Two-component Flow Research Articles

Properties of the black hole candidate XTE J1118+480 with the TCAF solution during its jet activity induced 2000 outburst

Galactic black hole candidate (BHC) XTE~J1118+480 during its 2000 outburst has been studied in a broad energy range using the archival data of PCA and HEXTE payloads of {\it Rossi X-ray Timing Explorer}. Detailed spectral and temporal properties of the source are studied. Low and very low frequency quasi-periodic oscillations (QPOs), with a general trend of increasing frequency are observed during the outburst. Spectral analysis is done using the combined data of PCA and HEXTE instruments with two types of models: the well known phenomenological power-law model and the current version of the {\it fits} file of two-component advective flow (TCAF) solution as an additive table model in XSPEC. During the entire period of the outburst, a non-thermal power-law component and the TCAF model fitted sub-Keplerian halo rate were found to be highly dominant. We suggest that this so-called outburst is due to enhanced jet activity. Indeed, the `outburst' subsides when this activity disappears. We estimated X-ray fluxes coming from the base of the jet and found that the radio flux is correlated with this X-ray flux. Though the object was in the hard state in the entire episode, the spectrum becomes slightly softer with the rise in Keplerian disk rate in the late declining phase. We also estimated the probable mass of the source from our spectral analysis with the TCAF solution. Our estimated mass of XTE~J1118+480 is $6.99^{+0.50}_{-0.74}~M_\odot$ i.e., in the range of $6.25-7.49~M_\odot$.

Two-phase Two-component Flow in Porous Media in Low Solubility Regime

We study a system of equations governing liquid and gas flow in porous media. The gas phase is homogeneous, while the liquid phase is composed of a liquid component and a dissolved gas component. It is assumed that the gas component is weakly soluble in the liquid. We formulate a weak solution of the initial boundary value problem and prove the existence theorem by passing to the limit in regularizations of the problem. The hypothesis of low solubility is given precise mathematical meaning.

Kinetic simulations of laser-induced plume expansion into a background gas under conditions of spatial confinement

Expansion of vapor plume induced by short-pulse laser irradiation of a bottom of a cylindrical cavity or planar trench in a copper target into helium, argon, and xenon background gases at pressure varying from zero to 1 bar is studied numerically. The simulations are performed based on a hybrid computational model that includes an unsteady heat conduction equation, Hertz-Knudsen model of evaporation, and a kinetic model of two-component gas flow implemented in the form of the Direct Simulation Monte Carlo method. It is found that increasing background pressure results in the formation of a complex structure of shock waves, which drastically changes the flow compared to the case of expansion into a vacuum. The moving shocks strongly affect the deposition of the ablated material inside the cavity. In particular, they induce the formation of a near-surface layer with a reduced fraction of vapor, which protects the cavity wall from vapor redeposition. The overall effect of the increasing background gas pressure on the flow structure and redeposition of vapor inside the cavity can be described as a trade-off between the confinement effect, i.e. a reduction in the propagation speed of the primary shock and overall rate of the plume expansion, and the focusing effect of moving shock waves that induce the radial flow towards the cavity axis, increase vapor density around the axis of symmetry, and reduce vapor density at the cavity wall. The efficiency of vapor removal out of the cavity can increase or decrease with increasing molar mass of the background gas depending on whether the flow is dominated by the focusing or confinement effect. These findings suggest that tuning the background gas parameters and geometrical parameters of spatial confinement can be used to effectively control the laser-induced plume expansion process in applications of laser ablation.

