The diffusion of moisture in sorbent solids—I. Diffusion cell and pore diffusion

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

• Publisher: Elsevier Science
• Year: 1977
• Tongue: English
• Weight: 912 KB
• Volume: 303
• Category: Article
• ISSN: 0016-0032
• DOI: 10.1016/0016-0032(77)90116-8

✦ Synopsis

A complete theory of diffusion of absorbing gases in porous

solids is developed. Both ordinary and thermal diffusion are considered. The thermodynamics of irreversible processes is used to derive the general flur equations. A new rheoretical model of surface diffusion is presented. Moreover, the proper method of combining surface and gas-phase fluxes is established. The total flux in the pores is represented by a 5 paramefer model, which includes the effects of (1) free (gaseous) diffusion, (2) Knudsen diffusion, and (3) surface diffusion. The design of a new diffusion cell is presented along with a stagewise method for analyzing results. The cell is unique in that specimens mounted in copper clad circuit board material permits nonisothermal as well as isothermal operation. Earlier designs were confined to isothermal operation due to mounting specimens in metallic materials such as brass and aluminum. Ordinary and thermal diffusion of moisture in activated alumina will be investigated in Part II of this paper using a new diffusion cell design and scheme of analysis, as discussed in Part I. Notation AA Aas, AK.., A,, AS BB G c Amax c *sat cc c OA CO EA&TR, constant to be determined combined constants for free and Knudsen diffusion, respectively total pellet cross-sectional area per stage, cm* specific surface area of sorbent, 2.1 (106) cm'/gm A.&A,, constant to be determined molar concentration of condensed phase, gmoles/cm3 of adsorbent maximum value of C, after boiling in liquid H,O the limit of C, as (P,/PS)+l ER/TC,~~,A,, constant to be determined molar gas concentration of A, gmoles/cm3 fre J4 uency factor in coefficient of resistance to surface flow, mmHg set/cm "K