Microfluidics and Valve Design

Mark Barineau

Ryan Slaughter

Presentation Overview

• Lincoln Laboratory goals• Micro- and Macroscale

Fluidics• Governing Physics• Valve and Actuator

Types• Related Technologies• Butane/LPG Properties• FEA Intro

Critical Findings

• Distinction between microfluidics and microvalves

• Applicable valve, actuator, and sensor technologies have been developed

• Butane/LPG is a good choice

LL: Fuel Metering Valve• 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 Average over any 1 second interval

Allowable Pulsation 0 to 200% of FS0 to 150% of FS0 to 120% of FS

< 10 msec10 to 50 msec

> 50 msec

Power Consumption < 50 mW@ 3 to 6 VDC

Includes any power dissipation for control signals

Mass < 10 grams

Interface TBD In: LPG Fuel canister

Out: Fluoropolymer tubingElectrical: Flying Lead

LL: Valve Concept

• Rough concept for initial performance requirements– Actual requirements driven by more thorough

design review

Pressure RegulatorLow FrequencyDC modulation

Flow RegulatorPulse WidthModulated

Valve Controller

FuelPvap(T)

FuelMass Flow

Te

mp

Flow SP

Valve Components

• Fluid reservoir• Actuator• Restrictive element• Sensor(s)• Controls• Interconnects

Micro- vs. Macrofluidics

• Microfluidic—devices and/or flow characteristics

• Knudsen number– Kn<0.3, Continuity – Kn>0.3, Statistical

mechanics

Fluids (2.005) Review

• Navier-Stokes Eq.

• Mass Continuity

• Reynolds Number

Working Fluid: Butane, LPG

• High heat of combustion (~50 MJ/kg)

• Stable storage and manipulation

• Clean burn

• Reliable, cost-effective valve solutions exist

• Safe for lab use => gas detection tools available

Butane Properties*

• 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

• Microfluidics/Valve to Fluidics/Microvalve

• Applicable valve, actuator, and sensor technologies are available for our device

• Butane/LPG is a reasonable fuel

Next Steps

• System concept/design refinement– Confirm valving liquid or gas– Actuation– Closed Loop Sensing/Controls

• Learn from other groups (especially related to DFM)

Questions?