DYNAMICS STUDY OF A CLOSED DIFFUSION CELL BY USING A FREQUENCY-RESPONSE METHOD - SINGLE RESONATOR

The frequency response (FR) of a closed diffusion cell with one resona tor is analysed theoretically using nonisothermal Fickian diffusion mo dels for both homogeneous and bi-porous particles. It is shown that wi th this diffusion cell configuration, the pressure response in the mod ulating reservoir has many significant characteristics: a larger phase difference with respect to the volume perturbation, a lower resonatin g frequency and most importantly a much higher sensitivity to the natu re of diffusion mechanisms when dealing with biporous pellets. This hi gh sensitivity makes it practically feasible to determine which diffus ional resistance is rate-limiting without experimenting on pellets of different sizes. The pressure response of the second reservoir exhibit s a large phase delay with respect to the volume modulation and also a high sensitivity to the diffusion mechanism. Finally, the pressure di fference between the two reservoirs has a significantly larger phase a ngle than the pressure response in a batch adsorber FR system. More im portantly, it is practically independent of the heat effect and has tw o distinct zones (only affected by macropore diffusion at lower freque ncies) making it an ideal monitored response for the study of mass tra nsfer.