Analytical investigation of boundary layer growth and swirl intensity decay rate in a pipe

In this research, the developing turbulent swirling flow in the entrance region of a pipe is investigated analytically by using the boundary layer integral method. The governing equations are integrated through the boundary layer and obtained differential equations are solved with forth-order Adams predictor-corrector method. The general tangential velocity is applied at the inlet region to consider both free and forced vortex velocity profiles. The comparison between present model and available experimental data demonstrates the capability of the model in predicting boundary layer parameters (e.g. boundary layer growth, shear rate and swirl intensity decay rate). Analytical results showed that the free vortex velocity profile can better predict the boundary layer parameters in the entrance region than in the forced one. Also, effects of pressure gradient inside the boundary layer is investigated and showed that if pressure gradient is ignored inside the boundary layer, results deviate greatly from the experimental data.     

On the unsteady-state species separation of a binary liquid mixture in a rectangular thermogravitational column

This paper investigates the unsteady-state species segregation of binary liquid mixtures in rectangular thermogravitational columns. The analysis leads to a procedure to obtain both molecular and thermal diffusion coefficients from transient separation measurements. Two models are presented: first, an ideal model where buoyancy only depends on temperature and second, a general model where buoyancy also varies with composition. Steady-state measurements are not required regardless of which model is chosen. As a result, the new procedure is faster than steady-state procedures. When either the molecular or thermal diffusion coefficient is known a priori, the other can be obtained without knowledge of fluid properties such as density, viscosity, thermal expansion, and compositional coefficients.     

An efficient method for discretizing 3D fractured media for subsurface flow and transport simulations

We introduce a new method to discretize inclined non‐planar two‐dimensional (2D) fractures in three‐dimensional (3D) fractured media for subsurface flow and transport simulations. The 2D fractures are represented by ellipsoids. We first discretize the fractures and generate a 2D finite element mesh for each fracture. Then, the mesh of fractures is analyzed by searching and treating critical geometric configurations. Based on that search, the method generates a quality mesh and allows for including finer grids. A solute transport problem in fractured porous media is solved to test the method. The results show that the method (i) adequately represents the fractured domain by maintaining the geometric integrity of input surfaces and geologic data, (ii) provides accurate results for both simple and complex fractured domains, (iii) is insensitive to spatial discretization, and (iv) is computationally very efficient. For inclined and vertical fractures, analytical and numerical solutions are shown to be in good agreement. The method is therefore suitable to discretize fracture networks for flow and transport simulations in fractured porous media. Copyright © 2010 John Wiley & Sons, Ltd.     

Permanent Alteration of Porous Media Wettability from Liquid-Wetting to Intermediate Gas-Wetting

Wettability of Berea and low permeability reservoir rocks are permanently altered from liquid-wetting to intermediate gas-wetting. We use water and decane as model liquid, and air and nitrogen as model gas in the experiments. New chemicals with various functional groups are used in the wettability alteration. We perform compositional analyses of the treated chemical solutions extracted from rock treatment by gas chromatography–mass spectrometry (GCMS) and by inductively coupled plasma-mass spectrometry (ICPMS). The analyses demonstrate reaction between the chemicals and the rock substrate. There is no measurable change in permeability from the chemical reaction for the low molecular weight chemicals. The results reveal the permanent alteration of wettability. Tests are conducted to measure contact angle, spontaneous imbibition, and flow to assess the effect of wettability alteration on flow performance as a function of chemical concentration and functionality. For Berea, the contact angle for the water–air–rock is altered from 0° to ~150° depending on the chemical concentration. For the reservoir rock, the contact angle is altered from ~70° to ~130°. As a result of the treatment, the water flow rate may increase two and a half times for a given pressure drop in the Berea. The permanent alteration of wettability with the new chemicals is intended for prevention of water blocking in gas production from tight reservoirs. Instead of hydraulic fracturing when water is introduced in formations with most of the water retained by the water-wet rocks, one may use the new chemical surfactants in fracturing to avoid water retention for high gas well productivity.     

