Dynamic and steady-state analysis and design of autonomous portable direct methanol fuel cell systems by means of modelling and experimental validation
Final Report Abstract
Direct methanol fuel cell systems for portable applications are required to be light and simple without any sacrifice of controllability and autonomous operation. In this research, we investigated various system designs in different points of view. First of all, the reference system in which each component has just one function, was simulated as a reference for all other designs and to determine the feasibility envelope envelope for autonomous operation. The region of infeasible operation at high temperature and low relative humidity increases with higher air flow rate and higher condenser temperature. This model-based prediction was validated experimentally in a climate chamber. In addition, the reference system is evaluated with feed forward control of the concentration in the anodic loop based on a simplified methanol cross over model. Subsequently, a double tank system equipped with an additional water tank to minimize methanol crossover was analysed. This system controls concentration rapidly at certain current density. To realize the assumption of perfect mixing in the model, in the experiment, the in-line mixer is employed in the system to blend neat methanol and water effectively. As a third system, we integrated selected processes in the DMFC system to reduce components and volume. The primary integration was to combine components which have identical functions in the system such as the anodic cooler and the cathodic cooler. In addition, the degasser and the condenser were combined in this mingled outlet system. For this system, we found that unused methanol at the anode outlet contacts high flow rate and hot air from cathode outlet, and evaporates more than in the reference system. Even though fuel efficiency was low, we achieved higher energy density due to higher heat transfer coefficient of the heat exchanger in the mingled outlet system than in the reference system because of the higher gas/liquid fraction. In a fourth system, further integration was undertaken in the separator and the mixer. The functions of these two components are not identical with each other but can coexist in one device. However, this process integration brings about worse fuel efficiency than in the mingled outlet system because neat methanol is directly exposed to the ambient air. Through these process integrations, we can get higher energy density of the system owing to reducing components while compromising on fuel efficiency. Finally, the important characteristic of portable power sources is orientation-independent operation. Effects of the required system modification were investigated in the fifth system. In the previous systems, the gas/liquid separator was designed based on separation by different densities using gravity. Using a hydrophobic membrane as in the fifth system, the DMFC system can be operated in any orientation free from gravity. In addition, the membrane separator enables feed forward control of water level without level sensing, which can make systems simpler and especially better to control. This project, in summary, revealed pros and cons of meaningful variations of DMFC system designs. The results give essential information to applied researchers, and industry to optimize and choose suitable system designs based on their applications needs.
Publications
- Experimental analysis of the separation efficiency of an orientation independent gas-liquid membrane separator, Separation and Purification Technology, 81(3):347-356, 2011
Maik Kraus and Ulrike Krewer
- Simple and reliable model for estimation of methanol cross-over in direct methanol fuel cells and its application on methanolconcentration control, Energy and Environmental Science, 4:519-527, 2011
Federico Zenith and Ulrike Krewer
- Effects of process integration in an active direct methanol fuel-cell system, Chemical Engineering and Processing: Process Intensification, 59:43-51, 2012
Federico Zenith, Youngseung Na and Ulrike Krewer
- Model-based analysis of microseparators for portable direct methanol fuel-cell systems, Computers and Chemical Engineering, 38:64-73, 2012
Federico Zenith, Maik Kraus and Ulrike Krewer
- Experimental Determination of the Feasibility Envelope for Autonomous Operation of DMFC systems. 9th World Congress of Chemical Engineering, Seoul Korea, August 2013
Youngseung Na, Ulrike Krewer
- Effects of Process Integration on the Performance of Direct Methanol Fuel Cell Systems, Fuel Cells 2014 Science and Technology-A Grove Fuel Cell Event, Amsterdam Netherlands, April 2014
Youngseung Na, Ulrike Krewer
