Electrical Energy Deposition Research Articles

Underwater electrical explosion of metallic wire and tube: A comparison study

With an initial energy storage of approximately 53.5 kJ, experiments on underwater electrical explosions of metallic wire and thin-wall tube were conducted. Two sets of controlled experiments were designed, and the wire and tube for each set were of the same length, cross-sectional area, and material. Load voltage, circuit current, and shock wave pressure were measured and analyzed, and electric power, energy deposition, and energy deposition rate were also calculated and investigated. Experimental results indicated that the underwater electrical tube explosion (UETE) always has higher and earlier local resistance peak, voltage peak, and electric power peak, as well as faster phase transition and ionization process than the underwater electrical wire explosion (UEWE). In addition, the energy deposition rate from the beginning of discharge or the decrease in current to the voltage peak is significantly increased when replacing a wire with a tube. For the shock-wave characteristics, the peak pressure, energy density, and impulse of the shock wave generated by UETE are greater than that generated by UEWE. The peak pressure at ∼33 cm increased from 21.1 to 24.5 MPa in the first set and from 18.1 to 21.7 MPa in the second when a tube was used instead of a wire. These experimental results help us understand the physical process of UETE and provide an alternative methodology for load design in industrial applications.

Electroacoustic tomography for real-time visualization of electrical field dynamics in deep tissue during electroporation

Despite the widespread applications of electroporation in biotechnology and medicine, monitoring the distribution of deep tissue electrical fields in real-time during treatment continues to pose a challenge. Current medical imaging modalities are unable to monitor electroporation during pulse delivery. Here we propose a method to use electroacoustic tomography (EAT) to prompt the emission of broadband ultrasound waves via electrical energy deposition. EAT boasts submillimeter resolution at depths reaching 7.5 centimeters and can deliver imaging speeds up to 100 frames per second when paired with an ultrasound array system. We’ve successfully detected EAT signals at electric field strengths ranging from 60 volts per centimeter to several tens of kilovolts per centimeter. This establishes EAT as a potential label-free, high-resolution approach for real-time evaluation of deep tissue electroporation during therapeutic procedures.

Water-augmented vaporizing foil actuator welding: Process performance and mechanisms clarifications

This paper proposes a novel impact welding method named water-augmented vaporizing foil actuator welding, in which liquid water is introduced to alter the foil’s vaporization process, thus altering the induced driving pressure and the final welding performance. A series of comparative experiments were performed to confirm the effectiveness of the process and to understand the underlying mechanism. The proposed process decreased the lower-bound required discharge energy by 58–69%, increased the peel strength by 30–60%, and significantly reduced the variability in the critical standoff distance at the lower bound of the weld window. In addition, the proposed process resolved the robustness issue by producing a much more regular and repeatable shape of the weld area compared to conventional VFAW. Furthermore, three potential mechanisms have been proposed to explain the process improvement: the added water 1) increased the electrical energy deposition, 2) introduced additional energy from the aluminum-water chemical reaction, and 3) provided a more efficient force-transfer medium. In summary, this paper introduces a novel impact welding method with much improved process capability and robustness compared to conventional vaporizing foil actuator welding. In addition, due to its simplicity, this method may be easily extended for other forms of impulse metalworking, which may stimulate a wide interest for the community of high velocity metalworking.

Enhanced productivity, quality and heating uniformity by stacking oil palm fruits under microwave irradiation

