Normal Fluid Flow Research Articles

Neuroendoscopic Removal of Large Choroid Plexus Cyst: A Case Report

Choroid plexus cysts (CPCs) are the most commom neuroepithelial cysts, occuring in more than 50% of some autopsy series. They are typically small and asymptomatic and are discovered incidentally in older patients, usually in the trigone of the lateral ventricle. Symptomatic CPCs (usually exceptionally large, 2-8 cm) are rare. The authors report a case of large symptomatic choroid plexus cyst, located in the trigone of the right lateral ventricle in a 26-yr-old man who presented with headache and vomiting. The patient underwent endoscopic removal through a burr hole placed 3 cm from the midline and just behind the hair line. The histological examination of the cyst wall was consistent with choroid epithelium. Despite of postoperative intraventricular hemorrhage and catheter infection, he discharged home without neurologic deficits. The endoscopic fenestration rather than excision should be considered as the first surgical procedure because the goal of treatment is shrinkage of the cyst until normal cerebrospinal fluid flow is restored.

Numerical study of two-phase flow of liquid helium in a vertical converging-diverging nozzle

The fundamental characteristics of the two-dimensional gas-liquid two-phase flow of liquid helium through a vertical converging-diverging duct near the lambda point are numerically investigated to realize the further development and high performance of new multiphase superfluid cooling systems. First, the governing equations of the two-phase flow of liquid helium based on the unsteady thermal nonequilibrium multifluid model with generalized curvilinear coordinates system are presented, and several flow characteristics are numerically calculated, taking into account the effect of superfluidity. Based on the numerical results, the two-dimensional structure of the gas-liquid two-phase flow of liquid helium though vertical converging-diverging nozzle is shown in detail, and it is also found that the generation of superfluid counterflow against normal fluid flow based on the thermomechanical effect is conspicuous in the large gas phase volume fraction region where the liquid- to vapor-phase change actively occurs. Furthermore, it is clarified that the mechanism of the He I to He II phase transition caused by the temperature decrease is due to the deprivation of latent heat for vaporization from the liquid phase. © 2005 Wiley Periodicals, Inc. Heat Trans Asian Res, 34(6): 432–448, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20071

Numerical Analysis of Cavitating Flow of Liquid Helium in a Converging-Diverging Nozzle

The fundamental characteristics of the two-dimensional cavitating flow of liquid helium through a horizontal converging-diverging nozzle near the lambda point are numerically investigated to realize the further development and high performance of new multiphase superfluid cooling systems. First, the governing equations of the cavitating flow of liquid helium based on the unsteady thermal nonequilibrium multifluid model with generalized curvilinear coordinates system are presented, and several flow characteristics are numerically calculated, taking into account the effect of superfluidity. Based on the numerical results, the two-dimensional structure of the cavitating flow of liquid helium though a horizontal converging-diverging nozzle is shown in detail, and it is also found that the generation of superfluid counterflow against normal fluid flow based on the thermomechanical effect is conspicuous in the large gas phase volume fraction region where the liquid to gas phase change actively occurs. Furthermore, it is clarified that the mechanism of the He I to He II phase transition caused by the temperature decrease is due to the deprivation of latent heat for vaporization from the liquid phase.

Numerical study of cavitating flow characteristics of liquid helium in a pipe

The fundamental characteristics of the two-dimensional cavitating flow of liquid helium in a vertical pipe near the lambda point are numerically investigated to realize the further development and high performance of new cryogenic superfluid cooling systems. It is found that the phase transition of the normal fluid to the superfluid and the generation of superfluid counterflow against normal fluid flow based on the thermomechanical effect is conspicuous in the large gas phase volume fraction region where the liquid to gas phase change with cavitation actively occurs. Furthermore, it is clarified that the mechanism of the He I to He II phase transition caused by the temperature decrease is due to the deprivation of latent heat for vaporization from the liquid phase.

