Showing papers by "Thomas Bauer published in 2008"

Latent heat storage above 120°C for applications in the industrial process heat sector and solar power generation

Abstract: 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.

Device and system for storing thermal energy

Abstract: A device is provided for the temporary storage of thermal energy with a solid storage medium and a pipe system made of individual pipes. The pipe system extends through the solid storage medium and an energy transfer medium flows through the pipe system. The solid storage medium and the pipe system being mechanically decoupled from one another.

Screening of phase change materials for process heat applications in the temperature range 120 to 250°C

Abstract: The utilization of solar generated steam in combination with a suitable storage technology could reduce the fossil fuel dependency significantly. Selection of basic storage concepts strongly depends on the working fluid. In systems using steam as a fluid, most of the heat is transferred at nearly constant temperature by evaporation and condensation. As a result, latent heat storage systems using phase change materials (PCMs) are suitable, since this storage concept can also operate at nearly constant temperature. The presented work covers material aspects and gives a comprehensive overview of potential organic and inorganic PCMs in the temperature range 120 to 250°C. Measurements of phase diagrams and latent heats of binary alkali nitrate/nitrite systems, previously not published are reported.

Vorrichtung und Anlage zum Speichern von thermischer Energie

Abstract: Die Erfindung betrifft eine Vorrichtung und Anlage zum Speichern thermischer Energie, z.B. bei solarthermischen Grosanlagen. Die thermische Energie wird dabei in einem monolithischen Betonblock (2) gespeichert. Hierzu verlauft eingebettet in diesem Block ein Rohrsystem, durch das eine warmeubertragende Flussigkeit fliest und das dadurch erlaubt, den Speicher mit thermischer Energie zu be- und entladen. Erfindungsgemas sind das Rohrsystem und der umgebende Betonblock mechanisch entkoppelt. Bevorzugt geschieht dies ohne grose Beeintrachtigung des Warmeuberganges zwischen Beton und Rohr (6) durch eine dunnschichtige Umhullung der Rohre mit Graphit.

Thermal storage device and use of multiple material systems

Abstract: The invention relates to a thermal storage device comprising at least one storage medium comprising a multiple material mixture and having a molten range between the solid phase of the mixture and the fluid phase of the mixture extending over at least 10 K.