scholarly journals Determination of the anisotropic permeability of a carbon cloth gas diffusion layer through X-ray computer micro-tomography and single-phase lattice Boltzmann simulation

2010 ◽  
Vol 67 (4) ◽  
pp. 518-530 ◽  
Author(s):  
P. Rama ◽  
Y. Liu ◽  
R. Chen ◽  
H. Ostadi ◽  
K. Jiang ◽  
...  
Keyword(s):  
Diffusion Layer ◽  
Lattice Boltzmann ◽  
Single Phase ◽  
Gas Diffusion ◽  
Carbon Cloth ◽  
Anisotropic Permeability ◽  
X Ray ◽  
Lattice Boltzmann Simulation ◽  
Micro Tomography

An Improved MRT Lattice Boltzmann Model for Calculating Anisotropic Permeability of Compressed and Uncompressed Carbon Cloth Gas Diffusion Layers Based on X-Ray Computed Micro-Tomography

2012 ◽  
Vol 9 (4) ◽  
Author(s):  
Yuan Gao ◽  
Xiaoxian Zhang ◽  
Pratap Rama ◽  
Rui Chen ◽  
Hossein Ostadi ◽  
...  
Keyword(s):  
Lattice Boltzmann ◽  
Gas Diffusion ◽  
Lattice Boltzmann Model ◽  
Anisotropic Permeability ◽  
Gas Diffusion Layers ◽  
X Ray ◽  
Diffusion Layers ◽  
X Ray Computed ◽  
Micro Tomography ◽  
Boltzmann Model

The gas diffusion layers (GDLs) in polymer proton exchange membrane fuel cells are under compression in operation. Understanding and then being able to quantify the reduced ability of GDLs to conduct gases due to the compression is hence important in fuel cell design. In this paper, we investigated the change of anisotropic permeability of GDLs under different compressions using the improved multiple-relaxation time (MRT) lattice Boltzmann model and X-ray computed micro-tomography. The binary 3D X-ray images of GDLs under different compressions were obtained using the technologies we developed previously, and the permeability of the GDLs in both through-plane and in-plane directions was calculated by simulating gas flow at micron scale through the 3D images. The results indicated that, in comparison with the single-relaxation time (SRT) lattice Boltzmann model commonly used in the literature, the MRT model is robust and flexible in choosing model parameters. The SRT model can give accurate results only when using a specific relaxation parameter whose value varies with porosity. The simulated results using the MRT model reveal that compression could lead to a significant decrease in permeability in both through-plane and in-plane directions, and that the relationship between the decreased permeability and porosity can be well described by both Kozeny-Carman relation and the equation derived by Tomadakis and Sotirchos (1993, “Ordinary and Transition Rdgime Diffusion in Random Fiber Structure,” AIChE J., 39, pp. 397–412) for porosity in the range from 50% to 85%. Since GDLs compression takes place mainly in the through-plane direction, the results presented in this work could provide an easy way to estimate permeability reduction in both through-plane and in-plane directions when the compressive pressure is known.

Comparing the Permeability Calculation Between Different System Size of the Computational Gas Diffusion Layer Sample in PEMFC

2014 ◽  
Author(s):  
Yuan Gao
Keyword(s):  
Fluid Flow ◽  
Diffusion Layer ◽  
Lattice Boltzmann ◽  
Gas Diffusion Layer ◽  
System Size ◽  
Gas Diffusion ◽  
X Ray ◽  
Layer Sample ◽  
Micro Tomography ◽  
Boltzmann Method

The gas diffusion layers (GDLs) are key components in proton exchange membrane fuel cells and understanding fluid flow through them plays a significant role in improving fuel cell performance. We used a combination of multiple-relaxation time (MRT) lattice Boltzmann method (LBM) and X-ray micro tomography imaging technology to compare results on dependence of the permeability calculation on the different system size of the computational gas diffusion layer sample. The micro-structures of the carbon paper (HP_1.76) and carbon cloth (HP_1.733) GDL were all digitizing 3D images acquired by X-ray computed micro-tomography at a resolution of 1.76 and 1.733 microns meter respectively, and the fluid flow was simulated by applying pressure gradient in both the through-plane and in-plane direction respectively. The lattice Boltzmann method for permeability calculation has already been tested in our previous work. In this work, we will focus on the permeability calculation of the realistic gas diffusion layer samples depend on the different size samples. The results show the permeability increases with fluctuations as the porosity rises. All the permeability and porosity converge to the value of large size sample that can be regarding a representative volume element. As the porosity and permeability of these Porous samples differs significantly for each other, the anisotropic permeability is nearly same for each one. We can choose part of the sample to calculate the characters if the sample is too big to calculate. We systematically study the effect of system size and periodic boundary condition and validate Darcy’s law from the linear dependence of the flux on the body force exerted.

