Effect Of Gas Density Research Articles

Improved Two-Fluid Model for Segregated Flow and Integrated Multiphase Flow Modeling for Downhole Pressure Predictions

This work presents an integrated multiphase flow model for downhole pressure predictions with the purpose of producing relatively more accurate predictions under wide-flowing conditions while maintaining a simple form. As a component of the integrated model, an improved two-fluid model for segregated flow is proposed. The new two-fluid model was developed by improving the modeling of the wetted perimeters and the liquid wall shear stress. It outperformed five other existing state-of-the-art models in predicting the liquid holdup and pressure gradient of 11 experimental datasets from the literature, with an average relative error of 37.6% for liquid holdup predictions and 24.0% for pressure gradient predictions. The model succeeds in capturing the effects of inclination angle, pressure or gas density, and liquid and gas superficial velocities on liquid holdup and pressure gradient. The integrated model incorporates the state-of-the-art onset of liquid loading predictive model and classifies the flow into two major categories based on the onset of liquid loading that are modeled by two different approaches, respectively. It outperformed the other multiphase flow models in predicting the downhole pressure of 313 field data points, especially the wells that have both segregated and intermittent (mixed) flows. The errors were reduced to 4.4% for the field cases with mixed flow regions and 5.1% for all the field data points.

Microbubble formation by flow focusing: role of gas and liquid properties, and channel geometry

Microfluidic flow focusing is a versatile method for the production of monodisperse microbubbles for biomedical applications involving ultrasound. Existing studies propose several theoretical models to predict bubble size and production rate as a function of the liquid and gas flow rate. Yet, they typically do not include physical fluid parameters such as density, viscosity and surface tension. Here, we present an exhaustive experimental and numerical investigation of the influence of physical properties of the gas and liquid, and of the channel geometry on bubble size and production rate. We find a particularly strong effect of (i) gas density on the production rate and (ii) liquid viscosity on the bubble size. We further discuss our findings within the context of existing theoretical models to reflect on gaps in our current understanding of the fluid mechanics of bubble formation by flow focusing.

A JWST/NIRSpec Exploration of the Connection between Ionization Parameter, Electron Density, and Star-formation-rate Surface Density in z = 2.7–6.3 Galaxies

We examine the factors responsible for the variation in the ionization parameter (U) of high-redshift star-forming galaxies based on medium-resolution JWST/NIRSpec observations obtained by the Cosmic Evolution Early Release Science survey. The sample consists of 48 galaxies with redshifts z spec = 2.7−6.3, which are largely representative of typical galaxies at these redshifts. The [S ii] λ λ6718, 6733 doublet is used to estimate electron densities (n e ), and dust-corrected Hα luminosities are used to compute ionizing photon rates (Q). Using composite spectra of galaxies in bins of [O iii] λ λ4960, 5008/[O ii] λ λ3727, 3730 (O32) as a proxy for U, we determine that galaxies with higher O32 have 〈n e 〉 ≃ 500 cm−3 that are ≳5 × larger than that of lower-O32 galaxies. We do not find a significant difference in 〈Q〉 between low- and high-O32 galaxies. Photoionization modeling indicates a large spread in of ≈1.5 dex at a fixed Z neb. On the other hand, the data indicate a highly significant correlation between U and star-formation-rate surface density (ΣSFR), which appears to be redshift invariant at z ∼ 1.6−6.3, and possibly up to z ∼ 9.5. We consider several avenues through which metallicity and ΣSFR (or gas density) may influence U, including variations in n e and Q, internal dust extinction of ionizing photons, and the effects of gas density on the volume filling fraction. Based on these considerations, we conclude that gas density may play a more central role than metallicity in modulating U at these redshifts.

