Elasticity of a magnetic fluid in a strong magnetic field

Complex measurements of the following elastic-magnetic parameters of a magnetic fluid suspended by magnetic levitation within a horizontal tube in a strong magnetic field were performed: the oscillation frequency and decay coefficient; the static, ponderomotive, and dynamic elasticity coefficients; the fluid displacement under hydrostatic pressure; magnetization curve; and the magnetic field strength and gradient. Calculations based on a model of ponderomotive elasticity with correction for the resistance of a viscous fluid in motion and on the fluid column displacement for two magnetic fluid samples agree well with the experimental magnetization curve. The discussed technique holds promise for research into magnetophoresis and nanoparticle aggregation in magnetic colloids.     

Experimental simulation of a liquid-metal heat-transfer fluid flow in a T-shaped mixer

The structure of the temperature field in a liquid-metal heat-transfer fluid flowing through a T-shaped mixer is studied experimentally. The experiments are carried out using Rose’s alloy as a working fluid. To find the temperature distribution over the wall of a working section, IR thermography is applied. It is shown that the wall temperature distribution in the zone where fluid flows with different temperatures mix is heavily nonuniform. The temperature distribution substantially depends on the ratio between the hot and cold fluid flow rates. The results can be used to verify the thermal hydraulic computational codes for fluid metal flows.     

Rotational friction coefficient of a permeable cylinder in a viscous fluid

An exact expression is derived for the rotational friction coefficient of a cylinder of infinite length and constant permeability immersed in an incompressible viscous fluid. An asymptotic expression for the translational friction coefficient of a permeable cylinder moving in a sheet of viscous fluid embedded on both sides in a fluid of much lower viscosity is also given.     

Flow of a non-Newtonian fluid

The objective of the present study is to calculate flows of a non-Newtonian fluid in a plane channel. An exact solution that determines the distribution of the fluid velocity in the transverse cross section of the channel is obtained under certain conditions concerning the dependence of viscosity on the velocity gradient. It is shown that this distribution differs substantially from a parabolic profile of a Newtonian fluid. It is indicated that, in the flow of a non-Newtonian fluid, its special features never disappear-only the region of a non-Newtonian flow shrinks, becoming localized in the vicinity of the velocity maximum.     

Force between the plates of a plane capacitor in a fluid: a rigorous thermodynamic analysis

Summary A critical analysis of the literature on the deduction of the well-known expression of the attractive force between the plates of a plane-parallel capacitor completely immersed in a linear dielectric fluid is presented. Then, rigorous deductions of this force are proposed. It is shown that, contrary to the statement reported in most references, no pressure difference exists between the fluid within the plates and the external fluid.     

The Force Acting on a Cylinder in a Ring Flow of a Viscous Fluid with a Small Eccentric Displacement

A system consisting of two circular cylinders one inside the other with parallel axes is considered. The outer cylinder of radius R₂ is fixed, and the inner cylinder of radius R₁ rotates with a sufficiently large angular velocity. The region between the cylinders is filled with an incompressible viscous fluid and, in the case of coaxial cylinders, Couette flow along circular trajectories arises. Upon an eccentric small displacement of the axis of the inner cylinder, the symmetry of the flow is disturbed and a force exerted on the inner cylinder by the fluid is created. Within the ideal fluid model, the force depends linearly on the transverse velocities and accelerations of the cylinder. In a viscous fluid, the force depends on the previous motion of the cylinder. It is expressed in terms of the velocity functional by analogy with the Basset force acting on a ball moving in a viscous fluid with a variable velocity.     

Motion and diffusion of a passive scalar in a two-dimensional fluid

The motion of a particle in two dimensions in a fluid is considered. The fluid flow is given and time independent. The complex fluid velocity potential can be viewed as a conformal transformation and after rescaling the time, the motion of the particle is uniform and rectilinear in the absence of diffusion. When diffusion of the particle also takes place the same ideas lead to a useful self-consistent approximation based on the average motion of the particle.     

