Delong Xu

Generation and control of acoustic cavitation structure.

The generation and control of acoustic cavitation structure are a prerequisite for application of cavitation in the field of ultrasonic sonochemistry and ultrasonic cleaning. The generation and control of several typical acoustic cavitation structures (conical bubble structure, smoker, acoustic Lichtenberg figure, tailing bubble structure, jet-induced bubble structures) in a 20-50 kHz ultrasonic field are investigated. Cavitation bubbles tend to move along the direction of pressure drop in the region in front of radiating surface, which are the premise and the foundation of some strong acoustic cavitation structure formation. The nuclei source of above-mentioned acoustic cavitation structures is analyzed. The relationship and mutual transformation of these acoustic cavitation structures are discussed.

Acoustic cavitation structures produced by artificial implants of nuclei

High-density controllable bubble structures are produced in the vicinity of radiating surface by artificially implant nuclei. Two kinds of typical cavitation structures produced by artificially implant nuclei are investigated. The focusing action and the physical origin of jet-induced cone-like bubble structure are analyzed. The sonochemical activity of cavitation structures is measured by using the standard method of potassium iodide dosimetry. The controllability of cavitation bubble cluster in the acoustic field is also discussed in this work.

Surface tension and quasi-emulsion of cavitation bubble cloud.

A quasi-emulsion phenomenon of cavitation structure in a thin liquid layer (the thin liquid layer is trapped between a radiating surface and a hard reflector) is investigated experimentally with high-speed photography. The transformation from cloud-in-water (c/w) emulsion to water-in-cloud (w/c) emulsion is related to the increase of cavitation bubble cloud. The acoustic field in the thin liquid layer is analyzed. It is found that the liquid region has higher acoustic pressure than the cloud region. The bubbles are pushed from liquid region to cloud region by the primary Bjerknes forces. The rate of change of CSF increased with the increase of CSF. The cavitation bubbles on the surface of cavitation cloud are attracted by the cavitation bubbles inside the cloud due to secondary Bjerknes forces. The existence of surface tension on the interface of liquid region and cloud region is proved. The formation mechanism of disc-shaped liquid region and cloud region are analysed by surface tension and incompressibility of cavitation bubble cloud.

A pilot test of ultrasonic viscosity reduction of heavy crude oil in oilfield

The high temperature, high pressure and high density inside a collapsed acoustic bubble are the mechanisms and the foundation of sonication in liquid. The development of acoustic cavitation in theory and in experiment is reviewed briefly from the first stage of the 20th century. The bottleneck problem of sonication in liquid on the industry scale is analyzed emphatically and up to now, it is still unsolved. In this paper, optimizing the spatial distribution of acoustic cavitation is investigated to overcome the bottleneck. The experiments show that it is feasible. Based on the experiments, an ultrasonic batch processing prototype of 10kW for reducing the viscosity of heavy crude oil is designed and developed. A pilot test is done in the oil field in the northwest of China. The pilot test shows that it can be used to reduce the viscosity of heavy crude oil for the practical production and transportation on the industrial scale. At last, the perspective of the acoustic processing is discussed.

Surface oscillations and fragmentation of bubbles in an acoustic field

Surface oscillations and fragmentation of individual bubbles confined in a thin liquid layer driven by an acoustic field have been investigated via high speed photography. It is show that under the experimental conditions, above a critical size threshold, the observed bubbles exhibit surface modes (standing Faraday waves on the bubble surface). Furthermore, With the increase of acoustic pressure, the amplitude of surface oscillation increases. Above a critical threshold, Jet formation and droplet ejection tear the bubble to pieces. The image analysis shows that the wavelength of Faraday wave on the bubble surface is independent of the acoustic pressure and the bubble radius, while the order of the surface mode is approximately proportional to the bubble radius. Based on a quasi-two-dimensional approximation, a physical model describing the surface oscillation of the bubble in the thin liquid layer is proposed. The mechanism of bubble splitting and its relationship with the acoustic parameters are analyzed...

Image analysis of Hydrodynamic-Acoustic-Cavitation

In this paper, an image analysis method based on high-speed photography of cavitation cloud is proposed. Considering the relationship between the optical transmission information and the state of cavitation, we construct a state function to characterize the cavitation. By analyzing the constructed state function of cavitation, the periodicity and the intensity distribution of the Hydrodynamic-Acoustic-Cavitation are analyzed. It is found that Hydrodynamic-Acoustic-cavitation has significantly widened the range and enhanced the strength of cavitation, and a period doubling phenomenon of the cavitation cloud is also discovered by this method.

Reducing the pour point of crude oil by using of ultrasonic wave

With the global economical development, high pour point crude oil (HPPCO) is getting more and more attentions. Due to its higher pour point and worse fluidity when it is cold, more difficulties are faced for its extraction. Ultrasonic wave technology is investigated to reduce the pour point of Sudan HPPCO in this paper. First, an ultrasonic horn is proposed and made. Then, after processing for 3 min by the horn, a decrease of more than 3 of the pour point of Sudan HPPCO is obtained. Furthermore, compared with that without ultrasonic processing, the percentage of higher molecular weight constituents becomes more, while that of heavier molecular weight component is less. The mechanism that the pour point of HPPCO can be changed through ultrasonic processing is analyzed and investigated by an experiment that three types of paraffin wax whose molecular weights are different are processed by ultrasonic wave. The main advantage of the ultrasonic processing for HPPCO is economical and environmental and the decre...

Quasi-emulsion between water and cavitation bubble cloud in an ultrasonic field

The cavitation bubble distribution (cavitation structure) is spatially inhomogeneous in ultrasonic field. A quasi-emulsion phenomenon of cavitation structure is reported in this paper. The inception process of cavitation bubble cloud in a thin liquid layer (the thin liquid layer is trapped between a radiating surface and a hard reflector) was investigated experimentally with high-speed photography. It is revealed that cavitation bubble cloud can be considered as a uniform fluid (cloud), and water without cavitation can be considered as another uniform fluid (water). The conversion from cloud-in-water emulsion to water-in-cloud emulsion occurs with the increase in the number of bubbles. The formation and stability of cloud-water emulsions is analyzed theoretically. It is found that surface tension of cavitation bubble cloud played a leading role. Findings of this research proved that cavitation bubble clusters can be considered and investigated as a whole. [This work was supported by the National Natural S...

Ultrasonic batch processing of ultra heavy oil for viscosity reduction on the industrial scale

Due to the shortage of the fossil fuel and with the increasing demand for it, heavy crude oil and ultra heavy crude oil whose density is less than 10API and 20API respectively are getting more attentions in the world. But their properties of heavier density, higher viscosity, and worse fluidity make it very difficult to produce and transport them. Ultrasonic wave technique is investigated to improve their rheological properties in lab and in the field in this paper. In lab, the viscosity of the emulsion of ultra heavy crude oil, water and viscosity reducer processed by ultrasonic wave has a more than 25% decrease of viscosity reduction and 20% less quantity of active macromolecule viscosity reducer is needed. When the initial temperature in not lower than 40°C, the uniformly-distributed emulsion can form when it is subjected to 10-30s ultrasonic irradiation. The mechanisms of effects of high intensity ultrasonic wave on the viscosity reduction are emphatically investigated. According to the experiments, an ultrasonic batch processing system with 4 ultrasonic horns whose basic frequency is 17 kHz is designed and installed in the Xinjiang oil field in the northwest of China. The pilots show that this system can be used to reduce the viscosity of ultra heavy crude oil for the practical production and transportation on the industrial scale.