Retrograde Region Research Articles

Electroosmotic peristaltic transport of magnetohydrodynamic Casson nanofluid in a non-uniform wavy porous asymmetric micro-channel

Magnetohydrodynamics (MHD) have numerous engineering and biomedical applications such as sensors, MHD pumps, magnetic medications, MRI, cancer therapy, astronomy, cosmology, earthquakes, and cardiovascular devices. In view of these applications and current developments, we investigate the magnetohydrodynamic MHD electro-osmotic flow of Casson nanofluid during peristaltic movement in a non-uniform porous asymmetric channel. The effect of thermal radiation, heat source, and Hall current on the Casson fluid peristaltic pumping in a porous medium is taken into consideration. The effect of chemical reactions is also considered. The mass, momentum, energy, and concentration equations were constructed using the proper transformations and dimensionless variables to make them easier for non-Newtonian fluids. A lubricating strategy is used to make the system less complicated. The Boltzmann distribution of electric potential over an electric double layer is studied using the Debye–Huckel approximation. The temperature and concentration equations are addressed using the homotopy perturbation method (HPM), while the exact solution is determined for the velocity field. The study examines the performance of velocity, pressure rise, temperature, concentration, streamlines, Nusselt, and Sherwood numbers for the involved parameters using graphical illustrations and tables. Asymmetric channels exhibit varying behavior, with velocity declining near the left wall and accelerating towards the right wall while enhancing the Casson fluid parameter. The pumping rate boosts in the retrograde region due to the evolution of the permeability parameter value, while it declines in the augment region. The temperature profile optimizes as the value of the heat source parameter gets higher. The concentration profile significantly falls as the chemical reaction parameter rises. The size of the trapped bolus strengthens with a spike in the parameter for the Casson fluid.

Dynamical Structures under Nonrestricted Hierarchical Planetary Systems with Different Mass Ratios

Secular dynamics have been extensively studied in both the inner and outer restricted hierarchical three-body systems. In the inner restricted problem, the quadrupole-order resonance (i.e., the well-known Kozai resonance) causes large coupled oscillations of eccentricity and inclination when the maximum inclination is higher than 39.2°, and the octupole-order resonance leads to the behavior of orbital flips. In the outer restricted problem, the behavior of orbital flips is due to the quadrupole-order resonance. Secular dynamics under the inner and outer restricted systems are distinctly different. The mass ratio of inner and outer bodies could change the ratio of circular orbital angular momenta β, which significantly influences dynamical structures of the system. But this influence is still unclear. In this paper, we focus on nonrestricted hierarchical planetary systems where β > 1 and investigate the secular dynamics by changing mass ratios. Dynamical structures are systematically explored from four aspects: periodic orbits, secular resonances, orbital flips, and chaos detection. We find that (a) it tends to lead to more bifurcations in the host family of prograde periodic orbits associated with Kozai resonance with smaller β; (b) with the decrease of β, fewer orbits inside the octupole-order resonance can realize flip; (c) for given initial conditions, the forbidden region appears in the retrograde region and becomes larger as β decreases, meaning that the mutual inclination cannot reach a very high value if β is small; and (d) chaotic orbits are distributed in the low-eccentricity, high-inclination region when β > 1.

PVT analyses as an effective tool in the hands of the petroleum engineer. Downhole reservoir fluid sampling for PVT analysis

