用三种方法研究双频超声空化增强效应

Enhancement Effect of Cavitation Activity by Two-frequency Ultrasound Irradiation Based on Three Methods

分别使用TA荧光法、碘释放法和电学法对 2 8kHz分别与 1.0 4MHz和 1.7MHz组成的双频超声辐照系统的空化增强效应进行了研究 .结果表明 ,双频超声辐照能明显增强空化效应 ,其声空化产额均显著大于各频率单独辐照方式的声空化产额之代数和 .对双束超声空化增强效应的机理从 3个方面进行了分析 :( 1)双频辐射增强样品的机械振动 ,有助于更多的空气经液体表面进入液体而导致空化核增加 ;( 2 )在双频超声作用下 ,各自产生空化过程 ,当各自空化内爆时 ,会产生许多新的空化核 ,这些空化核为另一频率的空化提供了更多与其共振频率接近的空化核 ;( 3)由于气泡在低频负压相内准静压力减小 ,从而降低了空化的阀值 .而在低频的正压相内 ,气泡的内爆强度增加 ,因而提高了其声空化产额 .

Three methods (TA fluorescence, iodine release and electrochemistry) are used to study the enhancement effects of cavitation activity by two-frequency ultrasound irradiation of 28 kHz combined with 1.04 MHz and 1.7 MHz respectively. The results show that two-frequency ultrasound can produce a significant increase in cavitation activity compared with single frequency irradiation, and the cavitation production is much larger than the algebraic sum of that under individual irradiation. The possible mechanism of the enhancement effect is briefly discussed from three aspects. First, the two-frequency irradiation accelerates the mechanical vibration, which helps more air enter into the liquid through its interface and thus cavitation nuclei increase. Second, when the two-frequency ultrasound irradiates, each frequency generates individual cavitation. With the collapse of the individual cavitation bubbles, many new cavitation nuclei are generated among which some cavitation nuclei are approaching the resonant frequency of the other frequency cavitation, so the whole cavitation effect is increased by their mutual influence. Third, the enhancement effect results from the production of new bubbles by the low frequency stimulating field and the diminishing quasi-static pressure during the negative pressure amplitude, whereas the cavitation threshold is lowerd. During the positive phase, as the inner-burst intensity of bubbles increases, the quantity of ultrasound cavitation activity is enhanced.