AbstractThis paper focuses on the development of a reaction zone dedicated to an absorption/desorption seasonal thermal energy storage. The modelling of the tube bundle constituting the reaction zone is described as well as the boundary conditions in worst working conditions and some modelling results are presented for the desorber/absorber. In parallel to this sizing work, investigations were lead on the tube bundle optimisation by studying the wetting and fluid distribution. A specific developed experimental set up based on imaging enabled to quantify the influence of tube texturing and to improve the manifold design. This work will lead to the reaction zone construction for an aqueous sodium hydroxide seasonal thermal energy storage prototype.