Four-body calculation of <Superscript>12</Superscript>C(<Emphasis Type="Italic">α, γ</Emphasis>)<Superscript>16</Superscript>O radiative capture reaction at stellar energies

On the basis of the four-alphamodel, the ¹²C(α, γ)¹⁶Oradiative capture process is investigated by using the four-body Faddeev–Yakubovsky equations as well as the two- and three-body electromagnetic currents. The present calculation is an application of our current conservation realistic potentials method for the ¹²C(α, γ)¹⁶Oradiative capture process. This work clears the way formore refinedmodels of radiative capture based on two- and three-body realistic potentials and current conservation. The calculation is carried out by considering the ⁴He + ¹²C (1 + 3) and the ⁸Be + ⁸Be (2 + 2) subamplitudes, respectively. Radiative capture ¹²C(α, γ)¹⁶Oreaction is one of the most important reactions in nuclear astrophysics. For this reaction, the electric dipole transitions between states with the same isospin are forbidden in the first order. Because the state 1⁺ and 0⁺ ground state nuclei ¹⁶O have zero isospin, thus the electric dipole radiations are not at the first order between two levels and electric dipole radiation will be the second order and electric dipole radiation is the same order as the electric quadrupole radiation. Therefore, we must consider the effects of both radiations. In comparison with other theoretical methods and available experimental data, good agreement is achieved for the E₁ and E₂ contribution to the cross section and the astrophysical S factor for this process.     

On measurement of thermal diffusion coefficients in multicomponent mixtures

We investigate the steady-state separation of the individual components of an incompressible multicomponent liquid mixture in a narrow two-dimensional thermogravitational column. Analytic working equations for measuring thermal diffusion coefficients analogous to the existing equations for a binary mixture are derived. Similar to the binary results, we find that when compositional variation has negligible effect on fluid density and vertical diffusive flux can be ignored, molecular diffusion does not affect steady-state separation. However, when compositional effects on density are taken into account, molecular diffusion does affect the bulk convective flow and the steady-state separation of the components. There may be also two distinct trends in the velocity and separation profiles. With one or more negative thermal diffusion coefficients, there may be more than one convection cell resulting in oscillatory behavior of separation. The working equations presented can be used to measure thermal diffusion coefficients of multicomponent mixtures. Such measurements have not yet been reported in the literature.     

Simple Woods-Saxon-type form for Ωα and Ξα interactions using folding model

We derive a simple Woods-Saxon-type form for potentials between Y=Ξ,Ωandαusing a single-folding potential method,based on a separable Y-nucleon Potential.The PotentialsΞ+αandΩ+αare accordingly obtained using the ESC08 c Nijmegens potential(in 3 S1 channel)and HAL QCD collaborationΩN interactions(in lattice QCD),respectively.In deriving the potential between Y andα,the same potential between Y and N is employed.The binding energy,scattering length,and effective range of the Y particle on the alpha particle are approximated by the resulting potentials.The depths of the potentials inΩαandΞαsystems are obtained at-61 MeV and-24.4 MeV,respectively.In the case of theΞαpotential,a fairly good agreement is observed between the single-folding potential method and the phenomenological potential of the Dover-Gal model.These potentials can be used in 3-,4-and 5-body cluster structures ofΩandΞhypernuclei.     

Wettability Alteration to Intermediate Gas-Wetting in Porous Media at Elevated Temperatures

Wettability alteration to intermediate gas-wetting in porous media by treatment with FC-759, a fluorochemical polymer has been studied experimentally. Berea sandstone was used as the main rock sample in our work, and its wettability before and after chemical treatment was studied at various temperatures from 25 to 93°C. We also studied recovery performance for both gas/oil and oil/water systems for Berea sandstone before and after wettability alteration by chemical treatment. Our experiment shows that chemical treatment with FC-759 can result in: (1) wettability alteration from strong liquid-wetting to stable intermediate gas-wetting at room temperature and at elevated temperatures; (2) neutral wetting for gas, oil, and water phases in two-phase flow; (3) significant increase in oil mobility for gas/oil system; and (4) improved recovery behavior for both gas/oil and oil/water systems. This work reveals a potential for field application for improved gas-well deliverability and well injectivity by altering the rock wettability around wellbore in gas condensate reservoirs from strong liquid-wetting to intermediate gas-wetting.