A multi-factorial experimental test of H2O vapour absorption by a falling film of LiBr(aq) over an horizontal smooth tube absorber is presented. The response parameters of the study are the average convective heat transfer and mass transfer coefficients of the falling film. The response is expressed as a function of the factors used in the study. Also a mathematical model for the prediction of the performance of the absorber is exposed which takes into account the wetting effects. Finally the predictions from the model and the experimental multi-factorial runs are compared and the conclusions discussed. (C) 2003 Elsevier Science Ltd. All rights reserved.