Underwater Discharge Research Articles

Generation of Electrohydraulic Shock Waves by Plasma-Ignited Energetic Materials: II. Influence of Wire Configuration and Stored Energy

Electrohydraulic shock waves (SWs) have been used for shale gas exploitation in recent years. The traditional method to generate SWs is underwater pulsed discharge with a water gap load or an electrical wire (EW) load, but the SW energy is limited heavily by the stored energy. To obtain stronger SW, the EW explosion ignited energetic material (EM) load is proposed here. To obtain a good ignition performance, the influence of capacitor charging voltage, stored energy, wire diameter, and wire material (Cu and Mo) were studied. The results show that the higher the charging voltage is, the more effective the ignition is; liquidation and vaporization will affect the discharge but will not ignite the EM explosion effectively; the EMs given in this paper are more sensitive to the arc plasma. Besides, the nonrefractory copper is more suitable for the EM ignition than the refractory molybdenum.

Generation of Electrohydraulic Shock Waves by Plasma-Ignited Energetic Materials: III. Shock Wave Characteristics With Three Discharge Loads

As an important plasma-assisted technology to generate shock waves (SWs), underwater pulsed discharge has drawn much attention in recent years for its complex physical process. Based on three discharge loads, the water gap (WG) load, the electrical wire (EW) load, and the energetic material (EM) load, the discharge processes are briefly introduced and the characteristics of the associated SWs are analyzed. First, the experimental setups were built and typical structures of the three loads were presented. Second, the inherent characteristics of SWs under the three loads, such as their peak pressure, impulse, and time duration of positive pressure and power spectral density (PSD), were studied and compared. Finally, a cracking effect experiment is carried out to study the SW fracturing characteristics. The results show that SWs generated with the WG load have the lowest peak pressure, impulse, and power density, SWs generated with the EW load have a better energy conversion efficiency and the largest peak pressure, and SWs generated with the EM load have the maximum impulse and power density. Furthermore, SW fracturing characteristics are mainly affected by its inherent characteristics. The peak pressure and impulse determine the shock number of fracturing, and the fracture pattern is significantly affected by the PSD.

An investigation of an underwater steam plasma discharge as alternative to air plasmas for water purification

An underwater steam plasma discharge, in which water itself is the ionizing media, is investigated as a means to introduce advanced oxidation species into contaminated water for the purpose of water purification. The steam discharge avoids the acidification observed with air discharges and also avoids the need for a feed gas, simplifying the system. Steam discharge operation did not result in a pH changes in the processing of water or simulated wastewater, with the actual pH remaining roughly constant during processing. Simulated wastewater has been shown to continue to decompose significantly after steam treatment, suggesting the presence of long-lived plasma produced radicals. During steam discharge operation, nitrate production is limited, and nitrite production was found to be below the detection threshold of (roughly 0.2 mg L−1). The discharge was operated over a broad range of deposited power levels, ranging from approximately 30 W to 300 W. Hydrogen peroxide production was found to scale with increasing power. Additionally, the hydrogen peroxide production efficiency of the discharge was found to be higher than many of the rates reported in the literature to date.

Correlation of the peak pressure generated by an underwater spark discharge with energy absorption in a spark channel

In this paper, we have explained the correlation between the amplitude of the underwater shock pressure generated by a spark discharge in water and the energy absorption in a spark channel. With the well-known theory of shock wave formation by an accelerating piston, the peak pressure is considered to be generated by the energy absorption in the spark channel until the expansion speed of the spark channel reaches its maximum value. To obtain the maximum channel speed, we solve the power balance equation with experimentally measured voltage and current waveforms as a transient heating source of the spark channel. It is found that the experimentally measured peak pressure is well correlated with the energy absorption until the maximum channel expansion speed, irrespective of the operating parameters such as the capacitance and the voltage. It is also found that the energy absorption in the spark channel is significantly influenced by the spark channel resistance, indicating that an appropriate resistance model for the spark channel is necessary for an improved analysis of an underwater spark discharge system. The physics-based estimation of the peak shock pressure presented in this paper is expected to be useful for optimizing underwater spark discharge systems utilized in various application fields.

Non‐thermal plasma degradation of dye using an underwater dielectric barrier discharge created inside a porous hydrophobic ceramic tube

An alternating‐current‐driven, atmospheric‐pressure, non‐thermal plasma reactor was applied to the degradation of dye in water. The plasma reactor, made of a porous hollow ceramic tube, was placed underwater and was able to disperse plasmatic gas containing various reactive species into aqueous dye solution as small bubbles through the micropores of the tube. The hydrophobic coating on the surface of the ceramic tube effectively prevented the water from permeating through it. This wastewater treatment system was able immediately to transfer plasmatic gas to aqueous solution across the porous ceramic tube and provide a large gas–liquid interfacial area, allowing efficient dye treatment. So as to simulate real dyeing wastewater, an aqueous solution comprising two different azo dyes was used. The effect of discharge power, treatment time, and flow rate of oxygen used for the creation of plasma was examined. The results suggest that this system may be useful for the treatment of organic wastewater.

