Baffled Tank Research Articles

CFD simulation of hydrodynamics characteristics in a tank with forward-reverse rotating impeller

BackgroundA forward-reverse rotating impeller was used in an unbaffled tank to improve the mixing efficiency. Flow field and power characteristics in the tank were numerically studied. MethodsComputational fluid dynamics(CFD) simulations were performed to investigate hydrodynamics in the unbaffled tank. The Reynolds stress turbulence (RST) model along with a sliding mesh approach was used to predict instantaneous flow fields in the stirred tank. Significant findingsFluid in the unbaffled tank flows periodically with the forward-reverse impeller agitation. Zonal flow phenomenon was found for the fluid affected by agitation in different directions. The effects of operating conditions on instantaneous fluid velocity vary with positions in the tank. Flow field characteristics in the forward-reverse agitated unbaffled tank are very different from those in constant agitated unbaffled and baffled tanks. Generally, transient power consumption is only the function of its corresponding transient rotational speed. The averaged impeller power number is a constant and is not affected by maximum rotational speed and cycle time. The averaged power number is the largest in the unbaffled tank with forward-reverse agitation, followed by the baffled tank at a constant agitation, and the smallest in the unbaffled tank at a constant impeller speed.

Mixing studies in an unbaffled bioreactor using a computational model corroborated with in-situ Raman and imaging analyses

• Designed a computational model of a non-standard 10 L bioreactor. • Single-phase mixing simulations validated against literature. • Tracer mixing experiments performed at various stirrer speeds & liquid viscosities. • Mixing times calculated from image analyses & inline Raman spectroscopy. • Simulated mixing times validated with experimental mixing data. A computational model of an unbaffled 10 L bioreactor fitted with a unique serpentine tubing structure and two standard six-blade Rushton impellers was developed using Reynolds Averaged Navier-Stokes (RANS) turbulence models (standard k-ε and k- ω SST) and multiple reference frame (MRF) CFD modeling. Flow and mixing time simulations were validated with literature findings for baffled stirred tanks ranging from laboratory to commercial scales, viz. 5 L, 38 L, 22 m 3 and 98 m 3 . Global quantities such as power number ( N p ), impeller flow number ( N Q ) and single-phase mixing times ( t 95 ) were verified with literature values. Flow and mixing simulations in the 10 L bioreactor were performed in full domain and a reduced 60° domain models. The reduced 60° domain model was selected for calculating mixing times at stirrer speeds from 50 to 500 rpm and fluid viscosities of 1 to 6 cP. This viscosity range corresponds to a typical high cell density E. coli fermentation run. For stirrer speeds more than 150 rpm in the 10 L bioreactor ( Re > 3000), the mixing pattern in such high-density cultures could be reliably simulated with the standard k-ε model. Mixing time simulations in the 10 L bioreactor were validated against tracer mixing experiments using an inert red dye with HD video recording and inline Raman spectroscopy. Analyses of video images, univariate calculations and multivariate chemometrics on Raman data yielded experimental mixing times to compare with simulation results at four distinct spatial positions in the unbaffled 10 L bioreactor.

Coupled vibration analysis of fluid-filled baffled tank equipped with Kirchhoff plate

In the present paper, free coupled vibration of partially fluid-filled baffled tank equipped with elastic thin plate is studied by a variational fluid-domain-decomposition scheme, focusing on obtaining the analytically approximate coupled plate bulging and fluid sloshing modes. Different types of fluid-coupled elastic thin plates are considered: partially submerged elastic baffle, elastic baffle partially covering the free fluid surface, immersed elastic baffle, and elastic thin plates forming the tank wall. The elastic thin plate is modeled by the Kirchhoff plate, and the lateral plate deflection is approximated using the summation of its dry (in vacuum) modes multiplied by unknown weight coefficients. The baffled tank is partially filled with a fluid having multi free surface and assumed to be inviscid, incompressible, and irrotational. The present scheme is based on a variational principle related to free linear vibration of the thin elastic plates coupled with bounded multi-layer immiscible fluid. The eigenfrequency equation of the coupled plate–fluid system obtained by the present scheme has a much more unified and compact form when compared with the previous domain-decomposition scheme employing the Rayleigh–Ritz method or the Galerkin method. This is realized by constructing the variational formulation of the coupled plate–fluid problem expressed in differential form. The convergence and accuracy of the present scheme are studied for both convex and non-convex liquid domains. The results from the present scheme agree well with published numerical or experimental results.

