Outlet Velocity Research Articles

Comparative efficiency testing for a newly designed cyclone type sediment trap for wind erosion measurements

The measurement of eolian sediment transport still remains one of the biggest challenges in eolian research. This paper presents the experimental results on the trap efficiency of a newly designed cyclone-type trap (BEST) and Wilson and Cook trap (WAC) under various wind speeds in the Eremology Wind Tunnel Facility at Gent University, Belgium. The performance of the two traps were tested for four different sediment sizes (<100, 100–200, 200–300 and 300–500μm) and under four free-flow wind speeds (12, 13, 14, and 15ms−1). The test results showed that the efficiency of the BEST was higher than that of the WAC, and the efficiencies of BEST and WAC varied between 75 and 100% and 12 and 52%, respectively. In addition, the coefficient of variation (CV) indicated that the variability in the efficiency of the BEST was lower with wind speed and particle size. These higher and more consistent efficiencies of the BEST were chiefly attributed to its cyclone design, which provided: i) separation of particles from air (particle settling) by means of the accelerated gravitational force achieved by a rapid air rotation, ii) the reduced stagnation pressure at the catcher inlet by gradually increasing the outlet velocity, and iii) the reduced turbulence within its body by a regular circulating path.

Numerical analysis of spontaneously condensing phenomena in nozzle of steam-jet vacuum pump

The primary fluid in a steam-jet vacuum pump is not assumed as a perfect gas as general research in the present study. A mathematic model based on the wet steam model for transonic flow is proposed to investigate the flow behaviours of primary fluid in the nozzle of a steam-jet vacuum pump. The simulation based on a wet steam model was carried out to predict the flow characteristics of primary fluid along the nozzle axis by a commercial computational fluid dynamics (CFD) code (FLUENT6.3). The simulation results showed that there was spontaneous condensation as the supersonic flow passing through the nozzle and the simulation results had a good agreement with the experimental data. It is found from the numerical simulation results that the steam flow characteristics in nozzle are quite different from a wet steam model and a perfect gas assumption: the outlet pressure of the nozzle predicted in the present study is higher than that as the primary fluid assumed as perfect gas, the outlet velocity is about 10% lower than that as the primary fluid assumed as a perfect gas, and the temperature at the outlet of the nozzle is much higher than that as the primary fluid assumed as a perfect gas. The simulation results demonstrate that the thermo-positive process due to steam condensation would hinder the supersonic expanding flow process in nozzle and depress the efficiency of the nozzle which would affect the pumping performance of steam-jet pump.

Computational water purification controls using second‐order adjoint equations with stability confirmation

SUMMARYThis paper presents a computational method for water purification using second‐order adjoint equations. In Japan, the waters of polluted rivers are purified by conveying the waters from other rivers into the main rivers or by using outflows from sewage plants. The shallow water flow equation based on the water velocity and elevation and the advection diffusion equation of COD concentration are governing equations. The control problem involves finding a flow velocity into the main river that can reduce the COD concentration as close to the target value as possible. In other words, the problem is to find a water velocity to minimize the performance function, which is the square sum of the discrepancy between the computed and the observed COD concentrations.The present research was motivated by the need to apply water purification controls to practical projects. We have found that the controls occasionally tend to be unstable, and the stability of control must be ensured. By expanding the extended performance function into the Taylor series, the necessary condition for the stationary state is derived. Based on this condition, the first‐and second‐order adjoint equations can be obtained. The backward solution of the adjoint equation leads to the gradient and the Hessian product; these serve as the basis of the quasi‐Newton method. From the condition that the performance function must be minimum, the stability confirmation index can be determined. Using this index, we have derived the trust region method, the computation of which confirms the stability of control.Verification was carried out using a simple channel model. By varying the peak value of the inflow velocity, the outlet velocity has been determined such that the water elevation at the target point is zero. Depending on the peak value of the inflow, unstable control arises; this is determined by the stability confirmation index presented in this paper. The trust region method with the stability confirmation index is shown to be adaptable to judge the stability of control.The present method was applied to the water purification of Teganuma river in Japan. The steady fundamental state was computed with the inflow, outflow, and COD concentration at the inlet being specified. The control velocity at the control point can be determined for a fixed control duration with and without the stability confirmation index. The inflow, outflow, and COD concentration are specified as functions of time. It is shown that this method is suitable for practical use because control stability can be ensured. Moreover, it is also noted that the maximum flow velocity for stable control depending on the given control duration can be obtained. Copyright © 2011 John Wiley &amp; Sons, Ltd.

