The diffusion of moisture in sorbent solids part II. activated alumina

✍ Scribed by Stanley H. Jury; Mark A. Pollock; Eul K. Kim

• Publisher: Elsevier Science
• Year: 1977
• Tongue: English
• Weight: 713 KB
• Volume: 303
• Category: Article
• ISSN: 0016-0032
• DOI: 10.1016/0016-0032(77)90022-9

✦ Synopsis

Ordinary and thermal diffusion of moisture in activated alumina are investigated using a new diffusion cell design and scheme of analysis reported earlier. The specific form of the mass flux equation has a pronounced effect on the magnitude of the associated thermal diffusion ratio. In the case of activated alumina-moist air, if a partial pressure gradient is used, then the thermal diffusion term is small if not zero. Free, Knudsen and surface diffusion all play a part in the diffusion through activated alumina. However, surface diffusion makes the major contribution and for this reason the model in this case can be simplified to a two parameter surface model. The activation energy for surface diffusion is constant and is approximately equal fo the mean isosteric heat of adsorption. In addition, mean pore radius, tortuosity, and other physical constants are computed from the least square fit of experimental data. Furthermore, the model is theoretically consistent over the entire concetration range (OS C, 5 C4,).

A new fact about activated alumina (Grade Fl) it that it does not transfer moisture in a nonisothermal condition so long as the partial pressures of moisture on the two sides of the pellet are the same. There appears to be no previous report of this fact in the periodical literature.

(1) HIGH/LOW: Diffusion from HIGH humidity (PA = 16.5 mmHg) supply air to LOW humidity (PA = 0.002 mmHg) supply air.