Chemical Engineering Science 60 (2005) 1965 – 1975 www.elsevier.com/locate/ces Thin film flow over structured packings at moderate Reynolds numbers Prashant Valluri, Omar K. Matar ∗ , Geoffrey F. Hewitt, M.A. Mendes Department of Chemical Engineering and Chemical Technology, Imperial College London, South Kensington Campus, Prince Consort Road, London SW7 2AZ, UK Received 15 July 2004; received in revised form 30 November 2004; accepted 1 December 2004 Abstract A model describing the dynamic evolution of waves on laminar falling wavy films at low to moderate Reynolds numbers (Re < 30) over corrugated surfaces is presented. This model is based on the integral balance method, which is used to simplify the analysis by assuming a parabolic velocity profile within the bulk of the film. The predictions of this model are compared to those obtained from a computational fluid dynamics (CFD) code for which no assumptions regarding the film velocity profile are made. The film evolution profiles, obtained via numerical solution of the model equations, are used to calculate the ratio of film interfacial area to that of the substrate. The model predicts suppression of wave growth on a corrugated surface. The model is also used to predict the effect of packing geometry on the flow characteristics, which may improve packing design. Solutions obtained for Re ∼ 200 using the CFD code demonstrate the degree of fluid accumulation within the ‘valleys’ of the structured substrate wherein re-circulation occurs.  2005 Elsevier Ltd. All rights reserved. Keywords: Distillation; Films; Modelling; CFD; Structured packings; Waves 1. Introduction Vapour–liquid hydrodynamics play a pivotal role in the design of distillation or absorption columns using structured packings since they determine the fluid-dynamic limits of the column and control rates of mass transfer, which is the main purpose of these unit operations. Thus, the accurate prediction of film hydrodynamics in structured packings is of major interest in column design. In this work, we focus on hydrodynamic modelling of the flow of films on corru- gated structured packings, which have now diversified into almost every gas–liquid contacting operation including su- percritical extraction (Wronski and Molga, 1998) and cryo- genic distillation of air (Rohde, 1991), etc. Current popular design procedures, such as those by Gualito et al. (1997) and references therein, are empirical and thus, their use beyond the range of their validation is risky (Engel et al., 2001). It is ∗ Corresponding author. Tel.: +44 207 594 5571; fax: +44 207 594 5629. E-mail addresses: o.matar@imperial.ac.uk, o.matar@ic.ac.uk (O.K. Matar). 0009-2509/$ - see front matter  2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.ces.2004.12.008 felt that the disadvantages of these empirical models could be overcome by using more reliable modelling techniques based on fundamental considerations. Although falling films over smooth substrates have been widely studied both theoretically and experimentally (see Lamb, 1932; Lin, 1955; Fulford, 1964; Alekseenko et al., 1994; Chang, 1994; Oron et al., 1997, and references therein), only few studies have examined thin film flow on structured packings (Shetty and Cerro, 1993; Shetty, 1995; Shetty and Cerro, 1997a,b, 1998); these studies are for very small Reynolds numbers over a singly circular surface. Some studies have examined thin film flow over rough surfaces at low Reynolds numbers, for example those by Stillwagon and Larson (1990), Kim et al. (1991), Kalliadasis and Bielarz (2000), Kalliadasis et al. (2000), Kalliadasis and Homsy (2001), and wavy substrates, for example those by Wang (1981), Dassori et al. (1984), Pozrikidis (1988, 2003) and Wierschem and Aksel (2003). Work by Bontozoglou and Papapolymerou (1997), Negny et al. (1998), Trifonov (1998), Malamataris and Bontozoglou (1999) and Negny et al. (2001a–c) dealt with higher Reynolds numbers, but