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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
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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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