Studies on microwave sterilisation of oil palm fruits have predominantly been qualitative in nature, with little focus on profiling the temperature and heat transfer involved during the process in real-time. The present study investigates the influence of different oil palm fruit arrangements on the heat transfer and distribution under microwave irradiation and its effect on product quality. The heat transfer characteristics of single-layered and stacked layers of fruits were investigated through experimentation (response surface methodology) and simulation, followed by qualitative analysis of the products. Microwave power and heating time were recognised as significant factors (p-value < 0.05) influencing the temperature and moisture content of the oil palm fruits. The established computational model predicted significantly denser electric energy deposition in stacked fruits than a single layer of fruits. Oil palm fruits fit for storage purposes (moisture content ≤15 wt%) and palm oil meeting special quality palm oil standards (free fatty acid content <2.5%, moisture and volatile matter content <0.2%) were obtained. Stacking reduced sterilisation time by ∼21% and produced ∼11% softer fruits with ∼27% less variation in hardness among the fruits than a single layer. The stacked arrangement proved advantageous in attaining a relatively uniform heat distribution, improved heating pattern, boosted the sterilisation process with a faster drying rate and eased the extraction stage with softer fruits. Thus, enhancement in both productivity and products was accomplished through stacking.

Plasma-assisted combustion with nanosecond discharges. I: Discharge effects characterization in the burnt gases of a lean flame

The prediction of a flame response to plasma assistance requires extensive knowledge of discharge-induced plasma kinetics. Detailed studies of nanosecond discharges are common in N2/O2 and fresh combustible mixtures but are still lacking in burnt gases. To fill this gap, we define a reference test case and investigate the effects of nanosecond repetitively pulsed (NRP) discharges placed in the recirculation zone of a lean (Φ = 0.8) CH4-air bluff-body stabilized flame at atmospheric pressure. In this zone, the plasma discharge is created in a mixture of burnt gases. Quantitative optical emission spectroscopy, coupled with measurements of electrical energy deposition, is performed to provide temporally (2 ns) and spatially (0.5 mm) resolved evolutions of the temperatures and concentrations of N2(B), N2(C), N2 +(B), OH(A), NH(A), and CN(B) in the discharge. At steady state, the 10-ns pulses deposit 1.8 mJ at a repetition frequency of 20 kHz. Spatially resolved temperature profiles are measured during the discharge along the interelectrode gap. The temperature variations are more pronounced near the electrodes than in the middle of the gap. On average, the gas temperature increases by approximately 550 K. The heat release corresponds to about 20% of the total deposited electric energy. The electron number density, measured by Stark broadening of H α , increases up to about 1016cm−3. These characteristics allow to classify the discharge as a non-equilibrium NRP spark, as opposed to the thermal NRP spark where the temperature can reach 40 000 K and the degree of ionization is close to 100%. These measurements will serve (i) as a reference for future studies in the mini-PAC burner at the same conditions, (ii) to test discharge kinetic models, and (iii) to derive a simplified model of plasma-assisted combustion, which will be presented in companion paper.

Plasma blasting of rocks and rocks-like materials: An analytical model

Plasma blasting technology (PBT) is a potential alternative to chemical blasting and mechanical cutting methods for fragmentation of natural rocks, concrete, geopolymers , and other rocks-like materials. We present an analytical model of PBT addressing currently inadequate understanding of the dynamics of shock waves generation and propagation versus the electric energy release conditions. The proposed model describes the operation of the electrical discharge circuit, plasma channel initiation and expansion, and the generation and propagation of shock and pressure waves in the destructible solid. The dynamics of the power generator energy conversion into the plasma channel and into the wave of mechanical stresses in the solid are considered and the main factors determining the efficiency of the method, namely the pulse generator circuit parameters, exploding wire length, and shock wave-transmitting media, are evaluated. Solid fracture efficiency is shown to depend on the pressure pulse wave shape which, in turn, is determined by the rate of electrical energy deposition into the plasma channel. Increasing the exploding wire length leads to an earlier formation of the tensile tangential stresses and to their higher magnitude and thus facilitates material's fragmentation. The use of acoustically stiff media for shock wave transfer marginally improves material's fracture efficiency. Preliminary verification of the functionality of the model was carried out using commercial concretes, with good agreement between the analytically derived and experimentally obtained values. The results demonstrate that the proposed model allows to simulate PBT fracture over a wide range of instrumental and process conditions and can therefore be used for PBT process design, thus realising environmental and economic benefits through significant savings in time and experimental confirmation costs. • Electrical energy deposition rate determines plasma blasting technology efficiency. • Electro-fracture induces up to four zones of change of stresses and deformations. • Superposition of direct and reflected shock waves facilitates rocks fracture. • Increasing exploding-wire length increases shock wave energy and improves fracture. • Acoustically stiff media for shock-wave transfer improves fracture marginally.

