Investigation Of Ultrasound Intensity Measurement And Glycirric Acid Leaching Kinetics

Ultrasound enhanced chemical processes are important applications of sonochemistry.Ultrasound cavitation is the fundamental of ultrasonic enhancement. It is essential tounderstand the distribution of ultrasound intensity field, as it is a reflection of the violence ofcavitation.In this work, aluminium foil was used to characterise the phenomenon of cavitation, andcavity bubble cloud was illustrated by high speed photograph technology. The cloud wasmainly located in the vicinity of the radiating surface and increased with the electric poweroutput.For the homogeneous water system, calorimetry method was used to measure the meanultrasound intensity. The results showed that the mean ultrasound intensity increased withelectrical power output with constant frequency; while at same electrical power output, themean intensity of20kHz was larger than30kHz. Then, the thermoelectric probe was used tomeasure the intensity at different locations in the flask. The results indicated that the acousticfield of ultrasound horn fitted well with the properties of spherical wave field. Higherintensity area was located in the vicinity of the irradiating surface, while at the locations thatfar away from the surface the intensity was lower. Supposing the flask was a cylinder type,the intensity attenuated along both the axial and radical directions with exponential form.Meanwhile, there were fluctuations in the axial direction. The distance between two adjacentwave peaks was equal to the wavelength of the driven ultrasound. Because of the cavitybubble cloud, the attenuation rate in axial direction was larger than that in radical direction. Atconstant frequency, the area with high intensity enlarged with the electric power output.Under same electric power output, the intensity of20kHz was larger then that of30kHz atsame locations.Based on the homogeneous water system, the inhomogeneous Glycirrice–water systemwas investigated. As same as water system, at constant frequency, the mean intensity and thehigh intensity area rose with the electric power output. Under constant power output, themean intensity of20kHz was larger than that of30kHz; at same locations, the intensity of20kHz was larger than30kHz. In the solid–liquid system, the attenuation rate was larger thanwater system, and the fluctuation of the intensity was eliminated. The glycirric acid (GA) leaching process was investigated. The results demonstrated thatthe leaching process can be divided into two steps. In the first step, the GA concentrationsoared, then slightly increased in the second step. The specific surface area of glyciricepowder was at a relative low level, thus the diffusion in the solid matrix was slow. Theleaching results showed that the initial rate and equilibrium concentration with ultrasoundwere larger than that with stirring. And the enhancement of20kHz was better than30kHz. Atsame frequency, the equilibrium concentration and initial rate fluctuated with electrical poweroutput. As the temperature increased, both the equilibrium concentration and initial rateincreased. The distribution of ultrasound intensity is underlying this phenomenon. Based onthe film theory and Peleg empirical equation, the kinetic model of GA leaching was obtained,which fitted the experimental data well, and the rate constant was calculated. The resultsshowed that during the GA leaching process, the driving force played a critical role. Therewas a conjunction between ultrasound frequency and electric power, when they matched well,the optimal enhancement could be achieved.