Transcript Vacuum break level control

Team Aquifers:
Flow Control Device
James Berg
Jamison Hill
Stephen Russo
Scott Weeks
CEE 454 - December 2004
Outline
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Introduction
Project Goals
Design Process
Our Design
Test Results
Use in Developing Countries
Recommendations for Further Research
System Modeling
Conclusions
Project Goals
Create a Point of Use Flow Control Device
THAT…
 Maintains constant flow rate (20 L/day)
through a slow sand filter
 Is easy to build, use, and maintain
 Has a low cost of construction
 Uses common materials
Our Design Process
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Brainstorm ideas:
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Float Valves
Clock Mechanism
Pulley/Balance
Chicken Waterer
Elimination based on design criteria
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No/minimal moving parts
No precision machining
Easy to adjust flow rate and maintain the system
Preliminary Design
Our Design: How it Works
Airtight
Raw Water
Tank
Aspirator
Tube
Filter
Constant
Head Basin
Clear Well
Orifice
Flow Control Animation
hL
Aorifice
Surface tension
effects here
Range of Flow Rates: Equations for
Constant Head Above an Orifice
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Flow rate:
Q  K orifice Aorifice 2 gh
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Surface Tension:
F  2r
Force of Gravity on a drop:
Fgravity
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4r 3

w g
3* 2
Pressure force from water above:
Fpressure   whr 2
Range of Flow Rates: Analysis
Range of Flowrate
35
30
(L/day)
Flow Rate
Head (cm)
25
20
Series1
15
No flow
10
5
Sufficient head
for flow
0
0
2
4
6
8
10
12
14
Flowrate (L/d)
Head
(cm)
Range: 16.5 – 28.6 L/D
16
Testing the System
Test Results: Volume in Clear Well
Steady flow into clear well = 14 mL/min
3000
2500
2000
volume (mL)
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1500
1000
500
0
0
2000
4000
6000
8000
10000
12000
14000
time (sec)
Graph: Volume in Clear Well vs. Time
Test Results: Derivative of Volume
30
flowrate (ml/min)
25
20
15
10
5
0
0
2000
4000
6000
8000
10000
12000
14000
time (sec)
Graph: Flow (Derivative of Volume) vs. Time
Test Results: Flow Through Filter
BUT flow through the filter varied greatly!!
180
160
140
120
flowrate (mL/min)
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100
80
60
40
20
0
0
2000
4000
6000
8000
10000
12000
14000
-20
time (sec)
Graph: Flow through Slow Sand Filter vs. Time
Testing: Steady State Solution???
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Observation: When vacuum in raw water
tank is completely lost, flow increases
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Hypothesis: Can minimize flow peaks by
maintaining vacuum in the tank
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Solution: Small hole in the side of the
aspirator tube allows steady flow of air
bubbles
Test Results: Conclusions
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Able to control the average flow rate out of the
flow control device
The flow through the sand filter was very
inconsistent
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Spikes of high flow
Long periods of no flow
Achieved high removal of turbidity
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Raw water initially had turbidity of 90 NTU
Water in the effluent had turbidity of 3 NTU
Applications in Developing World
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As a flow control device for chlorine or alum
delivery, our device is:
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Cheap
Easy to build
Has no moving parts, so as not prone to failure
With more research, it might be successfully used
after a sand filter. In this case, it also:
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Controls the flow of clean water, so it will not clog an orifice
Can be used for water that is extremely dirty as long as the
filter is working properly
Restrictions to Use in Developing
World
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Prototype was made from lab materials
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PVC could replace flexible tubing
Almost any type of waterproof container could be used for
the flow control basin
Biggest obstacle: creating an airtight raw water
tank
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We considered trying to make a regular 5 gallon bucket
airtight, but realized it would be hard to get it to form a
vacuum quickly.
Need Further Research!
Future Research
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Areas of focus:
Build with easily obtainable materials
 Test it as a chlorine delivery mechanism
 Minimize spikes
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Mathematical Model
Modeling our system
mathematically
Using a system of first-order nonlinear differential equations
Why Model
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We know our basic device works
Improve the design by testing (much
quicker through computer simulations!!)
Investigate fundamental relationships
 Investigate ways to improve device (adjusting head
loss, air flow)
 TWEAK Parameters
 As an example, it took me 6 seconds to simulate a 6
hour filter run
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The Model
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A system of three simultaneous differential
equations models:
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Rate of change of volume in the upper tank
Volume in the basin
Moles of air in upper tank
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Uses Energy Equation, Continuity (mass balance),
Darcy-Weisbach, Ideal Gas Law, and Orifice Flow
Equation
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Details on your handout
Model Diagram
Qair,Qwater
P=Ptank
CS#1
zt
Zt,o
aspirator
P=Patm
Tank
Qin
htube
CS#2
Basin
Zt,1
H
z=0
resistor
Filter
orifice
Qout
Simulation Results
Flow Through Filter
A Constant Head Device?
Conclusions
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Not a constant head device
But works as a good flow control,
oscillations small and approach zero with
increasing time
A self-dampening oscillator that approaches
steady-state.
Further tweaking will allow us to reduce
bias, and overshoot, calculate decay function
for peaks
Questions???
THE END