The two-fluid model is applied to a thin sliced kettle reboiler. The tube bundle is treated as a porous medium in which the drag coefficient and tube-wall force are deduced from the empirically-based, one-dimensional model. Methods available in the open literature are used in the two-phase pool surrounding the tube bundle. The predictions are verified by comparing them with experimental data and models available in the open literature. The boundary condition applied at the free surface of the pool is found to be crucial in determining the flow pattern within it. When only liquid re-enters through the boundary an all-liquid pool results. Comparison with the experimental evidence suggests that this boundary condition corresponds to bubbly flow within the tube bundle. Allowing a predominantly vapour re-entry produces a two-phase pool that IS consistent with intermittent flow in the tube bundle. When the appropriate boundary condition is applied, the two-fluid model predictions are shown to reproduce the visual records and pressure drop measurements reasonably accurately. (C) 2011 Elsevier Ltd. All rights reserved.