Ultrasonic cavitation monitoring by acoustic noise power measurement
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In this paper, a new tool is proposed to carry out acoustic cavitation monitoring and to have an overview of its effects in applications. After a brief review of the cavitation characterization techniques, it is shown that cavitation noise is a suitable and accurate indicator of the cavitation activity induced in a liquid. In the first part of this study, the origin of the first spectral component of the cavitation noise is discussed. The f/2 and 2 f component evolution measurement at a driving frequency around 1 MHz confirms Neppiras' ones and gives an indicator of the cavitation inception. In the second part, the cavitation noise spectrum distortion is considered as a function of the acoustic power transmitted to the liquid in order to obtain an indicator of cavitation activity. In the last part, this new tool is used to bring to the fore the hysteresis effect associated with the cavitation. An experimental correlation between cavitation noise power measurement and the sonochemical activity in an oxidization process is also presented.Keywords:
Distortion (music)
Hysteresis
Temperature effects on the critical cavitation number and rotating cavitation in a turbopump inducer have been experimentally investigated in water. Static pressures upstream and downstream of the inducer have been measured to determine the cavitation performance, and cavitation instabilities have been detected using unsteady pressure sensors and a high-speed camera. Two kinds of cavitation instabilities have been identified—rotating cavitation and asymmetric attached cavitation. To quantify temperature effects, nondimensional thermal parameter has been adopted. Increasing water temperature, or increasing nondimensional thermal parameter, lowers the critical cavitation number. Increasing nondimensional thermal parameter also shifts the onset of rotating cavitation to a lower cavitation number and reduces the intensity of rotating cavitation. However, for values larger than 0.540 (340 K, 5000 rpm), the critical cavitation number and the rotating cavitation onset cavitation number become independent of the nondimensional thermal parameter. The onset of the head coefficient degradation correlates with the onset of rotating cavitation regardless of temperature.
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Abstract The authors describe test apparatus and an experimental method used to determine the critical point of cavitation, or cavitation limit, of liquids flowing in a closed system as caused by the formation of vapor-filled cavities in the system. The experiments here described were directed to determine the cavitation limit, at which cavitation begins, and not to ascertain the consequences of maintained cavitation. The authors show that the experiments give results entirely consistent with the cavitation principle as now generally applied.
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To investigate the effect of tip clearance size on cavitation characteristics in a turbopump inducer, a series of experiments have been conducted in a newly developed visualization test facility using room temperature water as working fluid. The pressure fluctuations near the tip region were collected, and the cavity structures under various conditions were documented by a high-speed camera. It is found that large tip clearance distinctly reduces both the non-cavitation and cavitation performance. Three cavitation instabilities, super-synchronous rotating cavitation, synchronous rotating cavitation and cavitation surge have been carefully identified through combination of cross-correlation analysis of pressure signals and visualization results. Large tip clearance displays a remarkable stabilization effect on pressure fluctuation, cavitation surge totally disappears, and the range of occurrence of synchronous rotating cavitation becomes smaller for the large tip clearance, whereas super-synchronous rotating cavitation only occurs in the large tip clearance. The cavitation areas are smaller at large tip clearance, while the flow channels are more seriously choked when cavitation occurs heavily in comparison with those at small tip clearance, which may be responsible for the worse cavitation performance.
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본 연구는 타원형 노즐과 원형 노즐 내부에서 발생되는 cavitation의 발생 및 성장을 실험적으로 관찰하였다. 원형 노즐과 타원형 노즐의 cavitation 특성을 가시화 하기위해 투명한 아크릴로 노즐을 제작하였다. 실험에 사용된 노즐들은 같은 단면적으로 제작되었으며, 타원형 노즐의 경우 형상비(a/b)를 다르게 하였다. 분사압력의 증가에 따라 노즐내부 유동은 no cavitation, cavitation, hydraulic flip 영역으로 나뉘어졌다. 노즐의 형상에 상관없이 no cavitation과 cavitation 영역에서는 분사압력의 증가에 따라 유량은 증가하며, 유출계수는 감소하는 경향을 나타냈다. 그러나 hydraulic flip 영역에서의 유량계수는 일정한 값을 나타냈다. 타원형 노즐은 원형 노즐에 비해 높은 cavitation number에서 cavitation이 성장, 발달하였다. 특히 타원형 노즐에서는 장축의 cavitation length가 단축보다 길게 나타났다.
