Baffled Tank Research Articles

Simulation of orientation of fibre particles in a stirred tank and its influential factors

Different from spherical particles, orientation is an important property of fibre particles. It influences processing and utilizing of the irregular particles. In this paper, orientation distribution of fibre particles under different conditions in a turbulent stirred tank is simulated. The influences of virtual mass force and aspect ratio of fibre particles on the orientation are studied. The simulation is performed in a standard baffled tank stirred by a six-blade Rushton turbine impeller. Two-fluid model is employed to simulate the turbulent solid-liquid two-phase flow with fibre particles of different sizes and concentrations in the stirred tank. A novel method, which employs the rigid particle rotation equation directly, is presented for simulation of the orientation of fibre particles. Simulation results show that the inclusion of virtual mass force in the momentum equation changes the orientations. The effects of virtual mass force vary in different regions. Near the impeller blades, the influence of virtual mass force on orientation is nearly negligible at the center region. While near the wall of the tank, the orientation presents obvious difference with and without virtual mass force. The orientation of fibre particles varies with the aspect ratio. In the impeller discharging region, the orientations vary little with the aspect ratio in the center. Far from the center, the orientation decreases with the aspect ratio above the impeller and increases with the aspect ratio below the impeller. The inclusion of virtual mass force is unnecessary for spheres. However, for particles of irregular shape, especially those with different orientations, the presence of virtual mass force and aspect ratio can have significant effect on orientations.

Linear forced sloshing for a baffled rectangular fuel tank

AbstractSloshing in a fuel tank of a commercial vehicle, which is subdivided by a perforated plate as baffle, is investigated to predict occuring forces. Using linear potential theory and a two‐dimensional modal description, the eigenmodes and eigenfrequencies are determined for the baffled tank and compared to experimental results. Damping due to viscous boundary layers and the pressure drop at the baffle is examined and discussed with regard to experimental findings. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Intensification of sonochemical reactions in solid-liquid systems under fully suspended condition

Process intensification of sonochemical reactions due to the addition of solids is studied using very high solids concentrations (up to 0.5 (v/v)). The impacts of particle size, surface roughness, and solids concentration on sonochemical yields were studied experimentally by measuring the concentration of I3− formed in the cavitation of potassium iodide solution in an agitated baffled tank fitted with an ultrasonic generator (20kHz, 131W). Solids used were cation exchange resin (625μm), sand (303μm), and spherical glass beads (207, 551 and 1290μm). It was found that, due to the net effect of wave attenuation and increased number of nucleation sites available, cavitation level initially decreases with increasing solids concentration up to 0.1 (v/v), then increases up to 0.4 (v/v), followed by a further decrease. Cavitation activity increases with increasing particle diameter due to the reduction in the liquid tensile strength in the presence of larger particles, which decrease the cavitation threshold. The cavitation level is found to be enhanced due to an increase in the surface roughness. The results imply that particle size, concentration, and surface roughness all play important roles in the formation and subsequent collapse of cavities, which cumulatively influence sonochemical reaction yields.

Time evolution of the drop size distribution for liquid–liquid dispersion in an agitated tank

Agitating two immiscible liquids or a solid–liquid suspension is an operation frequently performed in the chemical and metallurgical industries, for example, in suspension/emulsion polymerization, heterogeneous/phase-transfer catalytic chemical reactions, and hydrometallurgical solvent extraction. For emulsification, suspension polymerization, solid particle dispersion, and crystallization, it is essential to be able to predict the mean drop/particle size and the drop/particle size distribution. A simple model was proposed for predicting the time evolution of drop size distribution during drop breaking, and was successfully tested on data published by Ruiz and Padilla (Hydrometallurgy 72:245–258, 2004) and by Sathyagal et al. (Chem Eng Sci 51: 1377–1391, 1996) and on our own data. The time evolution of DSD was investigated in a baffled tank agitated by a Rushton turbine for a liquid–liquid dispersion. The tests were carried out on a silicone oil–water dispersion (oil in water) with a dispersed-phase fraction of 0.00047. The drop sizes were determined by image analysis.