The Effect of the Structure of Collection Loop on Two-Phase Flow Field in Quenching Furnace

In order to analyses the effect of structure of collection loop on two-phase flow field in quenching furnace, the complex flow field in furnace for mixture of Nitrogen and spray water ejecting quenching under normal pressure and high velocity is numerically simulated with Mixture model of two-phase flow by CFD software FLUENT. Different inlet velocity, different volume percent of spray water, different velocity differences between Nitrogen and spray water, and different angle and dimension of collection loop affected on outlet velocity are analyzed. The research results show that the flow field is really complex, and around inner and outside canister and collection loop back flow exists. The angle of collection loop has less effect on outlet velocity, and the inner diameter of collection loop has more effect on outlet velocity. The simulation results show that the furnace can accelerate the flow of quenching media, which can cool specimen quickly.

FILM COOLING PERFORMANCE IN A LOW-SPEED 1.5-STAGE TURBINE: EFFECTS OF BLOWING RATIO AND ROTATION

This paper presents experimental investigations on film cooling performance under rotation in a low-speed 1.5-stage turbine using the thermochromic liquid crystal (TLC) technique. The experiment was accomplished in a test facility which was recently established to study rotating film cooling performance in realistic turbine stages. Eighteen blades of chord length of 0.1243 m and height of 0.099 m were installed in the rotor. A film hole with diameter of 0.004 m, angled 28 degrees and 36 degrees tangentially to the pressure surface and suction surface in streamwise, respectively, was set in the middle span of the rotor blade. All measurements were made at three different rotating speeds of 600, 667 and 702 rpm with the blowing ratios varying from 0.3 to 3.0. The Reynolds number based on the mainstream velocity of the turbine outlet and the chord length of the rotor blade was fixed at 1.89 x 10(5). Results show that on the pressure side, the film coverage and cooling effectiveness scaled up with the blowing ratio and the film deflected centrifugally; on the suction side, the maximum film coverage and cooling effectiveness were obtained at moderate blowing ratio and a centripetal deflection of the film was observed. The film deflection could be amplified by either decreasing the blowing ratio or increasing the rotation number on both sides. Overall, blowing ratio and rotation play significant roles in the film cooling performance.

Nanofibrous Resonant Membrane for Acoustic Applications

Because the absorption of lower-frequency sound is problematic with fibrous material made up of coarser fibers, highly efficient sound absorption materials must be developed. The focus of this paper is on the development of a new material with high acoustic absorption characteristics. For low-frequency absorption, structures based upon the resonance principle of nanofibrous layers are employed in which the resonance of some elements allows acoustic energy to be converted into thermal energy. A nanofibrous membrane was produced by an electrostatic spinning process from an aqueous solution of polyvinyl alcohol and the acoustic characteristics of the material measured. The resonant frequency prediction for the nanofibrous membrane is based on research into its production parameters. The distance between electrodes during the electrostatic spinning process determines the average diameter of the nanofibers, and the outlet velocity of the material determines its area density. The average diameter of nanofibers was measured using the Lucia software package directly from an electron microscope image. The resonant frequency of nanofibrous membranes was determined from the sound absorption coefficient and transmission loss measurement.

A Finite Element Analysis Simulation Model of one-Spacer Nozzle’s Flow Field of Al Roll-Casting Using Coupled Fluid-Thermal Analysis

To explore fluid-thermal analysis of the flow fields of front-box and One-spacer nozzle of aluminum roll-casting, a three-dimensional finite element simulation model has been developed to provide analyzing distribution of velocity and temperature of outlet of nozzle, by using coupled fluid-thermal FEM simulation of FLOTRAN module in ANSYS 6.0. Stricter analysis of postprocessing result was conducted by MATLAB. It was concluded that flow field of one-spacer nozzle was able to match cooling capacity of cast rollers, and one-spacer nozzle could be optimized to work in the case of speed increasing of the drawing-sheet and thickness reducing of the aluminium sheet during roll casting.

Flow Analysis of Spray Jet and Direct Jet Nozzle for Fire Water Monitor

In order to investigate the influence rules between the jet nozzle of fire water monitor and the jet performances, two typical jet nozzle, the spray jet and direct jet nozzle was designed to analysis the jet flow characteristics. Flow simulation of the jet nozzle was completed using fluent kits. The outlet velocity of the spray jet nozzle and direct jet nozzle were investigated in detail, and the influence rules of the nozzle structure on the outlet velocity was also discussed. The simulation results show that the steady velocity of the jet nozzle is about 34m/s that coinciding the contour magnitude, and the better extended length of the direct jet nozzle is about 50mm length that can improve the jet performances. The results can verify the reasonableness of the designed nozzle, it also can optimize the nozzle structure and increase the jet performance of the fire water monitor.

