Pressure losses in a conduit with a venturi tube

We present the experimental relationships for the coefficient of kinetic flow energy and static pressure as a function of conduit length following a Venturi tube. A formula is proposed for the determination of the coefficient of the hydraulic resistance of the Venturi tube as a function of its structural parameters, as well as a function of the length of the straight segment of the conduit behind the Venturi tube.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 16, No. 4, pp. 731–736, April, 1969.     

Contact interaction between a rigid die and an elastic layer in nonstationary frictional heat generation

Consideration is given to a new quasistatic contact thermoelasticity problem for an elastic layer fixed at its base and on whose surface a rigid heat-insulated die moves, when the interaction of the bodies is accompanied by the heat generation from the action of friction forces. Under the assumption that the process of heat generation is nonstationary, the problem has been reduced to an integral equation with integration limits varying with time. It has been shown that an increase in the heat-generation intensity produces a decrease in the upsetting of the die and equilibrium is possible for its negative values with decrease in the contact portion; for a die with a plane base this is equivalent to the separation of the body from the layer at the edges of the interaction interval. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 79, No. 1, pp. 185–195, January–February, 2006.     

Method for estimating off-axis pulse tube losses

Some Stirling-type pulse tube cryocoolers (PTCs) exhibit sensitivity to gravitational orientation and often exhibit significant cooling performance losses unless situated with the cold end pointing downward. Prior investigations have indicated that some coolers exhibit sensitivity while others do not; however, a reliable method of predicting the level of sensitivity during the design process has not been developed. In this study, we present a relationship that estimates an upper limit to gravitationally induced losses as a function of the dimensionless pulse tube convection number (N_PTC) that can be used to ensure that a PTC would remain functional at adverse static tilt conditions. The empirical relationship is based on experimental data as well as experimentally validated 3-D computational fluid dynamics simulations that examine the effects of frequency, mass flow rate, pressure ratio, mass-pressure phase difference, hot and cold end temperatures, and static tilt angle. The validation of the computational model is based on experimental data collected from six commercial pulse tube cryocoolers. The simulation results are obtained from component-level models of the pulse tube and heat exchangers. Parameter ranges covered in component level simulations are 0–180° for tilt angle, 4–8 for length to diameter ratios, 4–80 K cold tip temperatures, −30° to +30° for mass flow to pressure phase angles, and 25–60 Hz operating frequencies. Simulation results and experimental data are aggregated to yield the relationship between inclined PTC performance and pulse tube convection numbers. The results indicate that the pulse tube convection number can be used as an order of magnitude indicator of the orientation sensitivity, but CFD simulations should be used to calculate the change in energy flow more accurately.     

Induced flow in a curved tube by the oscillations of a rigid axial core

Summary When a rigid core in a curved tube of circular cross-section oscillates axially, the contained fluid acquires a composite motion that depends on the radius of the core relative to the radius of the tube and on the frequency of oscillation. For small values of the frequency, analytic solutions are derived for the axial and secondary flow, giving the flow configuration.With 4 Figures     

Thermoelastic contact problem for a layer interacting with a rigid substrate under transient frictional heat generation conditions

A thermoelastic problem has been solved for the interaction between an elastic layer and a rigid substrate from which a body may come off under localized pressing load. The paper addresses the influence of an accompanying transient frictional heat generation and functional relation of a pressing load on the process of the layer displacement over the surface of a heat-insulated substrate. It is demonstrated that an increase in heat generation intensity reduces the contact area, where the time variation of the latter is governed by selection of a load function and a motion speed function: if the load is time dependent, the contact area remains unchanged; if the speed varies, the contact area exhibits a monotonic reduction. __________ Translated from Problemy Prochnosti, No. 3, pp. 132–151, May–June, 2008.     

Heat losses in the plenum chamber of a gasdynamic laser by simulation in a shock tube

It is shown that the heat losses in the plenum chamber of gasdynamic laser simulated in a shock tube do not significantly affect the operating conditions of the laser apparatus under investigation.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 39, No. 3, pp. 486–490, September, 1980.     

Finite deformation analysis of a thin-walled tube sliding on a rough rigid rod

A thin-walled tube of finite length composed of a neo-Hookean material is sliding on a rough rigid rod under the action of forces distributed on its leading edge. A perturbation method is used to determine the stress and shape of the deformed tube to the second-order.     

Quasiharmonic oscillations of a two-mass frictional self-excited system with energy losses under conditions of periodic external perturbations

A generalized investigation of admissible quasiharmonic modes is performed within the framework of the first “refined” asymptotic approximation for a mechanical self-excited system with aftereffect under the conditions of weak periodic external perturbations. Ukrainian Transport University, Kiev, Ukraine. Translated from Problemy Prochnosti, No. 4, pp. 105–115, July–August, 1999.     

