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1、DR. AKSHAYA JENA AND DR. KRISHNA GUPTA POROUS MATERIALS, INC., ITHACA, NEW YORK, USA Characterization of Pore Structure of Fuel Cell Components for Enhancing Performance Outline Introduction Through pore throat diameter, distribution, gas permeability & surface area by: Capillary Flow Porometry Capi
2、llary Condensation Flow Porometry Hydrophobic through and blind pore volume & distribution by: Vacuapore Through pore volume, diameter, distribution & liquid permeability by: Liquid Extrusion Porosimetry Summary and Conclusion Introduction Pore structure governs kinetics of physicochemical processes
3、 & 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.
4、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 Area Importance of Such Properties Through Pores:Fluid flow Pore Diameters:Capillary fo
5、rces for liquid movement Throat diameters:Separation of undesirable particles Gas permeability:Overall rate of the processes Through pore surface area:Physicochemical processes Effects of stress, chemical environments & temperature: Influence of operating conditions Suitable Characterization Techniq
6、ues Advanced Capillary Flow Porometry Capillary Condensation Flow Porometry Through Pore Throat Diameters, Distribution, Gas Permeability and Surface Area Advanced Capillary Flow Porometry For wetting liquid: Wetting Liquids fill pores spontaneously Cannot come out spontaneously A pressurized inert
7、gas can displace liquid from pores provided: Work done by Gas = Increase in Interfacial Free Energy Basic Principle Advanced Capillary Flow Porometry Pressure needed to displace liquid from a pore: p = 4 cos / D p = differential gas pressure = surface tension of wetting liquid = contact angle of the
8、 liquid D = 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 Porometry Measured differential pressure & gas fl
9、ow through dry & wet sample yield pore structure The Technique Accurate Pressure transducers Flow transducers Regulators Controllers Sophisticated sample sealing mechanisms to direct flow in desired directions Internal computers To control sequential operations To execute automated tests Advanced Fl
10、ow Porometers The Technique Proper algorithms To detect stable pressure and flow To acquire data Software To convert acquired data to pore structure characteristics To present data in tabular, graphical and excel formats Advanced Flow Porometers An Example: The PMI Advanced Capillary Flow Porometer
11、The PMI Advanced Capillary Flow Porometer Features: Sealing with uniform pressure by pneumatic piston-cylinder device Automatic addition of measured amount of wetting liquid at appropriate time The PMI Advanced Capillary Flow Porometer Appropriate design & strategic location of transducers to minimi
12、ze pressure drop in the instrument Minimal operator involvement Use of samples without cutting and damaging the bulk product Analysis of Experimental Data Dry Flow, Wet Flow & Differential Pressure Flow rate and differential pressure measured in a solid oxide micro fuel cell component Analysis of Ex
13、perimental Data Pore diameter computed from pressure to start flow = Through Pore Throat Diameter Through Pore Throat Diameter Analysis of Experimental Data Computed from pressure to initiate gas through wet sample The Largest Through Pore Throat Diameter (Bubble Point Pore Diameter) The largest por
14、e size in a solid oxide micro fuel cell component Analysis of Experimental Data 50% of flow is through pores larger than the mean flow through pore throat diameter MFPD computed using pressure when wet flow is half of dry flow The Mean Flow Through Pore Throat Diameter Mean flow pore diameter of a s
15、olid oxide micro fuel cell component Analysis of Experimental Data Smallest pore is computed using pressure at which wet and dry curves meet The Smallest Through Pore Throat Diameter & The Pore Diameter Range Pore diameter range measured in a solid oxide micro fuel cell component Analysis of Experim
16、ental Data Flow Distribution Flow distribution in a membrane The flow distribution is given by the distribution function, fF fF = -d (Fw / Fd)p 100 / d D Fw = wet flow, Fd = dry flow Analysis of Experimental Data Flow Distribution Area under distribution function in any diameter range = % flow through pores in that range Analysis of Experimental Data Pore Fraction Distribution Pore Fraction Nj
