Flow Control
Creativity without a trip
Variations on a drip
Giving head loss the slip
Monroe L. Weber-Shirk
School of Civil and
Environmental Engineering
Overview
 Why is constant flow desirable?
 Reflections on Creative Design
 Constant head devices

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





Overflow tanks
Marriot bottle
Floats
Float valve
Orifices and surface tension
Flow Control Valve
If you had electricity
Variable head loss in the unit process
Why is constant flow desirable?
Slow constant treatment can use a smaller
reactor than intermittent treatment
It isn’t reasonable to expect to treat on
demand in a household
Flow variations are huge
System would be idle most of the time
Use a mini clearwell so that a ready supply
of treated water is always available
Applications of Constant Flow
Make a POU SSF that works
Reagent addition for community treatment
processes
Alum
Calcium or sodium hypochlorite
Could you make a meter that increased the
dose in proportion to the main flow?
UV disinfection, clay pot filters, arsenic removal
Hypochorinator Fix
http://web.mit.edu/d-lab/honduras.htm
Reflections on Creative Design
 Experience as Fuel for the Fire (or a prison that inhibits
new ideas)
3 ideas that are as unrelated as possible
 Be a Free Thinker
 Be an Extremist (variations over the domain)
Pick one
 List all the possible parameters that you could vary
 Vary them to the extreme (0 to infinity!)
 Be a Reductionist
How will performance vary?
 Tear the problem apart
 Identify the essential components and the role of each of the
components
Is there something else that could fill the role?
 Organize your ideas into a scheme showing relationships
 Evaluate your ideas
 Go back to the problem statement
Constant Head: Overflow Tanks
h
Aorifice
Surface tension
effects here
What controls
the flow?
Q  Korifice Aorifice 2 g h
Constant Head: Floats
Q  Korifice Aorifice 2 g h
Head can be
varied by
changing
buoyancy of
float
h
orifice
Supercritical
open channel
flow!
VERY Flexible hose
Unaffected by downstream conditions!
Constant Head:
Marriot bottle
hL
 A simple constant
head device
 Why is pressure at the
top of the filter
independent of water
level in the Marriot
bottle?
 What is the head loss
for this filter?
2
Vin2
pout
Vout
 zin   in
 hP 
 zout   out
 hT  hL

2g

2g
pin
Constant Head: Float Valve
Float adjusts opening
to maintain relatively
constant water level in
lower tank
(independent of upper
tank level) ?
Describe sequence of events after filling
Hole in a Bucket
h
Orifice
Avc  0.6 Aorifice
K orifice  0.6
Q  Korifice Aorifice 2 g h
Vena contracta
Surface Tension
Will the droplet drop?
Is the force of gravity stronger than surface tension?
4 r 3
Fg 
w g
3 2
Fs= 2rs
4 r 3
 w g   g h  r 2   2 rs
3 2
2

g

h

r


F p=
h
4 r 3
 w g   g h  r 2   2 rs
3 2
3s
r
w g
N

3  0.073 
m

r
1000 kg  9.8 m 

3 
2 
m 
s 

r  4.7 mm
Surface tension (N/m)
Surface Tension:
(droplet radius larger than h)
0.080
0.075
0.070
0.065
0.060
0.055
0.050
0
20
40
60
80 100
Temperature (C)
Surface Tension:
(droplet radius smaller than h)
4 r 3
 w g   g h  r 2   2 rs
3 2
h 
2s
 gr
N
2  0.073 
m

