A promising alternative to fossil fuels would be the utilization of a fuel cell as a powertrain for vehicles instead of a combustion engine. Inside the fuel cell, the reaction of hydrogen at a catalyst is used to convert chemical energy into electric energy and heat. This new technology offers a great potential for optimizing the components of this system. Reasonably, the on-going process can be realized with CFD-simulations.
It is a matter of common knowledge that the water content of the membrane influences proton conductivity. An option to ensure the supply of water, and to protect the membrane from dehydration, is to install a humidifier into the cathode stream before it enters the cell.
The humidifier itself contains a semipermeable membrane which separates liquid water (water-to-gas humidifier) or gas with a high relative humidity (gas-to-gas humidifier) from air for the supply of the cathode. Besides the exchange of heat, there is a transport of water against the gradient of activity. Consequently, this exchange results in a higher content of water in the cathode inlet stream.
STAR-CCM+ cannot handle the diffusion through a semipermeable membrane. Hence, it is necessary to develop a modelling approach to calculate the mass transfer through it. The amount of water which will permeate through the membrane is calculated with “user field functions”. These functions read the necessary properties and, concurrently, simulate the transport of water for each iteration. The mass transfer will produce a fluid film on the dry side of the membrane. This liquid evaporates into the cathode stream from there. Furthermore, the model will consider the condensation of vapor on the damp side of the gas-to-gas humidifier. The results of this methodology agree with validation data.
The developed simulation approach of a membrane humidifier in STAR-CCM+ with the help of the above mentioned “field functions” will be described in this presentation.