水平狭まり‐広がり流路内における液体ヘリウムキャビテーション流れの数値解析

The basic characteristics of the two-dimensional cavitating flow of liquid helium through a horizontal converging-diverging channel near the lambda point are numerically investigated to realize the further development and high performance of new multiphase superfluid cooling systems. First, the governing equations of the cavitating flow of liquid helium based on the unsteady thermal nonequilibrium multifluid model with generalized curvilinear coordinates system are presented, and several flow characteristics are numerically calculated, taking into account the effect of superfluidity. Based on the numerical results, the two-dimensional structure of the cavitating flow of liquid helium though horizontal converging-diverging channel is shown in detail, and it is also found that the generation of superfluid counterflow against normal fluid flow based on the thermo mechanical effect is conspicuous in the large gas phase volume fraction region where the liquid- to gas-phase change actively occurs. Furthermore, it is clarified that the mechanism of the He I to He II phase transition caused by the temperature decrease is due to the deprivation of latent heat for vaporization from the liquid phase.

Numerical simulation of cavitating flow of liquid helium in venturi channel

The fundamental characteristics of the two-dimensional cavitating flow of liquid helium through a venturi channel near the lambda point are numerically investigated to realize the further development and high performance of new multi-phase superfluid cooling systems. First, the governing equations of the cavitating flow of liquid helium based on the unsteady thermal nonequilibrium multi-fluid model with generalized curvilinear coordinates system are presented, and several flow characteristics are numerically calculated, taking into account the effect of superfluidity. Based on the numerical results, the two-dimensional structure of the cavitating flow of liquid helium though venturi channel is shown in detail, and it is also found that the generation of superfluid counterflow against normal fluid flow based on the thermomechanical effect is conspicuous in the large gas phase volume fraction region where the liquid-to-gas phase change actively occurs. Furthermore, it is clarified that the mechanism of the He I to He II phase transition caused by the temperature decrease is due to the deprivation of latent heat for vaporization from the liquid phase.

Resolution of Chiari Malformation after Repair of a Congenital Thoracic Meningocele: Case Report and Literature Review

Many theories have been proposed regarding potential causative factors for Chiari malformations. An unusual case is described in which regression of a congenital Chiari malformation was observed after repair of a thoracic meningocele without direct surgical intervention to decompress the craniocervical junction. This supports the importance of an in utero craniospinal pressure gradient as a potential cause for congenital, but reversible, cerebellar herniation. A newborn baby was observed to have a thoracic meningocele. Magnetic resonance imaging scan revealed a concomitant Chiari malformation. No neurological deficits were present at initial examination. The patient underwent surgical closure of the thoracic meningocele and untethering of the spinal cord at the site of the dural defect. A postoperative magnetic resonance imaging scan obtained 3 months after the operation revealed complete resolution of the cerebellar herniation. The resolution of the Chiari malformation in this child may have resulted from restoration of normal cerebrospinal fluid flow and elimination of the meningocele-related cerebrospinal fluid pressure gradient between the intracranial and intraspinal compartments.

液体ヘリウムのベンチュリ流路内キャビテーション流れに関する数値シミュレーション

The fundamental characteristics of the two-dimensional cavitating flow of liquid helium through a venturi channel near the lambda point are numerically investigated to realize the further development and high performance of new multiphase superfluid cooling systems. First, the governing equations of the cavitating flow of liquid helium based on the unsteady thermal nonequilibrium multifluid model with generalized curvilinear coordinates system are presented, and several flow characteristics are numerically calculated, taking into account the effect of superfluidity. Based on the numerical results, the two-dimensional structure of the cavitating flow of liquid helium though venturi channel is shown in detail, and it is also found that the generation of superfluid counterflow against normal fluid flow based on the thermomechanical effect is conspicuous in the large gas phase volume fraction region where the liquid-to-gas phase change actively occurs. Furthermore, it is clarified that the mechanism of the He I to He II phase transition caused by the temperature decrease is due to the deprivation of latent heat for vaporization from the liquid phase.

