Separation and Purification Technology 62 (2008) 659–667 Contents lists available at ScienceDirect Separation and Purification Technology journal homepage: www.elsevier.com/locate/seppur An experimental and theoretical analysis of turbulence promoter assisted ultrafiltration of synthetic fruit juice Srimanta Pal a , Ravi Bharihoke b , Sudipto Chakraborty b , Sobhendu Kumar Ghatak a , Sirshendu De b , Sunando DasGupta b,∗ a Department of Physics and Meteorology, Indian Institute of Technology, Kharagpur, Kharagpur, West Bengal 721302, India b Department of Chemical Engineering, Indian Institute of Technology, Kharagpur, Kharagpur, West Bengal 721302, India article info Article history: Received 10 January 2008 Received in revised form 5 March 2008 Accepted 6 March 2008 Keywords: Turbulence promoters Ultrafiltration Fruit juice Computational fluid dynamics Deposition thickness abstract Ultrafiltration of synthetic fruit juice (mixture of pectin and sucrose) is performed in continuous cross flow mode with an organic ultrafiltration membrane (PPE 30, poly phenylene ethersulfone) of 30 K molec- ular weight cut off. The permeate fluxes are measured under various operating conditions, namely, transmembrane pressure and cross flow velocity. Significant enhancement of permeate flux is achieved by incorporation of cylindrical promoters placed perpendicular to the flow. Image analyzing video microscopy is used to quantify the deposition profile of pectin on the membrane surface. The consis- tency of these measurements in relation to enhancement of permeate flux are examined. The coupled fluid flow and mass transfer processes including the effects of the promoters are modeled and solved using FLUENT. The geometry of the system is constructed using GAMBIT and special attentions are given to mesh sizes in the different zones of flow, e.g., finer mesh is used near the membrane surface. The calculated values of permeate flux under various operating conditions agree well with the experimental data. © 2008 Elsevier B.V. All rights reserved. 1. Introduction The decline in flux during membrane separation is attributed to the interlinked problems of concentration polarization and fouling of membrane. Concentration polarization leads to the formation of a concentrated layer near the membrane and may result in the formation of a gel layer over the membrane surface. This phe- nomenon is a function of system hydrodynamics, nature and size of solute molecules, membrane pore size (molecular weight cut off) and properties (hydrophilic, hydrophobic, surface charge etc). Considerable attention has been given to the development of tech- niques for reduction of the build-up of these additional resistances during operation. The techniques involve changing the hydrody- namics of the system, use of external body force and membrane surface modifications. Incorporation of turbulence promoters [1,2], pressure pulsation [3,4] etc. changes system hydrodynamics, suit- able electric field for charged species [5,6] are used as body force and plasma treatment [7–9] and surfactant treatment [10,11] etc. are techniques for surface modifications. The effectiveness of these methods is generally quantified by the increase in permeate flux, quality of separation and ease of membrane cleaning. ∗ Corresponding author. Tel.: +91 3222 283922; fax: +91 3222 255303. E-mail address: sunando@che.iitkgp.ernet.in (S. DasGupta). The uses of hydrodynamic approaches to reduce these flux- limiting phenomena are quite common in literature. The common methods are (i) pulsations using a collapsible-tube pulsation gener- ator [12], (ii) use of slug flow [13], (iii) introduction of air sparging [14], (iv) use of cross-corrugated membranes [15], (v) turbulence promoters, spacers [2,16–24]. Ultrafiltration is becoming an attractive unit operation for clari- fication of fruit juice. Reports on treatment of various juices such as pear [25], orange and lemon [26], pineapple [27] etc. using UF mem- branes are available in literature. However, pectin, a well-known gel forming agent present in fruit juices, often deteriorates the fil- tration performance during UF [28]. Therefore, de-pectinization is done before the fruit juice is filtered [29,30]. Nevertheless, it has been established that the left over pectin even after depectiniza- tion is sufficient to cause a flux decline during UF [30]. A change in hydrodynamics inside the channel by incorporating turbulence promoters can reduce pectin deposition and results in increase of permeate flux. The evaluation of deposition thickness profile [31] around a pro- moter and detailed simulation of the flow pattern are required to understand the basic physics of the process. Though some efforts are made for simple flow channels [32], few attempts are made for complicated systems like spacer-filled porous channels. Recently computational fluid dynamics (CFD) techniques are being used to simulate laminar and turbulent flow [33–42] in channels as well. 1383-5866/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.seppur.2008.03.010