As an alternative, Laser Doppler Anemometry (LDA) may be used since this technique only needs a small single optical access to the system. To our knowledge, LDA, which measures velocity of tracer particles within the fluid, has only been applied once in fuel cell context: Brett et al. [8] measured the flow within a single-channel fuel cell showing the applicability of this technique to measure in small geometries like in fuel cells. However, Brett et al. had difficulties with strong reflections of the laser beam on the walls that hamper data acquisition and data suffered from a lack of spatial resolution.