 2.31
Specific gravity
5/21/2018 Presentation FM(Fall 2013)
175/208
Introduction
5/21/2018 Presentation FM(Fall 2013)
176/208
UNEP 2006
Friction head
Resistance to flow in pipe and fittings
Depends on size, pipes, pipe fittings, flowrate, nature of liquid
Proportional to square of flow rate
Closed loop system
only has friction head(no static head)
Pumping System Characteristics
Frictionhead
Flow
Introduction
5/21/2018 Presentation FM(Fall 2013)
177/208
UNEP 2006
In most cases:
Total head = Static head + friction head
Pumping System Characteristics
System
head
Flow
Static head
Friction
head
System
curve
System
head
Flow
Static head
Friction
head
System
curve
Introduction
5/21/2018 Presentation FM(Fall 2013)
178/208
UNEP 2006
Pump performance curve
Relationship between
head and flow Flow increase
System resistance increases
Head increases
Flow decreases to zero
Zero flow rate: risk ofpump burnout
Pumping System Characteristics
Head
Flow
Performance curve for
centrifugal pump
Introduction
5/21/2018 Presentation FM(Fall 2013)
179/208
UNEP 2006
Pump operating point
Pumping System Characteristics
Duty point: rateof flow at certain
head
Pump operating
point:
intersection of
pump curve and
system curve
Flow
Head
Static
head
Pump performancecurve
System
curve
Pump
operating
point
Introduction
5/21/2018 Presentation FM(Fall 2013)
180/208
UNEP 2006
Pump suction performance (NPSH)
Cavitation or vaporization: bubbles inside pump
If vapor bubbles collapse Erosion of vane surfaces
Increased noise and vibration
Choking of impeller passages
Net Positive Suction Head NPSH Available: how much pump suction
exceeds liquid vapor pressure
NPSH Required: pump suction needed to avoid
cavitation
Pumping System Characteristics
Training Agenda: Pumps
5/21/2018 Presentation FM(Fall 2013)
181/208
UNEP 2006
Introduction
Type of pumps
Assessment of pumpsEnergy efficiency opportunities
Type of Pumps
5/21/2018 Presentation FM(Fall 2013)
182/208
UNEP 2006
Classified by operating principle
Pump Classification
DynamicPositive
Displacement
Centrifugal Special effect Rotary Reciprocating
Internal
gear
External
gearLobe
Slide
vane
Others (e.g.Impulse, Buoyancy)
Pumps
DynamicPositive
Displacement
Centrifugal Special effect Rotary Reciprocating
Internal
gear
External
gearLobe
Slide
vane
Others (e.g.Impulse, Buoyancy)
Pumps
5/21/2018 Presentation FM(Fall 2013)
183/208
Storm Water Runoff
Where Does Storm Water Go?
5/21/2018 Presentation FM(Fall 2013)
184/208
Absorbed by the ground/vegetation Runoff
Waterway
Street
Neighbor Detained on site
Detention/retention pond
Underground storage
Site Development
5/21/2018 Presentation FM(Fall 2013)
185/208
Includes improvements or changes to the site
Buildings
Pavement
Landscaping
Grading
Typically, development increases runoff and decreasesabsorption of storm water
Storm Water Management
5/21/2018 Presentation FM(Fall 2013)
186/208
Regulations have evolved in order to Protect the environment
Water quality
Sedimentation (grading and erosion control)
Protect property Reduce site runoff
Reduce impact on storm drainage systems
5/21/2018 Presentation FM(Fall 2013)
187/208
Watershed Characteristics Affecting Runoff Rainfall intensity Soil type
Slope/topography
Soil condition (compactness) Vegetation
Storm Water Management
5/21/2018 Presentation FM(Fall 2013)
188/208
Many regulations dictate that the post-developmentrunoff not exceed the pre-development runoff.
To calculate the impact of development on storm waterrunoff, we must calculate the pre-development storm
runoff and the post-development storm runoff. In general, the change in runoff (difference) must be
retained/detained onsite such that the additional runoffis not routed to the existing storm water system.