Comprehensive analysis of a zeolite‐packed upflow baffled septic tank using tracer tests and mathematical modelling

AbstractThis work analysed the hydraulic behaviour and treatment efficiency of an upflow baffled septic tank (UBST) through tracer tests and mathematical modelling using the axial dispersion and the tank‐in‐series (TIS) models. The tracer tests were performed under different HRTs (12, 18 and 24 h) and configurations (UBST, UBST with sludge and UBST with sludge and zeolite filter). UBST followed a non‐ideal flow, and configuration modifications, rather than HRT, altered its hydraulic behaviour. Mathematical modelling indicated that the TIS model calculated with mean squared error (φ) described adequately UBST hydraulic behaviour (R2 = 0.9833). Additionally, UBST is recommended to operate under 24 h HRT to reach satisfactory hydraulic and pollutant removal efficiencies. At this HRT, total COD and ammonium removals were 75.1% and 49.3%, respectively, which were better than those obtained without the zeolite (71.2% and 1.8%, respectively). However, it quickly saturated, so it is necessary to deepen the research on this topic.

Modeling mixing dynamics in uncovered baffled and unbaffled stirred tanks

AbstractThis paper presents results of measurements performed in uncovered baffled and unbaffled stirred tanks. The Laser Doppler Anemometry (LDA) set consists of a 300 mW argon‐ion laser generating two pairs of blue and green beams. Additionally, three turbulence models are verified to simulate mixing dynamics in uncovered baffled and unbaffled stirred tanks. Simulations are performed using both the steady‐ and the transient‐state approach. The unbaffled tank was modeled using both the single‐ and the multiphase approaches. The cited correlations of the central vortex depth are used to verify the multiphase calculations. In order to reduce the computational time, a simplified numerical model is proposed. It assumes a single‐phase simulation without the central vortex. The flow fields below the central vortex level are compared between the single‐ and the multiphase approach. The simplified model can be used both to design and optimize the mixing process.

CFD simulations of early- to fully-turbulent conditions in unbaffled and baffled vessels stirred by a Rushton turbine

Laboratory scale unbaffled tanks provided with a top cover and a baffled tank both stirred by a Rushton turbine were simulated by carrying out RANS simulations. Three different turbulence models were adopted (k-ωSST, k-ε and the SSG Reynolds stress model) to predict the flow field and the relevant performance parameters (power and pumping numbers) of the tank operated from early to fully turbulent conditions. CFD results were compared with literature experimental data and DNS simulation results to validate and properly compare the models. In the range of Reynolds numbers investigated, results showed that, for the unbaffled tank, the SSG model based on Reynolds stresses is a better choice at larger Re, while the k-ω SST model better reproduces the experiments at lower values. Conversely, no significant differences between the predictions of the three models were found in the baffled vessel.

Numerical investigation of sloshing in tank with horivert baffles under resonant excitation using CFD code

The sloshing phenomenon is predominant in partially filled tanks with fluids, which are under external excitation. Studies have been conducted by placing the vertical baffle in the fixed mass region and horizontal baffle in the variable mass region in the partially filled fluid tanks. In this study, Horivert baffles, a combination of horizontal and vertical baffles that are placed at the variable mass region of the tank were considered for the sloshing analysis. Water and air were the multiphase fluids in the fluid domain under consideration. The tanks with horivert baffle with slot configurations filled with 100 ​mm, 200 ​mm, and 300 ​mm of water were considered in this numerical study. The tank was excited with sinusoidal motion with excitation amplitude of 20 ​mm and frequency depending on the fill level of water in the tank. Numerical simulation results were validated with the outcomes of the experiment. The pressure, velocity, shear strain of water, and maximum elevation of water in the tank were the key parameters of investigation in this study. The baffled tank with slot configuration was proved to be efficient in the suppression of sloshing along with the free flow of fluid in the tank under consideration.

The effect of baffle on flow structures and dynamics stirred by pitch blade turbine

•In order for a better understanding of how baffle impacts on the flow field stirred by pitched blade turbine (PBT), the Particle Image Velocimetry (PIV) experiment was conducted in baffled and unbaffled tank, with time-averaged method, phase-resolved method and Proper Orthogonal Decomposition (POD) method applied to analyze the turbulent characteristics. The POD quadruple decomposition method was adopted to decompose the flow structures of different scales. As indicated by the experimental results, in the measured area, an independent circulation area develops under the impeller, thus forming a pattern of double circulation flow in the unbaffled tank. There is a relatively concentrated distribution of incoherent flow structures in the stirred flow field, and these small-scale flow structures hinder transfer to the whole stirred tank, which makes it easy for the difference in local concentration to arise. With the addition of baffle, the axial discharge of fluid is enhanced, and the independent circulation area under the turbine shows change, and the large-scale convection of main body develops. The stirring-induced incoherent flow structure shows a wider range of distribution, while the small-scale structure under the stirring tank creates a more favorable condition for the diffusion into the whole stirred tank.

