Vortexing, suppression

Vortex formation leads to a considerable drop in mixing efficiency and should be suppressed as much as possible in practical applications to increase the homogenizing effects of mixers. The preferable method of vortex suppression is to install vertical baffles at the walls of the mixing tank. These impede rotational flow without interfering with the radial or longitudinal flow. Figure 11 illustrates such a system. 

The distribution of velocity components (radial, tangential and axial) under conditions of mixing with baffles in comparison with the conditions of vortex formation is presented in Figure 12. The dashed lines in Figure 12 indicate non-baffled conditions. Comparison of the non-baffled and fully baffled velocity curves (solid line) leads to the following set of conclusions on vortex suppression when dealing with perfectly miscible liquids ... 

Sample volume is also important. Each probe has a specific detection coil that receives signals from only a finite volume in the core of the magnet. There is an optimum volume, greater than this detection coil volume which minimizes field distortions caused by the solution/air interface. When enough sample is available, this optimum volume should be used. For samples in small quantities, other strategies can be used e.g., capillary tubes, vortex suppressers, microprobes, etc.). 

The AP1000 reactor internals consist of two major assemblies the upper internals and the lower core support assembly. The upper internals consist of the upper support, the upper core plate, the support columns and the guide tube assemblies. Figure 3.9-6 of the Reference 6.1 shows the upper core support assembly. The major containment and support member of the reactor internals is the lower core support assembly, which is shown in Figure 3.9-5 of the Reference 6.1. This assembly consists of the core barrel, the lower core support plate, the secondary core support, the vortex suppression plate, the core shroud, neutron panels, radial supports and related attachment hardware. 

For turbine mixers that the width of a baffle should not exceed more than one-twelfth of the tank diameter and, for propeller mixers, no more than one-eighteenth the tank diameter. With side-entering, inclined or off-center propellers, as shown in Figure 13, baffles are not required. Instead, shrouded impellers and diffuser rings may be used to suppress vortex formation. These devices contribute to flow resistance and reduce circulation by creating intense shear and abnormal turbulence... 

Under low-frequency excitation, the flame front is wrinkled by velocity modulations (Fig. 5.2.5). The number of undulations is directly linked to frequency. This is true as far as the frequency remains low (in this experiment, between 30 and 400 Hz). The flame deformation is created by hydrodynamic perturbations initiated at the base of the flame and convected along the front. When the velocity modulation amplitude is low, the undulations are sinusoidal and weakly damped as they proceed to the top of the flame. When the modulation amplitude is augmented, a toroidal vortex is generated at the burner outlet and the flame front rolls over the vortex near the burner base. Consumption is fast enough to suppress further winding by the structure as it is convected away from the outlet. This yields a cusp formed toward burnt gases. This process requires some duration and it is obtained when the flame extends over a sufficient axial distance. If the acoustic modulation level remain low (typically v /v < 20%),... 

In liquid mixing systems, baffles are used to suppress vortexing. Since vortexing is a gravitational effect, the Froude number is not required to describe baffled liquid mixing systems. In this case the exponent y in equations 5.17 and 5.18 is zero and FryM = 1. 

The injection sequence, which results in a highly sooting flame (Fig. 6.13), occurs out of phase with the air vortex formation. The first fuel injection misses the air vortex and stays unmixed while also partially suppressing the roll-up of this air vortex. The second-fuel injection enters the void between the air vortices and stays separated from the air. The rich mixture results in the formation of soot at this point as shown by the white spots. Temperature profiles also show the energy release rate to be lower in this case. 

Figure 21.10 shows the transient behavior of the combustor pressure as the proper phase-delay was applied at time t = 0 and the comparison of the pressure spectra. The high-amplitude oscillations were quickly brought under control and all of the harmonics, as well as the fundamental, were effectively suppressed in this case. The RMS pressure amplitude under active control was maintained well below 0.5% of the combustor pressure. It should also be noted, however, that oscillations at a very small level are still needed to maintain the phase-lock and vortex-synchronized fuel injection. 

The present study was conducted in an effort to better understand ACC mechanisms and to design practical ACC based on pulsed liquid-fuel injection suitable for propulsion devices. The controller utilized a simple fixed phase-delay approach that has been studied previously, but the direct liquid-fuel injection and the novel use of vortex-droplet interaction made the present study unique. The demonstration experiment in a 102-millimeter dump combustor showed that combustion instabilities can be successfully suppressed using properly designed pulsed liquid-fuel injection. 

In liquid systems, we can suppress the effect of the Froude number by using baffles to eliminate vortexing and hence the gravitational effects. The Weber number is of some importance only when separate physical phases are present in the liquid mixing system. 

More recently Wang et al. have proposed analytical methods involving the use of UHPLC-MS/MS to determine four opiates and metabolites, live amphetamines, flunitrazepam and its two metabolites, cocaine and its four metabolites in OF. Samples were collected by spitting in a tube, then the fluids were diluted with twice the amount of distilled and deionized water and vortexed for 30 s. Liquid chromatography was performed with a gradient elution and the total run time was 7.5 min. The authors compared ESI, APCI, and APPI. The ion suppression ranged from 45 to 89 % and from 74 to 96 % on APCI and APPI, respectively. The authors... 

Po is a complex function of Rei and geometry. Figure 20 shows the Po versus Re relationships for a number of impellers in tanks fitted with baffles, which suppress the formation of a vortex (see dashed lines in Figure 19), and hence where Fr has little effect. The curves may be divided into the following flow regimes ... 

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