Mathematical models provide an insight into the physical and chemical processes within fuel cells and serve as a basis for the development and establishment of entirely new approaches. They are crucial for fuel cell research and development, right through to system optimisation. Computer-aided simulation helps reduce development time and costs with targeted optimisation, and also helps to provide an understanding of the physical and chemical processes in fuel cells. As well as being useful in model development, this also facilitates experimental verification of models. The results of this experimentally-backed modelling directly influence ZSW’s development work. In addition to this, numerous modellings have also been produced for industrial clients.
Modelling technologies are used and developed at ZSW in parallel with the experimental determination of the water distribution in gas diffusion layers. In addition to the macroscopic approaches used as part of Computer Fluid Dynamics modelling (CFD) , ZSW also performs spatially resolved modelling of the expected water distribution within a GDL. A custom model based on Monte Carlo (MC) methods, which is available in the form of a continuously maintained and refined in-house simulation code, is used for this purpose. This model can map the operating conditions of the cell and the structural and wetting properties of the materials. The simulation model can be extended flexibly if requested by the customer.
Virtually all areas of cell and stack design can be dealt with, generally by using the Fluent™ and AVL modelling software (including using user-defined functions (UDF)), the Fluent™ Fuel Cell Module and AVL Fire™. This includes determining and optimising local media concentration distributions and flow densities as part of the development of cell design.
As part of broader approaches, local GDL effects can also be taken into consideration and two-phase flows can be studied in channels (VOF, s. fig. above). In addition, CFD modelling can be used to study and optimise existing designs.
The use of CFD modelling (CFD = Computer Fluid Dynamics) as part of fuel cell development includes virtually all aspects from dimensioning media distributor channels in the bipolar plate through to entire fuel cell stacks (s. fig. on the right).
Using numerical simulation methods (FEM = Finite Element Method), fuel cell components can be dimensioned optimally in terms of weight and volume during the design phase, particularly as regards stack tensioning. In addition, functional components such as bipolar plates can already be studied in advance with the loads expected in fuel cell service and optimised accordingly in terms of dimensions, weight and reliability.
ZSW has modelling technologies available for fuel cell systems that represent an excellent approach to system optimisation and simplification. With regard to stationary and non-stationary system states, we can provide model-based forecasts and thus develop and establish an optimised system in iterative processes.
The stationary states of fuel cell systems are simulated using the IPSE-Pro software, which permits comprehensive modelling even of complex systems and thus facilitates a precise comparative evaluation of various system concepts.
Matlab-Simulink is generally used for simulations to study the dynamics of fuel cell systems.