A review on the application of liquid metals as heat transfer fluid in Concentrated Solar Power technologies

Among all renewable energy sources Concentrated Solar Power (CSP) systems are considered a technology that will play an important role in future energetic scenarios and that will become economically competitive with conventional fossil fuel power systems. As an example, among the next generation of CSP systems, Solar Central Receiver Systems (CRS) is a technology that is considered to have a high improving potential, especially if rising the operating temperature at about 1000 degrees C in order to increase the efficiency and thus reduce the dimensions of the receiver and the overall costs of the system. In order to achieve these temperatures liquid metals may be proposed to replace conventional fluids, namely water, air and molten salts, as a new generation of heat transfer fluids. Five candidate liquid metals with the best thermophysical properties have been selected among the Alkali, Heavy and Fusible metal groups: molten tin (Sn), gallium (Ga), lithium (Li), sodium (Na) and lead-bismuth (PbBi). The last two already have operational experience within the field of nuclear power engineering, while the other have no operational experience and their thermophysical properties have been calculated only in a limited temperature range. In this work the state of the art has been reviewed and the main critical issues (safety, compatibility with structural materials and integration with CFD software) have been analyzed and discussed. Future work and developments have been outlined, namely the need of extending the calculation of the thermophysical properties at the ideal operating temperature of 1000 degrees C, of further tests regarding the compatibility with structural materials both in dynamic and static conditions and of testing correlations and numerical methods for a better integration into CFD software. Copyright (C) 2016, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.