Gas Core Research Articles

Kinetics parameters evaluation on the first core of the RSG GAS (MPR-30) using continuous energy Monte Carlo method

The kinetics parameters, namely the effective delayed neutron fraction (βeff) and the generation time (Ʌ), of the first core of RSG GAS (MPR-30) multipurpose reactor were, for the first time, evaluated by using the recently released, continuous energy Monte Carlo code, MVP3, with latest nuclear data libraries (JENDL-4.0 and ENDF/B-VII.0). To check the accuracy and consistency of the MVP3 calculation results, independent MCNP-6.2 calculations with JENDL-4.0, ENDF/B-VII.0, and ENDF/B-VII.1 nuclear data libraries were also conducted. The calculated βeff was then used for re-evaluating the measured core excess reactivity and total control rod worth. The original βeff provided by the reactor vendor was 765 pcm, while the newly calculated βeff was found to be 738 pcm (MVP3, JENDL-4.0), i.e. the old value was approximately 4% larger. Using the newly calculated βeff, the first core excess reactivity and control rod worth were evaluated to be 8.16% Δk/k (11.054$; k = 1.08886) and 17.18% Δk/k, respectively. Using these new excess reactivity and control rod worth, the ratio of the calculation to the experiment results (MVP3, JENDL-4.0) of them were found to be 1.01 and 1.04, respectively. Other MVP3 calculation results using ENDF/B-VII.0 library, and the ones of MCNP-6.2 using JENDL-4.0, ENDF/B-VII.0, and ENDF/B-VII.1 libraries, showed very close values and consistent with the MVP3 (JENDL-4.0) results.

Pressure core analysis of geomechanical and fluid flow properties of seals associated with gas hydrate-bearing reservoirs in the Krishna-Godavari Basin, offshore India

Physical properties of the sediment directly overlying a gas hydrate reservoir provide important controls on the effectiveness of depressurizing that reservoir to extract methane from gas hydrate as an energy resource. The permeability of overlying sediment determines if a gas hydrate reservoir's upper contact will provide an effective seal that enables efficient reservoir depressurization. Compressibility, stiffness and strength indicate how overlying sediment will deform as the in situ stress changes during production, providing engineering data for well designs. Assessing these properties requires minimally-disturbed sediment. India's National Gas Hydrates Program Expedition 2 (NGHP-02) provided an opportunity to study these seal sediment properties, reducing disturbance from gas exsolution and bubble growth by collecting a pressure core from the seal sediment just above the primary gas hydrate reservoir at Site NGHP-02-08 in Area C of the Krishna-Godavari Basin. The effective stress chamber (ESC) and the direct shear chamber (DSC) devices in the suite of Pressure Core Characterization Tools (PCCTs) were used to measure permeability, compressibility, stiffness and shear strength at the in situ vertical stress. Geotechnical properties of the predominantly fine-grained seal layer at in situ vertical stress are in typical clay sediment ranges, with low measured permeability (0.02 mD), high compressibility (Cc = 0.26–0.33) and low shear strength (404 kPa). Though pressure and temperature were maintained throughout the collection and measurement process to stabilize gas hydrate, the lack of effective stress in the pressure core storage chamber and the chamber pressurization with methane-free water caused core expansion and gas hydrate in a thin coarser-grained layer to dissolve. The PCCTs can reapply in situ stress with incremental loading steps during a consolidation test to account for sediment compaction. Gas hydrate dissolution can be limited by storing cores just above freezing temperatures, and by using solid spacers to reduce the storage chamber's free volume.

Generalized Noh self-similar solutions of the compressible Euler equations for hydrocode verification

A family of exact self-similar solutions of the compressible Euler equations developed for hydrocode verification is described. This family generalizes the classic Noh problem, which has served as a standard verification test of numerical methods for modeling inviscid compressible flows for three decades. This generalization allows finite pressure initial conditions, nearly arbitrary equations of state, and describes shocked compression as well as isentropic expansion and compression of the gas. In particular, the solutions describe a) the propagation of a finite-strength spherical isentropic expansion wave into a moving uniform gas, leaving behind either a core of uniform gas at rest or a vacuum/cavitation; b) the convergence of a finite-strength isentropic compression wave into a uniform gas or a collapse of a cavity in a finite-pressure gas (a compressible analog of the Rayleigh problem); and c) the expansion of a finite-strength accretion shock wave into a converging isentropic flow of stagnating gas. Our proposed verification test seeks to numerically reproduce all three of these stages of gas motion in a single simulation run. The successful verification of a high-order Godunov Eulerian hydrodynamics code is presented as an example of the expected use of this family of exact solutions.

