Effect Of Baffles Research Articles

Effects of perforated baffle on reducing sloshing in rectangular tank: Experimental and numerical study

A liquid sloshing experimental rig driven by a wave-maker is designed and built to study liquid sloshing problems in a rectangular liquid tank with perforated baffle. A series of experiments are conducted in this experimental rig to estimate the free surface fluctuation and pressure distribution by changing external excitation frequency of the shaking table. An in-house CFD code is also used in this study to simulate the liquid sloshing in three-dimensional (3D) rectangular tank with perforated baffle. Good agreements of free surface elevation and pressure between the numerical results and the experimental data are obtained and presented. Spectral analysis of the time history of free surface elevation is conducted by using the fast Fourier transformation.

Faisabilité d’un observatoire de cancers ciblés sur le département des Bouches-du-Rhône

An experimental laboratory study was performed to measure the effect of acoustic noise on the magnitude of tube vibrations in a staggered tube array and to measure the effectiveness of baffles on suppressing transverse duct modes. The acoustically induced tube vibration was experimentally determined for a flexible tube in three different transverse locations in the tube array. It was found that a tube located in the center of the duct, where a nodal point of the acoustic pressure resided, was most influenced by the transverse mode. On the other hand, a tube located near the duct side wall, where the acoustic pressure oscillation was highest, was not affected by the acoustic standing wave since it produced almost imperceptible vibration. It is shown that the acoustic pressure gradient across a tube is the cause of the tube vibration. Experiments were also performed to determine the effect of baffles for reducing the noise of acoustic resonance. The results showed that a single baffle substantially reduced the first mode resonance, as long as it was located close to the center of the bundle. The insertion of two baffles, in various locations, effectively eliminated acoustic resonance in the 1st and 2nd transverse duct modes. It is seen that the third acoustic mode is not significantly affected by either one or two baffles.

Numerical Based Heat Transfer and Friction Factor Correlations of Rectangular Ducts Roughened With Transverse Perforated Baffles

A numerical investigation has been carried out for a range of flow and geometrical parameters in order to analyze the effect of transverse perforated baffles attached on the heated wall of rectangular duct on heat transfer and friction factor. An increase in heat transfer and friction loss over a smooth surface has been observed for duct having perforated baffles as a roughness element. Numerical results have been used to develop the Nusselt number and friction factor correlations as a function of flow and geometrical parameters for predicting performance of the system having investigated the type of roughness elements. doi: 10.14456/WJST.2014.33

Flow Field and its Flowability in a Stirred Tank with a Plate Propeller

The flow field produced by a plate propeller in a fully baffled flat bottomed cylindrical stirred tank with the diameter of 300 mm was measured using phase doppler particle analyzer. The radial distributions of the time-averaged, fluctuation velocity and turbulent kinetic energy were analyzed. The effects of off-bottom clearance and baffle on the flow field were investigated. The results showed that the fluctuation velocity and turbulent kinetic energy increased with increasing off-bottom clearance in the impeller region; meanwhile, the maximum values of the time-averaged and fluctuation velocity moved to the center of the stirred tank. The maximum axial velocity decreased with increasing off-bottom clearance in the bulk flow. The turbulent kinetic energy was higher in the impeller region. The maximum value of the turbulent kinetic energy increased with increasing off-bottom clearance and occurred near the end of the impeller. The baffle hindered the tangential velocity and exerted strong influence on the turbulent kinetic energy. The flow field in front of the baffle reflected the distribution of the turbulent kinetic energy in the impeller region.

Performance of annular centrifugal extractors: CFD simulation of flow pattern, axial mixing and extraction with chemical reaction

Annular centrifugal extractors (ACE) based on Taylor–Couette flow have been studied for axial mixing and mass transfer with chemical reaction. The residence time distribution (RTD) was measured in three size extractors having 50, 150 and 250mm rotor diameter. The power consumption per unit mass in the annular region was in the range of 25–750W/kg. Alkaline hydrolysis of a chloro-substituted ester was carried out in ACE-50 at various rotor speeds. The effect of helical baffles on axial mixing and in turn on chemical reaction was observed by conducting two separate sets of experiments, viz., in the absence and in presence of helical baffles. An excellent agreement has been observed between the experimental results and the CFD predictions of the extents of axial mixing and chemical reaction.

