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This paper presents expected THz radiation spectra emitted by micro-bunched electron beams produced using a slit-mask placed within a magnetic chicane in the FAST (Fermilab Accelerator Science and Technology) electron injector at Fermilab. Our purpose is to generate tunable narrow-band THz radiation with a simple scheme in a conventional photo-injector. Using the slit-mask in the chicane, we create a longitudinally micro-bunched beam after the chicane by transversely slicing an energy chirped electron bunch at a location with horizontal dispersion. In this paper, we discuss the theory related to the micro-bunched beam structure, the beam optics, the simulation results of the micro-bunched beam and the bunching factors. Energy radiated at THz frequencies from two sources: coherent transition radiation and from a wiggler is calculated and compared. We also discuss the results of a simple method to observe the micro-bunching on a transverse screen monitor using a skew quadrupole placed in the chicane., Comment: 25 pages, 8 figures

Soft x-ray self-seeding has been proved to be a feasible method to improve the longitudinal coherence of high gain free-electron laser. However, a pedestal-like sideband in the spectrum has been observed in the experiment, which generally limits the purity of the radiation pulse and the user’s application. The previous theoretical study indicates that the pedestal-like sideband is mainly induced by microbunching instability generated from LINAC. In this paper, three dimensional simulations have been performed to confirm the analytical results and show the formation process of the spectral sideband. A probable method is proposed to eliminate the pedestal-like sideband by simply inserting a magnetic chicane before the self-seeding FEL undulator. Theoretical and numerical simulations have been performed and the results show that the proposed method can efficiently eliminate the microbunching-instability-induced sideband in a soft x-ray self-seeding FEL.

In this paper, ultrashort bunch length monitoring was demonstrated based on Terahertz (THz) coherent transition radiation (CTR) in Tsinghua Thomson scattering X-ray (TTX) source. The radiation produced by electron bunch is split into three paths: one of them is used to detect the total energy, while the other two paths are filtered with different THz band-pass filters before detection. The bunch length variation can be obtained by calculating the ratio between the filtered energy and the total energy. The bunch is compressed by a chicane and via changing the current of chicane, the ratio of filtered energy and total energy changed correspondingly. It is a simple supplemental approach to monitor the bunch length during beam conditioning and facility operation. Bunch arrival-time jitter and nonlinear effects in chicane are observed in the experiment during the measurement of filtered energy and total energy.

The heat transfer performance of a novel type trisection helical baffle vertical condenser was experimentally investigated. The testing schemes have a common shell and replaceable tube bundles, including six tube bundles with different structured trisection helical baffles and a segmental one. The investigation is aimed at revealing the impacts on the heat transfer performance of structural improvements for facilitating condensate drainage, including inclined helical baffles of variable angles, dual threads and bent tail edges. The experimental results show that the best scheme, which adopts dual thread variable angled baffles with bent tail edges, has the average shell side heat transfer coefficient 131.8% higher than that of the segmental one. Taking the shell side heat transfer coefficient as the evaluation index, the single thread variable angle schemes are on average 25.47% higher than the single thread fixed angle ones; the dual thread variable angle schemes are on average 15.74% higher than the single thread ones; and the schemes with bent tail edges are on average 6.37% higher than the corresponding ones without bent tail edges. The results give a prospective way to overcome the deficiency of inferior heat transfer performance of the conventional segmental baffled vertical condenser to that of the horizontal one.

We present a method to control the two-dimensional transverse tilt of the electron bunch originated after the bunch compressor, affecting the X-ray free-electron laser performance. A head–tail tilt in both horizontal and vertical planes leads to a difference between the projected and the slice Twiss parameters, making it difficult to match the electron beam optics to the design one. The primary beam-tilt sources taken into accounts are the CSR generated in the chicane (horizontal tilt) and the misalignment of the high-order cavity used to linearize the compression process (vertical tilt). We show the experimental measurements performed to correct the both-plane beam tilts by using a tweak quadrupole and a skew quadrupole, respectively, placed in the chicane.

Coherent synchrotron radiation (CSR) induced microbunching instability has been one of the most challenging issues in the design of modern accelerators. We recently developed a semi-analytical Vlasov solver and applied it to the investigation of the physical processes associated with microbunching amplification for several types of recirculation arc lattices. In this study, we build on the concept of stage gain, proposed by Huang and Kim (2002), and develop an alternative view to characterize CSR microbunching development in terms of stage orders. The stage orders enable a fair and quantitative comparison of the impact of lattice optics on the microbunching development for different lattices under similar initial beam parameters. The multibend arcs considered in this study have a distinguishing feature of multistage amplification. The CSR microbunching gain grows as a six-stage amplification for the presented recirculation arcs with a total of 24 dipoles, while two-stage amplification was previously concluded for a three-dipole bunch compressor chicane. We also attempt to relate the lattice optics pattern with the obtained stage gain functions through a physical interpretation. The investigation in this paper may serve as a complementary discussion to our previous work (Tsai et al., 2017).