The most important aspect of laboratory analysis is undoubtedly to acquire data of the highest quality. The worldwide trend of drilling into deeper reservoirs characterised by the high temperature and high pressure (HTHP) conditions makes the newly discovered reservoirs challenging because of bearing fluids with an unprecedented diversity of phase behaviour and variability of phase parameters over time. Due to the high temperature of the deep horizons constituting the reservoir rock, many individual components of the reservoir fluids are located in a region close to their critical temperatures, i.e. gas condensate (retrograde condensation region) or volatile oil. In particular, gas condensate reservoirs are challenging to analyse. They are highly prone to the errors resulting from phase behaviour testing when using samples that are incompatible with the original reservoir in-situ fluid that saturates the reservoir rock pores. Taking the representative samples of reservoir fluid is an essential requirement to obtain reliable data that can characterise such phase-variable multicomponent reservoirs. The primary purpose of hydrocarbon fluid analysis in case of new discoveries is to determine the type of reservoir fluid system. It should also be borne in mind that without a sufficiently long production process from several intervals and/or several wells, it can be challenging to classify the fluid with confidence, especially at the initial analysis stage. The paper presents issues related to sampling of the reservoir fluid (such as crude oil and natural gas) for the physical property and phase behaviour analyses (PVT), usually accompanied by chemical analyses. The importance of representativeness of the samples in performing reliable tests that have a significant impact on the hydrocarbon production was discussed. The data obtained from the PVT laboratory are widely used in economic reports concerning local, regional or finally national hydrocarbon reserves. Other applications of the PVT data include coordination of reservoir exploitation methods related to a particular fluid composition, as well as input to design requirements for the surface facilities development, and selection of the suitable technology for hydrocarbon fluid treatment prior to introduction to the market. Various techniques of downhole sampling were mentioned and characterised with an explanation of their applicability. The criteria for selection of a proper method were also presented.

English

These article intents to analyze the behavior of second-grade dusty fluid flowing through a flexible tube whose walls are induced by the peristaltic movement. Coupled equations for the fluid and solid particles have been modelled by considering streamline conversions. Regular perturbation technique has been implemented to get the solutions and the outcomes are demonstrated through graphs. The impact of diverse parameters on the contour presentations and on the velocity of the solid grains and fluid has been illustrated. The velocity for both fluid and solid grains is increased with the enhancement in wave number and Reynolds number. In retrograde region, pumping rate increases with the increase in α and it decreases for increased values of δ.  Key words: Peristaltic flow, second-grade dusty fluid, tube, axisymmetric flow. &nbsp

Experimental determination of the dew point pressure for bulk and confined gas mixtures using an isochoric apparatus

A robust high precision experimental approach to determine the Dew Point Pressure (DPP) of the gas condensates in a nano-porous medium is presented in this study. Gas condensate reservoirs have been the center of attention for numerous numerical and experimental studies for decades. Therefore, accurate measurement of DPP is crucial in developing long-term production plans for these reservoirs. This paper presents for the first time a proof of concept for a procedure to study the effect of the pore size distribution on the degree and direction of the shift in the saturation pressure of hydrocarbon gas mixtures under confinement over a relevant range of pressures and temperatures.Isochoric method, an indirect high-precision way of phase transition point determination, is commonly used in other disciplines where a clear non-visual determination of phase transition of a fixed volume of fluid is needed. This study provides an insight into using this approach for determining DPP of gas mixtures inside and outside of the porous media. A semi-automated apparatus for measuring and monitoring equilibrium conditions along with fluid properties is designed based on the isochoric method. The apparatus provides constant volume, variable pressure (0–104 bar), and variable temperature (290–410 K) experimental conditions. Pressure and temperature measurements provide a way to detect the phase transition point along the constant-mole-constant-volume line based on the change in the slope of this line at the phase transition point. A packed bed of BaTiO3 nanoparticles, providing a homogenous porous medium with pores of 1–70 nm is used as a representative nano-scale porous medium. The synthesized porous medium is very helpful in uncoupling the effect of pore size from the effect of mineralogy on the observed deviations in behavior, providing a volume more than 1000 times larger than the typical nano channels.The result is a set of isochoric lines for bulk and confined sample, plotted on the mixture's corresponding phase envelope to demonstrate the change in the saturation pressure. Phase envelopes (P-T diagrams) of the same mixture using different equations of state are created and the accuracy of each of these equations of state in providing an estimate of the experimentally detected DPP is discussed. Many attempts in explaining the shift in saturation pressures of the reservoir fluid confined in the narrow pores of unconventional reservoirs compared to those of the bulk can be found in the literature. However, there are some contradictions between the predicted behavior using different mathematical approaches. Experimental data could be substantially helpful in both validating the models and improving the understanding of the fluid behavior in these formations. Contrary to what many published models proposed, our results show that confinement effect shifts the DPP towards higher values compared to the bulk for a fixed temperature in the retrograde region. Capillary condensation is identified as the main source of the deviations observed in the behavior of fluids inside the nanopores. We evaluated some published models, including those based on EoS modifications, by comparing those to the experimental results which provides a quantification of their accuracy in estimating saturation pressure values for the confined mixtures.

