Uniform Velocity Distribution Research Articles

Calibration Method of Current Meters

This paper presents a rapid method for propeller current meter calibration, enabling calibration of current meters in their actual working conditions using simpler equipment than what is currently used in traditional calibrations, and exploiting the uniform velocity profile present through submerged outflows (e.g., flow nozzles and orifices). Experiments were performed to confirm the fundamental hypothesis of uniform horizontal and vertical velocity distribution downstream of a submerged jet. Two experimental velocities were adopted to determine the calibration curve: one based on the discharge and the outflow area; the other derived from Torricelli's formula, which relies on the head difference between two reservoir levels. Because a current meter measures local velocity, the influence on the measurements' reliability as a function of current meter position in the submerged outflow jet was investigated. An uncertainty analysis was also performed, and a comparison of the results with the preexisting calibration lines obtained by towing tank is presented.

Trend prediction in velocity distribution among microchannels based on the analysis of frictional resistances

Velocity distribution among microchannel plays an important role in the performances of microchannel reactors. The optimization of structural parameters by enabling narrow uniform velocity distribution among microchannels is regarded as one of the effective design methods. On the basis of the previously developed model, the effects of structural parameters on the velocity distribution are studied and the relationship between frictional resistances and pressure drop are investigated in this work. It is found that the variation of pressure drop distribution among microchannels due to the variation of frictional resistances is the underlying reason for the variation of velocity distribution among microchannels. Compared with the manifold structural parameters, the microchannel structural parameters show more influence on the velocity distribution. High-aspect-ratio microchannels are in favor of obtaining relatively uniform velocity distribution. By the combination of the calculation of frictional resistances with descriptive geometry, it can predict the trend of velocity distribution among microchannels with the variation of structural parameters without applying complicated theoretical model or numerical simulation.

Simple Models for Laminar Thermally Developing Slug Flow in Noncircular Ducts and Channels

Solutions to the classical Graetz slug flow problem (uniform velocity distribution) in noncircular ducts are examined. These solutions have applications where a constant uniform velocity distribution exists across a channel or duct. These are most often realized in the laminar flow of low Prandtl number liquids, such as liquid metals, and low Reynolds number flows through porous media. Expressions are developed for a number of applications using the asymptotic correlation method of Churchill and Usagi. These expressions vary depending on the definition used for the dimensionless heat transfer coefficient, in the case of constant wall temperature boundary condition (T), and the dimensionless wall temperature for the constant flux boundary conditions (H) and (H1). Finally, simple expressions are developed for predicting the thermal entrance length and fully developed flow Nu values for noncircular ducts.

Numerical hydraulic analysis of the turbulent contraction nozzle flow for IFMIF target application

IFMIF (International Fusion Materials Irradiation Facility) is an accelerator based deuteron–lithium (D–Li) neutron source to simulate the neutron irradiation field in a fusion reactor. The target assembly of the IFMIF consists of a nozzle, which has to form a stable lithium jet. Therefore, a flat uniform velocity distribution at the nozzle outlets cross-section with a simultaneously low turbulence intensity is required to ensure a safe operation. The general idea in the nozzle design is to produce a constant slug shaped velocity profile at the nozzles outlet cross-section with a simultaneously low homogeneously spread turbulence intensity. Additionally, the contraction length should be kept as short as possible in order to reduce the spatial and the fabrication effort. Such flow conditions are attained by using Shimás function with an axial contraction ratio of 10 as considered as a reference for IFMIF. However, a one-step contraction causes a flow separation and hence the use of Shimás method requires a two-step nozzle with first a contraction ratio of 4 followed by another with 2.5 by which the axial dimensions of the nozzle increase in size. Within this article the turbulent flow within several one and two-step nozzle types are numerically analysed by means of the V2F model, which has been validated to depict the flow most accurately in a previous work. The study exhibits that an optimized one-step nozzle is capable to generate an optimal flow pattern the IFMIF lithium target requiring a significantly shorter dimension than the reference design.