We show that a standard Linac configuration (consisting of accelerating sections, linearizing section, and magnetic chicane compressor) currently used in drivers for single-pass EUV/x-ray FELs is compatible with energy recovery, provided that certain timing constraints are met. By circulating the spent, rather than the fresh beam as in a conventional high-power ERL FEL design, the beam brightness can be more easily preserved thus facilitating lasing at short wavelength. As in a conventional ERL, the proposed design allows for energy-spread compression, enabling low-energy beam dumping and high energy-recovery efficiency. Results from numerical simulations presented in this paper show that this configuration could, in principle, support the generation of multi-kW average radiation power required for high-volume production EUV lithography.

The paper evaluates the effectiveness of various traffic calming measures from the perspectives of traffic performance and safety, and environmental and public health impacts. The proposed framework was applied to four calming measures – two types of speed humps, speed tables, and chicanes – to demonstrate its usefulness and applicability. A field experiment using probe vehicles equipped with global positioning system devices was conducted to obtain vehicle trajectory data for use in more realistic simulations. In addition, a recently developed vehicle emissions model was used for more accurate evaluation of environmental and public health impacts. The results show that chicane is better than the other types of traffic calming measures considered, except in terms of vehicle emissions.

We present a novel modular magnetic system that can introduce a large and continuously-variable path length difference without simultaneous variation of the longitudinal dispersion. This is achieved by using a combination of an electrically-adjustable magnetic chicane and a mechanically-adjustable focus- ing chicane. We describe how such a system may be made either isochronous or with a given longitudinal dispersion, and show that the nonlinear terms in such a system are relatively small., Comment: 27 Pages, 19 Figures

The current activities and future perspectives involving the use of X-band technology at the Elettra Laboratory are presented. These are mainly related to the development of the FERMI@Elettra FEL project, a fourth generation light source facility, now under commissioning in Trieste. The facility, based on a seed scheme, requires sub-ps electron bunches (∼1 kA), with very high optical qualities, at the entrance of the undulator chain. This is achieved by compressing the beam with two magnetic chicanes. A large effort has been undertaken to develop an X-band accelerating structure, to be installed downstream the first bunch compressor, before the magnetic chicane. In addition, we are also evaluating the possibility of extending the FERMI FEL wavelength capabilities beyond the foreseen limit of 4 nm, by increasing the linac energy from 1.5 GeV to 2.4–2.5 GeV, using the X-band technology.

In this paper, the results of the experimental studies of the mixing time, as well as the power consumption and baffle presence in the stirred tank with dual eccentrically located impellers are presented. The experiments were carried out in an unbaffled flat-bottomed cylindrical vessel. Three types of impellers were used: Rushton turbine, six pitched blade turbine and six flat blade turbine. The obtained data show that eccentricity of dual impeller systems leads to reduction of mixing time. Moreover, the experimental data confirmed the enlargement of power consumption in such systems. In the paper the analysis of relation between eccentricity ratio and mixing time has been performed.

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.

Conventional static mixers typically require high length to diameter ratios to be effective. This paper considers static mixers design to increase first appearance times in short, fat reactors. Three types are considered: conical baffles and annular baffles for tubular reactors and axial baffles for reactors with a rectangular cross-section. Relatively simple designs allow production increases (or reactor volume decreases) on the order of 20–50%.

Unbaffled stirred tanks are seldom employed in the process industry as they are considered poorer mixers than baffled vessels. However, they may be expected to provide significant advantages in a wide range of applications (e.g. crystallization, food and pharmaceutical processes, etc.), where the presence of baffles is often undesirable. In the present work solid–liquid suspension in an unbaffled stirred tank is investigated. The tank was equipped with a top-cover in order to avoid vortex formation. A novel experimental method (the “steady cone radius method”, SCRM) is proposed to determine experimentally the minimum impeller speed at which solids are completely suspended. Experimental N js and power consumption data are provided over fairly wide ranges for particle size, density and concentration. Dependence of N js on particle density and concentration is similar to that observed in baffled tank. Conversely, a negligible dependence of particle diameter on N js is observed in the unbaffled tank, a difference from baffled vessels with important practical implications. Finally, the mechanical power required to achieve complete suspension in unbaffled tanks is shown to be much smaller than in baffled vessels. This, in conjunction with the previously ascertained excellent particle-fluid mass-transfer promotion, could make unbaffled tanks a best choice for many solid–liquid operations, where mass transfer is the main limiting factor.

We have found that periodic flow inversions of free-flowing materials may be used to effectively eliminate both size and density segregation in free-surface flows. In a rotating cylinder, these inversions may be induced by placement of an axially located baffle within the flow. In this work, we report on an experimental study of radial mixing and segregation for binary mixtures of granular materials in a rotating cylinder both with and without an axially-located baffle. Qualitative and quantitative measures of the segregation/mixing are shown via digitized images and the intensity of segregation, respectively. We define a mixing improvement factor (ψ) to quantify the relative impact of the axial baffle for a variety of baffle placements and geometries. We find that the maximum extent of mixing is achieved when the baffle size is equal to the radius of the cylinder and fixed either at the free surface or within the shear layer. In contrast, we show that segmenting the baffle, baffle placement outside the shear layer (in fixed bed), or placement at the periphery of the cylinder resulted in an insignificant increase in mixing. Mixing was found to be independent of the shape of a baffle.