Experimental study and thermodynamic modeling of clathrate hydrate stability conditions in carbon dioxide + cyclopentane + water system: Retrograde region

In this study, hydrate dissociation conditions for the carbon dioxide + cyclopentane + water system were measured. The pressure-search method at constant volume was employed to measure equilibrium conditions in the temperature range from 287.4–293.1 K and pressure range from 0.99–4.78 MPa. The results exhibit a retrograde behavior at pressures above 4 MPa for this system. Also, the experiments show that cyclopentane would significantly promote carbon dioxide hydrate stability conditions. In addition, based on the minimization of Gibbs free energy, a multiphase flash calculation was performed using the van der Waals and Platteeuw (vdW-P) solid solution theory along with the cubic plus association (CPA) equation of state to predict gas hydrate stability conditions. Modeling results are found in good agreement with the experimental data even in the retrograde region.

The potential of biochar as sorptive media for removal of hazardous benzene in air

Airborne benzene is hazardous even at sub-ppm levels. Therefore, an effective strategy is required for its removal, such as the use of a sorbent with large adsorption capacity or high breakthrough volume. To meet the goal, the performance for the removal of benzene was assessed by loading benzene at 5 Pa inlet partial pressure against seven types of biowaste-derived biochar: (1) paper mill sludge, (2) conventional biochar with magnetic properties, (3) biochar composites with carbon nanotubes (CNTs), (4) gasification biochar from mixed feedstock, (5) gasification biochar from a single feedstock, (6) modified gasification biochar, and (7) activated carbon (AC) as a reference. The 298 K maximum adsorption capacities (mg g−1), when measured at a benzene inlet pressure of 5 Pa (or 50 ppm in ultrapure nitrogen) and flow rate of 50 mL atm min−1, varied widely for different biochars, from 0.35 (MS: Swine manure + plastic mulch film waste) to 144 mg g−1 (XC-1: biochar from mixed feedstock); their 10% breakthrough volumes (BTV) were in the range of 0.22–492 L g−1, respectively. The experimental data (capacity vs. benzene outlet partial pressure) could be fitted to either two or three linearized Langmuir isotherms with distinctive sorption mechanisms ((1) a retrograde region (Type III isotherm: 0 to ∼0.2 Pa), (2) an intermediate pressure region (0.2 and 2.0 Pa), and (3) a higher pressure region (>2 Pa)) which was also confirmed similarly by Freundlich, Dubinin–Radushkevich, and Elovich fitting. About 65% of the maximum capacity was achieved in the retrograde region. The strongest biochar sorbent, XC-1, showed similar performance as activated carbon to prove its feasibility toward air quality management (AQM) applications.

PVTx and thermal-pressure coefficient measurements of the binary CO2 + n-decane mixtures in the critical and retrograde regions

