Transcript Pumps and Pipes

Pumps and Pipes
©2012 Dr. B. C. Paul
Note- These slides refer to many concepts commonly understood by people
with training in the field and published in numerous textbooks no single one of
which was used in compiling these slides. These slides do contain
screenshots of the program Slysel which was developed by GIW. Credit for
the program is attributed accordingly. Some figures were taken from “The
Centrifugal Pump” by Grundfos Research and Technology
Our Materials Handling Problem
• Water shows up in a lot of places in
mines and we would rather have it
someplace else
• Water is used as a carrier in a lot of our
mining and mineral processing
operations.
• We get water into pipes and pump it
around
• That is what this unit discusses
Assumed
• You have or are taking Fluid Mechanics
• You understand things like
• Laminar and turbulent flow
• Reynolds number
• What the Bernoulli Equation is
• Because we are not covering these fluid
fundamentals
Basic Equation for Our Task is
Bernoulli's Equation (with slight
modifications for non-ideal fluids)
2
2
V
P1  V 1  
P
2
2




z
H
H
z
1
f
p
2
c 2g
c
2g
Basically this is Newton’s second law for incompressible fluid flow
If you have two points – point 1 and point 2 – energy (indicated by pressure)
will be conserved between the two points.
Translating the Equation
2
2
V
P1  V 1  
P
2
2
Hp

 z2
z
1 H f
c 2g
c
2g
Z is the elevation
If the fluid is higher at Z1 than at Z2 the there is more potential energy due to
Elevation at point 1 than at point 2
We need to pick some arbitrary “datum” from which to measure Z. People often
Pick sea level, surface level, or some mine level.
More Translation
2
2
V
P1  V 1  
P
2
2




z
H
H
z
1
f
p
2
c 2g
c
2g
V
2
2g
The term is called velocity head – fluid in motion has energy
From that motion. The energy is measured by the velocity
Squared divided by 2 times the gravitational constant g.
We Are Still Translating
2
2
V
P1  V 1  
P
2
2




z
H
H
z
1
f
p
2
c 2g
c
2g
Hf is the energy lost to friction. Friction results from drag on the fluid as it moves
Over the pipe surface, and the fluid dragging on itself due to turbulance.
Hp is the energy added to the system by the action of a pump.
The Last Term in Our Translation
2
2
V
P1  V 1  
P
2
2




z
H
H
z
1
f
p
2
c 2g
c
2g
P is the pressure the fluid is already under at some point
P
c
C is a constant to make sure the pressure term is in the same
Units as all the other terms in the equation. (We often use units
Of the pressure from a column of water 1 ft tall – ie – ft of water
Gage).
Often the pipe system is open to the air at both ends – in this case
There is no net pressure at either end and the term goes away.
Sometimes in processing we may be pumping water into a device
That requires the water at some pressure – now its not zero.
The Meaning
2
2
V
P1  V 1  
P
2
2