Numerical Analysis of Two-Phase Pipe Flow of Liquid Helium Using Multi-Fluid Model

The two-dimensional characteristics of the vapor-liquid two-phase flow of liquid helium in a pipe are numerically investigated to realize the further development and high performance of new cryogenic engineering applications. First, the governing equations of the two-phase flow of liquid helium based on the unsteady thermal nonequilibrium multi-fluid model are presented and several flow characteristics are numerically calculated, taking into account the effect of superfluidity. Based on the numerical results, the two-dimensional structure of the two-phase flow of liquid helium is shown in detail, and it is also found that the phase transition of the normal fluid to the superfluid and the generation of superfluid counterflow against normal fluid flow are conspicuous in the large gas phase volume fraction region where the liquid to gas phase change actively occurs. Furthermore, it is clarified that the mechanism of the He I to He II phase transition caused by the temperature decrease is due to the deprivation of latent heat for vaporization from the liquid phase. According to these theoretical results, the fundamental characteristics of the cryogenic two-phase flow are predicted. The numerical results obtained should contribute to the realization of advanced cryogenic industrial applications.

Vortex dynamics in the two-fluid model

We have used two-fluid dynamics to study the discrepancy between the work of Thouless, Ao and Niu (TAN) and that of Iordanskii. In TAN no transverse force on a vortex due to normal fluid flow was found, whereas the earlier work found a transverse force proportional to normal fluid velocity u and normal fluid density. We have linearized the time-independent two-fluid equations about the exact solution for a vortex, and find three solutions which are important in the region far from the vortex. Uniform superfluid flow gives rise to the usual superfluid Magnus force. Uniform normal fluid flow gives rise to no forces in the linear region, but does not satisfy reasonable boundary conditions at short distances. A logarithmically increasing normal fluid flow gives a viscous force. As in classical hydrodynamics, and as in the early work of Hall and Vinen, this logarithmic increase must be cut off by nonlinear effects at large distances; this gives a viscous force proportional to u/ln(u), and a transverse contribution which goes like u/(ln u)^2, even in the absence of an explicit Iordanskii force. In the limit u goes to zero the TAN result is obtained, but at nonzero u there are important corrections that were not found in TAN. We argue that the Magnus force in a superfluid at nonzero temperature is an example of a topological relation for which finite-size corrections may be large.

Linear stability of laminar plane Poiseuille flow of helium II under a nonuniform mutual friction forcing

The calculation of the stability characteristics of superfluid helium II is complicated by the fact that we have to consider the interaction of two velocity fields: the normal fluid and the superfluid. We consider 2D channel flow and concentrate on the linear stability of the normal fluid under a mutual friction forcing from the superfluid. The linear stability of the superfluid component is also briefly discussed. We consider nonuniform distributions of superfluid vorticity, leading to a nonuniform mutual friction forcing. We derive a modified Orr–Sommerfeld equation for the stability of the normal fluid component and find the neutral stability curves for the normal fluid. We identify a new branch to the neutral stability curve, which can significantly lower the critical Reynolds number of the normal fluid flow.

Stability ofincompressible helium II: a two-fluid system

A numerical attempt to achieve stability of the two-fluid systemincompressible helium II is presented. The Orr-Sommerfeld equation forthe planar Poiseuille flow of normal fluid with relaxedvelocity slip along the interface with a superfluid is solved.The numerical approach is a modified version (with complex matrixpre-conditioning) of a spectral method. The relaxed results arecompared with non-relaxed ones which are subject tono-slip boundary conditions. The relaxed slip-flow effect becomesmore dominant as the interface parameter increases, because thenthe critical Reynolds number (or the critical velocity) decreases.

