Influence Of Baffles Research Articles

Flow modelling of particulate matter by using baffles placed in the flue tract of wood stove

It is very important to separate particulate matter before their leaving into the air because of their harmful impact on human health. It exists a lot of devices, which can separate these particles. But their implementation and operation in small heat source can be considerably difficult on finances, and often have complex maintenance. Therefore, it is important to look for solutions of reduction the producing of particulate matter with easier maintenance and also less financial difficulty. This article deals with flow modelling of particulate matter by using baffles placed in the flue tract of wood stove. Influence of baffles is observed by using CFD simulations.

Plane-wave decomposition and ambisonics output from spherical and nonspherical microphone arrays

Any acoustic sensor embedded in a baffle disturbs the spatial acoustic field to a certain extent, and the recorded field is different from a field that would have existed if the baffle were absent. Recovery of the original (incident) field is a fundamental task in spatial audio. For some sensor baffle geometries, such as the sphere, the disturbance of the field by the sensor can be characterized analytically and its influence can be undone to recover the incident field. However, for arbitrary shaped baffles, numerical methods have to be employed. In the current work, the baffle influence on the field is characterized using boundary element methods, and a framework to recover the incident field from measurements from sensors embedded on the baffle in the plane-wave function basis is developed. Field recovery also allows generation of high-order ambisonics representations of the spatial audio scene. Experimental results using both complex and spherical scatterers will be presented.

The baffle influence on sound radiation characteristics of a plate

The acoustic radiation characteristics of the baffle plates and unbaffle plates are calculated and compared by single-layer potential and double-layer potential. Based on the boundary integral equation, the sound pressure integral equation of the baffle and the baffle are deduced respectively. According to the boundary compatibility condition, the sound pressure and the vibration velocity of the plates are obtained. Further, the dynamic equation of the structure is substituted into the vibration equation in the form of the baffle plate and the baffle plate. The sound pressure difference and the displacement of a plate surface are in the form of the vibration mode superposition and the acoustic radiation impedance of the double integral form is obtained, which determines vibration mode coefficient and sound radiation parameters. The effect of the baffle on the acoustic radiation characteristics of the thin plate is analyzed by comparing the acoustic radiation parameters with the simple and simple rectangular plate in water.

INVESTIGATION OF ADMIXTURE SEDIMENTATION IN THE HORIZONTAL SETTLER

Purpose.Sedimentation by gravity is the most common and extensively applied treatment process for the removal of solids from water and wastewater and it has been used for over one hundred years. Sedimentation tanks are one of the major parts of a treatment plant especially in purification of turbid flows. Horizontal settlers are mainly used for purification of high quantity of water. In these tanks, the low speed turbid water will flow through the length of the tank and suspended particle have enough time to settle. Finding new and useful methods for calculating and increasing hydraulic efficiency of horizontal settlers is the objective of many theoretical, experimental and numerical studies.But currently used models and methods in Ukraine do not allow taking into account geometrical form and various design features. In this paper the numerical model was developed to evaluate the effectiveness of horizontal settler with modified structure. Methodology. Numerical model is based on: 1) equation of viscous fluid dynamics; 2) mass transfer equation. For numerical simulation the finite difference schemes are used. The numerical calculation is carried out on a rectangular grid. For the formation of the computational domain markers are used. Findings.The model allows obtaining the purification process in the settler with different form and different configuration of baffles. Originality. A new approach to investigate the mass transfer process in horizontal settler was proposed. This approach is based on the developed CFD model. The fluid dynamics model was used for the numerical investigation of flows and waste waters purification. To investigate influence of baffles on settler efficiency physical experiment was carried out. Practical value.The developed model has more capacity than the existing models in Ukraine. The developed model allows computing quickly the efficiency of water purification in settlers. The model is not computationally expensive. Calculation time of one variant of the problem takes few minutes.

