Folie 1 > PCM-Graphite Composites for High Temperature Thermal Energy Storage > Thomas Bauer PCM-Graphite Composites for High Temperature Thermal Energy Storage Thomas Bauer DLR – German Aerospace Center Institute of Technical Thermodynamics – Stuttgart Co-Authors: Rainer Tamme, DLR; Martin Christ, Oswin Öttinger, SGL Technologies GmbH The Tenth International Conference on Thermal Energy Storage, Atlantic City, 31. May – 2. June 2006
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Folie 1 > PCM-Graphite Composites for High Temperature Thermal Energy Storage > Thomas Bauer
PCM-Graphite Composites for High Temperature Thermal Energy Storage
Thomas BauerDLR – German Aerospace Center
Institute of Technical Thermodynamics – StuttgartCo-Authors: Rainer Tamme, DLR; Martin Christ, Oswin Öttinger, SGL Technologies GmbH
The Tenth International Conference on Thermal Energy Storage, Atlantic City, 31. May – 2. June 2006
Folie 2 > PCM-Graphite Composites for High Temperature Thermal Energy Storage > Thomas Bauer
Contents
Presentation is directed to fundamental aspects and correlation between material properties and manufacturing routes of PCM-graphite compositesPart of the work is funded by the Federal Ministry of Education and Research (BMBF) under contract 03SF0307A-F (LWSNet)
IntroductionCharacterization of alkali nitrate saltsPreparation and characterization of PCM-graphite compositesConclusions
Folie 3 > PCM-Graphite Composites for High Temperature Thermal Energy Storage > Thomas Bauer
Applications for PCM-Graphite Composites
320°C
130°C
High temperature applicationsImproved energy efficiency (Industrial process heat, CHP)Renewable energy (e.g. Solar thermal power)
Low temperature applications (e.g. Comfort Heating)
Folie 4 > PCM-Graphite Composites for High Temperature Thermal Energy Storage > Thomas Bauer
Materials for High Temperature Thermal Storage
Sensible heat storage materials
Phase change materials (PCM)Single or 2-phase heat transfer fluidVirtually isothermal operationHeat transfer limitations
Increased surface areaComposites
Alkali nitrate salts as PCMGraphite to enhance heat transfer
Enth
alpy
Temperature
Folie 5 > PCM-Graphite Composites for High Temperature Thermal Energy Storage > Thomas Bauer
Selected Alkali Nitrate/Nitrites as PCMs
0
50
100
150
200
250
300
350
400
100 150 200 250 300 350Temperature [°C]
Ent
halp
y [J
/g]
KNO3
NaNO3NaNO2
KNO3-NaNO3
LiNO3-NaNO3
KNO3-LiNO3
KNO3-NaNO2-NaNO3
LiNO3
Folie 6 > PCM-Graphite Composites for High Temperature Thermal Energy Storage > Thomas Bauer
KNO3-NaNO3 – Phase Diagram
Experimental DSC data by: Kramer, C.M., Wilson, C.J. (1980) Thermochimica Acta, 42, S. 253-264.
Folie 18 > PCM-Graphite Composites for High Temperature Thermal Energy Storage > Thomas Bauer
Composite made of the infiltrated MatrixSEM Pictures 5wt% graphite, density
of the matrix 0,07 g/cm3Before thermal cycling After 10 thermal cycles
PorosityPorosity
Folie 19 > PCM-Graphite Composites for High Temperature Thermal Energy Storage > Thomas Bauer
Conclusions
PCM storage attractive for 2-phase heat transfer fluid systemsSingle salt properties mostly in agreement with literature values
With PCM-Graphite composites suitable effective thermal conductivities can be achievedSEM and Laserflash examinations indicate thermally stable graphite structure in the composite
Of the investigated manufacturing routes, the infiltration route has the potential of high effective conductivities with a low graphite fractionInfiltration route needs still further R&D to realize composite materials with sufficient PCM content