Local normal-fluid helium II flow due to mutual friction interaction with the superfluid

Mutual friction, the scattering of rotons and phonons by quantized vortex lines, acts locally on the normal fluid component of helium II and is nonzero only in a volume very close to the quantized vortex line. We show that this localized mutual friction force forms a jetlike flow structure in the normal fluid, with a vortex dipole structure. The peak velocity of this normal fluid jet is a significant fraction of the velocity of the quantized vortex line and the width of the jet is on the order of 0.1 mm. The normal fluid jet velocity is highest at $T\ensuremath{\approx}1.9$ K and decreases to zero as the temperature goes to zero and also as the temperature approaches the lambda transition temperature. We report the circulation, energy per unit length, and the viscous dissipation of kinetic energy of this normal fluid flow structure as a function of temperature.

Hydrodynamic problems related to the electrodeposition of AuCu/B 4C composites

Hydrodynamic actions leading to the electrodeposition of AuCu/B 4C composites have been investigated experimentally and theoretically. Translation and rotation of cylindrical cathodes have been studied. Embedding of particles into disk electrodes rotating at various speeds has been analysed. The dependence of volume fraction of embedded particles on fluidisation conditions has been investigated. Higher volume fractions correlate with higher mass transport rate to the cathode and are found in points on which flow lines are closer to normal to the cathode surface (stagnation points), irrespectively of the overall flow sign. Hydrodynamic classification of particles diameters has also been observed: lower fluidisation velocities and tangential (to cathode surface) fluid flow components correlate with larger particles whilst higher fluidisation velocities and normal fluid flow components correlate with smaller particles. These effects have been modelled analytically on the basis of a hydrodynamic treatment of interactions among fluid flow, electrode surface and particles. Effects of the cathode roughness — and related local flow conditions — on particle embedding have also been disclosed and explained with the above-mentioned hydrodynamic model.

Two-Dimensional Numerical Analysis of Boiling Two-Phase Flow of Liquid Helium.

The two-dimensional characteristics of the boiling two-phase flow of liquid helium in a duct are numerically investigated to realize the further development and high performance of new cryogenic engineering applications. First, the governing equations of the boiling two-phase flow of liquid helium based on the unsteady drift-flux model are presented and several flow characteristics are numerically calculated, taking into account the effect of superfluidity. Based on the numerical results, the two-dimensional structure of the boiling two-phase flow of liquid helium is shown in detail, and it is found that the vapor gas phase rapidly spreads throughout the inner flow duct because of the change of the pressure gradient due to the effect of superfluidity which appears in momentum equations. Next, it is clarified that the distributions of the void fraction, the velocity field and the instantaneous streamline of two-phase superfluid helium flow show a tendency different from those of normal fluid helium because the counterflow of two-phase superfluid occurs against normal fluid flow. According to these theoretical results, the fundamental characteristics of the cryogenic boiling two-phase flow are predicted. The numerical results obtained would contribute to advanced cryogenic industrial applications.

Synthetic rough fractures in rocks

Natural fractures serve a very important function in the transport of fluid through rocks, as well as in the flow of electrical charge and heat. The creation of numerically synthesized fractures can aid the study of the physical processes connected with fractures. Synthetic fracture is the term used to describe fractures that are created numerically in such a way that they share the same mean geometrical characteristics as specific natural fractures measured by profiling, by a process known as tuning. We have modified methods for producing synthetic rough surfaces whose geometric properties are tuned to mimic natural fracture surfaces in rocks in order to create synthetic fractures that are statistically identical to those found in rocks. One important such modification has been the incorporation of a method that allows the surfaces to be matched at long wavelengths and unmatched at short wavelengths, with the degree of matching varying smoothly in between, as it does for real fractures. We have compared numerically synthetic fractures created using the new method with fractures created using an existing technique that uses a mismatch wavelength as a sudden discontinuity between matched and unmatched behavior, as well as data from fractures in real rocks. This comparison has shown that the new technique provides much more realistic numerically synthesized fractures than previous methods. Synthetic fractures created with the new method have been used in normal closure and fluid flow modeling, and the results are reported in a companion paper.