Spray Characteristics and Internal Flow Structures of Swirl Effervescent Atomizer

Spray characteristics and internal flow structures of an atomizer are important parameters in indicating their performances. Both parameters are affected by the operating conditions and atomizer geometries. This study investigates the effect of operating parameters and atomizer geometries on spray angle, breakup length and gas core diameter of swirl effervescent atomizer. This work is conducted specifically to find the most critical parameters that will produce the required spray characteristics and internal flow structure. The atomizer performance tests were carried out using water as the working fluid and nitrogen gas as the atomizing agent. High-speed shadowgraph technique was utilized to record the videos of the spray and internal flow structures. The video recordings were converted to image sequences and analyzed using image processing software. Geometrical parameters were found to be more dominant for characterizing the resultant sprays, but operating conditions was more critical in affecting the internal flow structures. The widest spray angle (~25°) and shortest breakup length (~10mm) were observed at the high level of swirl-generating vane angle and discharge orifice diameter. Gas core diameter expanded up to 1.13mm at the high level of GLR.

Study of bubbles entrapped into a gas-sheared liquid film

The surface of a thick liquid film under strong gas shear is covered by large-scale disturbance waves and small-scale ripples. Disruption of these ripples on top of disturbance waves by the gas stream leads to the creation of droplets that are entrained into the gas core and may deposit back onto the film surface. In addition, gas may be entrapped by the liquid film in the form of bubbles of various sizes. In this work, the study of gas bubble creation was performed in a horizontal rectangular duct using the brightness-based laser-induced fluorescence technique. With this technique, the instantaneous height of the liquid film was measured with a 40 µm spatial resolution over a 51 mm by 20 mm area at speeds of 10 kHz. The entrapped bubbles and entrained/depositing droplets are detectable in the data and can thus be studied simultaneously with the waves on the film surface. Several scenarios of bubble entrapment and collapse were identified and discussed. The dynamics of entrapped bubbles was studied quantitatively using an automatic processing algorithm, confirming and elucidating the results of qualitative observations. The effect of the flow parameters on the bubbles concentration, velocity and size distributions was studied separately for the bubbles inside the disturbance waves and inside the thin base film between the disturbance waves. It was shown that the bubbles are mostly created due to oblique impacts of droplets at the base film and are accumulated by the disturbance waves. A small number of bubbles of larger size are created in front of disturbance waves and remain inside the disturbance waves. The velocity of the bubbles is affected by the velocity of the surrounding liquid. Using the bubbles as tracers, a profile of longitudinal liquid velocity was constructed and a noticeable increase of wall shear under the rear slopes of disturbance waves was found.

Tunable Polymer Microcapsules for Controlled Release of Therapeutic Gases.

Encapsulation and delivery of oxygen, carbon dioxide, and other therapeutic gases, using polymeric microcapsules (PMCs) is an emerging strategy to deliver gas as an injectable therapeutic. The gas cargo is stored within the PMC core and its release is mediated by the physiochemical properties of the capsule shell. Although use of PMCs for the rapid delivery of gases has been well described, methods which tune the material properties of PMCs for sustained release of gas are lacking. In this work, we describe a simple method for the high-yield production of gas-in-oil-filled PMCs with tunable sizes and core gas content from preformed polymers using the sequential phase separation and self-emulsification of emulsion-based templates. We demonstrate that prolonged gas release occurs from gas-in-oil PMCs loaded with oxygen and carbon dioxide gas, each of which could have significant clinical applications.

