BasicHydraulics - PowerPoint PPT Presentation

Title: BasicHydraulics


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BasicHydraulics João Madureira
1st AQUALITY Symposium, April 2 - 7, 2004,
Oceanario de Lisboa, Portugal
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I still dont know how he does it!
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INTRODUCTION Hidraulics has accompained human
kind since very early stages, and it probably
started with the necessity of transporting water
to crops in Mesopotamia. Today hydraulics is one
of the most important areas in mechanics and is
present almost everywere.
1st AQUALITY Symposium, April 2 - 7, 2004,
Oceanario de Lisboa, Portugal
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TOPICS 1 Fluid Definition and Properties
viscosity density and specific gravity
pressure. 2 Characteristics of the fluids
transport speed flow friction the Reynolds
Number. 3 Flow in ducts Bernoulli's equation
minor losses in pipe systems (PVC pipes,
elbows, valves...). 4 Pumps types
centrifugal pumps available suction and
compression head performance curves
cavitation NPSH. 5 Calculations a practical
example presentation of the tables. 6 Water
hammer limitations on valve actuation (manually
or automatic). 7 References books and web
sites.
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FLUID DEFINITION AND PROPERTIES Definition of a
fluid matter that can not resist a shear stress
any shear stress applied to a fluid, will
result in motion of that fluid. Pressure Pa or
N/m2 stress at a point in a static
fluid. Viscosity ?(p,T) kg/(m.s) measures the
resistence to shear stress. Different from
kinematic viscosity (??/?). Density ?(p,T)
kg/m3 mass per unit volume. Specific gravity
ratio of a fluid density to a standard reference
fluid.
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1st AQUALITY Symposium, April 2 - 7, 2004,
Oceanario de Lisboa, Portugal
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CARACTERISTICS OF THE FLUID TRANSPORT Speed
m/s thrown distance per unit time. Flow
m3/s thrown volume per unit time. Friction
drag resistance to motion. The Reynolds Number
Re named after Osborne Reynolds (1842-1912),
its a dimensionless number and charecterises
the viscous behavior of newtonian fluids.
Re?.V.L/?
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1st AQUALITY Symposium, April 2 - 7, 2004,
Oceanario de Lisboa, Portugal
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FLOW IN DUCTS Bernoullis Equation Named after
Daniel Bernoulli (1700-1782) its the relation
between pressure, velocity and elevation in
frictionless flow. Its fundamental when
calculating headloss in a pipe system to write
this equation properly. In order to aply this
equation to a real problem, we need to convert
friction head losses in pressure losses (or
height).
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1st AQUALITY Symposium, April 2 - 7, 2004,
Oceanario de Lisboa, Portugal
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Example Q150 m3/h d250 sucton pipe ? fluid
velocity of 1,04 m/s d200 compression pipe ?
fluid velocity of 1,62 m/s. Z16m Z24,5m
Z31,5m From the equation below we will get the
TDH that will be the height the pump must
provide. On the left side of equation is suction
and on the right is compression. Note that
this equation does not take into account friction
head losses. TDH is greater then 6 m because of
the change in the energy of the fluid (increase
of speed).
1st AQUALITY Symposium, April 2 - 7, 2004,
Oceanario de Lisboa, Portugal
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• MINOR LOSSES
• Minor losses are the result of friction when a
  fluid is flowing on a duct. Most common ducts in
  aquaria are pipes and of those the great majority
  is in PVC. The most practical way to calculate
  those is using the manufacturer data.
• We can separate minor losses in two categories
• ? Pipe losses it gives a head loss per meter
  (feet) of pipe length.
• Valves and fittings it gives a head loss per
  unit. Valves will
• have different head losses for different
  opening positions.
• It is easier to have those head losses calculated
  in meters (or feet).

