Stirred vessels are being used not only in chemical processes for simple contacting or blending operations, but also in novel configurations and processes, as in mineral processing and/or wastewater treatment, with specific requirements, like low shear or regions in the vessel with high and low turbulence levels. The techniques that are available for the study of the flow patterns induced by the various types of agitators, e.g., classical pressure or velocity measurements with Pitot tubes or hot-wire anemometers, and novel ones like laser Doppler velocimetry, laser-induced fluorescence and particle image velocimetry are reviewed and their usefulness for particular situations is discussed.

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FLOW VISUALIZATION IN STIRRED VESSELS A Review of Experimental Techniques

[1] The correlation between the amplitude of the MHD turbulence in the upstream solar wind and the amplitude of the Earth's geomagnetic activity indices AE, AU, AL, Kp, ap, Dst, and PCI is explored. The amplitude of the MHD turbulence is determined by the fluctuation amplitude of the solar wind magnetic field. This “turbulence effect” in solar wind/magnetosphere coupling is more easily discerned when the interplanetary magnetic field (IMF) is northward, but the effect is also present when the IMF is southward. The magnitude of the effect is the same for northward and southward IMF, accounting for about 150 nT of the variability of the AE index. Tests are performed that conclude (1) that the turbulence effect is not caused by the turbulence amplitude acting as a proxy for ∣B∣ in the solar wind and (2) that reversals of the IMF from northward to southward in the turbulent fluctuations is not the cause of the correlations. An expression is derived for the total viscous-shear force on the surface of the magnetosphere; improved solar wind/magnetosphere correlations result when this expression is used. With insight from fluid-flow experiments, the turbulence effect is interpreted as an enhanced viscous coupling of the solar wind flow to the Earth's magnetosphere caused by an eddy viscosity that is controlled by the amplitude of MHD turbulence in the upstream solar wind: more upstream turbulence means more momentum transfer from the magnetosheath into the magnetosphere, resulting in more stirring of the magnetosphere, which produces enhanced geomagnetic activity indices.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2002JA009601

Role of solar wind turbulence in the coupling of the solar wind to the Earth's magnetosphere

The temperature dependence of the fluorescence emission of certain organic dyes such as rhodamine B has been widely utilized for measuring the temperature in liquid flows. Measurements are generally based on two assumptions: The fluorescence signal is proportional to the intensity of the laser excitation, and the temperature sensitivity of the dye is not affected by the laser irradiance. In the ratiometric methods, these assumptions allow justifying that the influence of the laser intensity can be totally eliminated in the intensity ratio of two spectral bands of the fluorescence emission and thus that measurements can be taken with no biases under experimental conditions, where the laser propagation is disturbed by the flow. However, when pulsed lasers are used (mainly in planar LIF measurements), the peak irradiance usually compares or exceeds the saturation intensity of the dyes. The present study assesses the consequences of a saturation of the dye emission on temperature measurements. Tests among fluoresceins and rhodamines reveal that the saturation can be accompanied by a significant loss of temperature sensitivity. The dyes, for which this loss of sensitivity is observed, mainly owe their temperature dependence to the fluorescence quantum yield and have a fluorescence signal decreasing with the temperature. The couple fluorescein/sulforhodamine 640 is finally proposed for an implementation of the ratiometric method, since its relatively high temperature dependence (+3 %/∘C) is not altered at high laser irradiances. The possibility of measuring instantaneous temperature fields with this pair of dyes using a single laser shot is finally demonstrated on a turbulent heated jet injected into quiescent water.

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The saturation of the fluorescence and its consequences for laser-induced fluorescence thermometry in liquid flows

Evolution of turbulence through a broadened preheat zone in a premixed piloted Bunsen flame from conditionally-averaged velocity measurements

/pdf/potential-core-lengths-of-round-jets-in-stagnant-and-moving-20rzqm5l3f.pdf

Potential core lengths of round jets in stagnant and moving environments

The mass transport properties of a round turbulent jet of water discharging into a low velocity co-flowing water stream, confined in a square channel, is investigated experimentally. The measurement region is the self-similar range from x/d=70 to x/d=140. Combined laser-induced fluorescence and 2D laser Doppler velocimetry are used in order to measure simultaneously, instantaneously and in the same probe volume, the molecular concentration of a passive scalar and two components of the velocity. This technique allows the determination of moments involving correlations of both velocity and concentration fields, which are necessary to validate the second-order modelling schemes. Both transport equations of Reynolds shear stress uv and turbulent mass flux vc have been considered. In both cases, advection, production and diffusion terms have been determined experimentally. The pressure-strain correlation and the pressure scrambling term are inferred with the help of the budget of Reynolds shear stress and mass turbulent transport equations. Second order closure models are evaluated in the light of the experimental data.

The turbulent Schmidt number is found to be almost constant and equal to 0.62 in the center region and decreases strongly to zero in the mixing layer of the jet. The effects of the co-flow on the turbulent mixing process are also highlighted.

Turbulent transport of a passive scalar in a round jet discharging into a co-flowing stream

Experimental Investigation on Thermal Turbulent Diffusion in Heated Jet Using Optical Method

Resume L'etude des ecoulements mixtes liquide-solide necessite la mise en place de methodes d'investigation aptes a determiner les champs dynamiques de chacune des deux phases. L'utilisation de la velocimetrie ultrasonore puisee a effet Doppler va nous permettre, non seulement d'acceder au champ des vitesses du fluide porteur, mais encore de determiner les vitesses absolues des particules solides presentes dans le melange.

Détermination des vitesses de glissement lors de l'écoulement d'une suspension non newtonienne par utilisation de la vélocimétrie ultrasonore à effet Doppler

Yan Antoine

Papers

Turbulent transport of a passive scalar in a round jet discharging into a co-flowing stream

Experimental Investigation on Thermal Turbulent Diffusion in Heated Jet Using Optical Method

Détermination des vitesses de glissement lors de l'écoulement d'une suspension non newtonienne par utilisation de la vélocimétrie ultrasonore à effet Doppler