Horizontal Baffle Research Articles

Development of gas entrainment mitigation devices for PFBR hot pool

The phenomenon of argon gas entrainment into primary sodium in the hot pool of a liquid Sodium cooled Fast Reactor (SFR) is investigated. A combined experimental and computational approach is proposed. Physical entrainment of argon into sodium is highly geometry dependent and the present study is focused on the Indian Prototype Fast Breeder Reactor (PFBR). The computational model which is used for parametric studies is validated against a 1/4 scale water model tests. Based on systematic experiments, the free surface velocity for onset of gas entrainment is determined to be 0.32m/s, and the corresponding threshold value for the surface vorticity has been estimated as 8.3s−1.A horizontal baffle plate attached to inner vessel is found to reduce the free surface velocity/vorticity effectively. The radial width of the baffle plate and its elevation has been optimized to be 0.125m and 0.315m from free surface by computational studies. The optimized device has been tested in the water model to confirm its satisfactory performance before its recommendation for PFBR.

Inverse Calculation Model for Optimal Design of Rectangular Sedimentation Tanks

Because of the difficulty of specifying optimal design parameters of rectangular sedimentation tanks using a forward numerical model, an inverse calculation model based on an optimization algorithm and a forward model were developed in this paper. Using this model, a numerical simulation of the sedimentation tank involving determination of the velocity field and the concentration distribution of the particles by the forward model was conducted. The eddy viscosity was obtained with the aid of k−ε turbulence model equations. The inverse model was applied to the optimal design of the horizontal baffle location in a given sedimentation tank. As a one-dimensional nonlinear optimization method, Brent’s method was used. Moreover, the effect of the horizontal baffle location on flow and solids removal ratio was also discussed. Compared with the traditional forward model for specifying optimal design parameters for rectangular sedimentation tanks, the inverse calculation model can search directly for the optimum design parameters and can obtain good results.

Improving the performance of power plant cooling ponds

A study was conducted on the effectiveness of using vertical baffles to improve the thermal performance of power plant cooling ponds. A small scale physical model of a rectangular cooling pond was used. A base case was established using traditional horizontal baffles to create a serpentine flow pattern through the pond. The horizontal baffles were then replaced by a series of underflow weirs that spanned the pond. An improvement in cooling of over 30% was realized.

Systematic Investigation of Particle Segregation in Binary Fluidized Beds with and without Multilayer Horizontal Baffles

Particle segregation was systematically studied in a binary fluidized bed of inner diameter 0.286 m with fine FCC and coarse millet particles as flotsam and jetsam, respectively. Segregation efficiencies of both flotsam and jetsam, axial and radial fraction profiles were studied and analyzed systematically. A new developed horizontal baffle was examined to see its effects on particles segregation. Experimental results showed that the baffle-free bed could only get high-purity flotsam particles at very low gas velocities. However, both nearly pure jetsam and flotsam particles were obtainable at much higher gas velocities after four layers of new baffle are installed. A wider operating range suitable for particle segregation and greater axial fraction gradients were found in the baffled bed, further proving the baffle’s effect on promoting particle segregation. This enables the baffled bed to be a promising continuous particle classifier in industry. Further analysis demonstrated that reduced bubble size, i...

Analytical and experimental evaluation on the effectiveness of upper mounted baffles with respect to commonly used baffles

In this paper, an experimental and an analytical investigation of the hydrodynamic damping due to lower and upper mounted vertical baffles as well as horizontal baffles in partially filled rectangular tanks are conducted. The analytical model earlier provided to estimate the hydrodynamic damping ratio of lower mounted vertical baffles is extended for upper mounted baffles. The semi-empirical Miles expression, which was originally developed to evaluate damping ratio of ring baffles in cylindrical tanks is also formulated for horizontal baffles in rectangular tanks. The comparisons between maximum hydrodynamic damping cased by various baffle configurations (upper and lower mounted vertical arrangements, as well as horizontal arrangements) are made and the validity of extended analytical models is discussed.

Fracture-controlled palaeohydrology of a secondary salt weld, La Popa Basin, NE Mexico

Abstract Isotopic and fluid inclusion analyses of veins and host rocks constrain the compositions, temperatures and sources of palaeofluids along the La Popa salt weld. Most veins formed after the salt was evacuated from the precursor salt wall; veins are generally more abundant on the downthrown side of the weld and near a significant bend in the trace of the weld. The spatial distribution of fluid types and temperatures suggests the weld served as a vertical fluid conduit and a horizontal baffle. Stable isotopes indicate there was significant fluid–rock interaction and little vertical fluid communication between rock units in areas away from the weld. Fluid temperatures along the weld ranged from 84 to 207 °C, salinities ranged from 4 to 25 wt% NaCl equiv. and methane was abundant in the weld zone and on the downthrown side of the weld. Strontium isotopes suggest that some of the vein-forming fluids were derived from the evaporites that once occupied the weld. Our results suggest the sealing potential of similar welds may be related to the presence of abrupt changes in weld geometry such as cusps or bends, the amount of shortening across the weld and the amount of vertical displacement across the weld.

