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What is a fuel cell?What is a fuel cell?A fuel cell is a device that generatesA fuel cell is a device that generates

electricity by a chemical reaction.electricity by a chemical reaction.

Anode : 2HAnode : 2H 22 4H4H++

+ 4e+ 4e--Cathode : OCathode : O22 + 4H+ 4H

++ + 4e+ 4e-- 2H2H22

Overall equation : 2HOverall equation : 2H22 + O+ O22 2H2H220 +0 +

EnergyEnergy

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Model Of Fuel CellModel Of Fuel Cell

http://var/www/apps/conversion/tmp/scratch_4/C:/paper/ren/paper%20details/Copy%20of%20fuel-cell-animation1.swf

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Types of fuel cellsTypes of fuel cells

Alkali fuel cellsAlkali fuel cells

Molten Carbonate fuel cellsMolten Carbonate fuel cells

Phosphoric Acid fuel cells (PAFC)Phosphoric Acid fuel cells (PAFC) Proton Exchange Membrane (PEM)Proton Exchange Membrane (PEM)

Solid Oxide fuel cells (SOFC)Solid Oxide fuel cells (SOFC)

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Fuel Cells In Space TechnologyFuel Cells In Space Technology

For space applications energy production is cyclicFor space applications energy production is cyclic

NASA power systemNASA power system

The Unitized Regenerative Fuel Cell (URFC)The Unitized Regenerative Fuel Cell (URFC)

Applications - high altitude balloons ,high altitudeApplications - high altitude balloons ,high altitude

solar airplanes, etc.solar airplanes, etc.

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Unitized Regenerative Fuel CellUnitized Regenerative Fuel Cell

SystemSystem

Proton Exchange Membrane in URFCProton Exchange Membrane in URFC Energy storage system.Energy storage system.

Potential ability to store large amounts ofPotential ability to store large amounts ofenergyenergy

URFC Fuel Cell + ElectrolyserURFC Fuel Cell + Electrolyser

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Energy DensityEnergy DensityEnergy delivered per unit mass of storageEnergy delivered per unit mass of storage

systemsystem

The Energy density is given byThe Energy density is given by

EEdd = (Output energy/Reactant weight)= (Output energy/Reactant weight)Output Energy = n Vd Id tdOutput Energy = n Vd Id td

VVdd = Discharge cell voltage, volts= Discharge cell voltage, volts

IIdd = Average discharge current, amps= Average discharge current, amps

n = Number of cells in the URFC stackn = Number of cells in the URFC stack

ttdd = Discharge time, hours= Discharge time, hours

MMww = Reactant weight= Reactant weight

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Parameters Influencing EnergyParameters Influencing Energy

DensityDensity

Where,

R = Ideal Gas Constant = (84.78 Kg-cm3)/(cm2-gmole-k)T = Temperature in KelvinMOPw = Maximum operating gas pressure (Kg/cm^2)f(Vd) = Id (Discharge current density in A/cm^2)Kw = 0.336*106 (cm) (Water-Tank-Figure-of-

Merit)Ka = The ratio of the total cell area to stack

weight=(As/w)Where , As = Total cell area

W = Stack weight

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Discharge Voltage And CurrentDischarge Voltage And Current

Density OptimizationDensity Optimization

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URFCS EFFICIENCYURFCS EFFICIENCYIt is defined as the ratio between outputIt is defined as the ratio between output

energy to the input energy with regard toenergy to the input energy with regard to

charging &discharging of the systemcharging &discharging of the system

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The Solar AirplaneThe Solar AirplaneThe solar airplane is an ultra light flying wingThe solar airplane is an ultra light flying wing

aircraftaircraft

Its surface of the wing is covered with solar cellsIts surface of the wing is covered with solar cells

that produce electric powerthat produce electric power

Need forNeed forURFCURFC in Solar aircraftin Solar aircraft

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Schematic Diagram Of URFCSSchematic Diagram Of URFCS

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URFC Energy Storage SystemURFC Energy Storage System

ComponentComponent

URFC StackURFC Stack

Gas Storage TanksGas Storage Tanks

Water TankWater Tank

CondensersCondensersRegenerative DryersRegenerative Dryers

Gas Regulators/ Check ValvesGas Regulators/ Check Valves

Energy Storage System ShellEnergy Storage System Shell

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URFC Energy Storage SystemURFC Energy Storage System

Operation DescriptionOperation Description

Electrolysis OperationElectrolysis Operation

Fuel Cell OperationFuel Cell Operation

Electrolysis To Fuel Cell TransitionElectrolysis To Fuel Cell TransitionFuel Cell To Electrolysis TransitionFuel Cell To Electrolysis Transition

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Packaging Of URFCSPackaging Of URFCS

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Summary Of URFCSSummary Of URFCS

URFCS capable of delivering 3500 watts during aURFCS capable of delivering 3500 watts during a

12 hour discharge period.12 hour discharge period.

The overall energy density is 791 w-hr/kg.The overall energy density is 791 w-hr/kg.

Lightweight energy storage system.Lightweight energy storage system.

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Variations In URFCS PerformanceVariations In URFCS Performance

The Size of Water Tank:The Size of Water Tank:

The water tank was sized to provideThe water tank was sized to providesufficient water storage for 3500 watts dischargesufficient water storage for 3500 watts discharge

power for 12 hourspower for 12 hours..The gas tank volume:The gas tank volume:

The gas tank volumes were sized such thatThe gas tank volumes were sized such that

the fully charged tanks had a peak storagethe fully charged tanks had a peak storage

pressure of approximately 28.1 kg/cm2 (400psia)pressure of approximately 28.1 kg/cm2 (400psia)

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URFCS Performance ParametersURFCS Performance Parameters

URFCS Stack Electrical PerformanceURFCS Stack Electrical Performance

URFCS Reactant Mass/PressureURFCS Reactant Mass/Pressure

Water Vapor ManagementWater Vapor Management

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ConclusionConclusion

Energy densities as high as 800 w-h/kg areEnergy densities as high as 800 w-h/kg arepossible for URFCS based energy storage systemspossible for URFCS based energy storage systems

The longer the discharge times for the URFCS theThe longer the discharge times for the URFCS the

greater the energy density possible.greater the energy density possible.

Over 90% of the volume could be saved from theOver 90% of the volume could be saved from theenergy storage system described in this paper.energy storage system described in this paper.

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BibliographyBibliography

Journal of Power SourceJournal of Power Source

Fred Mitlitsky, Blake Myers, and Andrew H.Fred Mitlitsky, Blake Myers, and Andrew H.Weisberg, Regenerative Fuel Cell Systems,Weisberg, Regenerative Fuel Cell Systems,

Energy & FuelsEnergy & Fuels

F. Mitlitsky, N. J. Colella, B. Myers, C. J. Anderson,F. Mitlitsky, N. J. Colella, B. Myers, C. J. Anderson, Regenerative Fuel Cells for High Altitude Long Regenerative Fuel Cells for High Altitude Long

Endurance Solar Powered Vehicles,Endurance Solar Powered Vehicles,

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