Computational fluid dynamics simulation of hydrodynamics in an uncovered unbaffled tank agitated by pitched blade turbines

Computational fluid dynamics (CFD) simulations were applied for evaluating the hydrodynamics characteristics in an uncovered unbaffled tank agitated by pitched blade turbines. A volume of fluid (VOF) method along with a Reynolds stress model (RSM) was used to capture the gas-liquid interface and the turbulence flow in the tank. The reliability and accuracy of the simulations are verified. The simulation results show that the vortex can be divided into central zone and peripheral zone, and flow field in the tank can be divided into forced vortex flow region and free vortex flow region. With the increase of impeller speed, the vortex becomes deeper, while the critical radius of the two zones keeps almost unchanged. The impeller clearance and the rotational direction have little effect on the vortex shape. The vortex becomes deeper with increasing of the impeller diameter or the blade angles at the same rotational speed. Power number is little influenced by the impeller speed, and decreases by about 30% when impeller diameter varies from 0.25T to 0.5T. When blade angle varies from 30° to 90°, power number increases by about 2.32-times. Power number in uncovered unbaffled tank is much smaller than that in baffled tank, but is very close to that in a covered unbaffled tank. The discrepancy of power number in uncovered unbaffled tank and that in covered unbaffled tank is less than 10%.

Scale-up rules for flocculation

We present here a study of three baffled tanks, 0.15m, 0.20m and 0.30m in inner diameter, agitated by Rushton turbine, with reference to scaling up the flocculation kinetics. A clay slurry was used as a model wastewater. The experiments were carried out at mixing intensity 40W/m3 and clay concentration 0.58g/L. The model wastewater was flocculated with the Sokoflok 16A organic flocculent (solution 0.1wt%) in the range of dimensionless flocculent dosage DF⁎ from 0.448 to 5.241mg/g. The flocs that formed were separated by means of sedimentation. The operational conditions were designed according to following proposed scale-up rules: i) P/V=const., ii) tF⁎=N·tF=const., iii) DF⁎=const. and iv) used=const. Applying the proposed scale-up rules, the flocculation efficiency was found to be practically the same irrespective of vessel size and flocculation dosage. For the given flocculated system and process conditions, the maximum degree of turbidity removal Ze⁎max=96.1±0.6% was found for dimensionless flocculation time 1916±5% and dimensionless flocculent dosage DF⁎=3.128mg/g±8%, regardless of vessel size. The approach to scale-up proposed by Camp (1955) is discussed and criticized in the light of present-day mixing theory, and an explanation is offered of the shortcomings of this approach, and why it gives incorrect scale-up results.

Experimental evaluation of helically coiled tube flocculators for turbidity removal in drinking water treatment units

The constant need to improve water treatment techniques allows for the emergence of new technologies for obtaining adequate water, both in terms of quality and quantity. In order to obtain an efficient, rapid and low-cost clarification system, this study proposes the use of helically coiled tubes (HCTs) as a coagulation-flocculation reactor coupled with a conventional decanter system. Eighty-four (84) turbidity removal tests were performed to evaluate the proposed clarification system, while varying hydraulic and geometrical parameters in HCTs. Removal efficiency values higher than 80% were obtained (with a maximum removal efficiency of 86.2%), presenting better results than systems using baffled tanks, which are traditionally applied for water treatment purposes in developing countries. In addition, significantly lower processing times (lower than 2 min, about 10% of baffled tank processing times) were observed for high efficiency process values, indicating that this clarification system can be useful in rational design of coagulation-flocculation units. It should be noted that the turbidity removal efficiency results obtained (with a rising-then-decreasing behaviour over time) differ significantly from those obtained by the commonly used models for flocculation evaluation (with asymptotic behaviour over time), presenting a maximum absolute percentage deviation of 48.9%, and indicating caution in the use of such models for alternative flocculation unit evaluation. Keywords: flocculation, drinking water, turbidity, turbidity removal efficiency, helically coiled tubes

On the assessment of power consumption and critical impeller speed in vortexing unbaffled stirred tanks

Unbaffled stirred tanks are increasingly recognized as a viable alternative to common baffled tanks for a number of processes and bio-processes where the presence of baffles is undesirable. Notwithstanding the increasing industrial interest towards unbaffled tanks, available experimental information on their behaviour is still very poor, even for important parameters such as mechanical power drawn and critical impeller speed (Ncr) at which the transition between non-aerated (sub-critical regime) and aerated (super-critical regime) conditions occurs.In this work the influence of Reynolds and Froude numbers on power consumption characteristics of unbaffled stirred tanks is presented for tanks operating both in non-aerated (sub-critical regime) and aerated (super-critical) conditions. Influence of scale-up, impeller to tank size, liquid height aspect-ratio and presence or not of a top-cover is investigated in order to provide a general correlation able to assess (i) the critical rotational speed Ncr and (ii) the power number Np under any fluid dynamic regime.Experimental results obtained show that the proposed general correlation is fully validated when scaling-up the system. Moreover, the variation of geometrical features such as impeller to tank size, liquid aspect ratio and the presence or not of a top-cover do not modify the functional dependencies of power number on Re and Fr and only different (dimensionless) multiplying shape factors must be adopted. Finally, an overall general correlation for critical rotational speed (Ncr) assessment is also proposed.

