Falling film plate exchanger are used in a wide range of systems thanks to their high heat and mass transfer performance for a low cost. In this study, a grooved plate is considered for it's ability to improve the wetting of the surface compared to a smooth plate. To characterize the heat transfer and evaporation rate of the system, a numerical model has been developed to take account of the new geometry and has been confronted to experimental results. Despite the high aspect ratio of the falling film, the fin effect is very high on the heat transfer and on the vaporization process due to the triple contact lines. The principal aim of this study is to develop a simple and light model able to accurately describe the heat and mass transfer behaviour of film while it flows down in the grooves of the vertical plate of the evaporator. The influence of the operating conditions on the evaporator effectiveness are evaluated thanks to numerical investigations.