Impact of Surrounding Gas Density on the Turbulent Liquid Jet

This numerical study aims to investigate the impact of surrounding gas density on liquid turbulent jet. Incompressible large eddy simulations (LES) with Wall-Adapting Local Eddy-Viscosity (WALE) sub-grid scale model in ANSYS-FLUENT were performed to capture the morphology of the breakup as well as the important flow field characteristics. A volume of fluid (VOF) approach was used to track the unsteady evolution and breakup of the liquid jet. Different variables have been examined to assess this impact. These variables are instantaneous velocity, liquid volume fraction, and turbulent kinetic energy. Also, the centerline values have been investigated to obtain the jet half-width and spray dispersion angle. The jet diameter and exit velocity are 0.2 mm and 100 m/s, respectively. Three different liquid-to-gas density ratios of 54.03, 32.42 and 23.49 are considered, corresponding to ambient gas density of 15, 25 and 34.5 kg/m3, respectively. It has been found that the jet speed and the liquid core length are inversely proportional to the density of the ambient gas. Regarding the liquid core length, it was noted that the effect of gas density on the liquid core length is considerably stronger in the gas density range between 15 - 25 kg/m³ (corresponding to density ratios of 54.03 - 32.42) than that in the range of 25 - 34.5 kg/m³ (corresponding to density ratios of 32.42 - 23.49). The results, also, showed that increasing the gas density leads to an increase in Weber number, which in turn causes a high instability, that makes the breakup initiates closer to the nozzle exit and occurs with higher rate. Likewise, it has been found that the jet width and the spray dispersion angle increase with increasing the gas density. HIGHLIGHTS Spray jets are included in many applications because its important in increasing the heat and mass transfer between the liquid and the surrounding fluid Large eddy simulations (LES) and volume of fluid (VOF) models are used to investigate the characteristics of turbulent liquid jet The investigation was characterized as a function of man variables such as turbulent kinetic energy, liquid potential core, the jet dispersion angle and more The investigation showed that the density of surrounding gas has an influence on the liquid jet characteristics GRAPHICAL ABSTRACT

A study of CO2 two-phase flow in a near horizontal pipe

In this article, the observations from two different experimental studies on CO2 two-phase flow regimes in a near horizontal pipe are analysed. These experiments show significant bubble entrainment in a stratified flow, and the bubble entrainment in liquid is found to be a dominant mechanism for the flow regime transition between the stratified and bubbly flow. The hydrodynamic slug flow is not observed in these experimental studies. The X-ray measurement of the experimental study in a near horizontal pipe of 44 mm internal diameter is processed to obtain the bubble volume fraction in the liquid layer, which is found to be a function of two-phase Froude number. This Froude number definition takes into account gas density and pipe inclination effects. A parametric study shows that the bubble entrainment into the liquid layer decreases significantly with an increase of pipe internal diameter.

Average charge states of heavy ions in rarefied hydrogen

We present the results of experiments on measuring the charges of heavy ions from Rn (Z=86) to Og (Z=118) in rarefied hydrogen performed at the DGFRS and DGFRS-2 separators. Two formulae are proposed that can be used to calculate the charges of ions in H2 and which take into account the influence of the shell structure of atoms on the charge value. The accuracy of estimating the charge of ions of superheavy atoms was measured to be 2%. The charges of Ra, Th, and No ions were measured at a hydrogen pressure from 0.5 to 3.3 mbar, which allowed us to evaluate the effect of H2 density on the charge value. A formula is proposed to account for the effect of gas density when performing experiments at different gas pressures. It is shown that the results of experiments performed at different separators DGFRS and DGFRS-2 are in good agreement with each other.

Effect of gas density and surface tension on liquid film thickness in vertical upward disturbance wave flow

Gas–liquid annular flows, such as the flow attached to the fuel rods of boiling water reactors, is a prevalent occurrence in industrial processes. At the gas–liquid interface of such flows, disturbance waves with diverse heights commonly arise. Because the thin liquid film between two successive disturbance waves leads to the dryout on the heating surface and limits the performance of the heating components, complete knowledge of the film thickness and disturbance waves is crucial. The properties of the base film and disturbance waves have been studied extensively through experimental and analytical approaches. However, most experimental data and analysis available in the literature are limited to the near atmospheric condition, and the liquid–gas density ratio under near atmospheric conditions is much higher than in practical nuclear applications. In this study, we use nitrogen gas and water under the system pressures of 0.2 and 0.4 MPa, as well as HFC134a gas and water under the system pressure of 0.7 MPa. Therefore, the density ratio can be varied between 32 and 434. Based on our experimental data, we report a direct link between the film thickness, wave height, and dimensionless numbers. The analysis indicates the Weber number which represents the ratio of the drag force to the surface tension force is critical for the film thickness behavior. To examine this, we perform the experiments using nitrogen gas and 95% (v/v) of aqueous ethanol solution under the system pressure of 0.2 MPa. Finally, two models are proposed to predict the averaged film thickness and wave height, which are then compared with previous data.

