On the measurement of local gas hold-up, interfacial area and bubble size distribution in gas–liquid contactors via light sheet and image analysis: Imaging technique and experimental results A. Busciglio n , F. Grisafi, F. Scargiali, A. Brucato Dipartimento di Ingegneria Chimica, Gestionale, Informatica e Meccanica, Universitá degli Studi di Palermo, Viale delle Scienze, Ed. 6 - 90128 Palermo, Italy AUTHOR-HIGHLIGHTS  Original data about gas–liquid dispersion properties in stirred vessels are presented and discussed.  The experimental technique is based on the adoption of a laser plane and a fluorescent liquid phase.  Highly detailed data can be obtained without affecting the system fluid dynamics.  Data presented are in agreement with the literature. article info Article history: Received 13 February 2013 Received in revised form 21 June 2013 Accepted 8 August 2013 Available online 20 August 2013 Keywords: Bubble Imaging Mixing Multiphase flow Gas–liquid dispersion Bubble size distribution abstract In this work a novel experimental technique for measuring local gas hold-up, interfacial area and bubble size distribution, in gas–liquid systems is proposed. The technique is based on advanced Image Processing coupled with experimental set-ups typically available for Particle Image Velocimetry. A fluorescent dye dissolved in the liquid phase allows to identify in-plane bubbles among all visible bubbles in the images. To this end, a suitable algorithm is proposed. The raw data so obtained are processed by previously developed statistical methods that result in a reliable reconstruction of actual dispersion properties. The technique is applied to the case of a gas-dispersed mechanically agitated vessel, and the data obtained are presented and discussed. & 2013 Elsevier Ltd. All rights reserved. 1. Introduction Gas–liquid contactors are widely employed as chemical and bio- chemical reactors in the process industry. In most of these applica- tions, gas–liquid mass transfer is the main rate-determining step. Significant attention has been devoted in the past to the experi- mental assessment of k L a i values in stirred vessels by means of several experimental techniques (e.g. Linek et al., 1982, 1989; Scargiali et al., 2007, 2010, 2012). Knowledge of the mass transfer product k La is important for equipment design, even if the separated k L and a i values are not known. However, experimental assessment of specific interfacial area is needed for properly modelling fast gas–liquid chemical reactions as well as in the realm of validation of CFD models. Local mass transfer areas depend on gas phase volume fraction as well as on bubble sizes, properties that are known to vary notably from place to place, even in small stirred tanks (Calderbank, 1958; Sridhar and Potter, 1980; Barigou and Greaves, 1992b, 1996; Laakkonen et al., 2005a). In the followings, some of the papers dealing specifically with measurements of bubble size distribution, gas hold-up and specific interfacial area are briefly reviewed. 1.1. Measurement techniques By exploiting suitably catalyzed chemical reactions the specific interfacial area may be obtained (Hassan and Robinson, 1980; Mandal et al., 2005; Mohanty et al., 2007). These chemical methods can only access global (vessel and time averaged) data and are affected by system coalescence alterations due to the presence of the added chemicals. Apart from these, a number of techniques, able to access local information on dispersion properties has been devised over the Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/ces Chemical Engineering Science 0009-2509/$ - see front matter & 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.ces.2013.08.029 n Corresponding author. Tel.: þ39 091 238 63779. E-mail addresses: antonio.busciglio@unipa.it (A. Busciglio), franco.grisafi@unipa.it (F. Grisafi), francesca.scargiali@unipa.it (F. Scargiali), alberto.brucato@unipa.it (A. Brucato). Chemical Engineering Science 102 (2013) 551–566