Diamond Shock Research Articles

The Effect of Different Pressure Conditions on Shock Waves in a Supersonic Steam Ejector

The complex flow phenomena in a three-dimensional supersonic steam ejector were simulated with a non-equilibrium condensation model including real physical properties in different pressure conditions. The different working conditions include discharge pressure, motive pressure, and suction pressure. The influence of different pressures on shock waves in the steam ejector was investigated comprehensively. The intrinsic causes of shock wave variation with pressure conditions were explained in detail. The results show that the width of the primary shock train region expand with an increase in the motive pressure or a decrease in suction pressure. The diamond shock waves move downstream with an increase in motive pressure or a decrease in suction pressure. The shocking position in the diffuser moves upstream until it reaches the diffuser entrance with an increase in discharge pressure or a decrease in motive pressure or suction pressure. The intensity and number of oblique shock waves in the diffuser increase with an increase in motive pressure and suction pressure or a decrease in discharge pressure. The existence of only one shock wave in the diffuser is a necessary and insufficient condition for the ejector to enter a double choking mode.

Under-expansion jet flame propagation characteristics of premixed H2/air in explosion venting

In premixed H2/air explosion venting, an under-expansion jet may be caused by the pressure difference between the inside and outside of the explosion vent. Based upon the under-expansion jet, studying the structure of the under-expansion jet flame and the factors influencing its formation is essential to hydrogen safety in explosion venting. This study explored the basic characteristics of the under-expansion jet flame in premixed H2/air explosion venting, and discussed the formation of two under-expansion structures (Mach disk and diamond shock wave) of such jet flames by conducting a premixed H2/air explosion venting experiment. The influences of hydrogen fraction, explosion venting diameter, and duct length on the structure of under-expansion jet flames were evaluated. The results showed that after successful explosion venting, the under-expansion jet flame would be generated when the hydrogen fractions were 30–60 vol.%, and as the hydrogen fractions were 30–50 vol.%, the lengths of the venting duct were 30 and 50 cm. The duration of under-expansion jet flame was the longest when the hydrogen fraction was 40 vol.%. With the explosion venting diameter and hydrogen fraction increased, the spacing between under-expansion jet flame structures (S) increased. However, an increase in duct length led to the attenuation of the S. During the explosion venting, the under-expansion jet caused a pressure imbalance near the explosion vent and high-intensity convection forms on both sides of a jet, which can generate two or more explosions. Therefore, understanding the basic characteristics of under-expansion jet flame can aid the effective development of measures to prevent, mitigate, and protect against premixed H2/air explosions.

Operation Rule of Steam Ejector and Influence Analysis of Ejection Position

In order to analyze the operation rule of steam ejector used in sewage treatment field, this paper established the mathematical model of steam ejector, simulated the internal flow state, analyzed the influence rule of external parameters on the performance of steam ejector, and analyzed the influence rule of ejector position on the water production ratio of steam ejector multi-effect evaporation desalination system. The research results show that under the same steam ejector structure, as the pressure of the working steam increases, the mixing and disturbance of the working steam and the ejected steam become more intense, and the diamond shock wave structure increases. As the pressure of the ejected steam increases, the momentum exchange effect of the shear blending of working steam and ejected steam is accelerated, and the speed increase rate becomes larger, and the diamond shock wave structure gradually gathers toward the nozzle. As the pressure rise of the ejected steam inlet and outlet increases, the backflow phenomenon near the wall in the mixing chamber becomes more serious, and the diamond shock wave structure is reduced. With the forward movement of the ejector position of the thermal steam compressor, the pressure of the ejected steam increases, and the water production ratio of the steam ejector multi-effect evaporation seawater desalination system shows a downward trend. Therefore, choosing appropriate working condition parameters can effectively improve the working performance of steam ejector and improve its operating efficiency in the field of sewage treatment.

Fluidic Injection Scenarios for Shock Pattern Manipulation in Exhausts

By numerically screening internal fluidic injection scenarios for the manipulation of the double diamond shock pattern in convergent–divergent nozzle exhausts, the individual importance of design parameters is demonstrated. It is found that the evolving shock pattern is sensitive to the injection location, whereas the persistence of the induced counterrotating vortex pairs is primarily governed by the injection pressure. Injection close to the nozzle exit generates secondary vortical structures, amplifying the fluctuations in the nozzle vicinity.