Pore-scale lattice Boltzmann simulation of two-component shale gas flow

Shale gas is usually a multi-component gas mixture dominated by CH4. Moreover, CO2 sequestration in shale reservoirs and CO2-enhanced shale-gas recovery also result in multi-component gas flow in shale reservoirs. Therefore, compared with single-component gas flow, multi-component gas flow is more often encountered in practice. Furthermore, shale rock contains a lot of nano-pores in which the micro-scale effect makes the multi-component gas flow become more complex. In this paper, the lattice Boltzmann method is employed to simulate the two-component shale gas flow in a two-dimensional micropore under different conditions. The pore-scale transport mechanism of the two-component shale gas is investigated and the gas separation phenomenon for the shale gas flow is discussed in detail. It is found that the molar fraction of each species in shale gas does not distribute uniformly along the micropore and the gas separation phenomenon exists in the two-component pressure-driven shale gas flow. The molar fraction distribution of each species along the micropore is affected by the Knudsen number, pressure ratio, shale gas composition and molar fraction of each species for the pressure-driven gas flows. In particular, we find that the molar fraction distribution and pressure distribution for two-component shale gas along the micropore are related to the pressure ratio and are unrelated to the pressure gradient. With increasing the molar fraction of CH4 in shale gas, both the gas-mixture velocity at the outlet and the slip velocity along the micropore become larger. Both the Knudsen number and pressure ratio affect the molar fraction distribution of CO2 for the CH4CO2 mixture in the micropore during CO2 injection, while the influence of them works oppositely. Furthermore, the concentration diffusion without the external force is affected by the micropore width and the concentration difference between the gas mixtures.

Experimental investigation of heat transfer of highly loaded structure elements upon cooling by a two-component gas-liquid flow

The paper considers a method of temperature stabilization of the limiter in the T-10 Tokamak with capillary-porous structure on the side facing of the plasma and saturated with liquid lithium, by dispersed gas-liquid flow. The spray pattern, formed by the spray generator, is directed along the axis of the limiter. The results of preliminary experiments for determining the geometric characteristics of a torch, a dispersed flow, the distribution of the velocity and the size of water droplets depending on the pressure of water and air entering the generator nozzle are presented. The paper presents the technique developed by the authors for processing experimental data, which makes it possible to calculate the heat flux density, as well as the temperature on the outer (heated) and internal (cooled) surface of the target walls. The design of the working area - limiter simulator is developed. It was experimentally established that the temperature of the target sharply decreased when air was supplied to the generator nozzle. The main experiments were carried out at excess water pressures (0.5 ÷ 1.0)·105 Pa, air (0.3 ÷ 2.8)·105 Pa, and heat flux densities of up to 4.9 MW/m2 applied to the target.

Microfluidic Control Board for High-Pressure Flow, Composition, and Relative Permittivity.

Flow control is central to microfluidics and chromatography. With decreasing dimensions and high pressures, precise fluid flows are often needed. In this paper, a high-pressure flow control system is presented, allowing for the miniaturization of chromatographic systems and the increased performance of microfluidic setups by controlling flow, composition, and relative permittivity of two-component flows with CO2. The system consists of four chips: two flow actuator chips, one mixing chip, and one relative permittivity sensor. The actuator chips, throttling the flow, required no moving parts as they instead relied on internal heaters to change the fluid resistance. This allows for flow control using miniaturized fluid delivery systems containing only a single pump or pressure source. Mobile phase gradients between 49% and 74% methanol in CO2 were demonstrated. Depending on how the actuator chips were dimensioned, the position of this range could be set for different method-specific needs. With the microfluidic control board, both flow and composition could be controlled from constant pressure sources, drift could be removed, and variations in composition could be lowered by 84%, resulting in microflows of CO2 and methanol with a variation in the composition of ±0.30%.