Abstract PVTx and temperature derivative of pressure (thermal-pressure coefficient), γ VX = ( ∂ P / ∂ T ) VX , of binary CO2 + n-decane mixtures have been measured in the critical, supercritical, and retrograde condensation regions (near the critical and cricondenterm points). Most measurements were made in the immediate vicinity of the dew-, bubble, and the critical point curves (in the single – and two-phase regions) to precisely determine the phase boundary properties, T S , P bub , P dew , ρ S ′ , ρ S ″ , ( ∂ P / ∂ T ) VX ′ , and ( ∂ P / ∂ T ) VX ″ .The measurements have been made using a high-temperature, high-pressure, nearly constant-volume adiabatic piezo-calorimeter for three concentrations of 0.095, 0.178, and 0.263 mol fraction of n-decane over the temperature range: (for mixture-1, x = 0.095) from (292 to 567) K along the liquid and vapor densities between (89 and 659) kg·m−3 at pressures up to 28.3 MPa; (for mixture-2, x = 0.178) from (302 to 557) K along the liquid and vapor densities between (85 and 467) kg·m−3 at pressures up to 24.3 MPa; and (for mixture-3, x = 0.263) from (361 to 568) K along the liquid and vapor densities between (298 and 520) kg·m−3 at pressures up to 25.4 MPa. The combined expanded uncertainty of the density, ρ , pressure, P, temperature, T, concentration, x, and the thermal-pressure coefficient, γ VX , measurements at the 68% confidence level with a coverage factor of k = 2 is estimated to be (0.2–0.5)%, (0.5–1.0)%, 15 mK, 0.01 mol%, and (0.2–2.0)% (depending on temperature and pressure), respectively. The critical (the critical temperature, T C , the critical pressure, P C , and the critical density, ρ C ), cricondentherm, and cricondenbar point data of CO2 + n-decane mixture were derived as a function of concentration from phase boundary properties studied. The Krichevskii parameter and isomorphism of the critical behavior of the mixture were studied using the critical curve data for the mixture and vapor pressure data for the pure solvent (CO2). Features of the P S - T S phase boundary diagram and thermodynamic behavior of the mixture near the critical and cricondentherm points and in the retrograde region were observed.

Two-phase filtration of multicomponent mixtures with a retrograde region of the phase diagram

The results of mathematical and physical modeling of an isothermal filtration of multicomponent mixtures with a retrograde region of the phase diagram are presented. By the example of mixtures of hydrocarbons of the methane line, the conditions at which the hydrocarbon-two-phase fluid−porous space system is a self-oscillation system are determined. The data obtained make it possible to explain certain regularities of the filtration of gas-condensate mixtures and can be used to increase the extraction of gas-condensate deposits.

“The City Too Busy to Care”: The Atlanta Youth Murders and the Southern Past, 1979–81

[ILLUSTRATION OMITTED] Atlanta: Long seen as the robustly optimistic capital of the New South. Throughout its regions racial troubles, Atlanta always seemed a healthy, bustling citadel of good sense and goodwill, offering its own unique prospect for racial reconciliation in the South. But now, this brave center of the Sunbelt has been touched by a shadow--a mindless evil loose in its midst, executing its children with a cruel and systematic regularity. What does it mean a like Atlanta when it finds something like this happening it? --Marshall Frady, ABC World News Tonight, February 27, 1981 (1) On May 25, 1981, an estimated three thousand people convened at the Lincoln Memorial in Washington, D.C., protest the slayings of black Atlanta youths. Rally organizers framed the demonstration as part of the March on Washington tradition. Promotional materials urged attendees to help pave the way living A reality that once was A dream, evoking Martin Luther King Jr.'s canonical 1963 speech. Therein King had shared his vision for a society in which his and other children could transcend the racial prejudice that negated the American precepts of freedom and equity. Eighteen years later, speakers at the Atlanta rally seemed less hopeful and more fearful for their children. Across this country our children are being killed in many ways, Camille Bell, a victim's mother, lamented. And our future is being wiped out. (2) From 1979 1981, the of Atlanta reeled as nearly thirty of its young, black, and poor residents were abducted and murdered. These slayings aggravated long-held black anxieties about racial violence, white hegemony, and the African American future. They also undermined Atlanta's image as a space of racial moderation and economic progress in an otherwise retrograde region. For nearly two years, the death toll mounted as the struggled determine who was preying on its black children, adolescents, and young adults. (3) Just as racial unrest seemed destined erupt in the spring of 1981, Atlanta investigators apprehended a twenty-three year old African American man named Wayne B. Williams in connection with two of the murders. The following year, Williams was convicted of the two killings, and officials implicated him in nearly all of the others. In effect, the case had been closed, and Atlanta had been vindicated. This article argues that the southern past shaped public perceptions of and community responses the Atlanta youth murders, which in turn dented Atlanta's reputation as a New South, postracial, and post-civil city. Poor black Atlantans and those within the city's biracial power structure developed fundamentally different approaches addressing the killings. Many African Americans conceived of the slayings as an attempt unmake the Civil Rights Movement. As black Atlantans mobilized against the forces of racism and indifference the crisis, they built on well-worn southern movement strategies that stressed consciousness raising, community protection, civic engagement, and a populist posture against both black and white elites. The city's biracial political and economic establishment took a different tack--downplaying the racial dimensions of the killings, drafting contingency plans prevent any potential civil unrest related the murders, securing the assistance of the private sector in alleviating local anxieties, and striving preserve Atlanta's image as the city too busy hate. (4) Observers outside of Atlanta generally understood the slayings as inconsonant with the city's moderate reputation yet consistent with the South's troubled racial past. These divergent yet imbricated reactions revealed inter- and intraracial contestations over Atlanta's meanings in regional, national, and global contexts. For many, the killings called into question the very gains of the classical civil rights struggle, demonstrated the endurance of Jim Crow violence, and challenged the city's position as an exceptional southern space. …