Numerical simulation of hydrodynamics in an uncovered unbaffled stirred tank

Numerical simulations were carried out to investigate the turbulent flow with free-surface vortex in an uncovered unbaffled stirred tank. An Eulerian–Eulerian multiphase flow model coupled with a volume-of fluid method was applied to capture the gas–liquid interface and describe the flow field in the tank. Turbulence is computed using a Reynolds stress model with seven equations. The reliability and accuracy of the simulations are verified by comparing the predicted free surface profiles and power numbers with experimental data in the literature. The overall agreements between the simulation results and experimental measurements are obtained. The simulation results show that vortex on the liquid free surface in the uncovered unbaffled tank can be divided into central zone and peripheral zone, and the critical radius of the two zones keeps almost unchanged with enhancing of impeller speeds. At the same impeller speed, vortex becomes deeper and larger with increasing of impeller diameter. However, vortex shape changes not very much with increasing of impeller diameter under the same power consumption. Impeller clearance has no significant influence on the vortex shape. Circumferential flow is dominant in the uncovered unbaffled tank, and the flow field can be divided into forced vortex region and free vortex region. Power numbers in uncovered unbaffled stirred tanks decrease slightly with increasing of the Reynolds number, and are far lower than that in baffled stirred tanks.

Coupled multimodal fluid-vehicle model for analysis of anti-slosh effectiveness of longitudinal baffles in a partially-filled tank vehicle

An efficient model is formulated for analysis of a coupled fluid slosh-vehicle dynamic system to study the effects of different baffle designs on directional dynamic performance of a partially-filled tank vehicle. A multimodal model of fluid sloshing within a baffled cylindrical tank is initially formulated using potential flow equations and linearized free-surface boundary condition considering maneuver-induced vehicle motions along the lateral, vertical and roll axes. Natural slosh modes/frequencies, hydrodynamic coefficients and Stokes-Joukowski potential associated with the multimodal model are then obtained by solving the eigenvalue problem of free fluid sloshing using a higher order boundary element method. Significant improvement in computational time is achieved by reducing the generalized eigenvalue problem to a standard one involving only the velocity potentials on the half free-surface length using the zoning method. The hydrodynamic force and moment obtained from the multimodal model are subsequently coupled with the TruckSim vehicle dynamic simulation platform through a MATLAB/Simulink model to obtain dynamic responses of a partially-filled tank vehicle with and without baffles under step-turn and double-lane change maneuvers. Two different designs of longitudinal baffles are considered: bottom- and top-mounted baffles. The validity and efficiency of the present boundary element method is demonstrated by comparing the results with those obtained using the boundary element method employing linear elements. The effective mass moment of inertial of the fluid in a clean-bore tank is also obtained as a function of fill ratio and compared with the reported analytical solutions for a half-full tank to further verify the model. The results suggest that directional dynamic responses of partly-filled tank vehicles can be efficiently analyzed using the coupled multimodal slosh-vehicle models with significantly lower computational effort than the methods employing computational fluid dynamic (CFD) fluid slosh models. The results further reveal that top-mounted baffles are most effective in suppressing the fluid slosh force under more likely loading conditions in road tankers.

CFD simulation of floating particles suspension in a stirred tank

Computational fluid dynamics (CFD) simulations were performed to predict the floating particles suspension in a baffled tank stirred by a standard Rushton turbine. An Eulerian multiphase model and a standard k-e turbulence model with mixture properties were used in the CFD simulation. The impeller rotation was solved using a moving reference frame method. Flow pattern, power number and solid holdup distribution were obtained and compared with the results in literature. The effects of operating condition on floating particles suspension characteristics were studied. It indicated that the influences of impeller speed and solid loading on particle suspension varied with particle sizes. For small particles, the impeller speed and solid loading have no obvious effects on solid holdup distribution and suspension quality. For large particles, particle suspension quality becomes better first, and then keeps almost unchanged with enhancing of the impeller speed. Suspension quality is better for higher solid loading of large particles. Within the scope of the present study, solid loading has no great effect on suspension quality. Suspension quality becomes worse with increasing of the particle size. Large particles are easy to accumulate in the centres of the liquid free surface and the upper circular loop, and the vicinity of the shaft.

