Effect Of Baffles Research Articles

Airborne dust deposition in the Okavango Delta, Botswana, and its impact on landforms

AbstractThis study investigated the local‐scale generation and movement of dust in the seasonal swamps of the Okavango Delta, Botswana, with a view to examining possible transfer of material between flood plains and islands. It was found that most of the dust load was carried in the lowest 3 m of the air column, and consisted mainly of amorphous silica, indicating that dust was generated largely on the flood plains. Dust loads were found to be highest above the flood plains and lowest over the interiors of islands, probably due to the baffling effect of the island trees on wind velocity. The contrast in dust loads between islands and flood plains suggests that there is a net transfer of dust from flood plains to islands, but it was not possible to quantify this transfer. It is evident, however, that flood plains experience net erosion and islands net aggradation. A strong seasonality in dust loads was observed, with the maximum dust loads coinciding with maximum wind velocity in October. This also coincides with peak seasonal flooding in the delta, and only non‐inundated flood plains are capable of generating dust. Years of low flood therefore appear to be more dusty. There may also be transfer of material from higher‐lying to lower‐lying flood plains, which may reduce the topographic contrast on the flood plains. Copyright © 2004 John Wiley & Sons, Ltd.

Numerical study on liquid sloshing in baffled tank by nonlinear finite element method

This paper introduces a velocity–potential-based nonlinear finite element method for the accurate simulation of the large amplitude liquid sloshing in two-dimensional baffled tank subject to horizontal forced excitation. As well, the effects of baffle on the nonlinear liquid sloshing are parametrically examined. The free surface configuration is tracked by a direct time differentiation of the convective term in the kinematic boundary condition with the help of the four-step predictor–corrector methods. The flow velocity is interpolated from the velocity potential by a second-order least square method. And, the finite element mesh is adapted in a semi-Lagrangian approach combined with the free-surface height correction, in order to keep the mesh regularity and the total liquid volume unchanged. By comparing with the available reference solutions, we verify the numerical accuracy and stability of the nonlinear finite element method proposed. Through the numerical experiments performed by varying the installation height and the opening width of baffles, the hydrodynamic characteristics of the large-amplitude liquid sloshing are parametrically investigated.

機械式撹拌炉内の固液混合に及ぼす邪魔板の効果

機械式撹拌炉内の固液混合に及ぼす邪魔板の効果

Interface effects on effective elastic moduli of nanocrystalline materials

Interfaces often play a significant role in many physical properties and phenomena of nanocrystalline materials (NcMs). In the present paper, the interface effects on the effective elastic property of NcMs are investigated. First, an atomic potential method is suggested for estimating the effective elastic modulus of an interface phase. Then, the Mori–Tanaka effective field method is employed to determine the overall effective elastic moduli of a nanocrystalline material, which is regarded as a binary composite consisting of a crystal or inclusion phase with regular lattice connected by an amorphous-like interface or matrix phase. Finally, the stiffening effects of strain gradients are examined on the effective elastic property by using the strain gradient theory to analyze a representative unit cell. Our analysis shows two physical mechanisms of interfaces that influence the effective stiffness and other mechanical properties of materials. One is the softening effect due to the distorted atomic structures and the increased atomic spacings in interface regions, and another is the baffling effect due to the existence of boundary layers between the interface phase and the crystalline phase.

단부 아연 과도금 방지를 위한 단부 와동 구조의 분석

In the gas wiping process of continuous hot-dip galvanizing, edge overcoating develops near the edge of the steel strip. The overcoating is supposed to occur due to the reduced impact pressure of wiping gas on the strip surface. The purpose of this study is to investigate the effect of edge vortex on the reduced impact pressure. Three-dimensional unsteady flows are simulated using a commercial code, STAR-CD. Standard k- model is used as a turbulence model. It is found that an alternating vortex structure in the vicinity of strip edge is developed by buckling of opposed jet streams and that the reduced amount of impact pressure at strip edge becomes smaller as the air knife gets closer to the strip. The effect of edge baffle on the reduced impact pressure is also investigated.

Evaluation of sloshing problem by variational boundary element method

In this study, a Variational Boundary Element Method (VBEM) based on the Hamilton's principle that produces symmetric matrices is presented. The effect of a rigid baffle on the natural frequencies of the liquid in a cylindrical rigid container is then investigated by the use of VBEM. Boundary integral equations are regularized by moving the singular points outside the domain. Fluid motion is assumed to be irrotational, incompressible and inviscid. Linearized free surface conditions are taken into consideration.

