Quantifying volume variation and agglomeration in thermochemical materials: An in-situ measurement methodology

The effectiveness of salt hydrate particles as thermochemical materials is significantly hindered by agglomeration and volume variation. To address these challenges, this study adopts a particle-level approach, focusing on the dynamic processes of swelling and shrinkage within potassium carbonate particles during cycling. Through in-situ measurements within a micro-climate chamber, the size variations of the material under different operating conditions are closely monitored. The analysis of the obtained images allowed for the calculation of the equivalent diameter of salt grains. Additionally, Micro-CT scans were employed to assess changes in particle porosity. The experiments are conducted under varied conditions, such as maintaining a constant temperature while adjusting the relative humidity and maintaining a constant relative humidity while increasing temperature. The results revealed both an increased equivalent particle diameter and porosity. This indicates increased hydration and thermal expansion, respectively. The findings emphasize the sensitivity of the material to environmental conditions. They highlight the material's ability to undergo significant structural changes in response to variations in temperature and humidity. When a large force, mimicking a real packed bed system, is exerted on the grains, agglomeration is observed, contrary to the absence of force under the same operating conditions. This finding is significant for explaining agglomeration in a packed bed system. The results are an initial step towards understanding agglomeration at the particle level. They illuminate the interplay between environmental conditions, structural changes, and cohesive forces within these materials. • In-situ cycling experiments shows the physics and conditions causing agglomeration in a salt-hydrate based TCM. • Quantified porosity and equivalent diameter show significant growth under varying conditions. • Estimation of porosity using Micro-CT imaging for salt hydrates. • Packed bed tests show agglomeration occurs only under mechanical stress, emphasizing swelling-induced stress effects.