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Title: Thermal charging study of compressed expanded natural graphite/phase change material composites

Abstract

The thermal charging performance of paraffin wax combined with compressed expanded natural graphite foam was studied for different graphite bulk densities. Constant heat fluxes between 0.39 W/cm 2 and 1.55 W/cm 2 were applied, as well as a constant boundary temperature of 60 °C. Thermal charging experiments indicate that, in the design of thermal batteries, thermal conductivity of the composite alone is an insufficient metric to determine the influence of the graphite foam on the thermal energy storage. By dividing the latent heat of the composite by the time to end of melt for each applied boundary condition, the energy storage performance was calculated to show the effects of composite thermal conductivity, graphite bulk density, and latent heat capacity. For the experimental volume, the addition of graphite beyond a graphite bulk density of 100 kg/m 3 showed limited benefit on the energy storage performance due to the decrease in latent heat storage capacity. These experimental results are used to validate a numerical model to predict the time to melt and for future use in the design of heat exchangers with graphite-foam based phase change material composites. As a result, size scale effects are explored parametrically with the validated model.

Authors:
ORCiD logo [1];  [2];  [1]
  1. Georgia Inst. of Technology, Atlanta, GA (United States)
  2. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Building Technologies Research and Integration Center (BTRIC)
Sponsoring Org.:
USDOE Office of Energy Efficiency and Renewable Energy (EERE), Building Technologies Office (EE-5B)
OSTI Identifier:
1324191
Grant/Contract Number:
AC05-00OR22725
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Carbon
Additional Journal Information:
Journal Volume: 109; Journal Issue: C; Journal ID: ISSN 0008-6223
Publisher:
Elsevier
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE

Citation Formats

Mallow, Anne, Abdelaziz, Omar, and Graham, Jr., Samuel. Thermal charging study of compressed expanded natural graphite/phase change material composites. United States: N. p., 2016. Web. doi:10.1016/j.carbon.2016.08.030.
Mallow, Anne, Abdelaziz, Omar, & Graham, Jr., Samuel. Thermal charging study of compressed expanded natural graphite/phase change material composites. United States. doi:10.1016/j.carbon.2016.08.030.
Mallow, Anne, Abdelaziz, Omar, and Graham, Jr., Samuel. 2016. "Thermal charging study of compressed expanded natural graphite/phase change material composites". United States. doi:10.1016/j.carbon.2016.08.030. https://www.osti.gov/servlets/purl/1324191.
@article{osti_1324191,
title = {Thermal charging study of compressed expanded natural graphite/phase change material composites},
author = {Mallow, Anne and Abdelaziz, Omar and Graham, Jr., Samuel},
abstractNote = {The thermal charging performance of paraffin wax combined with compressed expanded natural graphite foam was studied for different graphite bulk densities. Constant heat fluxes between 0.39 W/cm2 and 1.55 W/cm2 were applied, as well as a constant boundary temperature of 60 °C. Thermal charging experiments indicate that, in the design of thermal batteries, thermal conductivity of the composite alone is an insufficient metric to determine the influence of the graphite foam on the thermal energy storage. By dividing the latent heat of the composite by the time to end of melt for each applied boundary condition, the energy storage performance was calculated to show the effects of composite thermal conductivity, graphite bulk density, and latent heat capacity. For the experimental volume, the addition of graphite beyond a graphite bulk density of 100 kg/m3 showed limited benefit on the energy storage performance due to the decrease in latent heat storage capacity. These experimental results are used to validate a numerical model to predict the time to melt and for future use in the design of heat exchangers with graphite-foam based phase change material composites. As a result, size scale effects are explored parametrically with the validated model.},
doi = {10.1016/j.carbon.2016.08.030},
journal = {Carbon},
number = C,
volume = 109,
place = {United States},
year = 2016,
month = 8
}

Journal Article:
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  • The thermal charging performance of phase change materials, specifically paraffin wax, combined with compressed expanded natural graphite foam is studied under constant heat flux and constant temperature conditions. By varying the heat flux between 0.39 W/cm2 and 1.55 W/cm2 or maintaining a boundary temperature of 60 C for four graphite foam bulk densities, the impact on the rate of thermal energy storage is discussed. Thermal charging experiments indicate that thermal conductivity of the composite is an insufficient metric to compare the influence of graphite foam on the rate of thermal energy storage of the PCM composite. By dividing the latentmore » heat of the composite by the time to melt for various boundary conditions and graphite foam bulk densities, it is determined that bulk density selection is dependent on the applied boundary condition. A greater bulk density is advantageous for samples exposed to a constant temperature near the melting temperature as compared to constant heat flux conditions where a lower bulk density is adequate. Furthermore, the anisotropic nature of graphite foam bulk densities greater than 50 kg/m3 is shown to have an insignificant impact on the rate of thermal charging. These experimental results are used to validate a computational model for future use in the design of thermal batteries for waste heat recovery.« less
  • The effects of the surface area density of open-cell aluminum foams on the effective thermal conductivity of aluminum foam-phase change material (PCM) composites were investigated. Paraffin was selected as the PCM. The experimental results show that the effective thermal conductivity increases as the temperature increases. The experimental results suggest that the effective thermal conductivities can be different for different surface area densities of foams even though the relative densities of foams are similar. Therefore, for an accurate estimation of the effective thermal conductivity, a correlation including the surface area density effect is needed.
  • To reduce the energetic dependence of building, it has become necessary to explore and develop new materials promoting energy conservation. Because of their high storage capacity, phase change materials (PCMs) are efficient to store thermal energy. In this paper, a 3D model was studied for simulation of energy storing cycles to predict the performances of PCM loaded panels. Carbon was used as supporting material for the PCM. The simulation was based on the enthalpy method using Ansys Fluent software. The panel was exposed to a daily heat flow including the effects of convection and radiation. The results show that themore » temperature decreased of approximately 2.5°C with a time shift about 2 hours. The steady state was reached after four cycles. Thus, after four cycles the PCM showed its effects on the temperature conditioning.« less
  • Styrene-terminated polysulfone oligomers are part of an oligomeric class of compounds with end groups capable of thermal polymerization. These materials can be used as matrices for graphite reinforced composites. This paper summarizes the authors' initial evaluation of styrene-terminated polysulfone oligomer based composites in terms of fabrication methods, and mechanical and environmental properties. 10 references, 6 figures, 8 tables.