Study on the cleaning effect by ultrasonic cavitation accompanying with a water jet

在研究项目的第一阶段，我们主要研究了超声产生的空化特性。利用共振频率为28 kHz的超声波振子，在自来水中超声产生空化。用高速摄像机对空化行为进行了观察。用压力传感器测量了空化产生的冲击压力，用水听器测量了空化噪声。在第二学期中，我们使用一块覆盖有几μm厚的PbCl2薄膜的镍板作为测试墙，进行了一项了解流体运动引起的清洗效果的实验。将单个镍板放置在上静壁的表面，并暴露在三种不同的流体运动情况下，如(1)仅由水射流引起的流动，(2)仅由超声波空化引起的流动，(3)由(1)与(2)联合引起的流动。利用装有CCD摄像机的显微镜观察了镍板的损伤表面。根据壁面作用力的不同，(1)-(3)种情况下均可发生气膜分离，并用多种理论方法对空化气泡动力学进行了研究。所获得的一些成果已经发表在几种期刊上。

During the first term of the research project, we primarily investigated the characteristic of ultrasonically produced cavitation. Cavitation was ultrasonically generated in tap water by using an ultrasonic vibrator with the resonance frequency of 28kHz. The behavior of cavitation was observed with a high-speed video camera. Impulsive pressures caused by cavitation were measured with a pressure transducer and cavitation noise measurement was also conducted by using a hydrophone. The signals were fed into a FFT analyzer to examine their power spectra.During the second term, we carried out an experiment for understanding the cleaning effect due to fluid motion by employing a nickel plate covered with a PbCl_2 film several μm thick as a test wall. The individual nickel plates were set on the surface of an upper static wall and exposed to three different situations of fluid motion such as (1) flow induced only by a water jet, (2) flow induced only by an ultrasonic cavitation and (3) flow induced by (1) combined with (2). The damaged surface of the nickel plate was observed by employing a microscope equipped with a CCD camera. It was found that the film separation took place in all situations, (1)-(3), depending on the forces acting on the wall surface.Furthermore cavitation bubble dynamics has been investigated by means of several methods of theoretical approach. Some of the results obtained have been published in several journals.