Gas Jetting Research Articles

Droplet-gas interactions in nanoelectrospray multiphase flow

Electrospray (ES) is production of a charged droplet plume that transits from an electrically biased supply capillary to a counter electrode under the influence of an electric field. Drag interactions with the surrounding gas decelerate the droplets while transferring the momentum from droplets to accelerate the surrounding gas, resulting in an induced gas flow. This work seeks to characterize the structure of the resulting gas jet and identify the key mechanisms defining the flow structure. The phenomenon of gas jets produced by momentum transfer from nano-electrospray (nES) plumes is explored with schlieren visualization, thermal anemometry, and numerical simulations. Schlieren visualization experiments provide information on the flow structure in support of simulation predictions, and the hot thermistor anemometry measurements of gas velocities outside the spray demonstrate quantitatively validated simulation results. The study reveals the formation of a moderately high velocity coaxial gas jet within the nES plume and provides insight into the overall flow structure of the induced flow. The multiphase electrohydrodynamic simulations enable numerical experimentation to explore the fundamental physics of coupled droplet-gas transport and the resulting flow structure. The simulations, confirmed by the experiments, reveal gas jetting induced by nES with a narrow (sub hundred micrometers in diameter) core originating from the nES liquid-jet breakup region and a surrounding larger-in-extent zone (several hundred micrometers in diameter) of lower velocity gas flow within the electrospray plume. This behavior is due to nES ejecting a stream of droplets from the tip of a narrow liquid cone-jet, where the combined effect of many small droplets transferring momentum to a confined region of gas yields a narrow but high-velocity gas stream. The micro-jets produced by nES have practical utility for mass spectrometry, 3D printing and fabrication, and thermal management.

Experimental Investigation of Disturbing the Flow Field on the Vortex-Induced Vibration of Deepwater Riser Fitted with Gas Jetting Active Vibration Suppression Device

An experimental investigation on the disturbance effect of jet-type active vibration suppression device on vortex-induced vibration of deep-sea riser was carried out in the wave-flow combined flume. The vibration suppression device was designed in which the jet pipe was horizontally fixed to the front end of the riser. By varying three different excitation spacings and multi-stage outflow velocities, the influence law of the dominant frequency, dimensionless displacement and other dynamic response parameters was studied under different excitation spacings, and the mechanism and sensitive characteristics of the disturbance suppression were explored. The results indicate that the variation of excitation spacing makes gas curtain enter the strong disturbed flow region at different velocities and angles, and the coupling relationship between excitation spacing and reduced velocity is the key factor to enter the strong disturbed flow region to achieve the optimal disturbance suppression. In the strong disturbed flow region, the influence of gas curtain on the dominant frequency is obviously affected by the flow velocity, while the vibration displacement is stable at the same amplitude and is weakly affected by the flow velocity. Gas curtain can effectively disturb the formation of vortex shedding, destroy the strong nonlinear coupled vibration of the riser, and achieve better vibration suppression effect. In the weak disturbed flow region, the vortex length of the riser tail is prolonged, the strong nonlinear coupled vibration of the riser is gradually restored, and the vibration suppression effect of the device gradually decreases.

Variability of spider spatial configuration at the Martian south pole

Araneiform terrain, or “spider” (spider-like surface modifications) is suggested to form through basal sublimation of seasonal translucent CO2 slab ice and subsequent gas jetting, and so far only known to occur at the Martian south pole. Their spatial configuration characteristics remain incompletely understood. We observed non-random spatial distributions in seven study regions with significant regional variation of average spacings. This non-randomness results from the pressure release by jetting from one spider, inhibiting ice rupture in the vicinity to initiate a new spider. Rose diagrams constructed from our trough orientation mapping show that spider troughs do not have preferred orientations and appear randomly distributed. We suggest that substrate properties such as permeability, porosity and cohesion regulate and modify the spatial configuration of a spider population on a regional scale, and insolation and obliquity determine whether general conditions are favorable for spider formation. The limited areal distribution of spiders may be due to the strict formation constraints on the thickness of the seasonal translucent CO2 slab ice. This work provides insight into the regional variability of gas jetting and spider formation.

