Bibliographic record
Abstract
The durability and performance of commercially available polymer electrolyte membrane fuel cell (PEMFC) technology depends heavily on adequate humidification of the membrane electrode assembly (MEA). Early generation automotive fuel cell stacks will likely rely on an external humidification process based on gas-to-gas membrane planar humidifiers to humidify the inlet cathode stream. The membrane-based humidifier systems allow the reactants to receive recycled heat and moisture from the cathode outlet stream. \nThe objective of this thesis is to develop a flexible, computer-based simulation tool that can be used to aid in the design of these planar humidifier systems. The simulation is based on fundamental mass transfer concepts and experimental membrane behaviour based on literature results. It was determined that the mass transfer resistance through the membrane is several orders of magnitude higher than the resistance contributed by the gas diffusion media (GDM) and thus the mass transfer resistance through the GDM are not considered. An important point to note is that the Schroeder’s Paradox observed in perfluorosulfonic acid (PFSA) membranes implies that membranes in contact with liquid water will exhibit higher mass transfer than membranes in contact with saturated water vapour despite the fact that the water activity in both situations are unity. Initial simulations for which no liquid water was present resulted in a humidifier water transfer rate less than half the rate observed experimentally. Thus it was hypothesized that condensed liquid water was present on the wet-side of the humidifier membrane and as such this work assumes a fraction of the membrane surface is covered by liquid water while the rest of the membrane is exposed to gaseous water concentrations comparable to the bulk channel stream above the GDM. \nFor typical operating conditions the outlet wet-side stream retains 92% of the inlet water content and as such it was hypothesized that constant fractional liquid water coverage across the membrane could be assumed. Later simulations confirmed the validity of this hypothesis. Six models of water coverage estimation were derived using least squares and factorial design methods. The models were compared however no single method was determined to be superior for all situations as the methods exhibit similar sums of squared error.
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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 | 0.000 | 0.001 |
| Meta-epidemiology (narrow) | 0.001 | 0.001 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.002 | 0.001 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.003 | 0.001 |
| Insufficient payload (model declined to judge) | 0.004 | 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".