DR. AKSHAYA JENA AND DR. KRISHNA GUPTA POROUS MATERIALS, INC., ITHACA, NEW YORK, USA...

Click here to load reader

download DR. AKSHAYA JENA AND DR. KRISHNA GUPTA POROUS MATERIALS, INC., ITHACA, NEW YORK, USA Characterization of Pore Structure of Fuel Cell Components for Enhancing

of 67

  • date post

    11-Jan-2016
  • Category

    Documents

  • view

    213
  • download

    0

Embed Size (px)

Transcript of DR. AKSHAYA JENA AND DR. KRISHNA GUPTA POROUS MATERIALS, INC., ITHACA, NEW YORK, USA...

  • DR. AKSHAYA JENA AND DR. KRISHNA GUPTAPOROUS MATERIALS, INC.,ITHACA, NEW YORK, USACharacterization of Pore Structure of Fuel Cell Components for Enhancing Performance

  • OutlineIntroductionThrough pore throat diameter, distribution, gas permeability & surface area by:Capillary Flow PorometryCapillary Condensation Flow PorometryHydrophobic through and blind pore volume & distribution by:VacuaporeThrough pore volume, diameter, distribution & liquid permeability by:Liquid Extrusion PorosimetrySummary and Conclusion

  • IntroductionPore structure governs kinetics of physicochemical processes & Flows of reactants and products in fuel cells.Quantitative measurement of pore structure is essential for Design, development and performance evaluation. Technologies for pore structure measurement are currently being developed to characterize the complex pore structure of fuel cell components. We will discuss several innovative techniques successfully developed and applied for evaluation of pore structure of fuel cell components.

  • Through Pore Throat Diameters, Distribution, Gas Permeability and Surface AreaImportance of Such Properties

    Through Pores:Fluid flowPore Diameters:Capillary forces for liquid movementThroat diameters:Separation of undesirable particlesGas permeability:Overall rate of the processesThrough pore surface area:Physicochemical processesEffects of stress, chemical environments & temperature:Influence of operating conditions

  • Suitable Characterization Techniques

    Advanced Capillary Flow PorometryCapillary Condensation Flow Porometry

    Through Pore Throat Diameters, Distribution, Gas Permeability and Surface Area

  • Advanced Capillary Flow PorometryFor wetting liquid:Wetting Liquids fill pores spontaneouslyCannot come out spontaneouslyA pressurized inert gas can displace liquid from pores provided:Work done by Gas = Increase in Interfacial Free Energy

    Basic Principle

  • Advanced Capillary Flow PorometryPressure needed to displace liquid from a pore:

    p = 4 cos / D

    p = differential gas pressure = surface tension of wetting liquid = contact angle of the liquidD = pore diameter

    Pore diameter is defined for all pore cross-sections

  • Advanced Capillary Flow Porometry(Perimeter/Area)pore = (Perimeter/Area)cylindrical opening

    Pore Diameter = Diameter of Cylindrical Opening

    SKETCH

  • Advanced Capillary Flow PorometryMeasured differential pressure & gas flow through dry & wet sample yield pore structure

  • The TechniqueAccuratePressure transducersFlow transducersRegulatorsControllersSophisticated sample sealing mechanisms to direct flow in desired directionsInternal computersTo control sequential operationsTo execute automated testsAdvanced Flow Porometers

  • The TechniqueProper algorithmsTo detect stable pressure and flowTo acquire dataSoftwareTo convert acquired data to pore structure characteristicsTo present data in tabular, graphical and excel formatsAdvanced Flow Porometers

  • An Example:The PMI Advanced Capillary Flow Porometer

  • The PMI Advanced Capillary Flow PorometerFeatures:Sealing with uniform pressure by pneumatic piston-cylinder deviceAutomatic addition of measured amount of wetting liquid at appropriate time

  • The PMI Advanced Capillary Flow PorometerAppropriate design & strategic location of transducers to minimize pressure drop in the instrumentMinimal operator involvementUse of samples without cutting and damaging the bulk product

  • Analysis of Experimental DataDry Flow, Wet Flow & Differential PressureFlow rate and differential pressure measured in a solid oxide micro fuel cell component

  • Analysis of Experimental DataPore diameter computed from pressure to start flow = Through Pore Throat DiameterThrough Pore Throat Diameter

  • Analysis of Experimental DataComputed from pressure to initiate gas through wet sampleThe Largest Through Pore Throat Diameter(Bubble Point Pore Diameter)The largest pore size in a solid oxide micro fuel cell component

  • Analysis of Experimental Data50% of flow is through pores larger than the mean flow through pore throat diameterMFPD computed using pressure when wet flow is half of dry flowThe Mean Flow Through Pore Throat DiameterMean flow pore diameter of a solid oxide micro fuel cell component

  • Analysis of Experimental DataSmallest pore is computed using pressure at which wet and dry curves meetThe Smallest Through Pore Throat Diameter& The Pore Diameter RangePore diameter range measured in a solid oxide micro fuel cell component

  • Analysis of Experimental DataFlow DistributionFlow distribution in a membraneThe flow distribution is given by the distribution function, fFfF = -d [(Fw / Fd)p 100] / d DFw = wet flow, Fd = dry flow