Modeling of Fluid Behavior and Calculation of the Permeability of the Gas Diffusion Layer in PEM Fuel Cell Using Lattice Boltzmann Method

2010 ◽  
Author(s):  
Y. Gao
Keyword(s):  
Boundary Condition ◽  
Porous Medium ◽  
Lattice Boltzmann Method ◽  
Diffusion Layer ◽  
Lattice Boltzmann ◽  
Gas Diffusion Layer ◽  
Gas Diffusion ◽  
Carbon Paper ◽  
X Ray ◽  
Boltzmann Method

In the current work, a lattice Boltzmann method (LBM) is developed to study the fluid flow through digitally reconstructed 3D models of carbon paper GDLs generated by x-ray computed tomography, and the research on permeability calculation in the gas diffusion layer is also included. The methods involves the generation of a 3D digital model of a carbon paper GDL as manufactured using x-ray images acquired through x-ray micro-tomography at a resolution of 1.74 microns. The reconstructed 3D images then read into the LB model in order to predict three orthogonal permeability tensors when pressure is prescribed in the different flow direction. The Lattice Boltzmann method (LBM), an evolving pore-scale modeling approach, has received increasing attention in computational fluid dynamics. In the LBM, fluid is represented by a distribution of particles moving on a regular lattice. The LBM is extremely appealing in porous medium simulation, because the bounce-back boundary condition is efficient to treat solid boundary. It can deal with the boundary condition more easily than other tradition method. At the inlet/outlet boundaries, a pressure boundary condition is applied. This study characterizes the relationships between anisotropic permeability and porosity for gas diffusion layer, where hydrodynamics is analyzed in detail. The results indicate that the LBM is powerful and is able to provide excellent estimation on the permeability in a porous medium. The calculated permeability is in good agreement with existing measurements. The relationship between the permeability and the porosity is fitted well with the Kozeny-Carman equation and existing results.

Prediction the Differences of Permeability Between Carbon Fiber Paper and Carbon Fiber Cloth in PEM Fuel Cells

2011 ◽  
Author(s):  
Yuan Gao
Keyword(s):  
Fuel Cells ◽  
Carbon Fiber ◽  
Pem Fuel Cells ◽  
Gas Diffusion ◽  
Anisotropic Permeability ◽  
Gas Diffusion Layers ◽  
X Ray ◽  
Diffusion Layers ◽  
Carbon Fiber Cloth ◽  
Carbon Fiber Paper

This study is using the multiple relaxation time Lattice Boltzmann method to calculate the permeability of carbon fiber paper and carbon fiber cloth gas diffusion layers (GDL). The 3D gas diffusion layers are generated by X-ray computed tomography, This method involve generation of 3D digital model of gas diffusion layers acquired through X-ray micro-tomography at resolution of a few micros. The reconstructed 3D images were then read into the LBM model to calculate the anisotropic permeability of carbon fiber paper and carbon fiber cloth GDL. We investigated the relationships between the anisotropic permeability and porosity and compare the difference between the two different kinds of GDLs when they have the similar porosity. We also calculate the permeability with different viscosity and compare the two results from the carbon fiber paper and carbon fiber cloth. It is useful for selection of materials for high performance gas diffusion media and can improve the performance of the fuel cells.

scholarly journals Quantifying phosphoric acid in high-temperature polymer electrolyte fuel cell components by X-ray tomographic microscopy

2014 ◽  
Vol 21 (6) ◽  
pp. 1319-1326 ◽  
Author(s):  
S. H. Eberhardt ◽  
F. Marone ◽  
M. Stampanoni ◽  
F. N. Büchi ◽  
T. J. Schmidt
Keyword(s):  
High Temperature ◽  
Fuel Cell ◽  
Phosphoric Acid ◽  
Polymer Electrolyte ◽  
Diffusion Layer ◽  
Gas Diffusion Layer ◽  
Gas Diffusion ◽  
X Ray ◽  
Wide Range ◽  
Cell Components

Synchrotron-based X-ray tomographic microscopy is investigated for imaging the local distribution and concentration of phosphoric acid in high-temperature polymer electrolyte fuel cells. Phosphoric acid fills the pores of the macro- and microporous fuel cell components. Its concentration in the fuel cell varies over a wide range (40–100 wt% H3PO4). This renders the quantification and concentration determination challenging. The problem is solved by using propagation-based phase contrast imaging and a referencing method. Fuel cell components with known acid concentrations were used to correlate greyscale values and acid concentrations. Thus calibration curves were established for the gas diffusion layer, catalyst layer and membrane in a non-operating fuel cell. The non-destructive imaging methodology was verified by comparing image-based values for acid content and concentration in the gas diffusion layer with those from chemical analysis.

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