Analysis of a double pipe heat exchanger performance by use of porous baffles and pulsating flow

A numerical investigation is carried out to analyze the effect of porous baffles and flow pulsation on a double pipe heat exchanger performance. The hot fluid flows in the inner cylinder, whereas the cold fluid circulates in the annular gap. The Darcy–Brinkman–Forchheimer model is adopted to describe the flow in the porous regions and the finite volume method is used to solve the governing equations with the appropriate boundary conditions. The effects of the amplitude and frequency of pulsation, as well as the porous baffles permeability on the flow structure and the heat exchanger efficiency are analyzed. The results reveal that the addition of an oscillating component to the mean flow affects the flow structure, and enhances the heat transfer in comparison to the steady non pulsating flow. The highest heat exchanger performance is obtained when only the flow of the hot fluid is pulsating.

Numerical Simulation of the Effects of Baffle on Flow Field in a Stirred Tank

Flow characteristics of stirred tanks with different structures were calculated by taking RNG k-ε model as the turbulent flow model. The results showed that at the same rotational speed, a large number of axial and radial vortexes were formed in the stirred tank with the baffle. The velocity in the blade area was high, and it decreased rapidly with the increasing distance to the blade. The double peak area of the radial velocity was formed in the stirred tank with baffle, and the high and low speed cycles were obtained in the cross-section. The baffle increased not only the axial circulation of the liquid in the tank but also the radial circulation, which help to mix the liquid.

Acoustic Waves in Baffled Combustion Chamber with Radial and Circumferential Blades

A linear acoustic analysis has been conducted to study the combustion instability characteristics of three-dimensional baffled combustion chambers. The theoretical formulation is based on a generalized wave equation. Normal mode expansion and spatial averaging techniques are implemented to solve for the acoustic motions in the chamber. Several specific effects of radial and circumferential baffles, and the mechanisms by which baffles eliminate combustion instabilities, are presented. Longitudinalization of transverse waves inside baffle compartments, restriction of velocity fluctuations near the injector face, and reduction in oscillation frequency are studied systematically. The effects of mean flow, temperature nonuniformities, and combustion response on the baffle design and stability behaviors are investigated. Potential destabilizing influences of baffles are found to be the concentration of acoustic pressure at the injector face and of acoustic velocity near the baffle tips, as well as their ensuing interactions with local combustion processes.

Effect of semi-circular baffle blocks on local scour downstream clear-overfall weirs

Local scour downstream hydraulic structures may result in damage or complete structural failure and loss of life and property. In this paper, an experimental study was conducted to predict the scour geometry downstream a Fayoum type weir and to minimize the scour using a row of semi-circular baffle blocks. The considered shape in this research is easy to be used as an extra element to existing water structures in order to minimize local scour downstream these structures. A hundred 53 runs were carried out considering various heights and positions of baffle blocks with different flow conditions. A case of flat floor without baffles was included in the test program to estimate the influence of using the baffle piers. Results were analyzed and graphically presented, and simple formulae were provided to evaluate the scour parameters.

Effects of Transverse Baffle Design on Reducing Liquid Sloshing in Partially Filled Tank Vehicles

Longitudinal liquid sloshing in partially filled clear-bore tanks causes extensive degradation of tankers braking performance. To reduce the negative effect of longitudinal liquid sloshing on tankers, three kinds of transverse baffles were designed, namely, the conventional baffle, the circular baffle, and the staggered baffle. Each kind of baffle took several forms to investigate the impact of baffle installation angle, the sizes of holes pierced on the baffle, and their arrangement on the antisloshing effect. FLUENT software was used to simulate liquid sloshing in tanks equipped with different kinds of transverse baffles and subject to constant braking deceleration. A time-series analysis of the forces act on tank walls and transverse baffles was carried out. It was drawn that the baffle shape and its installation angle have great impact on the antisloshing effect of baffles. The study on the antisloshing effect of different transverse baffles is of great significance for tank vehicle driving and braking safety, as well as for the design of optimal transverse baffles.

Influences of geometry and flow pattern on hydrogen separation in a Pd-based membrane tube

The abatement of concentration polarization in a membrane tube is of the utmost importance for improving the efficiency of hydrogen separation. In order to enhance the performance of hydrogen separation, the characteristics of hydrogen permeation in a Pd-based membrane system under various operating conditions and geometric designs are studied numerically. The effects of Reynolds numbers, shell size, baffle, and pressure difference on hydrogen mass transfer across the membrane are evaluated. The predictions suggest that a larger shell deteriorates concentration polarization, stemming from a larger H2 concentration boundary layer. Baffles equipped in the shell are conducive to disturbing H2 concentration boundary layer and reducing concentration polarization at the retentate side, thereby intensifying H2 permeation. The more the number of baffles, the less the increment of improvement in H2 permeation is. The installation of one baffle is recommended for enhancing H2 separation and it is especially obvious under the environments of high pressure difference. Within the investigated ranges of Reynolds number at the permeate side and the retentate side, the feasible operating conditions are suggested in this study.