A Modified Bio-Ecological Process for Rural Wastewater Treatment

Limited water resources and ensuring access to clean water are critical environmental challenges, especially for the developing world. In particular, rural domestic wastewater has become a significant source for the pollution of freshwater bodies. A modified bio-ecological A2O-wetland system for rural wastewater treatment consisting of a biological unit (anaerobic baffled reactor, anoxic tank and oxic unit, A2O) and an ecological unit (horizontal flow constructed wetland) was developed, and key performance indicators were identified. The bio-ecological treatment system showed high removal efficiency for pollutants, successfully achieving 91%, 85%, 78%, and 92% removal efficiencies for chemical oxygen demand (COD), ammonium (NH4–N), total nitrogen (TN), and total phosphorus (TP), respectively. The concentrations of pollutants in the effluent from the system were lower than the Class 1 A regulated values of the Chinese National Standard GB18918-2002. The system offered high removal efficiency, simple operation, and low energy consumption. The A2O-wetland is a good alternative for rural wastewater treatment systems.

Effect of baffle geometry and air pressure on transient fluid slosh in partially filled tanks

Effects of baffle geometric parameters such as curvature, opening size and shape, and inclination on the transient load shift and slosh forces within a partly filled liquid tank are investigated under longitudinal and lateral acceleration fields using computational fluid dynamic (CFD) methods. Validity of the simulations is illustrated considering steady-state responses, and fundamental slosh frequencies of cleanbore and baffled tanks. The slosh forces imposed on the baffles and end caps are evaluated for different baffle design parameters. The results suggest that the liquid cargo load shift, longitudinal and lateral forces, and pitch moment due to transient fluid slosh are strongly influenced by the baffle shape, and opening size. It is further shown that sloshing with medium to high fill levels can cause substantial increase in pressure of air trapped between the end cap and baffle, and between adjacent baffles, which contributes considerably to the resultant forces on the baffles and opposes the force due to liquid phase of the flow.

Experimental investigation of fibre particles in a turbulent stirred tank with DPIV

In this paper, the experiments of fibre particles in turbulent solid-liquid two-phase flow fields using Digital Particle Image Velocimetry (DPIV) were conducted in a baffled tank stirred by standard six-blade Rushton. Fibre particles with different aspect ratios of 18.8, 25.0 and 37.5 are experimented with impeller speed from 100 to 400rpm, respectively. Both the orientations and the velocities of the fibre particles in the stirred tank under different conditions are obtained, as well as the turbulent velocity field. It is found that velocity of solid phase is very close to that of liquid phase. In the range of investigated solid concentration, liquid velocity exhibits close agreement at different solid concentrations. The velocities of two-phase flow are slightly greater than those of single phase. The influences of impeller speed, aspect ratio and solid concentration of fibre particles on the velocity field are discussed. With the increase of impeller speed, radial and axial particle velocities increase accordingly. With the increase of impeller speed and aspect ratio, orientation decreases slightly. Orientation seldom has any change with the increase of solid concentration. Meantime, the velocity profiles of solid-liquid two-phase flow with spherical particles are also compared with those of fibre particles. There is little discrepancy between velocities of fibre particle and spherical particle. All these can be used as the basis for industrial design as well as further simulation.

Design factors affecting the dynamic performance of soil suspension in an agitated, baffled tank

The effects of particle size, impeller clearance and impeller speed are assessed to show how condition variations influence power consumption in the water-solid slurry suspension in an agitated tank. The energy efficiency of slurry height variation, impeller type and diameter, and solid movement speed has been investigated with six soil series stirred in a soil-water slurry. Coarser sand particles are observed to significantly increase power consumption, while finer particles, for instance clay, decrease the stirring power requirement. The 3-blade HR100 SUPERMIX® impeller manufactured by SATAKE generally performs more efficiently than a conventional 4-pitched blade turbine. The impeller's geometric design, including diameter and number of blades influences the impeller's energy efficiency, and HR100 impellers with greater diameters remarkably reduce power consumption. The tests demonstrated that the power required to provide off-bottom solid suspension and solid dispersion can be reduced dramatically by increasing the slurry height rather than by accelerating the impeller, if this option is possible.