In the present study, the simplified conjugate-gradient method (SCGM) is combined with commercial CFD code to build an optimizer for designing the baffles locations with interdigitated channels of a centimeter-scale proton exchange membrane fuel cell (PEMFC). Using the optimizer, the locations of the baffles are adjusted toward the maximization of the average current density of the flow field. The approach is developed by using the commercial CFD code as the direct problem solver, which is able to provide the numerical solutions for the three-dimensional mass, momentum and species transport equations as well as to predict the electron conduction and proton migration taking place in a PEMFC. Results show that the optimal design process of the locations of the baffles can be completed by using the present optimization approach in just a finite number of iterations. The optimization process may lead to an appreciable increase by 14% in the power output from the fuel cell.

An attempt is made to enhance the productivity of the solar stills by connecting a mini solar pond, stepped solar still and a single basin solar still in series. Experiment is also carried out by replacing the single basin solar still into a wick type solar still. For further augmentation of the yield, baffle plate, pebble, fins, wicks and sponges are added. Day and night productivity of the solar stills for these modifications is studied. Daily efficiency and percentage increase in productivity for these modifications are also studied. Industrial effluent water is used as feed. Theoretical analysis gives very good agreement with experimental results.

The dynamics involved in powder mixing remains a topic of interest for many researchers; however the theory still remains underdeveloped. Most of the mixers are still designed and scaled up on empirical basis. In many industries, including pharmaceutical, the majority of blending is performed using “tumbling mixers”. Tumbling mixers are hollow containers which are partially loaded with materials and rotated for some number of revolutions. Some common examples include horizontal drum mixers, v-blenders, double cone blenders and bin blenders. In all these mixers while homogenization in the direction of rotation is fast, mediated by a convective mixing process, mixing in the horizontal (axial) direction, driven by a dispersive process, is often much slower. In this paper, we experimentally investigate a new tumbling mixer that rotates with respect to two axes: a horizontal axis (tumbling motion), and a central symmetry axis (spinning motion). A detailed study is conducted on mixing performance of powders and the effect of critical fundamental parameters including blender geometry, speed, fill level, presence of baffles, loading pattern, and axis of rotation. In this work Acetaminophen is used as the active pharmaceutical ingredient and the formulation contains commonly used excipients such as Avicel and Lactose. The mixing efficiency is characterized by extracting samples after pre-determined number of revolutions, and analyzing them using Near Infrared Spectroscopy to determine compositional distribution. Results show the importance of process variables including the axis of rotation on homogeneity of powder blends.

The process of particle sedimentation in a three-dimensional longitudinal basin with vertical baffles in a water treatment plant is studied using large-eddy simulations (LES). The objective of this study is to investigate the effect of the baffle installations on the particle settling performance of the sedimentation basin. The fluid mixture simulates typical contaminated water in which the contaminants are represented by a spectrum of 13 different particle sizes. The process of sedimentation of all classes of particles is simulated for tanks with zero, two, three and four baffles, respectively. The flow patterns, particle settling velocities, the particle settling efficiency and volume fraction are computed using LES and a multiphase model. The overall sedimentation efficiency of the basin for all the cases is calculated. Results show that the installation of baffles would effectively improve the performance of the tank in terms of settling. The baffles act as barriers and effectively suppress the horizontal velocities of the flow and force the particles to the bottom of the basin. Turbulence and vortices are generated at the shear zones near the baffles which significantly increase the settling velocity. The effect of varying number of baffles on the settling is also studied. Results indicate the performance of the basin increases with increasing number of baffles. The more the number of baffles the larger the suppression of the horizontal velocities and more chances the particles are forced to the bottom. The number of small eddies formed at the bottom of the basin also increases with the number of baffles. These results are important for the cost-effective design of longitudinal sedimentation basin in water treatment plants.

In this study, solids dispersion coefficients in fluidized beds of fine Group A particles were derived by modeling the data obtained in steady-state gas tracer experiments with a two-phase gas mixing model proposed by May [May, W.G., 1959, Fluidized-bed reactor studies. Chem Eng Prog 55 (12): 49–56]. Both baffle-free and baffled fluidized beds of FCC particles were tested in a two-dimensional cold model column with broad operating conditions covering both bubbling and turbulent flow regimes. Modeled results showed the axial solids dispersion coefficient of baffle-free fluidized bed ranges from 0.01 to 0.13 m 2 /s, increasing monotonously with increasing superficial gas velocity in both bubbling and turbulent flow regimes, agreeing well with previous solids-tracer studies with similar particles and operating conditions. The modeled results in baffled fluidized beds showed that the axial solids dispersion coefficient is significantly reduced when multilayer louver baffles are inserted in the bed, demonstrating louver baffle's strong suppression on solids backmixing. The suppression on solids backmixing by louver baffles augments with increasing superficial gas velocity. However, for the multilayer mesh-grid baffles, effective suppression of solids backmixing only functions at u 0 ≥ 0.6 m/s. As superficial gas velocity increases, the axial solids dispersion coefficients change in a similar trend as the axial gas dispersion coefficients in both baffle-free and baffled fluidized beds. The effects of different baffles on solids mixing are also similar to those on gas mixing. This demonstrates the close relationship between gas mixing and solids mixing in fluidized bed of fine particles.