h 
1000 kg  9.8 m  r

3 
2  
m  s 

1
h 
 67,000 1  r

2  
m 

100
h (mm)
2s
r
 g h
10
1
No flow!
0.1
0.1
1
10
r (mm)
100
Flow Control Valve (FCV)
Limits the ____
___
flow rate
through the valve to a
specified value, in a
specified direction
Calculate the sizes of
the openings and the
corresponding
pressures for the
flows of interest
Variable Process Head Loss
How do you design the system so that
increasing head loss in the unit process does
not result in decreasing flow rate?
Goal is no communication between process and
flow control device!
Of course, eventually high head loss will cause
some sort of failure (but you can make this be a
pleasant failure!)
If you had electricity…
 Metering pumps (positive displacement)
 Pistons
 Gears
 Peristaltic
 Valves with feedback from flow sensors
 So an alternative would be to raise the per capita
income and provide electrical service to
everyone…
 But a simpler solution would be better!
Reflections on Creative Design
 Experience as Fuel for the Fire (or a prison that inhibits
new ideas)
3 ideas that are as unrelated as possible
 Be a Free Thinker
 Be an Extremist (variations over the domain)
Pick one
 List all the possible parameters that you could vary
 Vary them to the extreme (0 to infinity!)
 Be a Reductionist
How will performance vary?
 Tear the problem apart
 Identify the essential components and the role of each of the
components
Is there something else that could fill the role?
 Organize your ideas into a scheme showing relationships
 Evaluate your ideas
 Go back to the problem statement
Be a Reductionist
Tear the potential solutions apart
Identify the essential components and the
role of each of the components
Identify substitutes
Constant head
Head loss that changes with flow
Integrate Flow Control Device
(FCD) into the Bigger Project
What are the options for where you place
the FCD?
Before
After
Up flow
Down flow
How is the FCD affected by changes
upstream and downstream?
Identify the Failure Modes
Moving parts
Wear
Corrosion
Precipitation
Incompatible materials
Clogging
Design errors…
Flow Control of Dirty Water
 Come up with at least 3 very different ways to get
around the clogging problem (may be context
specific)
 Why are you trying to control the flow of dirty
water?
 How could you eliminate the possibility that a
single particle could clog the FCD?
 How could you make your FCD able to handle
more particles?
 How could you make a FCD that could be easily
cleaned?
How could you reduce cost?
Size!
Use commonly available materials (tire
tubes, PVC pipe, bottles)
Eliminate precision components
Or use components that are already mass
produced (and cheap)
Water Tight Connections!!!!
O’ring seals
PVC glue
Pipe threads
Duct tape
Budget and Machining
 CEE is able to pay up to $30 per team for supplies
 Paul Charles, Tim Brock or I can order supplies for you
 Your team must keep track of your expenses
 Tim Brock is willing to supervise/assist you with
simple machining or fabrication tasks in the CEE
shop (basement of Hollister)
 Call (5-4201) or email ( teb4) to set up a time (between
1 and 4 pm)
This information is at the website
Where do you get supplies?
 Lab supplies
 4” filter columns
 ¼”, 3/8”, ½” flexible tubing
 Connectors
 Online Hardware store (McMaster)
http://www.mcmaster.com/
 Lab/medical supplier (Fisher Scientific)
https://www1.fishersci.com/
 Home Depot!
This information is at the website
Progress Report (1)
 Classify your flow control schemes according the
fundamental principles that each flow control
device uses. Represent this classification of flow
control devices in an outline form or (even better)
as a graphic.
 Evaluate the strengths and weaknesses (failure
modes) for each of the schemes. Explain what
strategies you will use to mitigate the failure
modes.
Progress Report (2)
 If you are designing your flow control device for a
particular application, describe how that
application is influencing the design. In any case,
explain how your flow control device will be used
and include a sketch showing how it will be
connected to the treatment process.
 Show design calculations that you used to
determine the sizes of the various components of
your flow control device. Explain what
constrained the size and what would fail if it were
made smaller.
Progress Report (3)
 Sketch to scale the most promising designs that you are
investigating.
 Pick the design that you plan to build and explain why it is
the best choice.
 Calculate the range of flow rates that your device will be
able to produce.
 List the materials that you will need to construct the device
including supplier, part numbers, and cost.
 Describe any machining or fabrication assistance that you
will need.
Reflections
Engineered design (not just trial and error!)
Explore as many possibilities as you can on
paper and assess which ones are the most
promising to succeed
Can you make a simple module that can be
used in many applications?