Visualization and Measurement of Hygroscopic Water Distribution in a Unit Cell of Silica-Gel Adsorber by Neutron Radiography

Evaluation or hygroscopic water distribution in adsorber is important to design adsorption refrigerating system, because the adsorption and desorption process strongly affect on the cycle performance. A neutron radiography method was applied to a diagnosis of a silica-gel adsorber, such as nondestructive testing of the structure of particle layer and real-time measurement of hygroscopic water distributions. Silica gel particles of diameter around 0.5 mm were used. The attenuation coefficient of neutron beam for the silica gel particle layer was measured using a sample rectangular capsule. Then, a silica-gel unit was made by filling the silica-gel particles between fins on the outside of an aluminum cylinder. The particles were fixed with vinyl acetate glue. The internal structure of the unit was successfully visualized with the spatial resolution of 107 mu m. From the visualized images, 3-D structure of the unit was clearly obtained by a computed tomography method. From the comparison between dry and wet condition, hygroscopic water distribution could be measured. Moreover, radial distribution could be obtained by Abel transform assuming the axial symmetry.