Thermoviscous Effects in Steady and Oscillating Flow of an Isotropic Superfluid: Theory

A calculation is presented of thermoviscous effects in both steady and oscillating flow of an isotropic superfluid through small apertures and channels. These calculations, which are based on the two-fluid model, are motivated by the work of Robinson and Atkins which included only the thermal effects of flow through a superleak. This paper extends these calculations to include the effects of normal fluid flow, compressibility, and thermal expansion. These effects are found to be both dissipative and reactive(nondissipative). The motivation for the extension is to provide a clear understanding of the reactive and dissipative forces at work in superfluid flow experiments. In the paper which immediately follows this one, predictions based on the results of this paper are compared with a wide array of experimental data. This work takes on importance due to the recent discovery of gyroscopic effects, and the possible development of sensitive gyroscopes in experimental cells whose geometry is similar to the one considered in this paper.

Thermoviscous effects in steady and oscillating superfluid flow with applications to Helmholtz oscillators

The two fluid nature of superfluid 4He can lead to interesting behavior when it is used in a Helmholtz oscillator. If the oscillator’s constriction is narrow enough, the normal fluid can be locked by its own viscosity leaving only the superfluid component to flow in and out of the oscillator volume. This leads to an accompanying temperature oscillation that can cause dissipation and/or frequency shifts depending on the thermal properties of the walls of the oscillator. If the constriction is somewhat larger, the normal component is able to move and the thermal effects are partially canceled. These same effects lead to dissipation when steady flow is forced through the constriction. Equations have been derived which include superfluid flow, normal fluid flow, compressibility, thermal expansion, and the properties of the oscillator walls. These have been solved for the resistance to steady flow and the resonant frequency and Q of a Helmholtz oscillation. The calculations will be compared with a wide array of recent measurements. [Work partially supported by the Office of Naval Research and NASA.]

Microanatomical basis for the third ventriculostomy.

In the last few years, there has been a resurgence of interest in endoscopic third ventriculostomy as a treatment for obstructive hydrocephalus. Although various techniques have been used to perform this procedure, not enough emphasis has been placed on the microanatomical details of the third ventricle and surrounding cisterns in relation to this procedure. Using a surgical microscope we examined the microsurgical anatomy of the floor of the third ventricle floor and related subarachnoid cisterns in 20 adult brains using the "immersion technique" in conjunction with microsurgical dissection. We believe that the optimal place to fenestrate is the midline of the floor of the third ventricle, behind the infundibular recess and in front of the mammillary bodies, communicating the third ventricle with the anterior interpeduncular cistern, minimizing the risk for vascular lesions. Stereotactic third ventriculostomy is a safe and effective way of re-establishing normal cerebrospinal fluid flow dynamics in selected cases of obstructive hydrocephalus. However, in an endoscopic exposure only a small portion of the anatomy can be seen at any one time, and important neurovascular structures may be located adjacent to the endoscope, but outside of the visual range of the lens. A thorough understanding of the microanatomy of the neural and vascular structures surrounding the third ventricle and related cisterns is essential in order to improve surgical results avoiding complications.

Multiple discrete TI states of superfluid turbulence

We report a most unusual new observation in thermal counterflow of liquid helium II in a weakly nonuniform circular channel: the appearance of multiple discrete states of superfluid turbulence. These states are in the TI regime of heat currents but exhibit a lower level of dissipation than the ordinary TI state present in both uniform and nonuniform channels. Interestingly, these new states are only observed for diverging heat flow and are completely suppressed in converging flow. In contrast to the ordinary stable TI state, these new states are metastable. Transitions between the metastable states and to the TI state can be induced by weak mechanical perturbation. We have observed as many as five discrete metastable states at 1.75 K, but the number of states decreases markedly with temperature. Confirmatory data were obtained with a second channel of different size and shape. Although current theories of superfluid turbulence do not provide any obvious explanations for these new states, we offer some speculations based upon competing normal fluid flow profiles and a quantized vortex mill.