Latent heat storage above 120°C for applications in the industral process heat sector and solar power generation
Tamme, Rainer and Bauer, Thomas and Buschle, Jochen and Laing, Doerte and Müller-Steinhagen, Hans and Steinmann, Wolf-Dieter (2008) Latent heat storage above 120°C for applications in the industral process heat sector and solar power generation. International Journal of Energy Research, 32 (3), pp. 264-271. John Wiley & Sons Ltd. DOI: 10.1002/er.1346. ISSN 0363-907X.
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This paper is focussed on thermal storage technologies using phase change materials (PCMs) in the temperature range of 120-300 °C for solar thermal power generation and high temperature process heat. As state-of-the-art reference system a steam accumulator is described, which typically has a volume-specific thermal energy density of 20-30 kWh/m³. Regarding efficiency, a fundamental demand on thermal storage is the minimization of temperature differences between working fluid and storage medium. This requires isothermal storage systems for processes using water/steam. An obvious solution is, therefore, the application of PCMs. The selection of the PCMs depends strongly on the operation conditions of the respective application. At present, the main emphasis is directed to alkali metal nitrates and nitrites and their mixtures. For example, the eutectic mixture of the binary system KNO3-NaNO3 has been identified as an excellent system to be used for processes using saturated steam at around 25 bar. At around 5 bar the ternary system KNO3-NaNO2-NaNO3, commonly used as heat transfer fluid, can also be used as a PCM. To overcome the low thermal conductivity of the salt systems, approaches of increased surfaces area and increased thermal conductivity using expanded graphite (EG) have been investigated. Using EG/PCM-composites the effective thermal conductivity can be increased from below 0.5 W/(mK) to 3-20 W/(mK). Three design concepts have been developed. In the macro-encapsulated design, the PCM is enclosed in metal tubes, giving a short distance for heat transfer and increasing the heat transfer area. In the second design, the heat exchanger tubes are embedded in EG/PCM-composite storage material. The third design option uses graphite foils arranged perpendicularly onto the heat exchanger tubes and a suitable salt system filled in between. The upgrade of existing steam accumulators using these PCM concepts is also proposed.
|Title:||Latent heat storage above 120°C for applications in the industral process heat sector and solar power generation|
|Journal or Publication Title:||International Journal of Energy Research|
|In ISI Web of Science:||Yes|
|Page Range:||pp. 264-271|
|Publisher:||John Wiley & Sons Ltd|
|Keywords:||Phase Change Materials, Thermal Energy Storage, Steam Storage, Process Heat, Solar Power Generation|
|HGF - Research field:||Energy|
|HGF - Program:||Efficient Energy Conversion|
|HGF - Program Themes:||E EV - Energy process technology|
|DLR - Research area:||Energy|
|DLR - Program:||E EV - Energy process technology|
|DLR - Research theme (Project):||E - Thermochemische Prozesse (old)|
|Institutes and Institutions:||Institute of Technical Thermodynamics > Thermal Process Technology|
|Deposited By:||Dörte Laing|
|Deposited On:||28 Feb 2008|
|Last Modified:||27 Apr 2009 14:05|
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