Parametric studies on sloshing in a three-dimensional prismatic tank with different water depths, excitation frequencies, and baffle heights by a Cartesian grid method

This paper aims to numerically investigate violent sloshing in a partially filled three-dimensional (3D) prismatic tank with or without a baffle, further to clarify the suppressing performance of the baffle and the damping mechanism of sloshing. The numerical model is based on a Cartesian grid multiphase flow method, and it is well validated by nonlinear sloshing in a 3D rectangular tank with a vertical baffle. Then, sloshing in an unbaffled and baffled prismatic tank is parametrically studied. The effects of chamfered walls on the resonance frequency and the impact pressure are analyzed. The resonance frequencies for the baffled prismatic tank under different water depths and baffle heights are identified. Moreover, we investigated the effects of the baffle on the impact pressure and the free surface elevation. Further, the free surface elevation, pressure and vortex contours are analyzed to clarify the damping mechanism between the baffle and the fluid.

A variational domain decomposition scheme for the natural sloshing modes in the baffled tanks

A variational domain-decomposition scheme is presented to obtain the analytically approximate natural sloshing modes in the rigid baffled tanks. The scheme consists of three steps: (i) dividing the unperturbed complicated liquid domain into several simple sub-domains by introducing artificial interfaces, and auxiliary artificial non-dimensional densities of fluids in these sub-domains are also introduced; (ii) obtaining spectral matrix problem by combing the approximate variational formulation of the approximate natural sloshing problem with the Trefftz method, eigenvalues of the spectral matrix problem are computed and plotted; (iii) extracting the pursued analytically approximate natural sloshing modes from the eigenfunctions given by the spectral matrix problem with artificial non-dimensional densities sufficiently close to 1. The fluid velocity potential in each sub-domain is expressed as a linear combination of a set of harmonic functions with unknown weight coefficients. A variational principle for natural sloshing of multi-layer immiscible fluid with multi free surface is developed and modified to be employed in step (ii). The extraction of the pursued analytically approximate natural sloshing modes is realized by classifying the obtained spectral parameters into two classes, one of which is dominated by the free-surface wave effect, whereas the other one is dominated by the effect of the artificial interfaces between adjacent sub-domains. To verify the present scheme, the results obtained are compared with results published or given by finite element analysis.

3D flow simulation of a baffled stirred tank for an assessment of geometry simplifications and a scale-adaptive turbulence model

Flow simulations are performed on single-phase flow in a baffled tank stirred by a Rushton turbine at a Reynolds number of 40000. The flow physics are discussed, and the benefits of a scale-adaptive simulation (SAS) compared with classical unsteady Reynolds-averaged Navier-Stokes (URANS) models are highlighted. The effect of geometry simplifications, i.e., infinitely thin blades, is illustrated. Furthermore, due to the existence of low-frequency flow instabilities, the necessity of utilizing a full 360° computational domain and the consideration of up to 150 impeller revolutions in the simulation is demonstrated. By a zonal grid refinement within the blade and wake region, the successively resolved portion of the turbulent spectrum is investigated. Even on computational grids typically employed for URANS simulations, the SAS shows a considerably improved prediction of mean velocity and turbulence statistics, compared with conventional URANS models, and should thus be preferred, e.g., to an under-resolved large eddy simulation (LES).

Performance of real-scale anaerobic baffled reactor-swim bed tank system in treating fishmeal wastewater

This study evaluates the process performance of a real-scale anaerobic baffled reactor (ABR) coupled with swim bed tank (SBT) as an aerobic post-treatment process in treating fishmeal wastewater discharged from an actual fishmeal processing factory in Bali, Indonesia. The industrial wastewater released from the aforementioned factory contains high concentrations of organic COD (more than 10 g COD·L−1) and ammonia (100 to 200 mg-N·L−1). During the study period, ABR demonstrated a high organic removal of 95.7 ± 2.9%, with an organic loading rate of 2.1 ± 1.3 kg COD·m−3·day−1. Furthermore, the average total COD influent and effluent of the proposed system were 37,800 ± 15,000 mg COD·L−1 and 435 ± 113 mg COD·L−1, respectively, during the entire experimental period. Based on the determination of volatile fatty acids (VFAs) and microbial community analysis of the ABR-retained sludge, the first and second columns of the ABR were utilized as hydrolysis zones and the third column functioned as an acidification zone. The remaining columns were used for methane production and as final removal zones. The results concluded that this system has the potential to treat fishmeal wastewater under onsite industrial conditions.

