Measurement of Concentration Fluctuations during Mixing in a Stirred Tank and in a Channel Flow by Laser Induced Fluorescence Spectroscopy

André, Christophe; David, R.; Villermaux, J.; Gence, J. N.

doi:10.1007/978-94-015-7973-5_21

Cited by 4 publications

(4 citation statements)

References 2 publications

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“…In a second continuous experiment, the tank was fed with the same fluorescein solution as before and an additional quencher solution instead of pure water. The results are , Andre et al [12]): /I2 was found to range between 6x depending on the specific power input P in the present tank of 1125cm'. Hence, IciI/(A+CI)# lcil/2CI -is generally small.…”

Section: Resultsmentioning

confidence: 51%

A new fluorescence method for measuring cross‐fluctuation fo two non‐reactive components in a mixing device

et al. 1992

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A novel method for measuring local deviations from perfect mixing of two non-reactive tracers is presented. It is based on the partially quenched fluorescence of one fluorescent tracer by a second tracer. When the concentration fluctuations are small, the deviation from the linear behaviour yields the cross-correlation of the fluctuating components of the concentrations of both tracers from an -easy to record -average value of fluorescence intensity obtained in the focus of a laser beam. The method was proven to be suitable for measuring these quantities in a 1125 cm3 well-stirred tank as a function of location and stirring speed.The measurement of local concentrations of two tracers injected by separate feed streams in a mixing device (stirred tank, in-line or recycle mixer) provides useful information about the mixing pattern and mixing quality. Among the different methods which have been developed for such a purpose, molecular fluorescence spectroscopy has proven its high resolution in space and time (Gaskey However, an important mixing situation is the contacting down to molecular scale of two initially unmixed feed streams of different chemical compositions which may possibly react further. This situation is for instance encountered in reactive systems with multiple selectivity and especially in double-jet precipitation (also called reactive crystallization). In the latter case, since the depletion rate of the reactants by primary nucleation remains relatively small during a short mixing period (see for instance Aslund and Rasmuson [4] or Marcant and David [ 5 ] ) , the reactive system initially behaves as the mixing process of two inert tracers. Moreover, the primary nucleation process is determinant for the further crystal size distribution of the solid product (Aslund and Rasmuson [4], Tovstiga and Wirges[a]). It is thus important to accurately determine the local concentrations of both tracers during the initial mixing steps. Measurement PrincipleGaskey et al. 11-31 have demonstrated that it is possible to record a value of the local fluorescence intensity which is proportional to the instantaneous concentration of a fluorescent species F with a high space and time resolution. The significance of Eq. (2) is that the presence of quencher molecules around those of the fluorescent species reduces the fluorescence quantum yield without any chemical consumption.Eq. (2) is an approximation: it applies if the concentration ranges of F and I are not too wide. A typical linear experimental plot of Zfo/Z, against C1 is shown in Fig. 1. In a batch experiment, the fluctuations disappear after an initial mixing period, and the concentrations become uniform throughout the entire mixer volume; C,, and CI, being the mixing concentrations, it is thus possible to determine the constants k and A in Eq. (2) by varying CF = C,, and CI = CIm. Note that k depends on several factors such as temperature, laser flux, quality of optical apparatus, and geometry, whereas A only depends on temperature and slightly on ionic strength...

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Section: Resultsmentioning

confidence: 51%

A new fluorescence method for measuring cross‐fluctuation fo two non‐reactive components in a mixing device

et al. 1992

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“…The methods which were used in stirred tanks yielded segregation indices. After analyzing such experiments, Gaskey et al [I] and AndrC et al [2] are of the opinion that spatial resolution of their probes plays a major role in the accuracy of these indices.…”

Section: Comparison Of Single and Double Inert Tracer Fluctuation Meamentioning

confidence: 99%

“…The measurements were taken at the same location as in [2]. However, although the iodide behaves as a fluorescence quencher, both tracers may be considered as non-reactive, because neither is consumed by the quenching process [3].…”

Section: Comparison Of Single and Double Inert Tracer Fluctuation Meamentioning

confidence: 99%

Comparison of single and double inert tracer fluctuation measurements in a continuous stirred tank

David

André

1993

Chem Eng & Technol

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A comparison is made between two different methods using laser induced fluorescence spectroscopy for measuring local concentration fluctuations in the same stirred tank. The first method using a single inert fluorescent tracer yields a segregation index quite different from that determined by the second method, which requires two inert tracers, a fluorescent one and a fluorescence quencher. By recalling the theoretical background, it is demonstrated that the characteristic segregation indices should be equal for the experiments under consideration. According to the discussion, it is likely that the double tracer method gives more reliable results.

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“…Initially, the technique was used for measuring point concentrations 64,65,83 ,117,179 or temperatures 4 , since some of the photochromi c dyes are also sensitive to heat. LIF was further developed to determine simultaneously concentration and velocity at a given point 144 , and the advent of laser sheet illuminatio n allowed the determination of whole-plane¯ow patterns in various process vessels 18,43,85,87,88,129,201,21 1 .…”

Section: Laser-induced Fluorescencementioning

confidence: 99%

Flow Visualization in Stirred Vessels

Mavros

2001

Chemical Engineering Research and Design

136

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Measurement of Concentration Fluctuations during Mixing in a Stirred Tank and in a Channel Flow by Laser Induced Fluorescence Spectroscopy

Cited by 4 publications

References 2 publications

A new fluorescence method for measuring cross‐fluctuation fo two non‐reactive components in a mixing device

A new fluorescence method for measuring cross‐fluctuation fo two non‐reactive components in a mixing device

Comparison of single and double inert tracer fluctuation measurements in a continuous stirred tank

Flow Visualization in Stirred Vessels

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