Measurement of Average Contact Angles of Gas Diffusion Layers Using a Novel Fluorescence Microscopy Method
Bibliographic record
Abstract
One of the major problems of current proton exchange membrane (PEM) fuel cells is water management. The gas diffusion layer (GDL) of the fuel cell plays an important role in water management since humidification and water removal are both achieved through the GDL. Various numerical models were developed to illustrate the multiphase flow and transport in the fuel cell. The accuracy of these models depends on the accurate measurement of the GDL properties such as wettability, surface energy, and porosity. Most of the studies conducted for measuring the wettability of the GDL are based on the external contact angle measurements. However, the external contact angle does not describe adequately the capillary forces acting on the water inside the GDL pores. In a recent study, the capillary penetration technique has been used to measure indirectly the wettability of the GDL based on the experimental height increase due to penetration of the liquid into the porous sample. In essence, the height penetration technique was used along with the general Washburn equation to determine the surface properties of GDLs [Friess and Hoorfar, 2010, “Measurement of Internal Wettability of Gas Diffusion Porous Media of PEM Fuel Cells,” J. Power Sources, 195, pp. 4736–4742]. The shortcoming of this method is that it is only effective for thin GDL samples with low poly(tetrafluoroethylene) (PTFE) loading since the digital images acquired to find the height of penetration has a limited contrast between the penetrated and unpenetrated areas. Since fuel cells need to use different combinations of PTFE loading and thickness depending on the desired use of the cell, it is important to find a way to measure the contact angle of the GDLs with different PTFE loadings and thicknesses. This paper presents a novel fluorescence microscopy method that drastically improves the contrast in the images and allows for the accurate measurement of the height of penetration of the test liquid at each time step. This penetrated height values are then used along with an optimization method (which finds the best fit between the general Washburn equation and the experimental data) to calculate the contact angle of the test liquid on the GDL sample.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.001 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.001 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".