Underwater discharge plasma-induced coating of poly(acrylic acid) on polypropylene fiber

An underwater diaphragm discharge generated at atmospheric pressure by high voltage pulses was used for plasma polymerization of acrylic acid and simultaneously for the deposition of polymer coating on polypropylene multifilament fibers. The deposition process was monitored by Fourier transform infrared spectroscopy in combination with scanning electron microscopy. Possible schemes of polymerization are suggested also.

The Optical Diagnosis of Underwater Positive Sparks and Corona Discharges

In this paper, two types of underwater discharges, spark discharge and corona discharge, are investigated by optical diagnosis using a high speed framing camera (HSFC) with the framing time within nanoseconds under the same experimental conditions. In order to capture the photographs of streamer propagation, the influence of the randomicity of the pre-breakdown duration is taken into consideration. By increasing the conductivity of water, the randomicity reduces effectively. Experimental results show that, for a spark discharge, the process can be separated into three stages: the generation and propagation of a streamer, the generation and expansion of the discharge channel, and the development and annihilation of the plasma. The streamers do not directly move to the opposite electrode, but form a bush-like figure. With the increase of the number of branches, the velocity of streamer propagation slows down. The trajectory of the initial channel between electrodes is not straight. However, with the channel expanding, its shape transforms into a straight column. For a corona discharge, there are two stages: the generation and propagation of a streamer, and the stagnation and annihilation of the streamer. The initial streamer in a corona discharge is generated later than in a spark discharge. The forms of streamers for both kinds of discharge are similar; however, streamers generated by a corona discharge propagate with a slower velocity and the number of branches is less compared with a spark discharge. When the energy injection stops, the luminescence of plasma inside the discharge channel (spark discharge) or streamers (corona discharge) becomes weaker and weaker, and finally disappears.

Underwater capillary discharge with air and oxygen addition

The aim of this work was to present an effective method of generating an underwater capillary discharge at low power through gas injection (O2, air) and generating OH radicals. A flowing water (0.1 L/min) discharge was created in a quartz capillary tube (Φ = 4 mm outer; Φ = 2 mm inner; thickness = 2 mm) by applying a continuous negative DC voltage (0–4 kV) across tungsten electrodes (Φ = 0.5 mm) separated by a variable distance (1–2 mm) in the pin-pin electrode configuration. The air- and oxygen-injected capillary discharges at a constant water flow rate, similar gas injection variation rates, and two different interelectrode gaps were compared. A reduction in the breakdown voltage with increasing gas injection rate was shown. Compared to air, oxygen was proven to be more effective for generating an underwater discharge of a pulsating nature with the characteristics of high energy per pulse, higher power per pulse, short pulse width, and short pulse repetition rate. The emission spectrum of the oxygen-injected discharge showed a higher concentration of OH radicals than that of the air-injected discharge. The imaging diagnostic results showed that the discharge was brighter and more expanded when oxygen was added than it was when air was added.

Two Successive Shock Waves Generated by Underwater Pulse Electric Discharge for Medical Applications

This paper reports on analysis of two different types successive underwater shock waves generated by a device incorporating a compact shock-wave generator with a magnetic pulsed compression circuit. To generate shock waves, underwater pulsed electric discharges in high-impedance saline water were used. The saline water made possible underwater shock waves propagation in tissue with low reflection between the solution and tissue boundary, owing to their similar acoustic impedances. A cylindrical electrode holder and a semiellipsoidal shock-wave focusing reflector/generator were used in this paper. The diameter of the compact shock-wave reflector was 20 mm. Two kinds of successive underwater shock waves, one generated by electric discharge plasma expansion and the other by bubble collapse, were observed. The shock waves were studied by time-resolve high-speed visualization and direct pressure measurement using a fiber optic probe hydrophone pressure transducer. The former method elucidated propagation of underwater shock waves and behavior and collapse of the bubble near the electrodes, while the later measured two kinds of underwater shock waves pressures at different voltage amplitudes using the cylindrical electrode holder and the shock focusing generator. This paper clearly shows the importance of the secondary shock waves, their control, and damping, for effective and safe medical application of shock waves.

Observation of Underwater Streamer Discharges Produced by Pulsed Power Using High-Speed Camera

Pulsed power, used to produce underwater discharges, has been the subject of numerous studies to elucidate its mechanisms and applications. This paper reports on observation by a high-speed camera of the production and progress of streamer discharges created using a magnetic pulse compression pulsed power generator with maximum output energy of 40 Joules per shot in the medium of both tap and distilled water. Bubble production along streamers, bubble collapse, generation of shock waves, and extinction of bubbles was also observed by a high-speed camera.

