Charges In Air Research Articles

Largely Enhanced Output of the Non‐Contact Mode Triboelectric Nanogenerator via a Charge Excitation Based on a High Insulation Strategy

AbstractThe non‐contact triboelectric nanogenerator (TENG) based on floating plane motion can achieve a very low interface abrasion and high durability. However, the output performance of non‐contact TENG is still less than 72 µC m−2, due to the decay of tribo‐induced charges in air. Here, this work proposes two different charge excitation strategies for non‐contact mode TENG by elevating the electric insulation strength to avoid air breakdown, while both the external charge excitation and the self‐excitation system are developed. A double dielectric layer capacitance model is also established to analyze the change of charge density. A maximum output charge density of 260.15 µC m−2 is obtained using the external charge excitation with 6 kV excitation voltage. In addition, the self‐excitation strategy with non‐contact mode and more compact system is also demonstrated and an output charge density of 212.5 µC m−2 is achieved with the help of developed voltage multiple circuit, which is 2.97 times of the reported highest record for non‐contact TENG. The charge‐excited TENG via high electric insulation strategy realized in this work provides a promising way for boosting the output performance of TENGs.

Study on the characteristics of blast loads due to two simultaneous detonated charges in real air

Most studies about the air blast loads due to a single explosion have been widely reported based on the assumption that the air is an ideal gas. However, this assumption is not applicable for investigating the blast load due to multiple charge explosions in a realistic environment. In this paper, according to the existing data, the mathematical relationship between the specific internal energy and adiabatic index under high pressure is determined, and a new equation of state(EOS) for the real gas is derived. Then, the new EOS is implemented in LS-DYNA to simulate the reflected procedure of blast waves near the ground, and the average errors of overpressure and positive impulse are less than 10% and 21%, respectively. Finally, the validated model is used to investigate the effects of the total charge weight, scaled distance, and distance between the charges on the characteristics of the blast load due to two simultaneous detonated charges. Numerical simulation results show that under the condition of real gas, the total mass and distances between charges will heavily affect the starting and optimal positions of overpressure and impulse enhancement, which lays a foundation for characterizing the closed flow field of multiple charge explosions.

Chemical reaction zone measurements in pressed trinitrotoluene (TNT) and comparison with triaminotrinitrobenzene (TATB)

Photonic Doppler velocimetry and digital high-speed shadowgraphy have been used to characterize the chemical reaction zone parameters of pressed trinitrotoluene (TNT) samples with an initial density of 1.568 g cm−3. Comparison of the nanosecond time-resolved particle velocity histories of the free surfaces of detonating charges in air and light vacuum and of the interfaces between TNT detonation products and lithium fluoride or polymethyl methacrylate windows allow one to bracket the von Neumann spike pressure between 24.8 and 28.8 GPa. Our velocity waveforms confirm the two-step reaction pathway already observed in TNT, triaminotrinitrobenzene (TATB), and nitromethane, with a first fast energy release over 80 ns followed by a slower release over 250 additional ns. We consider the end of the first release zone as the locus of the Chapman–Jouguet (CJ) state, and the CJ pressure thus lies between 17.6 and 17.7 GPa. The energy release is not completed in this Jouguet plane but only after about ≈280 ns when the carbon cluster formation process ends. This corresponds to both the end of the slow release part of the interface velocity profiles and to the moment at which the free surface velocity profiles reach their maximum. Our shadowgraphy images confirm that carbon formation occurs very rapidly after the detonation breakout, in good agreement with previous time-resolved small-angle x-ray scattering measurements. The comparison with similar results previously obtained on TATB allows one to further highlight their similarities, which mainly result from their excess carbon production at late times.

Blast Wave Shaping by Altering Cross‐Sectional Shape

AbstractStandoff distances for people and equipment are determined using a scaled distance calculation that assumes a uniform distribution of explosive energy, which only occurs with center‐initiated spherical charges in free air without ground effects. There is a significant amount of data available for spheres and cylinders in air and hemispheres on the ground, but little has been published for other geometries. Published studies of spherical, cylindrical, and planar charges demonstrate that there is a focus on the blast wave resulting from charge geometry. From these studies, it appears that the highest overpressure occurs in the orientation of the largest presented surface area. This paper presents experimental pressure data recorded from the detonation of spherical, cylindrical, and cubic charges at two scaled distances. The non‐spherical charges were instrumented normal to two adjacent sides and the interjacent edge. The pressure normal to the sides of the cubic and cylindrical charges was up to 1.5 times that of the spherical charge in the near field, but lower in the far‐field indicating that a simple multiplication factor will not accurately predict the overpressure over distance for complex charges from spherical data. The sides of the cubic charge produced a near field overpressure relative to its surface area consistent with those observed from the side and end of the cylindrical charge. In the far‐field, the pressure from the sides of the charge was less than that of the sphere indicating that there is a lateral movement of energy behind the shock front causing a reversal of peak pressure in the measured orientations.

