Near-critical Fluids Research Articles

How Does Wetting in a Near-Critical Binary Fluid Affect Stokes Drag?

How Does Wetting in a Near-Critical Binary Fluid Affect Stokes Drag?

CARS diagnostics of near-critical fluid in small mesopores

Due to the high spacial resolution and theinterference nature, coherent anti-Stokes Ramanscattering (CARS) spectroscopy is well suited forthe diagnostics of composites based on transparentnanoporous hosts. In particular, the adsorption of afluid on the walls of nanopores and the formation ofa condensed phase in their volume leads to obvioustransformation of the CARS spectra. Recently wehave developed a model which describes thebehavior of molecular spectra at isothermalcompression in cylindrical nanopores. Calculationsbased on the model have shown a good agreementwith the experimental results for carbon dioxide innanoporous glass with pores of diameter of severalnanometers. Here we use the developed approach toinvestigate the phase behavior of carbon dioxide inglass nanopores at near-critical temperatures. It hasbeen experimentally shown that condensation innanopores occurs at relatively low pressures atsubcritical and even at supercritical temperatures.The analysis based on the developed model allowsto reveal some qualitative and quantitativecharacterizations of the shift of critical point.

A numerical study of fluid injection and mixing under near-critical conditions

Nitrogen injection under conditions close vicinity of the liquid-gas critical point is studied numerically. The fluid thermodynamic and transport properties vary drastically and exhibit anomalies in the near-critical regime. These anomalies can cause distinctive effects on heat-transfer and fluid-flow characteristics. To focus on the influence of thermodynamics on the flow field, a relatively low injection Reynolds number of 1 750 is adopted. For comparisons, a reference case with the same configuration and Reynolds number is simulated in the ideal gas regime. The model accommodates full conservation laws, real-fluid thermodynamic and transport phenomena. Results reveal that the flow features of the near-critical fluid jet are significantly different from their counterpart. The near-critical fluid jet spreads faster andmixes more efficiently with the ambient fluid along with a more rapidly development of the vortex pairing process. Detailed analysis at different streamwise locations including both the flat shear-layer region and fully developed vortex region reveals the important effect of volume dilatation and baroclinic torque in the near-critical fluid case. The former disturbs the shear layer and makes it more unstable. The volume dilatation and baroclinic effects strengthen the vorticity and stimulate the vortex rolling up and pairing process.

Buoyancy driven convection in near-critical and supercritical fluids

Buoyancy driven thermal transport in a pure fluid (carbon dioxide) near its gas–liquid critical point is investigated using a two-dimensional numerical model. A square enclosure is considered with side heating. For all cases considered, the initial pressure and temperature of carbon dioxide is pi (>pc) and Ti (>Tc) respectively. The two side-walls of the enclosure are initially at temperature Ti and the left wall temperature is temporally raised to TL∞. The model considers the strong variable property effects (functions of both temperature and pressure) near the critical point, including the bulk viscosity variations. As thermal diffusivity approaches zero near the critical point, the divergence of thermo-physical properties near the critical point gives rise to large Rayleigh number flows even for very small temperature differences. The steady-state convective heat transfer coefficient near the critical point is investigated and a correlation for the steady state, spatially averaged Nusselt number along the vertical walls is developed as a function of the Rayleigh number and the ratios (pi−pc)/pc, (Tm−Tc)/Tc and Tpc′=(Tpc−Tc)/Tc, where Tm=(Ti+TL∞)/2. The subscripts ‘i’, ‘m’, ‘c’, ‘pc’ and refer to the initial, mean, critical, pseudo-critical conditions respectively while the subscript ‘L∞’ refers to the final value of the left (heated) wall temperature. The effect of critically diverging bulk viscosity on the flow field and heat transport induced by buoyancy in near-critical fluids is also investigated.