Particle Suspension in Vortexing Unbaffled Stirred Tanks

Three-phase processes in which particle suspension has to be achieved in conjunction with gas dispersion are traditionally carried out in sparged, baffled stirred tanks. The operation of such tanks can suffer, however, from particles tending to block the sparger holes. A viable alternative might be provided by uncovered unbaffled stirred tanks (UUSTs), where gas self-injection can occur when the free-surface vortex reaches the impeller blades and gas bubbles begin to be ingested by the liquid. In this work, the particle suspension and liquid aeration performances in three-phase UUSTs were experimentally investigated and compared with relevant literature correlations concerning baffled systems. The results show that, at least at the investigated scale, UUSTs are more efficient for suspending particles than relevant baffled systems. Impeller clearance scarcely affects power requirements. Finally, a down-pumping PBT with D/T = 1/3 was found to be the best choice for attaining complete suspension under self-a...

2D Numerical ISPH Wave Tank for Complex Fluid–Structure Coupling Problems

In this paper, we provide a hybrid incompressible Smoothed Particle Hydrodynamics (ISPH) model for fluid-structure interactions. The numerical algorithms include the mirroring treatment of solid boundary, free surface tracking, wave damping using sponge layer and fluid-solid coupling model. The proposed ISPH wave tank is applied to a series of wave-structure coupling problems including the sloshing in a baffled tank, solitary wave impact on an underwater obstacle, water entry of a cylinder and balance dynamics of a floating object. The simulation results demonstrate that the ISPH model provides an accurate simulation technique in various fluid-structure coupling studies.

Numerical analysis of the mixing characteristic for napier grass in the continuous stirring tank reactor for biogas production

The objective of this work is to conduct a parametric study on the design variables and flow distribution of a Continuous Stirred Tank Reactor (CSTR). The numerical solutions were obtained by using Lattice Boltzmann Method (LBM) technique. Three different designs of CSTR with Napier grass as substance were evaluated for mixing efficiency, vorticity, and flow behavior, Model 1: one propeller no baffle tank, Model 2: one propeller with baffles tank, and Model 3: double propellers with baffles tank. The results show that the fluid velocity and the direction of fluid motion play the major role on the mixing characteristic. The propellers, baffles plates, and stirring speeds are significant factors on the fluid direction and thus the mixing performance. The solid–liquid mixing efficiency can be calculated from the numerical results of Discrete Phase Model (DPM) by image analysis technique. The mixing efficiency of Models 1, 2, and 3 are 10.08%, 23.77% and 34.66%, respectively. The power numbers which indicate the power consumption of the system of Models 1, 2, and 3 are 0.91, 1.20 and 2.00, respectively. Therefore, Model 3 gives the best mixing efficiency but requires higher energy consumption. This work also characterized the mixing quality in various depth levels. The predictions implement along with the mixing efficiency in order to evaluate mixing efficiency of the system completely.

Numerical investigation of a vertically baffled rectangular tank under seismic excitation

The damping effect of the vertical baffles inside a liquid storage tank is studied in this paper. A numerical model based on the finite volume method is established and used to evaluate the accuracy of an analytical model developed to estimate the hydrodynamic damping caused by the vertical wall bounded baffles. For this purpose, several full scale baffled tanks with different aspect ratios are numerically analyzed. The numerical results were then used to validate the analytical model. The reduction in sloshing wave height caused by the baffles is estimated for selected tanks subjected to the seismic excitations. Finally, a simple procedure to estimate the reduction in sloshing amplitude due to the presence of baffles is proposed and validated using the time history numerical results.

Modified Septic Tank Treatment System

Water pollution is a major global problem. One of the main causes of ground water contamination is the effluent from septic tanks. Treatment of domestic wastewater using conventional septic tank is found to be inefficient leading to increased soil and ground water contamination. It's very important to protect surface and ground water from contamination. So there is a need for improving conventional septic tank. The purpose of this study was to investigate the effect of a modified septic tank system for treating domestic wastewater. Modified septic tank system is a simple means of treating domestic wastewater using the treatment mechanisms such as anaerobic digestion and disinfection. The effect of vertical baffles coupled with an anaerobic reactor on septic tank system was analysed. The reactor selected for the study consists of copper modified zeolite as an adsorbent which will also act as filter media on which attached growth process takes place. The results showed that vertical baffled septic tank(VBST) coupled with zeolite filter shows a good treatment system. The results also showed that vertical baffled septic tank coupled with zeolite filter with disinfection shows a removal of 99.99% total coliforms, 99.57% of TSS, 46.83% Ammonia nitrogen, 31.08% of nitrate nitrogen, 48.39% of total kjeldahl nitrogen, 94.4% of BOD and 71.74% of Phosphates. This study focuses on an economical and efficient decentralized treatment method for treating domestic waste water.