  • Analysis of Experimental DataFlow DistributionArea under distribution function in any diameter range = % flow through pores in that range

  • Analysis of Experimental DataPore Fraction DistributionPore FractionNj = the number of through pores of throat diameter DjFj = [1/(4 cos / pj)4] [(Fw,j / F d,j) (Fw,j-1 / Fd,j-1)]pj = differential pressure to remove wetting liquid from pore of diameter Dj

  • Analysis of Experimental DataPore Fraction DistributionFlow fraction distribution of a membrane

    Chart2

    0.000038

    0.000042

    0.000046

    0.000048

    0.000049

    0.000051

    0.000055

    0.00006

    0.000065

    0.000067

    0.000066

    0.000063

    0.000061

    0.000063

    0.000067

    0.000071

    0.000075

    0.00018

    0.000681

    0.001314

    0.002376

    0.004061

    0.034131

    0.157645

    0.272848

    0.277387

    0.204321

    0.028494

    0.003771

    0.002707

    0.002476

    0.001919

    0.001723

    0.001228

    0.000887

    0.000739

    Diameter, microns

    Ni / Sum(Ni)

    Chart1

    -1.48-2.59-0.92-10.13-6.94

    -1.530.4-0.811.80.57

    -0.812.181.878.326.37

    3.8434.734.734.734.7

    SS#1

    SS#2

    SS#3

    Hovosorb

    Papere

    Surface tension, dynes/cm

    (D-Dav), micrometers

    Sheet1

    Surface tensionss#1ss#2ss#3Hovopaper

    wetting liquid25.0425.428.7150.4943.77

    1623.56-1.4822.81-2.5927.79-0.9240.36-10.1336.83-6.94

    20.123.51-1.5325.80.427.9-0.8152.291.844.340.57

    22.324.23-0.8127.582.1830.581.8758.818.3250.146.37

    34.728.883.84

    Sheet2

    0.9660.000038

    0.92810.000042

    0.8930.000046

    0.86050.000048

    0.83030.000049

    0.80210.000051

    0.77580.000055

    0.75110.00006

    0.7280.000065

    0.70620.000067

    0.68580.000066

    0.66610.000063

    0.64760.000061

    0.63010.000063

    0.61350.000067

    0.59770.000071

    0.58280.000075

    0.56850.00018

    0.5550.000681

    0.54460.001314

    0.53460.002376

    0.52490.004061

    0.51580.034131

    0.50740.157645

    0.50050.272848

    0.49380.277387

    0.48420.204321

    0.47810.028494

    0.4710.003771

    0.46510.002707

    0.4590.002476

    0.45390.001919

    0.44850.001723

    0.4430.001228

    0.4380.000887

    0.43290.000739

    Sheet3

  • Analysis of Experimental DataGas PermeabilityFrom Darcys Law:F = k (A / 2 l ps) (Ts / T) (pi + po) [pi po]F = gas flow rate in volume at STPps = standard pressureTs = standard temperaturek = permeabilityA = area = viscosityl = thicknessT = test temperature in Kelvinpi= inlet gas pressurepo = outlet gas pressure

  • Analysis of Experimental DataGas PermeabilityPermeability computed from dry flow

    Flow rate through a dry sample

  • Analysis of Experimental DataThrough Pore Surface AreaKozeny-Carman equation relates through pore surface area to flow[F l / p A] = {P3 / [K(1 - P)2 S2 ]} + [Z P2 ] / [1 - P) S (2 p ) ]F = flow rate in volume at average pressure p (p = [pi + po / 2]), and test temperatureP = porosityS = surface area per unit volume of solid = density of gas at average pressureK = 5Z = (48/13 )Flow rate through a dry sample

  • Analysis of Experimental DataThrough Pore Surface AreaChange of envelope surface area with flow rate

  • Enhanced CapabilityAdvanced Porometers with special attachments can test samples under a variety of conditions

  • Enhanced CapabilitySample under compressive stress or cyclic compressive stressCompression & Cyclic Compression PorometryEffects of compressive stress on gas permeability of GDL

  • Enhanced CapabilitySample under desired controlled humidity and temperatureControlled Thermal & Chemical Environment PorometryThe PMI Fuel Cell Porometer

  • Enhanced CapabilitySamples exhibiting very low flow ratesFuel cell componentsMembranesDense ceramicsTightly woven fabricsTiny partsSilicon wafersStorage materialsMicroflow PorometrySmall flow rates through a fuel cell component measured in the microflow porometer

  • Enhanced CapabilityIn-Plane pore structure of sample or pore structure of each layer of multilayer componentsFuel cell componentsBattery separatorsNonwoven filtersFeltsPaperIn-Plane Porometry (Directional Porometry)Pore structure of each layer of a ceramic component

  • Capillary Condensation Flow PorometryCapillary Condensation Flow Porometry is a recently patented novel technique

    Condensation of Vapor of a Wetting Liquid in PoresVapor at p

  • Capillary Condensation Flow PorometryFree Energy Balance shows condensation occures in pores smaller than DcBasic PrincipleDc = - [4 V l/v cos / RT] / [ ln (p/po)]

    V = molar volume of condensed liquidR = gas constant l/v = surface tensionT= test temperature = contact a