Visualization of the Internal Water Distribution at Pemfc Using Neutron Imaging Technology: Feasibility Test at Hanaro

The polymer electrolyte membrane fuel cell (PEMFC) is one of the most promising candidates for automotive applications due to its high energy conversion efficiency and absence of chemical pollution. PEMFC usually uses hydrogen and oxygen as fuel in order to generate electricity, and heat and water are generated as byproducts during that procedure. These byproducts create several problems coupled with fluid flow, heat, and mass transfer processes. Moreover, water more seriously affects the efficiency of the PEMFC system since the proton conductivity of the membrane is highly influenced by the water content. If the water content at the membrane and channel is too low, the conductivity of proton is decreased and the efficiency is dropped. Conversely, too much water content causes flooding at the channel. The flooding impedes gas flow and also reduces the efficiency [1]. Therefore, it is necessary to visualize the channel and MEA of PEMFC to maintain the water content and distribution properly. Moreover, knowledge of the water movement and distribution in the channel and membrane of PEMFC is helpful to increase the efficiency [2,3]. However, since PEMFC is usually made of metallic parts, it is difficult to visualize it by ordinary methods, such as optical light. The neutron imaging technique is one of the radiography methods which is a visualization technique that uses the attenuation of a radio ray at its transmission through the irradiated materials. X-ray, gamma-ray, and thermal neutrons can be used as a radio ray. A thermal neutron beam is the best choice to examine the inside of the PEMFC among these because the thermal neutron beam has unique characteristics for the attenuation coefficient compared with an X-ray and gamma-ray. Fig. 1 shows the mass attenuation coefficients of various elements for thermal neutrons and X-rays [4]. The mass attenuation coefficients of an X-ray increase monotonically with the atomic number. Thus, the X-ray imaging method does not supply sufficient contrast for light elements (for example, hydrogen and its compounds) when they are surrounded by heavy elements.