General symmetries of a string fluid space-time

It is shown that a string fluid is the simplest anisotropic fluid with vanishing heat flux. Furthermore it has the property that the Ricci tensor is obtained from the energy momentum tensor, and vice versa, if one interchanges the fluid variables. We use previous works on the collineations of anisotropic fluids, which include the string fluid as a particular case, to compute the kinematic and the dynamic effects of certain collineations of a string fluid. It is found that the possible spacetimes, which can carry a string fluid, are severely restricted and the possible string fluids in spacetimes, which can admit them are more or less fixed. We recover previous results on the effect of symmetries in string fluid spacetimes and get many new ones, for example the matter inheritance collineations. The study and the results are presented in a systematic manner, which allows the comprehension and the comparison of the restrictions imposed by each collineation. Finally one can use the same method of work for a systematic study of similar problems.     

Point-force excited vibrations of a thin,infinite panel separating a fluid layer from a fluid half-space

A coupled system consisting of a thin, infinite panel separating a fluid layer and a fluid half-space is considered. The response of the panel when driven by a point harmonic force is evaluated by using Hankel transform analysis in conjunction with complex variable integration techniques. The emphasis is placed on frequencies well below the panel critical frequency, on dense fluid loading, and on the condition of shallow layer depth. The analysis yields the free propagation wave numbers of the coupled system: below the critical frequency, all but one are complex. From the solutions of the response integrals, the panel flexural velocity, the acoustic pressures, the power transmitted into the structure and into the fluid layer, and the radiated acoustic power, are obtained.     

Critical behavior of a heavy particle in a granular fluid

A second order phase transition is observed for the homogeneous cooling state of a heavy impurity particle in a granular fluid. The order parameter straight phi is the ratio of impurity mean square velocity to that of the fluid, with a conjugate field h proportional to the mass ratio. A parameter beta, measuring the fluid cooling rate relative to the impurity-fluid collision rate, is the analog of the inverse temperature. For beta<1 the fluid is "normal" with straight phi = 0 at h = 0, as in the case of elastic collisions. For beta>1 an "ordered" state with straight phi not equal0 occurs at h = 0, representing an extreme breakdown of equipartition. Critical slowing and qualitative changes in the velocity distribution function near the transition are noted.     

Experimental dynamics of a vortex within a vortex

We report the experimental dynamics of a new two-dimensional (2D) fluid phenomenon that occurs when an intense, pointlike vortex is placed within a diffuse, circular vortex. Our observations, made using strongly magnetized electron columns to model the 2D fluid, support the analysis performed by Jin and Dubin.     

Transmission of free waves across a rib on a panel

The transmission of free waves across a rib is investigated on a singly ribbed panel. The panel is in the form of a membrane that is made to possess dispersive properties similar to those of a thin plate. Of particular interest in the investigation is the influence that fluid loading and compliant coating may have on the transmission. It is shown that the influence due to fluid loading is significant in the frequency range below, and especially in the vicinity of, the critical frequency. It is also shown that compliant coating can modify significantly the influence of fluid loading on the transmission.     

Behavior of a free surface of a magnetic fluid containing a magnetizable cylinder

The deformation of the free surface of a magnetic fluid containing a cylinder made of a magnetizable material subjected to a uniform applied magnetic field is analyzed. The statics and dynamics of a magnetic fluid free surface is studied theoretically and experimentally. A discontinuous (jump-like) change of the surface shape is shown to occur when the applied magnetic field gradually increases or decreases. If the applied magnetic field increases and then decreases, a hysteresis of the shape is observed.     

Rheological flow from a die and painting on a moving solid wall

1IntroductionThemanufacturesoffluidfilmandpolymerrequireanunderstandingofthehydrodynamicprocess[1,2].Theenlargedcross-sectionofthefluidjetwasobservedinthepolymerprocessing,wherethedieswellisanimportantphenomenon.TheSwellorDieSwelleffectisexplainedusuallybyrheologicalpropertiesoftheliquidmedium.TannersuggestedatheoryofDie-Swell,andassumedthatthevelocityvectorhasonlyonecomponentalongthejet[3].Becauseofthenon-uniformityofthecross-section,theflowfieldintheDie-Swelltheoryshouldbeatleasttwo-dime…     

Formation of a wave on an ice-sheet above the dipole, moving in a fluid

Theory of wave motions of a fluid with an ice-sheet was developed due to the necessity of solving of a number of problems of marine and land physics. The main attention in these investigations was focused on propagation and interaction of free waves, and also on appearance of waves under action of different loadings on the ice-sheet. From the other side, the problems dealing with waves on the fluid surface, free from the ice due to motion in the mass of the fluid of rigid bodies, has the known solutions. In this connection, it seems natural to disserminate the formulation and methods of such problems to the case of the fluid with the ice-sheet. In the present note we describe the character of formation of waves from the singularity, localized in the fluid of infinite depth beneath the ice-sheet. We use the example of the dipole, which models a cylinder in the infinite mass of the fluid. The character of the formation does not depend on the type of singularity. The ice-sheet is considered as a thin elastic plate of a constant width, floating on the water surface.     

