sayed hossein masrouri saadat

Proton exchange membrane fuel cells with a dead-ended anode and cathode can obtain high hydrogen and oxygen utilization by a comparatively simple system. Accumulation of the water in the anode and cathode channels can lead to local fuel starvation, which degrades the performance of fuel cell. In this paper, for the first time, a new design for proton exchange membrane fuel-cell stack is presented that can achieve higher fuel utilization without using fuel recirculation devices that consume parasitic power. Unified humidifier is another novelty that is applied for the first time. The basic concept of the design is to divide the anodic cells of a stack into two blocks by conducting the outlet gas of each stage to a separator and reentering to next stage, thereby constructing a multistage anode and cathode. In this design, higher gaseous flow rate is maintained at the outlet of the cells, even under dead-end conditions, and this results in a reduction of purge-gas emissions by hindering the accumulation of liquid water in the cells. The result shows that with this new design the dead-end mode has the same performance as open-end mode. All performance tests were carried out at an integrated power system.

For conquering the crisis of the diminution of fossil fuels resources and environmental problems owing to their excessive consumption, some alternative technologies have been introduced. Among these possible choices, the fuel cell technology is a prominent candidate for a large scale and long term energy source. Between different types of fuel cells, the Polymer Electrolyte Membrane Fuel Cell (PEMFC) attracts greatest interest for its noticeable advantages and more over for being a “Green Energy” as it simply generates electricity by combining Oxygen and Hydrogen and producing merely water. However, the most important hindrances in the way of commercializing this technology are those associated with water and heat management in PEM fuel cells. In the present work the dynamic and droplet motion mechanisms is simulated by Volume of Fluid (VOF) two phase technique and implementing of Hoffman function as hysteresis model. In this study, the dynamic contact angle of the droplet motion is considered and the dynamic motion of the droplet is investigated in an application geometry that includes the manifolds of the gas flow distributor in the PEMFC. The effect of the manifold slopes on the discharge of liquid water droplets compare to straight manifold has also been studied. By changing the geometry of the inlet and outlet manifolds, the problem created in conventional geometry, which causes the obstruction of the channel caused by liquid water, is overcome, thus improving geometry improves water management in the channels.

In a PEMFC, the proton conductivity of the membrane depends on its water content and using saturated reactants can improve the performance of the fuel cell. The heat transfer between saturated reactants and the walls causes condensation of part of the water vapor in the inlet gas. Phase change affects the distribution of gas flow among the cells in the stack. In this paper, CFD is used to study the effect of water vapor phase change on the distribution of oxygen flow in the cathode side of a polymer electrolyte membrane fuel cell stack with 26 cells. For this purpose, a code is developed in OpenFOAM software and validated with experimental data for the single-phase flow distribution. Three different boundary conditions are applied to the walls of the manifold: constant temperature, free and forced heat convection. The results indicate that water generated from condensation on the lower wall of the inlet manifold enters the first cell. Also, the accumulation of water in this area reduces the flow velocity at the entrance of the first cell. The condensed water vapor on the upper wall of the inlet manifold moves to the end of the stack. Part of the water enters into the four last cells, and the other part returns to the manifold due to the vortex. Therefore, the first cell and the last four cells receive less reactant than other cells. The non-uniform flow distribution parameter increases by up to 1425% on using saturated oxygen and under forced convection conditions.

The management of consumption the reactive gas in PEMFC is classified into three types: open-end, recirculation and dead-end. In dead-end mode, reactant gasses due to accumulating of water and inert gas should be purged alternatively. In this paper a PEMFC stack with transparent end plates and a unique design for investigation of water management is designed, manufactured and fabricated. In this paper, for the first time, the discussion of water management in a dead-end anode and cathode PEMFC stack with details of form and remove of water has been investigated. The results have shown that at the current density lower than 200 mA/cm2 the produced water is in the form of separate droplets and there is no film flow and slug flow of water in the channel. Also, as expected, the accumulation of droplets and film flow in the lower half was more than the upper half and therefore the reduction of the number of channels to increase gas speed and effective water removal in this part was essential. The results have shown that for steady-state operation, the maximum time possible for closing the output valves is 5 seconds and the minimum time required to open it is 5 seconds.