In falling film heat and mass transfer models, complete wetting of the substrate is usually assumed. In this paper, a practical model for the simultaneous heat and mass transfer processes in an internally cooled dehumidifier paired with a newly developed ionic liquid desiccant from Evonik Industries is presented. The heat and mass transferred were estimated using heat and mass transfer coefficient analogies from the literature incorporating variable film thickness and partial wetting model; therefore, accounting for the change in the film thickness and wetted area in each control volume, respectively. Comparison between the predicted results from the partial and complete wetting models with the experimental data showed a better agreement for the former. Absolute deviations for the air outlet humidity ratio were within 15 and 35% for the partial and complete wetting models, respectively. The model with partial wetting is suggested for preliminary design and optimization of internally cooled contactors.