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Fuel Cell Thermal Managmenet William G. AndersonRichard W. Bonner, III Advanced Cooling Technologies, Inc. 8th International Energy Conversion Engineering ConferenceJuly 25-28, 2010Nashville, Tennessee : 

ISO9001-2008 & AS9100-B Certified Fuel Cell Thermal Managmenet William G. AndersonRichard W. Bonner, III Advanced Cooling Technologies, Inc. 8th International Energy Conversion Engineering ConferenceJuly 25-28, 2010Nashville, Tennessee

Agenda : 

Agenda Cooling Plates and Vapor Chambers Variable Conductance Heat Pipe Heat Exchangers Hydrogen Permeation Barriers ISO9001-2008 & AS9100-B Certified 2

Hydrogen-Oxygen Fuel Cell Stacks : 

Hydrogen-Oxygen Fuel Cell Stacks Hydrogen-Oxygen Fuel Cells for Spacecraft Applications Stacks of Proton Exchange Membrane Fuel Cells Heat generated during operation is removed by cooling plates located between the cells in the stack Plates transfer heat to the edge of the stack, where it is removed by cold rails Heat Transfer ~ 0.3 W/cm2 heat flux ~ 10 cm length ΔT < 3°C Operate around 80-90°C Thin plates, ~ 1 mm Any orientation Passive cooling plates Highly Conductive Solid Very Thin Heat Pipe (Vapor Chamber)

Fuel Cell Cooling Plates : 

Fuel Cell Cooling Plates Burke & Colozza et al (IECEC 2008, 2009) have demonstrated examined cooling with Highly Oriented Pyrolytic Graphite (HOPG) 1500 W/m K thermal conductivity before encapsulation Rough surface, no abrasion resistance Need to encapsulate to protect Very Thin Titanium/Water Vapor Chamber is an alternate Higher effective conductivity Suitable for larger fuel cell areas

Vapor Chambers : 

Vapor Chambers Planar heat pipes used for cooling high heat flux electronics Accept high heat flux, reject at lower flux Copper/Water Typically 0.125 to 0.20 inch (3.2 to 5.1 mm) thick Typically 25 W/cm2 heat flux.

DARPA Thermal Ground Plane : 

DARPA Thermal Ground Plane DARPA has a program that is developing thermal ground planes (vapor chambers) for electronics cooling 10 Teams, including ACT/UCLA/University of Michigan team Technical Challenges Thin – approximately 1mm 0.040 inch – 0.020 inch vapor space Large - 10cm x 20 cm Low CTE - matched to Si, SiC, AlN and/or GaAs Operation under high g-load accelerations (2 to 20gs) Requires the development of new wick structures Bi-Porous Type Wick Structures 3 dimensional wick structures to manage liquid feed and vapor exiting Successfully fabricated 0.3cm x 3cm x 3cm prototype with wick 500 W/cm2 heat flux Working to reduce thickness, scale size

Fuel Cell Balance of Plant – VCHPs : 

Fuel Cell Balance of Plant – VCHPs The Navy is investigating fuel cells for distributed ship service power Smaller Scale 50kW fuel cell system demonstrator 4kW heat exchanger Operation on diesel fuel requires a reformer system Convert the fuel into a hydrogen rich stream Diesel fuel must be steam reformed to produce hydrogen Reactant flow rates vary as electrical demand changes Reformer and shift reactor inlet temperatures must be kept constant to maintain efficiencies and ensure safety Current temperature/process control is complicated, needs mass- and volume- intensive valves, and is unreliable during power outages ISO9001-2008 & AS9100-B Certified 7

Fuel Cell Balance of Plant – VCHPs : 

Fuel Cell Balance of Plant – VCHPs Control of Reactor Operating Temperature is Crucial Reformer and shift reactor inlet temperatures must be kept constant to maintain efficiencies and ensure safety Inlet and Outlet Temperatures must be maintained within ±30°C Changes in electrical load cause changes in reactant flow rates Turndown ratio of 5:1 or greater Current control system utilizes bypass valve Consumes space, Requires power Reliability suspect - a moving part Requires higher heat exchanger pressure drop Variable Conductance Heat Pipes offer a passive temperature control solution ISO9001-2008 & AS9100-B Certified

VCHP Heat Exchangers for Fuel Cells : 

ISO9001-2008 & AS9100-B Certified VCHP Heat Exchangers for Fuel Cells Fuel Reformer Schematic

Variable Conductance Heat Pipe (VCHP) Operation Summary : 

