Non-Newtonian effects in the peristaltic flow of a Maxwell fluid

We analyzed the effect of viscoelasticity on the dynamics of fluids in porous media by studying the flow of a Maxwell fluid in a circular tube, in which the flow is induced by a wave traveling on the tube wall. The present study investigates novelties brought about into the classic peristaltic mechanism by inclusion of non-Newtonian effects that are important, for example, for hydrocarbons. This problem has numerous applications in various branches of science, including stimulation of fluid flow in porous media under the effect of elastic waves. We have found that in the extreme non-Newtonian regime there is a possibility of a fluid flow in the direction {\it opposite} to the propagation of the wave traveling on the tube wall.Comment: to Appear in Phys. Rev. E., 01 September 2001 issu

Theory of Breakup of Core Fluids Surrounded by a Wetting Annulus in Sinusoidally Constricted Capillary Channels

Analysis of core-annular dynamics in the presence of base flow for arbitrary fluid viscosities leads to an equation describing the temporal evolution of the fluid/fluid interface. The equation follows from the conservation of mass in the small-slope approximation. Its useful applications occur, for example, in chemical engineering and petroleum recovery. The nonlinear equation allows inexpensive numerical analysis. For sinusoidally constricted pores, a purely geometric criterion exists that enables or prohibits the core-fluid breakup in the necks of the constrictions. The geometrically favoring condition sets up capillary-pressure gradients that ensure a continuous outflow of the core fluid from the necks into the crests of the profile. Such behavior is indeed observed in the numerical solutions of the evolution equation. For relatively large slopes of the initial configuration, setting up larger pressure gradients, the interface shape remains smooth, the evolution times are relatively fast, and the breakup is typically achieved by the growing film-fluid collar touching the axis of the channel at a single point. No satellite droplets are produced. Decreasing the slope lengthens the evolution times, allowing the formation and growth of wavy disturbances on the initial interface profile, which may touch the axis of the capillary in several places forming satellite drops. Thinner initial annuli also slow down the evolution process. Instability develops for the cases of the core both more and less viscous than the film. Finally, if the geometry prohibits the snap-off altogether, the initial interface configurations decay into steady-state solutions, and no breakup takes place. The solutions of the evolution equation validate well against two computational-fluid-dynamics codes

Viscosity Effects in Vibratory Mobilization of Residual Oil

The last decade has seen clarifications of the underlying capillary physics behind stimulation of oil production by seismic waves and vibrations. Computational studies have prevailed, however, and no viscous hydrodynamic theory of the phenomenon has been proposed. For a body of oil entrapped in a pore channel, viscosity effects are naturally incorporated through a model of two-phase core-annular flow. These effects are significant at the postmobilization stage, when the resistance of capillary forces is overcome and viscosity becomes the only force resisting an oil ganglion\u27s motion. A viscous equation of motion follows, and computational fluid dynamics (CFD) establishes the limits of its applicability. The theory allows inexpensive calculation of important geophysical parameters of reservoir stimulation for given pore geometries, such as the frequency and amplitude of vibrations needed to mobilize the residual oil. The theoretical mobilizing acceleration in seismic waves for a given frequency is accurate to within approximately 30% or better when checked against CFD. The advantages of the viscous theory over the inviscid one are twofold. The former can calculate complete time histories of forced displacement of an oil blob in a pore channel, including retardation by capillary forces, mobilization by vibrations, and an ensuing Haines jump. It also provides an approximately factor-of-two improvement in the calculation of the mobilizing acceleration needed to unplug a static ganglion

Nano-reinforced Quartz Composites

We have studied the process of interaction between the components in the system «β-SiO2–Fe3O4–Na2O» in the temperature range from 20 to 1100 °C. Nano-reinforced composite building materials were developed on the base of quartz raw material. Developed materials are produced by low-temperature cal-cining technology. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3524

Nano-reinforced Quartz Composites

We have studied the process of interaction between the components in the system «β-SiO2–Fe3O4–Na2O» in the temperature range from 20 to 1100 °C. Nano-reinforced composite building materials were developed on the base of quartz raw material. Developed materials are produced by low-temperature cal-cining technology. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3524