A new radiofrequency balloon angioplasty device for atherosclerosis treatment

BackgroundRestenosis remains a challenge in the treatment of atherosclerosis due to damage to the endothelial layer and induced proliferation of smooth muscle cells. A novel radiofrequency (RF) heating strategy was proposed to selectively ablate atherosclerosis plaque and to thermally inhibit the proliferation of smooth muscle cells while keeping the endothelial cells intact.MethodsTo realize the proposed strategy, a new radiofrequency balloon catheter, consisting of three ports, a three-channel tube, a balloon and an electrode patch, was designed. To evaluate the feasibility of this new design, a phantom experiment with thermocouples measuring temperatures with different voltages applied to the electrodes was conducted. A numerical model was established to obtain the 3D temperature distribution. The heating ability was also evaluated in ex vivo diseased artery samples.ResultsThe experimental results showed that the highest temperature could be achieved in a distance from the surface of the balloon as designed. The temperature differences between the highest temperature at 0.78 mm and those of the surface reached 9.87 °C, 12.55 °C and 16.00 °C under applied 15 V, 17.5 V and 20 V heating, respectively. In the circumferential direction, the heating region (above 50 °C) spread from the middle of the two electrodes. The numerical results showed that the cooling effect counteracted the electrical energy deposition in the region close to the electrodes. The thermal lesion could be directed to cover the diseased media away from the catheter surface. The ex vivo heating experiment also confirmed the selective heating ability of the device. The temperature at the targeted site quickly reached the set value. The temperature of the external surface was higher than the inner wall surface temperature of the diseased artery lumen.ConclusionBoth the experimental and numerical results demonstrated the feasibility of the newly designed RF balloon catheter. The proposed RF microelectrodes heating together with the cooling water convection can realize the desired heating in the deeper site of the blood vessel wall while sparing the thin layer of the endothelium.

Feasibility of Electroacoustic Tomography: A Simulation Study.

The feasibility of electroacoustic tomography (EAT) was investigated for in situ monitoring the electric field distribution in soft tissue. EAT exploits the phenomenon that the amplitude of acoustic emission generated by an electric field is proportional to the electrical energy deposition in tissue. After detecting these acoustic waves with ultrasound transducers, an image of the electric field distribution can be reconstructed in real-time. In our computer simulations, the electric field distribution in soft tissue was generated by solving general partial differential equations (PDEs) using finite element analysis (FEA). The electric field distributions were converted into initial pressure distributions, and the propagation of the induced acoustic waves was simulated using K-Wave simulation. A circular array of 128 ultrasound transducers was placed around the target to detect the acoustic waves, and a time reversal reconstruction algorithm was used to reconstruct the EAT image. A different number of electrodes set at different distances with different voltage inputs on the electrodes were performed to simulate different electric field distributions during electroporation. It was found that the electrical energy deposition in reconstructed EAT imaging is decreased as the distance of the electrodes increases. We also have investigated the sensitivity of the EAT imaging with different voltage inputs. The minimal voltage we can detect with EAT is 970 V at the pulsewidth of 180 ns. The results of this study demonstrated that EAT is a feasible technique for monitoring the electric field distribution and guiding the electrotherapy in future clinical practice.