A Study on Velocity Profiles between Two Baffles in a Horizontal Circular Tube

The shell and tube heat exchanger is an essential part of a power plant for recovering transfer heat between the feed water of a boiler and the wasted heat. The baffles are also an important element inside the heat exchanger. Internal materials influence the flow pattern in the bed. The influence of baffles in the velocity profiles was observed using a three-dimensional PIV (Particle Image Velocimetry) around baffles in a horizontal circular tube. The velocity of the particles was measured before the baffle and between them in the test tube. Results show that the velocity vectors near the front baffle flow along the vertical wall, and then concentrate on the upper opening of the front baffle. The velocity profiles circulate in the front and rear baffle. These profiles are related to the Reynolds number (Re) or the flow intensity. Velocity profiles at lower Re number showed complicated mixing to obtain the velocities and concentrate on the lower opening of the rear baffle as front wall. Numerical simulations were performed to investigate the effects of the baffle and obtain the velocity profiles between the two baffles. In this study, a commercial CFD package, Fluent 6.3.21 with the turbulent flow modeling, k-e are adopted. The path line and local axial velocities are calculated between two baffles using this program.

Velocity profiles between two baffles in a horizontal circular tube

The shell and tube heat exchanger is an essential part of a power plant for recovering heat transfer between the feed water of a boiler and the wasted heat. The baffles are also an important element inside the heat exchanger. Internal materials influence the flow pattern in the bed. The influence of baffles in the velocity profiles was observed using a three-dimensional particle image velocimetry around baffles in a horizontal circular tube. The velocity of the particles was measured before the baffle and between them in the test tube. Results show that the flows near the front baffle flow were parallel to the vertical wall, and then concentrate on the upper opening of the front baffle. The flows circulate in the front and rear baffles. These flow profiles are related to the Reynolds number (Re) or the flow intensity. The velocity profiles at lower Re number showed a complicated mixing, concentrating on the lower opening of the rear baffle as front wall. Swirling flow was employed in this study, which was produced using tangential velocities at the inlet. At the entrance of the front baffle, the velocity vector profiles with swirl were much different from that without swirl. However, velocities between two baffles are not much different from those without swirl.

Fluid-Structure Interaction Modelling of Internal Structures in a Sloshing Tank Subjected to Resonance

In this paper we develop a three-dimensional, fully coupled, partitioned-based fluid-structure interaction (FSI) model for liquid sloshing analysis in partially filled containers. Different tank geometries are considered in the present study focusing on both the rigid and flexible baffles and their influence on slosh loads at the tank walls. For the purpose of validation, we develop a stand-alone CFD model and compare the results with the previously existing numerical model and experimental data from the literature. Once such a validation is complete, we incorporate a rigid baffle like obstruction to study the effect of the baffle on sloshing using the stand alone CFD model. The numerical simulations predict that the influence of baffle like obstructions can help in mitigating the tank resonance. Using the standalone CFD model as a base, we develop a FSI model by incorporating the elastic-plastic material properties on the baffle to study the effect of a flexible baffle inside a sloshing tank. A comparative study between the force response of the rigid and flexible baffles during various slosh loads is examined by varying the amplitude of the tank excitation for the same fill level and frequency. The FSI model reveals details on slosh forces experienced by the baffle that are dampened owing to its flexibility. In addition to predicting the forces on the baffle, the FSI model also helps to predict the corresponding nodal displacements and stress states of the baffle under various slosh loads.

Interactions of spout jets in a multiple‐spouted bed

A three‐dimensional (3D) computational fluid dynamics (CFD) model, coupling with two‐fluid model (TFM) approach is adopted to investigate the interactions of spout jets and to evaluate the effects of baffles in a multiple‐spouted bed. For two typical flow patterns, that is single spouting and double‐spouting, characteristics of flow patterns, solid velocity and voidage are investigated with varying spouting gas flow rates. Influence of baffles set in the bottom of the bed is also studied in three typical flow patterns. Results show that for double‐spouting, the central spouting push off the lateral spouts, and the push force is increasingly obvious with increasing central spouting gas flow rate; for single spouting, when the lateral spouting gas flow rates increase, the central spout is destroyed and the gas‐solid flow becomes unstable. Baffles in different flow patterns (single spouting, double‐spouting and triple‐spouting) exert different effects on the solid movements.

