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The Boeing version of the PARMELA code has been modified to compute the space charge effects for electron pulses with highly elliptical transverse cross-sections. A dynamic gridding routine has been added to allow good resolution for pulses as they evolve in time. The results from calculations for the chicane buncher in the 1 kW visible FEL beam line at Boeing indicate that the old circular algorithm of the SCHEFF subroutine overestimates the emittance growth in the bend plane by 30–40%.

Emittance preservation in beam bending systems is vitally important in the production of bright, high-current electron microbunches. Generally, the emittance increase occurs in the bend plane and results from changes in the microbunch energy distribution as the beam transits the bend. This redistribution of electron energies increases the beam's divergence, and hence the emittance, by spoiling the achromatic transport of the bending system. In this paper we investigate the correlated emittance growth in a three dipole chicane compressor due to coherent synchrotron radiation (CSR). Breaking the symmetry of the chicane partially cancels the CSR-induced correlation thereby reducing the bend plane emittance growth. The consequences of this emittance compensation scheme are discussed.

Effects of geometrical configurations of crystallizers upon the crystal size distribution have been quantitatively investigated using four types of baffles with different geometries, in batch crystallization of aluminum potassium sulfate in a seeded batch crystallizer agitated by a 6-bladed flat paddle. Two evident maxima in size distribution were obtained for a vessel with normal wall baffles, whereas the maximum at larger size disappeared and only single maximum was observed for other types of vessels. The difference was infered to the difference in the ability of agglomeration of crystals depending the geometries.

This work demonstrates the applicability of more generalized sluice gate equations to the design of baffle sluice modules. The generalized equations allow the module to be designed for any upstream head. These equations also offer additional understanding of the behavior of the baffle sluice module and demonstrate that the first baffle of the module is largely redundant. The constraint of having the minimum water level coincide with the crest of the first baffle has been removed. Through an optimization procedure, an alternative design method is suggested that will theoretically improve the performance of the baffle sluice module. Through this design technique, a module can be designed with any practical number of baffles. The effect of combined orifice-weir flow and width of the module is also discussed.

Several characteristics that involve the gas/liquid flow pattern, the mixing time and the ozone utilization rate of a modified gas-induced ozonator were studied. In such an ozonator, four narrower baffles having a width 1/25 of the vessel diameter and two in-series 45° downward pitched blade turbines (PBTs) were employed. At high impeller speeds, the gas induction enhanced the gas-liquid utilization. A model heterogeneous ozonation of the C.I. Reactive Blue 19 dye (RB19) was conducted to examine the effect of various operational parameters. Results concluded that the modified gas-induced ozonator provides high ozone utilization rate under stable gas induction and proper inlet gas flow rate. In addition, a comparison between the present ozonator and other gas inducing reactors in the literature was also made.

The minimum impeller speed needed to obtain complete liquid-liquid dispersion in baffled vessels is examined experimentally for six-blade disk turbines, flat paddles, pitched paddles and four-blade propellers of three different sizes. The minimum impeller speed for complete liquid-liquid dispersion is detected by the method developed by using a multimeter. From the data obtained in this work, the impeller position above the vessel base to get the minimum power input for complete liquid-liquid dispersion is determined. The correlation for the minimum impeller speed for complete liquid-liquid dispersion in baffled vessels is also proposed.

The particle dynamics in a gas-solid contactor with inclined baffle plates forming a zig-zag path have been numerically simulated by a two-fluid model. In this contactor, solid particles slide down along the baffle plates and are fluidized at the openings between the wall and the edge of the baffle plates by the upflowing gas. Thus this structure is called a “moving-fluidized bed.” In the present two-fluid model, both the gas and particles are considered to be in continuum and fully interpenetrating and their behavior are described in terms of four hydrodynamic equations; conservation equations of mass and momentum for the respective phases.The computer simulated porosity distributions in a two-dimensional moving-fluidized bed show that the gas bubbles appear in the fluidized bed region at the opening for the gas velocity exceeding a critical value. The average diameter of the bubbles and the distribution of the particle velocity along the baffle plate have been calculated. These results are in good agreement with the experimental results.

When an electron bunch is compressed in a chicane compressor, the CSR (coherent synchrotron radiation) will induce energy redistribution along the bunch. Such energy redistribution will affect the longitudinal emittance as a direct consequence. It will also excite betatron oscillation due to the chromatic transfer functions, and hence a transverse emittance change. So, it is indispensable for us to find a way to alleviate the CSR-caused emittance dilution and the bad result of chicane compressor in PKU-FEL.