Modeling Hot Spot Experiments on Shocked Octahydro‐1,3,5,7‐Tetranitro‐1,3,5,7‐Tetrazocine

AbstractFor the first time, mesoscale simulations of shocked explosives are validated with hot spot temperature data. Following recent experiments, we simulate a 25 μm aluminum flyer impacting a powder bed of octahydro‐1,3,5,7‐tetranitro‐1,3,5,7‐tetrazocine (HMX) with an initial speed of 1.4 to 3.6 km s−1. The powder bed has a density of 0.56 g cm3, or 29 % crystal density, and an average grain size of 4 m. Simulations are performed in the multi‐physics code, ALE3D. We employ a comprehensive HMX material model that accounts for the chemistry, unreacted and product equation‐of‐states (EOSs), elastic‐plastic response, as well as melting and melt viscosity. Simulations show compaction, reaction, and gas jetting during the initial stages of shock in the powder bed. Shock reflection at the glass window interface increases hot spot temperatures in HMX product gas in excess of 7000 K at higher impact speeds which is readily observable using pyrometry techniques. We extract a temperature histogram from simulations at discrete times, using it to calculate an effective emission spectrum and effective temperature, Teff, for comparison to data. Simple T‐ and T4‐based methods inadequately weight the higher temperature regions and result in a low Teff that is in poor agreement with data. However, calculating Teff based on Planck's Law with a gray body assumption demonstrates good agreement with hot spot temperature data. A modified Arrhenius model is fit to the normalized reaction rates predicted by mesoscale simulations and inferred temperatures range from 1544 K to 1779 K; these temperatures are approximately 4x lower than the peak hot spot temperatures but 2‐3x higher than the bulk shock temperatures. The agreement with experimental results validates our mesoscale simulations as useful tools for elucidating the role of hot spot mechanisms in the shock initiation of heterogeneous explosives.

Simulation of underwater explosions in close-proximity to a submerged cylinder and a free-surface or rigid boundary

The response of a submerged structure to an underwater explosion (UNDEX) depends on highly nonlinear interactions between the structure, nearby boundaries, the shock wave and the bubble of gaseous explosion products. These complex interactions may significantly influence the loads imparted to a submerged structure by an underwater explosion. This research presents the experimental validation of a coupled Eulerian–Lagrangian numerical modelling approach for simulating the interaction between an underwater explosion, a submerged cylinder, and a free surface or rigid bottom. The three-dimensional simulations in account concurrently for shock wave propagation, cavitation, and gas bubble migration and jetting. The validated simulation methodology is employed to demonstrate how the presence of a submerged cylinder influences bubble migration and its period of oscillation in the vicinity of a boundary.

Analysis of gas jetting and fumarole acoustics at Aso Volcano, Japan

The gas-thrust region of a large volcanic eruption column is predominately a momentum-driven, fluid flow process that perturbs the atmosphere and produces sound akin to noise from jet and rocket engines, termed “jet noise”. We aim to enhance understanding of large-scale volcanic jets by studying an accessible, less hazardous fumarolic jet. We characterize the acoustic signature of ~2.5-meter wide vigorously jetting fumarole at Aso Volcano, Japan using a 5-element infrasound array located on the nearby crater. The fumarole opened on 13 July 2015 on the southwest flank of the partially collapsed pyroclastic cone within Aso Volcano's Naka-dake crater and had persistent gas jetting, which produced significant audible jet noise. The array was ~220m from the fumarole and 57.6° from the vertical jet axis, a recording angle not typically feasible in volcanic environments. Array processing is performed to distinguish fumarolic jet noise from wind. Highly correlated periods are characterized by sustained, low-amplitude signal with a 7–10Hz spectral peak. Finite difference time domain method numerical modeling suggests the influence of topography near the vent and along the propagation path significantly affects the spectral content, complicating comparisons with laboratory jet noise. The fumarolic jet has a low estimated Mach number (0.3 to 0.4) and measured temperature of ~260°C. The Strouhal number for infrasound from volcanic jet flows and geysers is not known; thus we assume a peak Strouhal number of 0.19 based on pure-air laboratory jet experiments. This assumption leads to an estimated exit velocity of the fumarole of ~79 to 132m/s. Using published gas composition data from 2003 to 2009, the fumarolic vent area estimated from thermal infrared images, and estimated jet velocity, we estimate total volatile flux at ~160–270kg/s (14,000–23,000t/d).

Characterization and interpretation of volcanic activity at Karymsky Volcano, Kamchatka, Russia, using observations of infrasound, volcanic emissions, and thermal imagery