Optimization of Baffled Rectangular and Prismatic Storage Tank Against the Sloshing Phenomenon

The fluid motion in partially filled tanks with internal baffles has wide engineering applications. The installation of baffles is expected to reduce the effect of sloshing as well as the consequent environmental damages. In the present study, a series of experimental tests are performed to investigate the sloshing phenomenon in a baffled rectangular storage tank. In addition, the sloshing phenomenon is also modeled by using OpenFoam. Based on the experimental and numerical studies, optimization of the geometric parameters of the tank is performed based on some criteria such as tank area, entropy generation, and the horizontal force exerted on the tank area due to the sloshing phenomenon. The optimization is also carried out based on the entropy generation minimization analysis. It is noted that the optimum baffle height is in the range of hb/hw=0.5–0.75 in the present study (where hb and hw are the baffle height and water depth, respectively). Based on the results, the optimal design of the tank is achieved with RA= 0.9–1.0 (where RA=L/W, L and W are the length and width of the tank, respectively). The results also show that the increase of hb can lead to a decrease of the maximum pressure and horizontal force exerted on the tank. It is also noted that the horizontal force exerted on the tank firstly continues to increase as the sway motion amplitude increases. However, as the normalized motion amplitude parameter, a/L (The parameter a is the motion amplitude), exceeds 0.067, the effect of motion amplitude on the force is not obvious. The same optimization is also performed in the multiple-variable-baffled tank and prismatic storage tank.

Liquid Vibrations in Cylindrical Tanks with and Without Baffles Under Lateral and Longitudinal Excitations

The paper is devoted to issues of estimating free surface elevations in rigid cylindrical fluid-filled tanks under external loadings. The possibility of baffles installation is provided. The liquid vibrations caused by lateral and longitudinal harmonic loadings are under consideration. Free, forced and parametrical vibrations are examined. Modes of the free liquid vibrations are considered as basic functions for the analysis of forced and parametric vibrations. The modes of the free liquid vibrations in baffled and un-baffled cylindrical tanks are received by using single-domain and multi-domain boundary element methods. Effects of baffle installation are studied. The problems of forced vibrations are reduced to solving the systems of second order ordinary differential equations. For parametric vibrations the system of Mathieu equations is obtained. The numerical simulation of free surface elevations at different loadings and baffle configurations is accomplished. Beat phenomena effects are considered under lateral harmonic excitations. The phenomenon of parametric resonance is examined under longitudinal harmonic excitations.

Liquid vibrations in circular cylindrical tanks with and without baffles under horizontal and vertical excitations

The paper is devoted to issues of numerical simulation of free surface elevations in rigid circular cylindrical fluid-filled tanks under external vertical and horizontal loadings with usage boundary element methods. The liquid in reservoirs is assumed to be ideal and incompressible, and its flow is irrotational. The influence of horizontal and vertical baffle installation is considered and damping effects due baffles are estimated. The influence of elasticity effects is considered. Free, forced and parametrical vibrations are examined. Modes of the free liquid vibrations present basic functions for analysis of forced and parametric vibrations. The modes and frequencies of the free liquid vibrations in baffled and un-baffled circular cylindrical tanks are received by using single- and multi-domain boundary element methods. The new effective procedure is developed for numerical solution of resolving system of singular integral equations. The problems of forced vibrations are reduced to solving the systems of second order ordinary differential equations. For parametric vibrations the system of Mathieu equations with non-zero right-hand parts is obtained. The numerical simulation of different kinds of loadings and baffle configurations is accomplished. The instability conditions of the fluid-filled tank subjected to both horizontal and vertical excitations are considered.

Analysis of immiscible liquid-liquid mixing in stirred tanks by Electrical Resistance Tomography

In this work, the dispersion of diesel fuel in water in a baffled tank stirred by a Rushton turbine is investigated. The impeller speeds corresponding to the initial drawdown, the just dispersed regime and the completely dispersed regime are identified by suitable variables obtained by means of the Electrical Resistance Tomography technique. The effect of the dispersed phase volume fraction and of the impeller off-bottom clearance on the different dispersion regimes is considered. The impeller Froude number, the Archimedes number and a dimensionless distance between the liquid-liquid interface position and the impeller elevation are adopted for the data interpretation. For the investigated system, the local volume fraction profiles show that the completely dispersed condition is practically achieved above the just dispersed impeller speed, with negligible gradients of the local volume fraction distribution in the axial direction.