STORM WATER MANAGEMENT PLAN
The Rational Method
5/21/2018 Presentation FM(Fall 2013)
189/208
The Rational Formula
Q = C i A
Q = Peak runoff rate (cubic feet/sec)
i = Rainfall intensity (inches/hour)
A = Area in acresC = Runoff coefficient (dependent on surface type)
The Rational Method
5/21/2018 Presentation FM(Fall 2013)
190/208
The Rational Formula (with recurrence adjustment)
Q = Cf C i A
Q = Peak runoff rate (cubic ft/sec)
Cf= Runoff coefficient adjustment factor
C = Runoff coefficient (dependent on type of surface)i = Storm intensity (in./hour)
A = Area in acres
The Rational Method
5/21/2018 Presentation FM(Fall 2013)
191/208
The Rational Formula (with recurrence adjustment)
Q = Cf C i A
Return Period Cf
1, 2, 5, 10 1.0
25 1.1
50 1.2
100 1.25
Storm Characteristics
5/21/2018 Presentation FM(Fall 2013)
192/208
Duration (minutes or hours) during which rain fallsin a single storm
Depth (inches) of rainfall resulting from storm
Intensity (inches per hour)
depthintensity =
duration
Design Storm
5/21/2018 Presentation FM(Fall 2013)
193/208
Storm magnitude for which storm watermanagement facilities are designed
Dictated by local regulations
Described by return period and duration
Return period
Average length of time betweenstorms of a given duration and depth
100 year storm has a 1 percent chance of occurring inany given year
10 year storm has a 10 percent chance of occurring inany given year
Rainfall Intensity
5/21/2018 Presentation FM(Fall 2013)
194/208
Rainfall (storm) intensityfor a given design stormcan be found from maps,tables, or charts.
NOAA Tech. Paper No. 40
Rainfall Intensity
5/21/2018 Presentation FM(Fall 2013)
195/208
Intensity Chart for Gordon, PA
http://hdsc.nws.noaa.gov/hdsc/pfds/index.html
Rainfall Intensity
5/21/2018 Presentation FM(Fall 2013)
196/208
Intensity-Duration-Frequency (IDF) chart for Gordon, PA
http://hdsc.nws.noaa.gov/hdsc/pfds/index.html
Example
5/21/2018 Presentation FM(Fall 2013)
197/208
Suppose a developer purchased a 3-acre farm inNashville, Tennessee. A 30,000 sq ft asphalt parkinglot will be placed on the plot. Local regulations requirethat post-development runoff be limited to pre-development runoff for a 25 year, 1 hour rainfall.
Find the change in peak runoff (i.e., find the differencein the pre-developmentpeak runoff and post-developmentpeak runoff).
Pre-Development Analysis
5/21/2018 Presentation FM(Fall 2013)
198/208
A = Area of the property in acres
A = 3 acres
Using the Rational Formula (withrecurrence adjustment)
Q = CfC i A
Pre-Development Analysis
5/21/2018 Presentation FM(Fall 2013)
199/208
i = Rainfall intensityUse the Weather Bureau Intensity chart for Nashville, TN
(http://hdsc.nws.noaa.gov/hdsc/pfds/index.html)
i = 2.54 in./hr
Pre-Development Analysis
5/21/2018 Presentation FM(Fall 2013)
200/208
C = Runoff Coefficient
Pre-development: Farmland
From Rational Method Runoff Coefficients table
C = 0.05 0.3
Use an average
say
0.05 0.30.175 0.18
2C
Pre-Development Analysis
5/21/2018 Presentation FM(Fall 2013)
201/208
Cf= Runoff Coefficient adjustment factor= 1.0 for a 10 year storm.
Return Period Cf
1, 2, 5, 10 1.0
25 1.1
50 1.2
100 1.25
Pre-Development Analysis
5/21/2018 Presentation FM(Fall 2013)
202/208
cfs
(1.1)(0.18)(2.54)(3)
1.5
p r e f Q C CiA
Post-Development Analysis
5/21/2018 Presentation FM(Fall 2013)
203/208
i = Rainfall intensitySame as pre-development intensity = 2.54 in./hr
2
130000
43,560
acreA
ft
0.69 acres
3 0.69A 2.31 acres
Parking
Farmland
A = Area
Post-Development Analysis
5/21/2018 Presentation FM(Fall 2013)
204/208
C = Runoff Coefficient
Farmland: Use C = 0.18Asphalt pavement: Use C = 0.95
Post-Development Analysis
5/21/2018 Presentation FM(Fall 2013)
205/208
Composite Runoff coefficient, Cc
c
C A C AC
A A
1 1 2 2
1 2
( . )( . acres) ( . )( . acres)
acres
.
c
c
C
C
0 18 2 31 0 95 0 69
3
0 36
Post-Development Analysis
5/21/2018 Presentation FM(Fall 2013)
206/208
(1.1)(0.18)(2.54)(2.31) + (1.1)(0.95)(2.54)(0.69)=
= 3.0 cfs
( ) ( )p o s t f far m f p ar k in g
Q C CiA C CiA
= (1.1)(0.36)(2.54)(3)
= 3.0 cfs
p o s t f Q C CiA
ALTERNATE METHOD
Change in Site Runoff
5/21/2018 Presentation FM(Fall 2013)
207/208
Calculate the difference
= 3.0 cfs - 1.5 cfs
= 1.5 cfs
p o s t p r e Q Q Q
Storm Water Management Plan
5/21/2018 Presentation FM(Fall 2013)
208/208
The engineer uses this information to create astorm water management plan. This planwould include:
Release rate not to exceed the peak pre-development Q
Swales (ditches)
Storm water pipes