Investigation on the kinetic models for the regeneration of silica gel by hot air combined with power ultrasonic

Regeneration of dehumidizers (a typical drying process) is the most important stage in the working cycle of desiccant system. Ultrasonic technology, as a non-heating method, can enhance drying kinetics and improve energy utilization efficiency in the drying process. This work has made an investigation on five different drying models, i.e., the Lewis, the Henderson & Pabis, the Logarithmic, the Weibull and the Gaussian model, that quantify the drying kinetics of silica gel during the regeneration by hot air combined with power ultrasonic according to the experimental data. The experiments were performed under different drying air temperatures (i.e. 45 °C, 55 °C, 65 °C and 75 °C) plus power ultrasonic with three kinds of frequencies (i.e. 21 kHz, 26 kHz and 38 kHz) and three power levels (20 W, 40 W and 60 W). The models were identified by fitting the experimental data with Matlab’s curve fitting tool, and the suitability of these models for predicting the moisture ratio evolution in silica gel during the regeneration was evaluated by the percent error (PE, %). The results showed that the Gaussian and the Weibull model were much more accurate than the other ones in describing the drying kinetics of silica gel assisted by the power ultrasonic. The parameter, β, in the Weibull model, which is like the drying rate constant (K) in the semi-theoretical models (e.g., the Lewis, the Henderson & Pabis and the Logarithmic model), can be found to have a regular relation with the drying temperatures, and hence, will be more convenient for modeling.

► We examine five models for the silica gel regeneration assisted by ultrasonic.
► The Gaussian and the Weibull model are superior to the others for the modeling.
► The Weibull model is recommended for its parameters can be identified more easily.
► The validity of the model depends greatly on that of the equilibrium moisture content.