Conical Diffuser Research Articles

Low Reynolds number flow through nozzle-diffuser elements in valveless micropumps

Flow characteristics of low Reynolds number laminar flow through gradually expanding conical and planar diffusers were investigated. Such diffusers are used in valveless micropumps to effect flow rectification and thus lead to pumping action in one preferential direction. Four different types of diffuser flows are considered: fully developed and thin inlet boundary layer flows through conical and planar diffusers. The results from the numerical analysis have been quantified in terms of pressure loss coefficient. The variation of pressure loss coefficient with diffuser angle is presented for Reynolds numbers of 200, 500 and 1000. The pressure loss coefficients have been used to calculate the diffuser efficiency for two different types of nozzle-diffuser elements. The general trend of variation of pressure loss coefficient with diffuser angle was found to be similar to that for high Reynolds number turbulent flow. However, unlike at high Reynolds numbers, pressure loss coefficients at low Reynolds numbers vary significantly with Reynolds number. It was also observed that trends of variation in the pressure loss coefficient with Reynolds number are different for small and large diffuser angles. Also, at low Reynolds numbers, the pressure loss coefficients for a thin inlet boundary layer are not always smaller than those for fully developed inlet boundary layer, in contrast to the behavior for high Reynolds number flows. Contrary to past claims, flow rectification is shown to be indeed possible for laminar flows. The two different types of nozzle-diffuser elements considered led to pumping action in opposite directions. Further, it was observed that flow rectification properties of both kinds of nozzle-diffuser elements improved with increasing Reynolds number.

Laminar Heat Transfer of a Swirled Flow in a Conical Diffuser. Self-similar Solution

Heat transfer in a laminar swirled air flow in the divergent channel between a disk and a cone whose vertex touches the disk is studied. A self-similar solution of the Navier-Stokes and energy equations is derived using group analysis. An exact numerical solution of the problem is obtained for different radial-to-tangential velocity ratios at the channel inlet.

円すいディフューザの脈動流れ特性(O.S.2-2 内部流の実験と計算,OS2:乱流中の渦構造および流れの制御)

円すいディフューザの脈動流れ特性(O.S.2-2 内部流の実験と計算,OS2:乱流中の渦構造および流れの制御)

Characteristics of Pulsating Flow in Conical Diffusers

Characteristics of Pulsating Flow in Conical Diffusers

Comparative Studies: CFD, Experimental and Analytical Techniques in the Fluids Laboratory

This task is concerned with the recovery of pressure in a fluid as it flows through various conical diffusers of the same inlet (d) and outlet (D) diameters, but with different included angles (2θ). In particular, it involves comparison of the measured and computational fluid dynamics (CFD) predicted pressure recovery coefficients (PRC) and, for modelling purposes only, illustrating the effect of the choice of boundary conditions, pressure recovery patterns along the diffusers and the use of PreBFC. The fluid is air (density ρ and dynamic viscosity μ); the test rigs available are existing open-circuit wind tunnels.

1418 多ノズルを用いた高流量比ジェットポンプ特性

As the result of flow analytical studies of the high flow-ratio Jet Pump using a five-nozzle, the number of nozzles and the diffuser configuration were selected as the parameter that affected Jet Pump efficiency. The experimental studied were performed for four types of nozzle from a single to seven nozzles at best-efficient-point flow-ratio of about 7 and for two added diffuser configurations called as a "trumpet" type and a "bell" type using a five nozzle. And the efficiency data were obtained experimentally under room temperature conditions. Increasing the number of nozzles enhanced the Jet Pump efficiency. However, it was to five that efficiency improved and in case of seven nozzles, efficiency decreased conversely. The diffuser configuration was the most efficient at a conventional conical diffuser, and a "trumpet" type or a "bell" type made efficiency decrease so that the flow-ratio was large.

Antiferroelectric liquid-crystal mixture without smectic layer shrinkage at the direct Sm-A*-Sm-C(*)(a) transition.

We report results of x-ray, optic, electro-optic, and dielectric investigations on an antiferroelectric liquid-crystal mixture exhibiting a direct second-order phase transition between the Sm-A* and Sm-C(*)(a) phases with virtually no shrinkage in the smectic layer spacing. The birefringence measurements and texture observations suggest that the phase transition follows the diffuse cone model of Adrian de Vries, which explains the constant layer spacing. The antiferroelectric nature of the tilted phase is verified by the presence of twin polarization reversal peaks in the current response and by the absence of strong absorptions in the dielectric spectrum. The threshold for switching this phase to the synclinic, ferroelectric state is sharp and occurs at a very low voltage.