Properties of water surface discharge at different pulse repetition rates

The properties of water surface discharge plasma for variety of pulse repetition rates are investigated. A magnetic pulse compression (MPC) pulsed power modulator able to deliver pulse repetition rates up to 1000 Hz, with 0.5 J per pulse energy output at 25 kV, was used as the pulsed power source. Positive pulse with a point-to-plane electrode configuration was used for the experiments. The concentration and production yield of hydrogen peroxide (H2O2) were quantitatively measured and orange II organic dye was treated, to evaluate the chemical properties of the discharge reactor. Experimental results show that the physical and chemical properties of water surface discharge are not influenced by pulse repetition rate, very different from those observed for under water discharge. The production yield of H2O2 and degradation rate per pulse of the dye did not significantly vary at different pulse repetition rates under a constant discharge mode on water surface. In addition, the solution temperature, pH, and conductivity for both water surface and underwater discharge reactors were measured to compare their plasma properties for different pulse repetition rates. The results confirm that surface discharge can be employed at high pulse repetition rates as a reliable and advantageous method for industrial and environmental decontamination applications.

Destruction of Direct Blue 106 Dye in Underwater Discharge

An application of underwater discharge is one possible way how make the destruction of organic dyes. This contribution presents results of Direct Blue 106 destruction in discharge generated in bubbles. The initial conductivity value of 30 μS.cm−1 was obtained using electrolyte; the starting dye concentration was 20 mg.l−1. The DC voltage from 1.5 kV to 3.0 kV was applied to generate the discharge at the mean current of 10-30 mA. The system was bubbled through the high voltage capillary electrode by He, Ar and N2 at the constant gas follow of 200 sccm. The dye destruction rate was directly proportional to the applied discharge current, so the highest efficiency was reached at the current of 30 mA. The destruction rate was strongly dependent on the filling gas. While using He and Ar only 4% destruction was obtained during the 20 minutes treatment at 10 mA of discharge current but the decomposition of 52 % was reached if nitrogen was introduced into the high voltage electrode. The destruction efficiency of about 40 % (He, Ar) and over 60 % in nitrogen was reached at discharge current of 30 mA. This enormous difference was probably connected not only to the production of hydrogen peroxide that seems to be usually the main oxidative specie in under water discharges but also atomic and excited nitrogen particles, both atomic and molecular, can have very positive effect in the dye destruction. The detailed study of the kinetic mechanisms leading to the Direct Blue 106 dye destruction will be a subject of the further studies.

Propagation of Underwater Shock Wave and Gas Bubble Behavior Induced by Electrical Discharge in Water

The basic behavior during underwater electrical discharge up to 10 kJ stored energy is investigated through both numerical analysis and optical-observation experiments. Since the authors have been investigating the use of underwater exploding phenomena for food processing and other applications, it is necessary to know the whole process which may affect the quality of the samples recovered. In the present investigation, the propagation of underwater shock wave was measured using a high-speed camera and compared with the numerically simulated results using LS-DYNA. Also, the motion of gas bubble, which is induced quite after the propagation of the shock wave, was measured and compared with the numerical simulation using the same code. The pressure of the bubble is not such high as the shock wave, but it is known that the impulse is not possible to be ignored due to its relatively long duration of the pressurization. Through a series of optical-observation experiments, it is confirmed that the numerical simulation is potentially possible to predict the whole phenomena for processing foods and other materials.

Dynamics of plasma evolution in a nanosecond underwater discharge

A positive discharge in water is generated by applying a 30 ns high-voltage (HV) pulse on a micrometre scale electrode. The applied voltage ranges from 6 to 15 kV and a fast plasma propagating mode is launched with a velocity of up to 60 km s−1. Time-resolved shadowgraphy and spectroscopy are performed to monitor the time evolution of the discharge structure and of the plasma emission spectra. By analysing the dynamics of the shock front velocity and the lateral expansion of the plasma channel, it is possible to estimate the pressure at the ignition of the plasma by two independent methods: very good agreement is found at 6 kV giving initial pressures of 0.4 GPa and 0.3 GPa, respectively. At 15 kV, only the shock front velocity method is applicable under our experimental conditions, giving an estimate of the initial pressure of 5.8 GPa. Such high initial pressures show that, under a nanosecond HV pulse, the plasma is ignited directly in the dense phase. Emission spectra show a strong continuum emission as well as a broad Balmer α line with a strong red shift, with an estimate of the initial plasma density of 1.3 × 1026 m−3. The relaxation of discharge pressure and plasma density is studied under a series of six successive pulses.

