Abstract
Inorganic salt hydrate phase change materials (PCMs) are of interest for near-room temperature thermal energy storage (TES) systems, but their low thermal conductivity, ~ 0.5 W/m-K, limits their performance. In this work, we report the thermal conductivity and bulk density of composites containing sodium sulfate decahydrate (SSD) Na2SO4·10H2O with three types of graphite: expanded graphite (EG), milled EG (MG), and graphite nanoplatelets (GnP). The effect of these thermophysical properties on TES performance is presented. The composites were made using a readily scalable one-pot synthesis procedure with graphite received as-is. A 583% increase in thermal conductivity (4.1 W/m-K) was achieved with 25 wt% EG. However, as EG fraction increases, bulk density decreases and thermal conductivity plateaus. This ultimately resulted in lower thermal performance at higher EG fractions despite higher thermal conductivity. This highlights the tradeoff between PCM composite properties and performance, and why thermal conductivity is insufficient to describe PCM thermal performance. GnP is added to EG-SSD to increase bulk density and energy storage density, but these density improvements do not offset lower thermal conductivity and thus thermal performance declined. Similarly, MG-SSD composites had a higher bulk density and energy storage density, but lower thermal conductivity and thermal performance than EG-SSD composites at similar compositions. Atomistic molecular dynamics simulations were performed to understand the structure-property relationship of graphite-SSD interfaces. The simulations support the hypothesis that atomic level contact resistance between graphite and SSD increases thermal resistance at the interfaces resulting in effectively lower bulk thermal conductivity in MG-SSD compared to EG-SSD.
| Original language | English |
|---|---|
| Article number | 104949 |
| Journal | Journal of Energy Storage |
| Volume | 52 |
| DOIs | |
| State | Published - Aug 15 2022 |
Funding
This material is based upon work supported by the U.S. Department of Energy 's Building Technologies Office under Contract No. DE-AC05-00OR22725 with UT-Battelle, LLC. The authors would like to acknowledge Mr. Sven Mumme, Technology Manager, US Department of Energy Building Technologies Office. DISCLAIMER: This manuscript has been authored by UT-Battelle, LLC under Contract No. DE-AC05-00OR22725 with the U.S. Department of Energy. The United States Government retains and the publisher, by accepting the article for publication, acknowledges that the United States Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce the published form of this manuscript, or allow others to do so, for United States Government purposes. The Department of Energy will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan ( http://energy.gov/downloads/doe-public-access-plan ). This work used resources of the Advanced Photon Source, a US Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02- 06CH11357. Beamtime for the data collection presented in this paper was allocated under GUP 67311. This research used resources of the Oak Ridge Leadership Computing Facility at the Oak Ridge National Laboratory, which is supported by the Office of Science of the U.S. Department of Energy under Contract No. DE-AC05-00OR22725. Part of the MD simulations was performed at the National Energy Research Scientific Computing Center (NERSC), a DOE Office of Scientific User Facility supported by the DOE Office of Science under Contract DE-AC02-05CH11231. This material is based upon work supported by the U.S. Department of Energy's Building Technologies Office under Contract No. DE-AC05-00OR22725 with UT-Battelle, LLC. The authors would like to acknowledge Mr. Sven Mumme, Technology Manager, US Department of Energy Building Technologies Office. This research used resources of the Oak Ridge Leadership Computing Facility at the Oak Ridge National Laboratory, which is supported by the Office of Science of the U.S. Department of Energy under Contract No. DE-AC05-00OR22725. Part of the MD simulations was performed at the National Energy Research Scientific Computing Center (NERSC), a DOE Office of Scientific User Facility supported by the DOE Office of Science under Contract DE-AC02-05CH11231. This work used resources of the Advanced Photon Source, a US Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02- 06CH11357. Beamtime for the data collection presented in this paper was allocated under GUP 67311.
| Funders | Funder number |
|---|---|
| DOE Office of Scientific User Facility | |
| US Department of Energy Building Technologies Office | |
| U.S. Department of Energy | |
| Office of Science | DE-AC02-05CH11231 |
| Argonne National Laboratory | DE-AC02- 06CH11357 |
| Bioenergy Technologies Office | DE-AC05-00OR22725 |
Keywords
- Expanded graphite
- Graphene nanoplatelets, molecular dynamics
- Phase change material
- Salt hydrate
- Thermal conductivity