Computational fluid dynamics (CFD) simulation of effect of baffles on separation in mixer settler

The main ideas in the development of the solvent extraction mixer settler focused on achieving clean phase separation, minimizing the loss of the reagents and decreasing the surface area of the settlers. The role of baffles in a mechanically agitated vessel is to ensure even distribution, reduce settler turbulence, promote the stability of power drawn by the impeller and to prevent swirling and vortexing of liquid, thus, greatly improving the mixing of liquid. The insertion of the appropriate number of baffles clearly improves the extent of liquid mixing. However, excessive baffling would interrupt liquid mixing and lengthen the mixing time. Computational fluid dynamics (CFD) provides a tool for determining detailed information on fluid flow (hydrodynamics) which is necessary for modeling subprocesses in mixer settler. A total of 54 final CFD runs were carried out representing different combinations of variables like number of baffles, density and impeller speed. CFD data shows that amount of separation increases with increasing baffles number and decreasing impeller speed.

Reaction Pathways for Hydrogen Uptake of the Li–Mg–N-Based Hydrogen Storage System

Hydrogen storage properties and mechanisms of the Li3N–xMg3N2 (x = 0, 0.25, 0.5, 1.0) composites were investigated in this paper. It was found that the Li3N–0.25Mg3N2 composite exhibited optimal hydrogen storage performances as it can store reversibly ∼8.4 wt % hydrogen with an onset temperature of 125 °C for dehydrogenation. Upon absorbing hydrogen, Li3N converted to Li2NH and LiH first and was further hydrogenated to generate LiNH2. The newly developed LiNH2 then reacted with Mg3N2 under hydrogen pressure to produce Li2Mg2N3H3 and MgNH. Finally, Li2Mg2N3H3 and MgNH along with LiNH2 further reacted with hydrogen to form the resultant products of Mg(NH2)2 and LiH. More Mg3N2 in the Li3N–xMg3N2 composites retarded Li3N to react with H2 at the beginning of hydrogenation due to the baffle effect but facilitated the hydrogenation of Mg3N2 at the second-stage hydrogenation because of the decreased particle size and the frequent contact of the constituent species.

Numerical study of sloshing liquid in tanks with baffles by time-independent finite difference and fictitious cell method

The numerical analysis of liquid sloshing in tanks is a big challenge when the fully nonlinear and viscous effects are all included in the analysis. The analysis will become more complicate as the tank is attached with internal structures, such as baffles. The width of the baffle is very thin compared with the breadth length and the numerical technique used to capture the detailed flow phenomenon (vortex generation and shedding) around the baffle is very rare in the literatures. In this paper, a time-independent finite difference scheme with fictitious cell technique is used to study viscous fluid sloshing in 2D tanks with baffles. The Navier–Stokes equations in a moving coordinate system are derived and they are mapped onto a time-independent and stretched domain. The developed numerical model is rigorously validated by extensive comparisons with reported results. An experiment setup was also made to validate the present numerical sloshing results in a tank with baffles. The method is applied to a number of problems including impulsive flow past a flat plate, sloshing fluid in a 2D tank with a surface-piercing baffle, sloshing fluid in 2D tanks with bottom-mounted baffles. The effects of baffles on the resonant frequency are discussed. The present developed numerical model can successfully analyze the sloshing phenomenon in 2D tanks with internal structures and can be easily extended to 3D model.

Enhancement of cell characteristics via baffle blocks in a proton exchange membrane fuel cell

In this study, the effects of baffle blocks located in the flow channel on fuel cell characteristics were investigated. The higher current densities were obtained from the cells with blockage than without blockage. It was observed that the gap between the tip of the baffle block and the channel wall had a significant effect on the current density produced and on the convergence of solutions. The number and the size of blocks that are providing the highest current density from the cell were determined. No significant effects were observed in the polarization curves for cells with more than four blocks and gap ratio of 0.3. A parametric study was conducted to investigate the effect of the relative humidity and velocity of inlet gases on cells with four blocks and gap ratio of 0.3. It was concluded that the current density is strongly dependent on the relative humidity for low inlet velocities and on the other hand, on the inlet velocity for low relative humidities.

