Stability of a moving interface in porous medium for non-newtonian displacing fluids and its applications in oil displacement mechanism

Summary In this paper a theoretical analysis regarding the rheological effects of non-Newtonian behavior of the displacing fluid on the stability of a moving interface in a porous medium. separating two immiscible and incompressible fluids, is performed. Conditions under which a piston-like displacement could be maintained in oil displacement mechanism with a non-Newtonian displacing fluid of power law are shown and discussed, with regard to the possibility of improving oil recovery from polymer flooding projects used in oil reservoir engineering.Nomenclature h layer thickness - H consistency index - k permeability - n rheological parameter for power law fluids - p pressure distribution - V interface velocity - v velocity - porosity - ₀ threshold gradient - viscosity - _ef effective viscosity - _ap apparent viscosity - ₀ yield stress - angle to the upward vertical     

Gevrey Order and Summability of Formal Series Solutions of some Classes of Inhomogeneous Linear Partial Differential Equations with Variable Coefficients

We investigate Gevrey order and summability properties of formal power series solutions of some classes of inhomogeneous linear partial differential equations with variable coefficients and analytic initial conditions. In particular, we give necessary and sufficient conditions under which these solutions are convergent or are k-summable, for a convenient k, in a given direction.     

Formation of Additive-Containing Nanothermites and Modifications to their Friction Sensitivity

Nanothermites can provide high energy densities and reaction rates but can also display extreme friction sensitivities. Additives that provide friction modification offer the potential to reduce the friction sensitivity of nanothermites. In the present work, MoS₂, graphene, and hexadecane additives were dispersed in MoO₃ prior to nanothermite formation with the aim of reducing friction sensitivity. Nanothermites were subsequently prepared using a palmitic acid–passivated nano-aluminum (L-Al) and additive-containing nano-MoO₃ by the resonant acoustic mixing of dry powders. In general, the incorporation of additives results in a reduction in friction sensitivity with the baseline minimum ignition friction rising from 10 to 120 N using 0.5% wt/wt micrometer-sized MoS₂ or 5% wt/wt hexadecane. However, the relationships between loading and performance are complex and vary by additive; for example, the friction sensitivity dependence using micrometer-diameter MoS₂ displays a maximum at 0.5% wt/wt and declines to 7 N using 5% MoS₂.     

Bio-Sourced Poly l-Lactide-Flax Composites with Close to Maximum Stiffness at Low Fiber Content through Two-Stage Annealing

Poly l -Lactide (PLLA) composites with short flax fibers (from 0 to 10 wt/wt%) with close to maximum theoretical stiffness are prepared by melt-compounding and injection-molding followed by a two-step isothermal crystallization protocol that fully separates the nucleation and growth stages (Tammann). The use of fast chip scanning calorimetry for thermal characterization avoids the complicating issues of crystal reorganization during the cooling and heating steps between the isothermal stages. Flax fibers are very efficient and selective nucleating agents of PLLA favoring the ordered α form. The resulting morphology exhibits trans-crystallization on the fibers surface, predominantly at fiber defects, with a clear reduction of crystal size and a very strong fiber matrix cohesion. Efficient nucleation further leads to a large reduction of the overall crystallization time. Avrami analysis evidences a reduction of crystal growth dimensionality, consistent with both optical and scanning electron microscopy. The high modulus of the composites is unambiguously related to the strong orientation of the fibers in the tensile direction, to their high aspect ratio and to the excellent matrix-fibers cohesion. On the other hand, the tensile strength and hardness appear isotropic within experimental uncertainty and are unfavorably influenced by the presence of the fibers and by the two-stage annealing.     

SiSiC Heat Exchangers for Recuperative Gas Burners with Highly Structured Surface Elements

Heat exchangers are used in gas burners as recuperators. Their efficiency is proportional to their surface which is usually limited by the burner length and diameter. Ceramic recuperators used nowadays in industrial burners are tubular. We studied and developed a new generation of ceramic heat exchanger with the final goal of increasing the efficiency or, at similar efficiencies, of reducing their size and weight. A commercial SiSiC heat exchanger component was used to guarantee safety and robustness. The use of structured textile geometries followed by their conversion into a ceramic is the main innovation of this work.     

