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Determination Of Two-Phase Flow Regimes Of A Condensing Water-Air Mixture In An Array Of Micro Channels

Sebastian Blessing, Moritz Lehle, Alexander Stroh, Jochen Kriegseis

Institute of Fluid Mechanics - Karlsruhe Institute of Technology, Karlsruhe, Germany


Proton exchange membrane (PEM) full cells (FCs) are a promising alternative to combustion engines for mobile applications. Their signature low operating temperature leads to the possible existence of product water in its liquid form. Liquid water formation and transport are important phenomena to understand and model in order to facilitate the development of new, more efficient PEMFCs. This contribution investigates the two-phase flow phenomena separately by introducing a gaseous air-vapor mixture into an optically accessible fuel cell flow plate with 14 parallel micro channels (confinement number Co = 7.3) and a carbon paper inlay representing the FC's gas diffusion layer and bringing it to the point of onset of condensation. Special care is taken to provide a controlled and reproducible air-vapor mixture with low pressure pulsation. One key feature of the experiment is that the flow plate used is designed to be as similar to a regular research fuel cell flow plate as possible, retaining its channel surface properties and electrical parameters. It can also be heated to a given temperature to mimic the fuel cell operating conditions. Therefore, the same plate can also be used in in-situ experiments in an operated fuel cell. An air mass flow rate of 500 - 1000 mLn / min with relative humidities of 75% - 95% at 65°C and 75°C was investigated. The emerging flow patterns were captured using a high-speed camera at 250 Hz and categorized using canonical two-phase flow regime nomenclature. It is shown that the present setup can produce the relevant two-phase flow patterns that can be found in operated fuel cells as reported by previous studies and is furthermore equipped to investigate flow states not easily reached with an operated fuel cell (e.g. flooded channels).

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