Higuchi Yuki, Setoyama Daigo, Isegawa Kazuhisa, Tsuchikawa Yusuke, Matsumoto Yoshihiro, Parker Joseph Don, Shinohara Takenao, Nagai Yasutaka
Toyota Central R&D Labs., Inc., Nagakute, Aichi 480-1192, Japan.
Japan Atomic Energy Agency (JAEA), Tokai 319-1195, Japan.
Phys Chem Chem Phys. 2021 Jan 21;23(2):1062-1071. doi: 10.1039/d0cp03887c.
This study is the first report on liquid water and ice imaging conducted at a pulsed spallation neutron source facility. Neutron imaging can be utilised to visualise the water distribution inside polymer electrolyte fuel cells (PEFCs). Particularly, energy-resolved neutron imaging is a methodology capable of distinguishing between liquid water and ice, and is effective for investigating ice formation in PEFCs operating in a subfreezing environment. The distinction principle is based on the fact that the cross sections of liquid water and ice differ from each other at low neutron energies. In order to quantitatively observe transient freezing and thawing phenomena in a multiphase mixture (gas/liquid/solid) within real PEFCs with high spatial resolution, a pulsed neutron beam with both high intensity and wide energy range is most appropriate. In the validation study of the present work, we used water sealed in narrow capillary tubes to simulate the flow channels of a PEFC, and a pulsed neutron beam was applied to distinguish ice, liquid water and super-cooled water, and to clarify freezing and thawing phenomena of the water within the capillary tubes. Moreover, we have enabled the observation of liquid water/ice distributions in a large field of view (300 mm × 300 mm) by manufacturing a sub-zero environment chamber that can be cooled down to -30 °C, as a step towards in situ visualisation of full-size fuel cells.
本研究是关于在脉冲散裂中子源设施上进行液态水和冰成像的首份报告。中子成像可用于可视化聚合物电解质燃料电池（PEFC）内部的水分布。特别是，能量分辨中子成像是一种能够区分液态水和冰的方法，对于研究在亚冰点环境下运行的PEFC中的结冰现象很有效。区分原理基于这样一个事实，即在低中子能量下，液态水和冰的截面彼此不同。为了以高空间分辨率定量观测实际PEFC中多相混合物（气体/液体/固体）中的瞬态冻结和解冻现象，具有高强度和宽能量范围的脉冲中子束最为合适。在本工作的验证研究中，我们使用密封在细毛细管中的水来模拟PEFC的流道，并应用脉冲中子束来区分冰、液态水和过冷水，以及阐明毛细管内水的冻结和解冻现象。此外，通过制造一个可冷却至-30°C的零下环境室，我们实现了在大视场（300毫米×300毫米）内观测液态水/冰的分布，这是朝着全尺寸燃料电池原位可视化迈出的一步。
