Seasonal Thermal Energy Storage with Aqueous Sodium Hydroxide – Experimental Methods for Increasing the Heat and Mass Transfer by Improving Surface Wetting
Using thermochemical storage based on water absorption/desorption in a fluid with high volumetric energy density like sodium hydroxide solution (NaOH-H2O) is an effective method for developing seasonal thermal energy storage. For the desorption process step which takes place in summer, a high renewable energy fraction can be reached by using solar thermal collectors. The system efficiency is influenced by the residence time of concentrated NaOH in the water vapor and the surface wetting behavior of the heat and mass transfer unit. This strongly depends on the solid surface characteristics and on the thermo-physical properties of sodium hydroxide, especially the high surface tension of the concentrated NaOH solution from the absorption process. An improved wetting of the concentrated NaOH was achieved by modifying liquid’s properties (e.g. surface tension) or by changing the solid surface structure and chemistry.