This study embodies experimental characterization of emitted particulate and filtration performance under varied situation in a pulse-jet cleaning process. Tests were conducted under simulated condition in a filtration apparatus consisting four bags. The effect of four different factors such as fabric punch density, baffle plate height, air to cloth ratio and cycle time have been investigated on the key parameters; emission, pressure drop along with PM2.5 and average particle diameter of emitted particulate matter in a pulse-jet filtration process. Experimental investigation based on L9-orthogonal design shows that emission is reduced with the increases in punch density and pulse cycle time; but it increases up to a certain extent with the increase in air to cloth ratio. However baffle plate height has no effect on the emission. On the other hand pressure drop across the tube sheet increases with the material consolidation, air to cloth ratio and pulse cycle time; but the above parameter first decrease with the increase in baffle plate height. PM2.5 (based on the number distribution) is found to be mainly affected by the baffle plate height and cycle time; as it first increases and then decrease with the increase in baffle plate height but it shows reverse trend with the increase in cycle time. Average particle diameter based on number volume is found to be mainly affected by the baffle plate height and cycle time. With the increase in time of filtration, both emission and pressure drop tend to increase without affecting PM2.5 and average particle diameter based on number volume.

A new device for inserting an absorber plate to divide a flat-plate channel into two parts with fins attached by baffles and external recycling at the ends is presented. The proposed device substantially improves the heat-transfer efficiency. Experimental and theoretical investigations into the device efficiency are presented. The theoretical prediction agreement with the measured values from the experimental results is good. The experimental and theoretical results are represented graphically and compared with data from the downward-type single-pass solar air heaters of the same size without recycling. Considerable heat-transfer improvement is obtained by employing baffled double-pass operations with external recycling and fin attached over and under the absorber plate. The recycle ratio and absorber plate location influences on the heat-transfer efficiency and on the power consumption increment are also discussed.

To disperse the unreacted overhead gas phase into the liquid in an agitated reactor without gas outlet, a gas-inducing impeller is usually employed. To determine the lowest critical rotating speed, the gas-induction mechanism was reconsidered by constituting a mechanical energy conservation equation between the gas inlet orifice in the gas phase and the gas outlet orifice in the liquid phase under a certain rotational speed. According to this model, the critical speed of the gas-inducing impeller could be basically determined by the submersion depth and the radial position of the gas outlet, and a novel design was proposed by introduction of six short pipes stretched radially from the axis of the impeller. The final design of the gas-inducing impeller was obtained by an optimal combination of the gas-inducing pipes, the blades of the impeller and the baffle dimension.

Fine powders were found to be fluidized in a rotating drum by internal cycling gas by the drum rotation. It is essentially a fluidized bed without requiring any external fluidizing gas. Such a rotating drum can be regarded as a new gasless fluidized bed for fine powders in contrast to a traditional fluidized bed, possibly leading to a considerable amount of energy savings. In addition, the fluidization quality of fine powders was found to be further improved with the assistance of drum rotation because of the shearing movement among particles that eliminates channeling and cracks and possibly also breaks agglomerates. Five regimes were identified in the rotating drum including slipping, avalanching-sliding, aerated, fluidization and re-compacted regimes. It was also found that drum wall friction plays an important role to fluidize fine powders because the friction carries particles to the freeboard, leading to gas cycling that fluidizes the powders. As well, three types of specially designed baffles were utilized to promote powder fluidization in rotating drums. These baffles effectively bring an early onset of all the regimes in rotating drums by reducing powder–wall slipping, carrying particles and bringing additional gas to the powders.

This paper illustrates the mechanism of gas–solid contacting in a multistage counter-current fluidized bed reactor attached with downcomers. Experimental hold-up study has been carried out extensively using the air and lime particles as gas and solid phases, respectively. The reactor was operated in continuous regime for two-phase system over a wide range of operating conditions including height of the downcomer to determine the solids hold-up at each stage of the reactor. The data was generated under steady and stable operation of the column. Based on the experimental data, empirical correlation is proposed for predicting the solids hold-up in the multistage fluidization. The results in this study assume importance from the standpoint of design and steady operation of multistage fluidized bed reactor with downcomer as an air pollution control system for control of gaseous emissions in the industries.

Two mechanisms for the drawdown of floating solids in baffled stirred tanks have been identified [Khazam, O. and Kresta, S., 2008, Mechanisms of solids drawdown in stirred tanks. Can J Chem Eng, 86(4): 622–634]: turbulent engulfment and mean drag. Baffling suppresses stable surface vortex formation and increases the intensity of mean drag and turbulence at the surface. Strong top to bottom liquid circulation is also promoted by baffling, however; this circulation rapidly brings particles back to the surface. In this paper, two alternate baffle configurations are proposed: half baffles and surface baffles. The objective is to maintain a high level of turbulence at the surface while reducing the return circulation from the bottom of the tank. The performance of the baffle configurations is compared using the just drawn down speed, Njd, and cloud depth, CD, for the PBTD, PBTU and A340 impellers. CFD simulations and measurements of the power number for the fully baffled and the surface baffled configurations are also reported. It is found that half baffles are very similar to full baffles in performance, but surface baffles offer several advantages: a significant reduction in Njd, more robust performance at large submergences, and a better distribution of solids.