Numerical Simulation of Sloshing Phenomena in Cubic Tank with Multiple Baffles

A two‐phase fluid flow model solving Navier‐Stokes equations was employed in this paper to investigate liquid sloshing phenomena in cubic tank with horizontal baffle, perforated vertical baffle, and their combinatorial configurations under the harmonic motion excitation. Laboratory experiment of liquid sloshing in cubic tank with perforated vertical baffle was carried out to validate the present numerical model. Fairly good agreements were obtained from the comparisons between the present numerical results and the present experimental data, available numerical data. Liquid sloshing in cubic tank with multiple baffles was investigated numerically in detail under different external excitation frequencies. Power spectrum of the time series of free surface elevation was presented with the aid of fast Fourier transform technique. The dynamic impact pressures acting on the normal and parallel sidewalls were discussed in detail.

Computational Fluid Dynamic Studies on Gas Entrainment in Fast Breeder Reactors

Primary sodium pools in fast reactors are covered with argon. There is strong potential for argon gas entrainment into sodium and associated reactivity perturbations if the free surface velocity is large. Basic CFD studies have been carried out on ideal models and the threshold value of free surface sodium velocity that avoids gas entrainment is arrived at employing the VOF method. Subsequently, 3-D CFD studies have been carried out for PFBR hot pool and the free s urface velocity is estimated to be 1.15 m/s. To reduce this value below the threshold limit, a horizontal baffle device has been identified.

배플을 적용한 Cargo용 연료탱크 내부의 슬로싱 저감 연구

최근 자동차, 선박, 항공기의 운행시 외력에 의해 연료탱크 내의 유체가 출렁거리는 슬로싱 현상으로 인하여 구조물 내부가 손상되어 큰 영향을 미치고 있다. 따라서 적재연료의 슬로싱 영향을 최소화하기 위해서 전산유체역학적으로 유체의 거동을 정확히 해석하는데 무엇보다 중요하다. 본 연구에서는 ADINA-CFD를 이용하여 Kia 프론티어 Cargo용 연료탱크에 수직배플과 수평배플의 길이 및 개수에 따른 유체유량 및 압력의 특성을 파악하고, 코너 및 언덕 주행시 슬로싱 감소를 위해 해석하였다. 그 결과로 슬로싱 감소효과를 위해 배플의 최적길이는 수직배플의 경우 0.19 m, 수평배플의 경우 0.08 m로 나타났다. 그리고 자동차주행 경우에 코너주행 시는 수직배플이 수평배플보다 슬로싱 감소효과를 보이는 반면에, 언덕주행 시는 수평배플이 효과적이며 안정성을 나타내었다.

Taylor vortex flow in presence of internal baffles

We present a study on Taylor vortex flow in between a rotating inner cylinder and a stationary outer cylinder with vertical or horizontal baffles. A mineral oil is used as the working fluid in the annular channel of 60 mm in height and 11.6 mm in gap width. The flow pattern in the annulus is investigated by particle image velocimetry (PIV) and computational fluid dynamics (CFD). Both the experimental and simulation results show that the presence of vertical baffles influences the vertical positions of vortices—it is primarily significant for the bottom vortex. Increasing number of vertical baffles gradually decreases the azimuthal variation in the vertical position. The baffles also lead to the occurrence of a circulation flow immediately upstream and downstream each baffle plate in the radial–azimuthal plane. On the other hand, an annular horizontal baffle with sufficient width alters the vortex structure in the gap, for instance, fewer vortices are observed. With two horizontal baffles in the annulus, the flow pattern is largely affected by the baffle width and the distance between the two baffles. This study provides a better understanding of Taylor vortex in presence of internal baffles, which will be important for practical applications of Taylor vortex devices.

Macrokinetic Modeling of Chemical Oxygen Demand Removal in Pilot-Scale High-Rate Anaerobic Ponds

Research published on bioreactors discusses the importance of integrating reactor kinetics and mixing as the basis for understanding process hydrodynamics and developing sound design procedures. Nonetheless, many studies are focused on either kinetics or mixing, but studies on the integration of both are seldom found in the literature. Despite the availability of several mixing models (e.g., completely stirred tank reactor, plug flow, dispersion model, completely mixed tanks in series model, and the compartments model), there is an intrinsic complexity in studying process kinetics and reactor hydrodynamics experimentally. In this sense, this work reports the results of a 6-month study for three pilot-scale anaerobic ponds (APs); of which, two had modified physical configurations (one with a mixing chamber, the other with horizontal baffles) and the third was a conventional AP run as a control unit. They were evaluated under three different hydraulic loading rates. The AP provided with the mixing chamber closely followed the completely stirred tank reactor model (r2 = 0.89), and the AP with horizontal baffles showed a high correlation with the Wehner–Wilhelm dispersed flow model (r2 = 0.86). The performance of these modified APs was comparable to those reported in the literature for high-rate anaerobic reactors such as Upflow Anaerobic Sludge Blankets (UASBs). The mixing and macrokinetic features of the modified APs (especially the one provided with the mixing chamber) clearly demonstrated their high-rate and better performance characteristics.

