Modeling Micro- and Macro-Scale Two-Phase Flow in 3D Flow Channels of Proton Exchange Membrane Fuel Cells PDF Download

Author: Jinyong Kim
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Languages : en
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Book Description
Water management is of paramount importance for improving the performances of proton exchange membrane fuel cells (PEMFCs). Fuel cell channel design plays the most significant role in not only water management but also species transport for electro-chemical reactions. To enhance the performance and durability of PEMFCs, uniform and high oxygen concentration at catalyst layer should be ensured. Unlike conventional PEMFCs, new generation PEMFCs (i.e. Toyota Mirai) maximize their performance by optimizing both macroscopic flow fields and configurations of micro-structures (i.e. baffle, blockages, obstacles). For a new generation of PEMFC technologies, macroscopic modeling of physical phenomena involved in micro-scale two-phase flow of 3D complex flow-fields (i.e. 3D fine-mesh flow-fields of Toyota Mirai) are crucial for large-scale fuel cell simulation.By making an analogy between flow-fields of PEMFCs and porous media, which is so-called porous media approach, two-phase flow models for flow-fields of PEMFCs are developed to numerically investigate and capture various macroscopic and microscopic two-phase flow behavior in flow-fields of PEMFCs. First, flow inertial effects in 3D complex flow-fields on macroscale and microscale two-phase behavior are investigated by considering Forchheimers inertial effect on two-phase flow. It is found that the Forchheimers effect plays a dominant role on liquid water removal and oxygen transport in 3D complex flow-fields of PEMFCs.Second, liquid water re-distributions caused by micro-pore structures attached to bi-polar plates of PEMFCs with 3D complex flow-fields are explored by a macroscopic modeling approach accounting for a capillary effect. It is revealed that the micro porous structures, which is macroscopically viewed as secondary porous media, can improve liquid water management and oxygen diffusion if the permeability of secondary porous media is above a threshold.Third, a two-phase flow model based on porous media approach is suggested to capture the effect of different micro-scale two-phase flow regime (slug, droplet/film, mist flow) in flow channels into a macroscopic PEMFC model. The macroscopic PEMFC model is then applied to explore the effect of two-phase flow regime in micro-channels on cell performance. It is found that flow mal-distribution can be alleviated as the two-phase regime changes from slug, droplet/film to mist flow.