| Ultrasonic reactor is a pivotal equipment for ultrasonic chemical reactions, which refers to the container or system where chemical reactions take placed under the irradiation of ultrasound. The research and application of ultrasonic reactor has attracted increasing attention for its simple operation, stable performance and high efficiency. In this paper, continuous multi-frequency ultrasonic reactors, self-designed as patent prototype, were used as reaction vessel, pure water and oil system as the research targets, to explore the ultrasonic field characteristics and distribution regularities changing with other variables, to investigate the influences of ultrasonic reactor acoustic field distribution regularities on the determination of optimum reaction conditions and sono-chemical yields, and to promote the sono-chemical technologies developing from laboratory scale to industrial chemical technology and providing guidance. The main contents and experimental results are as follows:(1) Sound field distributions in ultrasonic reactors were measured by sound intensity meter, which showed that similar distribution regularities exist among the X and Y directions, radial direction and planes of different heights, in addition to some uneven phenomena near transducers and reactor walls, the overall sound field distributions are uniform; Fluid flow (0 to 40L/h) and temperature differences (25 to 40℃) have little influence on the sound field distributions, compared with other factors:reactors’shape, transducer installation position and ultrasonic power; sound intensity values increase significantly with the increase of input power; comparisons of sound energy distribution regularities in oil and water in the continuous ultrasonic reactor under the same experimental conditions are made and we found that sound energy attenuations were severer in the oil, just because the coefficient of viscosity in oil is much higher, but the overall regularities were similar in the two media,.(2) Sound intensity values’change amplitude decreased to 7%(without additives can be as high as 40%) after adding some thin solid particles(suspended activated carbon) into the water systems, which means that addictives can significantly improve uneven phenomenon in ultrasound field. The particle size of activated carbon additives and adding quantity were investigated, test results of the 35kHz reactors showed that the optimal additive particle size was 200mesh(75μm), and addition amount was 7.5g (1.25 kg/m3). Sound intensity distribution in the optimal condition showed that the uneven distribution phenomena of sound intensity values near the radiating surface and corners did not exist, and the synergy of solid particles combined with ultrasound reached its optimal performance; Sound intensities change more regularly along with the change of the input power, which makes the control of ultrasonic reactor much easier, and provides certain measures to further improve the mass transfer.(3) Continuous biodiesel preparation experiments were conducted with acidic oil as the raw material, which revealed that in the multi-frequency ultrasonic irradiation(15-25-35-40kHz) with input powers 200W respectively, biodiesel yield rate (95.34%) is much higher than that on the condition of no ultrasonic irradiation(52.18%), and higher than that on the condition of single frequency(15kHz) radiation (87.95%), all above verified the importance of the sound intensity values and the uniformity of its distribution to further strengthen mass transfer(4) Through the numerical simulation of the cavitation bubbles motion equations in the ultrasonic field, we found that cavitation bubbles’radius amplitude decreases gradually with the increase of frequency, the time needed for cavitation bubble to reach the maximum radius is much longer and corresponding cavitation effect recedes; but cavitation effect can be enhanced with the increase of sound intensity; cavitation bubble movement damping effect in the high viscosity fluid is remarkable; to get the expected sound intensity or cavitation effect, the input power can be adjusted.The research results of this paper showed that sound intensity and its corresponding distribution uniformity in ultrasonic reactors are of great significance to strengthen the mass transfer process. Sound energy distribution regularities are verified through corresponding biodiesel continuous preparation experiments, and the movement of acoustic bubbles in the ultrasonic field has been simulated with Matlab, all these researches can offer great reference values for optimization of the performances of sono-chemical reactors in the process of actual operation. |
PDF Full Text Request