The paper presents results of an experimental study of heat transfer and friction in a rectangular section duct with fully perforated baffles (open area ratio of 46.8%) or half perforated baffles (open area ratio of 26%) at relative roughness pitch of 7.2–28.8 affixed to one of the broader walls. The Reynolds number of the study ranges from 2700 to 11,150. The baffled wall of the duct is uniformly heated while the remaining three walls are insulated. These boundary conditions correspond closely to those found in solar air heaters. The study shows an enhancement of 79–169% in Nusselt number over the smooth duct for the fully perforated baffles and 133–274% for the half perforated baffles while the friction factor for the fully perforated baffles is 2.98–8.02 times of that for the smooth duct and is 4.42–17.5 times for the half perforated baffles. In general, the half perforated baffles are thermo-hydraulically better to the fully perforated baffles at the same pitch. Of all the configurations studied, the half perforated baffles at a relative roughness pitch of 7.2 give the greatest performance advantage of 51.6–75% over a smooth duct at equal pumping power.

A series of experiments have been carried out in a developed liquid sloshing setup to estimate the pressure developed on the tank walls and the free surface displacement of water from the mean static level. The square tank attached to a shaking table can be moved to and fro by a cam arrangement driven by a DC motor. Pressure and displacement studies are done on the basis of changing excitation frequency of the shaking table and fill level in the tank. Experiments were carried out without and with baffles, and the consequent changes in the parameters are observed.

The paper deals with the experimentally obtained results of the direct-contact condensation of steam in contact with water in cascade column. Baffle trays were used to obtain contact between water and steam in DN 300 column at atmospheric pressure. Testing of Chernobilski equation showed poor correlation compared to the experimental results so we have found the following form of heat transfer rate Nu = 5.8 · 10 - 6 · Re 5 / 3 · Pr 1 / 3 · Fr - 2 / 3 which could be recommended for heat transfer calculations for this kind of apparatuses.

As a new kind of rotating equipment, rotating zigzag bed (RZB) is structurally unique and has many superior features. The RZB is characterized by a rotor coaxially combining a rotating disc with a stationary disk. Compared with a conventional rotating packed bed (RPB), the RZB can function without liquid distributors, eliminate one dynamic-seal, and easily accommodate and accomplish intermediate feeds in continuous distillation processes. The RZB also effectively increases the contact time of gas and liquid phases and thus, enhances the mass transfer capacity. In this work, the principles of the RZB are presented. The hydraulic and mass transfer performance of the RZB was investigated. Experimental results showed that the pressure drop of the RZB increases with the increase of the rotational speed and the gas flow rate, but decreases with the increase of the liquid flow rate. A semi-empirical equation was proposed to correlate the pressure drop data with good agreement. The mass transfer efficiency of the RZB decreases with the increase of the reflux rate at lower reflux rate, but levels off at higher reflux rate. The number of theoretical plates of the RZB increases with the increase of rotational speed of the rotor. However, at a higher rotational speed, this trend is not obvious. In addition, some considerations for further work are discussed.

Computational fluid dynamics simulations are employed to assess the effect of adding a vertical baffle at the feed section of a full-scale sedimentation tank for the improvement of solids settling in potable water treatment. A general CFD-based simulation strategy is developed based on the specific features and conditions met in practice for potable water treatment. The linearity of the particle conservation equations allows separate calculations for each particle size class – but performed for all classes of interest – leading to the uncoupling of the CFD problem from a particular inlet particle size distribution. The usually unknown and difficult to be measured particle density is found by matching the theoretical to the easily measured experimental total settling efficiency. The proposed strategy is computationally much more efficient than the corresponding strategies used for the simulation of wastewater treatment. This work compares simulations from a standard and a baffle-equipped tank. It is found that the baffle decreases the inlet recirculation zone and enhances the settling of solids by directing them towards the bottom of the tank with high velocities. It is noteworthy that even small differences in the particle velocity can cause large changes in the percent of settled particles; in this work, the overall solids removal efficiency increased when using the baffle from 90.4 to 98.6% leading to a reduction of the effluent solids concentration of approximately 85%.

A two-dimensional algebric slip mixture (ASM) CFD model was developed to simulate the flow and mixing of liquid-gas-particle system in a rotary drum. The simulations show that there are several flow regimes in slurry phase, including anti-clockwise circulation flow of liquid, rising stream of bubbles, circumferential flow and eddy. The gas disperses mainly in a limited area in the vertical region of bubble stream. Pyrite particle mixing is mainly arised from the movement of baffles, and the distribution of particles is well. The increase of aeration rates would give rise to an increase of the volumetric averaged gas holdup. The increase of rotation speed has little influence in the averaged gas holdup. When three gas spargers were molded in the drum, there is not obvious improvement of gas holdup and particle mixing. (C) 2007 Elsevier B.V. All rights reserved.

X-ray computed tomography (CT) is used to explore the differences in gas dispersion in a stirred-tank reactor (STR) for different operating conditions by varying the impeller speed and gas flow rate. X-ray imaging has been carried out in a 0.21 m ID acrylic STR equipped with a nylon Rushton-type impeller. From the CT images, major differences in local gas holdup are observed for different operating conditions. Completely dispersed conditions have a relatively uniform holdup profile while flooded conditions show a high gas holdup near the impeller shaft. The high resolution of the X-ray system allowed fine details such as recirculation regions behind the baffles to be visualized.

