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- Sauter mean diameter (1)
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The fluid dynamic (flow rates) and hydrodynamic behavior (local droplet size distributions and local holdup) of a continuous DN300 pump-mixer were investigated using water as the continuous phase and paraffin oil as the dispersed phase. The influence of the impeller speed (375 to 425 rpm), the feed phase ratio (10 to 30 volume percent), and the total flow rate (0.5 to 2.3 L/min) were investigated by measuring the pumping height, local holdup of the disperse phase, and the droplet size distribution (DSD). The latter one was measured at three different vessel positions using an image-based telecentric shadowgraphic technique. The droplet diameters were extracted from the acquired images using a neural network. The Sauter mean diameters were calculated from the DSD and correlated with an extended model based on Doulah (1975), considering the impeller speed, the feed phase ratio, and additionally the flow rate. The new correlation can describe an extensive database containing 155 experiments of the fluid and hydrodynamic within a 15 % error range
In this work, steady-state droplet size distributions in a DN300 stirred batch vessel with a
Rushton turbine impeller are investigated using an insertion probe based on the telecentric transmit-
ted light principle. High-resolution droplet size distributions are extracted from the images using
a convolutional neural network for image-analysis in order to investigate the influence of impeller
speed and phase fraction (up to 50 vol.-%). In addition, Sauter mean diameters were calculated and
correlated with two semi-empirical approaches, while the standard approach only accomplished 5.7%
accuracy, and the correlation of Laso et al. provided a relative mean error of 4.0%. In addition, the
correlated exponent in the Weber number was fitted to the experimental data of this work yielding a
slightly different value than the theoretical (−0.6), which allows a better representation of the low
coalescence tendency of the system, which is usually neglected in standard procedures.
A novel shadowgraphic inline probe to measure crystal size distributions (CSD),
based on acquired greyscale images, is evaluated in terms of elevated temperatures and fragile
crystals, and compared to well-established, alternative online and offline measurement techniques,
i.e., sieving analysis and online microscopy. Additionally, the operation limits, with respect to
temperature, supersaturation, suspension, and optical density, are investigated. Two different
substance systems, potassium dihydrogen phosphate (prisms) and thiamine hydrochloride (needles),
are crystallized for this purpose at 25 L scale. Crystal phases of the well-known KH2PO4/H2O system
are measured continuously by the inline probe and in a bypass by the online microscope during
cooling crystallizations. Both measurement techniques show similar results with respect to the crystal
size distribution, except for higher temperatures, where the bypass variant tends to fail due to
blockage. Thiamine hydrochloride, a substance forming long and fragile needles in aqueous solutions,
is solidified with an anti-solvent crystallization with ethanol. The novel inline probe could identify
a new field of application for image-based crystal size distribution measurements, with respect
to difficult particle shapes (needles) and elevated temperatures, which cannot be evaluated with
common techniques.
The digitization of extraction columns requires a profound knowledge of the present hydrodynamics/mass transport interaction as well as appropriate measurement techniques for the detection of relevant input and target values. In this article, the different techniques for droplet size distribution as well as concentration determination are presented and new methods for online evaluation are discussed. In combination with the simulation of droplet size, holdup and solute concentration distribution, an online-capable process tool for controlling and optimizing extraction columns will be obtained.