Estimates are presented of the radiation environment for POINT2 of the Large Hadron Collider, where the ALICE detector is to be located. The radiation environment is studied in terms of two points of accidental beam losses. The dose level in the region of the counting rooms is lower than the recommended CERN limit of 50 mSv. The radiation level behind the access shielding at the air-duct chicane is not higher than 10 mSv; this area is also appropriated for use as a public area. A more complicated situation is in the machine bypass region. The dose level in the tunnel is a few hundred millisieverts, and a decrease of this level could be achieved by increasing the thickness of the wall or the beam pipe shielding.

The influence of horizontally placed internals on the physical behaviour of a dense fluidized bed has been observed using an X-ray technique. The internals were sieve-like baffles with an aperture size two orders of magnitude larger than the diameter of the bed particles. Both a freely bubbling bed and single injected bubbles were observed. For the latter, the bubbles were made to emerge from a layer more opaque to X-rays into one more transparent. In this way, the flow pattern around the bubble and the wake could be observed. The results show that the baffles do not influence the mean bubble size or velocity significantly, confirming earlier indirect observations. It is also shown that the wake material is removed from the fluidization bubbles by the baffles. Results are given as statistics for bubble size and rise velocity as a function of the fluidization velocity with and without baffles present, and sequences of X-ray images showing the effect of the baffles.

From an industrial point of view, control of precipitated particles' quality turns out to be crucial. Experiments carried out in a pilot-scale baffled stirred tank with and without draft tube of two different diameters under different process conditions show a great influence of internal geometry and feed point locations on crystal size distribution and morphology of precipitated particles. Several results in contradiction with those expected by intuition show that much more work is needed to elucidate the interaction between mixing and precipitation phenomena in stirred tanks. In this context, the paper provides a frame of reference and some rules of thumb useful to industrial manufacturers for controlling the product quality.

An effect of the baffle length L on power consumption has been studied for an agitated vessel of inner diameter D =0.6 m equipped with short baffles. The measurements were carried out for the following agitators: Rushton and Smith turbines, pitched blade turbine ( β =45°, Z =3) and propeller. Power characteristics Ne =f( Re ) for different geometrical parameter L / H of the baffles were obtained within the turbulent regime of the fluid flow in the agitated vessel. The results of the experiments were approximated by means of Eqs. (7)-(13) .

Various numerical predictions are given for the containment testing of fume hoods with internal baffles of different sizes and at different locations and with a louvered bypass. The numerical predictions were compared with experimental data and a fairly good agreement for the air velocity was found, although there was only qualitative agreement for the concentration of the contaminant. It was found that the level of contaminant leakage at the working aperture depended not only on the size of the recirculating airflow behind the fume hood sash but also on the blockage caused by the baffles inside the fume hood near the exhaust duct. Finally, some new suggestions for the design of the fume hood have been proposed. However, before implementing these suggestions it is essential that either experimental testing be performed, or the cost-effective alternative of using numerical predictions for containment testing, to determine accurately the level of contaminant leakage from the working aperture.

The onset speed of gas induction and the power consumption after gas induction were studied in a gas-induced type agitated tank. In such an agitated tank, four unique baffles which were shorter and narrower than the conventional ones were adopted. Two 45° downward pitched blade turbines (PBT) in series were used as impellers. Gas induction could be formed by the dual impellers operated above the onset impeller speed. Several geometric factors and operation parameters were considered by theoretical aspects and the dimensionless analysis to study the onset of gas induction and the power consumption. In all experiments, air and tap water were used as working fluids. Results revealed that a lower agitation speed and less power consumption were needed for the present tank than a narrower full-length baffled agitated tank. In the present tank, the least specific power consumption was found when the liquid level was about 1.9 times the tank diameter. Two correlation equations were obtained to predict, respectively, the onset speed of gas induction and the power consumption after gas induction. Comparison between the present type and various other gas-inducing type agitated tanks were also discussed.

In this study, the effect that the top boundary has on the flow in the bottom region of a fully baffled stirred vessel of standard geometry, was investigated. Measurements of the three dimensional mean and fluctuating velocity components were made with Laser Doppler Anemometry. Calculations of the flow field were made with the commercially available CFD code FLOW3D. Three cases were studied. Two in which the top boundary was located at 30 mm, one with an air-liquid interface (open vessel) and one without (closed vessel). For the third case a closed vessel was also used and the top boundary was located at 150 mm. The effect of removing the air-liquid interface at 300 mm on the flow in the bottom region of the vessel was small enough to be within the experimental uncertainty. Lowering the closed top boundary from 300 to 1 SO mm had a rather small impact on the flow field in the lower part of the vessel, It was concluded that the detected change is due partly to a direct effect from the introduced l...