Optical and x-ray evidence of the "de Vries" Sm-A*-Sm-C* transition in a non-layer-shrinkage ferroelectric liquid crystal with very weak interlayer tilt correlation.

A non-layer-shrinkage fluorinated ferroelectric liquid crystal compound, 8422[2F3], has been characterized by means of optical, x-ray, and calorimetric methods. The orientational distribution within macroscopic volumes, determined through wide-angle x-ray scattering and birefringence measurements, was found to be identical in the Sm-A* and helical Sm-C* phases. Together with the absence of layer shrinkage, this constitutes strong evidence that the second-order Sm-A*-Sm-C* transition in this material is well described by the diffuse cone model of de Vries. The absolute values of the layer spacing show that the molecules aggregate to antiparallel pairs. The molecular interaction across the layer boundaries will then occur only between fluorine atoms, leading to unusually weak interlayer tilt direction correlation. This explains the experimental observations of a very easily disturbed Sm-C* helix and a peculiar surface-stabilized texture. Tilt angle and birefringence values as a function of field and temperature have been evaluated in the Sm-A* and Sm-C* phases and the results corroborate the conclusions from the x-ray investigations.

Control of diffusing flow at low Reynolds numbers with annular wall jets

During the course of experiments to determine the influence of coflowing streams of air on the lift-off height of a methane jet flame, it was necessary to achieve a smooth axial decay of the velocity field in a conical diffuser. It was also crucial that the mean axial velocity profile was flat in the central region of the flow. These criteria proved to be quite difficult to meet, even with diffuser half-angles limited to 12.6°, partly because of the low Reynolds numbers involved, which were in the range 780-3500 based on the inlet pipe diameter. A satisfactory solution, following Duggins, proved to be the injection of high-velocity air along the wall from a narrow annulus around the inlet. For diffusers with half-angles of 3.5, 7.5 and 12.6°, the optimum rates of injection were found to be independent of the half-angle but dependent on the Reynolds number and on whether a gauze mesh was present at the inlet. The efficiency of diffusion reached an optimum value of 60 per cent at the highest Reynolds numbers, and this was achieved both with and without the mesh.

Structure and Vibration Phenomenon of Swirling Flow through Conical Diffusers.

Experiments on swirling flows through conical diffusers have been carried out. Mean and fluctuating velocities, and static pressure in three diffusers of different included angle were measured under the various swirl intensity. In addition, relationships between static pressure recovery and flow characteristics were investigated. In the case of weak swirl that the static pressure recovery is improved, it is shown that the separation of the flow from the wall is prevented and the velocity is made rapidly uniform, and additionally that the turbulence is suppressed. In the meantime, the vibration of the pipe is observed in the flow with strong swirl and it is clarified that this vibration is induced by eccentricity of the center of the swirling flow, its center circulating about the pipe axis, from the results of the velocity measurement.

Suppression of Swirling Flow in a Conical Diffuser by use of J-groove.

The purpose of the study is to examine the validity of J-groove in controlling and suppressing swirl flow in conical diffuser, for draft surge suppression in a Francis turbine which is caused by the swirling flow from runner outlet into a draft tube. "J-groove" composed of shallow grooves mounted parallel to the pressure gradient on the diffuser wall is a very simple passive device to suppress several anomalous phenomena in turbomachinery. The experimental study has been performed using conical diffuser of divergent angle 20 degree. The measured results of velocity distribution in the diffuser show that considerable reduction of swirl intensity is attained by use of J-grooves. Besides, the amplitude of pressure fluctuation caused by rotation of vortex core around the dead water region near the diffuser inlet is reduced by J-grooves.

1546 A Numerical Study of Longitudinal Vortices Produced by VGJs in a Conical Diffuser

1546 A Numerical Study of Longitudinal Vortices Produced by VGJs in a Conical Diffuser

An effective high-power KrCl excimer barrier-discharge lamp

The effect of the pumping pulse power and shape on the discharge character and the efficiency of emission from KrCl* molecules (λ∼222 nm) is studied. In the coaxial quartz tube KrCl excimer lamps excited by a barrier discharge, the maximum emission efficiencies are observed for a discharge in the form of diffuse cones. Based on these results, an excimer lamp with an average output power of up to 100 W is created.

