This paper is concerned with the development of a mathematical model for an air-water system in order to simulate the system behaviour under steady and unsteady conditions. One of the targets is to present a computational method to determine heat and mass transfer coefficients. Results confirm the inherent superiority of the numerical approach over the graphical traditional method. The main purpose of this paper is to develop a dynamic model and to evaluate the validity of this model when applied to experimental data. The orthogonal collocation method is used to solve the model by means of a computer program. Despite the fact that simplifying assumptions have been made, the results clearly demonstrate that the simulation model predicts accurately the dynamical behavior of the system. © 1987.