(608e) Direct Measurement of the Mass Transport Coefficient of Water in Silica-Gel Using the ZLC Technique

Adsorption processes are important in the recovery of low grade heat. Silica gel/water is one of the reference pairs – material/adsorbate – in such processes and while equilibrium measurements are well-established, the measurement of the mass transport coefficient remains a challenge in part due to the fact that it is nearly impossible to decouple mass and heat transfer effects. A new approach for the determination of the mass transfer coefficient of water in commercial silica gel is proposed and demonstrated with measurements on a single particle using the zero length column technique. The methodology requires measurements at low flowrates to acquire equilibrium isotherms with thousands of points in less than one day, thus allowing numerical interpolation to calculate the relationship between vapour concentration and equilibrium adsorbed amounts. The same column is then run at high flowrates to achieve mass transfer control. The novel approach determines directly all the components needed to calculate the mass transfer coefficient from the measured signals without the use a specific model.

Adsorption and desorption experiments were carried out at different flowrates and three different temperatures. It is possible to determine an average mass transfer coefficient that is in line with literature values. The results show also a complex behaviour with surface diffusion as the main contribution to the transport process.

Reference:

Brandani S. and Mangano E. Direct Measurement of the Mass Transport Coefficient of Water in Silica-Gel Using the Zero Length Column Technique, Energy, 2022, 239A, 121945 https://doi.org/10.1016/j.energy.2021.121945