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What is a fuel cell?What is a fuel cell?
A fuel cell is a device that generates A fuel cell is a device that generates electricity by a chemical reaction. electricity by a chemical reaction.
Anode : 2H Anode : 2H 2 2 4H 4H+ +
+ 4e+ 4e--
Cathode : OCathode : O2 2 + 4H+ 4H+ + + 4e + 4e- - 2H2H2 2
Overall equation : 2HOverall equation : 2H2 2 + O+ O22 2H 2H220 0 + Energy+ Energy
Model Of Fuel CellModel Of Fuel Cell
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)
Fuel Cells In Space TechnologyFuel Cells In Space Technology
For space applications energy production is For space applications energy production is cyclic cyclic
NASA power system NASA power system
The Unitized Regenerative Fuel Cell (URFC) The Unitized Regenerative Fuel Cell (URFC)
Applications - high altitude balloons ,high Applications - high altitude balloons ,high altitude solar airplanes, etc.altitude solar airplanes, etc.
Unitized Regenerative Fuel Cell Unitized 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 of Potential ability to store large amounts of
energy energy
URFC – Fuel Cell + ElectrolyserURFC – Fuel Cell + Electrolyser
Energy DensityEnergy Density
Energy delivered per unit mass of storage system Energy delivered per unit mass of storage system
The Energy density is given by The Energy density is given by
EEd d = (Output energy/Reactant weight)= (Output energy/Reactant weight)
Output Energy = n Vd Id tdOutput Energy = n Vd Id td
VVd d = 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
MMw w = Reactant weight= Reactant weight
Parameters Influencing Energy Parameters Influencing Energy DensityDensity
Where,
R = Ideal Gas Constant = (84.78 Kg-cm3)/(cm2-gmole-k) T = Temperature in Kelvin MOPw = 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
Discharge Voltage And Current Discharge Voltage And Current
Density OptimizationDensity Optimization
URFCS EFFICIENCYURFCS EFFICIENCY
It is defined as the ratio between output It is defined as the ratio between output energy to the input energy with regard to energy to the input energy with regard to charging &discharging of the systemcharging &discharging of the system
The Solar AirplaneThe Solar Airplane
The solar airplane is an ultra light flying wing The solar airplane is an ultra light flying wing aircraft aircraft
Its surface of the wing is covered with solar cells Its surface of the wing is covered with solar cells that produce electric powerthat produce electric power
Need forNeed for URFCURFC in Solar aircraft in Solar aircraft
Schematic Diagram Of URFCSSchematic Diagram Of URFCS
URFC Energy Storage System URFC Energy Storage System ComponentComponent
URFC StackURFC Stack
Gas Storage TanksGas Storage Tanks
Water Tank Water Tank
Condensers Condensers
Regenerative DryersRegenerative Dryers
Gas Regulators/ Check ValvesGas Regulators/ Check Valves
Energy Storage System Shell Energy Storage System Shell
URFC Energy Storage System URFC Energy Storage System Operation DescriptionOperation Description
Electrolysis Operation Electrolysis Operation
Fuel Cell Operation Fuel Cell Operation
Electrolysis To Fuel Cell Transition Electrolysis To Fuel Cell Transition
Fuel Cell To Electrolysis Transition Fuel Cell To Electrolysis Transition
Packaging Of URFCSPackaging Of URFCS
Summary Of URFCSSummary Of URFCS
URFCS capable of delivering 3500 watts during URFCS capable of delivering 3500 watts during a 12 hour discharge period.a 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.
Variations In URFCS PerformanceVariations In URFCS Performance
The Size of Water Tank:The Size of Water Tank:
The water tank was sized to provide The water tank was sized to provide sufficient water storage for 3500 watts discharge sufficient 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 that The gas tank volumes were sized such that the fully charged tanks had a peak storage the fully charged tanks had a peak storage pressure of approximately 28.1 kg/cm2 (400psia) pressure of approximately 28.1 kg/cm2 (400psia)
URFCS Performance ParametersURFCS Performance Parameters
URFCS Stack Electrical Performance URFCS Stack Electrical Performance URFCS Reactant Mass/Pressure URFCS Reactant Mass/Pressure Water Vapor Management Water Vapor Management
ConclusionConclusion
Energy densities as high as 800 w-h/kg are Energy densities as high as 800 w-h/kg are possible for URFCS based energy storage possible for URFCS based energy storage systems systems
The longer the discharge times for the URFCS The longer the discharge times for the URFCS the greater the energy density possible. the greater the energy density possible.
Over 90% of the volume could be saved from the Over 90% of the volume could be saved from the energy storage system described in this paper.energy storage system described in this paper.
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. F. Mitlitsky, N. J. Colella, B. Myers, C. J. Anderson, “ Regenerative Fuel Cells for High Anderson, “ Regenerative Fuel Cells for High Altitude Long Endurance Solar Powered Altitude Long Endurance Solar Powered Vehicles,” Vehicles,”