Investigation on sound propagation for the measurement of diffusion in microporous solids
The basic definitions of micropore diffusivities and the experimental techniques applied for their measurement are reviewed. Through a historical perspective, the techniques are briefly described, with an emphasis on the measured property, the theoretical and practical limitations. As a result the need for a novel experimental technique has been identified. The extension of the frequency response (FR) method to frequencies in the audible sound range is proposed. A detailed mathematical model is presented to describe the propagation of sound between two parallel adsorbing plates. The main body of the thesis is the description and derivation of a model that relates an acoustic quantity (i.e. propagation constant) to adsorption parameters (i.e. diffusivity and equilibrium constant) in microporous solids. The theoretical analysis describes the ranges of physical parameters where the complete model reduces to simplified versions: classical absorption isothermal limit equilibrium control temperature control. Based on the theoretical study a prototype apparatus has been designed and constructed. The system allows for flexibility in the loading of adsorbent material, geometrical properties and gas used. Preliminary experimental results are reported and interpreted based upon the theory of acoustics described above.