谱分析法与改进电导率法测量超声空化强度

Measurement of Ultrasonic Cavitation Intensity by the Spectral Analysis and Improved Electrical Conductivity Methods

随着超声化学的发展,超声空化强度的定性和定量测量已成为一个热点问题.实验中对电导率法进行改进,排除了温度升高的影响,将其与谱分析法相结合测量超声空化场强度,并利用荧光法对该方法进行了验证.结果表明,改进的电导率法、谱分析法和荧光法结果具有一致性,验证了改进电导率法的有效性.之后将该方法用于测量不同超声频率和反应器形状对空化强度的影响.进一步实验表明,在20~80 kHz频率范围内,空化强度随超声频率的增加而增大.对不同形状超声反应器内超声空化强度的测量表明,由于八角形反应器具有更开放的结构,其空化强度几乎是矩形反应器的10倍.换能器位置的实验表明,由于更容易形成驻波而对空化产生消极影响,底部布置换能器产生的空化强度低于侧壁.最后,对多频声场空化强度的测量结果表明,在原有20 kHz侧壁换能器形成的声场中引入40 kHz侧壁换能器,稳态和瞬态空化强度均有较大提高,因此多频声场对提高空化强度具有积极作用.在本实验所探究的参数范围内,确定了单频矩形反应器空化强度最好运行条件为80 kHz;八角反应器在侧壁布置多频换能器可以获得最好空化强度.本文提出的改进电导率法具有操作简便以及不受限于液体性质的特点,可适用于不同场合下测定和比较超声空化强度.

Qualitative and quantitative measurements of the ultrasonic cavitation intensity have become a controversial topic with the development of ultrasonic chemistry.This study improved the electrical conductivity method by excluding the effect of temperature increase and combining it with spectral analysis to measure the ultrasonic cavitation intensity.Then,the combined method was verified by the fluorescence method.The results of the improved electrical conductivity,spectral analysis,and fluorescence methods were consistent,which verified the effectiveness of the improved electrical conductivity method.Then,the proposed method was used to measure the ultrasonic cavitation intensity at various frequencies and reactor geometries.Further investigation showed that the ultrasonic cavitation intensity decreases with the increase in frequency in the range of 20—80 kHz.Measurements of the ultrasonic cavitation intensities of various ultrasonic reactors indicate that because of its open structure,the ultrasonic cavitation intensity of the octagonal reactor is nearly 10 times that of the rectangular reactor.The results of the experiment on the position of the transducer show that the ultrasonic cavitation intensity produced by the bottom transducer is lower than that produced by the sidewall transducer because standing waves are more likely to form in the bottom transducer,which would have a negative effect on cavitation.Finally,the results of the multifrequency experiment show that after the introduction of the 40 kHz sidewall transducer into the sound field formed by the original 20 kHz sidewall transducer,the steady-state and transient ultrasonic cavitation intensities are both considerably improved,indicatingthat the multifrequency sound field has a positive effect on the improvement of the ultrasonic cavitation intensity. Underthe parameters used in the experiment,the best operating conditions for the ultrasonic cavitation intensity aredetermined to be 80 kHz for rectangular reactor with a single frequency and octagonal reactor with sidewall transducerswith multiple frequencies. The improved electrical conductivity method proposed in this study is easy to use andnot limited to liquid properties;thus,it can be used to measure and compare ultrasonic cavitation intensities underdifferent conditions.