Warming automotive catalysts with pulsating flows

Temperatures of an automotive catalyst substrate warmed by convection pre-light-off have been measured. Direct comparison has been made of warm-up by steady and pulsating flow for a one-dimensional flow case. The 32 Hz pulsating mass flow did not feature flow reversal. Pulsations were achieved by interruption of the airflow by a rotating disc. Very small differences between steady and pulsating cases were observed because the effect of mass flow pulsations on heat transfer is minimal. Two different computational fluid dynamics methods were used to predict temperature. A one-dimensional porous medium model, which required input of an assumed heat transfer coefficient, was compared with a single-channel model. Predictions agreed closely and there was also qualitative agreement with measurements. Similar mass flow pulsations in the range 32-100 Hz have been studied for a case with a larger diameter automotive catalyst supplied via a conical diffuser. The radial flow distribution is controlled by pulsation frequency and the effect of frequency on temperature at different depths in the substrate was observed experimentally. Pulsations will affect catalyst warm-up in practical systems because of their effect on flow distribution, rather than on heat transfer.

The morphology of Portevin–Le Chatelier bands: finite element simulation for Al–Mg–Si

A constitutive model for dynamic strain ageing together with a three-dimensional finite element analysis were used to simulate discontinuous yielding behaviour associated with the Portevin–Le Chatelier effect. The deformation behaviour of both flat and round specimens of a dynamically strain ageing material was simulated, utilizing constitutive parameters for an Al–Mg–Si alloy. Finite element simulations showed the occurrence of propagative zones of localized deformation and provided insight into the strain rate distribution in the zones, characterized by a sharp strain rate peak. The localized deformation zones in round specimens were found to have a diffuse double cone morphology. Propagative deformation bands in flat strip specimens were planar and inclined with respect to the tensile axis by approximately 35°. The dependence of the morphology of the localized deformation zones on specimen geometry and deformation conditions, as well as the serrated stress–time curves obtained, are in good agreement with experimental measurements in Al–Mg–Si.

Performance Chart and Optimum Geometry of Mixed-Flow-Type Conical Walled Annular Diffusers Having Asymmetric uniform Shear Inlet Velocity Profiles.

One of the important factors affecting the diffuser performance is the shape of the inlet velocity profiles. Experiments have been performed systematically to investigate the performance for a wide range of mixed-flow-type conical walled annular diffusers having asymmetric uniform shear velocity profiles in the inlet core region except for a thin inlet boundary layer. The configuration of this type of diffusers consists of a circular inlet cross-sectional portion and conically diverging inner and outer walls having the same cone angle. Pressure recovery of diffusers reduces markedly with an increase in the inlet shear ratio. Systematic data on pressure recovery coefficients are presented comprehensively on the performance charts together with optimum geometry lines of diffusers both at constant diffuser length and at constant diverging area ratio for four degrees of the inlet shear ratio.

K-1113 J-Grooveによる拡がり管内旋回流抑制に関する研究 : 圧力変動特性(S18-3 旋回失速・不安定流動)(S18 流体機械に関する諸問題)

The purpose of this study is to show the applicability of J-Groove for controlling swirl flow in a draft tube of water turbine. J-Groove is very simple device composed of shallow grooves mounted parallel to the pressure gradient on the diffuser wall. Experiment with J-Groove has been performed using the conical diffuser with the divergent angle of 20 degrees. The pressure fluctuation on the wall has been measured to show the effect of J-Groove for the spiral vortex core in the diffuser.

Low frequency sound generated by flow separation in a conical diffuser

The sound field in a circular pipe generated by a concentric jet flow entering the pipe is studied. In the first case the air flow enters the pipe through a convergent nozzle only. In the second case a short diffuser is attached to the nozzle. When the diffuser half angle is small enough to ensure attached flow conditions, the sound pressure level in the duct is reduced over the entire frequency range measured. When the diffuser angle is increased up to the point where flow separation occurs, an increase in the duct sound pressure level is observed. It is shown by means of cross-correlation measurements involving the unsteady wall pressures in the diffuser and the sound pressure in the duct that the increased sound levels are in fact caused by the flow separation in the diffuser.

Flow of aqueous suspensions of fine particles in diffusers

The flow of dilute aqueous suspensions of micron-size carbon black particles in diffusers was studied by visualization and by measurements of pressure drop. For particle concentrations from 0.1 to 1.0% by weight and for conical diffusers with half angles of 5 and 11°, the measurements show that pressure recovery was less than that for plain water. The reductions were of order 10% and increased with particle concentration. To understand this effect, the flow was visualized in a two-dimensional diffuser, using computed sonography because of liquid opacity. The sonographic images show that the flow separated earlier than it did with water, which explains the reduced pressure recovery. At the same time, it is not understood how such minute particles at such small concentrations affect flow separation.

618 渦誘起ジェットを施した円すいディフューザ内の流れ

618 渦誘起ジェットを施した円すいディフューザ内の流れ