Thermoacoustic transport in supercritical fluids at near-critical and near-pseudo-critical states

► Numerical simulations of the generation and propagation of thermoacoustic waves in near-pseudo-critical carbon dioxide. ► Accurate representation of the thermo-physical properties of supercritical carbon dioxide near the critical and pseudo-critical states. ► Increase of the relative strength of the generated acoustic field as the initial state of the fluid approaches critical or pseudo-critical states. ► Characterization of the strengths of the generated acoustic field as a function of the rate of boundary heating. ► Investigation of a novel thermoacoustic wave driven thermal transport device using near-critical and near-pseudo-critical carbon dioxide. Thermoacoustic wave induced transport in carbon dioxide near its critical and pseudo-critical states is investigated numerically. A real-fluid computational fluid dynamic model has been developed considering all of the relevant fluid property variations (including bulk viscosity) near the critical and pseudo-critical states. The predicted results provide interesting details regarding the thermal transport mechanisms at near-critical and pseudo-critical state fluids. As a layer of supercritical fluid (near the critical or the pseudo-critical states) is heated rapidly, the combination of very high thermal compressibilities and vanishingly small thermal diffusivities affect the thermal energy propagation, leading to the formation of acoustic waves as carriers of thermal energy (the so called piston effect ). The results show that under the same temperature perturbation at the boundary, the induced acoustic field becomes stronger as the critical point or the corresponding pseudo-critical state is approached. The heating rate, at which the boundary temperature is raised, is a key factor in the generation of these acoustic waves. We also study the effect of critically diverging bulk viscosity and different rates of boundary heating on the temperature equilibration mechanism near the critical point. An application of the piston effect in near-critical and near-pseudo-critical fluids for effective thermal transport over a long distance is demonstrated for a supercritical heat pipe.

Inhalable Antibiotics Manufactured Through Use of Near-Critical or Supercritical Fluids

The development of unit-dose, inhalable, antibiotic microparticles for use in primary and combined therapy approaches to treating tuberculosis (TB), multi-drug-resistant (MDR-TB), and extensively drug-resistant TB is explored using the gentle drying process of Carbon-dioxide Assisted Nebulization with a Bubble Dryer (CAN-BD). The microparticles produced using this method contain capreomycin, kanamycin, and isoniazid, respectively, imbedded in L-leucine. Antibiotics were developed into inhalable antibiotic formulations for their utility in both first line and second line antibiotic treatment regimens. Capreomycin and kanamycin are typically administered by injection making them desirable candidates for the development of a needle-free delivery system that addresses the Grand Challenges in Global Health Initiative #3. In response to this challenge, unit-dose packaging that preserves powder properties by protecting them from moisture, oxidants, and UV exposure, and a low cost “active” dry powder inhaler, the...

Casimir amplitudes and capillary condensation of near-critical fluids between parallel plates: Renormalized local functional theory

We investigate the critical behavior of a near-critical fluid confined between two parallel plates in contact with a reservoir by calculating the order parameter profile and the Casimir amplitudes (for the force density and for the grand potential). Our results are applicable to one-component fluids and binary mixtures. We assume that the walls absorb one of the fluid components selectively for binary mixtures. We propose a renormalized local functional theory accounting for the fluctuation effects. Analysis is performed in the plane of the temperature T and the order parameter in the reservoir ψ(∞). Our theory is universal if the physical quantities are scaled appropriately. If the component favored by the walls is slightly poor in the reservoir, there appears a line of first-order phase transition of capillary condensation outside the bulk coexistence curve. The excess adsorption changes discontinuously between condensed and noncondensed states at the transition. With increasing T, the transition line ends at a capillary critical point T=T(c) (ca) slightly lower than the bulk critical temperature T(c) for the upper critical solution temperature. The Casimir amplitudes are larger than their critical point values by 10-100 times at off-critical compositions near the capillary condensation line.