Bridge Burst Characteristics of Aluminum and Copper Thin-Film Bridges in Electrical Initiation Devices

The optimal design of electrical initiation devices for explosive charges and other high energy materials critically depends on the bridge burst or the electrical explosion of the thin-film metallic bridges. It is therefore quite important to select the right material with suitable explosion properties for the metallic bridge film. However, so far, no dedicated studies, experimental or theoretical, have been carried out to quantify those explosion properties for thin-filmed bridges of various metals. This study employed numerical modeling of the joule heating and bridge plasma expansion by intense electrical energy deposition in aluminum and copper bridges to evaluate and compare the explosion properties such as bridge burst time, bridge burst current density, and threshold charging voltage for the two metallic bridge materials. The prediction model of bridge burst also considered a pulsed electrical input from an RLC initiation circuit as well as plasma property calculations of the aluminum and copper plasma vapor for the state equation of the ionized vapor and the plasma electrical conductivity. The numerical predictions were in excellent agreement with the corresponding measured data of bridge bursts in a series of exploding foil initiator firing tests. The copper bridge was found to possess better explosion properties than the aluminum bridge, showing significantly higher bridge burst current density and threshold charging voltage. These findings confirmed that the copper bridge may provide higher safety and reliability in electrical initiation devices. The theoretical model and results in the present study could be useful for selecting bridge materials and designing electrical initiators or other metallic bridge explosion applications. (Received December 4, 2017; Accepted January 10, 2018)

Effect of high-voltage electrode geometry on energy deposition into exploding wire in vacuum

Based on electrical and optical diagnostics and electrostatic calculations, the relationship between distribution of radial electric field and energy deposition of electrically exploded wires in vacuum was investigated. Copper plates with different diameters were used to modify the distribution of radial electric field along wire surface in the experiments. The calculated radial electric field showed good consistency with the wire core outline in optical images, and there is a saturated positive correlation between maximum specific energy (Esm) and averaged radial field strength over the wire length. It can be concluded that the direction and amplitude of radial electric field significantly affects Esm and dominates the structure of energy deposition.

Electrical energy deposition on mitochondria and the different substrates

Mitochondria were deposited via dip coating on different substrates, namely, commercial glass, copper plate (Cu), aluminum plate (Al), and poly (methylmethacrylate). Mitochondria are organelles that are found in live cells. Mitochondria produce most of the ATP via oxidative phosphorylation. First, mitochondria were extracted for the thin film, as described in the literature. Capacitance properties of thin films were measured with Agilent LCR meter. SEM analysis was used for the surface analysis. The structure of mitochondrion was characterized with FTIR, whose spectrum was measured using a Perkin Elmer Spectrum 400 spectrometer. The stretching vibration of the P-O bond was observed at 1236 cm−1 in FTIR spectrum of the thin film. The capacitance and dielectric permittivity were first measured and calculated for the substrates, and then for mitochondria plated substrates. The properties, such as dielectric permittivity, capacitance, energy density, and power density of some substrates have been changed when their surface has been coated with mitochondria.

A non-conforming multi-element DGTD method for the simulation of human exposure to electromagnetic waves

The great majority of numerical calculations of electric energy deposition in human tissues exposed to microwaves are performed using the finite-difference time-domain FDTD method and voxel-based geometrical models of the tissues. The straightforward implementation of the method and its computational efficiency are among the main reasons for FDTD being currently the leading method for numerical assessment of human exposure to electromagnetic waves. However, the rather difficult departure from the commonly used Cartesian grid and cell size limitations regarding the discretization of very detailed structures of human tissues are often recognized as the main weaknesses of the FDTD method in this application context. In particular, interfaces between tissues where sharp gradients of the electromagnetic field may occur are hardly modeled rigorously in these studies this is generally referred as the staircasing effect. We present here an alternative numerical dosimetry methodology that is based on a DGTD method designed to work with non-conforming cubic-tetrahedral meshes for more flexibility in the discretization process of complex propagation scenes. For example, in the context of head tissues exposure to mobile phone radiation, the computation domain is divided in two regions: an unstructured tetrahedral mesh-based heterogeneous model of head tissues and an orthogonal cartesian mesh of the vacuum part of the propagation domain. We present numerical results comparing this approach with strategies based on fully Cartesian and fully tetrahedral meshes of the whole computational domain. Copyright © 2013 John Wiley & Sons, Ltd.

