Error in the Estimation of Effective Diffusion Coefficients from Sorption Measurements

Bobok, D. and Besedová, E. Error in the Estimation of Effective Diffusion Coefficients from Sorption Measurements Chemical Papers, Vol.54, No. 6b, 2000, 482-488

Document type: Článok z časopisu / Journal Article
Collection: Chemical papers  
 
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Author(s) Bobok, D.
Besedová, E.
Title Error in the Estimation of Effective Diffusion Coefficients from Sorption Measurements
Journal name Chemical Papers
Publication date 2000
Year available 2000
Volume number 54
Issue number 6b
ISSN 0366-6352
Start page 482
End page 488
Place of publication Poland
Publisher Versita
Collection year 2000
Language english
Subject 290000 Engineering and Technology
290600 Chemical Engineering
Abstract/Summary A gravimetric sorption method was employed for the estimation of effective diffusion coefficients of water in silica gel particles. Air with a certain concentration of water passed through an adsorber with a fixed bed of silica gel particles with a height equal to the diameter of a single particle. The adsorber was weighed at chosen time intervals. This method is based on the assumption of zero mass transfer resistance in the fluid phase surrounding the adsorbent particles. From the two- lm theory it follows that for the measurement conditions employed here, the maximum resistance in the fluid phase is 12.5 %. Hence, the resistance in the solid phase is loaded by a maximal error of 12.5 %. The total error of the estimated values of the effective diffusion coefficients is not greater than 40 %. The values of the effective diffusion coefficients obtained by the measurements of the stepwise adsorption and the values of the effective diffusivity obtained by the measurements of the stepwise desorption are within the range 0.90 x 10−10—2.1 x 10−10 m2 s−1. Data obtained in this way are in agreement with data published in the literature. Comparison of the estimated values of the effective diffusion coefficients with those calculated under the assumption that the water transport in silica gel particles takes place solely by molecular diffusion or by Knudsen diffusion demonstrates that the latter does not occur under the conditions investigated.
 
 
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