Measurement of apparent solid-side mass diffusivity of a water vapor–silica gel system

A measurement of the apparent solid-side mass diffusivity of water vapor adsorbed in a regular density silica gel is performed by using a constant-pressure thermal gravimetrical apparatus. The diameter of the silica gel particles is 2 mm. Six adsorption isotherms, individually correspond to 5.1, 22.2, 34.3, 49.5, 64.4 and 79.6 °C, are measured. The covered range of moisture content is from 0% to 40%. Using a previously developed model, which considers both surface (film) heat and mass transfer resistances, the measured uptake curves yield the apparent solid-side mass diffusivities. The apparent solid-side mass diffusivity is expressed as a function of temperature and moisture content. The thermal effect and importance of surface mass transfer resistance are individually discussed.