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Abstract: Conventional phase change materials (PCMs) are already well known for their high thermal capacity and constant working temperature for thermal storage applications. Nevertheless, their low thermal conductivity (around 1Wm−1 K−1) leads to low and decreasing heat storage and discharge powers. Up to now, this major drawback has drastically inhibited their possible applications in industrial or domestic fields. The use of graphite to enhance the thermal conductivity of those materials has been already proposed in the case of paraffin but the corresponding applications are restricted to low-melting temperatures (below 150°C). For many applications, especially for solar concentrated technologies, this temperature range is too low. In the present paper, new composites made of salts or eutectics and graphite flakes, in a melting temperature range of 200–300°C are presented in terms of stability, storage capacity and thermal conductivity. The application of those materials to thermal storage is illustrated through simulated results according to different possible designs. The synergy between the storage composite properties and the interfacial area available for heat transfer with the working fluid is presented and discussed. [Copyright &y& Elsevier]

Selecting a heat transfer fluid (HTF) depends on the value of thermophysical parameters. In response to the need for innovative heat transfer fluids in concentrated solar power (CSP) plants, vegetable oil offers a promising solution. The relevant thermophysical properties are density, thermal conductivity and specific heat capacity. Moreover, a rheological property, the dynamic viscosity is also relevant. The objective of this work was to study and compare these properties for seven different vegetable oils (rapeseed, soybean, sunflower, palm, copra, cotton and jatropha) in the temperature range from ambient to 250 °C. For all the properties studied, the values evolved with increasing temperature and were influenced by the fatty acid composition of each vegetable oil. Experimental results are compared with those in the literature and are found to be consistent. The temperature dependencies are correlated to temperature using polynomial equations. The correlations presented here may be useful as a database for the selection of innovative heat transfer fluids. [ABSTRACT FROM AUTHOR]

Abstract: Alternative low cost materials are evaluated through the valorization of by-products derived from mining and metallurgical industry for solid sensible heat based energy storage systems. They were used either as received or formulated as aggregates in mortars, and their thermal and mechanical properties were characterized. A selection methodology was applied in order to compare them with available materials found in the literature for applications as (STES) materials, and with materials from Cambridge Educational Software (CES) Selector database. It was demonstrated that these recycled materials have a high potential for these thermal energy storage applications. [Copyright &y& Elsevier]

Compatibility tests involving four vegetable oils and three different solid materials were performed, with a focus on rapeseed oil and quartzite rock. The objective was to verify the relevance of using vegetable oils as heat transfer fluid in concentrated solar power plants with direct thermocline thermal energy storage. First tests consisted in using small crucibles to put in contact rapeseed oil respectively with quartzite, blast furnace slags and alumina for 2160 h and at 210 °C. On a chemical point of view, the oil composition was modified by ageing and contact with solids. However, thermal properties that drive heat transfer (density, specific heat, thermal conductivity and dynamic viscosity) were not modified. Thermal stability temperature and flash point decreased and a correlation with the index of acidity of the samples has been found. Second set of tests consisted in putting in contact quartzite with rapeseed, palm, soybean and jatropha oils for 720 h and at 210 °C. Results confirmed that index of acidity can be a good indicator of the vegetable oil ageing. From the whole study, no incompatibility has been concluded, but one may recommend a limit value of 25 mg KOH.g−1 for the index of acidity to consider partial replacement of the vegetable heat transfer. • Compatibility tests involving several vegetables oils and solid materials. • Aging for more than 2000 h of tests performed at temperatures above to 200 °C. • Oils chemical composition and oils thermal properties evolutions. • Definition of a convenient indicator of vegetable oil aging. [ABSTRACT FROM AUTHOR]