Experimental study on breakup of a single bubble in a stirred tank: Effect of gas density and liquid properties

AbstractBubble breakup plays an important role in gas–liquid flows, but detailed studies are still scarce. In this work, the breakup behavior of a single bubble in a stirred tank was experimentally studied with a high‐speed camera, focusing on the effect of gas density, liquid properties, agitation speed, and mother bubble size. The bubble breakup time, breakup probability, breakup rate, and daughter bubble size distribution were determined. The internal‐flow phenomenon that the gas flowed from the smaller part to the larger part of a deformed mother bubble was observed by a high‐speed camera. The results showed that with increasing gas density, agitation speed, mother bubble size and decreasing surface tension, the bubble breakup rate and probability of equal‐size distribution significantly increased. With increasing liquid viscosity, the bubble breakup rate decreased especially in the high viscosity range. An M‐shaped daughter bubble size distribution was observed, which was consistent with our previous bubble breakup model.

Influence of Gas Density on the Clay Wettability: Implication for CO2 Geo-Sequestration

Carbon dioxide capture and storage (CCS) is considered as the most promising technological method to decrease atmospheric Carbon dioxide (CO2) emissions. However, due to density difference between the injected CO2 and the formation brine, CO2 tends to move vertically upwards in the reservoir, which results in leakage risk. This vertical migration of CO2 can be prevented by four trapping mechanisms, i.e. structural/residual trapping, capillary trapping, solubility trapping, and mineral trapping. The capacities of structural and residual trapping are highly affected by rock wettability. Clay wettability is one of the crucial parameters in evaluation CO2 geo-sequestration. However, the literature data show that there are many uncertainties associated with clay experimental measurements. One of these uncertainties is the influence of the effect of gas density on the clay mineral wettability. Thus, here, we compared the wettability of a clay mineral (i.e. montmorillonite) with three different gas densities scenarios (i.e. low (Helium), moderate (Nitrogen) and high (CO2) gas densities). To do so, we measured the advancing and receding contact angle (i.e. wettability) of montmorillonite for CO2/water, nitrogen/water, and Helium/water systems at a constant (333 K) under four different pressures (5, 10, 15, and 20 MPa). The brine composition used was 4 wt% NaCl, 4 wt% CaCl2, 1 wt% MgCl2 and 1 wt% KCl, for all gas density scenarios. The results indicate that gas density has a significant effect on the clay mineral wettability and that both advancing and receding contact angles increase with an increase in gas density. The results show that the higher gas density gas has higher contact angle with montmorillonite, measured at the same temperature and pressure. For example, the advancing contact angle of montmorillonite at 333 K and 15 MPa was only 50 (water-wet) for the Helium/water system, while it was 101 (intermediate-wet) for the CO2/water system. Thus, we conclude that the gas density affects the clay wettability and that higher gas density leads to increase the CO2-wettability of the clay. This phenomenon reduces the estimated CO2 geo-sequestration capacity and containment security. This implication can be utilised to improve the wettability predictions, and thus, the assessments of reservoir CO2 geo-sequestration capacity.