Effect of vertical baffles on particle mixing and drying in fluidized beds of group D particles

This study reports the effect of vertical baffles on the group D powder mixing and drying characteristics in a batch fluidized bed dryer. Results obtained in this study showed that operating the fluidized bed dryer with vertical baffles gave better particle mixing. This is due to the fact that the vertical baffles acted to limit the growth of small bubbles into large bubbles and the small bubbles caused more vigorous mixing in the bed of particles before finally erupting at the bed surface. Thus, insertion of vertical baffles is a useful way to process group D particles in a fluidized bed, especially when the fluidized bed is large.

Use of porous baffles to enhance heat transfer in a rectangular channel

An experimental investigation was carried out to measure module average heat transfer coefficients in uniformly heated rectangular channel with wall mounted porous baffles. Baffles were mounted alternatively on top and bottom of the walls. Heat transfer coefficients and pressure loss for periodically fully developed flow and heat transfer were obtained for different types of porous medium (10, 20, and 40 pores per inch (PPI)) with two window cut ratios ( B h/ D h=1/3 and 2/3) and two baffle thickness to channel hydraulic diameter ratios ( B t/ D h=1/3 and 1/12). Reynolds number ( Re) was varied from 20,000 to 50,000. To compare the effect of foam metal baffle, the data for conventional solid-type baffle were obtained for ( B t/ D h=1/3). The maximum uncertainties associated with module Nusselt number and friction factor were 5.8% and 4.3% respectively. The experimental procedure was validated by comparing the data for the straight channel with no baffles ( B h/ D h=0) with those in the literature [Publications in Engineering, vol. 2, University of California, Berkeley, 1930, p. 443; Int. Chem. Eng. 16 (1976) 359]. The use of porous baffles resulted in heat transfer enhancement as high as 300% compared to heat transfer in straight channel with no baffles. However, the heat transfer enhancement per unit increase in pumping power was less than one for the range of parameters studied in this work. Correlation equations were developed for heat transfer enhancement ratio and heat transfer enhancement per unit increase in pumping power in terms of Reynolds number.

Suppression of Acoustic Waves in Steam Generator and Heat Exchanger Tube Banks

Tube banks located in flow channels and exposed to crossflow have a low resistance to acoustic resonance and vibration in general. Such resistance can be increased substantially by placing acoustic baffles inside the tube banks. The locations and the number of baffles play an important role in the degree of their effectiveness of suppressing acoustic waves. One or two baffles placed within a tube bank will raise the threshold to acoustic vibration significantly. Optimum baffle locations suppressing acoustic resonance and vibration or reducing noise levels at resonance can be determined. A general procedure based on acoustic particle velocity mode shape functions is presented for the evaluation of the acoustic baffle effects.

Characteristics of boundary plasmas after the removal of divertor baffle plates and boronization on JFT-2M

A dense and cold divertor ( n e div∼2×10 19 m −3, T e div∼6 eV) during H-mode, was realized with the closed divertor (CD2) on JFT-2M. By removing all baffle plates, such a condition was compared between open (OD) and closed configurations. When a strong gas-puff is introduced into the divertor region during L-mode, the baffling effect of CD2 is verified definitely by the reduction of neutral particle backflow and the enhanced radiation localization in the divertor region. Introducing a strong gas-puff during H-mode for the OD case, H-mode is terminated in an early stage when the radiation loss fraction exceeds a critical level. A dense and cold divertor, as shown in the CD2 case, is not obtained. This is attributed to the lack of particle-handling capability for the OD compared with the CD2 configuration. As an initial result, the radiation loss fraction was reduced by half after the boronization which prevents the H–L transition.

