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Generic Fuel Cell Modelling Environment

Final Report Summary - GENFC (Generic Fuel Cell Modelling Environment)

Fuel cell is one of the key technologies for energy production from sustainable source. In the short and medium term fuel cells can be used to generate electricity from fossil fuels at high electrical efficiency. In the long term they are expected to facilitate energy from hydrogen exploitation.

GENFC project aimed to accelerate the progress regarding fuel cells technology by producing various models related to different scientific problems as well as by combining all the available modelling tools under one structured framework. Its main objectives were to increase synergy effects in modelling, to share knowledge among the various professionals related to fuel cells and to organise the in-house development process. Thus the GENFC software, an open source program with database capability and interfaces that link individual fuel cell models and experimental data, was developed. The model addressed issues related to the description of the processes within a fuel cell, the improvement of modelling tools that will be helpful towards an industrial product development and the current lack of models regarding fuel cells systems as part of a combined unit supplying heat and electricity to residential buildings. In addition, the software was designed so as to be user friendly and easily extendable by programmers.

Low temperature operating fuel cells, whose operating temperature is below 100 degrees Celsius, share complicated interactions of gaseous and liquid components which result in multiphase phenomena. In order to overcome the difficulties in modelling these phenomena special attention was given during the software development. Computational fluid dynamics (CFD) was applied to simulate fuel cells or fuel cell stacks, through the use of existing commercial tools. The pipe flow within a gas channel was simulated as one-dimensional flow, depending only on the channel length. Meshing the other fuel cell parts in a three-dimensional way allowed for the one-dimensional gas channels to penetrate the complicated mesh, thus exchanging mass, species and heat with it. In that way the transport along terminal and lateral connections was treated fully implicitly and software robustness and numerical stability were increased compared to a purely explicit handling.

It was necessary for the model development to get a qualitative impression of the formation and movement of the liquid phase within a fuel cell. This was feasible through the creation of a transparent fuel cell operating with a mixture of water and methanol. However, the device could not provide data on the pressure drop in a channel as a function of the amount of liquid or the gas flow rate, nor could data concerning droplets formation be extracted from literature. Hence two-dimensional simulation studies were performed to examine the droplets effect on the course of the pressure drop.

Similar studies were also carried out to analyse the influence of the air channel outlet geometry on the drops movement, which showed that the design of the channel strongly affects the droplets outflow. The developed one-dimensional multiphase model could only be used when continuous outflow was guaranteed, since it did not comprise drops accumulation at the channel end.

The drag force coefficient, depending on the average air velocity and the drop diameter, was identified through a virtual test rig, with the test environment being a two-dimensional image of the fuel cell air channel. The Eulerian approach was chosen to calculate the two-phase flow in a channel, so as to adapt the one-dimensional channel simulation to the three-dimensional environment, with the momentum and continuity equations being solved for each phase.

A model simulation of a realistic fuel cell, which was the largest of its kind up to the project completion, was carried out successfully after the software tool development.

Fuel cell models available within the GENFC model database could also be applied in test rig based components and systems development using the hardware-in-the-loop (HIL) approach. In HIL, production or prototype hardware system components were interfaced in order to be able to investigate the combined operation of an overall system. The components could be operated as if the entire system were present, although only selected components were actually available and operated in a laboratory test rig environment. Fuel cell models with HIL capabilities are mainly required for automotive industry applications, process engineering and fuel cells systems components development.

GENFC provided two main functions for HIL applications, a real time core and a visualisation terminal prototype function. Error handling and communication interfaces were also readily implemented to ensure a maximum level of safety in real time operation. The visualisation terminal was provided by the software along with communication interfaces from and to the application terminal, so that communication was enabled between the test rig and a remotely located desktop PC.

Fuel cell systems could, among other uses, be applied in cogeneration devices in buildings which provide heat for space heating and domestic hot water combined with electric power production. In that case the control strategy of the complete device needed to be aligned, the energy supply system overall performance had to be determined and the device optimal size ought to be defined. The necessary decisions could be facilitated using the GENFC software, which included tools and models for the load generator, the elaboration of an economic and social analysis, the cogeneration device modelling and the assembly of a combined building and system simulation model.

The load generator tool used a stochastic approach to produce electrical loads for an entire simulation period. The load profiles could then serve as input data for dynamic building and system simulations.

In order to add ecological and economic analysis to a system, relevant indicators were used for its assessment within a life cycle perspective. System boundaries were always identical for both analyses. The economic analysis was based on the total annual costs, whereas the ecologic analysis relied exclusively on the electricity inputs and outputs and the fuel input calculated for a year time period.

Cogeneration device modelling was calibrated using actual measured data of an operating prototype. After calibration the thermal efficiency was adapted in order to take into account the industry expectations for improvement of the electrical efficiency in the near future. Different building energy demand levels were considered by defining two building sizes and three energy standard levels.

The finally developed software consisted of a back end server and a graphical user front end. Both ends were multi-user and platform independent, designed to follow a client-server architecture. The program was recommended to be restricted to local applications. The data were organised in three different objects, the model, parameter and object. The integration of GENFC models to system simulation software could be separated into two programming interfaces. While the general application interface was almost independent from the system simulation software, the application specific interface was dedicated to employed third party software, such as Matlab or Simulink.

GENFC product was released as an open source software, available without the need to purchase a license. A user manual and tutorials were available to explain its main functionalities. Finally, a semi-commercial dissemination was planned, in order to demonstrate the software use benefits to prospective clients.