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Title: Development of graphite foam infiltrated with MgCl 2 for a latent heat based thermal energy storage (LHTES) system

Abstract

Thermal energy storage (TES) systems that are compatible with high temperature power cycles for concentrating solar power (CSP) require high temperature media for transporting and storing thermal energy. To that end, TES systems have been proposed based on the latent heat of fusion of the phase change materials (PCMs). However, PCMs have relatively low thermal conductivities. In this paper, use of high-thermal-conductivity graphite foam infiltrated with a PCM (MgCl2) has been investigated as a potential TES system. Graphite foams with two porosities were infiltrated with MgCl2. The infiltrated composites were evaluated for density, heat of fusion, melting/freezing temperatures, and thermal diffusivities. Estimated thermal conductivities of MgCl2/graphite foam composites were significantly higher than those of MgCl2 alone over the measured temperature range. Furthermore, heat of fusion, melting/freezing temperatures, and densities showed comparable values to those of pure MgCl2. Results of this study indicate that MgCl2/graphite foam composites show promise as storage media for a latent heat thermal energy storage system for CSP applications.

Authors:
; ; ; ;
Publication Date:
Research Org.:
Argonne National Lab. (ANL), Argonne, IL (United States)
Sponsoring Org.:
USDOE Office of Energy Efficiency and Renewable Energy (EERE) - Office of Solar Energy Technology (SETO) - SunShot Initiative
OSTI Identifier:
1391670
DOE Contract Number:
AC02-06CH11357
Resource Type:
Journal Article
Resource Relation:
Journal Name: Renewable Energy; Journal Volume: 94; Journal Issue: C
Country of Publication:
United States
Language:
English
Subject:
25 ENERGY STORAGE; 36 MATERIALS SCIENCE; concentrated solar power; infiltration; latent thermal energy storage; phase change material

Citation Formats

Singh, Dileep, Kim, Taeil, Zhao, Weihuan, Yu, Wenhua, and France, David M. Development of graphite foam infiltrated with MgCl 2 for a latent heat based thermal energy storage (LHTES) system. United States: N. p., 2016. Web. doi:10.1016/j.renene.2016.03.090.
Singh, Dileep, Kim, Taeil, Zhao, Weihuan, Yu, Wenhua, & France, David M. Development of graphite foam infiltrated with MgCl 2 for a latent heat based thermal energy storage (LHTES) system. United States. doi:10.1016/j.renene.2016.03.090.
Singh, Dileep, Kim, Taeil, Zhao, Weihuan, Yu, Wenhua, and France, David M. 2016. "Development of graphite foam infiltrated with MgCl 2 for a latent heat based thermal energy storage (LHTES) system". United States. doi:10.1016/j.renene.2016.03.090.
@article{osti_1391670,
title = {Development of graphite foam infiltrated with MgCl 2 for a latent heat based thermal energy storage (LHTES) system},
author = {Singh, Dileep and Kim, Taeil and Zhao, Weihuan and Yu, Wenhua and France, David M.},
abstractNote = {Thermal energy storage (TES) systems that are compatible with high temperature power cycles for concentrating solar power (CSP) require high temperature media for transporting and storing thermal energy. To that end, TES systems have been proposed based on the latent heat of fusion of the phase change materials (PCMs). However, PCMs have relatively low thermal conductivities. In this paper, use of high-thermal-conductivity graphite foam infiltrated with a PCM (MgCl2) has been investigated as a potential TES system. Graphite foams with two porosities were infiltrated with MgCl2. The infiltrated composites were evaluated for density, heat of fusion, melting/freezing temperatures, and thermal diffusivities. Estimated thermal conductivities of MgCl2/graphite foam composites were significantly higher than those of MgCl2 alone over the measured temperature range. Furthermore, heat of fusion, melting/freezing temperatures, and densities showed comparable values to those of pure MgCl2. Results of this study indicate that MgCl2/graphite foam composites show promise as storage media for a latent heat thermal energy storage system for CSP applications.},
doi = {10.1016/j.renene.2016.03.090},
journal = {Renewable Energy},
number = C,
volume = 94,
place = {United States},
year = 2016,
month = 8
}
  • Organic materials, such as paraffin wax, are sought as stable and environmentally friendly phase change materials (PCM) for thermal energy storage, but they suffer from low thermal conductivity which limits the rate at which thermal energy flows into and out of the material. A common method to improve the PCM thermal behavior is through loading with high thermal conductivity particulate fillers. However, the stability of these composites in the molten state is a concern as settling of the fillers will change the effective thermal conductivity. In this work, we investigate the stability of wax loaded with exfoliated graphite nanoplatelets eithermore » of 1 m (xGnP-1) or 15 m (xGnP-15) diameter. The effect of dispersants, oxidation of the wax, viscosity of the wax, mixing time, and hydrocarbon chain length on stability is reported. It was found that the addition of octadecylphosphonic acid (ODPA) is an effective dispersant for xGnP in paraffin and microcrystalline wax. In addition, mixing time, viscosity, and oxidation of the wax influence stability in the molten state. Overall, it was found that a mixing time of 24 hours for xGnP-15 along with ODPA mixed in a high viscosity, oxidized microcrystalline wax results in composite PCM systems with the greatest stability determined at 80 C in the molten state.« less
  • The results of Contract DEN 3-38, Active Heat Exchanger System Development for Latent Heat Thermal Energy Storage Systems are documented. The overall project consisted of five tasks to select, design, fabricate, test and evaluate candidate active heat exchanger modules for future applications to solar and conventional utility power plants. Alternative mechanizations of active heat exchange concepts were analyzed for use with heat of fusion Phase Change Materials (PCMs) in the temperature range of 250 to 350/sup 0/C. Twenty-six heat exchange concepts were reviewed, and eight were selected for detailed assessment. Two candidates were selected for small-scale experimentation: a coated tubemore » and shell heat exchanger and a direct contact reflux boiler. A dilute eutectic mixture of sodium nitrate and sodium hydroxide was selected as the PCM from over 50 candidate inorganic salt mixtures. Using an economic assessment program coupling the candidate salt mixtures and heat exchange concepts, NaNO/sub 3/, NaNO/sub 2/, and NaOH appeared to be the most attractive major components in the temperature range of 250 to 350/sup 0/C. The two active heat exchange concepts selected for test are shown. Experimental results with each concept were disappointing. Results from the Direct Contact Reflux Boiler experiment showed only 60% of the design steam pressure was achieved, and the Shell and Coated Tube Flowby Module experienced salt adhesion on the tube surfaces. Further experimentation is recommended.« less