Close‐to‐streamline numerical study on gas velocity distribution in industrial scale electrostatic precipitator gas inlet hood

AbstractThe uniformity of gas velocity distribution in gas inlet hoods is important to guarantee high dedust efficiency in electrostatic precipitators (ESPs), especially for high solid concentration applications. The close‐to‐streamline numerical method was developed to geometrically 1:1 simulate an industrial scale ESP gas inlet hood, which had complicated internal structures, such as dedust angle irons and gas distribution perforated plates with up to 10 000 holes. The realizable k‐ε model was used for the gas flow simulation. The numerical results of the gas velocity distribution show reasonable agreement with the field measurements. The outlet gas velocity distribution was non‐uniform, which was lower in the central region and higher in the near‐wall regions. The gas flow characteristics were analysed to reveal the main influence factors on gas velocity distribution and put forward corresponding modification methods. After the retrofit, the field measurements of the outlet gas velocities showed that the gas velocity distribution improved. The non‐uniform index of outlet gas velocity distribution decreased greatly from 0.355 to 0.244. The visible dust emissions from the chimney disappeared which indicated increased dedust efficiency. Therefore, the close‐to‐streamline method can simulate gas velocity distribution in complicated structures of ESP gas inlet hoods. Copyright © 2010 Curtin University of Technology and John Wiley & Sons, Ltd.

Numerical simulation of the liquid phase in SnO2 thin film deposition by sol-gel-dip-coating

The fluid flow of the liquid phase in the sol-gel-dip-coating process for SnO2 thin film deposition is numerically simulated. This calculation yields useful information on the velocity distribution close to the substrate, where the film is deposited. The fluid modeling is done by assuming Newtonian behavior, since the linear relation between shear stress and velocity gradient is observed. Besides, very low viscosities are used. The fluid governing equations are the Navier–Stokes in the two dimensional form, discretized by the finite difference technique. Results of optical transmittance and X-ray diffraction on films obtained from colloidal suspensions with regular viscosity, confirm the substrate base as the thickest part of the film, as inferred from the numerical simulation. In addition, as the viscosity increases, the fluid acquires more uniform velocity distribution close to the substrate, leading to more homogenous and uniform films.

A One-Dimensional Parametric Model for Undertow and Longshore Current Velocities on Barred Beaches

A one-dimensional parametric model for undertow and longshore current velocities assuming a triangular velocity distribution in a surface roller was developed. This model as well as a parametric model with the assumption of a uniform velocity distribution in a roller was compared with field data obtained on barred beaches at Hasaki in Japan and at Duck in the USA. The comparisons showed that the present model predicted the velocity fields at the two sites reasonably well, and the prediction accuracy of the present model is slightly better than that of the other model. However, the present model underpredicted the undertow velocities on the trough regions, and overestimated the longshore current velocities near the shorelines.

Numerical Simulation of Velocity Distribution among Microchannels with Bifurcation Structures as Manifolds

Manifold structure shows important effects on the velocity distribution among parallel microchannels. The bifurcation structure was adopted as the manifolds of microchannel array in a plane and a specific case was illustrated to estimate the effects of structural parameters on the velocity distribution using numerical simulation. Simulation result indicated that the velocity distribution appeared to be double W-shape, and somewhat symmetrical. In addition, the velocity values in each W-shape distribution also appeared symmetrical. It also indicated that two bifurcation channels from the same low-level bifurcation channel had different velocity values due to different singular losses. Larger microchannel length, smaller microchannel width or depth, larger RW or RL, suitable RZ were favor in obtaining relatively uniform velocity distribution among microchannels.

Investigation of the gas inlet velocity distribution in a fixed granular bed filter

Granular bed filter (GBF) technology can be applied for high-temperature gas cleanup in integrated gasification combined-cycle (IGCC) and pressurized fluidized-bed combustion (PFBC) advanced coal-fired power plants. The design of the gas inlet component of the granular bed filter is important to achieve a uniform gas distribution and higher usage rate of the filter media. Previous studies show that the gas velocity at the inlet is not uniformly distributed. This non-uniformity may lead to a lower usage rate of the filter media. In this study a baffle device is introduced to the inlet system in order to achieve a more uniform gas velocity distribution. A more uniform gas inlet distribution can be obtained by adjustment of the lengths and angles of the baffles. The gas velocities along the inlet and filtration surfaces are measured using a pitot tube. The uniformity of the gas velocity distribution can be characterized by looking at the distributions of the standard deviation of the gas velocity and the differences in the mean velocities between the two filtration surfaces.

Love-wave group velocity maps of Turkey and surrounding regions

SUMMARY We present the analysis of a Love-wave dispersion study performed across Turkey and the surroundings. Group velocity dispersion curves were obtained from the local and regional earthquakes recorded at both permanent and temporary stations operated in the region. Lovewave group velocity maps in the period range of 10–50 s were computed using a tomographic inversion method. The study shows the existence of significantly different crustal types in the area. The group velocity anomalies are associated with the major geological structures in the region. Low group velocities at shorter periods (10–20 s) are observed in the local sedimentary basins, the eastern Mediterranean and the Black Sea. The eastern Anatolia region is also characterized by low group velocities while Pontides and Bitlis–P¨ ot¨ urge massif display higher group velocities. The central Anatolia exhibits uniform velocity distribution indicating more homogenous crust. The Isparta angle is marked by a wedge-shaped low group velocity anomaly. The low velocities observed in the Isparta angle are related to crustal thickening and subduction-related complex. High velocities observed on the maps are associated with metamorphics, magmatic arcs along the orogenic belts of Pontides, P¨

