Session: 03-04 Sensible Energy Storage

Paper Number: 115239

115239 - Nanoconfined Polyethylene Glycol With Expanded Graphite for Energy-Efficient Thermal Energy Storage 

Heating, ventilation, and air conditioning (HVAC) systems consume 30-50% of energy used in the US for thermal comfort control. Tremendous developments have been made to improve the efficiency of HVAC systems, such as photothermal conversion, geothermal system, waste heat recovery, and radiative cooling. Recently, phase change materials (PCMs) have been applied to HVAC systems to improve energy efficiency by exploiting the latent heat released and absorbed during phase transition process. However, the use of PCMs in buildings is constrained by major challenges of (1) poor shape stability, (2) low thermal conductivity, and (3) reduced energy density. To address these challenges, recent research has revealed several supporting matrices to encapsulate PCMs. Particularly, expanded graphite (EG) is one of the most promising candidates due to its low cost, high thermal conductivity, high porosity, and good compatibility with PCMs.

Here we report a two-step synthesis of polyethylene glycol (PEG)/EG composite for high energy density TES in HVAC systems. PEG is selected as PCMs mainly due to its melt temperature of 36 ℃. A facile method—microwave irradiation—was employed to prepare EG and PEG is then vacuum-infiltrated into the porous EG matrices to form PEG/EG composite. We optimized the porous structure of EG as a function of microwave irradiation power and time and investigated its impact on the phase change properties of PEG/EG composite. With EG prepared by an irradiation power of 900 W and time of 30 s, PEG/EG composite shows a high melting enthalpy of 156.2 J/g. More intriguingly, due to the interaction between EG matrix and PEG molecules, the composite also exhibits an improved heat storage efficiency as indicated by its superior crystallization fraction of 107.6%. The extraordinary shape stability and thermal stability after multiple thermal cycles also indicate the practicability of the obtained PCM in TES applications.

Presenting Author: Lyu Zhou Mechanical Engineering, the University of Texas at Dallas

Presenting Author Biography: Lyu Zhou received his PhD degree from the State University of New York at Buffalo in 2022. During his PhD research, he was focusing on the optical material and system development for radiative cooling, and metasurface for biosensing and super-resolution imaging. He joined the University of Texas at Dallas in Prof. Shuang Cui's group as a post-doc after graduation, and has been working on phase change material, hydrogel, radiative cooling and thermal energy storage since then.