Influence of drop size and superimposed mass transfer on coalescence in liquid/liquid dispersions – Test cell design for single drop investigations

Abstract

Postprint: Kamp, J. & Kraume, M.: Influence of drop size and superimposed mass transfer on coalescence in liquid/liquid dispersions -Test cell design for single drop investigations, Chem. Eng. Res. Des., Elsevier, 2014, 92, 635-643 http://dx.doi.org/10.1016/j.cherd.2013 1 Influence of drop size and superimposed mass transfer on coalescence in liquid/liquid dispersions -Test cell design for single drop investigationsJohannes Kamp a *, Matthias Kraume a a Chair of Chemical & Process Engineering, Technische Universität Berlin, FH 6-1, Fraunhoferstr. 33-36, 10587 Berlin * Corresponding author, e-mail: johannes.kamp@tu-berlin.de, phone: +49 30 314 23171 The detailed understanding of droplet coalescence is important for the accurate description of liquid/liquid dispersions. A test cell is designed which enables serial examinations of the random coalescence process with high repetition rate, good observability and accuracy of experimental parameters. Within this rectangular test cell a rising droplet collides with a pendant one, while recorded by a high speed camera. The gained experimental data allows a validation and further development of appropriate models. The investigated parameters in this work are the drop size and the superimposed mass transfer influencing the coalescence probability. These examinations were carried out in the EFCE standard test system toluene / acetone / water. The effect of varying the drop size seems to be interfered by the different rising velocities due to buoyancy. Introducing a transferring component has a significant impact on the coalescence process. A transfer direction from disperse to continuous phase results in a coalescence probability of almost 100%, whereas the reverse mass transfer direction induces a repulsion of nearly all droplets. Keywords coalescence; test cell; single drop; mass transfer; drop size; coalescence probability IntroductionDispersions of at least two liquids showing a miscibility gap are an integral part of several unit operations. Therefore, a detailed understanding and quantitative description of the characteristics and conditions of these systems is important for various technical applications. The most important characteristic of an emulsion is the drop size distribution which affects e.g. the interfacial area and settling time. The drop size distribution is determined by the phenomena breakage and coalescence of single droplets. Thus, these interactions determine the macroscopic behaviour of an emulsion directly. Although various models are available in literature for both phenomena Lucas, 2010, 2009), the prediction of the drop size distribution is only possible with restrictions when varying for example the power input or material and process conditions. Consequently, excessive and expensive experimental investigations are still necessary at different scales for process development. For instance, the design of extraction columns still requires pilot plants using high amounts of the original physical system. To diminish the number of influencing...

Automated image analysis for trajectory determination of single drop collisions

“…The applied liquid phases were toluene as disperse and water as continuous phase according to the EFCE standard test systems for extraction [15]. The entire automated set-up was described in detail by Kamp and Kraume [8]. Using Hamilton syringe pumps the drop volumes could be determined precisely and drop sizes between 1.5 mm -3.0 mm were investigated.…”

“…The number of necessary image sequences was determined by Kamp and Kraume [8] by analysing the trend of coalescence probability over the analysed sequences. The recording was implemented entirely in the LabVIEW automation of the test cell.…”

“…The relative collision velocity of the droplets was determined by varying the rising distance of the bottom drop, which was detached from a cannula at the bottom of the test cell. Therefore, the distance between the cannulas could be varied from drop contact up to 100 mm [8]. Three different monochrome digital high speed camera systems were used to record the drop collisions:…”

“…These so called population balance equations allow the separate implementation of * corresponding author Email address: johannes.kamp@tu-berlin.de (Johannes Kamp) URL: www.vt.tu-berlin.de (Johannes Kamp), www.cv.tu-berlin.de (Ronny Hänsch) breakage and coalescence which occur simultaneously in a general dispersion [1,2,3]. Several research groups investigated the breakage [4,5,6,7] and coalescence [8,9,10,11] separately in order to validate and improve these modelling approaches. The investigations use digital high speed cameras to obtain a high spatial and temporal resolution.…”

“…The huge amount of recorded image sequences has to be analysed automatically by applying specific computer vision methods. This paper proposes a first step in the direction of fully automatic coalescence detection: Based on the test cell described in [8], a system is developed to automatically detect and track drops within the videos. From the established trajectories the time points of drop detachments as well as drop collision are reliably determined.…”