Stability rating tests using a pulse gun, one type of artificial disturbance device, have been performed to optimize and to limit the axial baffle length of a combustor. To determine whether the combustor is stable when it is exposed to strong external perturbations or pressure oscillations, the decay time and amplitude ratio have been analyzed to quantify the stabilization capacity of the combustor. A baffle not big enough to cover the flame zone considered as the collision plane of the F-O-O-F impinging injector was not able to suppress external perturbations sufficiently. The combustion stability boundary limit of the present combustor can be determined with respect to the axial baffle length.

Granular materials are utilized in a wide variety of industrial applications. The complex hydrodynamics of granular flow is still not fully understood. The flow characteristics of solid particles in a two-dimensional moving bed were studied experimentally and theoretically. The effects of mass velocity, properties of particles and the shape of moving bed on flow pattern were examined. The experiments show that the mass velocity of solid particles and the placement of baffles in stagnant zones have no effect on flow pattern. The shape, size and repose angle of particles affect the flow pattern greatly. The particles have more liquidity and the mixture between particles is easier with the increasing of sphericity degree of particles and the decreasing of particle size. The shape of flowing zone becomes more sharp-angled with the increasing of the repose angle, and the stagnant zone becomes larger. The kinematic model was used to simulate the particle flow. For center discharge the simulation results are in agreement with experiment data very well, while for eccentric discharge the simulation couldn't show the effects of side walls on particle flow. An analytic solution of kinematic model was obtained by Lie transformation group. It shows that the velocity of particle flow is the maximum when x equals 0. The method of translational coordinate was used to modify the traditional kinematic model in order to make sure the x value of each point on the maximum particles velocity distribution lines is zero. The modified kinematic model could simulate the eccentric discharge well, and the field of kinematic model applications was expanded.

Macromixing characteristics, power number and visual observation of the vortex behaviour and micromixing in an unbaffled tank agitated with a Rushton turbine are reported. The latter has also been compared in detail with earlier results from an identical tank containing baffles. The maximum mean specific energy dissipation rate, e ¯ T , in the unbaffled tank that can be utilised without severe air incorporation is ∼ 0.18 W / kg compared to ∼ 1.2 W / kg with baffles. However, at this lower e ¯ T , the micromixing efficiency is always significantly greater without baffles except when addition is made onto the top of the liquid or into the trailing vortex very close to the impeller. In these latter cases, they are approximately the same but even a small submergence of the feed tube below the liquid surface greatly enhances micromixing in the unbaffled case whilst it is still very poor with baffles. This good micromixing performance of the unbaffled vessel was very unexpected. Furthermore, an established method of estimating the local e T gave values of e T / e ¯ T = φ ⪢ 1 at every feed position where measurement was undertaken. Since the spatially averaged value of φ = 1 , this result suggests the possibility that the accepted concept of micromixing being totally controlled by the local e T at the feed point may not be valid for such swirling flows.

The chicane scheme adopted for the elliptically polarized undulators (EPU) in the ID10 section at the Canadian Light Source (CLS) not only permits independent operation of two beamlines, but also allows to redirect beams from two EPUs into a single beamline with a performance similar to a “dedicated” configuration. Fast switching at kHz rates will be achieved by piezo shutters located after exit slits which will block the light of alternate polarization.

The hydrodynamic characteristics of the Maxblend TM impeller have been investigated in the case of viscous Newtonian fluids. Both laboratory experiments and 3D finite element based computational fluid dynamics (CFD) simulations have been carried out. The power consumption, the mixing evolution yielding the mixing time, and the effect of baffles in the laminar and transition flow regimes have been determined. It was found that the limit Reynolds number between the laminar and transition regimes is approximately 25 and 38 for the unbaffled and baffled configurations, respectively. Based on the range of Reynolds numbers studied in this work, the best window performance of the Maxblend TM mixer where fast and homogenous mixing is achieved is the end of the laminar regime and the early transition regime with baffles.

Heat transfer enhancement in a heat exchanger tube by installing a baffle is reported. The effect of baffle size and orientation on the heat transfer enhancement was studied in detail. Three different baffle arrangements were considered. The results show that for the vertical baffle, an increase in the baffle height causes a substantial increase in the Nusselt number but the pressure loss is also very significant. For the inclined baffles, the results show that the Nusselt number enhancement is almost independent of the baffle inclination angle, with the maximum and average Nusselt number 120% and 70% higher than that for the case of no baffle, respectively. For a given baffle geometry, the Nusselt number enhancement is increased by more than a factor of two as the Reynolds number decreased from 20,000 to 5000. Simulations were conducted by introducing another baffle to enhance heat transfer. The results show that the average Nusselt number for the two baffles case is 20% higher than the one baffle case and 82% higher than the no baffle case. The above results suggest that a significant heat transfer enhancement in a heat exchanger tube can be achieved by introducing a baffle inclined towards the downstream side, with the minimum pressure loss.