An exact analysis of sliding frictional contact of a rigid punch over the surface of magneto-electro-elastic materials

This article performs an exact analysis for a frictional triangular or cylindrical punch acting on the surface of magneto-electro-elastic materials. The punch moves relative to the surface of magneto-electro-elastic materials. Inside the contact area, the Coulomb friction law is applied. Eigenvalue distribution is analyzed, and then appropriate fundamental solutions are given. The stated problem is reduced to a system of singular integral equations of the second kind. The exact solution of the obtained singular integral equations makes it easy to get the explicit expressions of the surface physical quantities. Through plotting figures, the influences of the friction coefficient on contact behavior are shown and interesting results are observed. The in-plane stress, electric displacement and magnetic induction tend to be infinite near the leading edge of the frictional triangular punch, while having spikes at one edge of the frictional cylindrical punch, which may explain why surface damage occurs on the surface of magneto-electro-elastic materials.     

The dynamic contact with perfect adhesion and frictional slip between a rigid indentor and an elastic half-space

Summary The problem of the dynamic indentation in loading of an elastic half-space by a rigid axisymmetric punch when a finite friction in the contact region is assumed to exist is considered. The problem involves the determination of a timedependent unknown contact area which is composed of an adhesive circular region whose time-dependent radius is a priori unknown, surrounded by a frictional annulus. A numerical procedure based on an iterative process is developed, which is continued until the complete solution is obtained. This solution is determined by the elastodynamic equations of motion, the moving mixed boundary conditions, the requirement that the contact normal stresses are compressive and that no interpenetration occurs outside the contact region. Furthermore, the radius of separation between the locked and slip regions is determined from the requirement that the current shear stresses at the adhesive region cannot exceed the product of the coefficient of friction and the normal stresses, and that within the slip annulus Coulomb law holds. The method is illustrated for a paraboloid indentor and the effect of friction on the elastic field is exhibited.

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Der dynamische Kontakt bei perfekter adhäsion und Reibungsschlupf zwischen einem starren Stempel und einem elastischen Halbraum

Zusammenfassung Das Problem der dynamischen Beanspruchung eines elastischen Halbraumes bei Belastung durch einen starren, achsensymmetrischen Stempel mit begrenzter Reibung in der Kontaktzone, wird betrachtet. Das Problem betrifft die Bestimmung einer zeitabhängigen unbekannten Kontaktzone, bestehend aus einem Kreisbereich mit Haftung, dessen zeitabhängiger Radius apriori unbekannt ist und einem umgebenden Kreisbereich, wo Reibung auftritt. Ein numerisches Verfahren basierend auf einer Iterationsmethode wird entwickelt, das bis zum Erhalt der kompletten Lösung fortgesetzt wird. Die Lösung ist bestimmt durch die elastodynamischen Bewegungsgleichungen, die bewegten gemischten Randbedingungen, der Bedingung, daß die Kontaktnormalspannungen Druckspannungen sind und keine gegenseitige Durchdringung außerhalb der Kontaktzone auftritt. Weiters wird der Radius der Separation zwischen der Haft- und Rutschzone durch die Forderung festgelegt, daß die auftretende Schubspannung in der Haftzone nicht das Produkt aus Reibungskoeffizient und Normalspannung erreichen kann und während der Schlupfabnahme das Coulombsche Reibungsgestz gilt. Die Methode wird für einen parabolischen Stempel angewendet und der Effekt der Reibung auf das elastische Feld aufgezeigt.

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With 3 Figures     

Heating of a newtonian liquid when extruded through a matrix

Calculations are carried out of the dynamic forces and viscous heating when a layer of Newtonian liquid at the bottom of a rigid container is extruded through a matrix in the form of a circular opening or a narrow slit.Notation r, z axes of a Cartesian (k=0) or a cylindrical (k=1) system of coordinates - u, v velocity components of the liquid in the directions r and z, respectively - V velocity of the liquid in the opening - p pressure - ₁ and ₂ temperature of the liquid under the die and in the opening - m, n rheological constants of the material - tangential stress - shear velocity - _o, c_p, _o density, heat capacity, and thermal conductivity of the liquid - S, M, w area of the working surface, mass and velocity of motion of the die - r_o,l,a, R linear dimensions of the matrix and the container - F operating force on the instrument - Re, Pe similitude criteria Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 39, No. 4, pp. 710–715, October, 1980.     

