Cesar E. Damian-Ascencio

Entropy Generation Analysis for a PEM Fuel-Cell With a Biomimetic Flow Field

The present paper shows an entropy generation analysis for a PEM fuel cell. The numerical model takes into account the complete solution of Navier-Stokes, energy conservation, species conservation and two potential fields for the transport of electrons and protons in the collectors and membrane respectively. The entropy generation equation is added to the governing equations using the solutions provided from the energy, momentum, species and potential flow equations. The entropy generation analysis reveals the locations where the main losses (irreversibilities) are produced. This in consequence shows the best flow field to minimize the entropy production. A new parameter is proposed in this work that will compare the entropy production due to the mass flow to the total entropy production.Copyright

Three Dimensional Analysis of a PEM Fuel Cell with the Shape of a Fermat Spiral for the Flow Channel Configuration

This work presents the analysis of a non-isothermal three-dimensional model in single phase of a PEM fuel cell with an innovative flow field path in the form of the Fermat spiral, i.e. two concentric spirals. The model is used to predict the current density contours and the water content in all of the zones of the fuel cell. The three-dimensional model includes: the gas flow channels with the shape of the new geometry proposed, the current collectors, gas diffusion layers, catalyst layers on both sides of the model, anode and cathode, and a proton exchange membrane in between. The model solves the energy equation, mass conservation, and species transport equations, including the source terms due the electrochemical effects occurring in the cell. The results show a higher average current density than the fuel cells with conventional flow paths, showing also that the current density attained is more uniform from the inlet to the outlet of the flow channels.Copyright

Assessing the Exergy Costs of a 332-MW Pulverized Coal-Fired Boiler

In this paper, we analyze the exergy costs of a real large industrial boiler with the aim of improving efficiency. Specifically, the 350-MW front-fired, natural circulation, single reheat and balanced draft coal-fired boiler forms part of a 1050-MW conventional power plant located in Spain. We start with a diagram of the power plant, followed by a formulation of the exergy cost allocation problem to determine the exergy cost of the product of the boiler as a whole and the expenses of the individual components and energy streams. We also define a productive structure of the system. Furthermore, a proposal for including the exergy of radiation is provided in this study. Our results show that the unit exergy cost of the product of the boiler goes from 2.352 to 2.5, and that the maximum values are located in the ancillary electrical devices, such as induced-draft fans and coil heaters. Finally, radiation does not have an effect on the electricity cost, but affects at least 30% of the unit exergy cost of the boiler’s product.

Experimental Analysis of PEM Fuel Cells With Biomimetical Mixed Flows as Gas Distributors

A proton exchange membrane fuel cell (PEMFC) is an electrochemical device that converts the chemical energy from the gases into electrical energy. The PEMFCs consist of many parts, and the current collector plate is one of the key components among them. Channels in the bipolar plate distribute air on the cathode side and hydrogen on the anode side. Theoretically a fuel cell produces more current as more fuel is supplied. However the way in which the gases are supplied affects dramatically the performance of the cell. The present paper shows how the mixed flows improve the current density produced by fuel cells. Polarization and power density curves are presented. The results suggest that a flow with two levels of bifurcations is preferred for the anode side. This behavior is expected due to the similitude with the performance of the natural world in which geometries with this type of bifurcations transport the nutrients inside the tree leaves and plants.Copyright