The hydrodynamics of a circulating fluidized bed with a bubbling bed section separated by an inner rim baffle are examined both by experiment and mathematical analysis. To maintain sufficient solids holdup in the upper section, the inner rim baffle was set up in the middle of the riser. It is found that the solids holdup in the section above the baffle is greatly increased. Investigation into the baffle dimensions shows that the variation of the baffle clearance has little effect on the solids holdup in the upper section when the clearance is greater than a certain value, whereas the variation of the baffle height has a significant effect on the solids holdup in the upper section, i.e. the lower the baffle height, the higher solids holdup. A hydrodynamic model is developed based on the mass balance and the pressure balance of the solids circulation loop. With respect to gas-solids flow behavior in the upper section, the clustering suspension and the core-annulus flow are taken into account; for the lower section, a bubbling fluidized bed model is included. By comparing the calculated results with the experimental ones, the model is found to predict fairly well the gas-solids flow behavior of the compact bubbling-circulating fluidized bed.

The behaviors of particles in a gas-solid contactor with inclined baffle plates that form a zig-zag path are experimentally studied. To improve the gas-solid contact efficiency, a table discharger is installed at the bottom of the column. In this contactor solid particles slide down along the baffle plates and are fluidized at the openings between the wall and the edge of the baffle plates by the upflowing gas. This structure, called a “moving-fluidized bed”, has some of the advantages of both moving and fluidized beds.The feed rate of solid particles, the open spacing fraction and the inclination angle of the particle reflector were chosen as parameters for experimental conditions. The formation of bubbles was observed between the fluidized bed and moving bed regions and the bubble diameters were measured by using fiber optic probes. Particle velocities in the moving bed region along the baffle plate were measured as a measure of the circulating motion of the particles in the moving and fluidized bed region. It is concluded that the present apparatus performs at a high efficiency of gas-solid contact under dense flow conditions, as compared with a gas-solid contactor which was used in our earlier study.

The maximum O2 uptake by Rhizopus oligosporus grown in a 200 litre rotating drum bioreactor at 0.5 rpm ranged from 6.7 to 7.6 mmol per min per kg initial dry substrate (IDS), for runs done with 4 baffles each 17 cm wide, and 12 baffles each 5 cm wide. Without baffles, the maximum O2 uptake rate at 5 rpm was 6.9 mmol/(min.kg IDS), compared to 5.1 mmol/(min.kg IDS) obtained at 0.5 rpm. Therefore O2 supply is adequate in rotating drum bioreactors as long as slumping flow regimes of the substrate bed are avoided. © Rapid Science Ltd. 1998

The objective of the work presented here was the development of a method of modeling the effect of an impeller on the velocity distribution in a stirred vessel. The developed model makes it possible to numerically investigate the flow field almost independently of any experimental data. The starting point was a force balance around an impeller blade, which took into consideration the lift and drag forces. The obtained volume forces were circumferentially averaged in the impeller region. The calculations were carried out time-averaged for the case of a pitched blade impeller. The results were compared with experimental data which were obtained by laser Doppler anemometry. The comparison of the axial velocity components shows a good agreement between numerical and experimental data. Furthermore some characteristic integral values were calculated, which demonstrate the efficiency of the impeller.

The effects of width and number of baffles in mechanically agitated vessels with standard Rushton turbine impellers are examined for systems with and without aeration. The insertion of the appropriate number of baffles clearly improves the extent of liquid mixing. However, excessive baffling (i.e. n b > 8or B/T> 0.2 ) and sparging gas through the impeller would interrupt liquid mixing and lengthen the mixing time. This study found that sparging gas through the impeller leads to an increase in the mixing time of more than 20% because it reduces the liquid pumping capacity of the impeller. A numerical technique was applied to examine the same effect on several extreme baffle conditions and the cases of higher gas flow rates and rotational speeds. To generalize our results obtained, the numerical technique was applied to simulate for a system with triple impellers. The trends of the mixing time were found to be very similar to the single impeller system. By correlating the mixing time with n b , B/T, Q g and N , the following correlation is obtained for the system with single Rushton turbine impeller under non-gassed and aerated systems.Nt M = 55.7(n b ) −0.30 ( B/T ) −0.1535 ( Q g /ND 3 ) 0.0296 and the similar correlation for the triple impeller system can be given asNt M = 46.5(n b ) −0.295 ( B/T ) −0.327 ( Q g /ND 3 ) 0.010

This paper presents a method of influencing the axial mixing of particles and promoting segregation in fluidized beds without otherwise changing the character of the bed substantially (at least at low to moderate gas velocities). The method is based on the introduction in the bed of horizontal screen-like baffles with a relatively large free area. It will be shown that such baffles promote the particle segregation significantly, producing a layer of almost pure heavy/large particles in a binary mixture which would be well mixed when fluidized in a conventional bed at the same velocity. The effect of three different types of baffles, of the number of baffles and of the fluidization velocity on the quality of separation is examined. A physical reason for the demixing effect is suggested.