Measurement and correlation of frictional pressure drop of refrigerant-based nanofluid flow boiling inside a horizontal smooth tube

The objective of this paper is to investigate the effect of nanoparticle on the frictional pressure drop characteristics of refrigerant-based nanofluid flow boiling inside a horizontal smooth tube, and to present a correlation for predicting the frictional pressure drop of refrigerant-based nanofluid. R113 refrigerant and CuO nanoparticle were used for preparing refrigerant-based nanofluid. Experimental conditions include mass fluxes from 100 to 200 kg m^?2 s^?1, heat fluxes from 3.08 to 6.16 kW m^?2, inlet vapor qualities from 0.2 to 0.7, and mass fractions of nanoparticles from 0 to 0.5 wt%. The experimental results show that the frictional pressured drop of refrigerant-based nanofluid increases with the increase of the mass fraction of nanoparticles, and the maximum enhancement of frictional pressure drop is 20.8% under above conditions. A frictional pressure drop correlation for refrigerant-based nanofluid is proposed, and the predictions agree with 92% of the experimental data within the deviation of ±15%.     

A momentum integral solution for pulsatile flow in a rigid tube with and without longitudinal vibration

A momentum integral solution is obtained for fully developed pulsatile flow in a circular, rigid tube of infinite length. A fourth-order polynomial with unknown coefficients is used to represent the radial variation of axial velocity across the tube. Boundary conditions applied at the tube wall and the centerline give the velocity profile in terms of centerline velocity. The momentum integral equation then gives a differential equation for the centerline velocity; and complete solutions, including mass flow rate, are obtained for a sinusoidal pressure gradient, with and without a sinusoidal longitudinal wall velocity. Excellent agreement is found with Womersley's results for a stationary tube. For wall motion at the same frequency as the pressure gradient, both an increase in mass flow magnitude and an exact cancellation are found, depending on phasing. These results are used to discuss the application of momentum integral methods to pulsatile flows and possible fluid-dynamical aspects of cardiovascular behavior during whole-body vibration.     

Volumetric rate of a turbulent newtonian fluid flow in a cylindrical channel

A new formula to calculate the volumetric rate of a turbulent Newtonian fluid flow is suggested. Experimental verification of the validity of the formula for fluids of different physicochemical nature passed through a cylindrical channel of a laboratory rig has been made. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 81, No. 5, pp. 856–859, September–October, 2008.     

Dynamic behaviour of a porous medium saturated by a newtonian fluid

The macroscopic dynamical behaviour of a porous elastic medium the cavities of which are filled with a Navier-Stokes liquid can be described with equations obtained from certain assumptions and the homogenization method, based on the use of periodic solutions of space variables. The so-determined linear behaviour is a generalization of Biot and Levy works: particularly, strain rates of the solid are taken into account for the flow law of the liquid. Then, some special relationships are determined for coefficients which are involved in the macroscopic equations and determined by particular solutions of the boundary problem at the pore scale.     

Investigation of the influence of frictional viscosity regularization on quasi-static gas-solid flow predictions in a conical spouted bed with non-porous draft tube

The stress in the quasi-static particle flow is often modeled through the Mohr-Coulomb failure criterion. In the extension to complex three-dimensional flows, a granular viscosity is introduced through a tensorial rheology and the deviatoric frictional stress tensor is assumed aligned with the strain rate tensor. This granular viscosity is singular as the shear rate approaches zero, regardless of the local rheology. We discuss the influence of regularizing such a frictional viscosity on the particle circulation rate and other measured characteristics in a laboratory scale draft tube spouted bed. The friction between particles is modeled either with a constant Coulomb rheology or using a local particle pressure and strain-rate based friction known as $\mu \left(I\right)$-rheology. The predictions appear very dependent on the regularization parameter introduced by the method. The mean properties of the flow (e.g. circulation and pressure drop) monotonically converge towards the measurements when the regularization parameter tends to zero. In other respects, the two regularization models regarded in this study induced similar hydrodynamics within the spouted bed of interest. But the analysis of the conditional averages of the inertial number and the fraction of the solids in the quasi-static regime shows that the extent and staticity of the quasi-static region is sensitive to changes to the regularization parameter or regularization function.     

Application of the “rigid stream tube” method to calculate micelle-polymer flooding in a staggered system of wells

The applicability of the simplified “rigid stream tube” method to many practical situations of calculating micelle-polymer flooding in a system of wells is shown. The scheme of motion of the oil fringe in the pool and the influence of the main parameters on the efficiency of the considered method for increasing oil recovery are analyzed. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 80, No. 1, pp. 15–21, January–February, 2007.     

Pulsatile Flow in Microfluidic Systems

This review describes the current knowledge and applications of pulsatile flow in microfluidic systems. Elements of fluid dynamics at low Reynolds number are first described in the context of pulsatile flow. Then the practical applications in microfluidic processes are presented: the methods to generate a pulsatile flow, the generation of emulsion droplets through harmonic flow rate perturbation, the applications in mixing and particle separation, and the benefits of pulsatile flow for clog mitigation. The second part of the review is devoted to pulsatile flow in biological applications. Pulsatile flows can be used for mimicking physiological systems, to alter or enhance cell cultures, and for bioassay automation. Pulsatile flows offer unique advantages over a steady flow, especially in microfluidic systems, but also require some new physical insights and more rigorous investigation to fully benefit future applications.