CHARACTERIZATION OF A LOW-SPEED WIND TUNNEL SIMULATING URBAN ATMOSPHERES

A new low-speed boundary-layer wind tunnel has been designed and constructed at the University of Assiut. A series of flow-characteristic evaluations were performed in this wind tunnel to determine the uniformity of flow and to verify its adequacy to simulate the atmospheric boundary layer (ABL) for environmental flow studies and pollutants dispersion in urban atmospheres. This paper presents the measurements of mean velocity and turbulence intensity distributions in the wind tunnel. The measurements showed uniform velocity distributions and low turbulence intensities at the entrance of boundary development section in the empty wind tunnel. The simulated ABL at the entrance of the test section using the Irwin's method that consists of a combination of spires and roughness elements has a thickness up to 500 m corresponding to urban area. The results show that the present wind tunnel is capable to maintain long run steady flow characteristics and reproducible flow patterns. In addition, the capability of the wind tunnel to simulate the flow in the urban area atmospheres is verified by comparing the measured mean velocity and turbulence intensity distributions against its counterparts obtained from Computational Fluid Dynamics (CFD) which employ two-equation k-e turbulence model around and above buildings model. The numerical results agree well with the experimental data.

Influence of exit opening location on mixed convection in a channel with volumetric heat sources

Mixed convection heat transfer in a channel with volumetric heat source and different opening ratio at the exit has been analyzed numerically. Steady, laminar, two-dimensional model based on the finite-volume method is used for solving the mass, momentum and energy transfer governing equations. The flow is injected to the duct with a uniform velocity distribution. The problem is studied in three aspect ratios ( A = 1, 3 and 5) and three opening cases as single opening near the ceiling, single opening near the bottom and double openings. The study is also tested for different Richardson numbers between 0.01 and 10. Streamlines, isotherms, Nusselt numbers and temperature profiles were obtained for indicated cases. It is found that both the Richardson number and the locations of exit openings have strong effects on flow and temperature distribution in the presence of volumetric heat sources. The highest heat transfer was formed when the outlet port is located onto top of vertical wall.

Cyclic Operation Strategies in Trickle Beds and Electrical Capacitance Tomography Imaging of Filtration Dynamics

The dynamics of propagating liquid pulsations generated via various cyclic operation strategies in trickle beds was monitored through electrical capacitance tomography (ECT) for gas and liquid superficial velocities in the range of trickle flow regime. The characteristics of ON−OFF liquid, ON−OFF gas, and gas/liquid alternating cyclic operations were compared in terms of mean liquid holdup, pressure drop, pulsation intensity, pulsation propagation velocity, and spatial maldistribution maps of liquid holdup and liquid pulsation propagation velocity. The morphological features of liquid holdup pulsations as a function of cycle frequency were characterized in terms of breakthrough, plateau, and decay times. Gas/liquid alternating cyclic strategy was shown to produce long-lived liquid pulsations under the applied operating conditions and thus could be viewed as a new process intensification means to achieve uniform phase holdup and velocity distributions. In ON−OFF liquid cyclic operation, pulsation velocity ...

Mathematical model of mass transfer in an electrodialyzer with net-like spacers

Data on DC current have been recorded for EDR-III/200-0.8 electrodialysis stack available from MEGA a.s., Czech Republic, as a function of feed electrolyte (NaCl) concentration and applied voltage. The flow rates and temperature have been fixed during the tests. Spacers used between the ion-exchange membranes in the stack are of net-like type. Different approaches to the mathematical modeling of mass transfer in an electrodialyzer have been verified to select one that best fits experimental data obtained for the stack. The “turbulent flow” model has been evaluated to be the most suitable for this purpose. The model assumes uniform distribution of linear velocities, ideal cross mixing of the liquid in the flow phase and presence of the stationary diffusion layer. In addition, a correlation coefficient has been introduced into the model to take the effect of a turbulence promoter on electrical field shielding into account.