Extending the Density Functional Tight Binding Method to Carbon Under Extreme Conditions

We report herein on simulations of carbon under pressures up to 2000 GPa and 30 000 K using the density functional tight binding method (DFTB) with a parameter set we have specifically designed for these conditions. The DFTB method can provide a high throughput simulation capability compared to Kohn–Sham density functional theory while retaining most of its accuracy. We fit the DFTB repulsive energy to measured and computed diamond isothermal compression data and show that this yields accurate compression curves for diamond, graphite, and the BC8 phase, as well as material properties for all three phases. We then show that our new repulsive energy yields predictions of the Hugoniot of diamond shock compressed to the conducting liquid that are within the range of different experimental measurements. Our results provide a straightforward method by which DFTB can be extended to studies of covalently bonded materials under extremely high pressures and temperatures such as the interiors of planets and other la...

X-RAY EMISSION FROM PROTOSTELLAR JET HH 154: THE FIRST EVIDENCE OF A DIAMOND SHOCK?

X-ray emission from about ten protostellar jets has been discovered and it appears as a feature common to the most energetic jets. Although X-ray emission seems to originate from shocks internal to jets, the mechanism forming these shocks remains controversial. One of the best studied X-ray jet is HH 154 that has been observed by Chandra over a time base of about 10 years. We analyze the Chandra observations of HH 154 by investigating the evolution of its X-ray source. We show that the X-ray emission consists of a bright stationary component and a faint elongated component. We interpret the observations by developing a hydrodynamic model describing a protostellar jet originating from a nozzle and compare the X-ray emission synthesized from the model with the X-ray observations. The model takes into account the thermal conduction and radiative losses and shows that the jet/nozzle leads to the formation of a diamond shock at the nozzle exit. The shock is stationary over the period covered by our simulations and generates an X-ray source with luminosity and spectral characteristics in excellent agreement with the observations. We conclude that the X-ray emission from HH 154 is consistent with a diamond shock originating from a nozzle through which the jet is launched into the ambient medium. We suggest that the physical origin of the nozzle could be related to the dense gas in which the HH 154 driving source is embedded and/or to the magnetic field at the jet launching/collimation region.

Numerical Studies on the Effects of Stagnation Pressure and Temperature on Supersonic Flow Characteristics in Cold Spray Applications

Low-temperature particle coating requires supersonic flow. The characteristics of this supersonic flow are investigated using a nonlinear turbulence model. The low-temperature, supersonic particle deposition technique is valuable because its rapid and dense coating minimizes thermal damage to both particles and substrate. It has excellent potential for industrial production of low-cost thin films. Stagnation pressures and temperatures of the supersonic nozzle range from 4 < P o < 45 bar and 300 < T o < 1500 K, respectively. The exit Mach number, M e, and velocity, V e, range from 0.6 to 3.5 and 200 to 1400 m/s, respectively. The effects of stagnation pressure (P o) and stagnation temperature (T o) on supersonic flow impinging upon a substrate are described. In other words, the energy loss through shockwaves and shear interactions between the streaming jet and surrounding gas are quantified as functions of P o and T o. P o is decreased because of friction (loss ranges from 40 to 60%) while T o is nearly conserved. To realize the nozzle exit condition of P e = P amb, we demonstrate that P o should be adjusted rather than T o, as T o has little effect on exit pressures. On the other hand, T o is more influential than P o for varying the exit velocity. Various nozzle geometries yielding different flow characteristics, and hence, different operating conditions and coating performances are investigated. The corresponding supersonic flows for three types of nozzles (under-, correctly , and over-expanded) are simulated, and their correctly expanded (or shock-free) operating conditions are identified. Diamond shock structures induced by the pressure imbalance between the exiting gas and the surrounding atmosphere are captured.