z
H
H
z
1
f
p
2
c 2g
c
2g
All the pressure in a pipe system at any point has to go somewhere and here is a
List of places it can go.
Lets Put This Equation to Work
(and meet a new software friend while we
are at it)
Back flow prevention
valve
Once upon a time there was a mine that needed
To pump water out of a collection sump in the
Mine into a drainage ditch on the surface.
pump
water
Ditch on the
surface
Fire-Up Slysel by GIW
(GIW is a pump company)
(Metso puts out a similar program
Called Pumpdim)
Oh – Way Cool – The Program
Starts
Click Ok that
You are not
Going to steal
The source
Code or sue
Them if your
Design does
Not work out.
Design Generally Will Require
You to work through a series of
tabbed inputs and outputs – left
to right
File and Help Have Drop Down
Menus
Most important is your ability to save and
Open specific projects saved in filenames
That you chose.
The Help Options
Pump manuals lets you review
Literature on pumps made by
GIW
The documentation area lets
You get to the program users
Manual
You can regularly go to the GIW
Website to update Slysel
Put In Our Title Information that
Will Appear on Output Reports
Pick Your Units
Usually Best to Just Take the
Default Program Operations
Options
Economics are An Important
Selection Criteria
Input the interest rate on
Capital. 10% is typical for
“levered” investments but
All investor equity in Mining
Is more like 15 to 18%.
GIW probably has best guess
On rebuild cost
Belt drive pumps are about 90% efficiency in moving
Power from motor to pump (electrical consumption is
Often a major cost)
Hours of operation is one of
Your design plan items
Your cost for power. Program calculates headloss but quick estimate gets costs in
The ballpark.
Click the Next Tab to Describe
Your Piping System
Two major relationships
Between pumps and
Sumps.
1- water level is higher
Than pump.
Water Level is Below the Pump
So Why Do I Care?
Common Centrifugal Pump Uses an blade
Or impeller in a metal housing.
The impellor spins imparting momentum to
The water or fluid. Once in motion water
Tries to travel in a straight line – right through
The pump outlet.
Now there is an absence of water – a kind of
Vacuum that will try to pull water into the
Pump.
The Pressure Difference
On the outside there is the weight
Of the atmosphere plus the height
Of the water column above the
Pump pushing down.
On the inside
There is a
Partial
vacuum
Water moves from higher pressure outside the pump to
Lower pressure inside and refills the pump.
You Did Say the Pressure Was
Higher Outside?
• Well – maybe not
• Things that push back from inside the
pump
• What ever fluid pressure that remains – no
pump draws a perfect vacuum – a zero.
• Vapor pressure of the liquid (there are always
molecules trying to break away from the fluid –
the hotter the fluid the more the pressure from
the break-away molecules)
And In This Corner On the
Outside
• The weight of the atmosphere
• (of course the higher the elevation the lower that
is)
• The pressure in the tank
• If there is no pressurized tank then its only the
weight of the atmosphere
• The pressure from the column of water above
the pump.
• But what if the water level is below the pump?
The Suction Lift
Atmospheric Pressure
Minus pressure of
Needed water column
Pressure of
The atmosphere
Pressure from
A column of water
Tall enough to
Get to the pump
Yipes!
Now the
Pressure
Outside is
Not higher
Than inside
Result
• No Water Flows into the pump
• This can also happen with hot liquids
that have a lot of back-pressure in the
pump from the vapor pressure of the
fluid.
So Why Do I Care About
Whether the Water Level is
Above or Below My Pump
• If it is below I better check my suction lift
or I may have a dry pump.
• (I also need to watch out if the
atmospheric pressure is very low or the
fluid has a very high vapor pressure)
Common Pipe Design
• Designs often have larger intake pipes
than discharge pipes
• Suction lift is absolutely limited by weight of
the atmosphere
• Want to limit frictional losses even though
the choice may not be most economic
• Have to make things work first
Enter My Basic Suction Lift Data
My pump is in an
Above water position
My project elevation is 8000 feet which does reduce
The weight of the atmosphere above.
I have a pump intake point that will always be 3 feet underwater.
My sump has up to 5 feet of freeboard. I am using a large pump that stays above
Water level.
What Happens to Water When It
is Discharged
• In this case I will
discharge it into an
open ditch at
atmospheric
pressure
• Ie – gage pressure of
0
• In processing I
might have a
required pressure as
I inject into a
cyclone.
Lets Start Describing Our Pipe
System
Back flow prevention
valve
We will fill in our line here
5
Ditch on the
surface
pump
8
water
The first thing that happens is the water comes in an inlet
This creates an extra disruption as water swirls into a confined
Environment. We deal with a K factor.
Describing Our Piping System
Note that when I type the name of the pipe portion
It goes immediately into the highlighted line.
We highlight the
Part of the system
We will describe
Before starting
The input line
Pipe Section Roughness
Applying the Stanton Diagram
In laminar flow frictional
Losses are a linear
Factor of Reynolds
Number.
2
H
f
PipeLength V
f*
*
PipeDiameter 2 g
Where the f from the
Stanton Diagram
Goes into the Darcy
Weisbach Equation
A Closer Look at Darcy
Weisbach
2
H
PipeLength V
f*
*
PipeDiameter 2 g
f
Stanton Diagram gets us this value of f used to calculate the frictional
Headloss.
2
2
V2 
P1  V 1  
P
2



