| The phenomenon of cavitation effect and micro-jet, can strengthen the process of fluid mixing and mass transfer when ultrasonic propagating in liquor medium.Multiphase mixing and reaction are widely applied in the fields of chemistry, energy,light industry and food, materials as well as environmental engineering protection.The ultrasonic field has a huge impact on efficiency improvement of mass transfer,enhancement of reaction rate and selectivity, control of reaction process, reduction of the reaction time, increase of product yield, etc. There are few studies report that ultrasound acting as a new type of method strengthening mass transfer how to influence the law of residence time distribution(RTD) in the reactor. The regularities of residence time distribution in the ultrasonic field lay an important basis for the scientific design of ultrasonic chemical reactor. It is helpful to optimize the reactor design, ensure efficient reaction process with high efficiency, improve the product quality, cut down the energy consumption of chemical reaction and operation cost as well, so it is necessary to explore the regularities of residence time distribution in the reactor with an ultrasonic field. This thesis mainly studied it from the following aspects. Several important conclusions are obtained and they are listed as below:(1) In order to test the stability of tracer in ultrasonic field, solutions of alizarin red with two different concentration are prepared under the operating condition of that the ultrasonic power is 200 W and the ultrasonic frequency are 25 k Hz, 70 k Hz respectively, and sample the solution of alizarin red in the ultrasonic field with ultrasound radiation every five minutes. We found that the absorbance of the alizarin red solution has slightly changed, which means alizarin red degradation does not occur in the ultrasonic field. And under condition of that ultrasonic power is 200 W and the flow mediums are water, 10%(V%) glycerin-water mixture, 30%(V%)glycerin-water mixture respectively with the ultrasonic frequency of 25 k Hz. Alizarin red acting as the tracer has made repeat measurement of the curve of the residence time distribution, we found that the curve exhibited good reproducibility and came to the conclusion that method of ultraviolet spectrophotometry is a reliable used to studyIV the regularities of residence time distribution in the ultrasonic reactor.(2) Regularities of the residence time distribution have been studied the when the fluid medium is water. The influence of ultrasonic power on the residence time distribution regularities is that minimum degree of fluid back-mixing in the ultrasonic reactor when the ultrasonic power is 100 W, under operating condition of that the flow rate are 15L/h, 25L/h, 35L/h respectively. The average residence time has slightly reduced with the increase of ultrasonic power when the flow rate remains constant.The influence of flow rate on the performance of residence time distribution is that when the ultrasonic power is 0W, 100 W, 150 W respectively. The maximum degree of back-mixing in the system is on the condition of flow rate of 25L/h. But when the ultrasonic power is 200 W, the maximum degree of back-mixing is on the condition of flow rate of 35L/h. The average residence time is significantly reduced with the increase of flow rate when the ultrasonic power remains the same.(3) Regularities of the residence time distribution have been studied when the fluid medium is 10%(V%) glycerin-water mixture. The influence of ultrasonic power on the residence time distribution regularities is that minimum degree of fluid back-mixing can be obtained in the ultrasonic reactor when the ultrasonic power is150 W at different flow rate. When increase the ultrasonic power, the average residence time cut down within the same flow rate. The influence of flow rate on the performance of residence time distribution is that the maximum degree of back-mixing in the system is the condition of flow rate of 35L/h at different ultrasonic power.(4) Regularities of the residence time distribution have been studied when the fluid medium is 30%(V%) glycerin-water mixture. The influence of ultrasonic power on the residence time distribution regularities is that the system can get minimum degree of fluid back-mixing and have the best mixing effect in the ultrasound reactor at the ultrasonic power of 200 W when the flow rate has increased from 15L/h to35L/h. The influence of flow rate on the performance of residence time distribution is the same as that of medium acted by 10%(V%)glycerin-water mixture, the maximum degree of back-mixing in the system is on the condition of flow rate of 35L/h whenthe ultrasonic power are 0W,100 W,150W,200 W respectively. The influence of fluid properties on the residence time distribution regularities are that the average residence time is longer and has a character of slow peak flowing out when the viscosity of the fluid is increased.(5) The influence of interaction effects between the factors of ultrasonic power,fluid flow and fluid properties on the regularities of residence time distribution has been studied. Under interaction effects between fluid physical properties and ultrasonic power, the order about the degree of back-mixing is: 35L/h > 25L/h >15L/h. Under interaction effects between fluid physical properties and flow rate, the order about the degree of back-mixing is: 200W>150W<100W<0W. Under interaction effect between flow rate and ultrasonic power, order about back-mixing degree is: 30%(V%) glycerin-water mixture<10%(V%) glycerin-water mixture<water. An equation has developed as-0.4629-0.4825-0.89760750.9066(1)(Re) Pt V P(28)(10)by regression under the experimental conditions to predicate the mean residence time.The calculated values by the equation are compared with the experimental results which show that the regression result meets the experimental values well by maximum deviation within ±15%.When ultrasonic power is 150 W, the fluid medium is 30%(V%) glycerin- water mixture acting as flow medium at the flow rate of 15 L/h, 25 L/h, 35 L/h respectively,tank-in-series model is used to simulate equations of the density function of dimensionless residence time distribution E(θ), simulation results of model parameter are N =6.62, 4.43, 3.98 respectively. Which are in good agreement with the experimental results. |
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