Determination of steroid hormones in bovine milk by LC-MS/MS and their levels in Swiss Holstein cow milk

Synthetic and natural steroid hormones have attracted some attention in recent years as endocrine active substances (EAS) that interact or interfere with the endocrine system. Endogenous hormones occur naturally in food of animal origin, among which bovine milk represents an important source. This study was conducted to determine the occurrence of steroid hormones (oestrogens, androgens, progestogens and glucocorticoids) in cow’s milk samples from three farms in Switzerland. An isotope dilution liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed and validated for the quantification of 12 hormones in milk. Some hormonal levels from individual cows showed large variations. The average levels of the hormones analysed (17α-estradiol = 31 ng kg^–1, 17β-estradiol = 6 ng kg^–1, estrone = 159 ng kg^–1, 4-androstenedione = 684 ng kg^–1, progesterone = 15486 ng kg^–1, 17-hydroxyprogesterone = 214 ng kg^–1, cortisone = 112 ng kg^–1, and cortisol = 235 ng kg^–1) were comparable with literature data. Estriol, testosterone and androstenediols were not detected at their respective limit of quantification. No significant differences of hormonal content among milk from cows at different lactation/calving numbers were evidenced, except for progesterone and 4-androstenedione. Due to confounding parameters linked to the physiological stage of the animal, like pregnancy and gestational stage (pregnancy trimester), the causal correlation between the variation of the levels for these two hormones and the lactation/calving number could not be unambiguously demonstrated.     

Exploring the statistical applicability of the Poincaré inequality: a test of normality

A new test of normality based on Poincaré inequality is proposed and analyzed. It rests on the characterization of the normal distribution given by Borovkov and Utev, i.e., a r.v. is normal if and only if its Poincaré constant is equal to its variance.     

Modeling and control of a direct laser powder deposition process for Functionally Graded Materials (FGM) parts manufacturing

Functionally Graded Materials (FGM) parts are heterogeneous objects with material composition and microstructure that change gradually into the parts. The distinctive feature of FGM structure gives the possibility of selecting the distribution of properties to achieve the desired functions. Today, multi-material parts manufactured with additive manufacturing processes are not functional. To move from these samples to functional and complex parts, it is necessary to have an overall process control. This global approach requires a control of process parameters and an optimal manufacturing strategy. This paper presents a process modeling and a system control to manufacture FGM parts with a direct laser deposition system. This works enable to choose an adapted manufacturing strategy and control process parameters to obtain the required material distribution and the required geometry.     

Interfacial Reactions During Titanium Dissolution in Liquid Iron: A Combined Experimental and Modeling Approach

The dissolution behavior of Ti in liquid Fe has been investigated experimentally and theoretically within the framework of inclusion formation in steel. In the experimental study, Ti cylinders have been immersed into liquid Fe and, subsequently, water-quenched. Macroscopic observation of quenched samples shows the initial solidification of an Fe shell around the Ti. Microstructural analysis of the Fe-Ti interfacial area with a scanning electron microscope equipped with an energy dispersive X-ray spectrometer reveals that a reaction zone develops in a three-step process: formation of a first liquid eutectic layer rich in Ti, formation of a second eutectic layer rich in Fe, and then mixing of both layers. The reaction zone grows in thickness up to 40 pct of the original sample radius and dissolves both parts of the Ti sample and the Fe shell. A simplified, one-dimensional, implicit finite volume model has been used to describe these phenomena theoretically. Good qualitative agreement is achieved between experiment and model. The model has been used to estimate the influence of original addition size, preheating, convection, and superheating on the required melt-back time.     

Cellular genetic algorithms without additional parameters

Cellular genetic algorithms (cGAs) are a kind of genetic algorithms (GAs) with decentralized population in which interactions among individuals are restricted to close ones. The use of decentralized populations in GAs allows to keep the population diversity for longer, usually resulting in a better exploration of the search space and, therefore, in a better performance of the algorithm. However, it supposes the need of several new parameters that have a major impact on the behavior of the algorithm. In the case of cGAs, these parameters are the population and neighborhood shapes. We propose in this work two innovative cGAs with new adaptive techniques that allow removing the neighborhood and population shape from the algorithm’s configuration. As a result, the new adaptive cGAs are highly competitive (statistically) with all the compared cGAs in terms of the average solutions found in the continuous and combinatorial domains, while finding, in general, the best solutions for the considered problems, and with less computational effort.