3차원 수치모의를 통한 침사지에서의 부유사 밀도류 해석

A sedimentation basin is used to remove suspended sediments which can cause abrasive and erosive wear on hydraulic turbines of hydropower plants. This sediment erosion not only decreases efficiency of the turbine but also increases maintenance costs. In this study, the three-dimensional numerical simulations were carried out on the overseas hydropower project. The simulations of flow and suspended sediment concentration were obtained using FLOW-3D computational fluid dynamics code. The simulations provide removal efficiency of a sedimentation basin based on particle sizes. The influence of baffles on the flow field and the removal efficiency of suspended sediments in the sedimentation basin has been investigated. This paper also provides the numerical simulations for sediment-induced density currents that may occur in the sedimentation basin. The simulation results indicate that the formation of density currents decreases the removal efficiency. When a baffle is installed in the sedimentation basin, the baffle provides intensive settling zones resulting in increasing the sediments settling. Thus the enhanced removal efficiency can be achieved by installing the baffle inside the sedimentation basin.

Experimental Study of the Influence of Baffles on Hydrodynamics of Gas- Solids Fluidized Bed System

Experimental Study of the Influence of Baffles on Hydrodynamics of Gas- Solids Fluidized Bed System

The Influence of Baffles on the Natural Convection in Trapezoidal Cavities

This article presents an investigation into natural convection in trapezoidal cavities. It examines a cavity whose floor and upper inclined walls are both adiabatic, while the vertical walls are isothermal. For these isothermal walls, we consider two thermal boundary conditions. Under the first condition, the short wall on the left side is heated as the tall one on the right side is cooled. The second condition is the reverse of the first—the short wall is cooled as the tall one is heated. Considering laminar conditions and a two-dimensional system, steady-state computations are carried out to assess the effects of one and two baffles, the baffle's height (H b ), Rayleigh number, 103 ≤ Ra ≤ 106, and three Prandtl number values. To demonstrate the various effects, the results from several designed case studies are shown in terms of isotherms, streamlines, and local and average Nusselt numbers in order. Predictions reveal that the second baffle decreases the cavity's fluid flow and heat transfer. As the height of the baffle rises, the heat transfer drops drastically. Also, two baffles produce more pronounced thermal stratification than only one.

Passive Control of the Flow Around the Stratospheric Observatory for Infrared Astronomy

The unsteady flowfield around the Stratospheric Observatory for Infrared Astronomy, a reflecting telescope carried inside an open port of a Boeing 747SP, has been simulated by means of detached eddy simulations and unsteady Reynolds-averaged Navier–Stokes simulations. Vortex generators have been placed upstream of the cavity to control the shear layer spanning the opening. The influence of baffles and displacement bodies placed inside the telescope port on the frequencies of acoustic resonant modes was investigated by acoustic simulations, based on the solution of the homogenous Helmholtz equation. The objective of this study is to improve the telescope’s performance by mitigating the amplitudes and changing the characteristic frequencies of the pressure fluctuations inside the cavity. The present simulations show that the investigated measures have a high potential to increase the telescope’s pointing stability.

Spatio-temporal analysis of macro-instability in a stirred vessel via digital particle image velocimetry (DPIV)