A NUMERICAL STUDY OF FLUID INJECTION AND MIXING UNDER NEAR-CRITICAL CONDITIONS

Nitrogen injection under conditions in close vicinity of liquid-gas critical point is studied through numerical simulation. The thermodynamic and transport properties of fluid exhibit anomalies in the near-critical fluid regime. These anomalies can cause distinctive effects on heat transfer and hydrodynamics. To focus on the influence of the highly variable properties and avoid the difficulties encountered in modeling high Reynolds number flows, a relatively low injection Reynolds number is adopted. A reference case with the same configuration and Reynolds number is also simulated in the ideal gas regime. Full conservation laws, real-fluid thermodynamic and transport phenomena are accommodated in the model. The obtained results reveal that the flow features of the near-critical fluid jet are significantly different from the ideal gas case. The near-critical fluid jet spreads faster and mixes better with the ambient fluid compared to the ideal gas jet. It is also identified that vortex pairing process develops faster in the near-critical case than in the ideal gas case. Detailed analysis of data at different streamwise positions including both flat shear layer region and fully developed vortex region reveals the effect of volume dilatation and baroclinic torque plays an important role in the near-critical fluid case. The volume dilatation effect disturbs the shear layer and makes it more unstable. The volume dilatation and baroclinic effects strengthen the vorticity and stimulate the vortex rolling up and pairing process.

Heat can cool near-critical fluids

We report experiments with very compressible fluids near the liquid-gas critical point. These experiments are performed (i) under microgravity in low Earth orbit by using SF(6) at liquidlike density and (ii) under Earth's gravity with CO(2) at gaslike density. The sample fluid is filled in an interferometer cell with its walls maintained at constant temperature. In situ thermistors measure the local fluid temperature. One of the thermistors is also used as a heat source to generate heat pulses. With no gravity-induced fluid convection, the evolution of fluid temperature is governed by the balance of heat flux between the thermal boundary layer of the heat source, which compresses the bulk fluid, and the thermal boundary layer at the wall, which expands it. When heat pulses are applied to the fluid under weak or Earth's gravity, a long thermal transient is observed at the end of the heat pulse where the bulk fluid temperature reaches significantly below the initial temperature. This unconventional cooling originates from the fast decompression of the fluid, which is induced by the rapid convectively disappearing hot boundary layer at the heat source, and the persistence of an anomalously thin cold boundary layer convectively induced at the cell wall. This striking phenomenon is observed in a large range of temperature, density, and various thermodynamic conditions. This anomalous cooling effect persists for an appreciable period of time corresponding to the diffusive destruction of the cold boundary layer. We found that the effect is also more pronounced when the free fall acceleration is large. We have analyzed the result by using a simple one-dimensional model with ad hoc convective heat losses.

Near-Critical Fluid Micellization for High and Efficient Drug Loading: Encapsulation of Paclitaxel into PEG-b-PCL Micelles

Paclitaxel, an expensive first-line anticancer drug, is known to have better pharmacokinetics and therapeutic efficacy if encapsulated in polymeric micelles. However, the conventional encapsulation methods using incompressible aqueous solutions are limited to low drug loading, less than 3% of micelle weight, and low efficiency, more than two-thirds of the drug in solution remains unencapsulated, and hence wasted, not to mention the burst release problems. This work demonstrates that expansion of near-critical fluid solutions, for example in compressible dimethyl ether and trifluoromethane not too far from their critical region, can lead to a much higher drug loading, for example in micelles formed from poly(ethylene glycol)-block-poly(e-caprolactone) (PEG-b-PCL). By controlling the drug precipitation within the micellar solution region, the loading of paclitaxel in PEG-b-PCL can reach over 12% with a loading efficiency of 87%, which is unattainable by conventional methods. Moreover, the burst release frac...

Synthesis of light hydrocarbons from syngas in near-critical phase

Selective synthesis of light hydrocarbons from synthesis gas (syngas) over hybrid catalysts based on the Cu–Zn oxide and Pd-β zeolite in a near-critical phase was investigated. Light hydrocarbons were directly synthesized from syngas over the catalysts through an intermediate of methanol or DME. Introduction of near-critical fluid remarkably decreased the yield of CO 2 by suppressing the water–gas shift reaction. Differences in activity, CO 2 selectivity, hydrocarbon distributions, catalyst stability and heat transfer between near-critical and conventional gas phase light hydrocarbons synthesis were compared. Efficient removal of reaction heat increased the stability of the catalysts and selectivity of light hydrocarbons in the reaction.

