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PCM-Graphite Composites for High Temperature Thermal Energy Storage

Bauer, Thomas and Tamme, Rainer and Christ, Martin and Öttinger, Oswin (2006) PCM-Graphite Composites for High Temperature Thermal Energy Storage. In: Tenth International Conference on Thermal Energy Storage. Ecostock 2006, 2006-05-31 - 2006-06-02, Pomona, NJ (USA).

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Official URL: http://intraweb.stockton.edu/eyos/page.cfm?siteID=82&pageID=29


Latent thermal energy storage systems use the heat absorbed during melting and released during solidification of phase change materials (PCMs). From an energy efficiency point of view, PCM storage systems have the advantage that they operate with a small temperature difference between charging and discharging of the storage. Also, these storage systems have high energy densities compared to sensible heat storages assuming such energy efficient operation. PCMs considered for temperatures between 100 and 300°C are mainly anhydrous salts. Applications include industrial process heat utilisation and solar power generation using direct steam technology. However, there are heat transfer limitations on the storage design due to the low thermal conductivity of the salts. Major approaches to overcome this inadequate heat transfer are the enlargement of the heat exchanger surface or the use of composite latent heat storage materials (CLHSM). This work selects the latter, where the properties of the high latent heat of the PCM and the good thermal conductivity of graphite are combined. As a PCM, this work uses the equimolar composition of potassium nitrate (KNO3) and sodium nitrate (NaNO3) with a melting temperature of about 220°C. There is a variety of potential preparation routes for CLHSM and these processes have a decisive impact on the interconnectivity of the graphite. Generally a highly interconnected graphite matrix is desirable in order to achieve a high effective thermal conductivity. We present in this paper the preparation of CLHSM from graphite and the eutectic KNO3-NaNO3 by the compression and the infiltration route using natural graphite flakes, ground expanded graphite particles and compressed expanded graphite plates. This results in composites with a different level of interconnectivity of the graphite. The composites are characterized in terms of their effective thermal conductivity as a function of temperature using the laser-flash method. The impact of thermal cycling on the effective thermal conductivity, segregation, form stability and expansion of the CLHSM is also discussed. The CLHSM show a considerable enhancement of the thermal conductivity compared with those of the single PCM.

Item URL in elib:https://elib.dlr.de/46656/
Document Type:Conference or Workshop Item (Speech, Paper)
Title:PCM-Graphite Composites for High Temperature Thermal Energy Storage
AuthorsInstitution or Email of AuthorsAuthor's ORCID iD
Date:31 May 2006
Journal or Publication Title:Tenth International Conference on Thermal Energy Storage
Refereed publication:Yes
Open Access:No
Gold Open Access:No
In ISI Web of Science:No
Keywords:storage, thermal, graphite, expanded, salt, nitrate, high temperature, phase change material, PCM, composite, direct steam, KNO3, NaNO3, effective thermal conductivity
Event Title:Ecostock 2006
Event Location:Pomona, NJ (USA)
Event Type:international Conference
Event Dates:2006-05-31 - 2006-06-02
Organizer:Richard Stockton College of New Jersey
HGF - Research field:Energy
HGF - Program:Renewable Energies, Efficient Energy Conversion (old)
HGF - Program Themes:E SF - Solar research (old), E VG - Combustion and Gas Turbine Technologies (old)
DLR - Research area:Energy
DLR - Program:E SF - Solar research, E VG - Combustion and Gas Turbine Technologies
DLR - Research theme (Project):E - Solare Hochtemperatursysteme (old), E - Thermische Energiespeicher (old), E - Wärmetauscher (old)
Location: Stuttgart
Institutes and Institutions:Institute of Engineering Thermodynamics
Deposited By: Bauer, Dr.phil. Thomas
Deposited On:15 May 2007
Last Modified:12 Dec 2013 20:22

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