1st AQUALITY Symposium, April 2 - 7, 2004,
Oceanario de Lisboa, Portugal
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• PUMPS
• A pump is a machine that adds energy to a system.
  They are as old as 1000B.C. (the undershot-bucket
  waterwheel). They can be divided in two different
  types
• Positive displacement pump force the fluid
  along with
• volume changes (plunger, squeegee,).
• Dynamic pump acelerates the fluid on a casing
  by
• rotary movement (centrifugal pump).
• The most common pump in aquaria is the
  centrifugal pump. As all dynamic pumps, the flow
  can be controlled by flow restriction on the
  compression of the pump.

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1st AQUALITY Symposium, April 2 - 7, 2004,
Oceanario de Lisboa, Portugal
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TYPES OF CENTRIFUGAL PUMPS ? Radial flow
centrifugal force ? Axial flow forced by
impeller vanes ? Mixed flow both SOME PUMP
TERMS ? Atmospheric pressure ? Absolute
pressure ? Vacuum ? Specific Gravity ? Suction
head ? Suction lift ? Total dynamic
head ? Cavitation
1st AQUALITY Symposium, April 2 - 7, 2004,
Oceanario de Lisboa, Portugal
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PUMP PERFORMANCE CURVES
1st AQUALITY Symposium, April 2 - 7, 2004,
Oceanario de Lisboa, Portugal
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1st AQUALITY Symposium, April 2 - 7, 2004,
Oceanario de Lisboa, Portugal
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CAVITATION Very destructive phenomena that
occurs when the pressure of the fluid drops below
vaporization point. The result is the formation
of tiny bubles that colapses when pressure
increase on the impeller. Those implosions work
as small explosions on the impeller that will
destroy it. Itll happen mainly for 3
reasons ? Bad system design. ? Clogging of
pre-filters. ? Valves closed on the suction
side. Cavitation is audible in the form of high
pitch screeching.
1st AQUALITY Symposium, April 2 - 7, 2004,
Oceanario de Lisboa, Portugal
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1st AQUALITY Symposium, April 2 - 7, 2004,
Oceanario de Lisboa, Portugal
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1st AQUALITY Symposium, April 2 - 7, 2004,
Oceanario de Lisboa, Portugal
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• NPSH _ net positive suction head
• Pressure on the centre of the impeller. A
  centrifugal pump, to operate, needs to be
  pressurized. There are two different NPSH
• NPSHA Available NPSH takes into account
  friction losses,
• heights and vapour pressure of the fluid.
• NPSHR Required NPSH manufacturer data that
• determines point of cavitation under specified
  conditions.
• NPSHA gt NPSHR
• Otherwise pump will cavitate.

1st AQUALITY Symposium, April 2 - 7, 2004,
Oceanario de Lisboa, Portugal
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NPSHA _ net positive suction head (available)
1st AQUALITY Symposium, April 2 - 7, 2004,
Oceanario de Lisboa, Portugal
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The equation is diferent from suction lift to
flooded suction
SUCTION LIFT
Pa - atmospheric or reservoir pressure Zi -
height from water level to pump inlet Pv -
vapor pressure of the fluid hfi - friction
losses on the suction side
1st AQUALITY Symposium, April 2 - 7, 2004,
Oceanario de Lisboa, Portugal
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FLOODED SUCTION
Pa - atmospheric or reservoir pressure Zi -
height from water level to pump inlet Pv -
vapor pressure of the fluid hfi - friction
losses on the suction side
1st AQUALITY Symposium, April 2 - 7, 2004,
Oceanario de Lisboa, Portugal
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PRACTICAL EXAMPLE The following example will
help setting down some ideas.
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1st AQUALITY Symposium, April 2 - 7, 2004,
Oceanario de Lisboa, Portugal
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• EXAMPLE
• PVC piping
• Q150 m3/h
• d250 sucton pipe ? fluid velocity of 1,04 m/s
• d200 compression pipe ? fluid velocity of 1,62
  m/s.
• Z16m Z24,5m Z31,5m
• Suction carachteristics
• ? 2 x 90º elbows and 3 meters of piping
• 1 x 100 opened buttwerfly valve
• 4 meters pipe
• ? 1 prefilter
• Compression carachteristics
• ? 2 x 45º elbows
• 1 x 50 opened butterfly valve
• 15 meters of pipe
• ? 1 rapid sandfilter with 1,5 bar drop pressure
  at rated flow