ISO9001-2000 & AS9100-B Certified Variable Conductance Heat Pipe (VCHP) Operation Summary ISO9001-2000 & AS9100-B Certified Vapor Space Liquid Film Non-Condensable Gas (NCG) is added to the VCHP fluid inventory During operation, the working fluid drives the NCG to the condenser The portion of the condenser blocked by NCG is not available for heat transfer by condensation Inactive condenser region Remaining condenser is available for heat transfer Active condenser region Active and inactive length depend on working fluid pressure Non-condensable Gas (NCG) Reservoir

VCHP Heat Exchanger : 

ISO9001-2008 & AS9100-B Certified VCHP Heat Exchanger VCHP Heat Exchanger Schematic

VCHP Heat Exchanger Principles : 

Hydrogen Gas @ 85°C City Water @ 25°C Water @ ~50°C Hydrogen @ 400°C Mdot = 2.55kg/hr PH2=0.72atm Non-condensable Gas Water Working Fluid VCHP Heat Exchanger Principles NCG front responds to changes in flow rate and inlet temperature The result is a near constant outlet temperature. A turndown to 15-25% of the maximum flow is required, with an outlet temperature difference of ±30°C. Reduce size, weight and cost compared to the existing technology

Fuel Cell Simulation Test Apparatus : 

Fuel Cell Simulation Test Apparatus VCHP Fuel Cell Test Apparatus

VCHP Heat Exchanger Test Apparatus : 

VCHP Heat Exchanger Test Apparatus Test apparatus allows testing various heat exchanger designs Extensive safety features were built in for hydrogen use Hydrogen Preheater 1/3 Scale Monel/Water VCHP HX

Hydrogen Testing : 

Hydrogen Testing

VCHP Heat Exchanger Test Data : 

VCHP Heat Exchanger Test Data 16°C outlet temp. variation over 212°C inlet temp. variation 53°C outlet temperature variation for CCHP HX Tested at 1.0kg/hr H2 Flow Rate

VCHP Heat Exchanger Test Data : 

VCHP Heat Exchanger Test Data 8°C outlet temp. variation over 208°C inlet temp. variation Overall 20°C outlet temp. variation with 2:1 mass flow turndown Tested at 0.55kg/hr H2 Flow Rate

Hydrogen Permeation : 

Hydrogen Permeation Hydrogen permeation is a potential problem for a heat pipe in an environment that contains hydrogen Adsorption of the gas molecules on the surface of a solid Disassociation of the diatomic molecules into atomic species Diffusion of the dissociated atoms through the solid Recombination of atomic species to diatomic molecules on the surface at the external surface Desorption from the surface Need to add a hydrogen permeation barrier Gold has very low permeation rates

Hydrogen Permeation : 

Hydrogen Permeation Accumulation equal to 1% of the total volume at the design heat pipe conditions is plotted Between 350 K to 425 K Bare Monel will accumulate too much hydrogen. Accumulation of the same pipe with several thickness of gold are shown

Hydrogen Permeation – Experiments : 

Hydrogen Permeation – Experiments Hydrogen permeation into heat pipe was a concern Hydrogen Permeation tests performed using Monel/water heat pipes with bare wall and gold plated wall ISO9001-2008 & AS9100-B Certified 20

Hydrogen Permeation Test Data : 

Hydrogen Permeation Test Data Hydrogen barrier identified by this test

Conclusions : 

Conclusions Operation on diesel fuel requires a reformer system to produce Hydrogen Convert the fuel into a hydrogen rich stream Reformer and shift reactor inlet temperatures must be kept constant to maintain efficiencies and ensure safety VCHP Heat Exchanger is a passive thermal management device used to maintain a constant feed temperature for reactors Accommodates a wide range of flow rates and inlet temperatures. Passive system, no controls required Next Steps Design, Manufacture and Test VCHP Heat Exchangers for 50kWe PEM Fuel Cell System Design VCHP Heat Exchangers for 250kWe PEM Fuel Cell System ISO9001-2008 & AS9100-B Certified 22

Fuel Cell Thermal Managmenet William G. AndersonRichard W. Bonner, III Advanced Cooling Technologies, Inc. 8th International Energy Conversion Engineering ConferenceJuly 25-28, 2010Nashville, Tennessee : 

ISO9001-2008 & AS9100-B Certified Fuel Cell Thermal Managmenet William G. AndersonRichard W. Bonner, III Advanced Cooling Technologies, Inc. 8th International Energy Conversion Engineering ConferenceJuly 25-28, 2010Nashville, Tennessee

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