Correlation of heat transfer coefficient for two-component two-phase slug flow in a vertical pipe

The prediction of heat transfer coefficient for gas–liquid two-phase flows in vertical pipes is important for designing many industrial and engineering apparatuses such as nuclear power plants, solar collectors and petroleum pipelines. The mechanism of two-component two-phase heat transfer is more complicated than that of single-phase heat transfer. This study aims at developing a robust correlation of heat transfer coefficient for two-component two-phase slug flows in vertical pipes. The theoretical framework for the correlation development is inspired by considering classic Reynolds and Chilton–Colburn analogies. The framework demonstrates that the functional dependence of the two-component two-phase heat transfer coefficient on a void fraction or a two-phase multiplier is expressed by the Reynolds and Chilton–Colburn analogies. The correlation for the heat transfer coefficient of two-component two-phase slug flows in vertical pipes has been developed and validated by more than 200 existing data. The newly developed correlation predicts 95.1% of the collected two-phase heat transfer data within ± 30% error and the mean absolute relative deviation of the correlation is estimated to be 14.2%. The extended applicability of the newly developed correlation to other flow regimes such as bubbly, churn and annular flow regimes has been verified by the existing experimental data. The possible application of the newly developed correlation to large pipes is also discussed. In summary, it is expected that the newly developed correlation can predict the heat transfer coefficient of two-component two-phase flows under various conditions such as vertical upward and downward flows, developing and fully developed flows, laminar and turbulent flows and all two-phase flow regimes. The application of the correlation to vertical large pipes is also considered to be reasonable.

A Model for Spectral States and Their Transition in Cyg X-1

Abstract A new accretion picture based on a small disk surrounding a black hole is developed for the wind-fed source Cyg X-1. The hard and soft spectral states of Cyg X-1 are interpreted in terms of co-spatial two-component flows for the innermost region of an accretion disk. The state transitions result from the outward expansion and inward recession of this inner disk for the hard-to-soft and soft-to-hard transition, respectively. The theoretical framework for state transitions in black hole X-ray binaries with high-mass companions involving a change in the inner disk size, thus it differs from systems with low-mass companions involving the change in the outer disk size. This fundamental difference stems from the fact that matter captured and supplied to the black hole in wind-fed systems has low specific angular momentum and is hot essentially heated in the bow and spiral shocks, whereas it has high specific angular momentum and is cool in Roche lobe overflow systems. The existence of a weak cool disk around the ISCO region in the hard state allows for the presence of a relativistically broadened Fe K line. The small disk fed by gas condensation forms without an extensive outer disk, precluding thermal instabilities and large outbursts, resulting in the lack of large amplitude outbursts and hysteresis effects in the light curve of high-mass black hole X-ray binaries. Their relatively persistent X-ray emission is attributed to their wind-fed nature.

Modelling mist flow for investigating liquid loading in gas wells

This paper presents a dynamic simulation approach to investigating liquid loading in gas wells for a fluid flowing in the mist flow regime. Two-component gas-liquid two-phase flow is considered, using coupled thermodynamic and hydrodynamic models as well as constitutive equations that incorporate the Peng-Robinson equation of state and the convex hull algorithm. The behaviour of the flow properties is investigated as phase change occur during flow. The accumulation of liquids is explored by investigating the distribution of the liquid density in the tubing, which is explicitly determined from the flow variables. The calculated phase densities are validated using data obtained from NIST RefProp and the results show good agreement. This procedure can provide substantial benefits in investigating the phenomena of liquid loading in gas wells compared to critical velocity predicting models that determine the stagnation velocity under isothermal conditions.

Heat transfer correlation for two-component two-phase slug flow in horizontal pipes

Two-component gas-liquid two-phase slug flow in horizontal pipes occurs frequently in many industrial applications. The flow and heat transfer characteristics are complicated due to the intermittent flow structures. In view of the importance of predicting the heat transfer characteristics of the slug flow, this present study aims at developing a semi-theoretical heat transfer correlation for two-component two-phase slug flow based on the concept of Reynolds and Chilton-Colburn analogies. Firstly, an extensive literature review on existing databases and correlations of heat transfer coefficient for two-component two-phase slug flow was conducted. More than 500 experimental data and 8 heat transfer correlations were collected. The comparison between collected database and correlations indicated that none of the correlations could estimate the whole database satisfactorily. The relationship between heat transfer and pressure drop was investigated theoretically and an improved semi-theoretical heat transfer correlation was developed based on Reynolds and Chilton-Colburn analogies and the collected experimental results from 16 sources. The comparison analysis demonstrated that the newly-developed correlation achieved an excellent predictive capability with a wide range of test conditions. The newly developed correlation demonstrated that 91.5% of the data was predicted within ±30% error with the mean absolute relative deviation of 14.0%. In addition, the extension of the new correlation to other horizontal two-phase flow regimes was discussed. The newly-developed semi-theoretical correlation would be useful for predicting heat transfer coefficient of two-component two-phase flow in horizontal pipes.