Solubilities and Adsorption Equilibria of β-Carotene in Supercritical and Near-Critical Fluids

A systematic investigation of solubility and adsorption equilibria of β-carotene in carbon dioxide and propane, respectively, at elevated pressures was carried out. Investigated at (303, 313, and 323) K and over a pressure range from (3.2 to 13.4) MPa, the solubility of β-carotene in propane was in the range of (110 to 450) mg·kg−1 propane and approximately 2 orders of magnitude higher than that in supercritical carbon dioxide. Adsorption equilibria of β-carotene in carbon dioxide with a modifier and in propane were studied on nonpolar chromatographic adsorbents. Concerning adsorption equilibria of β-carotene in carbon dioxide with 2-propanol as a modifier, the loading decreases with increasing modifier content and increasing pressure. Regarding the adsorption equilibrium of β-carotene in propane, the loading achieved is much lower than in carbon dioxide due to the higher solubility of β-carotene in propane.

On the transition from thermoacoustic convection to diffusion in a near-critical fluid

Acoustic waves can be generated in response to thermal disturbances near the critical point, due to the diverging compressibility. We study the thermomechanical effect in a slab of supercritical nitrogen subjected to various forms of boundary heating by numerically solving the governing hydrodynamic equations. The results show that, dependent on the rapidity of the heating, inherently different fluid-dynamical wave behaviors occur on the acoustic timescale with respect to acoustic emission, propagation, and reflection patterns. Specifically, the sudden ramp of the boundary temperature is capable of triggering a strong thermoacoustic pulse in the fluid, whose reflection at the isothermal boundary introduces complex features. In contrast, linear compressive waves dominate under the gradual heating. On a longer timescale, both types of fast processes lapse into slow thermal diffusion coupled by pronounced density inhomogeneities, via different routes nonetheless.

Numerical Analysis of Deterioration in Heat Transfer to Near-Critical Rocket Propellants

Liquid propellants, which are typically used for regenerative cooling of rocket thrust chambers, can flow in channels at supercritical pressures and in the neighborhood of pseudocritical temperature (near-critical fluid). This could be for instance the case for the envisioned liquid-oxygen/liquid-methane engines with chamber pressures larger than about 50 bar. When the fluid is in such a near-critical condition, deterioration in heat transfer can occur if the heat transfer level is higher than a threshold value. Aiming to improve flow prediction capabilities for the design of such systems, the present study is devoted to numerical simulations of near-critical fluids flowing in uniformly heated straight tubes. After code validation against experimental data of near-critical-hydrogen flow, numerical simulations of near-critical-methane flow in heated tubes are carried out, each characterized by a different wall heat flux. Results are discussed in detail and the near-critical-methane flow condition that exhibits the heat transfer deterioration is identified and emphasized.

On oscillating flows in randomly heterogeneous porous media

The emergence of structure in reactive geofluid systems is of current interest. In geofluid systems, the fluids are supported by a porous medium whose physical and chemical properties may vary in space and time, sometimes sharply, and which may also evolve in reaction with the local fluids. Geofluids may also experience pressure and temperature conditions within the porous medium that drive their momentum relations beyond the normal Darcy regime. Furthermore, natural geofluid systems may experience forcings that are periodic in nature, or at least episodic. The combination of transient forcing, near-critical fluid dynamics and heterogeneous porous media yields a rich array of emergent geofluid phenomena that are only now beginning to be understood. One of the barriers to forward analysis in these geofluid systems is the problem of data scarcity. It is most often the case that fluid properties are reasonably well known, but that data on porous medium properties are measured with much less precision and spatial density. It is common to seek to perform an estimation of the porous medium properties by an inverse approach, that is, by expressing porous medium properties in terms of observed fluid characteristics. In this paper, we move toward such an inversion for the case of a generalized geofluid momentum equation in the context of time-periodic boundary conditions. We show that the generalized momentum equation results in frequency-domain responses that are governed by a second-order equation which is amenable to numerical solution. A stochastic perturbation approach demonstrates that frequency-domain responses of the fluids migrating in heterogeneous domains have spatial spectral densities that can be expressed in terms of the spectral densities of porous media properties.