Features of Investigations of Multilayer Nitride Coatings Based on Cr and Zr

The studies of the structure and properties of nanoscale multilayer coatings of Zr- and Cr-based refractory metals obtained by the vacuum arc cathode deposition are summarized in a brief review of the literature data. A comparative analysis of the microstructure and properties of ZrN/CrN composite coatings depending on the deposition conditions (constant negative potential of the substrate, pulsed high-voltage bias potential, partial pressure, reaction gas velocity) and modulation period for multilayered structure is carried out. General regularities consisting in the presence of the columnar structure and the growth texture are revealed. They show that there is a prevailing (111) orientation for investigated coatings. Conditions for obtaining improved physical, mechanical, and tribological properties of the coatings are determined.В кратком обзоре литературных данных обобщены результаты исследований структуры и свойств наномасштабных многослойных покрытий нитридов тугоплавких металлов на основе Zr и Cr, полученных методами вакуумно-дугового осаждения катода. Проведён сравнительный анализ микроструктуры и свойств композиционных покрытий ZrN/CrN в зависимости от условий осаждения (постоянного или импульсного отрицательного потенциала подложки, импульсного высоковольтного потенциала смещения, парциального давления, скорости потока рабочего газа) и периода модуляции многослойной структуры. Выявлены общие закономерности, состоящие в наличии столбчатой структуры и текстуры роста. Показано, что для исследуемых покрытий имеет место преимущественная ориентация (111). Установлены условия получения улучшенных физико-механических и трибологических характеристик покрытий.У короткому огляді літературних даних узагальнено результати досліджень структури та властивостей наномасштабних багатошарових покриттів тяжкотопких металів на основі Zr та Cr, одержаних методами вакуумно-дугового осадження катоди. Проведено порівняльну аналізу мікроструктури та властивостей композиційних покриттів ZrN/CrN, залежно від умов осадження (постійного неґативного потенціялу підложжя, імпульсного високовольтного потенціялу зміщення, парціяльного тиску, швидкости потоку робочого газу) та періоду модуляції багатошарової структури. Виявлено загальні закономірності, що полягають у наявності стовпчастої структури та текстури росту. Показано, що для досліджуваних покриттів має місце переважна орієнтація (111). Визначено умови одержання поліпшених фізико-механічних і трибологічних властивостей покриттів

Pocket Deformable Mirror for Adaptive Optics Applications

Adaptive/active optical elements are designed to improve optical system performance in the presence of phase aberrations. For atmospheric optics and astronomical applications, an ideal deformable mirror should have sufficient frequency bandwidth for compensation of fast changing wave front aberrations induced by either atmospheric turbulences or by turbulent air flows surrounding a flying object (air optical effects). In many applications, such as atmospheric target tracking, remote sensing from flying aircraft, boundary layer imaging, laser communication and laser beam projection over near horizontal propagation paths the phase aberration frequency bandwidth can exceed several kHz. These fast-changing aberrations are currently compensated using relatively small size (a few inches or less) deformable mirrors, such as micro-electromechanical systems (MEMS) based DMs [1], piezoelectric deformable mirrors based on semi-active or passive bimorph elements (bimorph mirrors) [2,3], or DMs with an array of push-pull type actuators [4-8]. These DMs are difficult to scale to larger size without either significant reduction of their operational speed or substantial increase of optical system complexity and cost, when DM scaling is performed by combining small size DMs to a larger size phased array. To match small size DM diameter d the optical telescope aperture of diameter D\u3e\u3ed is re-imaging with demagnification factor M = D/d. In most practical applications the demagnification factor M can be extremely large (on the order of 100 or even more). Re-imaging of the telescope pupil with a high magnification factor requires installation of additional optical elements, including one or more optical relay systems, resulting in a substantial increase of size, weight, and cost of the entire optical system. This high magnification factor also makes it highly sensitive to vibrations, “high g” and high-thermal gradient environmental factors. The deformable mirror described in the presented paper intends to overcome the mentioned drawbacks of the existing DMs by offering the deformable mirror design scalable up to the aperture diameter of the optical telescope primary mirror. The proposed Pocket-DM (PDM) can be directly used as a primary adaptive mirror of optical telescope and laser beam delivery system eliminating the need for additional optical elements used for incorporation of a small size DM into telescope optical train

Enhacement in the dymanic response of a viscoelastic fluid flowing through a longitudinally vibrating tube

We analyzed effects of elasticity on the dynamics of fluids in porous media by studying a flow of a Maxwell fluid in a tube, which oscillates longitudinally and is subject to oscillatory pressure gradient. The present study investigates novelties brought about into the classic Biot's theory of propagation of elastic waves in a fluid-saturated porous solid by inclusion of non-Newtonian effects that are important, for example, for hydrocarbons. Using the time Fourier transform and transforming the problem into the frequency domain, we calculated: (A) the dynamic permeability and (B) the function $F(\kappa)$ that measures the deviation from Poiseuille flow friction as a function of frequency parameter $\kappa$. This provides a more complete theory of flow of Maxwell fluid through the longitudinally oscillating cylindrical tube with the oscillating pressure gradient, which has important practical applications. This study has clearly shown transition from dissipative to elastic regime in which sharp enhancements (resonances) of the flow are found

High Entropy Alloys Based on Nitrides of Refractory Metals – a New Solution for Protective Coatings on the Instruments Working at High Temperatures

The coatings based on (Ti-Al-Zr-Nb-Y)N and (Ti-Zr-Hf-V-Nb-Ta)N were obtained by means of vacuum-arc deposition from the cathodes based on Ti+Al+Zr+Nb+Yand Ti+Zr+Hf+V+Nb+Tasystems in the atmosphere of nitrogen. Their physical and mechanical properties, as well as tribotechnical characteristics have been studied. The coatings are characterized by a columnar structure and their hardness reaches 51.02GPa. The adhesion strength of the coatings has also been studied, the coefficient of friction of the system “coating – Al2O3“ is 1.1.The results of tribological tests at high temperature showed that at 460 °C coatings had greater wear resistance, lower coefficient of friction compared to similar tests of coatings at 20 °C.These coatings are perspective as protective coatings for friction pairs and cutting tools