Note: Determination of effective gas diffusion coefficients of stainless steel films with differently shaped holes using a Loschmidt diffusion cell

Abstract

Note: Determination of effective gas diffusion coefficients of stainless steel films with differently shaped holes using a Loschmidt diffusion cell Astrath, N. G. C.; Shen, J.; Astrath, F. B. G.; Zhou, J.; Huang, C.; Yuan, X. Z.; Wang, H.; Navessin, T.; Liu, Z. S.; Vlajnic, G.; Bessarabov, D.; Zhao, X.Note: Determination of effective gas diffusion coefficients of stainless steel films with differently shaped holes using a Loschmidt diffusion cell In this work, an in-house made Loschmidt diffusion cell is used to measure the effective O 2 -N 2 diffusion coefficients through four porous samples of different simple pore structures. One-dimensional through-plane mass diffusion theory is applied to process the experimental data. It is found that both bulk diffusion coefficient and the effective gas diffusion coefficients of the samples can then be precisely determined, and the measured bulk one is in good agreement with the literature value. Numerical computation of three-dimensional mass diffusion through the samples is performed to calculate the effective gas diffusion coefficients. The comparison between the measured and calculated coefficient values shows that if the gas diffusion through a sample is dominated by one-dimensional diffusion, which is determined by the pore structure of the sample, these two values are consistent, and the sample can be used as a standard sample to test a gas diffusion measurement system.

Measurement of effective gas diffusion coefficients of catalyst layers of PEM fuel cells with a Loschmidt diffusion cell

“…Using a Loschmidt cell, bulk binary diffusion coefficients of O 2 -N 2 were precisely measured under the experimental conditions of different temperatures (25-80 • C) and relative humidity values (0-80%) [18]; the EGDCs of gas diffusion layers of PEM fuel cells were also studied at different temperatures [11]. Moreover, the measured EGDC of a porous sample of a stainless steel film with simple straight pores was found to be in good agreement with the result of numerical computation of threedimensional mass diffusion through the sample [19], exhibiting the usefulness of the Loschmidt cell in studying porous material.…”

“…Zhang et al [9] used a Wicke-Kallenbach diffusion cell to measure the EGDC of a catalyst monolith washcoat. A closedtube method with a Loschmidt diffusion cell is considered as one of the most reliable methods to determine binary diffusion coefficients of gases [16][17][18][19]. Using a Loschmidt cell, bulk binary diffusion coefficients of O 2 -N 2 were precisely measured under the experimental conditions of different temperatures (25-80 • C) and relative humidity values (0-80%) [18]; the EGDCs of gas diffusion layers of PEM fuel cells were also studied at different temperatures [11].…”

Improved experimental method for measuring gas diffusivity through thin porous media

“…produces an equivalent diffusion coefficient, , that represents the heterogeneous diffusion through the bulk gas and the sample. Following the procedure used in previous studies, the resistance network method may be applied between the oxygen probe (3) and sliding gate interface (5) in Figure in order to solve for the effective diffusion coefficient of the porous sample. The equivalent diffusive resistance, R eq , is the sum of the diffusive resistance through the binary gas, R binary , and the sample, R eff …”

“…or, where l is the thickness of the porous sample. The validity of solving for R eff with the resistance network method has not been discussed in previous studies . Dong et al demonstrates that the method is only accurate within a specific range of Fourier numbers where t is the characteristic time, or the length of time the experiment is run for (see Figure ).…”

“…The Loschmidt cell must be modified to measure gas diffusion through porous media by allowing a sample to be placed near the midpoint of the long tube. A schematic of the apparatus used in this study is provided in Figure , whose design is an evolution of the modified Loschmidt cell in literature . Different gas species are contained in the upper and lower chambers of the cell separated by a sliding gate (5a), in this study nitrogen and oxygen, respectively.…”