In-situ optical microscopy of structural changes in thermochemical storage materials

Kurzfassung

The energy demands are increasing day by day and the reserves of conventional energy sources are depleting and getting more expensive. Renewable energy sources are a solution to this but their supply is not consistent and will depend on various factors. As a solution for this, improvisation is done in the field of heat storage technologies thereby leading to a sustainable energy system. Thermochemical energy systems is an efficient solution for the energy crisis, out of which the reversible solid- gas reactions is an effective method when referring to energy storge systems at higher temperature ranges. Energy gets stored after the charging (endothermic) process when the material is split up (energy stored as reaction enthalpy) and later on energy can be recovered at any particular time when discharging (exothermic) phase occurs (the separated materials reacts). An efficient material that performs well in the temperature range of 150°C - 300°C is Strontium Bromide. Previous work showed that even though the material functioned well, voids were created inside the reactor after conducting the experiments. This led to the interest in studying the structural changes that occurs on the salt hydrate when similar experimented under the same temperature range. The study was done on a micrometre to millimetre scale. Even though multiple particles were used initially, formation of agglomerates were also observed in the reactor as the experiments progressed. This was another motivation which led to the interest in the study of structural changes happening to the salt hydrate. The presented work focuses on the study of structural development of Strontium Bromide under various reaction conditions in micrometre to millimetre scale, over the cycles. The studies showed that the changes happening to Strontium Bromide over various ramp conditions were different. The main factors that influence the rate of changes were the mass of sample used and the rate at which temperature increases as the ramp progresses. An in-house built evaporator was also used to perform simultaneous dehydration and hydration cycles and to understand the salt hydrate in a much better way. The dimensions of the samples experimented did not changed in any experiment showing that even though there was a loss in mass of the material, it did not affect the material dimension.