Effect of baffles on fluid flow field in stirred tank with floating particles by using PIV

AbstractPIV technique was applied to elucidate the effect of baffles at different shaft positions and different impeller off‐bottom clearances on the flow field in a stirred tank with floating particles. The investigation was carried out in a cylindrical tank with a flat base, and five different baffle configurations: standard baffles, narrow baffles with a width of 15 mm, narrow baffles with a width of 10 mm, down triangular baffles and up triangular baffles. The measurements show that down triangular baffles offers several advantages over standard baffles at C = T/3: high axial and radial velocities, relatively Low critical agitation speed and power consumption for just drawdown of 1.0 vol.% floating particles. While at C = T/2 this superiority disappears and the fluid flow field is similar to that for standard baffles. The other baffles are similar in performance except for a small difference in the critical agitation speed. An off‐centred shaft helps reduce the critical just drawdown speed and the corresponding power consumption for baffle configurations considered. With down triangular baffles, the critical power consumption to draw down the floating particles for the most eccentric shaft is about 42% of that for a centred shaft. © 2012 Canadian Society for Chemical Engineering

Effects of Baffle on Entropy Generation in Separated Convection Flow Adjacent to Inclined Backward-Facing Step

Numerical simulations of a two-dimensional laminar forced convection flow adjacent to inclined backward-facing step in a rectangular duct are presented to examine effects of baffle on flow, heat transfer and entropy generation distributions. The main aim of using baffles is to enhance the value of convection coefficient on the bottom wall. But the useful energy can be destroyed due to intrinsic irreversibilities in the flow by the baffle. In the present work, the amount of energy loss is estimated by the computation of entropy generation. The values of velocity and temperature which are the inputs of the entropy generation equation are obtained by the numerical solution of momentum and energy equations with blocked-off method using computational fluid dynamic technique. Discretized forms of the governing equations in the (x, y) plane are obtained by the control volume method and solved using the SIMPLE algorithm. Numerical expressions, in terms of Nusselt number, entropy generation number, Bejan number and coefficient of friction are derived in dimensionless form. Results show that although a baffle mounted onto the upper wall increases the magnitude of Nusselts number on the bottom wall, but a considerable increase in the amount of entropy generation number takes place because of this technique. For validation, the numerical results for the Nusselt number and entropy generation number are compared with theoretical findings by other investigators and reasonable agreement is found.

Passive protection of the ITER diagnostic mirrors

A conservative engineering model of the impurity deposition on the diagnostic mirrors is proposed. The model is applied to analyze numerically the effect of protecting structures (ducts) with and without baffles in the conditions of the ITER main chamber. It was found that the gross deposition rate in the ducts with baffles, if they are long enough, can be made by an order of magnitude smaller than that in the ducts of an equivalent length without baffles. This model prediction can be tested experimentally. The calculated efficiency of the impurity flux attenuation depends strongly on the model assumption: the variation between the ‘best’ and ‘worst’ cases reaches two orders of magnitude. A case study with the real 3D geometry of one specific diagnostic, core-CXRS, is conducted. For this particular geometry, the effect of baffles is nearly marginal; that is, this is not a universal solution.

Numerical Investigation of Baffle Effect on the Flow in a Rectangular Primary Sedimentation Tank

Numerical Investigation of Baffle Effect on the Flow in a Rectangular Primary Sedimentation Tank

Effects of Baffle Configurations on the Performance of a Potable Water Service Reservoir

AbstractBecause a baffle is a device used for altering the flow pattern in a tank, the use of a baffle wall was considered to modify an existing potable water service reservoir operating as a storage tank to achieve better water quality. Therefore, it is of great interest to study the effects of baffle configurations on the performance of the service reservoir. With the advancement of computational science and resources, a Computational Fluid Dynamics (CFD) method has become a reliable alternative to flow and tracer tests. Adopting dynamic meshes, this study investigates the effects of baffles, located at various locations, on the flow pattern and chlorine concentration distribution of a potable water service reservoir in Singapore during the refilling phase. The results of this study show a dual effect of the baffles located at the flow recirculation region. On one hand, it can break up the vortex to shorten the flow path. On the other hand, the velocity magnitude of the fluid is reduced after flowing pa...