Chemical Engineering Science 59 (2004) 1079 – 1086 www.elsevier.com/locate/ces An experimental study of interfacial surface area concentration in a short vertical column subject to paper pulp–water–gas three-phase ow M.K. Akbar a , S.M. Ghiaasiaan a ; * , S. Karrila b a George W. Woodru School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA 30332-0405, USA b Institute of Paper Science Technology, Atlanta, GA 30318, USA Received 5 August 2003; received in revised form 8 October 2003; accepted 5 December 2003 Abstract The interfacial surface area concentration in a short vertical column subject to the through ow of a solid–liquid–gas slurry made by mixing aqueous brous paper pulp with a nitrogen–carbon dioxide gas mixture was measured in the study. The gas absorption technique was applied, using CO2 as the transferred species and sodium hydroxide as the alkaline agent in water. The ow regimes in the experiments were visually identied, and the test section void fraction was measured using a Gamma-ray densitometer. The test section was a 1:83 m-long column with 5:08 cm inner diameter. The ranges of experimental parameters were as follows: liquid-pulp supercial velocity 15–94 cm= s; average gas-supercial velocity 17–54:5 cm= s; pulp consistency in the water/pulp mixture 0.0– 2.18%; and average mole fraction of carbon dioxide in the gas mixture 0.19–0.95. A total of 33 data points were obtained, each representing the average of three to nine tests that conrmed reasonable repeatability. Statistical analysis of the experimental data indicates strong dependence of interfacial area on average gas supercial velocity and void fraction; and a relatively weak dependence on pulp consistency and liquid supercial velocity. The eect of pulp consistency on the interfacial area concentration in the test section was particularly interesting. The test section average interfacial surface area concentration decreased with increasing consistency up to a consistency of 1.6%, but increased signicantly when consistency was further increased to 2.18%. The experimental data were empirically correlated. ? 2004 Elsevier Ltd. All rights reserved. Keywords: Vertical column; Through ow; Three-phase; Fibers; Mass transfer; Interfacial area; Pulp; Fiber slurry; Three-phase ow; Interfacial surface area; Void fraction; Statistical model 1. Introduction The importance of gas–liquid–solid slurry three-phase ows in various branches of chemical, petrochemical, and process industries is well recognized, and numerous stud- ies have addressed its various aspects (Dudukovic et al., 1999). Relatively, little is understood about the basic hy- drodynamics and transport phenomena in gas–liquid–ber slurry three-phase ow systems, however, despite its crucial role in several important branches of industry. The scarcity of published investigation dealing with three-phase brous slurries is primarily a result of the complexity of these systems. Gas–liquid–ber slurry three-phase ow occurs in a number of stages of paper production and recycling, ∗ Corresponding author. Tel.: +1-404-894-3746; fax: +1-404-894-8496. E-mail address: seyed.ghiaasiaan@me.gatech.edu (S.M. Ghiaasiaan). including delignication and bleaching. Bleaching is achieved by dissolving an oxidizing agent such as chlo- rine, oxygen, or ozone in an aqueous ber suspension. The oxidizing agent is typically introduced into the mixture as ne bubbles. It must dissolve in water, be transported to the suspended pulps, and diuse towards the ber–liq- uid interface, before it can chemically react with lignin. The relatively low solubility of oxygen and ozone in wa- ter can cause poor eciency in oxygen and ozone-based bleaching devices, and the performance of these devices can be improved by increasing the gas–liquid interfa- cial area. Understanding the role and eect of pulp bers on the hydrodynamics of ber–liquid–gas three-phase slurries is evidently crucial for the development of prac- tical methods that would lead to the optimization of bleaching devices. The main cause of the complexity of pulp slurry hydro- dynamics is occulation (entanglement of ber groups to conformations that possess mechanical strength) that leads 0009-2509/$ - see front matter ? 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.ces.2003.12.010