5 - 2/7/2011 MEM 415 FUEL CELL ENGINES - Lecture #5...

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2/7/2011 1 -- Lecture #5 -- MEM 415– FUEL CELL ENGINES THERMODYNAMICS AND POLARIZATION MEM 415– Lecture #5 Dr. E. Caglan Kumbur Assistant Professor of Mechanical Engineering Office: Curtis 160 Ph: 215.895.5871 e-mail: eck32@drexel.edu -- Feb 7, 2011 -- Polarization and Performance Curve E 00 =E max (Ideal Case) = 1.23 V Polarization curve represents _______________________ , which is the key tool for evaluation of cell performance. Heat Dissipation Due to the resistances (in different forms) inside the cell. Cell dies after reaching some limiting current density. Useful Power • These losses can be categorized in __________________ MEM 415– Lecture #5
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2/7/2011 2 Polarization Curve Regions Region 1: Activation Polarization – Component of interest: Catalyst Layer Reason: Activation overpotential at the electrodes (Kinetic losses) Region 2: Ohmic Polarization – Component of interest: Electrolyte, Catalyst Layer, GDL Reason: Dominated by electrical and ionic conduction losses. Region 3: Concentration Polarization – Component of interest: Catalyst Layer, GDL Reason: Dominated by mass transport limitations. Region 4: Crossover Losses – Component of interest: Electrolyte Reason: Reactant crossover through the electrolyte. Region 5: Departure from maximum thermal voltage – Thermodynamics losses Reason: Departure from the maximum thermal voltage due to entropy change Ideal Gas Enthalpy- Constant Specific Heats- Summary of Last Lecture Gas phase specific heat Enthalpy and Internal Energy Calculation using Specific Heats- ! " # 2 1 ) ( 1 2 T T dT T c u u $ v dT du T c " ) ( % ) ( 1 2 1 2 T T c u u u # " # " & P p dT dh T c " ) ( ! " # 2 1 ) ( 1 2 T T p dT T c h h ) ( 1 2 1 2 T T c h h h p # " # " & Entropy and Gibbs Function- MEM 415– Lecture #5
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2/7/2011 3 work available maximum work electrical actual " th 2) 1) Thermo definitions: Summary of Last Lecture W e = - & G = n F E o !!! ( E nF G " & # Maximum Available/ Possible Voltage (Open Circuit Voltage) oo th H E E nF #& "" W e = - & H = - ! G = n F E ºº Maximum/Total Theoretical Voltage (Impossible in Reality !!) S T S T H E nF G G o & & # & & # & 1 work electrical Maximum S T & 1 H H E nF H H thermal & # " & " " & # " & " " work available Total 00 max , H t & # " Maximum thermodynamic efficiency 3) where x can be h, u, s, g, etc…. . MEM 415– Lecture #5 Summary of Last Lecture Do the same process for S, U, G… (products-reactants) D C B A d c b a % $ ) * ) +, R R i P P i R P x v x v x x x - - # " # " & , , Reactants Products Where x can be h, u, s, g, etc…. . Refer to your Thermo Book and Chapter 3 in your text book for detailed explanation !!!! MEM 415– Lecture #5
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2/7/2011 4 i u ref P P R P T s T s 0 ln ) , ( ) ( # " Change in Entropy and Gibbs Function D C B A d c b a % $ ) * ) Reactants Products Entropy Summary of Last Lecture f Re - - # " # " & R i R i P i P i R p s s s s s ) ( ) ( , , - - # # # " R f i u ref R i P f i u ref P i P P R P T s P P R P T s ) ln ) , ( ( ) ln ) , ( ( Re 0 , Re 0 , 0 Gibbs Function ) ( ) ( ref ref f s s T h h g g # # # ) " ) ( 1 2 1 2 1 2 s s T h h g g # # # " # - - # " # " & R i R i P i P i R p g g g g g ) ( ) ( , , Refer to your Thermo Book for detailed explanation !!!!
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5 - 2/7/2011 MEM 415 FUEL CELL ENGINES - Lecture #5...

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