The effect of flow geometry parameters on transient entropy generation for turbulent flow in a circular tube with baffle inserts has been investigated. Different flow geometry parameters of pitch to diameter ratio (H/D), baffle orientation angle (β), ratio of smooth to baffled cross-section area (So/Sa) and ratio of tube length to baffle spacing (L/H) were varied parametrically during the experiments. One smooth tube and nine different baffle inserted tubes geometries were tested. The characteristic parameters of the baffled tubes are pitch to tube inlet diameter ratio H/D = 1, 2 and 3; baffle orientation angle β = 45°, 90° and 180°. The time averaged entropy generation corresponding to the flow geometry parameters were compared under the condition of constant heat flux. Air having a Prandtl number of 0.71 was used as working fluid, while stainless steel was considered as the pipe and baffle material. Nine empirical equations were derived to correlate the time averaged entropy generation as a function of the Reynolds number and the other experimental individual flow geometry parameters, pitch to diameter ratio, baffle orientation angle, ratio of smooth to baffled cross section area and ratio of tube length to baffle spacing. Finally, the general empirical correlation of the time averaged entropy generation was developed and considered to be applicable within the range of Reynolds number 3000 ⩽ Re ⩽ 20,000 in the form of S gen ave ( t ) = 0.0054 Re - 0.793 Pr 0.4 ( H / D ) - 0.656 ( S o / S a ) - 14.006 β - 0.0264 ( L / H ) - 0.6051 .

The present work involves single-phase computational fluid dynamics (CFD) simulations of continuous flow pump-mixer employing top-shrouded Rushton turbines with trapezoidal blades. Baffle—impeller interaction has been modeled using sliding mesh and multiple reference frame approaches. Standard k–ε model has been used for turbulence modeling. Several CFD runs representing different combinations of geometric and process parameters have been carried out. Results of CFD simulations have been used to find out two macroscopic performance parameters of pump-mixer—power consumption and head generated by the impeller. The simulation results have been compared with the experimental data obtained on a pilot-scale setup. Good agreement between CFD predictions and experimental results is observed. In most cases, sliding mesh approach is found to perform better than multiple reference frame approach. Details from CFD simulations have been used to have an insight into the pumping action of the impeller., © Elsevier

The hydrodynamic performance of a dual shaft mixer consisting of a low-speed, wall-scraping, Paravisc-type impeller and an off-centered, high-speed, high-shear Deflo disperser have been experimentally investigated in the case of dispersing fine solids in a viscous Newtonian continuous phase. The experiments were restricted to the laminar regime and made use of two different types of solid particles namely: calcium carbonate and glass beads, at a constant concentration of 10 wt%. Glucose solutions were used as the Newtonian continuous phases. The single phase hydrodynamic characterization showed that the Paravisc impeller power consumption can be significantly affected by the rotation of the Deflo disperser, revealing the importance of the turbine on the overall mixing performance. Mixing time measurements showed that the Paravisc effectively controls the bulk flow movement but requires the presence of a baffle, or a second shaft acting as such, in order to output effective mixing performance. This observation is also valid in solids dispersion where the Paravisc impeller exerts a major influence on the time required to achieve a stable dispersion. The homogenization efficiency tests performed showed the ability of the Deflo disperser to efficiently break up the agglomerates in the vessel.

Liquid distributors are a key component to optimal performance in packed distillation columns. Their design is commonly based on the drip point density. For modern baffle plate distributors, however this is not appropriate, because the liquid is delivered to the packing in form of drip lines rather than drip points. This problem can be eliminated by analyzing the liquid distribution below the first layer of packing. The ratio of wetted to total geometrical surface is used as a quantitative measure (Wetting Index) to describe distributor performance. It allows comparing different distributor systems, e.g. those with conventional drip points and those with drip lines. The Wetting Index depends on the geometry of the outlet system, the orientation of the distributor relative to the packing and the packing geometry.

The use of dissolver-discs results in characteristic vortices (trombes). Vortices are also an important phenomenon in emulsification processes. Size and geometry as well as their stability are influenced mainly by the viscosity of the product, the rotation speed and the geometry of the discs, vessels and baffles used and the height of the liquid above the disc. Visualization of vortices carried out in a highly viscous (η = 600 m Pa s), optical transparent fluid are shown and compared to images obtained from real emulsification processes with different dissolver-discs. It is shown how the vortex can be used to ad the disperse phase (oil) into the emulsion and that this oil will merely float on the surface of the emulsion if there is no vortex present.

The effect of axial baffles in non-circular channelled membranes on the critical flux has been investigated. Various geometric configurations of inserts, namely cylindrical rod, helical baffles and alternating direction helical baffles have been used. Higher critical fluxes were achieved with most of the inserts. Under the conditions of the present study i.e. at a fixed hydraulic dissipated power, the introduction of alternating direction helical baffles led to the greatest improvements (up to 37.7%). These improvements are ascribed to the turbulence generated and mixing that this encourages within the flow channel. Helical and cylindrical rod inserts produce comparable results which are unexpected and is attributed to the star-shaped flow channel which reduces the effectiveness of the rotational flow field that the helical baffles are thought to produce. In this study, helical baffles having two turns per 25 mm produce optimum flow conditions leading to the best performance in terms of the critical flux in the helical baffle series. An increase in the rod diameter seems to lead to a decrease in the flux enhancement. The results are explained in terms of the hydrodynamics that each axial baffle structure produces and their interaction with the star-shaped channel geometry within the filtration system.