A multiparameter data set including measurements of infrasound, volcanic emissions, and thermal imagery is used to characterize and interpret diverse volcanic activity observed during field campaigns in August 2011 and July 2012 at Karymsky Volcano, Kamchatka, Russia. Four activity types are visually identified and characterized according to: SO2 emission rate, ash mass, event duration, peak temperature, thermal radiation energy, infrasound onset and frequency, reduced infrasonic pressure, and acoustic energy. These activity types include: (1) ash explosions, (2) pulsatory degassing, (3) gas jetting, and (4) explosive eruption. Unique infrasound signals are associated with all four activity types suggesting that infrasound can be used to help remotely and continuously detect and characterize volcanic activity at Karymsky and other similar volcanoes. Our observations suggest that SO2 is emitted continuously, though in varying abundance, while ash is emitted discontinuously and is only associated with certain types of activity. Our data set supports previous models that attribute variations in surface activity to changes in conduit permeability at Karymsky Volcano. Evidence for a decrease in conduit permeability as a trigger for ash explosions and explosive eruption activity types is supported by weakened but still detectable SO2 emission rates prior to eruption, along with the highly impulsive infrasonic onset and large reduced infrasound pressure indicating high pressure at the vent. We speculate that changes in conduit permeability at Karymsky Volcano result from changes in magma supply from the shallow‐crustal storage region though additional measurements are required to validate this hypothesis.

Pilot study on jetting pre-oxidation fluidized bed gasification adapting to caking coal

Caking coal is difficult to be gasified in fluidized bed (FB) because of the inevitable particle agglomeration caused by caking in the dense bottom of the bed. Literature studies have shown that pre-oxidizing the coal can suppress its caking propensity, while quick dispersion of coal particles, for example, by gas jetting in the plastic stage of heating is critical to such a suppression of the caking agglomeration. Thus, the so-called jetting pre-oxidation fluidized bed gasification (JPFBG) is devised in this study to gasify caking coal in FB. Coal particles usually below 5mm are blown into the space above the bottom dense bed surface by an O2-containing gas jet to disperse and meanwhile to pre-oxidize the particles. The resulting char particles with little, even without caking propensity fall into the dense bottom of the bed to allow their gasification there. After validating the destruction of caking agglomeration by jetting pre-oxidation in a laboratory FB apparatus, a 150kg/h pilot JPFBG plant was built and the coal with the caking index of about 20 was successfully gasified in this plant using normal air and O2-enriched air. The heating vale of the produced gas varied in 2.9–5.0MJ/mN3 and decreased with raising the oxygen percentage applied to the jet feeding. Raising the oxygen percentage for the jet caused more of the produced gas formed in the bottom dense bed of char gasification to burn off in the jetting zone. The optimal proportion of the oxygen applied to the jet feeding or coal pre-oxidation was found to be about 37% against the total oxygen supply. Enriching the O2 content in the gasification agent to about 30vol.% enhanced greatly the gasification rate of the tested low-reactivity coal in JPFB.

Failure Analysis of Physical Explosion due to Gas Jetting from High-Pressure Pipeline

Jetting of the combustible gas with high pressure is a prelude to bringing into action of the chemistry explosion of gas cloud. Comparing with the leakage and diffusion of combustible gas and the chemistry explosion effect of gas cloud, the distribution of pressure, temperature and velocity formed by high-pressure gas jetting after the destruction of a pipeline, has been paid less attention to in the related field. There are a few fundamental data on the subject of evaluation of physical explosion parameters. In this paper, a physical explosion case of hydrogen gas transported through a high-pressure pipeline is reported, and a cause analysis of the explosion accident is proposed. Numerical simulation yields the field state parameters and the damage characteristics in the process of high-pressure gas jetting. In front of the leakage gas flow, a shock wave forms due to high-pressure gas jetting. The physical explosion can trigger the combustion of leaked hydrogen gas. Though the pressure rapidly attenuates behind the shock wave, a relatively high velocity is maintained until the control valve in the pipeline system is closed down or the jetting finishes. In the given accident case, the shock wave pressure reaches an order of 1 MPa and the temperature reaches 200–300 °C. This temperatures is obviously less than the igniting temperature of hydrogen gas, 400 °C. But the combustion of leaked gas may be triggered by the spark caused by the impact of instrument plates. Since the instrument plates near the leaking port of pipeline has been damaged already before the leaked gas burns, the electric spark from the line short or the strike spark between metal parts are also completely possible to trigger this combustion.

Parent body depth–pressure–temperature relationships and the style of the ureilite anatexis

