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Communication Dans Un Congrès Année : 2019

Relevance of digital in line holography for multiphase flows characterization

Fabrice Lamadie

Résumé

Digital in-line Holography for investigating multiphase flows is reviewed and discussed in the scope of the development of apparatus convenient for nuclear fuel reprocessing. As a volumetric imaging technique, it allows to measure the 3D-position, dynamics, shape and size of flowing micron-to millimeter-sized particles, even considering complex pipe flows. Besides addressing this typical issue of multiphase flows characterization, it can also be, when considering transparent particles, a way to recognize materials and/or to monitor exchange between phases. Context A significant part of the chemical processes involved in recycling industry are based on multiphase flow (liquid-liquid extraction, dissolution, leaching, filtration, precipitation , etc.). Therefore, complementing the chemical investigations , achieved at lab-scale, fluid mechanics studies are carried out, where possible at a larger scale, to apprehend the possible flow effects on the chemical processes efficiency. Such studies are conducted using computational fluid dynamics (CFD) but an experimental validation, especially regarding the properties of the dispersed phase (concentration, shape and size distribution, etc.), remains mandatory. Many techniques are implemented and adapted in this aim and, among them, digital in-line holography (DIH) is particularly relevant as it allows to get simultaneously a detailed geometrical description (size, shape, trajectories, etc.) of the dispersed phase and information about transfer (heat, mass,etc.) between phases thanks to refractive indexes measurements. Digital In-Line Holography principle Digital in-line Holography (DIH) is based on the diffraction intensity pattern, called hologram, produced by the interaction between the diffracting particles and a coherent laser beam. Thanks to a digital processing of the hologram, proper images of the particles can be reconstructed and the particles parameters estimated (mainly their size and 3D position in the setup). As it provides size, tridimensional position of particles, and the related quantities (velocity, acceleration, holdup , etc.), DIH is becoming a reference technique for the characterization of multiphase flow at lab scale (Hinsch 2004; Pan 2003; Tian 2010). Moreover, thanks to the direct illumination of the sensor, the use of high speed imaging is achievable, allowing the monitoring of transient phenomena. Relevance for multiphase flows characterization With a limited number of particles (fewer than 30), individual tracking is achievable by analyzing a series of reconstructed holograms separated by time intervals. In this case, holo-gram optimization by inverse approaches (Lamadie 2014), makes it possible to obtain submillimeter resolution on parti-cle's center position in space. Such a precision allows parti-cle's path reconstruction with only one sensor and the visual-ization and can reveal interactions between particles as well as local phenomena in time and space (changes in direction and/or speed) with a good sensitivity. When a larger number of particles is considered (around 80), mean values can be computed from several holograms. The number of measurable particles is mainly limited by overlapping diffraction patterns, which is exacerbated when large-diameter particles mask the signals from smaller ones. Basically, for the 1-mm diameter particles considered here, the method remains accurate until 1% in volume fraction of dispersed phase. Fig. 1 displays the 3D visualization of both the position and the diameter of more than 70 oil droplets rising in water and ranging from 0.5mm to 1.5mm. Using current holograms processings, DIH remains dedicated to the characterization of diluted media. This limitation is quite similar to that of a conventional one point-of-vue imaging setup while retaining a complete 3D reconstruction including a focus capacity in any plane of the observed volume like a plenoptic camera (Lamadie 2012).
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Dates et versions

hal-02370258 , version 1 (19-11-2019)

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  • HAL Id : hal-02370258 , version 1

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Fabrice Lamadie, Fabrice R.A. Onofri. Relevance of digital in line holography for multiphase flows characterization. 10th International Conference on Multiphase Flow (ICMF 2019), May 2019, Rio de Janeiro, Brazil. ⟨hal-02370258⟩
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