Signature of Two-Component Advective Flow in several Black Hole candidates obtained through time-of-arrival analysis of RXTE/ASM Data

We study several Galactic black hole candidates using long-time RXTE/ASM X-ray data to search for telltale signatures of differences in viscous timescales in the two components used in the Two-Component Advective Flow (TCAF) paradigm. In high-mass X-ray binaries (HMXBs) mainly winds are accreted. This nearly inviscid and dominant sub-Keplerian flow falls almost freely towards the black hole. A standard Keplerian disc can form out of this sub-Keplerian matter in presence of a significant viscosity and could be small in size. However, in low-mass X-ray binaries (LMXBs), highly viscous and larger Keplerian accretion disc is expected to form inside the sub-Keplerian disc due to the Roche-lobe overflow. Due to two viscous timescales in these two components, it is expected to have a larger lag between the times-of-arrival of these components in LMXBs than that in HMXBs. Direct cross-correlation between the photon fluxes will not reveal this lag/delay since they lack linear dependence; however, they are coupled through the viscous processes which bring in both matter. To quantify the aforesaid time lag, we introduce an index ({\Theta}), which is a proxy of the usual photon index ({\Gamma}). Thus, when {\Theta}, being dynamically responsive to both fluxes, is considered as a reference, the arrival time lag between the two fluxes in LMXBs is found to be much larger than that in HMXBs. Our result establishes the presence of two dynamical components in accretion and shows that the Keplerian disc size indeed is smaller in HMXBs as compared to that in LMXBs.

Images and spectra of time-dependent two-component advective flow in presence of outflows

Two Component Advective Flow (TCAF) successfully explains the spectral and tem- poral properties of outbursting or persistent sources. Images of static TCAF with Compton cloud or CENtrifugal pressure supported Boundary Layer (CENBOL) due to gravitational bending of photons have been studied before. In this paper, we study time dependent images of advective flows around a Schwarzschild black hole which include cooling effects due to Comptonization of soft photons from a Keplerian disks well as the self-consistently produced jets and outflows. We show the overall image of the disk-jet system after convolving with a typical beamwidth. A long exposure image with time dependent system need not show the black hole horizon conspicuously, un- less one is looking at a soft state with no jet or the system along the jet axis. Assuming these disk-jet configurations are relevant to radio emitting systems also, our results would be useful to look for event horizons in high accretion rate Supermassive Black Holes in Seyfert galaxies, RL Quasars.

Accretion flow dynamics during 1999 outburst of XTE J1859+226—modeling of broadband spectra and constraining the source mass

We examine the dynamical behavior of accretion flow around XTE J1859+226 during the 1999 outburst by analyzing the entire outburst data ($\sim$ 166 days) from RXTE Satellite. Towards this, we study the hysteresis behavior in the hardness intensity diagram (HID) based on the broadband ($3 - 150$ keV) spectral modeling, spectral signature of jet ejection and the evolution of Quasi-periodic Oscillation (QPO) frequencies using the two-component advective flow model around a black hole. We compute the flow parameters, namely Keplerian accretion rate (${\dot m}_d$), sub-Keplerian accretion rate (${\dot m}_h$), shock location ($r_s$) and black hole mass ($M_{bh}$) from the spectral modeling and study their evolution along the q-diagram. Subsequently, the kinetic jet power is computed as $L^{\rm obs}_{\rm jet}\sim 3 - 6 \times 10^{37}$ erg~s$^{-1}$ during one of the observed radio flares which indicates that jet power corresponds to $8-16\%$ mass outflow rate from the disc. This estimate of mass outflow rate is in close agreement with the change in total accretion rate ($\sim 14\%$) required for spectral modeling before and during the flare. Finally, we provide a mass estimate of the source XTE J1859+226 based on the spectral modeling that lies in the range of $5.2 - 7.9 M_{\odot}$ with 90\% confidence.