Abstract– New analyses of mafic silicates from 14 ureilite meteorites further constrain a strong correlation (Singletary and Grove 2003) between olivine‐core Fo ratio and the temperature of equilibration (TE) recorded by the composition of pigeonite. This correlation may be compared with relationships implied by various postulated combinations of Fo and pressure P in models for ureilite genesis by a putative process of anatectic (depth‐linked, P‐controlled) smelting. In such models, any combination of Fo and P together fixes the temperature of smelting. Agreement between the observed correlation and these models is poor. The anatectic smelting model also carries implausible implications for the depth range at which ureilites of a given composition (Fo) form. Actual ureilites (and polymict ureilite clasts: Downes et al. 2008) show a distribution strongly skewed toward the low‐Fo end of the compositional range, with approximately 58% in the range Fo76–81. In contrast, the P‐controlled smelting model implies that the Fo76–81 region is a small fraction of the volume of the parent body: not more than 3.2%, in a model consistent with the Fo‐TE observations; and even ignoring the Fo‐TE evidence not more than 11% (percentages cited require optimal assumptions concerning the size of the parent body). This region also must occur deep within the body, where no straightforward model would imply a strong bias in the impact‐driven sampling process. The ureilites did not derive preponderantly from one atypical “largest offspring” disruption survivor, because cooling history evidence shows that after the disruption (whose efficiency was increased by gas jetting), all of the known ureilites cooled in bodies that were tiny (mass of order 10−9) in comparison with the precursor body. The Ca/Al ratio of the ureilite starting matter cannot be 2.5 times chondritic, as has been suggested, unless the part of the body from which ureilites come is at most 50% of the whole body. Published variants of the anatectic, P‐controlled smelting model have the ureilites coming from a region that is >50 vol% of their parent body; and to invoke a larger body would have the drawback of implying that the Fo76–81 spike represents an even smaller fraction of the parent body’s interior. The ureilites’ moderate depletions in incompatible elements are difficult to reconcile with a fractional fusion model. It is not plausible that melt formed grossly out of equilibrium with the medium‐sized ureilite crystals. The alternative to pressure‐controlled smelting, i.e., a model of gasless or near‐gasless anatexis, has very different implications for the size and evolution of the original parent body. To yield internal pressures prohibitive of smelting in even the shallowest and most ferroan portion of its anatectic mantle, the body would have to be larger than roughly 690 km in diameter. A 400 km body would have approximately 12 vol% of the interior (or 13 vol% of the interior apart from the thermal “skin” that never undergoes anatexis) prone, if both extremely shallow and extremely ferroan, to mild smelting. Gasless anatexis also implies that this large parent body was compositionally, at least in terms of mg, grossly heterogeneous before anatexis, probably (in view of the oxygen isotopic diversity) as a result of mixed accretion.

Thermal observations of gas pistoning at Kilauea Volcano

Data acquired by three continuously recording thermal infrared thermometers situated on the north rim of Pu`u `O`o Crater at Kilauea Volcano during 2002 revealed episodes of periodic thermal pulses originating from a degassing vent on the crater floor. These thermal pulses are interpreted as gas release (jetting events) associated with gas pistoning, a mechanism observed previously at both Mauna Ulu and Pu`u `O`o. During a 35‐day‐long period spanning June and July 2002, gas pistoning was frequently the dominant mode of gas release, with as many as several hundred pulses occurring in uninterrupted series. On other days, degassing alternated between periods of quasi‐continuous gas jetting and intervals of gas pistoning that contained a few to a few dozen pulses. Characteristic time intervals between pistoning events ranged from 2 up to 7 min. We identify three types of pistoning. Type 1 involves emission of lava, followed by gas jetting and drain back; type 2 is the same but the elevated position of the vent does not allow postjet drain back; and type 3 involves gas jetting only with no precursory lava flow. To explain gas pistoning, we apply a model whereby a stagnant cap of degassed magma develops in the conduit below the vent. Gas bubbles rise through the magma column and collect under the cap. The collective buoyancy of these bubbles pushes the cap upward. When the cap reaches the surface, it erupts from the vent as a lava flow. Unloading of the conduit magma in this way results in an abrupt pressure drop (i.e., the overburden felt by the bubbles is reduced), causing explosive gas expansion in the form of gas jetting from the vent. This terminates the event and lava drains back into the conduit to start the cycle anew. In the case where there is no surface lava emission or drain back, the cap instead pushes into and spreads out within a subsurface cavity. Again, this unloads the conduit magma and terminates in explosive gas release. Once gas is expelled, lava in the cavity is free to drain back. We hypothesize that pistoning is a stable mode of degassing for low‐viscosity basaltic magmas with appropriate conduit geometries and volatile supply rates.

Propagation characteristics of pressure disturbances originated by gas jets in fluidized beds

An experimental investigation has been carried out on velocities and amplitudes of pressure disturbances in fluidized beds made of 100–200 μm glass ballotini. Disturbances were originated by gas jetting in a 0.35 m i.d. fluidized bed. A fluidization tube 0.10 m i.d. has also been used. Different types of disturbances have been induced in the bed contained in this tube: injection of a freely rising bubble and of a captive bubble; injection of a bubble chain; and compression of the bed free surface. The dynamic wave character of the disturbances has been shown. Velocities and amplitudes of waves moving through the beds have been measured. In particular, wave velocities have been compared with theoretical results obtained by the application of “pseudo-homogeneous” and “separated phase flow” models.