Investigation of evaporating sprays in a medium speed marine engine

The understanding of diesel sprays is very important to enable a better and cleaner marine engine design, but unfortunately little knowledge is openly available on marine engine fuel sprays. In this paper, evaporating sprays for medium speed marine engines were studied in a constant volume combustion chamber by performing optical measurements through Schlieren and Mie diagnostic techniques. The effects of ambient gas temperature and ambient gas density on vapor and liquid penetration were investigated by changing the target condition in the combustion chamber. A comparative study of two injectors with different nozzle diameters (0.38 mm and 0.44 mm) was also carried out at ambient density of 22.5 kg/m3. Some empirical correlations of spray penetration have been modified to fit the spray measurement data. Due to the transient characteristics of the pump-line-nozzle injection system, a time-dependent injection pressure profile is suggested for calculation of spray penetration. The spray tip penetration at large distance under low density (7.6 and 15.2 kg/m3) conditions is expected to be proportional to t2/3, which is supported by the model considering spray-induced gas turbulence effect. The t1/2 law, where turbulence is not taken into account, is still valid under high density (22.5 kg/m3) conditions with higher engine load. The comparison of two models demonstrates that the effect of gas turbulence is influenced by the ambient gas density and engine load.

Effects of Bubble Size and Gas Density on the Shock-induced Collapse of Nanoscale Cavitation Bubble

In this paper, we studied the nature of shockwave induced cavitation bubble collapse using molecular dynamics (MD) simulation. A major objective of this study is to determine how the variation of nanoscale bubble size and entrapped gas density affects the bubble dynamics. It is known that cavitation bubble collapse/implosion is a robust dynamic event that occurs when the potential energy of the acting pressure performs work in a rapid and violent manner. Usually, the energy converges into a significantly smaller region compared to the original cavitation bubble. While the mechanisms of cavitation have been studied for more than a century, recently, it has received renewed interests due to its connection with biomedical applications and traumatic brain injury (TBI). One of the common causes of TBI is blast-induced shock exposure. A shockwave, as a moving discontinuity of pressure, can lead to the formation and collapse of cavitation bubble and produce an impactful jet stream. The jet stream may cause a localized mechanical/thermal damage to the structures that come on its path. We have considered two different bubble sizes (10 and 20 nm). We found that different gas densities inside the cavitation bubble largely change the intensity of the aftermath. We also found the peak temperature during the collapse is linked to the bubble size but unrelated with the peak pressure.

Droplet impact onto a solid sphere in mid-air: Effect of viscosity, gas density, and diameter ratio on impact outcomes

Collision of a droplet and a hydrophobic particle in mid-air was investigated. To study the impact outcomes, specifically the lamella formation, a numerical simulation tool was developed and verified with impact experiments (water droplets and glass particles, ρrel = 0.41). The velocity field within the lamella showed that the flow inside the liquid film moves in two opposite directions along the lamella axis of symmetry: one is generated through the momentum transfer from the particle, and the other is due to the droplet initial velocity. This causes the lamella to be stretched in the same direction as the particle moves and forms a rim at the end of the lamella. Although a larger droplet-to-particle diameter ratio (Dr) increased the impact duration, it did not change the collision outcomes and two opposite flows still exist inside a thicker liquid film. However, the liquid viscosity affects impact outcomes; as viscosity increased, a thicker film remained on the particle, the liquid film became shorter, and the lamella formation was hindered accordingly. The pressure of the ambient gas also affects the liquid film formation. Unlike the literature of the drop impact on a flat surface, our results indicate that by increasing the ambient pressure, the lamella formation will be suppressed (hence chance of splashing). The pressure gradient around the liquid film creates a downward force that hinders the stretching of the liquid film. The effect of the ambient pressure on lamella formation is only significant for relatively higher gas pressures (i.e., Pamb > 2 Patm).

Gas pressure and density effects on vibration of cylindrical pressure vessels: analytical, numerical and experimental analysis

The present research deals with the natural frequencies and mode shapes of cylindrical pressure vessels filled with different gasses in various internal pressures. The Hamilton’s principle is employed to derive the governing equations, which are solved using analytical and finite element analyses, and a closed form relation as the equivalent density is obtained to include the gas properties. The experimental modal analysis is performed and the obtained results are compared and validated with analytical and finite element results. The results show that the type of the gas, as well as the gas pressure have significant effect on vibrational behavior of the structure and should be accounted in the design and analysis of vessels.

Experimental and theoretical investigation on the OH + CH3C(O)CH3 reaction at interstellar temperatures (T=11.7-64.4 K).