c 2 g z1 H f H p c
2g z2
Hf is the term in the Bernoulli Equation which tells us how energy is distributed in
A pump pipe system.
Back to Our Stanton Diagram
In Turbulent Flow over
A perfectly smooth
Surface the value of
f declines at an incline
As a function of
Reynolds Number
The Transition Zone
At a point that depends
On disturbance of the
Water the water
Suddenly starts churning
And jumps from
Laminar to Turbulance
Flow.
Another Transition
Real pipe is never
Fully smooth which
Means bumps on the
Sides of the pipe
Pertrude into the
Churning and turbulent
Fluid.
At higher Reynolds
Number these bumps
Into the turbulent fluid
Fully control the pipe
Friction.
This area is called the
Wholly Rough Zone
The Wholly Rough Zone
In the Wholly Rough Zone the friction factor is
A constant that depends only on the design of
The pipe.
In pump and pipe problems almost all pumped
Flow is in the Wholly Rough Zone. Thus if you
Know what kind of pipe you have you know
Your friction factor.
Pipe Roughness In Slysel
Select the box with a right click
Left click to drop down a menu
Put the Curser on the common
Value line – out pops a side
Menu of friction factors for
Different types of pipe
Left click on your type of pipe.
I’m going to assume High
Density Polyethylene plastic
Pipe.
Click Enter and the HDPE Value
Goes in and it Moves to the Next
Box
Oh the Nasty Catch
It wants
Internal pipe
diameter
Do the right click and menu trick to get a
List of standard sizes.
My HDPE is 10 inch schedule 80.
Press Enter
Now we describe the length of this section of pipe.
We Enter the Length and Rise for
the first section of pipe
Our Last Challenge is that K value
K values are used to describe “shock” or minor losses such as in this case water
Moving from an open sump into the open end of a submerged pipe.
K Values
• Minor losses are
described by the
following equation
2
V

K
*
H
2g
f
K values depend on what is being encountered.
In our case it is water going from an open sump into a confined pipe.
Time for the Good Old Right
Click Trick
And We Are Done With Our First
Length of Pipe
Move to Our Second Section of
Pipe
Back flow prevention
valve
Ditch on the
surface
This section of pipe has
No rise in elevation
5
pump
water
But it does have a 90
Degree bend in a piece
Of pipe 8 to 10 inches
In diameter (which is why
We have to pick a K
Factor)
Doing My 3rd Section of Pipe
Back flow prevention
valve
Ditch on the
surface
pump
water
1200 feet
As is common my outlet
Pipe is smaller than the
Inlet pipe – in my case
It is 8 inches.
Now for My Lift to the Surface
Back flow prevention
valve
Ditch on the
surface
600 feet
pump
water
In this case I have a
90 degree elbow in a
Piece of 8 inch pipe.
Enter My Next Section
Back flow prevention
250 ft.
valve
Ditch on the
surface
This one features a gate
valve
pump
water
Why A Gate Valve?
• The Case of the Illinois Quarry
• There was a sump in the bottom of the
quarry that pumped water to the surface
and into a ditch.
• They had a heavy rain. The pump worked
and filled the ditch to where the pipe
discharge was below the ditch water level.
• Then the power went out.
What Do You Call This?
Oh My Gosh It’s a Siphon!
They filled the quarry half way with water
And almost lost the equipment before
God had mercy on their poor stupid souls
And stopped the rain.
After that they put in a valve so they they
Could stop backflows.
Now Lets Do the Line Coming
Out of the Gate Valve
Back flow prevention
valve
5
pump
water
Ditch on the
surface
Finishing My Pipeline
Back flow prevention
valve
2
Ditch on the
surface
pump
water
Commentary #1
• Slysel’s menu includes K values for most
common single minor losses
• Of course for combinations the possibilities are
infinite
• I broke my pipe sections so that no section
had any more than 1 minor loss
• I could have more than 1 minor loss in a
section but then I would have to separately
add up and enter the K values
Commentary #2
Note that the K factor for
A minor loss when the
Water discharges to the
Open is 1.
2
V

