The oxygen concentration discharged from a compact adsorption-type oxygen concentrator decreases when water attaches to the zeolite particles used as a nitrogen adsorbent. In order to estimate the expansion of the water adsorption region in the zeolite column, it is necessary to measure the water diffusion occurring in a zeolite column after stopping PSA (Pressure Swing Adsorption) operations. Li-X type zeolite particles (molecular sieve OXYSIV-700) with particle diameters in the range of approximately 0.4–0.5 mm were used as a nitrogen adsorbent column of length 157 mm and of inner diameter 33 mm. By comparing the water concentration distributions obtained from MR (Magnetic Resonance) images and the distributions calculated by analytical solution of a one-dimensional diffusion equation under transient conditions, the counter diffusion coefficient of water absorbing on zeolite particles in the column was determined. The apparent diffusion coefficient of water absorbing on the zeolite particles moving into the zeolite column with macroscale pores was determined to be 1.25 ± 0.15 × 10−11 m2/s.
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