The use of a fully predictive numerical model of flow in a stirred, baffled tank is presented and validated for the laminar flow regime. This approach employs a commercial computational fluid dynamics (CFD) package with sliding mesh facility. The comparison of computed and experimental values for various flow characteristics shows a very good agreement without the need to input any experimental values for the boundary or initial conditions. It is proposed that the model/experiment error ratio (involving relative errors) may be generally adopted as a criterion for the quality of CFD modelling. This ratio should not be much larger, and does not need to be smaller, than unity. The ratio obtained in this work was just over unity. The state of the art CFD packages are now believed to be able to form a suitable basis for the process engineering aspects of an integrated design of stirred tanks, including mechanical engineering and other related issues.

We report flow visualisation results in a modified Pulsed Baffled Reactor (PBR) where fluid oscillation is achieved by oscillating orifice baffles in contrast to the conventional bellows or piston driven arrangement. A comprehensive set of experiments has been carried out and the effects of orifice diameter, baffle spacing and oscillation amplitude and frequency on the flow patterns have been established in both the modified PBR and a Multi Disc Vibratory Column. The results indicate that the modified PBR can produce highly efficient eddy mixing patterns for a range of operating conditions examined and has the added advantage of eliminating many of the scale-up problems encountered with the conventional PBRs. Combined with the minimal internal surface area of the modified PBR it would allow application of this type of configuration to industrial-scale processes such as suspension polymerisation to be feasible.

This paper describes the effect of surfactant (0·025%w/w octanol) on mass transfer of oxygen into water–glycerol solutions of viscosity up to 21 mPa s in a pulsed baffled reactor. We also report the effect of air entrainment on the volumetric mass transfer coefficient in the open reactor system. The results show that the presence of octanol in solutions increases the mass transfer rate for all the experimental conditions tested, in particular, a higher percentage increase in kLa was obtained for more viscous solutions. This behaviour can be attributed to the non-coalescing characteristics of the octanol that is added to the water–glycerol solutions. The results of air entrainment on kLa suggest that the effect of the surface air entrained into the system on kLa measurement is insignificant. © 1997 SCI.

The behavior of sloshing dynamics modulated fluid systems driven by the orbital accelerations including gravity gradient and jitter accelerations with partially-filled rotating fluids has been studied. Present study is applicable to a full-scale Gravity Probe-B Spacecraft dewar tank with and without baffle. Results of slosh wave excitation along the liquid—vapor interface induced by jitter acceleration-dominated orbital accelerations provide a torsional moment with an up-and-down movement of bubble oscillations in the rotating dewar. The results show rightward and leftward movement of bubble oscillations transverse to the rotating axis, and up-and-down movement of bubble oscillations longitudinal to the rotating axis of dewar container. The orbital accelerations also induce an eccentric contour of bubble oscillations in a horizontal r—θ plane. As viscous force between liquid—solid interface, and surface tension force between liquid—vapor—solid interface can greatly contribute to the damping effect of slosh wave excitation, the rotating dewar with baffle provides more areas of liquid—solid and liquid—vapor—solid interfaces than that of a rotating dewar without baffle. Results show that the damping effect provide by a baffle reduce the amplitude of slosh wave excitation and reduce the degree of asymmetry in liquid—vapor distribution. Computation of bubble (helium vapor) mass center fluctuations also verifies that a rotating dewar with baffle produces less fluctuations than that of a rotating dewar without baffle.

An agitated tank having two 45° pitched blade downward turbines in series and four thin baffles which were narrower than the conventional ones was studied. At higher impeller speeds, a gas and liquid vortex induces the gas above the liquid surface vertically downward into the turbines, which in turn cuts the gas stream into bubbles which then circulate in the liquid. Consequently gas-induction increases the gas utilization ratio as well as simplifying the ancillary equipment otherwise required to recycle the escaped gas. The relationship between tank geometrical factors and the liquid mixing time was also investigated. The experimental variables investigated were the impeller speed, the baffle width, the turbine diameter, the space between two impellers, the liquid level, and the clearance between the lower turbine and the bottom of the tank. The results showed that all but the clearance between the lower turbine and the bottom of the tank had significant effects on the mixing time under normal gas-induction, revealing results in contrast to the conventional agitated tank. © 1997 SCI.

