Monroe L. Weber-Shirk

School of Civil and

Environmental Engineering

Flow Control

Creativity without a tripVariations on a drip

Giving head loss the slip

Overview

Why is constant flow desirable? Reflections on Creative Design Constant head devices

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 householdFlow variations are hugeSystem 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 worksReagent addition for community treatment

processesAlumCalcium 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 Fixhttp://web.mit.edu/d-lab/honduras.htm

Reflections on Creative Design

Experience as Fuel for the Fire (or a prison that inhibits new ideas)

Be a Free Thinker Be an Extremist (variations over the domain)

List all the possible parameters that you could vary Vary them to the extreme (0 to infinity!)

Be a Reductionist Tear the problem apart Identify the essential components and the role of each of the

components Organize your ideas into a scheme showing relationships Evaluate your ideas Go back to the problem statement

3 ideas that are as unrelated as possible

Pick one

How will performance vary?

Is there something else that could fill the role?

Constant Head: Overflow Tanks

Surface tension effects here

What controls the flow?

2orifice orificeQ K A g h

h

orificeA

Constant Head: Floats

orifice

VERY Flexible hose

Head can be varied by changing buoyancy of floatSupercritical open channel flow!

Unaffected by downstream conditions!

2orifice orificeQ K A g h

h

Constant Head: Marriot bottle

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 2

2 2in in out out

in in P out out T Lp V p Vz h z h h

g g

Lh

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

Vena contracta0.6vc orificeA A

Orifice

2orifice orificeQ K A g h

h

0.6orificeK

Surface Tension

hIs the force of gravity stronger than surface tension?

343 2g wrF g

2rF=

Fp= 3

24 2 r3 2 wr g g h r 2g h r

Will the droplet drop?

Surface Tension:(droplet radius larger than h)

0.0500.0550.0600.0650.0700.0750.080

0 20 40 60 80 100

Temperature (C)

Surf

ace

tens

ion

(N/m

)

3 2

3 0.073

1000 9.8

Nmr

kg mm s

3

w

rg

4.7r mm

3

24 2 r3 2 wr g g h r

Surface Tension:(droplet radius smaller than h)

3 2

2 0.073

1000 9.8

Nmh

kg m rm s

3

24 2 r3 2 wr g g h r

2rg h

2hgr

2

1167,000

hr

m

0.1

1

10

100

0.1 1 10 100

r (mm)

h (m

m)

No flow!

Flow Control Valve (FCV)

Limits the ____ ___ 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

flow rate

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)PistonsGearsPeristaltic

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)

Be a Free Thinker Be an Extremist (variations over the domain)

List all the possible parameters that you could vary Vary them to the extreme (0 to infinity!)

Be a Reductionist Tear the problem apart Identify the essential components and the role of each of the

components Organize your ideas into a scheme showing relationships Evaluate your ideas Go back to the problem statement

3 ideas that are as unrelated as possible

Pick one

How will performance vary?

Is there something else that could fill the role?

Be a Reductionist

Tear the potential solutions apartIdentify the essential components and the role of each of the components

Identify substitutesConstant headHead loss that changes with flow

Integrate Flow Control Device (FCD) into the Bigger Project

What are the options for where you place the FCD?BeforeAfterUp flowDown flow

How is the FCD affected by changes upstream and downstream?

Identify the Failure Modes

Moving partsWearCorrosionPrecipitationIncompatible materialsCloggingDesign 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 componentsOr use components that are already mass

produced (and cheap)

Water Tight Connections!!!!

O’ring sealsPVC gluePipe threadsDuct tape

Budget and Machining

CEE is able to pay up to $30 per team for suppliesPaul Charles, Tim Brock or I can order supplies for youYour 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 supplies4” filter columns¼”, 3/8”, ½” flexible tubingConnectors

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?