Parametric study on silica gel regeneration by hot air combined with ultrasonic field based on a semi-theoretic model

To improve the adaptability of the proposed semi-theoretic model in our previous paper (Ref. [1]), the equations of heat and mass transfer coefficient dependent on the regeneration temperature, the air flow rate, the ultrasonic power and frequency are formulated based on a series of experimental data. The semi-theoretic model with the empirical equations of heat and mass transfer coefficient has been validated by experiments. Afterward, the ultrasonic-assisted regeneration for a silica gel packed bed is simulated with the theoretic model under a wide range of conditions, i.e., the inlet air temperature and humidity ranges from 35 to 80 °C and from 0.01 to 0.035 kg/(kg dry air), respectively; the regeneration air flow rate from 0.1 to 1.5 m/s; the acoustic frequency from 20 to 35 kHz combined with the power from 20 to 80 W; the particle size of silica gel in the bed from 1.0 to 7.0 mm. The key variables during the ultrasonic-assisted regeneration are then investigated based on the simulation data, including the acoustic pressure distribution and corresponding oscillation velocity induced in the packed bed, the temperature and moisture ratio distribution in the packed bed and the enhancement of silica gel regeneration brought by ultrasound.