The mixing of water and air has been studied in an agitated tank with narrow baffles. In such an agitated tank, the gas induction could be formed by the dead impellers operated above the critical impeller speed. Experimental parameters considered were the impeller speed, the baffle width, the clearance between lower impeller and tank bottom, the impeller diameter, the space between two impellers and the liquid level. Dimensional analysis and data regression gave a good correlation between the mixing time, the tank geometry and operational variables. It was found that an increase in impeller speed reduced significantly the mixing time. Too much reduction of baffle width, a decrease in the impeller diameter or a raise of liquid level can increase the mixing time. However, after gas induction achieved, the clearance between the lower turbine and the tank bottom has no significant effect on the mixing time.

3D periodical turbulent flow induced by a low shear hyperboloid stirrer in a fully baffled stirred tank reactor is experimentally studied at a constant Reynolds number, 5600, by using a diode fiber laser-Doppler anemometer. The ratio D:T:H of the hyperboloid stirrer diameter, D = 50 mm, the inner tank diameter, T, and the filled fluid height, H, is 1:3:3. Three low stands of hyperboloid stirrer clearance, D/10, D/7 and D/5, are also targeted to evaluate influence on flow structure. The experimental results are applied to verification of CFD-code based on a standard k–e model.The flow field close to the hyperboloid stirrer is characterized by a series of vortex jets that are trailing periodically down within a radial extension of 0.5D to 0.7D. The maximum measured tangential velocity was 96% of the tip stirrer velocity. In this “near-of-flow area”, the kinetic energy is extensively dissipated itself due to impingement of velocity components. The axially-symmetric separation zone in the spatial form of λ-character induces two large-scale vortices above and below the separation. A highly rated kinetic energy lies within the head stream of λ-separation. Variation of the clearance at a factor less than D/5 sensibly influences flow structure and kinetic energy distribution. It is considered that computing on a turbulent hyperboloid flow field based on a k–e model at a relatively high Reynolds number may result in a discharge of kinetic energy induced within the “near-of area”.

The damaging effect of coherent synchrotron radiation (CSR) on the emittance and energy spread of high-energy beams in accelerator light sources can significantly constrain the machine design and performance. We propose a mitigation approach in which the dynamical effect of the longitudinal component of CSR is suppressed by appropriately preparing the initial longitudinal current profile of the beam. In a chicane, a linear theory for the mechanism of CSR-induced emittance growth is used to demonstrate how this procedure can produce a beam whose core experiences suppressed transverse emittance growth. The dynamics of such a beam is illustrated for the Berlin-Zeuthen CSR benchmark chicane.

With an eye toward extending optical wave-mixing techniques to the x-ray regime, we present the first experimental demonstration of a two-color x-ray free-electron laser at the Linac Coherent Light Source. We combine the emittance-spoiler technique with a magnetic chicane in the undulator section to control the pulse duration and relative delay between two intense x-ray pulses and we use differently tuned canted pole undulators such that the two pulses have different wavelengths as well. Two schemes are shown to produce two-color soft x-ray pulses with a wavelength separation up to $\ensuremath{\sim}1.9%$ and a controllable relative delay up to 40 fs.

For wakefield based acceleration schemes, use of an asymmetric (or linearly ramped) drive bunch current profile has been predicted to enhance the transformer ratio and generate large accelerating wakes. We discuss plans and initial results for producing such bunches using the 20 to 23 GeV electron beam at the FACET facility at SLAC National Accelerator Laboratory and sending them through plasmas and dielectric tubes to generate transformer ratios greater than 2 (the limit for symmetric bunches). The scheme proposed utilizes the final FACET chicane compressor and transverse collimation to shape the longitudinal phase space of the beam.

An unusual mode of operation of internal-loop airlift reactors is described as being of potential use in extending the range of practicable operating volumes or turndown ratios in wastewater treatment applications. Unlike normal operation, the new mode employs an inital static liquid level that is lower than the upper edge of the draft-tube or the splitting baffle. Hydrodynamics of the operation are analyzed using fundamental principles and an equation is developed for predicting the minimum required gas flow for attaining recirculation of the liquid. The equation is proven experimentally using data for air-water in split-cylinder reactors (aspect ratio = 7; volume = 0.08 m3; riser-to-downcomer cross-sectional area ratio = 2.44; − 0.03 < hc ≤ 0.12, where hc is the dimensionless clearance between the upper edge of the baffle and the static height of gas-free liquid), Effects of the clearance hc on gas holdup in the riser and downcomer, mixing behavior and liquid circulation rate are presented. In ...