The rate coefficient, k(T), for the gas-phase reaction between OH radicals and acetone CH3C(O)CH3, has been measured using the pulsed CRESU (French acronym for Reaction Kinetics in a Uniform Supersonic Flow) technique (T = 11.7-64.4 K). The temperature dependence of k(T = 10-300 K) has also been computed using a RRKM-Master equation analysis after partial revision of the potential energy surface. In agreement with previous studies we found that the reaction proceeds via initial formation of two pre-reactive complexes both leading to H2O + CH3C(O)CH2 by H-abstraction tunneling. The experimental k(T) was found to increase as temperature was lowered. The measured values have been found to be several orders of magnitude higher than k(300 K). This trend is reproduced by calculations, with a special good agreement with experiments below 25 K. The effect of total gas density on k(T) has been explored. Experimentally, no pressure dependence of k(20 K) and k(64 K) was observed, while k(50 K) at the largest gas density 4.47×1017 cm-3 is twice higher than the average values found at lower densities. The computed k(T) is also reported for 103 cm-3 of He (representative of the interstellar medium). The predicted rate coefficients at 10 K surround the experimental value which appears to be very close to the low pressure regime prevailing in the interstellar medium. For gas-phase model chemistry of interstellar molecular clouds, we suggest using the calculated value of 1.8×10-10 cm3 molecule-1 s-1 at 10 K and the reaction products are water and CH3C(O)CH2 radicals.

Influence of the pressure and temperature on laser induced breakdown spectroscopy for gas concentration measurements

Laser induced breakdown spectroscopy (LIBS) is an effective technique to obtain quantitative concentration information for the fuel injection and combustion processes. Practical applications of fuel injection and combustion usually involve a wide range of ambient pressures and temperatures, but understanding of the influence of these parameters on LIBS is far from adequate. The objective of this paper is therefore to investigate the pressure and temperature effects on LIBS over a wide range for gas concentration measurements, and further correct these effects to improve the measurement accuracy. The calibrations at various ambient pressures show that the peak intensity ratios (PIRs) exhibit better linear correlations with the equivalence ratios than the area intensity ratios (AIRs) for H656/N746. The intensities of H656 and N746 are remarkably influenced by the gas pressure due to the combined effects of varied gas density and self-absorption. While the PIR of H656/N746 depends greatly on gas pressures from 0.3 to 1.0 bar, the gas pressure effects on the PIR of H656/N746 are very slight at gas pressure above 1.0 bar. The effects of gas temperature on the PIR of H656/N746 are investigated at both constant gas pressure and constant gas density. The results show that the temperature differences between the calibrations and test conditions would significantly degrade the measurement accuracy, especially at low gas pressures. Then, a novel method to correct the gas temperature effects on LIBS for gas concentration measurements is proposed, based on a linear correlation between the PIR of H656/N746 and the gas temperature, with the gas temperature estimated by the full width at half maximum (FWHM) of H656.

Integration of phase distribution from gamma-ray tomography technique with monolith reactor scale modeling

In this work, a monolith reactor model was developed to study the effect of phase distribution on the performance of the monolith reactors by integrating phase distribution data from the experiments. To obtain the phase distribution at the reactions conditions, gamma ray computed tomography (CT) was used. Effect of gas density, surface tension of liquid and operating conditions on the phase distribution were studied using gamma-ray computed tomography. Experiments were conducted in Taylor flow regime. With the increase in gas density, uniformity increases. Surface tension has little effect on the distribution in the investigated conditions. Liquid with lower surface tension and gas with lower density has higher cross-sectional liquid saturation. Further, the monolith reactor model with uniform phase distribution and actual distribution were compared. It was found that at higher velocities both gives the same reactor performance irrespective of the maldistribution, however at low velocities, they differ significantly due to the maldistribution. If the maldistribution is present at both low and high velocities, catalyst utilization plays a major role, thus it is recommended to operate at higher velocities where catalyst utilization is high due to high mass transfer.

