Chemical Engineering Science 42 (2009) 1143--1153 Contents lists available at ScienceDirect Chemical Engineering Science journal homepage: www.elsevier.com/locate/ces Solid–liquid mass transfer analysis in a multi-phase tank reactor containing submerged coated inclined-plates: A computational fluid dynamics approach Francisco J. Trujillo, Tomasz Safinski, Adesoji A. Adesina ∗ Reactor Engineering and Technology Group, School of Chemical Sciences and Engineering, University of New South Wales, Sydney, NSW 2052, Australia ARTICLE INFO ABSTRACT Article history: Received 7 February 2008 Received in revised form 31 October 2008 Accepted 7 November 2008 Available online 18 November 2008 Keywords: Solid–liquid mass transfer coefficient Submerged inclined-plates CFD simulation Mathematical modeling Photoreactor design Although there is a voluminous literature on the estimation of interphase transport parameters in con- ventional slurry bubble column reactors, these correlations are inadequate in photoreactors equipped with specialized internals to facilitate light harvesting efficiency of the photocatalyst. This is particularly germane to the present externally illuminated bubble column reactor containing titania-coated plates immersed in the liquid column at different angles of inclination. Thus, a computational fluid dynamics (CFD) procedure utilizing the Eulerian–Eulerian approach has been used to solve the governing differential equations for the solid liquid mass transport problem based on the standard k– model incorporating additional terms that take account of the interfacial turbulent momentum transfer. Mass transfer from the surface of the coated-quartz plates to the liquid phase was modeled using the Launder–Spalding wall functions. The plates were coated with benzoic acid as solid substrate with water and air as the liquid and gas phases, respectively. The increase in mass transfer due to reduction of the boundary layer thickness during air-induced liquid recirculation on either side of the submerged inclined plates was correlated with difference between turbulent and molecular Schmidt numbers via an adjustable parameter, A. CFD simulation using the Launder–Spalding wall function (with A = 1.08) gave better agreement with experi- mental transient concentration profiles than calculations based on FLUENT's enhanced wall function for the plate orientations ( = 0 ◦ , 22.5 ◦ , and 45 ◦ ) studied. The solid-to-liquid mass transfer was higher on the lower-side of the plate than the upper-side. In particular, mass transfer coefficient was higher with the inclined plate than with the vertical or horizontal orientation suggesting an added advantage for the application of the system as a solar photoreactor. © 2008 Elsevier Ltd. All rights reserved. 1. Introduction Photocatalysis has emerged as a promising new route for high quality water purification and advanced tertiary treatment of waste water containing biologically recalcitrant pollutants (Bahnemann et al., 1991; Robert and Malato, 2002). Although recent reports on the development of visible-light activated catalysts are encouraging (Nogueira and Jardim, 1996; Alfano et al., 2000; Guillard et al., 2003; Noorjahan et al., 2003), commercial exploitation has been stymied by inadequate understanding of solar photoreactor design and scale-up due to the complex interplay of mixing, interphase mass transport, light scattering and maximization of the illuminated cata- lyst surface area for adsorption–reaction steps in the heterogeneous system. In order to eliminate or reduce these coupled phenomena, ∗ Corresponding author. Tel.: +61 2 9385 5268; fax: +61 2 9385 5966. E-mail address: a.adesina@unsw.edu.au (A.A. Adesina). 0009-2509/$ - see front matter © 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.ces.2008.11.004 various solar photoreactor designs have been proposed depending upon the light-focusing method for externally placed illumination source and whether the catalyst is suspended or immobilized in the fluid phase (Adesina, 2004). For example, in the double skin sheet so- lar reactor (DSSR), the photocatalyst particles are kept in suspension by circulating the liquid mixture through a plexiglass box to receive both diffuse and specular fractions of solar radiation (Dillert et al., 1999). However, the thin-film fixed-bed reactor is an immobilized catalyst system through which the liquid feed flows under laminar flow conditions (Nogueira and Jardim, 1996). Whilst it possesses a high optical efficiency and requires no catalyst separation from the treated liquid it suffers from poor mass transfer attributes and is not suitable for use with high feed throughput since a large catalyst surface area is required. This is in contrast to the excellent mass transport characteristics of the DSSR, simplicity of construction and low capital costs. Nonetheless, photocatalyst separation and low optical efficiency are major drawbacks of the well-mixed flow DSSR. The present solar photoreactor design adopts a hybrid approach involving the integration of the advantages of a bubble column