The maximum turbulence energy dissipation rate per unit mass, emax, is an important variable in dispersion systems, particularly for drop breakup and coalescence, and for gas dispersion. The effect of tank geometry (number of baffles, impeller diameter, and off-bottom clearance) on emax for four impellers (the Rushton turbine, RT; the pitched blade turbine, PBT; the fluidfoil turbine, A310; and the high-efficiency turbine, HE3) is examined. Mean and fluctuating velocity profiles close to the impellers were measured in a cylindrical baffled tank using laser doppler velocimetry. Local and maximum turbulence energy dissipation rates in the impeller region were estimated using e = Av3/L with A = 1 and L = D/10 for all four impellers. Factorial designs were used to test for the effects of single geometric variables under widely varying conditions and interactions between variables. Several factorial designs were used to ensure that real effects were separated from effects that appeared as an artifact of the experimental design. Results show that the tank geometry has a significant effect on emax, primarily with respect to variations in impeller diameter and interactions between the off-bottom clearance and impeller diameter. For the same power input and tank geometry, the RT consistently produces the largest emax and/or emax scaled with N3D2.

We report experimental measurements on air—water mass transfer characteristics in two pulsed baffled reactors in a scale-up format. The experiments have, for the first time, investigated the scale-up parameters involved in such reactors and identified the optimal baffle spacing and the optimal superficial gas velocity for enhanced mass transfer performance. The experimental results indicate that the mass transfer rate strongly depends on the combination of the baffle spacing, aeration rate and oscillation frequency and amplitude. The mass transfer data, corrected for temperature effect and oxygen probe responses, are correlated in terms of power density and superficial gas velocities to show the scale-up correlation for the pulsed baffled reactors where the mass transfer performance is better in a large diameter reactor than in a small diameter reactor.

In spite of the fact that vortex formation, in unbaffled agitated vessels, is in most cases an undesirable phenomenon, many cases exist in chemical engineering where unbaffled systems can be used with greater effectivness than systems with baffles, at the same or even smaller energy consumption levels. Satisfactory results can also be obtained in unbaffled agitated vessels without an air-liquid interface. These facts, viewed in the light of energy problems in the chemical industry, show the current importance of comparative studies of baffled and unbaffled systems. In this review article some characteristic cases from the fields of fluid dynamics, homogeneous distribution processes, suspension, as well as mass-transfer and heat-transfer operations in baffled and unbaffled agitated vessels are presented and comparatively discussed in relation to their effectivness

The turbulent flow of water in a cylindrical, baffled vessel with an axial flow hydrofoil impeller, either a Chemineer HE3 (CHE3) or a Prochem Maxflo T (PMT), has been studied using a laser Doppler anemometer. Using ensemble averaging, the mean axial and radial flow and the associated fluctuating components were obtained for the whole of the vessel; plus similar data for the tangential component close to the impeller. Assuming axial symmetry, flow rates were calculated as were flow numbers and circulation flow numbers. Power numbers were also determined. All the data obtained were used to compare the circulation efficiency of the two hydrofoils plus a pitched blade and a Rushton turbine. This comparison showed that the CHE3 required a power input of about 2/3 of that for the PMT and about 1/3 of that for the pitched blade and Rushton turbine to obtain the same axial-radial circulation in the tankz.

An approach for trajectory optimization for vehicles maneuvering in a constrained environment is developed. Within this framework, a benchmark problem, the minimimzation of the transit time of a point mass vehicle through a chicane is proposed. This problem is solved using the projection operator Newton method with barrier functions to manage the acceleration and roadwidth constraints. The numerical solution of the benchmark problem is analyzed in detail as is the characteristics of the solution itself.

The frequencies of free oscillation of a fluid in a rectangular tank are reduced by the introduction of a rigid internal structure. This paper gives general, approximate methods for the calculation of the oscillation frequencies when the structure is a cylinder of arbitrary cross section spanning the tank, and with generators normal to one pair of vertical faces. Particular results are given for submerged, circular cylinders and both vertical and horizontal thin baffles.