Viscosity and Dew Point Measurements of {xCH4 + (1 – x)C4H10} for x = 0.9484 with a Vibrating-Wire Viscometer

The viscosity of {xCH4 + (1 – x)C4H10} with x = 0.9484 has been measured at temperatures and pressures in the range (200 to 423) K and (2 to 30) MPa, respectively, corresponding to densities between (20 and 371) kg·m–3. The measurements were made using a vibrating-wire-viscometer with the wire clamped at both ends and operated in steady-state mode with a combined relative uncertainty of 1 %. The viscometer was also used to investigate the ability of a vibrating-wire instrument to determine the upper and lower dew pressures of the mixture in the retrograde region at (263 and 273) K. The dew pressures were determined by identifying the point along an isothermal pathway at which the slope of the wire’s resonance half-width with pressure exhibited a discontinuity. At the upper dew pressures near 10 MPa the results were consistent to within 0.2 MPa of predictions made using the GERG-2008 equation of state (EOS), while at the lower dew pressures near 3 MPa the agreement was within 0.3 MPa. To facilitate future ...

Experimental phase behavior study of a five-component model gas condensate

In this work, the bubble points and dew points of a multicomponent mixture of methane, butane, heptane, decane and tetradecane as a model mixture representative of a gas condensate, have been measured experimentally. Ten samples with approximately the same composition were prepared and their bubble-point and/or their dew-point pressures were measured at several temperatures. The phase-behavior measurements were carried out in the temperature range of 240–410K, and at pressures up to 21.6MPa. The temperature and pressure ranges of the critical point for this system was measured and the cricondenbar and cricondentherm of the phase envelope were determined. The Peng–Robinson equation of state (PR EOS) was used for modeling of the phase behavior of this system. The PR EOS was able to successfully determine the bubble- and dew-points of this model gas condensate. Using the PR EOS, the retrograde region and liquid drop out characteristic of this model gas condensate were determined.

CHRISTOPHER P. IANNINI. Fatal Revolutions: Natural History, West Indian Slavery, and the Routes of American Literature.

Two of the most important literary figures of the early republic, J. Hector St. John de Crèvecoeur and John Audubon, were Frenchmen whose sensibilities had been shaped by their experiences in the dynamic plantation world of the circum-Caribbean. Audubon, indeed, was the son of a Saint-Domingue sugar planter who would not have emigrated to the United States if not for the trauma (as he saw it) of the Haitian Revolution. In this short, dense, and rewarding series of essays on writers on nature in the lower South and the West Indies—from Hans Sloane at the start of the eighteenth century through to naturalists Mark Catesby, William Bartram, and Audubon—the plantation world was not some exotic and culturally retrograde region at the edge of a cosmopolitan non-slaveholding world. For Audubon and Crèvecoeur as well as Thomas Jefferson (who is the subject of a very interesting chapter), these were places that were central to the scientific and literary culture of Enlightenment America. But the very novelty of the plantation world and the cruelty it engendered as capitalist social institution and economic engine made this idea difficult to articulate. Both Audubon and Crèvecoeur wanted to efface the Caribbean from their consciousness, to drop a curtain, as Audubon put it, over the dire picture of slave revolt, and to escape as soon as they could from what Crèvecoeur called a “chaos of men, negroes and things” (pp. 143, 255).

