Measuring and modeling thermal conductivity of hydrogel phase change materials for thermal energy storage

Glauber's salt, a salt hydrate, possesses a relatively high volumetric latent heat (~0.3 GJ per cubic meter in solid form) but suffers from supercooling and phase segregation. Recent work on integrating the salt into a polymer hydrogel shows that phase segregation and supercooling can be mitigated over hundreds of cycles. Future practical realization of the salt-hydrogel complex as a thermal storage material requires an accurate characterization of thermal conductivity and strategies for enhancement since the rate of absorption and release of thermal energy increases with higher thermal conductivity. Here, we report a method for measuring the thermal conductivity of polymer hydrogels that improves over existing methods in accuracy. Specifically, we use a modified 3-omega method where heat flow from a microfabricated heater is split between that through the gel and that through its substrate. We report measurements on both gels and liquids and discuss advantages compared to existing transient plane heat source or transient hot-wire methods. We also use the 3-omega method on samples with and without a thin film to measure the thermal conductivity of a porous silicon film. Next, we present measurements of salt-hydrogel complexes as a function of temperature. Lastly, to investigate the origin of peaks in thermal conductivity during the phase transition, we compare data with analytical models of heat conduction with and without phase change. Our thermal conductivity setup and measurements combined with measurements of stored thermal energy, transition temperature range and physical stability are essential to develop models for thermal storage systems for efficient provision of heating and cooling in buildings.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Mechanical Engineering

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2024

Author dc:creator

• Hsieh, Daniel Hwai-En

Contributors dc:contributor

• Sinha, Sanjiv
• Braun, Paul V
• Cai, Lili
• Smith, Kyle

• Phase Change
• 3-omega
• Hydrogel
• Thermal Conductivity
• Thermal Storage

Statement dc:rights

• Copyright 2024 Daniel Hsieh

Language dc:language

en, eng

Handle dc:identifier

https://hdl.handle.net/2142/125717

OAI record oai:identifier

https://www.ideals.illinois.edu/oai-pmh?verb=GetRecord&metadataPrefix=etdms&identifier=oai%3Awww.ideals.illinois.edu%3A2142%2F125717