Effects of Fracture Boundary Conditions on Matrix-fracture Transfer Shape Factor

The matrix-fracture transfer shape factor is one of the important parameters in modeling naturally fractured reservoirs. Four decades after Warren and Root (1963, SPEJ, 245–255.) introduced the double porosity concept and suggested a relation for it, this parameter is still not completely understood. Even for a single-phase flow problem, investigators report different shape factors. This study shows that for a single-phase flow in a particular matrix block, the shape factor that Warren and Root defined is not unique and depends on the pressure in the fracture and how it changes with time. We use the Laplace domain analytical solutions of the diffusivity equation for different geometries and different boundary conditions to show that the shape factor depends on the fracture pressure change with time. In particular, by imposing a constant fracture pressure as it is typically done, one obtains the shape factor that Lim and Aziz (1995, J. Petrolean Sci. Eng. 13, 169.) calculated. However, other shape factors, similar to those reported in other studies are obtained, when other boundary conditions are chosen. Although, the time variability of the boundary conditions can be accounted for by the Duhamel’s theorem, in practice using large time-steps in numerical simulations can potentially introduce large errors in simulation results. However, numerical simulation models make use of a stepwise approximation of this theorem. It is shown in this paper that this approximation could lead to large errors in matrix-fracture transfer rate if large time-steps are chosen.     

Phase-Change Materials Exhibiting Tristability: Interconverting Forms of Crystalline α-, β-, and Glassy K(2)ZnSn(3)S(8)

We show that K(2)ZnSn(3)S(8) is a phase-change system that exhibits tristability. Kinetic and thermodynamic forms of different compounds in the K/Zn/Sn/S system have been synthesized and thoroughly characterized. We report an example where slow and rapid cooling of a melt of K(2)CO(3)/S/Sn/Zn leads to different kinetically stable products (crystalline layered α-K(2)ZnSn(3)S(8), 1, and glassy K(2)ZnSn(3)S(8), A, respectively). These forms convert to a thermodynamically stable compound (crystalline cubic β-K(2)ZnSn(3)S(8), 2) upon annealing below their melting points. The band gaps of compounds 1, A, and 2 are 2.30, 2.15, and 2.55 eV, respectively.     

Copper(II) and nickel(II) complexes of tetradentate Schiff base ligand: UV-Vis and FT-IR spectra and DFT calculation of electronic,vibrational and nonlinear optical properties

The experimental fourier transform infrared (FT-IR) and ultraviolet-visible (UV-Vis) spectra of copper(II) and nickel(II) complexes of the deprotonated tetradentate Schiff base ligand N,N′-bis(2-hydroxybenzylidene)-2,2-dimethyl-1,3-propanediamine (H₂L) are compared with their corresponding theoretical ones. The applied theoretical method is based on the density functional theory and time-dependent density functional theory at the UPBE0/PBE0 levels using Def2-TZVP basis set. The computational optimised geometric parameters of the complexes are in good agreement with their corresponding experimental data. The FT-IR and UV-Vis spectra of the complexes were reproduced on the basis of their optimised structures. The vibrational assignments of some fundamental modes of the complexes are performed. The highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) energies are calculated. The analyses of the calculated electronic absorption spectra of the complexes are carried out to elucidate the electronic transitions assignments and their characters. Second-order nonlinear optical property of the complexes is evaluated by the above-mentioned theoretical method that implies much greater values for the complexes in comparison with the corresponding value of urea.     

On Vanishing and Cofiniteness of Generalized Local Cohomology Modules

Pure braid groups and pure mapping class groups of a punctured sphere have many features in common. In this article, we study the graded Lie algebra of the descending central series of the pure mapping class group of a 2-sphere. A simple presentation of this Lie algebra is obtained.     

Asymptotic Behaviour and Artinian Property of Graded Local Cohomology Modules

In this article, considering the difference between the finiteness dimension and cohomological dimension of a finitely generated graded module, we investigate the asymptotic behaviour of grades of components of a graded local cohomology module with respect to the irrelevant ideal. To this end, we study some Artinian and tameness properties of certain graded local cohomology modules.     

Assessment of thermal performance of the functionally graded materials in annular fins

Heat transfer enhancement in the annular fins with uniform profile is investigated in the present study. Conventional fin materials are replaced with the functionally graded materials in order to increase the rate of heat transfer and corresponding fin efficiency. Here, the fin material properties, such as conductivity, are assumed to be graded along the annular fin radius, R, as a linear function. The governing equation of the annular fin is computed with an approximate analytical method using the mean value theorem. It is revealed that the in-homogeneity index, β, of the fin material plays an important role on the thermal characteristics of the annular fins. Alternatively, heat dissipation between the fin surface and surrounding fluid in the annular fins increases with increasing the inhomogeneity indices, β. Finally, it is stated that application of the functionally graded material in the annular fins enhances the fin efficiency in comparison to the annular fins with homogeneous material. It is hoped that the results obtained from this study arouse interest among thermal designers and heat exchanger industries.     

Prediction of CO2 and H2 solubility,diffusion, and permeability in MFI zeolite by molecular dynamics simulation

Structural Chemistry - Molecular dynamics simulation has been employed to calculate the amounts of solubility, diffusion coefficient, and permeability for the pure and volumetric binary mixture of...     

Synthesis of SnO<Subscript>2</Subscript> nanopowders by a sol-gel process using propanol-isopropanol mixture

A simple sol-gel process is proposed for synthesizing SnO₂ nanopowders utilizing normal propanol and isopropanol mixture instead of just using normal alcohols such as ethanol, propanol or butanol for Sol preparation. No surfactant was used in this Sol preparation process. The structure of sol is studied by FT-IR-ATR technique. On altering propanol to isopropanol ratio, three different nanopowders were obtained. X-ray powder diffraction, high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction pattern (SAED) and BET techniques were used to characterize prepared powders. Results show that smaller grain size was obtained via altering alcohols ratio. In addition, Merck commercial SnO₂ powder was also used as a reference material for comparing purposes; because it has nanometer scale (ca. 60 nm). HRTEM images show that obtained nanopowders were polycrystalline and their average diameters fall into the range of 6–80 nm. Finally, the effect of alkoxide ligand size through sol-gel synthesis on product particle size is discussed.