The behavior of inducted gas from liquid surface and the; power requirements in an agitated tank using a mechanical agitator are studied in order to increase the amount of gas self-induction and the gas retention time for gas absorption. A 45° six-blade downward impeller turbine was utilized in this study. Air and water, air and 40 wt% 60 wt%, and 80 wt% of glycerin water, and air and 106 cP silicon oil were employed as gas and liquid phases. Variables which were studied included geometrical factors (immersed depth of impeller, baffle with and diameter of impeller) and the physical properties of the liquid (viscosity, density, and surface tension). The correlations for the onset speed of impeller and power consumption after gas induction in the agitated tank are established from our experimental results. The amount of gas self-induction from the liquid surface in the agitated tank increases with increasing impeller diameter and speed and decreases with increasing baffle width, depth of impeller and viscosity of liquid.

The electron optical properties of a beam separator made of a “Chicane” type close packed prism array proposed by Kolarik et al. [Optik 87 (1991) 1] have been analyzed. The total deflection angle of the illumination beam is 90° and that of the image forming beam is 0°. The second order aberrations are estimated using the eikonal method developed by Rose [Optik 51 (1978) 15] under the SCOFF approximation. It has a limitation in the analysis of the close packed prism array, because of the overlapped fringing field distributions. The magnetic field distributions of the separator are numerically calculated using the three dimensional finite difference method followed by direct ray tracing. The angles of the edge were readjusted by trial and error to get the stigmatic focus of the beam.

Large-diameter flotation columns are essentially well-mixed devices and attempts to reduce mixing by the insertion of baffles have generally not been effective. Substantial reductions in mixing can be achieved by inserting baffles which rise above the froth-slurry interface level; however, if gas rate into the compartments between the baffles is unevenly distributed, different levels in the compartments result. Computer simulation has previously been used to explore the use of rigid baffles pivoted around a certain level zp above the base of the baffle showing that substantial improvements can be achieved. For zp < 0 the imbalance in the gas distribution between the compartments is partially corrected by the movement of the base of the baffle and the difference in interface levels is reduced; however, if zp is too large the system becomes unstable and oscillates. In this paper the use of flexible rubber baffles is discussed. The baffle is fixed to a rod at the base of the column and to the sides of the column, and deforms as pressure differences develop across it. Hold-up differences between compartments are smoothed out, and differences in interface levels are minimal. The effect of using a rigid baffle of a given height at the base of the column, and of having the baffle fixed to a rod at a given height above the base of the column (these options are required for ensuring adequate mechanical strength of tall columns) is explored. It is proposed that the use of flexible baffles will be the most effective method of reducing mixing in flotation columns while avoiding the development of different levels in the compartments.

Time-averaged power dissipation rates have been measured in water in a 19.4 cm diameter reciprocating plate column operating at frequencies 0.6 to 3 Hz and amplitudes 5 to 20 mm. Measurements were also taken in water in a 15 cm diameter column operated at 1 to 5.7 Hz with amplitudes 1 to 10 mm. Several different types of doughnut reciprocating plates, fitting close to the column wall, were investigated. Power consumption at high amplitudes agreed with the predicted values using the quasi-steady flow model, while at low amplitudes the data were more in agreement with a recently proposed acoustic model. The measured power dissipations were slightly affected by the spacing between adjacent plates, and by the alignment of the holes in the case of plates with 3 holes. Flow patterns around the reciprocating plates were also observed with the aid of a thin beam of light reflecting from small particles suspended in the liquid. Well-developed circulation patterns were observed, depending strongly on the axial spacing between the plates. Les taux de dissipation d'energie moyennes dans le temps ont ete mesures dans l'eau dans une colonne a plateau reciproques de 19,4 cm de diametre fonctionnant a une frequence de 0,6 et 3 Hz et une amplitude de 5 a 20 mm. Des mesures ont egalement ete prises dans l'eau dans une colonne de 15 cm de diametre entre 1 et 5,7 Hz et 1 et 10 mm. On a etudie differents types de plateaux reciproques toriques, a faible degagement a la paroi de la colonne. La consommation d'energie aux amplitudes elevees montre un bon accord avec les valeurs predites au moyen du modele d'ecoulement en regime quasi permanent, tandis qu'a de faibles amplitudes les donnees sont davantage en accord avec un modele acoustique propose recemment. Les dissipations d'energie mesurees ont ete legerement modifiees par l'espacement entre les plateaux adjacents ainsi que par l'alignement des trous dans le cas des plateaux a trois trous. Les profils d'ecoulement autour des plateaux reciproques ont egalement ete observes a l'aide d'un mince faisceau de lumiere se reflechissant sur des petites particules suspendues dans le liquide. Enfin, on a observe des profils de circulation bien developpes, qui dependent fortement de l'espacement axial entre les plateaux.