Sediment transport and deposition on a river‐dominated tidal flat: An idealized model study

A 3‐D hydrodynamic model is used to investigate how different size classes of river‐derived sediment are transported, exported and trapped on an idealized, river‐dominated tidal flat. The model is composed of a river channel flanked by sloping tidal flats, a configuration motivated by the intertidal region of the Skagit River mouth in Washington State, United States. It is forced by mixed tides and a pulse of freshwater and sediment with various settling velocities. In this system, the river not only influences stratification but also contributes a significant cross‐shore transport. As a result, the bottom stress is strongly ebb‐dominated in the channel because of the seaward advance of strong river flow as the tidal flats drain during ebbs. Sediment deposition patterns and mass budgets are sensitive to settling velocity. The lateral sediment spreading scales with an advective distance (settling time multiplied by lateral flow speed), thereby confining the fast settling sediment classes in the channel. Residual sediment transport is landward on the flats, because of settling lag, but is strongly seaward in the channel. The seaward transport mainly occurs during big ebbs and is controlled by a length scale ratio Ld/XWL, where Ld is a cross‐shore advective distance (settling time multiplied by river outlet velocity), and XWL is the immersed cross‐shore length of the intertidal zone. Sediment trapping requires Ld/XWL &lt; 1, leading to more trapping for the faster settling classes. Sensitivity studies show that including stratification and reducing tidal range both favor sediment trapping, whereas varying channel geometries and asymmetry of tides has relatively small impacts. Implications of the modeling results on the south Skagit intertidal region are discussed.

Upgrading the flow path of the K-500-6.4/3000 turbine’s low-pressure cylinder to increase the turbine power output

Results obtained from upgrading the flow paths of the low-pressure cylinders of OAO Turboatom K-500-6.4/3000 steam turbines installed at the Kursk, Smolensk, and Leningrad nuclear power stations are presented. With the annular area of steam outlet from the last stages increased from 6.3 to 8.19 m2, it became possible to reduce the loss due to outlet velocity by a factor of 1.8 and increase the turbine power output by 16MW, which is equivalent to increasing the power unit efficiency by 3.2%.

Coupled Fluid-Thermal Finite Element Analysis of Droplike-Shape-Spacer Nozzle’s Fluid Field of Al Roll-Casting

A three-dimensional finite element simulation model of fluid field including front-box and droplike-shape-spacer nozzle of aluminum roll-casting has been developed to provide analyzing distribution of velocity and temperature of outlet of nozzle. The computation was performed by using coupled fluid-thermal FEM simulation of FLOTRAN module in ANSYS 6.0. The boundary conditions of the roll-casting model of fluid and thermal fields, were loaded on front-box and nozzle. Based on the data from postprocessing function of ANSYS, the strict result analysis was conducted by MATLAB. Results based on the allowable inhomogeneity of velocity and temperature of outlet show the most possible broken regions of outlet could be predicted in the case of speed increasing of the drawing-sheet and thickness reducing of the aluminium sheet. Droplike-shape-spacer nozzle in this example only applied to normal speed, and must be optimized to be appropriate in high roll cast speed.

Effect of Velocity of Fluid Field of 3-Spacer Nozzle in Roll-Casting Models Using Coupled Fluid-Thermal Finite Element Analysis

A finite element model of fluid field of front-box and 3-spacer nozzle of aluminum roll-casting has been developed to provide a comparison of analyzing distribution of velocity and temperature of outlet of nozzle with variable velocity. The computation is performed by using coupled fluid-thermal FEM simulation of FLOTRAN module in ANSYS 6.0. The boundary conditions of the roll-casting model of fluid and thermal fields, were loaded on front-box and nozzle. Based on the postprocessing function of ANSYS, the strict result analysis was conducted by MATLAB. Results based on the allowable inhomogeneity of velocity and temperature of outlet show the most possible broken regions of outlet could be predicted in the case of speed increasing of the drawing-sheet and thickness reducing of the aluminium sheet. The profile parameters of the nozzle including distribution, shapes and sizes of the nozzle spacers, and shapes of inner nozzle must be optimized to be appropriate in high roll cast speed.