On the shape and evolution of a cosmic-ray-regulated galaxy-wide stellar initial mass function

In this paper, we present a new derivation of the shape and evolution of the integrated galaxy-wide initial mass function (IGIMF), incorporating explicitly the effects of cosmic rays (CRs) as regulators of the chemical and thermal state of the gas in the dense cores of molecular clouds. We predict the shape of the IGIMF as a function of star formation rate and CR density and show that it can be significantly different with respect to local estimates. In particular, we focus on the physical conditions corresponding to IGIMF shapes that are simultaneously shallower at high-mass end and steeper at the low-mass end than those of a Kroupa IMF. These solutions can explain both the levels of α-enrichment and the excess of low-mass stars as a function of stellar mass, observed for local spheroidal galaxies. As a preliminary test of our scenario, we use idealized star formation histories to estimate the mean IMF shape for galaxies of different |$z$| = 0 stellar mass. We show that the fraction of low-mass stars as a function of galaxy stellar mass predicted by these mean IMFs agrees with the values derived from high-resolution spectroscopic surveys.

An engine-relevant kinetic investigation into the anti-knock effect of organometallics through the example of ferrocene

Abstract A detailed study on the ignition of ferrocene-containing mixtures has been undertaken in a Rapid Compression Machine (RCM). Two hydrocarbon fuels, isooctane and 3-hexene, were investigated in order to assess the hypothesis of an inhibiting effect of iron oxide particles on HO2 radicals and H2O2. Ignition delays were measured at core gas temperatures of 700 K and 850 K, pressures from 6 to 20 bar, and ferrocene mole fractions in the original fuel from 0 to 900 ppm. These experiments provide insight into the kinetics of the antiknock effect of ferrocene on both the non-octane sensitive (isooctane) and octane sensitive (3-hexene) fuels. Experimental results show that doping reactive mixtures with ferrocene always lengthens the total ignition delay. Also, the increment in auto-ignition delay is monotonic with increasing amount of ferrocene while no loss of effectiveness was noticed, even at the highest mole fractions. On the other hand, in the event of two stage ignition, the first stage delay is not affected by any doping with ferrocene. The kinetic mode of action of ferrocene is investigated, based on these statements, in an effort to better understand the impact of organometallic octane boosters on the combustion of fuels. A kinetic short sub-mechanism was built in order to describe the influence of ferrocene on the reactivity of isooctane and 3-hexene in a RCM, yielding qualitative agreement.

The extreme initial kinetic energy allowed by a collapsing turbulent core

We present high-resolution hydrodynamical simulations aimed at following the gravitational collapse of a gas core, in which a turbulent spectrum of velocity is implemented only initially. We determine the maximal value of the ratio of kinetic energy to gravitational energy, denoted here by $\left(\frac{E_{\rm kin} }{E_{\rm grav}}\right)_{\rm max}$, so that the core (i) will collapse around one free-fall time of time evolution or (ii) will expand unboundedly, because it has a value of $\frac{E_{\rm kin}}{E_{\rm grav}}$ larger than $\left( \frac{E_{\rm kin}}{E_{\rm grav}}\right)_{\rm max}$. We consider core models with a uniform or centrally condensed density profile and with velocity spectra composed of a linear combination of one-half divergence-free turbulence type and the other half of a curl-free turbulence type. We show that the outcome of the core collapse are protostars forming either (i) a multiple system obtained from the fragmentation of filaments and (ii) a single primary system within a long filament. In addition, some properties of these protostars are also determined and compared with those obtained elsewhere.

Chemical Survey toward Young Stellar Objects in the Perseus Molecular Cloud Complex

