The wetting of the flow surfaces in heat exchangers, trickle-bed reactors and columns containing structured packing has been shown to be discrete in nature involving rivulets. Detailed, fundamental modelling of the flow structure and transport processes occurring in rivulet flow is required in order to provide a basis from which more complex models can be built describing the overall processes occurring in the particular application of interest. To demonstrate the applicability of detailed rivulet modelling, theoretical analysis of the velocity and mass transfer characteristics in rivulet flows in an inclined, flat plate absorber has been performed. These theoretical results are compared with experimental data.