Effect of ultrasonic waves on dissociation kinetics of tetrafluoroethane (CH2FCF3) hydrate

Abstract

The effect of ultrasonic waves on formation and dissociation kinetics of gas hydrates has been experimentally studied by several researchers. Some results indicated that ultrasonic waves have the effect of reducing gas hydrate induction time before the initiation of hydrate formation, while others reported on the effect of prohibiting the growth kinetics during hydrate formation. There have also been reports regarding an increase in the amount of gas consumed and a decrease in the hydrate formation time. The present study examines the influence of ultrasonic waves on gas hydrate dissociation. Gas hydrate formation and dissociation occurred in a temperature-controlled 15L horizontal cylindrical reactor. The reactor was agitated with a pair of flat blades installed in radial direction and a pair of rollers, which were driven by a motor connected through a magnetic coupler. R-134a, a gas that can form hydrates at a relatively low pressure, was used to form gas hydrate slurry. Dissociation was augmented by 20kHz ultrasonic waves generated with a piezoelectric converter and transmitted through a vibrating horn whose tip was in contact with the hydrated slurry in the reactor. To compare the effect of energy input in the form of ultrasonic waves with that of the same amount of heat input, equivalent amount of heat was provided to the reactor. Dissociation rate and the accumulated dissociation time were compared between the cases of heat addition and ultrasonic wave irradiation. Results show that not only does the dissociation rate increase with an increase in the ultrasonic wave power, but the irradiation of ultrasonic waves also enhances the dissociation of R-134a hydrate more effectively than the application of an equivalent amount of energy in the form of heat at the same location.