A theoretical and experimental investigation into the modifications in optical and thermal performance resulting from the introduction of a baffle into the cavity of a compound parabolic concentrating solar energy collector has been performed. Results are presented in the form of velocity vector diagrams and isothermal plots. A comparison is made of the collector loss coefficient and Hottel-Whiller-Bliss graphs are produced for cavities with and without a baffle present. The introduction of a baffle reduces internal convection thereby reducing heat losses. The associated reduction in optical efficiency is small.

We report experimental data of mass transfer of oxygen into yeast re-suspension and yeast culture in a batch pulsed baffled bioreactor and a stirred tank (ST) fermenter. Air bubbles are sparged into the bottom of both reactors and the kinetics of the liquid oxygen concentration followed using dissolved oxygen probes together with the dynamic gassing-out technique for both systems. The kLa measurements and correlation with power density calculations for yeast re-suspension show that the kLa data in the pulsed baffled bioreactor are on average 75% higher than those obtained in the ST fermenter. Similar trends for kLa are also measured when yeast culture of different ages were used in the two systems.

The dynamical behavior of fluids affected by the asymmetric gravity gradient acceleration has been investigated. In particular, the effects of surface tension on partially filled rotating fluids applicable to a full-scale Gravity Probe-B Spacecraft dewar tank with and without baffles are studied. Results of slosh wave excitation along the liquid-vapor interface induced by gravity gradient acceleration indicate that the gravity gradient acceleration is equivalent to the combined effect of a twisting force and a torsional moment acting on the spacecraft. The results are clearly seen from one-up one-down and one-down one-up oscillations in the cross-section profiles of two bubbles in the vertical (r, z)-plane of the rotating dewar, and from the eccentric contour of the bubble rotating around the axis of the dewar in a horizontal (r, θ)-plane. As the viscous force, between liquid and solid interface, greatly contributes to the damping of slosh wave excitation, a rotating dewar with baffles provides more areas of liquid-solid interface than that of a rotating dewar without baffles. Results show that the damping effect provided by the baffles reduces the amplitude of slosh wave excitation and lowers the degree of asymmetry in liquid-vapor distribution. Fluctuations of angular momentum and fluid moment caused by the slosh wave excited by gravity gradient acceleration with and without baffle boards are also investigated. It is also shown that the damping effect provided by the baffles greatly reduces the amplitudes of angular momentum and fluid moment fluctuations.

A magnetic chicane based on four electromagnetic dipoles is going to be realized by INFN-LNS to be used as an Energy Selection System (ESS) for laser driven proton beams up to 300 MeV and C6+ up to 70 MeV/u. The system will provide, as output, ion beams with a contrallable energy spread varying from 5% up to 20% according to the aperture slit size. Moreover, it has a very wide acceptance in order to ensure a very high transmission efficiency and, in principle, it has been designed to be used also as an active energy modulator. This system is the core element of the ELIMED (ELI-Beamlines MEDical and Multidisciplinary applications) beam transport, dosimetry and irradiation line that will be developed by INFN-LNS (It) and installed at the ELI-Beamlines facility in Prague (Cz). ELIMED will be the first user's open transport beam-line where a controlled laser-driven ion beam will be used for multidisciplinary research. The definition of well specified characteristics, both in terms of performance and field quality, of the magnetic chicane is crucial for the system realization, for the accurate study of the beam dynamics and for the proper matching with the Permanent Magnet Quadrupoles (PMQs) used as a collection system already designed. Here, the design of the magnetic chicane is described in details together with the adopted solutions in order to realize a robust system form the magnetic point of view. Moreover, the first preliminary transport simulations are also described showing the good performance of the whole beam line (PMQs+ESS).

The effects of the geometrical parameters of non-standard baffles on heat transfer coefficient were experimentally studied for agitated vessels equipped with a Rushton disc turbine, pitched-blade turbine and propeller. The following geometrical parameters of the baffles were tested: number J, width B, length L and distance p between the lower edge of the baffle and the bottom of the vessel. Measurements were carried out in accordance with a second-order rotatable experimental design. The results of the investigations have been approximated analytically.

Rhizopus oligosporus grew better on wheat bran in a rotating drum when baffles were fitted. The maximum O2 uptake rates for the baffled and unbaffled runs were 9.0 and 5.7 mmol/min.kg initial dry substrate respectively. The RQ remained at 1.0 throughout the baffled run but varied between 1.0 and 1.2 for the unbaffled run.