Chemical diversity of the gas in low-mass protostellar cores is widely recognized. In order to explore its origin, a survey of chemical composition toward 36 Class 0/I protostars in the Perseus molecular cloud complex, which are selected in an unbiased way under certain physical conditions, has been conducted with IRAM 30 m and NRO 45 m telescope. Multiple lines of C2H, c-C3H2 and CH3OH have been observed to characterize the chemical composition averaged over a 1000 au scale around the protostar. The derived beam-averaged column densities show significant chemical diversity among the sources, where the column density ratios of C2H/CH3OH are spread out by 2 orders of magnitude. From previous studies, the hot corino sources have abundant CH3OH but deficient C2H, their C2H/CH3OH column density ratios being relatively low. In contrast, the warm-carbon-chain chemistry (WCCC) sources are found to reveal the high C2H/CH3OH column density ratios. We find that the majority of the sources have intermediate characters between these two distinct chemistry types. A possible trend is seen between the C2H/CH3OH ratio and the distance of the source from the edge of a molecular cloud. The sources located near cloud edges or in isolated clouds tend to have a high C2H/CH3OH ratio. On the other hand, the sources having a low C2H/CH3OH ratio tend to be located in inner regions of the molecular cloud complex. This result gives an important clue to an understanding of the origin of the chemical diversity of protostellar cores in terms of environmental effects.

A new model for improving the prediction of liquid loading in horizontal gas wells

There are great differences in predicting the onset of liquid loading among vertical, directional and horizontal gas wells. To date, most models for predicting the critical gas rate in horizontal wells are based on a liquid-droplet model, and the corresponding predictions deviate significantly from the actual status and are considerably controversial. Experimental results (Xiao et al., 2010; Wang, 2014) show that the liquid-film model is more reasonable. By respectively analyzing the force state of the gas core and the liquid film, we developed a new liquid-film model for predicting the critical gas rate in horizontal wells. Subsequently, a correction term is introduced for a convenient comparison between the new model and the popular models (Turner et al., 1969; Nosseir et al., 2000; Li et al., 2002). In addition, we carefully conducted a sensitivity analysis of the correction term related to the three parameters: liquid viscosity, Bond number and lift force factor. Well data from Liao (2012) were employed to verify the new model. The prediction results show that the new model demonstrates a significant improvement over conventional models in matching the field data in the Sebei gas reservoirs in China.

The Role of Microbubble Echo Phase Lag in Multipulse Contrast-Enhanced Ultrasound Imaging.

In this paper, we assess the importance of microbubble shell composition for contrast-enhanced imaging sequences commonly used on clinical scanners. While the gas core dynamics are primarily responsible for the nonlinear harmonic response of microbubbles at diagnostic pressures, it is now understood that the shell rheology plays a dominant role in the nonlinear response of microbubbles subjected to low acoustic pressures. Of particular interest here, acoustic pressures of tens of kilopascal can cause a reversible phase transition of the phospholipid coatings from a stiff elastic organized state to a less stiff disorganized buckled state. Such a transition from elastic to buckled shell induces a steep variation of the shell elasticity, which alters the microbubble acoustic scattering properties. We demonstrate in this paper that this mechanism plays a dominant role in contrast pulse sequences that modulate the amplitude of the insonifying pulse pressure. The contrast-to-tissue ratio (CTR) for amplitude modulation (AM), pulse inversion (PI), and amplitude modulation pulse inversion (AMPI) is measured in vitro for Definity, Sonazoid, both lipid-encapsulted microbubbles, and the albumin-coated Optison. It is found that pulse sequences using AM significantly enhanced the nonlinear response of all studied microbubbles compared to PI (up to 15 dB more) when low insonation pressures under 200 kPa were used. Further investigation reveals that the origin of the hyperechoicity is a small phase lag occurring between the echoes from the full-and half-amplitude driving pulses, and that the effect could be attributed to the shell softening dynamics of lipid and albumin coatings. We assess that this additional phase in microbubble ultrasound scattering can have a dominant role in the CTR achieved in contrast sequences using AM. We also show that the pressure dependent phase lag is a specific marker for microbubbles with no equivalent in tissue, which can be used to segment microbubbles from the tissue harmonics and significantly increase the CTR.

Hydrodynamically Formed Uniform Thick Coatings on Microspheres.

Forming uniform thick coatings on microspheres remains a significant challenge in various surface modification and drug delivery applications. In this work, a hydrodynamic method is demonstrated for centering microspheres in droplets with sizes ranging from tens to hundreds of micrometers. The core microspheres stay at the center of the droplets due to the hydrodynamic pressure generated in the surrounding liquid shells, despite the significant density difference between the core microsphere and the liquid shell. Therefore, by using polymerizable liquids that can be solidified thermally or by illumination as the shell layer, core-shell particles with gas, liquid, or solid cores can be surrounded with uniform coatings using the present method.