To characterize the flow instability in mechanically agitated vessels, digital particle image velocimetry (DPIV) was used to measure the near-instantaneous flow fields in a baffled, stirred vessel, equipped with a Rushton turbine impeller of large diameter ratio of impeller to vessel. From the measured near-instantaneous flow fields, distinct large-scale flow patterns were identified and the formation mechanisms of the patterns were explored via multi-scale analysis. Further investigations show that the flow patterns are rather complex. Macro-instability (MI) appears as a switch among those flow patterns. Spectral distribution function P( f), equivalent to probability distribution function from a purely mathematical point of view, was introduced to extract information on MI from the time series of the vorticity of the fluctuating velocity field. The two-dimensional distribution of MI and its dependence on Reynolds number were studied. Results show that probability analysis via spectral distribution function can be successfully used to quantify the relative intensity of macro-instabilities. Low-frequency, large-scale fluctuations of flow patterns were much more intensive in the lower and upper corner of the vessel than in the rest parts of the vessel. The fluctuations of flow patterns also had an offset to the core of the vessel due to the influence of baffles. Compared with visual observation technique, this new analysis method via DPIV is more objective and can be used to give deep understanding to the spatio-temporal properties of macro-instability.

Linear and non-linear pressure oscillations in baffled combustion chambers

Abstract Linear and non-linear analyses of acoustic waves in baffled combustion chambers have been developed by means of perturbation-expansion techniques. The formulation is based on a generalized wave equation derived from the conservation equations for a two-phase mixture, and accommodates all influences of non-linear gas dynamics and combustion responses. Several specific effects of baffles are presented as mechanisms by which baffles eliminate combustion instabilities. Included are longitudinalization of transverse waves inside baffle compartments, restriction of velocity fluctuations near the injector face, and decreased oscillation frequency. A potential destabilizing influence of baffles is found to be the concentration of acoustic pressure at the injector face. Primary aspects of limit cycles are examined by considering second order non-linear acoustics for both two- and three-dimensional cases. Conditions for the existence of limit cycles were obtained, as well as explicit formulas for the oscillation amplitudes and frequencies in terms of linear and non-linear parameters. Important features of the energy cascade among acoustic modes are elucidated, including the energy balance during limit cycles and transfer of energy by non-linear gas dynamics.

Mass transfer to viscous liquids in bubble columns and air-lift reactors: influence of baffles

Gas—liquid mass transfer has been studied in highly viscous Newtonian and non-Newtonian liquids contained in (i) a bubble column of 0.14 m diameter and (ii) an air-lift reactor formed by introducing a draft tube, 0.09 m in diameter, into the bubble column. The mass transfer coefficient, k L a, has been calculated from the rate of mass transfer determined experimentally by noting continuously the weight of pure CO 2 gas absorbed in these liquids. Effects of liquid viscosity, liquid height and gas sparger have been investigated in the bubble column. In addition, the influence of baffles such as baffle caps and sieve plates, introduced into (i) the bubble column and (ii) the draft tube of the air-lift reactor, has also been studied. The effect of sparger (number and diameter of holes) on gas hold-up and k L a was found to be strong at low liquid height: at a given gas velocity, gas hold-up and k L a decreased with increasing liquid height up to 0.8 m; above this height, they remained unaffected. Liquid viscosity strongly influenced k L a but hardly affected the gas hold-up: k L a decreased as viscosity increased; this decrease was marked up to about 0.3 Pa s, above which value, the decrease was gradual. For viscous Newtonian liquids, k L a values in the air-lift reactor were lower than those in the bubble column; this is due to the lower gas hold-up in air-lift reactor caused by the higher liquid circulation velocity and the bubble coalescence in the draft tube. Introduction of baffles in the bubble column and air-lift reactor enhanced the interfacial area and hence k L a. For shear thinning liquids contained in the air-lift reactor, the increased liquid circulation velocity also resulted in a lower value of apparent viscosity, this had a favourable effect on mass transfer. Following a similar argument, the introduction of baffles in the bubble column and air-lift reactor reduced liquid circulation velocity and increased the apparent liquid viscosity. Hence for the shear thinning liquids, the benefit of bubble break-up caused by the baffles is partially offset by the effect of higher liquid apparent viscosity.