Turbulent blend times with off‐centre v‐mounted agitators

AbstractExperimental measurements in a flat‐bottom tank with narrow‐blade hydrofoil and pitched‐blade impellers are used to develop guidelines for off‐centre, or eccentric, placement of vertical agitators in unbaffled tanks. The guidelines are based on providing a turbulent blend time that is no more than 20% longer than that of the same impeller operating at the same rotational speed on the centreline of a baffled tank. In addition to investigating the effect of impeller type, impeller diameter and off‐bottom clearance are also considered. The results support the commonly noted rule of thumb that as off‐centre distance is increased, performance in an unbaffled vessel approaches that in a baffled tank. A notable exception to this axiom occurs when a large impeller is located close to the tank base (specifically, D/T = 0.40, C/T = 0.10, and O/T = 0.25). In this case, a stable impeller tip vortex forms with both impeller types, with slow exchange of material between the vortex and bulk liquid leading to long blend times. Besides blend time decreasing with increasing off‐centre distance, the uncertainty or run‐to‐run variation in blend time also decreases dramatically. In most cases, the pitched‐blade turbine requires a smaller off‐centre distance than the hydrofoil impeller to approximate the blending performance provided during baffled operation.

Wax removal from textile wastewater using an innovative hybrid baffle tank

Textile industries are among the biggest water consumers and hazardous wastewater generators. Due to the use of wax as physical resistance in textile industries’ procedures, efficient pre-treatment is required before conventional wastewater treatment process. Conventional methods of wax removal suffer from efficiency per hour of less than 50%. This study proposes a sustainable design and application of a baffle separation tank with nano sodium silicate, as a key chemical, in order to remove waxes, from textile wastewater. The baffle tank is equipped with eight baffle layers of different heights, encompassing three separation zones. Different design parameters and related design equations for baffle tank, were studied. Based on the results, optimum operational conditions were discovered and applied for two sets of synthetized textile wastewater containing constant amounts of wax, dye and nano sodium silicate but different reactive dyes. The results indicate the total wax removal efficiency by the baffle tank in the optimum pre-treatment time (one hour) was more than 95%, while the conventional method achieved less than 89% in the optimum operational time (eight hours) in both sets. The efficiency of other chemicals removal (e.g. sodium-silicate) during pre-treatment was in the range of 29–32.4% and 12.5–13.6% for sets one and two, respectively.

A Concurrent Multi-Process Refinement method applied in two-dimensional strong-coupled fluid-structure interaction problems

A Concurrent Multi-Process Refinement method for fluid-structure interaction (FSI) problems is developed and applied in a SIMPLE-based monolithic implicit method (SBMIM) initially presented by Hu et al. (2016). Concurrent Multi-Process Refinement method refines the computational domain of FSI simulations as several subdomains in multi-processes with multi-grid sizes and multi-time steps. Through file mapping, velocity and pressure data are transmitted between two processes using proper interpolations and time advance strategy. Numerical implementation and algorithm procedure of the method are explained in detail. Simulations of the liquid sloshing in a baffled tank are conducted to give an error estimation on different grid systems using the Grid Convergence Index (GCI). Simulations of the dam breaking flow slamming a vertical wall are conducted to verify the accuracy of present methods and to discuss the area selection of the localized FSI simulation. Simulations of the green water impact caused by freak wave are conducted to show the performance of this method in dealing with multi-scale ocean engineering problems and high-frequency structural vibrations. From results, it is seen that Concurrent Multi-Process Refinement method shows advantages in multi-scale FSI simulations using monolithic FSI methods and in predicting high-frequency structural vibrations, especially with low-cost computational facilities.

Design and Hydrodynamic Characterization of a Draft Tube Baffle Tank for Lab‐Scale

AbstractFor process development on lab‐scale, it is necessary to have equipment that represents the industrial apparatuses as similar as possible to offer short time‐to‐market. Accordingly, a draft tube baffle (DTB) crystallizer was scaled down from typical m3‐scale to 1 L filling volume. The suspension characteristics were determined for fluidized crystals in saturated solution. For further characterization of the DTB tank, the residence time of the liquid and solid phases were experimentally determined for the continuous operation mode. Additionally, the classifying behavior of the particles in the DTB was investigated.