Dynamics of contained liquids: A personal odyssey

Dynamics of contained liquids: A personal odyssey

FREE VIBRATION ANALYSIS OF BAFFLED LIQUID-STORAGE TANKS BY THE STRUCTURAL-ACOUSTIC FINITE ELEMENT FORMULATION

In fluid–structure interaction systems, baffles as a dynamic damping device are being widely used to suppress the fluid sloshing motion. Meanwhile, natural and dynamic behaviors of such systems are significantly influenced by the baffle parameters, such as the baffle number, the installation location, the inner-hole diameter and the liquid fill height. This paper intends to numerically investigate the parametric eigen characteristics, by the coupled structural-acoustic finite element method (FEM), of baffled cylindrical liquid-storage tank. According to the symmetric two-field formulation, a test FEM program is developed, in which the reduced integration for avoiding the shear and membrane locking and the modified shear correction factor as well as degenerated 8- and 6-node shell elements and 3-D trilinear acoustic elements are used. Through the comparison with the available analytic solutions of no-baffled axisymmetric tank, the validity of the test program and theoretical work is verified. Next, with the verified test FEM program, various combinations of major baffle parameters are intensively examined, in order for the parametric baffle effects on the natural frequency of baffled tanks.

배플이 장착된 로켓엔진 연소기의 음향장 해석

Acoustic behavior in baffled combustion chambers is numerically investigated by adopting linear acoustic analysis. Partial blade baffle. which is a variant of blade baffle. and hub-blade baffle with six blades are employed as baffle models. Through modal analysis. natural frequencies of each acoustic mode in baffled chambers are calculated and the reduction in natural frequencies caused by baffle installation is examined. Through harmonic analysis. acoustic pressure responses of each chamber to acoustic oscillating excitation are shown. The first tangential mode is found to be most sensitive to acoustic oscillation. Acoustic damping effect of baffle is quantified by damping factor. Damping effect of hub-blade baffle is the most appreciable and damping lac for of partied blade baffle is much lower than that of blade baffle. Damping effect of six-blade baffle on the second tangential mode is as much as on the first tangential mode and hub-blade baffle can damp out appreciably the first tangential as well as the first radial mode with the aid of hub.

Dispersion in Populations of Tropiometra carinata (Crinoidea: Comatulida) in the São Sebastião Channel, São Paulo State, Brazil

To understand the patterns of spatial distribution in populations of Tropiometra carinata (Lamarck), bi-monthly samples were collected in two areas of shallow water (Ponta do Baleeiro; PB, and Cabelo Gordo Beach; CG), in the São Sebastião Channel, using a grid superimposed on the habitat. A pattern of clumped dispersion was observed, with values for Morisita's Index significantly different from those of a random pattern. The mean densities at PB and CG, from December 1997 to October 1998, were respectively 2·20±0·21 (SD) and 2·32±0·28 (SD) individualsm−2. The length of the longest arm was used as an indicator of specimen size. The mean size at PB was 11·76±0·53cm and at CG, 9·65±0·18cm. The mean size of solitary individuals was greater than for clumped individuals in both areas. Small individuals tended to attach near clumps of greater individuals. The five principal microhabitats selected by these crinoids were lateral, upper and lower rock surfaces and lateral and upper rock crevices, with preferential attachment to lateral rock surfaces. The extent of substratum coverage by the zoanthidPalythoa caribaeorum varied between areas (74·1% at PB and 38·1% at CG), as did the association Tropiometra-Palythoa (81·4% at PB and 44·5% at CG). The clumped dispersion seen here optimizes filtration by enhancing the baffle effect.

Effect of operating variables on the yield of recombinant trypsinogen for a pulse-fed dilution-refolding reactor.

The inclusion body process route for manufacturing proteins offers distinct process advantages in terms of expression levels and the ease of initial inclusion body recovery. The efficiency of the refolding unit operation, however, does determine the overall economic feasibility of a process. Dilution refolding is the simplest and most extensively used refolding operation, although significant yield losses often occur due mainly to aggregation. Operating variables may have a significant effect on the degree of aggregation, but a systematic study has not been reported. This study investigates the effect of operating variables on the dilution refolding of solubilized r-trypsinogen inclusion bodies in a pulse-fed stirred reactor. Variables investigated were inclusion body washing, stirring speed, feed rate, concentration of solubilized r-trypsinogen, and concentration of urea during solubilization of the inclusion bodies. Additionally, the effect of baffles in the reactor was investigated. The yield of renatured r-trypsinogen varied between 12 +/- 0.2% and 21 +/- 1.0% depending on the specific combination of operating variables employed. It is clear that a suboptimal operating strategy can significantly reduce protein yield. In particular, we note that an increased intensity of mixing adversely affected yield in contrast to previous reports indicating that enhanced dispersion increases yield. We conclude that yield is determined not only by the efficiency of dispersion, but also by the local chemical environment of the protein as it folds, and the rate of change of this environment. This will be controlled by micromixing effects, and hence the intensity of agitation, in a complex manner requiring further characterization.