A Test of Initiation of Submarine Leveed Channels by Deposition Alone

Abstract Leveed submarine channels play a critical role in the transfer of sediment from the upper continental slopes to intraslope basins and ultimately deeper marine settings. Despite a reasonable understanding of how these channels grow once established, how such channels are initiated on previously unchannelized portions of the seafloor remains poorly understood. We conducted a series of experiments to test whether leveed channels can start by deposition on a planar rigid bed. We systematically varied the current density and outlet velocity to explore the relative influence of inertia and excess density on the depositional dynamics of currents entering a basin and undergoing abrupt unconfinement. Under flow conditions ranging from supercritical to subcritical (bulk Richardson numbers of 0.02 to 1.2) our experiments failed to produce deposits resembling or exhibiting the potential to evolve into levees needed to create a self-formed channel. In the absence of excess density, a submerged sediment-laden flow produced sharp-crested lateral deposits bounding the margins of the flow for approximately a distance of two outlet widths down-basin. These lateral deposits terminated in a centerline deposit that greatly exceeded marginal deposits in thickness. As excess density increased relative to the outlet velocity, the rate of lateral spreading of the flow increased relative to the downstream propagation of the density current, transitioning from a narrow flow aligned with the channel outlet to a broad radially expanding flow. Coincident with these changes in flow dynamics, the bounding lateral deposits extended for shorter distances, had lower, more poorly defined crests that were increasingly wider in separation than the initial outlet, and progressively became more oblong rather than linear. Based on our results and a review of previous experimental and numerical models, we suggest that initiation of leveed channels from sediment-laden density currents traversing non-erodible beds is unlikely. Partial confinement of these currents appears to be necessary to establish the hydrodynamic conditions needed for sediment deposition along the margins of a density current that ultimately may create confining levees. We suggest that erosion into a previously unchannelized substrate is the most likely source of this partial confinement.

Experimental study on airflow fluctuation characteristic of an underfloor air supply terminal unit

In order to investigate dynamic characteristic of underfloor air supply terminal unit, an IFV900A hot-wire anemometer was used to measure the corresponding velocity field. Turbulence intensity and power spectrum density exponent of air velocity signal were analyzed. The result showed that the outlet velocity distribution of underfloor air supply terminal unit was uniform. With increment of height, the velocity distribution trends to be uniform. Two velocity attenuation regions appear during airflow development. Turbulence intensity changes obviously with height. It is lower than that of mechanical wind. Turbulence intensity goes up with the increment of jetting distance. Power spectrum density exponent trends to the value of natural wind with increase of jetting distance and decrease of wind velocity. The exponent value approaches to the value of typical natural wind for the air velocity is 0.5 m/s under high supply air rate. With airflow diffusion, the fluctuation characteristic of airflow varies obviously with the jetting direction. The fluctuation characteristic of airflow changes to that of natural wind with the increase of height which can improve comfort of indoor environment.

Heat flux measurements in stagnation point methane/air flames with thermographic phosphors

Light-induced phosphorescence from thermographic phosphors was used to study the wall temperatures and heat fluxes from nearly one-dimensional flat premixed flames. The investigated flames were stoichiometric, lean and rich laminar methane/air flames with equivalence ratios of φ = 1, φ = 0.75 and φ = 1.25 at ambient pressure. The flames were burning in a stagnation point arrangement against a water-cooled plate. The central part of this plate was an alumina ceramic plate coated from both sides with chromium-doped alumina (ruby) and excited with a Nd:YAG laser or a green light-emitting diode (LED) array to measure the wall temperature from both sides and thus the heat flux rate from the flame. The outlet velocity of the gases was varied from 0.1 to 1.2 m/s. The burner to plate distance (H) ranged from 0.5 to 2 times the burner exit diameter (d = 30 mm). The measured heat flux rates indicate the change of the flame stabilization mechanism from a burner stabilized to a stagnation plate stabilized flame. The results were compared to modeling results of a one-dimensional stagnation point flow, with a detailed reaction mechanism. In order to prove the model, gas phase temperatures were measured by OH-LIF for a stoichiometric stagnation point flame. It turns out that the flame stabilization mechanism and with it the heat fluxes change from low to high mass fluxes. This geometry may be well suited for further studies of the elementary flame wall interaction.

Optimum geometric arrangement of vertical rectangular fin arrays in natural convection

The optimal spacing between isothermal laminar natural convection plates cooled by air for maximal heat transfer has been determined analytically and numerically. It is found that the optimal plate’s allocation spacing is different from the conventional way, where the boundary layers of the plates merge early, it is the distinguishing feature of the outlet velocity that causes an enhancement of heat transfer. Further comparison results verify that our expression and numerical results and Rohsenow expression are very consistent. In the general condition, an optimized spacing expression of the maximum heat transfer density for a given volume is derived. It may be expected that the heat transfer enhancement can be accomplished by inserting multi-scale plates into the boundary layer according to the constructal theory.