Assessment of the Armor Plate Response to the Blast Action of Differently-Shaped Charges in Air and in a Metallic Container

The stress-strain state variations of the armor plate after the explosion of spherical and cylindrical charges in air and their location in a metallic container were evaluated. It is used for estimating the anti-mine stability of combat armored vehicles by an AEP-55 Vol.II STANAG 4569 Test Procedure. Investigation results were employed to establish the relation between the deflections in the center of the armor plate on the explosion of spherical and cylindrical charges in air and in the metallic container. The difference in the deflections between the blast of the spherical charge in air and the cylindrical one in the metal container makes up 2.8 times. It is established that the detonation point localization does not practically influence the plate deflection. The results may be applied to the comparisons of data on the protective structures of combat armored vehicles, obtained for explosive charges without regard for the metallic container and permit of objective evaluation of their anti-mine stability according to an AEP-55 Vol.II procedure of a STANAG 4569 NATO Standard.

Measurement of space charges in air based on sound pulse method

The space charge in air is closely related to the mechanism of corona discharge. In order to study the onset and sustainability of corona discharge, acquiring the distribution of space charge is necessary but there still exists a puzzle which has not been settled. According to the sound pulse method, in this paper we present a kind of signal processing algorithm to analyze the electric field which is generated by modulating the space charge in the sound field. The electric filed is dependent on the form of sound emission and space charge density. The waveform of electric field is related to space charge density. Through the proposed algorithm, the space charge density can be obtained by analyzing electric field signal. The area in which the space charges need to be measured, is divided into elements. Each element is small enough so that the space charge quantity in each element is assumed to be the same. The following assumption is accepted during numerical simulation: space charge densities in the wave fronts are the same. The curve of electric field produced, received by electric field antenna, is the vector sum of electric filed produced by each element, and then calculated by numerical simulation. In order to satisfy the assumption in each measurement case, the requirements for sound emission system under different cases are discussed. In different cases, different sound emission systems are required. For space charges which are distributed uniformly, plane wave or spherical wave is suitable; for one-dimensional space charge distribution, plane wave is necessary; for space charge two-dimensional or three-dimensional space charge distribution, plane wave array is availed. What is more, a corresponding measuring system is developed which can be used for measuring the space charge density. This system mainly contains the producing of sound pulse, producing of space charges and the receiving of electric field signal. The producing of sound pulse is designed according to the measurement requirement for multi-needle-to-plate geometry which is assumed that space charge is distributed uniformly in the gap. With the experimental model, the space charge density in multi-needle-to-plate geometry is calculated according to the algorithm proposed in this paper. The result is compared with the calculated one by the method of corona currents, verifying the proposed method.

Quantitative Evidence of Reaction during Hypervelocity Penetration of Aluminum through Oxygenated Fluids

Qualitative evidence of chemical reactions between combustible metal shaped charges in air and water has previously been reported based on high-speed photography, spectroscopy, and calorimetry. This report covers investigations directed towards quantifying the conditions under which reaction occurs and the consequences on terminal encounter with submerged inert steel plates. In order to distinguish effects hypervelocity long-rod and shaped charge jet impact experiments were conducted in inert fluid, water and concentrated hydrogen peroxide. It is shown that reaction causes foreshortening of aluminum penetrators at rates that are more competitive at impact velocities towards the slow end of an effective penetrating jet, and that localized reaction and thermal expansion of ablative particulates prior to and after impact can cause substantial plate deformation. The results are consistent with hydrodynamic penetration theory when modified for reaction induced foreshortening. Predicted impact and penetration effects against submerged steel plates submerged in a chemically inert fluid are shown to agree with experiment, and the effect of density difference between the selected spindle oil inert simulant, water and concentrated hydrogen peroxide are shown to be within experimental variation.

Generation of Electric and Magnetic Fields by Air, Surface, and Underground Explosions

Results of an experimental investigation of electric and magnetic fields generated by explosions of charges of a chemical high explosive in the frequency range of 0–10 kHz are presented. It is shown that the characteristics of signals of the electric and magnetic fields registered in explosions of high‐explosive charges in air, on the ground surface, and in underground explosions are significantly different.