Recycling and neutral transport in the DIII-D tokamak

Several diagnostics have been used to characterize the edge plasma in the DIII-D divertor region and thereby to understand the particle recycling and neutral particle transport in an open divertor. An array of Langmuir probes mounted on the carbon divertor plates determines that generally the electron temperature is low ( T e ⋍ 10–20 eV ), and the electron density is high ( n e ⋍ 5 × 10 19 m −3 ). The edge plasma temperature and density are also measured by a moveable Langmuir probe mounted at the midplane of the plasma; the data from these shot-by-shot edge radial scans are then connected with the data for the core plasma obtained by Thomson scattering. The heat flux to the divertor plates is measured by an absolutely calibrated infrared camera; a plasma model is used to compare the heat flux with the measured T e and n e . The molecular neutral pressure at the edge of the plasma at several poloidal and toroidal locations is obtained from absolutely-calibrated pressure gauges; a gas puff enables in-situ gauge calibrations before each plasma shot. Typically, the divertor pressure is 10–50 times larger than that at the midplane. Time-resolved H α brightness measurements are obtained from an absolutely calibrated television camera viewing the divertor region from above; both strike points are viewed simultaneously. The emission from the inner and outer strike points are usually equal after the H-mode transition, but are often unequal after the first ELM in H-mode and during some phases of L-mode discharges. A tangential camera measures the falloff in emission from the X-point to the plasma midplane. These measurements have been modeled with the DEGAS neutral transport code specifically modified for DIII-D. The wall geometry, wall composition, measured magnetic geometry, and measured plasma parameters are inputs to the model. The code calculates the gauge pressure as a function of position and the H α television picture directly. During H-mode, we find a factor of two agreement in both the measured pressures and the absolute H α brightnesses with one exception: the measured divertor pressure is higher than the code prediction. However, we find that a local gas source located below the X-point equal to only 10% of the divertor recycling source will bring the divertor pressure into agreement with the data. A difference in the electron temperature and density at the two strike points has been used to model the asymmetric H α emissions. Comparisons have been made between the model and the data during H-mode periods of the discharge. The model has also been used to predict the influence of baffles to form a more closed divertor configuration.

Influence of baffles upon natural-convective steady-state heat transfers inwards across horizontal eccentric annuli

Flow patterns, temperature distributions and steady-state heat transfers inwards across a horizontal annular, atmospheric-pressure, air-filled eccentric cavity have been determined. Several different configurations of two low-conductivity baffles (arranged symmetrically with respect to the vertical plane through the centre-lines of the pipes), inserted across the cavity and extending its whole length, were tested. With the horizontal inner pipe located at a vertical eccentricity of −0·65 (i.e. in the lower region of the outer pipe), the optimal inclination of the two baffles, corresponding to the least rate of convective heat exchange, was achieved at ±140° from the vertically downwards radius vector emanating from the centre of the inner pipe. This enabled a reduction of ∼6% in the steady-state convective heat leak to be achieved compared with that for the plain eccentric annulus under similar temperature differences between the pipes. However, by using a vertical baffle (i.e. at an angle of 0°), an increase of ∼ 14% in the convective heat leak through the air occurred. The results agree qualitatively with those expected on the basis of previous studies for the inverse case (of a concentric annulus) with the heat flowing outwards.

Flow pattern, circulation velocity and pressure loss in loop reactor.

A loop reactor is regarded as a new type of reactor for bulk polymerization of olefins. Several approaches to evaluate its performance are made herein. A simple model of discharge flow is proposed and related with the results obtained by measurement of average circulation velocity. The average circulation velocity is proportional to impeller speed and the sine of the impeller blade angle. It depends upon Reynolds number and dimensions of the impeller. Flow pattern was measured and the influence of baffles and impeller geometry is discussed qualitatively. In the case of unbaffled conditions, fluid flows in a helical motion. Intensity of this motion increases with impeller speed and pitched angle. In the case of baffled conditions, tangential velocity component is suppressed and normalized distribution of axial velocity is independent of impeller geometry. Pressure distribution was measured and pressure loss was obtained. Total pressure loss shows good agreement with the value calculated by superposition of frictional loss in straight parts and bend loss in bends obtained from established correlations.

The influence of baffles in packed beds on radial transport

The influence of baffles in packed beds on radial transport