Optical diagnostics for high power pulsed underwater electrical discharge characterization

In order to evaluate the behavior of a high power pulsed underwater electrical discharge, and especially characterize the pressure generated by such a discharge, we implemented several optical diagnostics. We first observed directly the expansion of the plasma produced by the dielectric breakdown of the water between the electrodes and the resulting gaseous pulsating bubble. This observation led to an estimate of the pressure inside the bubble with respect to time. We then visualized the propagation of the pressure wave generated by the discharge with shadowgraph and Schlieren setup. The obtained velocity was then used to evaluate the theoretical maximum pressure at the pressure front. Finally, we measured the velocity induced by the pressure wave on a thin aluminum disk with a heterodyne velocimeter and used numerical simulation to obtain a temporal form of pressure. These methods and results can be used to develop and assess performances of processes using underwater electrical discharges to generate pressure waves such as electrohydraulic forming.

Development of a pulsed power system using MOSFETs and underwater pulsed electric discharge

Development of a pulsed power system using MOSFETs and underwater pulsed electric discharge

A Method of Cyanobacteria Treatment Using Underwater Pulsed Streamer-Like Discharge

Water bloom (named cyanobacterial bloom) is becoming a serious pollution problem all over the world. In this paper, a method of cyanobacteria treatment using underwater streamer-like discharge is reported. Repetitive underwater discharges are generated by all solid-state pulsed power system. Output voltage of the pulsed power system is 30 kV with 4 μs pulse width. We can generate repetitive underwater streamer-like discharge by the pulsed power system. And we have the system mounted in the water-bloom treatment apparatus. The size of streamer-like discharge is about 30-mm diameter. We conducted the experiment at a dam in Kyushu district in Japan. We have measured chlorophyll concentration, turbidity, potential of hydrogen, dissolved oxygen, conductivity, and temperature of water during treatment of cyanobacteria bloom. The treatment time is 60 min. All of them could be reduced. In particular, the chlorophyll concentration and the turbidity are remarkably decreased. Initial chlorophyll concentration is 600 μg/L, and initial turbidity is 1000 nephelometric turbidity unit (NTU). We obtained that treatment results of chlorophyll concentration and turbidity were 85 μg/L and 80 NTU, respectively.

Novel technique to enhance the disintegration effect of the pressure waves on oilseeds

A novel technique for continuous disintegration of oilseeds was designed. The operating principle consists of gasification of deshelled oilseeds mash using small amounts of gas. These were subsequently subjected to the pressure waves generated externally by underwater high-voltage discharges, which are then followed by expansion of the water plasma. It was observed that gasification using small amounts of gas may enhance the destruction effects of the edges of the pressure waves, resulting in deeper lignocellulose disintegration. Breakage of the cell walls increased the level of oil extraction from oil-rich vacuoles up to 93% and also accelerated the subsequent anaerobic fermentation of the presscake residue.

Low-voltage underwater electric discharges: Physical properties and application possibilities

Electrical discharges that burn inside an electrolyte bulk and have challenging practical applications are presented. The data on electrophysical and spectral properties of an underwater end-face discharge allowed suggesting the scenario of the discharge origination and development. It includes three stages: bubble growth, a quiet discharge, and an active discharge stage.

Tuning stem cell fate with physical energies

Defocused extracorporeal low-energy shock waves (DLSW) have long been used successfully in the treatment of bone and joint diseases as well as in the management of pain and inflammatory conditions. Shock waves are generated by an underwater highvoltage condenser spark discharge and focused at the diseased area, using an elliptic reflector. Shock waves are high-amplitude sound waves from a transient pressure disturbance that propagate in three-dimensional space with a sudden increase from ambient pressure to maximum pressure at the wave front. A shock wave is a sonic pulse that has certain physical characteristics. There is an initial increase of a high peak pressure, sometimes >100 MPa (500 bar) within <10 ns, followed by a low tensile amplitude (up to 10 MPa), a short life cycle of approximately 10 ms and a broad-frequency spectrum of 16e20 MHz. There are two basic effects of shock waves: The primary effect is direct generation of mechanical forces that result in the maximally beneficial pulse energy concentrated at the point where treatment is to be provided, and the secondary effect is indirect mechanical forces by cavitation, which may cause a negative effect or damage to the tissues. In the current issue of Cytotherapy, Zhao et al. (1) investigated the effects produced by DLSW on stem cell homeostasis in vitro. The authors used an electromagnetic shock wave machine and exposed rat bone marrow-derived stem cells (BMSCs) to 800 impulses of DLSW at an energy flux density of 0.1 mJ/mm. This treatment was performed before each passage. The shocked BMSCs were found to secrete more vascular endothelial growth factor and CXC ligand 5 than the BMSCs that were not shocked. The expression of CD166, CD44 and CD34 was not affected. The shocked BMSCs also exhibited higher