Flows of a generalized second grade fluid in a cylinder due to a velocity shock

Unsteady axial flows of second grade fluids with generalized fractional constitutive equation in a circular cylinder are studied. Flows are generated by a time-dependent pressure gradient in the axial direction, an external magnetic field perpendicular on the flow direction and by the cylinder motion. Two different problems are analyzed; one in which the cylinder velocity supports a shock at the instant t = 0 and another in which the cylinder motion is a translation with time-dependent velocity along the axis of cylinder. The generalized fractional constitutive equation of second grade fluid is described by the Caputo time-fractional derivative. Analytical solutions for the velocity field are obtained by using the Laplace transform with respect to time variable and the finite Hankel transform of order zero with respect to the radial coordinate. The influence of the fractional parameter of Caputo derivative on the fluid velocity has been studied by numerical simulations and graphical illustrations. It is found that the fractional fluid flows are faster than the ordinary second grade fluid.     

Physiological Transportation of Casson Fluid in a Plumb Duct

This paper is devoted to a study of the peristaltic motion of a Casson fluid of a non-Newtonian fluid accompanied in a horizontai tube.To characterize the non-Newtonian fluid behavior,we have considered the Casson fluid model.Suitable similarity transformations are utilized to transform the governing partial differential momentum into the non-linear ordinary differential equations.Exact analytical solutions of these equations are obtained and are the properties of velocity,pressure and profiles are then studied graphically.     

The onset of convection of a poorly conducting fluid in a modulated thermal field

The stability of a poorly conducting fluid in a constant electric field of a horizontal capacitor is investigated under a variable temperature gradient. It is assumed that free charge in the fluid is generated only due to the nonhomogeneous conductivity of the fluid. The Floquet theory is used to determine the convection thresholds. The instability boundaries and the characteristics of critical perturbations are determined. In addition to the synchronous and subharmonic responses to an external action, the instability can be attributed to quasiperiodic perturbations. The low-frequency limit of modulation is considered by an asymptotic method. The critical electric Rayleigh number is represented as a function of inverse frequency and heating level.     

Phase behaviour of a Lennard-Jones fluid in a pore with permeable walls of a finite thickness: a density functional approach

A confinement of a Lennard-Jones fluid in a system of slitlike pores separated by semipermeable walls of a finite width is studied. The walls are modelled by square-well repulsive potential wells. The structure of the confined fluid is investigated by means of a density functional method. For high potential barriers separating the pores, the phase behaviour of the system is similar to that for a single slitlike pore with impenetrable walls. For intermediate and low potential barriers the system shows different phase behaviour. Within some temperature range the isotherms exhibit two hysteresis loops, which characterize the condensation of the fluid in different parts of the system, namely in the pore and inside the semipermeable walls. The systems characterized by low and intermediate potential barriers exhibit the triple point, such that at temperatures below that triple point the condensation instantaneously takes place in both the pore and inside the permeable wall.     

Finite element modeling of a microparticle manipulator

The contactless movement of microparticles and cells to known locations within a fluid volume is of interest in the fields of microtechnology and life sciences. A device which can position such inhomogeneities suspended in a fluid at multiple locations is described and modeled. The device consists of a thin fluid layer contained in a channel etched into a silicon wafer. Waves are excited by a macro-piezoelectric plate with electrodes on the top and bottom surfaces and, as a result, waves propagate into the adjacent fluid. The result is a pressure field throughout the fluidic volume. When an inhomogeneity in a fluid is exposed to an ultrasonic field the acoustic radiation force results; this is found by integrating the pressure over the surface of the particle, retaining second order terms, and taking the time average. Thus, due to the presence of a pressure field in the fluid in which the particles are suspended, a force field is created. The particles are then collected at the locations of the force potential minima. In the device described here, the force field is used to position particles into lines. The locations of the particles are predicted by using a finite element model of the system. The experimental and modeling results, presented here, are in good agreement.