Effect of the Circuit and Wire Parameters on Exploding an Al Wire in Water

The underwater electrical explosion of an aluminum wire is influenced by many factors, such as wire parameters, pulsed power energy, etc. In this paper, underwater electrical explosion of an aluminum wire was investigated with pulsed voltage in the time scale of a few microseconds. A self-integrated Rogowski coil and a voltage divider were used for the measurements of current and voltage at the wire load, respectively. The deposited energy before breakdown was calculated based on experimental waveforms of current and voltage by mathematical method. Effects of the applied voltage, circuit inductance and parameters of Al wire on the electrical explosion and energy deposition were analyzed by means of experiments and calculation. The results show that the current rise rate has an important influence on explosion process, such as the energy deposition before breakdown, the electrical power as well as the various explosion stages. A higher current rise rate can be achieved by increasing applied voltage and decreasing circuit inductance. The inhomogeneity of the energy deposition will result in prematured breakdown as well as lowered energy deposition, making the explosion process of wire more complicated.

Development of a nanosecond discharge-enhanced laser plasma spectroscopy

A nanosecond pulse discharge circuit is developed and used to enhance the optical emission of laser plasma. An intense discharge spark was observed with a peak discharge current of 1.9 kA and a peak power of 6.5 MW. The main electric energy deposition only lasted for ∼40 ns. An intense optical emission was observed. The line intensity of plasma emission was greatly increased along with an improved signal-to-noise ratio, in comparison with that using a microsecond pulse discharge circuit. From the measured spectra, electron temperature and electron number density were estimated. The mechanism of the optical emission enhancement was briefly discussed.

Interaction Between Solid Copper Jets and Powerful Electrical Current Pulses

The interaction between a solid copper jet and an electric current pulse is studied. Copper jets that were created by a shaped-charge device were passed through an electrode configuration consisting of two aluminum plates with a separation distance of 150 mm. The electrodes were connected to a pulsed-power supply delivering a current pulse with amplitudes up to 250 kA. The current and voltages were measured, providing data on energy deposition in the jet and electrode contact region, and flash X-ray diagnostics were used to depict the jet during and after electrification. The shape of, and the velocity distributions along, the jet has been used to estimate the correlation between the jet mass flow through the electrodes and the electrical energy deposition. On average, 2.8 kJ/g was deposited in the jet and electrode region, which is sufficient to bring the jet up to the boiling point. A model based on the assumption of a homogenous current flow through the jet between the electrodes underestimates the energy deposition and the jet resistance by a factor 5 compared with the experiments, indicating a more complex current flow through the jet. The experimental results indicate the following mechanism for the enhancement of jet breakup. When electrified, the natural-formed necks in the jet are subjected to a higher current density compared with other parts of the jet. The higher current density results in a stronger heating and a stronger magnetic pinch force. Eventually, the jet material in the neck is evaporated and explodes electrically, resulting in a radial ejection of vaporized jet material.

High frequency excitation waveform for efficient operation of a xenon excimer dielectric barrier discharge lamp

The application of a high frequency (∼2.5 MHz) burst (amplitude-modulated sinusoidal) excitation voltage waveform is investigated for driving a fluorescent dielectric barrier discharge (DBD) light source. The excitation waveform presents a novel method for generating spatially stable homogeneous Xe DBD possessing a high conversion efficiency from electrical energy to VUV excimer radiation (∼172 nm), even at a significantly higher electrical energy deposition than realized by pulsed excitation. Simulation and experimental results predict discharge efficiencies around 60%. Lamp efficacy above 74 lm W−1 has been achieved. VUV emission and loss mechanisms are investigated extensively and the performance of burst and pulsed waveforms is compared both theoretically and experimentally.