A Numerical Study of Swirl Blade Effects in Uphill Teeming Casting

The initial filling period during ingot casting was studied theoretically. The motivation was that it is crucial to achieve a preferred flow pattern which can lead to a smooth filling condition, particularly during the initial teeming stage. In this study, a twist-tape swirl blade was applied in a mathematical model to create a swirl flow in the inlet of the mold. The swirl blade was set vertically just beneath the inlet, which was made of a gradually divergent cross section area. The results showed that combinations of the inlet swirl flow and mold with gradually divergent bottom contributes to: i) Inlet flow passes along the wall of the mold, ii) the formation of a very uniform velocity distribution within only 6 s after the molten steel filled into the mold and iii) No formation of a hump on the free surface of the mold during the entire filling times. These phenomena will ensure that the mold flux is spread onto the surface of liquid steel evenly. Besides, the stable surface also prevents the mold flux from being dispersed into the molten steel.

G104 同一空間を分煙化するための換気システムの開発(GS1-流体一般,一般セッション)

We often perceive odors of smoking at the seats for non-smokers of cafes and restaurants. A new ventilation system was proposed by using the knowledge that no flow separation and backward flow could occur in the case of increasing velocity distribution near walls. Air was supplied with uniform velocity distribution from the whole surface of one side wall and exhausted from the slits set at upper and lower positions of the opposite side wall. The effects were examined experimentally and by CFD, and it was confirmed that no separation and backward flow occurred even in the case furniture was set. Further more, it was examined experimentally and was confirmed that supplying unsteady flow was effective to prevent the growth of wake behind a rectangular column and to decrease amount of remaining smoke there, when the frequency of unsteady flow was set close to that of Karman vortex.

Laser Surface Hardening Considering Coupled Thermoelasticity

AbstractThermoelastic temperature, displacement and stress in heat transfer during laser surface hardening are solved in both Lagrangian formulation and Eulerian formulation. In the Eulerian formulation, the heat flux is fixed in space and the work-piece is moved through a control volume. In the case of uniform velocity and uniform heat flux distribution, the Eulerian formulation leads to a steady-state problem, while the Lagrangian formulation remains transient. In the Eulerian formulation, the reduction to a steady-state problem increases the computational efficiency. Also, in this study, an analytical solution is developed for an uncoupled transient heat conduction equation in which a plane slab is heated by a laser beam. The thermal results of the numerical models are compared with the results of the analytical model. A comparison of the results shows that numerical solutions in the case of uncoupled problem are in good agreement with the analytical solution.

Determining local wear equation based on friction and wear testing using a pin-on-disk scheme

Based on pin-on-disk friction and wear testing, the parameters of the wear rate as a function of sliding velocity and pressure with account for their distribution over the contact spot are computed. The parameters are compared to those obtained assuming a uniform distribution of velocities and pressures. It is assumed in the work that the contact spot does not vary, the disk does not wear out, and the study is carried out under steady-state wear conditions.

Investigation of Turbulent Rectangular Shaped Contraction Nozzle Flow for IFMIF Target Application, Validation of Turbulence Models

The target assembly of the International Fusion Materials Irradiation Facility (IFMIF) consists of a nozzle, which has to form a stable lithium jet. Therefore, a flat uniform velocity distribution at the nozzle outlets cross-section with a simultaneously low turbulence intensity is required to ensure a safe operation. These boundary conditions necessitate a detailed knowledge on the turbulent flow in contraction nozzles in order identify turbulence models accurately predicting experimental findings within the velocity range of interest for nuclear target and hence can then act as design optimization tool.In order to validate commercially available Computational Fluid dynamic codes (CFD) and the turbulence models incorporated in them a series of experiments using water as model fluid are conducted in the Liquid-Metal-Laboratory KALLA at the research center Karlsruhe. A number of turbulence models with different extensions for the near wall treatment were tested versus the experimentally obtained data. Based on this comparison a hydraulic analysis of the contraction nozzle flow is performed taking into account the relaminarization of the accelerated flow, the occurrence of secondary motions and their impact on the development of the boundary layer. In summary the V2F turbulence model exhibits the best agreement between numerical and experimental data and thus can be considered to be most suitable for the simulation of the accelerated nozzle flow for free surface target applications.

CFD-based Study of Velocity Distribution among Multiple Parallel Microchannels

A three-dimensional computational fluid dynamics (CFD) model was used to calculate the velocity distribution among multiple parallel microchannels with triangle manifolds. The influences of structural parameters on velocity distribution among microchannels were analyzed. The simulation results showed that the velocity distribution became more uniform with larger microchannel length, depth or smaller width. Larger horizontal ordinate, longitudinal ordinate and radius of inlet/outlet, smaller lengths of bottom and side of symmetrical manifolds could favor obtaining narrow velocity distribution among microchannels. Symmetrical manifold structure could achieve more uniform velocity distribution among microchannels than that asymmetrical manifold structure.