|Title||Isothermal Ice Crystallization Kinetics in the Gas-Diffusion Layer of a Proton-Exchange-Membrane Fuel Cell|
|Publication Type||Journal Article|
|Year of Publication||2012|
|Authors||Dursch, Thomas J., Monica A. Ciontea, Clayton J. Radke, and Adam Z. Weber|
|Pagination||1222 - 1234|
|Keywords||catalyst layer, cold-start, growth, model, nucleation, pefc, performance, porous-media, temperature, water|
Nucleation and growth of ice in the fibrous gas-diffusion layer (GDL) of a proton-exchange membrane fuel cell (PEMFC) are investigated using isothermal differential scanning calorimetry (DSC). Isothermal crystallization rates and pseudo-steady-state nucleation rates are obtained as a function of subcooling from heat-flow and induction-time measurements. Kinetics of ice nucleation and growth are studied at two polytetrafluoroethylene (PTFE) loadings (0 and 10 wt %) in a commercial GDL for temperatures between 240 and 273 K. A nonlinear ice-crystallization rate expression is developed using Johnson-Mehl-Avrami-Kolmogorov (JMAK) theory, in which the heat-transfer-limited growth rate is determined from the moving-boundary. Stefan problem. Induction times follow a Poisson distribution and increase upon addition of PTFE, indicating that nucleation occurs more slowly on a hydrophobic fiber than on a hydrophilic fiber. The determined nucleation rates and induction times follow. expected trends from classical nucleation theory. A validated rate expression is now available for predicting ice-crystallization kinetics in GDLs.