Compartmentalization or gravity segregation? Understanding and predicting characteristics of near-critical petroleum fluids

Abstract Compartmentalized reservoirs can be identified based on a variety of criteria most commonly using structural geometries and stratigraphic barriers. This paper reviews several case studies from West African fields in which an additional variable, fluid chemistry, is used to identify compartmentalization at an early stage in the production history. Fluid characterization is important to constrain productivity, connectivity, facilities planning, and commercial value. Near-critical, single-phase fluids offer a case in which underestimation fluid PVT behaviour and variability can have a significant impact on all of these elements – resulting in incorrect interpretations of resource type and distribution.

Temperature-dependent structural arrest of silica colloids in a water–lutidine binary mixture

We study the onset of structural arrest and glass formation in a suspension of silica nanoparticles in a water–lutidine binary mixture near its consolute point. By exploiting the near-critical fluid degrees of freedom to control the strength of an attraction between particles and multispeckle X-ray photon correlation spectroscopy to characterize the particles' collective dynamics, we show that this model liquid undergoes a glass transition both on cooling and on heating, and that the intermediate liquid realizes unusual logarithmic relaxations. We are able to characterize in unprecedented detail how vitrification occurs for the two different glass transitions observed, and draw comparisons to recent theoretical predictions for glass formation in systems with attractive interactions.

Phase behavior and anomalies of thermodynamic properties in a multi-component near-critical fluid mixture

Phase behavior and temperature dependencies of the pressure and isochoric heat capacity C ρ , x near the liquid–vapor critical point of a hydrocarbon ternary mixture (methane + 0.35 mol fr. of propane + 0.15 mol fr. of pentane) have been studied by high-resolution adiabatic calorimetry. The temperature dependence of the pressure has been investigated for ten different isochores in the density range 0.185–0.444 g/cm 3. The heat capacity C ρ , x has been measured for four near-critical isochores. It is shown that in fluid mixtures, in contrast to one-component fluids, an anomaly in the derivative (∂ P/∂ T) ρ , x emerges along with an anomaly in the isochoric heat capacity C ρ , x . A general approach for the description of physical properties of multi-component mixtures in the vicinity of their critical points based on transformation of scaling fields to experimental field variables is addressed in the theoretical part of the paper. The approach enabled us to describe quantitatively all the data obtained in the experiment. The suggested approach is universal since that it does not depend on the number of the components in fluid mixtures.

Thermoacoustic wave propagation and reflection near the liquid-gas critical point

We study the thermoacoustic wave propagation and reflection near the liquid-gas critical point. Specifically, we perform a numerical investigation of the acoustic responses in a near-critical fluid to thermal perturbations based on the same setup of a recent ultrasensitive interferometry measurement in CO2 [Y. Miura, Phys. Rev. E 74, 010101(R) (2006)]. The numerical results agree well with the experimental data. Different features regarding the reflection pattern of thermoacoustic waves near the critical point under pulse perturbations are revealed by the proper inclusion of the critically diverging bulk viscosity.

Experimental Determination of Relative Permeabilities for a Rich Gas/Condensate System Using Live Fluid

Summary Measurement of gas and condensate relative permeabilities typically is performed through steady-state linear coreflood experiments using model fluids. This study addresses experimental measurement of relative permeabilities for a rich gas/condensate reservoir using a live, single-phase reservoir fluid. Using a live, single-phase reservoir fluid eliminates the difficulties in designing a relatively simple model fluid that replicates the complicated thermodynamic and transport properties of a near-critical fluid. Two-phase-flow tests were performed across a range of pressures and flow rates to simulate reservoir conditions from initial production through depletion. A single-phase multirate experiment was also performed to assess inertial, or non-Darcy, effects. Correlations were developed to represent both the gas and condensate relative permeabilities as a function of capillary number. A nearly 20-fold increase in gas relative permeability was observed from the low- to high-capillary-number flow regime. Compositional simulations were performed to assess the impact of the experimental results for vertical- and horizontal-well geometries.