Session: 19-04: Symposium to Honor Professor Jane Davidson IV

Paper Number: 155568

155568 - Impact of Cycling on the Structure of Crystal Nanocellulose-Salt Composite Materials for Thermal Energy Storage 

Abstract: 

A significant amount of the energy demands in buildings are for thermal end-uses. As such, effective thermal energy storage is needed for intermittent renewable energy sources and to help enhance the performance of heat pumps. Thermal energy storage is often categorized by how the energy is stored: sensible, latent, and thermochemical. In thermochemical storage, the energy is stored in the chemical bonds between reactants of a reversible reaction. Thermochemical energy storage represents a promising technology due to its high energy density with long-term storage efficiency. One thermochemical reaction of interest for energy storage in buildings is the hydration-dehydration of hygroscopic salts. However, these salts have challenges including particle agglomeration, deliquescence, and structural degradation over the course of hydration-dehydration cycling that directly influence material performance. Composite materials have been investigated to address the cycle stability issue. One promising composite utilizes crystal nanocellulose (CNC) as a stabilizing additive. The CNC stabilizes the salt by improving the structural integrity and reducing some of the issues related to particle agglomeration. However, as a nascent composite material, there is a lack of information as to how the structure of composite material changes with cycling. Understanding structural changes is important to the continued refinement and improvement of the material. Thus, the purpose of this study is to investigate how this new composite material changes over the course of repeated hydration-dehydration cycles. Various salt-CNC composite materials as well as controls of pure salts are investigated. The composite materials include salts of strontium chloride (SrCl₂) with CNC and a binary salt blend of strontium chloride and calcium chloride (CaCl₂) at the ratio of 80 wt% SrCl₂ to 20 wt% CaCl₂ with CNC. The composites at percent weight ratios of 90:10 and 80:20 salt-to-CNC were investigated. The cycle behavior was assessed by measuring the hydration water uptake. The structural changes of the materials were determined through visual inspection at the macroscale while the microstructural changes were assessed via scanning electron microscopy. The cycling of the material was conducted in an environmental chamber wherein the samples were hydrated at 25 °C and relative humidity of 65% for a fixed hydration time. To dehydrate, the samples were heated in the environmental chamber, at a rate of 2 °C/min, to a dehydration temperature of 90 °C and relative humidity of ~5%. The samples were held at the dehydration conditions for a fixed period. Samples were removed at regular intervals to assess the structural changes. A total of 40 hydration-dehydration cycles were conducted. The results indicate the samples have relatively stable water uptakes with a slight decrease for the salt-CNC composites throughout cycling. The macrostructure of the composites is retained through cycling. The samples do not deliquesce and retain powderlike form without particle agglomeration. The results are useful for guiding future material development, particularly salt-CNC composites, for thermochemical storage.

Presenting Author: Navid Anjum North Dakota State University

Presenting Author Biography: Navid Anjum is a Mechanical Engineering graduate student at the North Dakota State University. He is currently working as a graduate research assistant at NDSU where his research focuses on thermochemical energy storage, exploring innovative salt-based materials for sustainable energy solutions. He received a bachelor's degree in Mechanical Engineering from the Military Institute of Science & Technology, Bangladesh.