Adsorption 7: 211–219, 2001 c  2001 Kluwer Academic Publishers. Manufactured in The Netherlands. Thermal Diffusivity and Adsorption Kinetics of Silica-Gel/Water J.M. GURGEL AND L.S. ANDRADE FILHO UFPB/LES/CT/DTM/CPGEM, 58.059-100 Jo˜ ao Pessoa, PB, Brazil PH. GRENIER LIMSI/CNRS, B.P. 133 F-91403 Orsay Cedex, France F. MEUNIER ∗ CNAM-IFFI, 292 rue Saint-Martin, 75141 Paris Cedex 03, France Received September 7, 2000; Revised June 18, 2001; Accepted June 18, 2001 Abstract. There have been performed experimental measurements of effective thermal conductivity of silica-gel for a stagnant cylindrical fixed bed under transient and steady state conditions in the presence of dry air at different pressures and for different amounts of adsorbed water. The Bauer-Schl¨ under and Kunii-Smith models have been used to identify the thermal solid conductivity of silica gel pellets from measurements of the conductivity in an adsorbent bed. Sorption rates of water vapor in silica gel were measured using a single-step thermal method by monitoring the sample surface temperature by infrared detection. In order to obtain the mass diffusivity it is necessary to match the numerical solution of the mathematical model to the experimental data. Keywords: silica-gel, adsorption, conductivity, mass diffusivity Introduction Silica-gel is a solid adsorbent utilized as drying agent in industrial processes. Silica gel-water vapor is proposed as a working couple for solar refrigerators, heat pumps and desiccant cooling systems. The relatively regen- erating temperature makes it very attractive for such applications. The analysis of the thermal behavior of devices using silica-gel shows that their performance is very sensitive on heat and mass transfer rates inside the adsorbent beads. Therefore it is necessary to mea- sure the thermal diffusivity and sorption rates in these beads. Thermal conductivity of silica-gel from differ- ent suppliers was previously investigated by Bj¨ urstr¨ om et al. (1984) and Gurgel and Kl ¨ uppel (1996). The results here presented are intended to be used in the modeling of the heat and mass transfer processes occurring in ∗ To whom correspondence should be addressed. sorption systems. The silica-gel here studied is com- mercially known as “type R Sorbead”, produced by Kalichemie  . It is presented as spheroidal beads with an average diameter d = 3.5 mm, with a specific surface of 750 m 2 /g, an average pore diameter of 2.0 µm, and a pore volume of 0.35 ml/g, according to what is reported by the maker (Kalichemie  . AG 1979). Bed porosity ε and density ρ b have been found experimentally to be ε = 0.36 ± 0.01 and ρ b = 746 kg m -3 (Gurgel and Kl¨ uppel, 1996). The present work aims at giving a contribution for determining mass diffusivity of water in silica gel and the effective thermal conductivity of the silica gel bed. In order to measure the thermal conductivity of packed beds, a great variety of methods have been used. Those methods can be classified as steady and transient methods and are classed as very good in a review make by Tsotsas and Martin (1987). In the present work, two different techniques to measure thermal conductivity