Determination of Sorption Rate and Apparent Solid-Side Diffusivity of Pure H2O in Silica Gel Using a Constant Volume/Variable Pressure Apparatus

[+] Author and Article Information
L. T. Lu, D. Charoensupaya, Z. Lavan

Mechanical and Aerospace Engineering Department, Illinois Institute of Technology, Chicago, Illinois 60616

J. Sol. Energy Eng 113(4), 257-263 (Nov 01, 1991) (7 pages) doi:10.1115/1.2929971 History: Received June 01, 1989; Revised July 01, 1991; Online June 06, 2008


Silica gel-water vapor is commonly suggested as a working media for solar-powered desiccant cooling systems since the system can be regenerated at relatively low temperatures. In the present study the sorption rates of water vapor by regular density silica gel particles were measured in the pressure range of 1–25 torr using a constant volume/variable pressure apparatus. The sorption rate was determined from recorded time variation of water vapor pressure in a test unit of known volume during the sorption process. The mass transfer film resistance was eliminated by evacuating the system and by introducing pure water vapor into the test unit. The apparent solid-side diffusivity was obtained by matching the analytical solution of the simultaneous heat and mass transfer governing equations to the experimental data. The uptake measurements had been performed for three particle sizes of silica gel (150 μm, 1 mm, and 3 mm). The tests were performed sequentially in small steps over a range of initial silica gel moisture content ranging from near zero up to 0.25 kg H2 O per kg dry silica gel. The effect of moisture content and particle size on the sorption rate and apparent diffusivity were determined. The effect of charging on time variation of pressure was evaluated and used for correction on all sorption data.

Copyright © 1991 by The American Society of Mechanical Engineers
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