This paper presents a mathematical model for the prediction of solid layer growth from melt contained in a crystallization tube of a bubble column crystallizer. The model was solved by using the integral formulation approach together with the assumption of a second-degree polynomial approximation of temperature profile within the solid layer. In the model, the convective heat transfer coefficient at solid layer-melt interface was calculated by analogy between heat and mass transfer from the models developed for mass transfer in the case of Taylor bubbles rising in a vertical liquid column. The predicted growth rates of solid layer were compared with experiments of caprolactam melt solidification which were carried out in a 19 mm inner diameter crystallization tube at superficial gas velocities of 0.04 and 0.08 m s(-1). A good agreement was obtained between experimental and predicted data. Different characteristics of layer growth for slug units passing through different growing stages were also described and discussed. (C) 2003 Elsevier Ltd. All rights reserved.