Discharge coefficient
Cavitation Erosion
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The present report describes about the effects of the amount of the alternate cutting back of the leading edges on the steady cavitation, its stability and the onset region of rotating cavitation. It was found that, by increasing the amount of cutting back, we can increase the range of cavitation number with stable cavitation and diminish the onset region of rotating cavitation.
Cavitation Erosion
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본 연구는 타원형 노즐과 원형 노즐 내부에서 발생되는 cavitation의 발생 및 성장을 실험적으로 관찰하였다. 원형 노즐과 타원형 노즐의 cavitation 특성을 가시화 하기위해 투명한 아크릴로 노즐을 제작하였다. 실험에 사용된 노즐들은 같은 단면적으로 제작되었으며, 타원형 노즐의 경우 형상비(a/b)를 다르게 하였다. 분사압력의 증가에 따라 노즐내부 유동은 no cavitation, cavitation, hydraulic flip 영역으로 나뉘어졌다. 노즐의 형상에 상관없이 no cavitation과 cavitation 영역에서는 분사압력의 증가에 따라 유량은 증가하며, 유출계수는 감소하는 경향을 나타냈다. 그러나 hydraulic flip 영역에서의 유량계수는 일정한 값을 나타냈다. 타원형 노즐은 원형 노즐에 비해 높은 cavitation number에서 cavitation이 성장, 발달하였다. 특히 타원형 노즐에서는 장축의 cavitation length가 단축보다 길게 나타났다.
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Hydrodynamic cavitation is used in various engineering fields, such as water treatment and chemical processing. Cavitation initiation is critical to assessing the cavitation effect in cavitation reactors, so cavitation initiation should be studied to improve cavitation in various fields. This paper investigates the mechanisms and characteristics of cavitation initiation in jet pump cavitation reactors (JPCRs) to intensify the cavitation. A criterion derived for cavitation initiation focuses on the fluctuating pressures caused by the velocity gradients. Experiments show that the criterion predicts low pressure cavitation and strong shear dominant cavitation in a JPCR. Then, the characteristics of these two cavitation mechanisms are investigated for various geometric parameters and operating conditions and a cavitation initiation regime map is developed for JPCR. The results show that cavitation occurs more easily, and the two cavitation mechanisms become increasingly more difficult to distinguish in the JPCR as the inlet pressure increases. The velocity gradient and loss coefficient increase with a decrease in suction pressure, which promotes cavitation. The low pressure cavitation and strong shear dominant cavitation are both more likely when the area ratio is relatively small. The induced pressure spectra further show that the low frequency component dominates during the formation of the low pressure cavitation, while the high frequency component dominates during the formation of the strong shear dominant cavitation. This study clarifies the cavitation mechanisms with special emphasis on the fluctuating pressure and the corresponding characteristics in the JPCR to provide guidance for JPCR applications in industry.
Supercavitation
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Cavitation in a 3D axisymmetric rectangular groove occurred in various types of cavitation, such as vortex cavitation, cloud cavitation, traveling cavitation and sheet cavitation. In this experimental study, some aspects of cavitating flow were clarified. Prediction and experimental calculations were also made for incipient cavitation of both the cavitating vortex ring in the groove and the sheet cavitation at the downstream of the groove. The calculations indicate that the observed cavitation is not vaporous cavitation, but gaseous cavitation. The results of this study are useful for understanding the cavitation in this type of groove structure in order to control cavitation damage.
Groove (engineering)
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Ultrasonic electroplating produces various effects, including refinement of the plating film structure, by generating localized agitation through cavitation bubbles. However, details of the agitation mechanism have not been clarified because ultrasonic cavitation is very small in scale and occurs rapidly, and its reproducibility is low. Therefore, using laser-induced cavitation, which can generate cavitation similar to ultrasonic waves with high reproducibility, the author attempted to elucidate the conditions and frequency of cavitation generation that affect the agitation phenomenon in ultrasonic electroplating. By controlling the laser irradiation position, three different cavitation conditions were established, and the microstructures of the plated films produced were compared. Microstructural refinement was the most advanced under the condition of microjet generation. The frequency of cavitation generation at any position in the ultrasonic electroplating was estimated to be < 1 Hz.
Sonochemistry
Plating (geology)
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