A CFD based empirical model for assessing gas holdup in bubble columns

ABSTRACTBubble columns are widely used in many industrial applications. Gas holdup knowledge is an essential element in bubble column design and process optimization. Despite the simple structure of bubble columns, the behaviour of the bubbly flow is still not well understood owing to the complexity of gas–liquid interactions and coupling between the phases. Variation of gas density and initial liquid height are the most likely reasons for gas holdup changes in bubble columns. These parameters affect bubble breakup and coalescence as well as the rise velocity of small bubbles, which causes change to bubble size distribution that finally affect the gas holdup. In this work, through the application of computational fluid dynamics (CFD) and by investigating the effect of gas density and the initial liquid height on the bubbly flow condition, a new correlation for deducing the total gas holdup is developed. To achieve this, a wide range of bubbly flows are modelled, and gas holdup values are determined for different heights and operating pressures. Ranges of the normalized pressure (P/P0), superficial Reynolds number (Resup), and the aspect ratio of the bubble column (H0/D) were 1 ≤ P/P0 ≤ 15, 3000 ≤ Resup ≤ 57000, and1.5 ≤ H0/D ≤ 8, respectively. The proposed correlation has been found to predict the experimental as well as CFD gas holdup data fairly well. The results of this research provide a fast and accurate method for predicting gas holdup in bubble columns that work either in atmospheric or high‐pressure conditions.

Variable gas density effects on transport from interacting evaporating spherical drops

The paper reports an analytical approach to model heat and mass transfer from neighbouring spherical drops accounting for the dependence of the gas mixture density on temperature and composition. The conservation equations for single-component non-identical spherical drops evaporating in gaseous quiescent environment are analytically solved in a bi-spherical coordinate system. Analytical expressions for the local heat and mass fluxes on drop surfaces and for the evaporation and the sensible heat rates are reported. The effect of relieving the commonly adopted assumption of constant gas density is quantified by comparison with existing constant density solutions for different evaporating species and operating conditions. The model applies to any value of Lewis number. Comparison with analogous results for single isolated drops allows to quantify the screening effect on vapour and heat fluxes and evaporation and heat rates.

Prediction of gas density effects on bubbly flow hydrodynamics: New insights through an approach combining population balance models and computational fluid dynamics

Detailed measurements and computational fluid dynamics (CFD) investigation of the hydrodynamics in a bubble column containing internal features causing flow disturbances are presented for both air and helium gases. An optical needle probe has been used to measure profiles of bubble size, bubble velocity, and gas holdup at different locations across the cross section of the column. An approach combining CFD with population balances is able to represent observed multiphase flow phenomena such as the effect of the pipes to remix and redistribute the gas as well as the tendency of the gas to channel through a slit in the pipes rather than go around the pipes. The comparison of CFD simulation to experimental measurements reveal that the overall decrease in gas holdup observed when switching from air to helium gas can be explained by swarm effects, whereas the steeper decrease in the gas holdup profile across the column is due to coalescence effects. © 2018 American Institute of Chemical Engineers AIChE J, 64: 3764–3774, 2018

Inter-plume aerodynamics for gasoline spray collapse

The collapse or merging of individual plumes of direct-injection gasoline injectors is of fundamental importance to engine performance because of its impact on fuel–air mixing. However, the mechanisms of spray collapse are not fully understood and are difficult to predict. The purpose of this work is to study the aerodynamics in the inter-spray region, which can potentially lead to plume collapse. High-speed (100 kHz) particle image velocimetry is applied along a plane between plumes to observe the full temporal evolution of plume interaction and potential collapse, resolved for individual injection events. Supporting information along a line of sight is obtained using simultaneous diffused back illumination and Mie-scatter techniques. Experiments are performed under simulated engine conditions using a symmetric eight-hole injector in a high-temperature, high-pressure vessel at the “Spray G” operating conditions of the engine combustion network. Indicators of plume interaction and collapse include changes in counter-flow recirculation of ambient gas toward the injector along the axis of the injector or in the inter-plume region between plumes. The effect of ambient temperature and gas density on the inter-plume aerodynamics and the subsequent plume collapse are assessed. Increasing ambient temperature or density, with enhanced vaporization and momentum exchange, accelerates the plume interaction. Plume direction progressively shifts toward the injector axis with time, demonstrating that the plume interaction and collapse are inherently transient.