Fuel Cell Modelling

To date, there is no complete computational model for fuel cell stacks including all the phenomena together. Nevertheless, increasing focus on this topic has produced rudimentary attempts which will probably support later studies. Available experimental data and mathematical models have been obtained for very restricted and idealized situations, and do not take into account of phenomena other than the one investigated. Both experimental and analytical/numerical studies need to be conducted and compared with each other for describing a complete fuel cell system. Future research should focus on the performance and integration of fuel cell stacks and associated sub-systems including fuel storage, reforming and processing, air delivery systems, heat exchangers and thermal integration, humidification and water management, DC power processing, sensors and controls.

A comprehensive fuel cell model should include following requirements:

1. Equal current distribution must be ensured via uniform velocity distribution of the reactants at the gas channel/electrode interfaces. Otherwise, parasitic current may be observed between the channels due to potential differences

2. Cell operation is maintained at stable by controlling the flow of water within the cell. The polymer membrane must remain hydrated to maintain its protonic conductivity, and water produced by the reaction must be removed from the cathode. It is ensured by flowing air through the cathode channel which removes water both in liquid and vapor form. The transport of water from cathode to anode is governed through the membrane by onic drag and mass diffusion.

3. Flooding may occur on the porous electrode if liquid water can not be removed properly. This phenomenon causes the transport of reactants through the electrode encumber and overall system performance drop

4. Cell temperature must be kept in uniform temperature. Therefore, heat produced by electrical resistance and electrochemical reaction must be removed from the cell.

Phenomena in the fuel cell is summarized as follows; Mass, momentum and energy transport through gas channels, electric current transport through porous media (electrodes and membrane) and electrochemical reactions at the electrode-membrane-catalyst interface.

In the last years, commercial CFD codes have found an application area on fuel cell modelling at large scales. [2-9]. Parallel processing is also a necessity for the calculations at a large-size and complex computational domain. In this connection, some of the recent studies may be useful to see the problems faced with in the field of fuel cell technology; These are presented in the references [12-15]. In addition to the numerical performance, the physical validity of the models should be tested through comparisons with experimental data of polarization curves. The selected studies[16-22] are some of the examples on software package usage in PEMFC technology. It requires a tremendeous effort to predict polarization curves by numerical techniques.The results were presented as polarization curves in some of the recent studies on PEMFC’s [10,11].