Design and Jet Characteristics Study of a Liqumatic Fire Water Monitor with Self-Swinging Device

Fire water monitor plays an important role in the fire fighting. A liqumatic fire water monitor with self-swing device was designed, the working principle and its components were also expounded in detail. The internal flow performance was simulated using fluent software, the influence rules on outlet velocity were analyzed by changing different angles of the monitor head and diameters of the monitor body. At the same time, the experimental tests were also carried out on the test rig. The simulation results accorded with the theory calculations in general. So, the rationality and accuracy of the designed fire water monitor was verified, and the relevant results can also provide a certain theoretical references for the design of other types of fire water monitor.

Hydraulic Performance Research of a Fixed Fire Water Monitor

A manual fixed fire water monitor of type 100 was designed. The monitor can rotate 360º in horizontal direction. It can rotate from the angle of -40º to the angle of 70º in vertical direction. The monitor spraying position can be adjusted by operating the handwheel and it can also automatically be locked. The flow simulation was completed using Fluent kits. The influence of the flow channel which affects the velocity and pressure field was analyzed. The energy loss was explained. The influence of the flow structure which affects the internal flow's turbulence and outlet velocity was obtained. The experiments were carried out on the test rig. The experimental results accorded with the simulation results in general. The relevant results can verify the reasonableness of the designed fire water monitor. It can provide some theory reference to the further optimization of the monitor design.

A mathematical analysis of hollow fiber spinning: Bore and dope velocity profiles in the air gap

Hollow fiber membranes are the most applicable form of membranes in laboratory and industrial scale with their large surface to volume ratios. Hollow fiber membranes usually are fabricated by dry–wet solution spinning, where a polymer solution is co-extruded through an annular region with a bore fluid and the nascent hollow fiber passes through an air gap and then enters a liquid coagulation bath. The spinneret dimension, dope and bore fluid flow rates, air gap length, bore fluid and dope compositions and their physical properties, coagulant composition and condition, shear stress within a spinneret, the ratio of dope to bore fluid volumetric flow rate, and the take-up-to-initial velocity ratio (draw ratio) are the primary factors that determine the final hollow fiber morphology and separation properties. All of the aforementioned parameters are not independent and some of them are functions of others. The objective of this paper is to elucidate the interdependence between some of the above parameters. For this purpose, dope and bore fluid axial velocity in the air gap was assumed as a function of the axial distance from the spinneret outlet, z, and radial velocity as a function of the radial distance from the center of the hollow fiber, r, and z. Dimensionless equations of motion and continuity were then simplified and solved simultaneously based on preceding assumptions. It was found from the analysis that the dimensionless axial velocity of dope was a function of the Reynolds number, Capillary number and Stokes number indicating that the axial velocity acceleration in the air gap is determined by viscous, capillary, and gravity force gradients. It was also concluded that the optimum value of the ratio of bore liquid flow rate to dope flow rate is equal to 0.8 of the ratio of the cross-sectional area of the bore fluid to that of the dope at the spinneret outlet.

On the (de)stabilization of draw resonance due to cooling

We study the drawing of a Newtonian viscous sheet under the influence of cooling with temperature dependence of the viscosity. Classically this problem has an instability called draw resonance, when the draw ratio Dr, which is the ratio of the outlet velocity relative to the inlet velocity, is beyond a critical value Drc. The heat transfer from the surface compared to the bulk energy advection is conveniently measured by the Stanton number St. Usual descriptions of the problem are one-dimensional and rigorously apply for St ≤ 1. The model presented here accounts for variations of the temperature across the sheet and has therefore no restriction on St. Stability analysis of the model shows two different cooling regimes: the ‘advection-dominated’ cooling for St ≪ 1 and the ‘transfer-dominated’ cooling for St ≫ 1. The transition between those two regimes occurs at St = O(1) where the stabilizing effect due to cooling is most efficient, and for which we propose a mechanism for stabilization, based on phase shifts between the tension and axial-averaged flow quantities. Away from this transition, the sheet is always shown to be unstable at smaller draw ratios. Additionally, in the limit of St → ∞, the heat exchange is such that the temperature of the fluid obtains the far-field temperature, which hence corresponds to a ‘prescribed temperature’ regime. This dynamical situation is comparable to the isothermal regime in the sense that the temperature perturbation has no effect on the stability properties. Nevertheless, in this regime, the critical draw ratio for draw resonance can be below the classical value of Drc = 20.218 obtained in isothermal conditions.