Measuring and modeling thermal conductivity of hydrogel phase change materials for thermal energy storage
Hsieh, Daniel Hwai-En
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Permalink
https://hdl.handle.net/2142/125717
Description
Title
Measuring and modeling thermal conductivity of hydrogel phase change materials for thermal energy storage
Author(s)
Hsieh, Daniel Hwai-En
Issue Date
2024-07-12
Director of Research (if dissertation) or Advisor (if thesis)
Sinha, Sanjiv
Doctoral Committee Chair(s)
Sinha, Sanjiv
Committee Member(s)
Braun, Paul V
Cai, Lili
Smith, Kyle
Department of Study
Mechanical Sci & Engineering
Discipline
Mechanical Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
phase change
3-omega
hydrogel
thermal conductivity
thermal storage
Abstract
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.
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