Analysis and prediction of input multiplicity for the reactive flash separation using reaction-invariant composition variables

In this study, we introduce a new approach for predicting and analyzing the input multiplicity in reactive flash separation processes. Specifically, we have identified necessary conditions to detect these multiple states in reactive flash separations using reaction-invariant composition variables. The presence of the input multiplicity is studied for the reactive systems of MTBE and TAME production to illustrate the capabilities of our methodology. For these reactive systems, we report the existence of multiple states for different operating conditions. In summary, our strategy can be applied with any reactive system and thermodynamic model, assuming that all reactions are reversible and in thermodynamic equilibrium and the operating conditions are away from the retrograde region. In general, our method is a robust procedure for the multiplicity analysis in flash separation of multi-reactive and multi-component systems.

Calculating Transfer Families to Periodic Distant Retrograde Orbits Using Differential Correction

The existence of collision orbits in the vicinity of the distant retrograde region is well documented in works involving satellite capture. This study uses the orderly arrangement of collision regions and a dynamical analysis to calculate transfer families to periodic distant retrograde orbits. The work provides a systematic procedure to produce transfer families, providing an alternative to other methods and a framework in which to understand the design space.

Internal pressure measurements of the binary 0.7393H 2O + 0.2607NH 3 mixture near the critical and maxcondetherm points

The pressure, P, and their temperature derivative ( ∂ P / ∂ T ) V , of binary mixture 0.7393H 2O + 0.2607NH 3 has been measured in the near- and supercritical regions. Measurements were made in the immediate vicinity of the liquid–gas coexistence curve (one- and two-phase regions) using a high-temperature, high-pressure, nearly constant-volume adiabatic piezo-calorimeter. Measurements were made along 40 liquid and vapor isochores in the range from 120.03 kg m −3 to 671.23 kg m −3 and at temperatures from 403 K to 633 K and at pressures up to 28 MPa. Temperatures at the liquid–gas phase transition curve, T S ( ρ ) , for each measured density (isochore) were obtained using the quasi-static thermograms technique. The expanded uncertainty of the pressure, P, and temperature derivative, ( ∂ P / ∂ T ) V , measurements at the 95% confidence level with a coverage factor of k = 2 is estimated to be 0.05% and 0.12–1.5% (depending on temperature and pressure), respectively. The direct measured pressures, P, and temperature derivatives, ( ∂ P / ∂ T ) V , has been used to calculate the internal pressure (or energy-volume coefficient) as ( ∂ U / ∂ V ) T = T ( ∂ P / ∂ T ) V − P . We also measured the temperature derivatives of the internal energy ( ∂ U / ∂ T ) V = C V (isochoric heat capacity) using the same apparatus. The measurements were made at isochoric heating of the system at quasi-equilibrium conditions. The effect of pressure, temperature, and concentration on the internal pressure was studied. The measured values of pressure ( P S ), temperature derivative, ( ∂ P / ∂ T ) V S , temperature ( T S ) and density ( ρ S ) at the saturation curve together with isochoric heat capacity measurements were used to calculate other thermodynamic properties of the mixture at the bubble- and dew-pressure points curves. Some unusual “appendix type shape” behavior of the ( ∂ P / ∂ T ) V and internal pressure, P int , near the critical and maxcondetherm points (in the retrograde region) was found.

