Showing papers by "Thomas Bauer published in 2009"

Sodium nitrate for high temperature latent heat storage

Abstract: In this paper the results of material investigations of sodium nitrate (NaNO3) with a melting temperature of 306 °C as a phase change material (PCM) are presented. The thermal stability was examined by long duration oven tests. In these experiments the nitrite formation was monitored. Although some nitrite formation in the melt was detected, results show that the thermal stability of NaNO3 is sufficient for PCM applications. The compatibility of graphite foil and molten NaNO3 was also examined. Results show that the molten NaNO3 oxidizes graphite. Measurements on thermophysical properties of NaNO3 are also reported. These properties include the thermal diffusivity by the laser flash method and the heat capacity by a heat flux differential scanning calorimeter. Reliable temperature dependent thermophysical values of the density, heat capacity, diffusivity and conductivity are identified. Results show that there is a lack of consistent conductivity and diffusivity data in the solid phase.

Advanced high temperature latent heat storage system - design and test results

Abstract: Processes with a two-phase heat transfer fluid (e.g. water/steam) require isothermal energy storage. Latent heat storage systems are an option to fulfil this demand. For high temperature applications nitrate salts are suitable materials for phase change storage. The main drawback of these materials is the low thermal conductivity, limiting the power density during the charging/discharging process. At DLR the so called sandwich-concept has been developed to realize latent heat storage with high power densities for applications in solar thermal power plants and process industry. This concept has already been demonstrated successfully for three different storage units ranging from 2-100 kW at melting temperatures of 142 °C and 222 °C. In 2008, a test storage using sodium nitrate as phase change material (PCM) with a melting temperature of 306 °C was operated in a 5 kW laboratory loop. The designed heat transfer rate was achieved and after 172 cycles no degradation was observed.

Heat Storage Media

Abstract: 1. Introduction 2. Practical Principles for Heat Storage Media 3. Storage of Sensible Heat 3.1. Solid Storage Materials 3.2. Liquid Storage Materials 4. Storage of Latent Heat 4.1. Cold storage (0 °C and below) 4.2. Low temperature storage (0 to 120 °C) 4.3. High-temperature storage (above 120 °C) 4.4. Heat transfer concepts and composites 5. Storage of Chemical Heat 5.1 Thermochemical Transformer and Chemical Heat Pump 5.2 Adsorption Processes 5.3. Absorption Processes

Development of a Thermal Energy Storage System for Parabolic Trough Power Plants With Direct Steam Generation

Abstract: For future parabolic trough plants direct steam generation in the absorber pipes is a promising option for reducing the costs of solar thermal power generation. These new solar thermal power plants require innovative storage concepts, where the two phase heat transfer fluid poses a major challenge. A three-part storage system is proposed where a phase change material (PCM) storage will be deployed for the two-phase evaporation, while concrete storage will be used for storing sensible heat, i.e. for preheating of water and superheating of steam. A pinch analysis helps to recognize interface constraints imposed by the solar field and the power block and describes a way to dimension the latent and sensible components. Laboratory test results of a PCM test module with approx. 140 kg NaNO3, applying the sandwich concept for enhancement of heat transfer, are presented, proving the expected capacity and power density. The concrete storage material for sensible heat was improved to allow the operation up to 500 °C for direct steam generation. A storage system with a total storage capacity of approx. 1 MWh is described, combining a PCM module and a concrete module, which will be tested in 2009 under real steam conditions around 100 bar.

Thermal Energy Storage for Parabolic Trough Power Plants with Direct Steam Generation

Abstract: For future parabolic trough plants direct steam generation in the absorber pipes is a promising option for reducing the costs of solar thermal power generation. These new solar thermal power plants require innovative storage concepts, where the two phase heat transfer fluid poses a major challenge. A three-part storage system is proposed where a phase change material (PCM) storage will be deployed for the two-phase evaporation, while concrete storage will be used for storing sensible heat, i.e. for preheating of water and superheating of steam. A pinch analysis helps to recognize interface constraints imposed by the solar field and the power block and describes a way to dimension the latent and sensible components. Laboratory tests of a PCM test module with approx. 140 kg NaNO3, applying the sandwich concept for enhancement of heat transfer, proved the expected capacity and power density. The concrete storage material for sensible heat was improved to allow the operation up to 500 °C for direct steam generation. A storage system with a total storage capacity of approx. 1 MWh is described, combining a PCM module and a concrete module, which will be tested in 2009 under real steam conditions around 100 bar.

Thermische Speichervorrichtung und Verwendung von Mehrstoffsystemen

Abstract: Es wird eine thermische Speichervorrichtung bereitgestellt, umfassend mindestens ein Speichermedium, welches ein Mehrstoffgemisch ist mit einem Schmelzbereich zwischen der festen Phase des Gemischs und der flussigen Phase des Gemischs, welcher sich uber mindestens 10 K erstreckt.