This experimental study attempts to explore the local heat transfer in rectangular channel with baffles, and analyzes the experimental results of baffles with different heights and pores in the event of five Reynolds numbers and three heating quantities. Apart from increasing the perturbation of flow field, the channel's flow field with baffles, which is similar to a backward-facing step flow field, is very helpful to heat transfer. To obtain an optimized baffle and increase the perturbation of flow field, this experiment employed baffles with five heights ( H = 10–50 mm) and different numbers of pores ( N = 1–3), as well as heat flux: Q = 40–100 l/min, Reynolds number: 702–1752, and heating quantity: q in = 90–750 W/m 2 . In addition to measurement of overall temperature distribution, emphasis is also placed on analysis of local heat transfer coefficient. Furthermore, heat transfer distribution of channel can be applied to explain how the baffles of pores have an influence upon backward-facing step flow field, shear layer, recirculation region, reattachment region and redeveloped boundary layer. Finally, some empirical formulas derived form experimental results may provide a reference for future design.

Heat transfer in particulate materials affects a wide variety of applications ranging from multi-phase reactors to kilns and calciners. In catalyst manufacturing, heat transfer through granular media (catalyst) occurs in the impregnation and calcinations stages. We use the discrete element model to simulate flow, mixing, and heat transport in granular flow systems in rotary calciners and impregnators. Granular flow and heat transport properties are taken into account in order to develop a fundamental understanding of their effect on dryer and calcination performance. Simulations have shown that as rotation speed decreases, both heat transfer and temperature uniformity of the granular bed for both calciner and impregnator increase. Depending on baffle size, baffles can either increase or decrease heat transfer in double cone impregnators. Granular cohesion does not affect heat transfer in the range of values examined.

Despite the importance of thermoeconomic analysis in shell and tube heat exchanger design, the determination of the optimum baffle spacing by using the thermoeconomic analysis is usually neglected. On the other hand, baffle spacing is one of the most important parameters used in the design of shell and tube heat exchangers, and there is no precise criterion for the determination of baffle spacing in the literature. In this study, thermoeconomic analysis is used to determine the optimum baffle spacing, accompanied by an example of such an optimization of baffle spacing for a shell and tube heat exchanger. The results of this example are then used to demonstrate how the optimum ratio of baffle spacing to shell diameter is determined precisely and affected by the varying values of the geometrical parameters. Finally, the results are compared to those obtained by classical approaches.

Although the distribution of gas hold-up in stirred tanks is a key factor to their design and operation, systematic experimental data on local gas hold-up of surface-aerated stirred tanks are not available in open literature. In this work, turbulent two-phase flow in a surface aeration stirred tank with a diameter of 0.380m was investigated experimentally and numerically. The gas hold-up was measured with a conductance probe at various operating conditions. A surface baffle to improve the efficiency of surface aeration of a Rushton disk turbine was designed and tested. The experimental data suggest that the gas hold-up distribution in the surface aeration tank is very non-uniform, and the surface baffle improves the aeration rate particularly at a high agitation speed. A three-dimensional in-house computational fluid dynamic (CFD) two-fluid model with the standard k-epsilon-A(P) turbulence model was used to predict the gas-liquid flow, and the impeller region was handled using the improved inner-outer iterative procedure. Based on Kolmogoroff's theory of isotropic turbulence, a constitutive equation for surface aeration strength was proposed. The numerical prediction, in combination with the measurements, gives insight to the surface aeration performance of stirred tanks. it was found that the simulation reasonably predicted the gas hold-up distribution in the upper tank, but underestimated it in the region below the stirrer. (c) 2006 Elsevier Ltd. All rights reserved.

For the cultivation of microorganisms, baffled shake flasks are employed when increased levels of oxygenation and mixing are required. Their use has been discouraged, however, due to the danger of a wetted sterile plug and the lower reproducibility of the experimental results. Consequently, there are only few studies dealing with this type of shaken bioreactor, and there is practically no characterization of this reactor type from a chemical engineering viewpoint. Therefore, a systematic study to elaborate the basic characteristics of the volumetric power consumption and the unfavorable out-of-phase phenomenon in baffled shake flasks is undertaken. A new type of measuring device was developed to measure the volumetric power consumption in a single shake flask. The volumetric power consumption was found to increase with increasing shaking frequency and with decreasing filling volume. Further, an independency of power consumption on the shaking diameter was observed as long as the fluid motion is in-phase. A comparison of two different baffle geometries demonstrated that deeper baffles cause more resistance to fluid flow. For the commonly employed shaking diameter of 25 mm, the investigated baffled flask types may not be operated in the in-phase state. A larger shaking diameter must therefore be employed. It was found for the first time that for all in-phase conditions, the dimensionless Newton number Ne ′ is independent of the Reynolds number Re. Power consumption in baffled shake flasks may therefore be described by a characteristic Ne ′ only dependent on the filling volume V L and the flask type. Even though there are quantitative differences, a qualitative similarity between fluid flow in stirred tanks and shake flasks has been demonstrated.