Investigation of sloshing damping in baffled rectangular tanks subjected to the dynamic excitation

In this research, an analytical model is developed to estimate the hydrodynamic damping ratio of liquid sloshing for wall bounded baffles using the velocity potential formulation and linear wave theory. Here, an analytical solution approach and experimental investigations are conducted for describing the hydrodynamic damping which is provided by vertical and horizontal baffles in partially filled rectangular liquid tanks. In order to evaluate the accuracy of the analytical solution which is developed in present work, a series of experiments are carried out with a rectangular liquid tank excited by harmonic oscillation. The parametric study is conducted on the damping efficiencies of both vertical and horizontal baffles with various dimensions and locations. According to the results of the present investigations, the hydrodynamic damping is significantly affected by the size and location of baffles. Furthermore, the validity of the developed analytical approach as well as the effectiveness of various baffle configurations are discussed. Finally, a simple approach is proposed for estimating the damping ratios of the baffles during earthquake motions.

Experimental and Numerical Study of Mixing in a Hot-Water Storage Tank

Thermal mixing and stratification are explored numerically and experimentally in a cylindrical tank, which simulates a storage of water heated by a solar collector. The tank is 70cm in height and 24cm in diameter. The inlet and outlet are vertical and located off the centerline of the tank. The study is conducted in a transient mode, namely, the tank is filled with hot water, and as the hot water is being withdrawn, the tap water replaces it in a stratified way or by mixing. The flowrates of 2l∕min, 3l∕min, 5l∕min and 7l∕min, which correspond to superficial velocities of 4.35cm∕min, 6.52cm∕min, 10.87cm∕min, and 15.2cm∕min, are explored. Temperature of hot water ranges within 40–50°C, while the tap water is about 25–27°C. Installation of one and two horizontal baffles above the inlet is examined. Simultaneous experimental and numerical investigations are performed. In the experiment, both flow visualization and temperature measurements are used. Three-dimensional transient numerical simulations are done using the FLUENT 6 software. Validation of the numerical model is achieved by comparison with the experimental results. Then, the numerical model is applied to a study of various possible changes in the system. The results show that at low flowrates, up to a superficial velocity of about 11cm∕min through the tank, the baffles have no effect on tap water mixing with the stored hot water. At higher flowrates, a single horizontal baffle prevents the mixing and preserves the desired stratified temperature distribution in the storage tank.

Removal of Algae in Stabilization Ponds Effluent using Moringa Oleifera Coagulant

A number of studies have proved natural coagulants achieve high turbidity removal in water treatment. A pilot scale study was conducted to evaluate the effectiveness of natural coagulant (moringa oleifera) with respect to algae removal. Required effluent from stabilization ponds was diverted into the horizontal baffle flocculator and then treated by coagulation and flocculation using dry moringa oleifera seeds. Using moringa oleifera, chlorophyll-a, turbidity and TSS were reduced by 78%, 85% and 82% respectively at optimum dosage of 175mg/l. This was achieved at optimum flocculation conditions ie retention time of 4.1 minutes and 33.3% degree of agitation. These parameters were used in evaluating removal rates of algae. Sludge was found to contain protein content in the range of 40-45%, which can act as protein substitute in animal feeds. Hence moringa oleifera as coagulant can effectively remove algae and improve effluent quality. Keywords : Moringa oleifera, Coagulant, Stabilization pond effluent, Turbidity, algae Journal of Civil Engineering Research and Practice Vol. 5 (1) 2008: pp. 53-61

Buoyancy convection in a square cavity with mutually orthogonal heat generating baffles

A two-dimensional numerical solution for buoyancy induced convection in a square cavity with discretely heat generating baffles is presented in the context of cooling of electronic equipments. The walls of the cavity are subjected to either isothermal temperature or outward isoflux. The Grashof number and Prandtl number are fixed at 10 6 and 0.71, respectively. The effects of different locations of the baffles are reported in terms of streamlines and temperature contours. The results obtained clearly show that the fluid flow and temperature fields strongly depend on location of the baffles. The movement of either the horizontal or vertical plate produces no significant changes in the overall heat transfer rate except when one of them is wall mounted in the presence of isothermal cavity walls. In the case of isoflux cavity walls the overall heat transfer rate gets suppressed for the upward movement of the horizontal baffle and enhanced for the horizontal movement of the vertical baffle in the core region of the cavity. When one of the baffles moves closer to a cavity wall thermal boundary layer is formed and hence conduction becomes dominant in between them in the case of isothermal cavity walls. But in general the presence of isoflux cavity walls arrests crowding of isotherms.