Frictional pressure drop of aqueous-organic two-phase flow through packed and unpacked rectangular serpentine millichannel

This research work depicts the pressure drop characteristics of single-phase as well as aqueous-organic liquid-liquid two-phase flow through the rectangular serpentine millichannel in a horizontal orientation. Experiments were performed to investigate the pressure drops for both single and immiscible two component liquid-liquid aqueous-organic flows through the same rectangular serpentine channel with medium sand packing. The experimental results are enunciated with the available models for both empty and packed channels. Empirical models are developed to predict the pressure drop and friction factor for both single and two-component liquid-liquid flows through the prescribed serpentine geometry based on operating variables. The present work may be useful for further understanding of the multiphase system in the serpentine micro-dimensional unit for its design and development.

Algebraic multigrid preconditioners for two-phase flow in porous media with phase transitions

Multiphase flow is a critical process in a wide range of applications, including oil and gas recovery, carbon sequestration, and contaminant remediation. Numerical simulation of multiphase flow requires solving of a large, sparse linear system resulting from the discretization of the partial differential equations modeling the flow. In the case of multiphase multicomponent flow with miscible effect, this is a very challenging task. The problem becomes even more difficult if phase transitions are taken into account. A new approach to handle phase transitions is to formulate the system as a nonlinear complementarity problem (NCP). Unlike in the primary variable switching technique, the set of primary variables in this approach is fixed even when there is phase transition. Not only does this improve the robustness of the nonlinear solver, it opens up the possibility to use multigrid methods to solve the resulting linear system. The disadvantage of the complementarity approach, however, is that when a phase disappears, the linear system has the structure of a saddle point problem and becomes indefinite, and current algebraic multigrid (AMG) algorithms cannot be applied directly. In this study, we explore the effectiveness of a new multilevel strategy, based on the multigrid reduction technique, to deal with problems of this type. We demonstrate the effectiveness of the method through numerical results for the case of two-phase, two-component flow with phase appearance/disappearance. We also show that the strategy is efficient and scales optimally with problem size.

Comparison of two configurations to improve heat and mass transfer in evaporating two-component liquid film flow

This paper deals with a numerical analysis of comparison of two configurations to improve heat and mass transfer by the evaporation of two-component liquid film in a vertical channel under mixed convection. The liquid mixture falling down on one plate of the channel consists of water and ethanol. Two configurations are considered in this study, the first one consists in applying a uniform heat flux density to the wetted wall while in the second case, the same quantity of heat, was used for preheating the liquid mixture at inlet. The model solves the coupled governing equations in both phases together with the boundary and interfacial conditions. The systems of equations obtained by using an implicit finite difference method are solved by Tridiagonal Matrix Algorithm. The main purpose of this study is to compare the heat and mass transfer in two studied configurations. The result shows that the configuration with preheated film at the inlet of channel is the best technique to obtain a significant average evaporated mass flux density.

Application of Regularized Hydrodynamic Equations for Direct Numerical Simulation of Micro-Scale Flows in Core Samples

The paper is devoted to numerical simulation of three-dimensional isothermal two-phase two-component viscous fluid flows with surface effects in the pore space of core samples. The voxel representation of the flow domain is used suitable for digital rock physics applications. The flow is described by viscous compressible Navier-Stokes-Cahn-Hilliard equations. In order to use simple and computationally efficient explicit numerical algorithms with central difference approximations of spatial terms, a quasi-hydrodynamic regularization of equations is used. Simulation results of fluid displacement in pore space of realistic core sample (sandstone) are presented. The results demonstrate the applicability and good prospects of quasi-hydrodynamic regularization technique to solve the problem.