A mechanistic model for expansion loss coefficient in upward vertical annular flow

• Differential effect of flow deceleration on gas, droplets and liquid film postulated. • Developed semi-analytical expressions for velocity profile correction factor in pipe flow. • Carried out CFD simulations of gas-droplet flow in a rough-walled pipe expansion. • Effect of droplet deceleration on pressure variation elucidated. • Mechanistic correlation developed for expansion loss coefficient for annular flow. Gas–liquid annular flow draws different responses from its three constituents, namely, the liquid film, the entrained liquid droplets and the gas core, as they flow through a diverging section in a pipe. The resulting change in the pressure profile is a combination of several effects associated with the dynamic interactions among these three fields. Accurate simulation of the response using Eulerian–Eulerian computational fluid dynamics is not feasible because the processes are inherently complex and a framework of relevant and validated constitutive relations describing the physical processes is not yet available. In the present work, a simpler approach is adopted by studying the interactions individually in idealized settings, and bringing together the separate effects into a phenomenological model for pressure loss in upward vertical annular flow. The overall pressure change is expressed as a sum of three contributors: change in area of cross-section available for gas flow, change in the effective interfacial roughness leading to peaking of the velocity profile, and droplet-gas momentum exchange in the immediate downstream of the expansion. Using air–water experimental data from two expansion ratios and three half-angles of the diverging sections, a mechanistic correlation is proposed to evaluate the overall pressure loss coefficient.

Atmospheric gas dynamics in the Perseus cluster observed with Hitomi

Abstract Extending the earlier measurements reported in Hitomi collaboration (2016, Nature, 535, 117), we examine the atmospheric gas motions within the central 100 kpc of the Perseus cluster using observations obtained with the Hitomi satellite. After correcting for the point spread function of the telescope and using optically thin emission lines, we find that the line-of-sight velocity dispersion of the hot gas is remarkably low and mostly uniform. The velocity dispersion reaches a maxima of approximately 200 km s−1 toward the central active galactic nucleus (AGN) and toward the AGN inflated northwestern “ghost” bubble. Elsewhere within the observed region, the velocity dispersion appears constant around 100 km s−1. We also detect a velocity gradient with a 100 km s−1 amplitude across the cluster core, consistent with large-scale sloshing of the core gas. If the observed gas motions are isotropic, the kinetic pressure support is less than 10% of the thermal pressure support in the cluster core. The well-resolved, optically thin emission lines have Gaussian shapes, indicating that the turbulent driving scale is likely below 100 kpc, which is consistent with the size of the AGN jet inflated bubbles. We also report the first measurement of the ion temperature in the intracluster medium, which we find to be consistent with the electron temperature. In addition, we present a new measurement of the redshift of the brightest cluster galaxy NGC 1275.

ALMA view of a massive spheroid progenitor: a compact rotating core of molecular gas in an AGN host at z = 2.226

We present ALMA observations at 107.291 GHz (band 3) and 214.532 GHz (band 6) of GMASS 0953, a star-forming galaxy at z=2.226 hosting an obscured AGN that has been proposed as a progenitor of compact quiescent galaxies (QG). We measure for the first time the size of the dust and molecular gas emission of GMASS 0953 that we find to be extremely compact ($\sim$1 kpc). This result, coupled with a very high ISM density (n$\sim$10$^{5.5}$ cm$^{-3}$), a low gas mass fraction ($\sim$0.2) and a short gas depletion timescale ($\sim$150 Myr) imply that GMASS 0953 is experiencing an episode of intense star-formation in its central region that will rapidly exhaust its gas reservoirs, likely aided by AGN-induced feedback, confirming its fate as a compact QG. Kinematic analysis of the CO(6-5) line shows evidence of rapidly-rotating gas ($V_{rot}$=320$^{+92}_{-53}$ km s$^{-1}$), as observed also in a handful of similar sources at the same redshift. On-going quenching mechanisms could either destroy the rotation or leave it intact leading the galaxy to evolve into a rotating QG.