K
*
H
2g
f
When water discharges the entire body of
Energy associated with its momentum is also
Discharged.
(With mine ventilation fans it is common for the
Discharge to pass out an expanding cone called
An evasay – this drops the air velocity and cuts
The energy loss at the discharge – mine water
Volumes are usually much less than air volumes).
We Move Now to Pump Duty
or how much of what will we pump today
What Shall We Pump Today?
Note that the default properties of the liquid and slurry are for plain ordinary water.
We can use Slysel for selecting pumps for slurries but we won’t do that now.
Now For Entering How Much
I put in my
Quantity of water
And then checked
To let Slysel
Use my pipe
System to
Calculate the
Required pump
Head.
It filled in a bunch
Of other blanks
Including my
Total Head
Requirements.
Commentary on Service Class
• Service class does not seem to have a
definition that all agree on.
• It has to do with how much of the time it
runs and how critical that it is
• Things running more than about 2500
hours a year that are fairly critical seem
likely to be called class 1 duty
• Class one pump duty will result in pumps being
selected with tighter more critical specs.
You Can Filter and Limit Pump
Choices
But we won’t do that now.
Horizontal Pipe Flow Page
Checks for Slurries Settling Out
Not a big
Concern for our
Water pumping
Operation.
Pipeline Results is mostly on
what happens with a settling
slurry
Again a less
Critical
Parameter for
A water pump
Operation.
Next Tab Gives You a Chance to Do
Some Detail Pump Configurations
Your not well
Trained to do
That yet.
Now Lets See Which Pump it
Picked? – Best Selections Tab
Ouch it says no
Standard pump
Met our
Criteria.
So How Is this Selection Thing
Suppose to Work?
Each Pump has a output curve such as this.
The Centrifugal pump has spinning
Impellers that can put out a given
Amount of energy. That could be
High pressure for a small amount
Of liquid – or low for a lot.
The Pipe System
Head
At very low flow there is almost no frictional
Loss, but there is still the pressure of the lift
Of the water to overcome.
Water Volume
The Pipe System
As the flow quantity increases, loss from
Friction (and velocity head) increase.
Thus the shape of the pipe curve.
Head
Water Volume
Hooking Pumps and Pipes
Together in a System.
The system
Operates at the
Intersection of the
Pump curve and
The pipe curve.
It is the only point
Where both the
Pump and the pipe
Can operate.
So Why Didn’t It Work for Us?
These are the operating
Ranges for a bunch of GIWs
Pumps.
Getting 2500 GPM is easy
But the pumps only can put
Out about 300 ft of head.
(our static lift is 600 feet)
This is Us
Our Pipe Curve
Head
Pump Curve
Water Volume
How Could We Soup Things Up
a Bit?
• It works by momentum – lets speed up the
impeller!
NewSpeed
SpeedRatio
OldSpeed
Q
H
 Q * SR
Quantity goes up linearly with
speed

*
H
new
old SR
Head goes up with the square
Of the speed
new
old
2
Up – Up and Away Goes the
Curve
Just one little problem –
Spinning impellers
Produce back-thrust
Against the bearings.
They have pumps seals
Around a rotating
Shaft that have to work.
About 3600 RPM is
Highest typical speed.
I need a little more than
4 times the head – means
I need around 8000 RPM
We Could Use a Bigger Impeller
Get more speed
At the tip.
Many Pump Curve Have Multiple
Curves
They represent
Putting in bigger
impellers
Ouw- That Might Not Work
• I have a feeling I’m getting back to limits
on thrust against bearings on the
impeller shaft.
We might also have some impeller
Clearance and wear problems if there are
Particles in the water larger than the
Impeller to pump housing clearance.
(I found that out after one of my slurry pumps
Lost most of its pressure after the first half
Hour of operation).
How About Using Two Pumps?
The quantity that can be
Produced at a given head
Will double.
The problem is the given
Head does not change –
And we can’t make our
Static lift.
Pumps in parallel.
Ok – How About Adding in Series
In this case the head adds
Multi-stage pumps are
Actually built for such
applications
I Will Tell Slysel to Try 2 Pumps
in Series
Now I Have Choices on the Best
Selections Tab
Of course figuring out how to read this stuff
May be quite another matter.
Pump Codes
The first number is the pump
Outlet size
The second number is the pump
Inlet size.
(Since my pipe sizes are 10 inlet
And 8 outlet – I’d like an 8X10)
Third number is the impeller
Diameter.
Rest of the stuff is some real
Detailed pump construction
Codes.
Slysel Lists Pumps by Effeciency
Here is my top 8X10 choice – I’m pick it.
(It matches my chosen pipe sizes)
I’m running at a speed
Of 1380 RPM with a
Pump Efficiency of 68%
I will require 345 HP to run
The system.
Highlight and Click
I get some design choices in the middle box
(again details of pump construction are beyond our scope)
Now I Have A Report with Loads
of Stuff In It.
I’m going to check to
Make sure my
Suction lift is not going
To foul-up.
At My Elevation I Have 28 ft of
Head Available.
I require 13.6 – looks good
Scrolling Down It Gives Me
Points on My Pump Curve
One disturbing thing I note is that I’m running my pump well off of its efficiency
Sweet spot.
This Sounds Like a Job for My
Victims – Woops I Mean
Students
• I arbitrarily picked 10 inch and 8 inch pipes
• I arbitrarily picked 2 staged pumps
• Work with Slysel to produce a higher pump
efficiency and lower total horsepower
requirement.
• Minimum requirement (break 75%)
• Bonus points for the most efficient
Can Get Slysel for Yourself
• http://www.giwengr.com/GIWSLYSELusers.htm