©SJA Søren Juhl Andreasen and Søren Knudsen Kær Aalborg University Institute of Energy Technology Dynamic Model of High Temperature PEM Fuel Cell Stack Temperature

©SJA Presentation outline ∙HTPEM features ∙Experimental fuel cell system setup ∙Previous work ▫Stack temperature profile identification ∙Governing equations ▫Energy balance ▫Fuel cell power input ▫Convection ▫Conduction ∙Model definitions ∙Model assumptions ∙HTPEM FC stack temperature control ▫Current feedforward ▫PI controller ∙Model validation ▫Heating ▫Operation ▫Pulsating air flow

©SJA HTPEM PBI(H 3 PO 4 )-membrane features Operating conditions ▫FC operating conditions o C, preferred range ( o C) ▫Allowable CO content 1-3% ( ppm) ▫No humidification of anode- and cathode flows ▫Fast response to load changes due to high temperatures (even with CO) Advantages ▫No humidification of cathode or anode => Very simple FC system and stack design ▫No liquid water should be present in FC membranes=> Simple stack design ▫Large CO-tolerance (1-3%), LTPEM is typically ppm ▫Possible system integration with simple reformer, due to high CO tolerance ▫Storing hydrogen as a liquid hydrocarbon => methanol, ethanol etc. ▫Avoiding and extra cooling circuit, by using extra cathode air Disadvantages (Challenges) ▫Lower cell voltage = Lower efficiency (not as low as DMFC though) ▫Start-up time is often long because of high operating temperatures (min 100 o C) to avoid water condensation. ▫High demands for materials at these elevated temperatures

©SJA Performance of HTPEM fuel cell ©SJA 2007

5 HTPEM FC System- pure hydrogen

©SJA Previous work – Initial experimental results Stack temperature profile identification

©SJA Fuel cell stack energy balance Energy balance : Fuel cell heat input : External heat input : Forced Convection : Heat Conduction : Natural Convection :

©SJA Manifold and gas channel temperature

©SJA Model assumptions ∙Quasi-steady-state : Constant surface temperature. ∙Fuel cell stack modelled as three lumps. ∙Constant U rev of 1.2V. ∙Fuel cell heat generation calculated at steady-state. ∙No axial and in-plane heat conduction between lumps. ∙Additional heating in inlet plate and BPP junction modelled as small constant gain. ∙Heat transfer in the MEA is neglected. ∙Hydrogen heating and cooling effects neglected. ∙Constant air mass flow in channels, consumption subtracted. ∙Small natural convection term added.

©SJA HTPEM FC stack temperature control SystemController T measured T reference U blower I reference I->m Air FC air flow – PI controller with Current feedforward Stack temperature o C, what T measured should be used?

©SJA Typical stack temperature control case Middle temperature controlledEnd temperature controlled Initial heating followed by 20 A load step.

©SJA Model validation - Electrical heating Experiment : 400 W heating Simulation : 350 W heating

©SJA Model validation – Constant current Experiment : 20 A load Simulation : 1500 W heating, 20 A load

©SJA Model validation – Pulsating air flow Operation : small current ramp, 20 A load air flow pulsing no controls

©SJA Example of experimental data

©SJA Conclusions and future work Conclusions ∙Developed model can with good agreement predict fuel cell stack temperature dynamics. ∙Developed model can within acceptable ranges predict the steady-state values of the fuel cell stack temperatures. ∙The modelled exhaust temperature must be improved for use as a direct control feedback. ∙Minimization of measured temperatures should be examnied using model based control. Furture Work ∙Manifold and channel temperature dynamics ∙Air flow subtraction along the channel ∙Discrete (at cell level) model ∙Model validation on 1 kW HTPEM stack with other geometry

©SJA Thank you for your attention!