Generation of electric fields by dust grains during the explosions of condensed explosive charges in air

Results are presented from two-dimensional numerical simulations of the generation of electric signals during the explosions of chemical explosive charges in air. The calculated results are compared with the data from experiments carried out under the auspices of the International Science and Technology Center (project no. 835) at the Institute of Geosphere Dynamics (Russian Academy of Sciences), the Research Institute of Pulsed Technique (the Ministry of Atomic Energy of the Russian Federation), and the Zababakhin All-Russia Research Institute of Technical Physics, Russian Federal Nuclear Center (the Ministry of Atomic Energy of the Russian Federation). The electric field is assumed to be generated by charged dust grains produced during the explosion of a condensed chemical explosive charge. Numerical predictions based on the dusty plasma model for describing the parameters of dust grains are found to agree satisfactorily with experiment.

Focusing of Shock Waves Upon Explosion of Annular Charges in Air

The pressure field near the focus and at the axis of an annular charge for the case of its explosion in air is studied experimentally; the detonation is initiated at one point of the ring and propagates simultaneously along its two sides. It is found that, for different ways of detonation propagation, the pressure in the shock‐wave front at the axis of annular charges is almost identical at distances greater than three radii of the ring. At distances up to two radii from the plane of the annular charge, the pressure at the focus center is much greater than the pressure at the charge axis.

Shock-wave structure in the near zone upon explosion of spatial charges in air

Profiles and values of pressure in shock waves are determined for the case of spherical, linear, and spatial charges, such as a coil of a bulk spiral and plane annular coils and Archimedes’ spiral of various lenths, exploded in air. In the case of explosion of rings and spirals, a complex wave structure in the form of a sequence of several shock waves is registered near the charges along the spiral axes; a weaker attenuation of shock waves with distance and pressure amplitudes two to three times higher than in the case of a spherical charge of the same mass are observed. It was found that an increase in the length of a plane spiral does not lead to an increase in the maximum pressure in the shock wave at distances of the order of several pitches of the spiral from its plane. With distance from spatial charges of different shape but identical mass, the pressure values in the shock-wave fronts coincide and tend asymptotically to the parameters of a spherical explosion with a significant increase in the duration of a wave packet generated by the spatial charge. Dependences for evaluation of shock-wave pressure amplitudes in the near zone of the explosion are presented.

Aerosol Chargers Using Ionizing Radiation and Electric Field Collinear to Flow: Simulation and Experiment for Fine Particle Charging in Electronegative Air and Electropositive Nitrogen

Performances of aerosol chargers employing alpha- or beta-radioactive sources to ionize carrier gas and using applied electric fields up to 4 kV/cm collinear to the aerosol flow have been investigated. The study was done for fine particles with radii from 0.027 to 1.5 μm acquiring an electrical charge in the non-uniform bipolar atmosphere of ions in air and of electrons and N4 + ions in nitrogen. The charging process of aerosol particles of different concentrations has been analyzed by means of computer simulation, and the charge of the particles as they leave the charger has been calculated in two cases in which the velocity vector of the aerosol stream is either parallel or anti-parallel to the strength vector of the applied electric field. A comparison has been made between calculations and experimental results of particle charging in air, as well as between calculation results in air and ultrapure nitrogen under the same conditions. Two types of chargers with the charging zones irradiated totally or partially by ionizing radiation have been examined. The conditions for obtaining the maximum particle charges both in air and nitrogen as well as the conditions for the initial particle charge to be unaffected in air have been found. The experimental results of fine particle charging in air are in agreement with the theoretical calculations.

Anomalous electric fields associated with clouds growing over a source of negative space charge

Tests of influence mechanism explanations for thundercloud electrification have been attempted by modifying the initial atmospheric electrical conditions beneath some convective clouds. The modification was accomplished by the release of negative space charges into the air from elevated wires connected to a high‐voltage power supply. Anomalous distributions of charge were observed in some clouds with low bases that grew over the charge source. The results of the experiment suggest that influence mechanisms may be operative in the electrification of our mountain clouds and that, normally, the natural, positive space charges in the sub cloud air may initiate the electrification processes.

Products from the detonation of trinitrotoluene and some other navy explosives in air and nitrogen. I. Low molecular weight gases

A method of sampling and analysing the major and minor gaseous post-detonation products of 1.5–2.0 kg explosive charges in air and oxygen-deficient a