Effective elastic moduli and interface effects of nanocrystal-line materials

Many properties of nanocrystalline materials are associated with interface effects. Based on their microstructural features, the influence of interfaces on the effective elastic property of nanocrystalline materials is investigated. First, the Mori-Tanaka method is employed to determine the overall effective elastic moduli by considering a nanocrystalline material as a binary composite solid consisting of a crystal or inclusion phase with regular lattice connected by an amorphous-like interface or matrix phase. The effects of strain gradients are then examined on the effective elastic property by using the strain gradient theory to analyze a representative unit cell. Two interface mechanisms are elucidated that influence the effective stiffness and other mechanical properties of materials. One is the softening effect due to the distorted atomic structures and the increased atomic spacings in interface regions, and the other is the baffling effect due to the existence of boundary layers near interfaces.

Performance of airlift contactors with baffles

This work investigated the effect of baffles on hydrodynamics and gas–liquid mass transfer in an internal-loop airlift contactor (ALC). It was found that the introduction of baffles reduced liquid circulating velocity in the system. The riser gas holdup in the baffled contactor was found to be higher than the unbaffled, but due to the lower liquid circulation, the use of baffles resulted in a decreased downcomer gas holdup. The overall gas holdup and the rate of gas–liquid mass transfer were not significantly influenced by the presence of the baffles.

Mechanism of fluid flow in a continuous casting tundish with different turbo‐stoppers

The fluid flow in a continuous casting tundish affects the separation of non‐metallic particles and the cleanliness of the steel. Today, laser‐optical investigations of water models are state of the art and enable detailed information about the effect of baffles, i. e. dams, weirs and turbo‐stoppers, on the flow. In this work 3D‐LDA and 2D‐DPIV‐investigations for different turbo‐stoppers in a water model on a scale of 1:1.7 of a 16 t single strand tundish are presented. Three circular turbo‐stoppers are investigated. Detailed measurements of the mean velocity and turbulence intensity in the tundish with and without turbo‐stopper are shown. With a suitable turbo‐stopper geometry the recirculation area in the tundish centre and short‐circuit flows along the side walls can be avoided and thus more favourable residence time distributions can be obtained. It is shown that the turbo‐stopper produces higher turbulence in the inlet region of the tundish, which is spatially more limited, however, in relation to the flow without turbo‐stopper. Thereby a more homogeneous flow is created at the discharge of the tundish with better conditions for the particle separation. The experimental data yield a good understanding of the flow phenomena in a tundish with turbo‐stopper and are used as validating criterion for numerical simulations (Fluent 5.5) on the basis of the Reynolds equations. The turbulence modelling is based on a two‐equation model (realizable k‐ε model).

FEM based simulation of nonlinear effects in armature alerts

Although alerts or ringers have been used in wireless phones and pagers since their inception, design of these systems in the past has been limited to estimation of the Helmholtz resonance of the acoustic system followed by trial and error modification until the desired alert level is achieved. With the advent of reasonably fast Vibro-Acoustic Boundary Element and Finite Element solvers, a much more accurate and inclusive method of alert system design is possible. BEM and FEM alert models can take into account the baffling effects of the phone or pager case, losses due to surface absorption and transmission loss, geometrical characteristics of the system’s ports and cavities, and the frequency dependent vibration characteristics of the transducer. These simulation capabilities, combined with Doppler laser vibrometer based alert characterization, provide for an improved alert design cycle. This paper will discuss some of the new alert characterization and simulation techniques used in the Motorola PCS Research Advanced Products Lab. The results of this technique will be compared to measured data and earlier simulation attempts, and future enhancements to the current technique will also be discussed.

A New Method of Calculating Radiation Impedance for Vibrating Surface with Finite Baffle

In this paper, by defining a vibrating surface to be a set of small point sources, a new calculation method for the rectangular vibrating surface with a finite baffle is suggested by considering the effect of the finite baffle on the source strength of each point source. As an example, the variation in self-radiation impedance for a rectangular vibrating surface is calculated based on the size of the baffle.