Nanosized Powder Synthesis by Pulsed Wire Discharge in High-Speed Gas Flow

Copper nanosized powders were successfully synthesized by pulsed wire discharge (PWD) in high-speed gas flow. The maximum pressure of the gas blowing from the gas puff apparatus developed for PWD was 22 kPa at plenum pressure of 0.4 MPa. The experimental results have shown that, by using gas puff at background pressure of 130 Pa, the electrical energy deposition into the wire reached 40 J, which is almost the same as that obtained at pressure of 5 kPa without gas puff. However, the average particle size decreased from 39 nm (at steady pressure of 5 kPa) to 16 nm (at background pressure of 130 Pa with gas puff). Therefore, it has been proved that the gas puff has significant effect in the reduction of average particle size.

Modeling and Optimization of a Constant-Temperature In-Core Power Sensor

A controlled-calorimetric in-core instrument that can directly measure nuclear energy deposition has been developed and tested. This instrument works by heating an element of reactor fuel to a constant temperature with an electric heater, such that input electrical power is inversely related to the deposited nuclear power. Tests on first-generation sensor prototypes and subsequent modeling showed three problems: lack of proportionality in the relative neutron and photon response, a relatively low bandwidth, and drift. A model of the sensor has been developed and used to optimize the design of second-generation prototypes with respect to these three problems. Study of the predicted relative neutron and gamma response showed that a nonuniform distribution of nuclear and electrical energy deposition caused the temperature distribution within the sensor to change as the ratio of the energy components varies. This affects sensor power proportionality and increases response time. Heat transfer through the sensor power leads was demonstrated to cause most of the observed drift. The proposed second-generation sensor design forces almost all of the temperature gradient into a thin metal axial region, which gives uniform energy distribution from all sources and better control of thermal leakage and contact resistances. This results in a prediction of increased bandwidth with improved proportionality.

Homogeneous electrical explosion of tungsten wire in vacuum

Experimental results on Joule energy deposition upon initiation of a fast electrical explosion of 16-μm tungsten wire in vacuum at current densities of more than 108 A/cm2 are reported. We have found that explosion with a fast current rise time (∼170 A/ns into a short) results in homogeneous and enhanced deposition of electrical energy into the tungsten before surface flashover. The maximum tungsten wire resistivity reaches a value of up to ∼185 μΩ cm before surface flashover that significantly exceeds the melting boundary and corresponds to a temperature of ∼1 eV. The highest values for light radiation and expansion velocity of wire ∼1 km/s were observed for the fast explosion. For the explosion mode with a slower current rise time (∼22 A/ns into a short), we observed the existence of an “energy deposition barrier” for tungsten wire. In the slow explosion mode, the current is reconnected to the surface shunting discharge before melting. The maximum tungsten wire resistivity in this case reaches the value of ∼120 μΩ cm, which is less than indicative of melting. Also, the energy deposition along the wire is strongly inhomogeneous, and wire is disintegrated into parts. We attribute the early reconnection of the current to the surface discharge for the slow explosion to high electron emission from the wire surface, which starts before melting.

Numerical study of 2D and 3D flowfields in a high‐power pulsed chemical laser

High‐power chemical lasers operating in high repetitive rate show a decrease of the output energy laser beam. In such lasers, the characteristic time which depends on the laser output is short in comparison with those related to the flow. Consequently, shock waves, acoustic waves and thermal perturbations, induced by the strong electric energy deposition and remaining in the laser cavity between two pulses, may explain the decrease of output energy of the laser beam. For a better understanding of the flowfields, a numerical approach is carried out using flux corrected transport algorithms (FCT methods) associated with a Riemann solver on the computational domain boundaries. Under two‐dimensional assumptions, the inviscid flow in the convergent‐divergent laser cavity is computed to describe the creation and propagation of the wave system and the hot gas column in both single and multidischarge operating modes. Distortions of the contact surfaces are put into evidence through the study of flowfield instabilities. Finally, the limitations of the two‐dimensional modelization become apparent. The numerical resolution is extended to a 3D case in order to take into account the optical direction. This allows to study the influence of shock waves travelling between optics and being generated by a side effect developing at the electrodes. These waves have an effect of long duration on the flowfield and lead to a high residual perturbation level.