Comprehensive investigation of membrane sorption and CFD modeling of a tube membrane humidifier with experimental validation. (15th March 2023)

• Record Type: Journal Article
• Authors: Schmitz, M.; Welker, F.; Tinz, S.; Bahr, M.; Gössling, S.; Kaimer, S.; Pischinger, S.
• Is Part Of: International journal of hydrogen energy. Volume 48:Number 23(2023)
• Page Start: 8596
• Page End: 8612
• Publication Date: 2023-03-15
• Subjects: Humidification -- Tube membrane humidifier -- PEM fuel Cell -- Nafion sorption rate -- Experimental validation -- CFD model; Hydrogen as fuel -- Periodicals; Hydrogène (Combustible) -- Périodiques; Hydrogen as fuel; Periodicals; 665.81
• DOI: 10.1016/j.ijhydene.2022.11.081
• Languages: English
• ISSNs: 0360-3199

Abstract

Abstract: The humidification of PEM fuel cells is critical for their performance and efficiency and for ensuring a long durability. In most PEM fuel cell systems for mobile applications membrane humidifiers are used to humidify the fresh air. In this process, the water contained in the cathode exhaust gas is used to increase the humidity of the supply air. Despite the simple design of membrane humidifiers, the simulation of the water transfer is difficult and so far there exist hardly any precise models to calculate the absorption and desorption processes. Common approaches that use the Sherwood number to determine the sorption rates cannot account for the influence of the local water content of the membrane. This ultimately leads to an inaccurate simulation of humidifier behavior, as these models cannot consider the fact that desorption is nearly ten times faster than absorption. In this study, an empirical formula for an accurate determination of the sorption rate is derived based on experimental data. This function accounts for the different absorption and desorption rates by finding a sorption rate coefficient as a function of the local membrane water content, temperature, pressure and flow velocity. Furthermore, a CFD model is derived from the geometry of a commercially available membrane humidifier, which is also investigated on a test bench. Using the experimental data, the CFD model is validated and it is shown that the developed sorption rate formula leads to good agreements between simulations and experiments at steady-state operating points of the humidifier. Highlights: Novel function to determine absorption and desorption rate of Nafion membranes. Sorption strongly depends on local membrane water content and flow velocity. Comparison between CFD model of membrane humidifier and measurements. Sorption function leads to good agreements between simulations and measurements.