Chemical Engineering Journal 78 (2000) 21–28 Phenomenological model for bubble column reactors: prediction of gas hold-ups and volumetric mass transfer coefficients K. Shimizu, S. Takada, K. Minekawa, Y. Kawase ∗ Biochemical Engineering Research Center, Department of Applied Chemistry, Toyo University, Kawagoe, Saitama 350-8585, Japan Received 25 April 1999; received in revised form 8 October 1999; accepted 22 October 1999 Abstract Based on a phenomenological model for bubble break-up and coalescence, a new simulation model for gas hold-up and gas-liquid mass transfer in bubble column reactors is proposed. In order to describe bubble movements in a bubble column reactor, a compartment concept is combined with the phenomenological model for bubble break-up and coalescence. It is assumed that the bubble column reactor consist of a series of discrete compartments in which bubble break-up and coalescence occur and bubbles move from compartment to compartment with different velocities. Gas hold-up and gas-liquid mass transfer rate are evaluated on the basis of bubble behaviors, i.e., bubble break-up and coalescence. Reasonable agreement is found between the model predictions and the present experimental data obtained in two different size bubble column reactors with air–water system and available correlations in the literature. Simulation results indicate that the proposed model provides some insight into the transport phenomena in bubble column reactors and furthermore it is useful for improving CFD predicting gas hold-ups and gas-liquid mass transfer rates in bubble column reactors. © 2000 Elsevier Science S.A. All rights reserved. Keywords: Bubble column reactor; Bubble break-up; Bubble coalescence; Gas hold-up; Volumetric mass transfer coefficient 1. Introduction Bubble column reactors have been widely adopted in the chemical and biochemical industries. However, the design and scale-up of bubble column reactors are still very difficult and their approaches are largely empirical [1,2]. Although a number of empirical correlations have been used for bub- ble column reactor design, they can shed little light on the mechanism of physical processes occurring in bubble col- umn reactors. In bubble column reactors, the size of bubbles is the most important parameter deciding their performance. It determines the bubble rising velocity and the gas residence time and governs the gas hold-up, the interfacial area and as a result gas–liquid mass transfer rate. In gas–liquid two-phase systems, bubble break-up and coalescence can profoundly influence the overall performance, by altering the interfacial area available for mass transfer between the phases. There- fore, it is essential to understand the bubble behavior for ra- tional design of bubble column reactors and there have been extensive studies related to this aspect [2]. It is expected to obtain some insight into the phenomena in bubble column reactors through simulation models based on the mechanism of bubble phenomena, i.e., bubble break-up and coalescence. ∗ Corresponding author. Tel.: +81-492-39-1377; fax: +81-492-31-1031. E-mail address: bckawase@eng.toyo.ac.jp (Y. Kawase) Recently numerical simulation has been recognized as an ultimate tool for scale-up and design of chemical reactors and several studies have been conducted to understand hy- drodynamics in bubble column reactors using computational fluid dynamic (CFD) models [3–5]. In the numerical simu- lations proposed for hydrodynamics in bubble column reac- tors, bubble phenomena have not been sufficiently taken into account [4]. In order to provide comprehensive pictures of bubble phenomena in bubble column reactors, therefore, an establishment of simulation model based on bubble break-up and coalescence phenomena is required. Population balance models have been successfully used to describe liquid–liquid dispersion properties [6–9]. An advantage of the population balance approach is that the details of the break-up and coalescence processes can be in- cluded. Bapat et al. [10] and Ribeiro et al. [11] employed a population balance approach to predict the dispersed phase drop size distribution and mass transfer in liquid–liquid dis- persion systems. Unfortunately, few studies have focused on gas–liquid systems and the understanding of gas dis- persion in liquids is poor. Mihail and Straja [12] discussed bubble size distributions in bubble columns by applying a population balance concept. They did not examine the influ- ence of bubble size distributions on the overall performance of bubble columns, such as gas hold-up and mass trans- fer. Prince and Blanch [13] proposed a phenomenological 1385-8947/00/$ – see front matter © 2000 Elsevier Science S.A. All rights reserved. PII:S1385-8947(99)00165-5