Land Seismic Source Study: ABSTRACT

During the summer of 1980, faculty and students from the Colorado School of Mines Geophysics Department conducted an extensive series of seismic measurements in eastern Colorado, with the objective of characterizing and comparing land seismic sources under a variety of controlled conditions. This work was sponsored by 29 companies and one U.S. government agency, and results are reported in full in a series of Master of Science theses completed during the fall term, 1981, at Colorado School of Mines. The test site for the measurement program was located near Brush, Colorado, on gently rolling range land. The site was selected on the basis of easy access, geology suitable for the program objectives (thick Pierre Shale section near the surface and good reflectors at depth), nearby petroleum production and well-log information, and a landowner willing to establish a permanent test site. The seismic sources used in this study included: (1) vertical and horizontal vibrators, (2) land airgun, (3) weight drop, (4) conventional explosives in shot holes, (5) surface explosives, (6) suspended charges in air (Poulter method), (7) Marthor (registered trademark of IFP), and (8) Betsy (registered trademark of Mapco). The measurement program consisted of three phases: (1) three-component downhole measurements from 400 to 1,000 ft (120 to 300 m) in 100-ft (30 m) intervals for each source type over a range of horizontal offsets from 50 to 1,000 ft (15 to 300 m); (2) three-component noise spread on the surface for each source covering an offset range of 120 to 8,730 ft (37 to 2,660 m); and (3) a conventional CDP line for each source covering 3 mi (4.8 km) of subsurface with a maximum of 24-fold coverage over the center 1 mi (1.6 km). The primary test objectives consisted of: (1) quantitative comparison of source waveforms, amplitude and phase spectra, source repeatability, source directivity, and intensity levels from downhole measurements, (2) comparison of surface-wave noise-generation characteristics between different sources from noise spread data, and (3) quantitative comparison of reflection signal characteristics (e.g., bandwidth, S/N ratio, etc) from the CDP shooting. End_of_Article - Last_Page 1699------------

Calculation of the shock waves from spherical explosive charges in air

Calculation of the shock waves from spherical explosive charges in air

ELF Electromagnetic Radiation from Small Explosive Charges in Air and Water

Two short series of tests involving measuring low-frequency electromagnetic radiation from ten-gram explosive charges in air and water have revealed signals lower than 1 cps, of duration occasionally greater than fifteen seconds. Care was used to insure that the signals were not of microphonic or other spurious origin. While radiation from explosions is well known, it is believed that the extremely low frequencies and long persistence as well as their occurrence in water are novel. No theory appears to fit all aspects of the phenomenon. Possibly related natural signals are discussed and an experimental program to yield information to formulate a hypothesis is described briefly.

The initial behaviour of a spherical explosion II. Application to PETN charges in air and water

The initial fields of disturbance due to explosions of spherical charges of PETN in air and water are calculated, using the analysis developed in part I. The results in air compare favourably with earlier calculations (Berry & Holt 1954). In water it is found that the second blast wave immediately moves towards the centre of the explosion, with very small initial strength.

Atmospheric electricity observations taken on the “Belgica” in 1907 during the Duke of Orleans' arctic cruise

In 1907 the “Belgica” made a trip into the Kara Sea, and for the first time atmospheric electricity observations were made in high latitudes on board ship. Lieutenant Rachlew undertook and made observations in the dispersion (Zerstreuung) of electric charges in free air, and of the radioactivity of the atmosphere and snow. The Elster and Geitel apparatus was used, being mounted on a suitable stand amidships, and great care was taken to eliminate the flapping movements of the electroscope leaves due to the motion of the ship. The insulations were carefully watched and, despite the humidity of the air, were kept in good state.

On some continuous observations of the rate of dissipation of electric charges in the open air

During the latter part of 1902 and the early months of 1903 I resolved to take as many observations of the rates of dissipation of positive and negative electric charges as possible, and to continue them over the whole 24 hours of the day, and, when opportunity offered, over longer periods. There appeared to be little information regarding the rate of dispersion during the night hours. At about the same time that these observations were being made, Nilsson was doing similar work at Upsala, and found a noticeable maximum value for atmospheric conductivity at about midnight. The observations were made on the Canterbury Plains of New Zealand, at a station about 20 feet above sea-level and about five miles due west from the sea coast. The apparatus used was Elster and Geitel’s Zerstreuungs- apparat , and the formula of reduction used was that given by them, viz:- E = 1/ t log V 0 /V- n / t ' log V' 0 /V' . In this formula E is proportional to the conductivity of the gas surrounding the instrument—for positive or negative charges, as the case may be. The constant “ n ” = ratio of capacity without cylinder ____________________________________ capacity with cylinder was determined by me to be 0·47, as the instrument was always used, with the protecting cover. The cover was always at one height above the base of the instrument, and was set so as to be as nearly co-axial with the discharging cylinder as could be judged by eye. No attempt was made to determine the actual capacity of the condenser cylinder and protecting cover, which would be a somewhat variable quantity owing- (1) to the differences on different days in attempting to cause the two to be co-axial; (2) to a certain amount of looseness in the fit of the shank of the cylinder on to its hole. The value above given for “ n "is the mean of several deter­minations made with different settings of the cover and cylinder. The individual values of “ n ” varied over about 0.03.