Effect of baffle–cavity ratios on buoyancy convection in a cavity with mutually orthogonal heated baffles

Buoyancy driven convection in a square cavity induced by two mutually orthogonal and arbitrarily located baffles is studied numerically. The baffles are of different sizes and the flow is two-dimensional. The coupled governing equations were solved by finite difference method using Alternating Direction Implicit technique and Successive Over-Relaxation method. The steady state results are presented in the form of streamline and isotherm plots. It is found that buoyancy force plays a key role and overall heat transfer in the cavity is enhanced for higher values of both baffle–cavity ratios. Flow inhibition emerges as a deciding factor and diminishes heat transfer when the horizontal baffle is located above the center of the cavity.

Finite Element Analysis of Sloshing in Rectangular Liquid-filled Tanks

The focus of the present paper is on the development of a finite element formulation to investigate the sloshing of liquids in partially filled rigid rectangular tanks undergoing base excitation. The liquid domain is discretized into two-dimensional four-node rectangular elements with the liquid velocity potential representing the nodal degrees of freedom. Liquid sloshing effects induced by both steady-state harmonic and arbitrary horizontal base excitation are investigated in terms of the slosh frequencies, liquid velocity field, free surface displacement and hydrodynamic forces acting on the tank walls. The model is employed to study the effects of inserting a bottom-mounted vertical rigid baffle, as well as side-mounted horizontal baffles that are wholly immersed in the liquid region, in an attempt to investigate their viability in acting as slosh suppression devices.

Part I: Experimental studies on a pulverised fuel stove

This paper is concerned with development of a pulverised fuel stove with improved conversion efficiency and minimal emissions at near constant power level without the use of external power. The design originates from a cylindrical sawdust stove with a central porthole being lit from the bottom. Such a stove will have a flame in port with enhanced sooting tendency. For similar configuration, stable premixed combustion behaviour of the combustible gases from the port of the fuel block (known as the gasification mode) has been achieved by use of air supply through a thin slot at the bottom, for at least 30 min of stove operation. In order to ensure stable combustion of the gases at exit, a metal device is used. In an attempt to extend gasification duration, studies are conducted in single port configuration having air entry from the bottom with a horizontal baffle to control the flow rate. This configuration worked in gasification mode for about 20 min but there have been problems of flame extinction. To overcome these drawbacks multi-port design with vertical air entry is employed with success. The stove has exhibited conversion efficiency in excess of 37% due to well focused nature of flame at exit. CO emission factors are about 12 g (kg fuel) � 1 , a performance superior to conventional biomass stoves (� 45 g kg � 1 ). NOx emission factors are about 1 g kg � 1 fuel which falls in the range of reported data for NOx. Studies with different pulverised leafy fuels have indicated these fuels have lower volatile release rates and therefore exhibit lower power level operation for a given port configuration compared to sawdust fuel. r 2006 Elsevier Ltd. All rights reserved.

Sloshing in a vertical circular cylindrical tank with an annular baffle. Part 1. Linear fundamental solutions

The paper centres around fundamental solutions of the linearised problem on fluid sloshing in a vertical circular cylindrical tank having a thin rigid-ring horizontal baffle. It develops an analytically oriented approach, which provides accurate approximations of natural frequencies and modes. The singular asymptotic behaviour of the velocity potential at the sharp baffle edge is also captured. A numerical analysis quantifies the natural frequencies and modes versus vertical position and width of the annular baffle. Forthcoming parts will use these approximate fundamental solutions in both nonlinear modal modelling and estimating the damping due to vorticity stress near the baffle.

Flow pulsation and baffle’s effects on the opposing mixed convection in a vertical channel

Abstract This numerical study aims to investigate the effects of a horizontal baffle on the heat transfer characteristics of pulsating opposing mixed convection in a parallel vertical open channel. The influences of the dimensionless pulsating frequency Strouhal number and magnitude A, Prandtl number and baffle position Lb on the velocity and temperature distribution and long-time average Nusselt number 〈 Nu ¯ 〉 variation for the system at various Re and Gr/Re2 are explored in detail. Our results show that the channel with both flow pulsation and a baffle gives the best heat transfer. With a larger Re, the inlet flow pulsation dominates the whole velocity field in the channel. 〈 Nu ¯ 〉 always increases with a larger Re, pulsation magnitude A and Prandtl number. Maximum 〈 Nu ¯ 〉 occurs at some specific imposed pulsating frequencies which can be considered to be the natural frequency of the system.