Gas-liquid two-phase flow measurements by the electromagnetic flowmeter combined with a phase-isolation method

The electromagnetic flowmeter has presented excellent performance in single-phase flow. However, there are many fundamental difficulties when it is applied in two-phase flow. The presence of the insulating phase at various positions in two-phase flow strongly influences the distribution of the weight function, consequently resulting in the uncertainty and instability of the electromagnetic flowmeter's output. When the insulating phase contact with the electrode, it even leads to wrong alarm. In this paper, at the upstream of the electromagnetic flowmeter a phase-isolation method was used to change the inlet flow pattern into a uniform and symmetrical swirling core-annular flow, in which gas-liquid mixture was isolated to gas core and liquid annular flows flowing concurrently in the transmission pipe with a clear smooth interface between them. Then we analysed the behavior of the electromagnetic flowmeter performed in this specific flow pattern, and built the liquid flow rate measurement model. Besides, the void fraction was measured by image processing technique. Owing to the clear smooth interface, the difficulty of image processing and the measurement error of the void fraction can be reduced. The experimental results showed that, the combination of the phase-isolation method could improve the measurement accuracy and successfully make the electromagnetic flowmeter available for the gas-liquid two-phase flow where the original phase distribution is not uniform.

Variations of the stellar initial mass function in semi-analytical models II: the impact of Cosmic Ray regulation.

Recent studies proposed that cosmic rays (CR) are a key ingredient in setting the conditions for star formation, thanks to their ability to alter the thermal and chemical state of dense gas in the UV-shielded cores of molecular clouds. In this paper, we explore their role as regulators of the stellar initial mass function (IMF) variations, using the semi-analytic model for GAlaxy Evolution and Assembly (GAEA). The new model confirms our previous results obtained using the integrated galaxy-wide IMF (IGIMF) theory: both variable IMF models reproduce the observed increase of $\alpha$-enhancement as a function of stellar mass and the measured $z=0$ excess of dynamical mass-to-light ratios with respect to photometric estimates assuming a universal IMF. We focus here on the mismatch between the photometrically-derived ($M^{\rm app}_{\star}$) and intrinsic ($M_{\star}$) stellar masses, by analysing in detail the evolution of model galaxies with different values of $M_{\star}/M^{\rm app}_{\star}$. We find that galaxies with small deviations (i.e. formally consistent with a universal IMF hypothesis) are characterized by more extended star formation histories and live in less massive haloes with respect to the bulk of the galaxy population. While the IGIMF theory does not change significantly the mean evolution of model galaxies with respect to the reference model, a CR-regulated IMF implies shorter star formation histories and higher peaks of star formation for objects more massive than $10^{10.5} M_\odot$. However, we also show that it is difficult to unveil this behaviour from observations, as the key physical quantities are typically derived assuming a universal IMF.

Pressure drop for gas-liquid two-phase annular flow across grid spacer with mixing vane in vertical circular pipe

This study investigates the effects of mixing vane (MV) attached to a grid spacer on pressure drop for air-water annular flows in a vertical circular pipe of 16 mm I.D. In order to know the effects of MV, grid spacers with or without MV were installed in the test pipe. Three types of grid spacers with MV which has four MVs inclined 20, 30 degree from the vertical flow axis (4-MV20, 4-MV30) and two MVs inclined 30 degree (2-MV30) were used. In addition, two liquid injection methods (wall and center jet injections) are adopted to control liquid droplet entrainment faction in gas core. In the experiment, pressure drop along the channel upstream and downstream from the spacer was measured with a pressure transducer. In the analysis, the correlation of the pressure drop across the spacer is newly developed based on the present data.

Numerical study of heat and mass flow in layered heat storage

An analysis of argon gas flow in exemplary configuration of layered bed thermal energy storage is presented. The analysis incorporates URANS model with conjugate heat transfer between gas and solid storage core. The aim of this analysis was to identify key factors limiting exergy efficiency of this storage type and determine some details about storage transient behaviour. Three full cycles of storage loading and unloading having 17 hours physical time in total are simulated, with calculation of exergetic efficiency for each of the cycles. Conclusions regarding this storage type feasibility for indirect power storage in pumped heat systems are made.