Investigation of the combined effect of air pockets and air bubbles on fluid transients

AbstractThis paper presents numerical and experimental investigations of the combined effect on pressure transients of air pockets and homogenous water–air bubble mixtures. An air pocket can accumulate at a high point of a pipeline along the control section located at the transition between pipes with sub- and supercritical slope, forcing open channel flow conditions underneath the pocket that ends in a hydraulic jump at the downward sloping pipe. The turbulence action at the jump generates small air bubbles that are entrained and transported along the pipe producing a two-component bubbly flow within the continuous liquid phase. A numerical model is developed, combining the explicit–implicit scheme proposed by McGuire and Morris and the method of characteristics for solving the quasi-linear hyperbolic partial differential equations for transient two-phase flow expressed in conservation form. To verify the proposed model, an experimental apparatus made of PVC was used to carry out hydraulic transient experiments. Tests were conducted in a tank–pipe–valve system and a valve with a pneumatic actuator at the downstream end generated transients. Numerical results at the test section pipe compares favorably with experimental data. The results show that pressure transients are significantly reduced with increasing air-pocket volumes and bubbly flow air content.

Accretion Flow Properties of Swift J1753.5-0127 during Its 2005 Outburst

Abstract Galactic X-ray binary black hole candidate Swift J1753.5-0127 was discovered on 2005 June 30 by the Swift/BAT instrument. In this paper, we make a detailed analysis of spectral and timing properties of its 2005 outburst using the archival data of the RXTE/PCA instrument. A simultaneous observation of Swift/XRT with PCA is also used to study the broadband features. Here, we study the evolution of the spectral properties of the source from spectral analysis with an additive table model fits file of the Chakrabarti-Titarchuk two-component advective flow (TCAF) solution. From the spectral fit, we extract physical flow parameters, such as the Keplerian disk accretion rate, sub-Keplerian halo rate, shock location, and shock compression ratio, etc. We also study the evolution of temporal properties, such as the observation of low-frequency quasi-periodic oscillations (QPOs), and the variation of X-ray intensity throughout the outburst. From the nature of the variation of QPOs, and accretion rate ratios (ARRs = ratio of halo to disk rates), we classify the entire 2005 outburst into two harder (hard-intermediate and hard) spectral states. No signatures of softer (soft-intermediate and soft) spectral states are seen. This may be because of a significant halo rate throughout the outburst. This behavior is similar to a class of other short-orbital-period sources, such as MAXI J1836-194, MAXI J1659-152, and XTE J1118+480. We estimate the probable mass range of the source to be in between based on our spectral analysis.

Properties of X-Ray Flux of Jets during the 2005 Outburst of Swift J1753.5−0127 Using the TCAF Solution

Abstract Galactic black hole candidate Swift J1753.5−0127 was discovered on 2005 June 30 by the Swift Burst Alert Telescope. We study the accretion flow properties during its very first outburst through careful analysis of the evolution of the spectral and the temporal properties using the two-component advective flow (TCAF) paradigm. RXTE proportional counter array spectra in are fitted with the current version of the TCAF model fits file to estimate physical flow parameters, such as two-component (Keplerian disk and sub-Keplerian halo) accretion rates, properties of the Compton cloud, probable mass of the source, etc. The source is found to be in harder (hard and hard-intermediate) spectral states during the entire phase of the outburst with very significant jet activity. Since in the TCAF solution the model normalization is constant for any particular source, any requirement of significantly different normalization to have a better fit on certain days would point to an X-ray contribution from components not taken into account in the current TCAF model fits file. By subtracting the contribution using actual normalization, we derive the contribution of X-rays from the jets and outflows. We study its properties, such as its magnitude and spectra. We find that on some days, up to about 32% of X-ray flux is emitted from the base of the jet itself.