Experimental Study of the Critical Behavior of the Isochoric Heat Capacity of Aqueous Ammonia Mixture

The isochoric heat capacity of a NH3 + H2O (0.2607 mole fraction of ammonia) mixture has been measured in the near- and supercritical regions. Measurements were made in the single- and two-phase regions including the coexistence curve using a high-temperature, high-pressure, nearly constant-volume adiabatic calorimeter. Measurements were made along 38 liquid and vapor isochores in the range from 120.03 kg · m−3 to 671.23 kg · m−3 and at temperatures from 478 K to 634 K and at pressures up to 28 MPa. Temperatures at the liquid–gas phase transition curve, T S(ρ), for each measured density (isochore) and the critical parameters (T C and ρ C) for the 0.2607 NH3 + 0.7393 H2O mixture were obtained using the quasi-static thermograms technique. The expanded uncertainty of the heat-capacity measurements at the 95 % confidence level with a coverage factor of k = 2 is estimated to be 2 % to 3 % in the near-critical and supercritical regions, 1.0 % to 1.5 % in the liquid phase, and 3 % to 4 % in the vapor phase. Uncertainties of the density, temperature, and concentration measurements are estimated to be 0.06 %, 15mK, and 5×10−5 mole fraction, respectively. An unusual behavior of the isochoric heat capacity of the mixture was found near the maxcondetherm point (in the retrograde region). The value of the Krichevskii parameter was calculated using the critical properties data for the mixture and vapor-pressure data for the pure solvent (H2O). The derived value of the Krichevskii parameter was used to analyze the critical behavior of the strong (C P , K T ) and weakly (C V ) singular properties in terms of the principle of isomorphism of critical phenomena in binary mixtures. The values of the characteristic parameters (K 1, K 2), temperatures (τ 1, τ 2), and the characteristic density differences (Δρ 1, Δρ 2) were calculated for the NH3 + H2O mixture by using the critical-curve data.

Phase and Interfacial Tension Behavior of Certain Model Gas Condensates: Measurements and Modeling

This contribution reports on the phase and interfacial tension behavior of some model high-temperature–high-pressure gas condensates. On the one hand these types of gas condensate are becoming a subject of major interest for the oil industry, while on the other their phase and interfacial tension behavior have not been very well studied. For two different model gas condensates, both composed of the three n-alkanes, methane, butane, and decane, experimental results on their fluid phase behavior have been obtained in the temperature region 270 < T (K) < 490 and up to pressures as high as 24 MPa. Also, critical points of the two mixtures have been determined experimentally. Both mixtures show an extended retrograde region. Using the Peng–Robinson equation of state, the phase behavior of the two mixtures was modeled. In addition, the interfacial tension behavior of the model gas condensates was modeled. For that purpose, the Cahn–Hilliard theory was applied in combination with the Peng–Robinson equation of state. Satisfactory results were obtained.

Efficient, Robust, and Reliable Single-Stage Vapor−Liquid Flash Calculations

In this paper the problem of single-stage vapor−liquid flash calculations using equations of state is addressed. A solution scheme in the framework of complex domain is used in conjunction with a Newton-based formulation in block algebra, providing an efficient, robust, and reliable computation scheme. The new scheme minimizes the number of iterations, because it always ensures a direct-forward step toward the solution, making fewer calls to thermodynamic property evaluations during iterations and avoiding the use of pseudophases along the calculation path. Convergence to unambiguous results is assured for all cases of practical interest, because derivative discontinuities inherent to real-domain models, including the need for bounding mole fractions to lie between 0 and 1, are avoided. The efficiency and robustness of the proposed scheme are shown by calculations in the retrograde region and in the construction of phase envelopes for model mixtures.

Conversion of a deasphalting unit for use in the process of supercritical solvent recovery

In order to reduce energy consumption and to increase deasphalted oil yield, an old PETROBRAS deasphalting unit was converted for use in the process of supercritical solvent recovery. In-plant and pilot tests were performed to determine the ideal solvent-to-oil ratio. The optimum conditions for separation of the supercritical solvent from the solvent-plus-oil liquid mixture were determined by experimental tests in PVT cells. These tests also allowed measurement of the dew and bubble points, determination of the retrograde region, observation of supercritical fluid compressibility and as a result construction of a phase equilibrium diagram.