1st AQUALITY Symposium, April 2 - 7, 2004,
Oceanario de Lisboa, Portugal
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STEP 1 Write Bernoullis equation
1st AQUALITY Symposium, April 2 - 7, 2004,
Oceanario de Lisboa, Portugal
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STEP 2 Calculation of minor head
losses. Suction 2 x 90º Elbow hfi 2 x 0.04961
m 0.09922 m 1 100 open butterfly valve hfi
0.02105 m 4 meters d250 pipe hfi 4 x
0.00412 0.01648 m 1 pre-filter 12 clogged
hfi0.3 m Suction has a total of 0.09922
0.02105 0.01648 0.3 0.43675 m in minor
losses
1st AQUALITY Symposium, April 2 - 7, 2004,
Oceanario de Lisboa, Portugal
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Compression 2 x 45º elbow hfi 2 x 0.04443 m
0.08886 m 1 50 open butterfly valve valve
hfi 0.70685 m 15 meters d200 pipe hfi 15 x
0.01193 0.17895 m 1 sandfilerfilter 1.5 bar 15
m Compression has a total of 0.08886 0.70685
0.17895 15 15.9747 m in minor losses
1st AQUALITY Symposium, April 2 - 7, 2004,
Oceanario de Lisboa, Portugal
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Oceanario de Lisboa, Portugal
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Oceanario de Lisboa, Portugal
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Oceanario de Lisboa, Portugal
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Oceanario de Lisboa, Portugal
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We can now calculate our TDH It is wise to
apply a safety factor. Well aply 30. The result
is a final TDH of 29 m.
1st AQUALITY Symposium, April 2 - 7, 2004,
Oceanario de Lisboa, Portugal
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STEP 3 PUMP SELECTION For this application well
go for a horizontal centrifugal pump
1st AQUALITY Symposium, April 2 - 7, 2004,
Oceanario de Lisboa, Portugal
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1st AQUALITY Symposium, April 2 - 7, 2004,
Oceanario de Lisboa, Portugal
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WATER HAMMER Phnom result of fast manoeuvre of
valves or pump stop. Fast acceleration or
deceleration of the fluid will produce a pressure
wave that will reflect upstream and return
creating a loud bang followed by others of less
intensity. Quarter turn valves are peticularly
dangerous. Staff should be trained on valve
operation. Opening and closing times of actuated
valves should be calculated in order to avoid
phenomena. The following monograph may be used
for that purpose.
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1st AQUALITY Symposium, April 2 - 7, 2004,
Oceanario de Lisboa, Portugal
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200 ft pipe 20 fps velocity valve closure time of
1 second Result transient pressure pulse of 270
psi
1st AQUALITY Symposium, April 2 - 7, 2004,
Oceanario de Lisboa, Portugal
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REFERENCES BOOKS 1_ F. M. White, Fluid
Mechanics, WBC/McGraw Hill, Singapore,
1999. 2_ J. E. Huguenin and J. Colt, Design and
operating guide for aquaculture seawater
systems, Elsevier, Netherland, 1992. 3_ George
Fischer GF, Industrial Piping Systems-
Planning Fundamentals, Georg Fischer AG,
Schweiz, 2002. WEBSITES http/www.pumpworld.com/
http/Imoneng.com/
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1st AQUALITY Symposium, April 2 - 7, 2004,
Oceanario de Lisboa, Portugal
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João Madureira Basic Hydraulics
1st AQUALITY Symposium, April 2 - 7, 2004,
Oceanario de Lisboa, Portugal