Supersonic Nozzle Flow Simulations for Particle Coating Applications: Effects of Shockwaves, Nozzle Geometry, Ambient Pressure, and Substrate Location upon Flow Characteristics

Characteristics of supersonic flow are examined with specific regard to nano-particle thin-film coating. Effects of shockwaves, nozzle geometry, chamber pressure, and substrate location were studied computationally. Shockwaves are minimized to reduce fluctuations in flow properties at the discontinuities across diamond shock structures. Nozzle geometry was adjusted to ensure optimal expansion (i.e., Pexit = Pambient), where shock formation was significantly reduced and flow kinetic energy maximized. When the ambient pressure was reduced from 1 to 0.01316 bar, the nozzle’s diverging angle must be increased to yield the optimum condition of minimized adversed effects. Beyond some critical distance, substrate location did not seem to be a sensitive parameter on flow characteristics when Pamb = 0.01316 bar; however, overly close proximity to the nozzle exit caused flow disturbances inside the nozzle, thereby adversely affecting coating gas flow.

B216 数値シミュレーションによる高速フレーム溶射ガンからの超音速噴流の可視化

Supersonic jets from a high-velocity oxy-fuel thermal spraying gun have been simulated and visualized by numerical analysis. The thermal spraying gun in the present simulation has the same shape as that of a commercially used gun. To visualize the jet structure, the equi-Mach number contours of supersonic jets have been depicted, and the Mach number and static pressure distributions along the jet axis have been, calculated both for under-expanded and correctly-expanded supersonic jets. For under-expanded jets, the diamond shock pattern has been observed.

Electric discharge in the presence of supersonic shocks

A cone-shaped shock generator is placed in a Mach 2.5 flow to generate a conic shock attached to its tip. The tip and the body of the model are also designed as the cathode and anode, which are separated by a conical-shaped ceramic insulator providing a 5-mm gap for on-board gaseous discharge to produce plasma around the tip. The interaction of 60 Hz pulsed discharge with this shock wave is studied by means of the spatial distribution and temporal evolution of discharge-induced airglow images. As shown, when the flow becomes unstable during the discharge, signified by the sudden appearance of additional diamond shock in the flow, the discharge mode also starts to oscillate between the constricted arc and diffused arc, manifesting relaxation instability.

Radial distribution function of a new form of amorphous diamond shock induced from C60 fullerene.

Radial distribution function of a new form of amorphous diamond shock induced from C60 fullerene.

Emission spectroscopic study of a low pressure supersonic Ar-H2 DC plasma jet

An emission spectroscopic study is reported of the temperature and the electron density distributions in a DC plasma jet at atmospheric and low pressure conditions. A standard DC plasma spraying torch is used with an Ar-H2 mixture as the plasma gas (17% H2 by volume) at a power level of 30 kW (current=600 A, voltage=50 V). Results were obtained for chamber pressures of 100 kPa, 52 kPa and 20 kPa. Electron density measurements were carried out by the Stark broadening of the Hbeta line and from the continuum recombination of the Ar+ and H+ ions. The temperature is obtained by using a Boltzmann plot of the neutral argon lines and the absolute intensity measurements of the argon lines. The results confirm that local thermodynamic equilibrium (LTE) conditions prevail throughout most of the temperature field at pressures of 100 and 53 kPa. Important deviations from LTE conditions are noted at a chamber pressure of 20 kPa. The results at the lowest pressure condition (20 kPa) show important axial variations of the electron density which coincide with the observed diamond shock wave in the plasma jet.

Chemical Preparation and Shock Wave Compression of Carbon Nitride Precursors

Two synthetic routes have been developed to produce high‐molecular‐weight organic precursors containing a high weight fraction of nitrogen. One of the precursors is a pyrolysis residue of melamine‐formaldehyde resin. The second precursor is the byproduct of an unusual low‐temperature combustion reaction of tetrazole and its sodium salt. These precursors have been shock compressed under typical conditions for diamond and wurtzite boron nitride synthesis in an attempt to recover a new ultrahard carbon nitride. The recovered material has been analyzed by X‐ray diffraction, FTIR, and Raman microprobe analysis. Diamond is present in the recovered material. This diamond is extraordinarily well ordered relative to diamond shock synthesized from carbonaceous starting materials.