谐振声场强化纤维素超声微细化效果研究

研究20kHz超声破碎声场条件对纤维素微细化效果的影响。应用柱形声波导理论分析确定并选择合适的超声破碎料腔声场的几何参数,结合声模态方法获得了增强声能密度分布的谐振液位参数,利用有限元方法进行了超声破碎料腔的声场分析,并在2种功率条件进行了谐振液位与非谐振液位的超声破碎试验。结果表明,在谐振液位条件下,破碎料腔声场的声能密度分布与声模态密切相关,且声能密度显著增强,空化作用的分布范围扩大,空化破碎作用明显增强。纤维素超声破碎试验结果显示,与非谐振液位相比,在低功率(<140 W)和较短时处理时间(<7min)条件下,谐振液位状态超声处理的纤维素平均粒径D_3,2]和D_4,3]明显降低。随着超声时间和超声功率的增加,料腔内部声场致流动作用增强,超声场引起的空化效应不再遵循线性声场特点,谐振结构中的破碎能分布被非线性声流扰动,趋同于非谐振超声场的能量分布特性,相同处理条件下的物料粒径差显著降低,但谐振声场仍具有较好的破碎效果。

Study of resonant acoustic field on Ultrasonic Micronization of cellulose

Studied the effect on micronization of cellulose in 20 kHz ultrasonic crushing sound field conditions.It was determined and selected the geometric parameters of the ultrasonic resonant reactor for cavitation crushing field by using the analysis of sound propagation in a cylindrical pipe.Combining with the acoustic modal analysis,the height of liquid level foe resonant reactor was obtained,which could enhanced acoustic energy density distribution.Used the finite element method to analyze the acoustic field of ultrasonic material crushing cavitation.Finally,The ultrasonic crushing experiments were conducted with the resonant reactor liquid level and the non-resonant reactor liquid level by different power conditions.Results,the acoustic energy density distribution in the sound field of the crushing cavitation,under the condition of resonant reactor liquid level,was closely related to the acoustic mode. The acoustic energy density was significantly enhanced,the distribution of cavitation was expanded,and the cavitation crush effect was obviously enhanced.The results of cellulose sonication experiments showed that,under the condition of low power(<140 W)and short processing time(<7 min),the average size of D3,2]and D4,3]of cellulose treated by ultrasound in the resonant reactor liquid level was significantly reduced.However,with the increase of ultrasonic time and ultrasonic power,the acoustic flow would enhanced inside the cavity,and cavitation effect caused by the ultrasonic field almost no longer follows the linear sound field characteristics,the crush energy distribution in the resonant structure was disturbed by the nonlinear acoustic flow,which was similar to the energy distribution characteristics of the non-resonant ultrasonic field.As for the particle size difference of materials under the same treatment condition,although it was significantly narrowed,the resonant sound field still had a good crushing effect.