Transcript Microfluidics and Valve Design

Microfluidics and
Valve Design
Mark Barineau
Ryan Slaughter
March 12, 2009
Presentation Overview
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Lincoln Laboratory goals
Micro- and Macroscale
Fluidics
Governing Physics
Valve and Actuator
Types
Related Technologies
Butane/LPG Properties
FEA Intro
Critical Findings
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Distinction between microfluidics and
microvalves
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Applicable valve, actuator, and sensor
technologies have been developed
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Butane/LPG is a good choice
LL: Fuel Metering Valve
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Need compact, low-mass system to meter fuel flow in prototype TE
microgenerator system
 Relevant to other micropower applications, as well
Design goals:
 Automatic control to accommodate varying electrical loads
 Compensate for fuel vapor pressure
 Integration into fuel tank plumbing
 Very low mass: < 10 grams including tank adapter
 Very low power: < 50 mW
 Operability with LPG fuels: butane and propane
 Act as compact massflow controller
LL: Candidate Performance
Specification
Specification
Value
Comments
Target Fuel
Butane, LPG
Full scale massflow
200 sccm
Control Range
20% to 100%
and Off
Valve should be capable of being
commanded to these set positions using
TBD electrical signal (PWM, analog, or
other)
Fuel Temp
10C to 40C
Wide vapor pressure range is significant
design challenge
Accuracy
+/- 20% of Set Point
Allowable Pulsation
0 to 200% of FS
0 to 150% of FS
0 to 120% of FS
Power Consumption
< 50 mW
@ 3 to 6 VDC
Mass
< 10 grams
Interface
TBD
Average over any 1 second interval
< 10 msec
10 to 50 msec
> 50 msec
Includes any power dissipation for control
signals
In: LPG Fuel canister
Out: Fluoropolymer tubing
Electrical: Flying Lead
LL: Valve Concept
Fuel
Mass Flow
Fuel
Pvap(T)
Temp
Flow SP
Pressure Regulator
Low Frequency
DC modulation
Flow Regulator
Pulse Width
Modulated
Valve Controller
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Rough concept for initial performance requirements
 Actual requirements driven by more thorough
design review
Valve Components
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Fluid reservoir
Actuator
Restrictive element
Sensor(s)
Controls
Interconnects
Micro- vs. Macrofluidics
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Microfluidic—devices and/or flow
characteristics
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Knudsen number
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Kn<0.3, Continuity
 Kn>0.3, Statistical mechanics
Fluids (2.005) Review
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Navier-Stokes Eq.
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Mass Continuity
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Reynolds Number
Microvalve Design
[image of microvalve
(Koch pg 167?)]
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[diagram of microvalve
(Koch pg 155?)]
Physics are macro
Valve size is micro
Active versus passive
valves
• valve components
• normally open,
normally closed,
bistable
• valve properties
o leakage
o closing force
o valve capacity
Actuators
General valve features
Actuation Force
Diaphragm
Valve seat
Inlet
Outlet
Some functional requirement
considerations:
• Holding function/ leakage
• Dynamic function/
response time
• Energy density
• Efficiency
• Simplicity/ feasibility/ time
• Environmental factors
• Valve capacity
• Costs $$$
Actuator Technologies
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Actuator type greatly
depends on application
• Lots of unique technologies
o Pneumatic
o Thermo-pneumatic
o Thermo-mechanic/
Bimetallic
o Piezoelectric disc/ stack
o Electrostatic
o Electro-magnetic
o Electro-chemical
o Chemical / Gels
• Each option has flaws
Pneumatic
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Pressurized gas
presses flexible
diaphragm over valve
outlet
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Simple and time-tested
technology
• Strong holding force
• Wide range of possible
capabilities
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Additional components
increase complexity
and weight
Thermo-pneumatic
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Heaters increase
temperature of fluid
• P*V increases - closes
valve diaphragm
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High energy density
(~10^6 J/m^3)
Slow actuation time
(~0.01-1sec)
• Temperature of
environment affects
performance
Thermo-mechanic / Bimetallic
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Difference of thermal
expansion moves
diaphragm over valve outlet
Poor holding force
(~10^2 kPa) and small
displacement
• Slow actuation time
(~0.01-1sec)
• Temperature of
environment affects
performance - increased
leakage
Electrostatic
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Charged electrodes
create electric field
• Electrostatic force is
exerted on diaphragm
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Low power consumption
Low energy density
(~10^2 J/m^3)
• Small displacement
• Tight tolerances needed
Electro-magnetic
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Electrically activated
solenoid moves
diaphragm
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Large displacement
(~.1mm)
• Good response time
(~1ms)
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Low efficiency
Heavier than most
Piezoelectric (Discs and Stacks)
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Applied electric field
causes mechanical
strain to generate large
stresses
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Lowest power
consumption
• One of the earliest
microvalve actuators
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Small displacement
(~0.01mm)
Electro-Chemical
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Uses electrolysis to
generate gas bubbles
and increase volume
to close diaphragm
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Energy efficient
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Slow response time
(~1sec)
• Outside expertise
needed
Chemical / Gels
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Convert chemical energy into
mechanical energy
Hydrogels swell with small
environmental changes
Relies on micro scale t utilize
diffusion
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More common in bio-related
applications
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very specific technology, so
outside expertise needed
Comparing Actuator Characteristics
Time
Response
Energy
Density
Pressure
Range
Actuator Comparison
Pneumatic
Pressure Range
Time response
Environmental
sensitivity
Energy density
Leakage
Activation
strength
Complexity
Displacement
Applied voltage
Power
consumption
ThermoThermoElectro- Electro- Chemical
Piezoelectric Electrostatic
pneumatic mechanic
magnetic chemical
(gels)
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Existing Technologies and
Examples
www.rainbird.com/drip/products
www.orbitalresearch.com/Medical
www.cyclelogicmo
torsports.com/
www.globalspec.com/FeaturedProducts/
Detail/BeswickEngineering
www.eng.uwo.ca/rerc/prototype.html
Working Fluid: Butane, LPG
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High heat of combustion (~50
MJ/kg)
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Stable storage and
manipulation
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Clean burn
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Reliable, cost-effective valve
solutions exist
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Safe for lab use => gas
detection tools available
Butane Properties*
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Density:
 2.46 kg/m3 gas (288 K)
 600 kg/m3 liquid (272 K) (roughly half that of H20)
MP: 135.4 K, BP: 272.6 K
Flash Point: 213 K
Auto-ignition Temp: 773 K
Cost: ~0.70 $/gal
*all values for 1 atm
Butane Properties
Butane Properties
Butane Properties
Butane Properties
Fundamentals of FEA
Conclusions
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Microfluidics/Valve to Fluidics/Microvalve
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Applicable valve, actuator, and sensor
technologies are available for our device
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Butane/LPG is a reasonable fuel
Next Steps
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System concept/design refinement
 Confirm
valving liquid or gas
 Actuation
 Closed Loop Sensing/Controls
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Learn from other groups (especially
related to DFM)
Questions?