Analysis of application of liquid metal coolants as heat transfer fluid for concentrated solar power systems

Abstract

In the near future renewable energy sources should play an important role in reaching economic competitiveness with fossil fuel for a change in the global energetic scenario in view of the fight against climate change. Concentrated Solar Power (CSP) is into the portfolio of renewable technologies that are called to have a significant contribution to that future sustainable scenario. Nowadays, its economic competitiveness has a high improving potential due to technological development and scale factors that should be confirmed during the next decades. For reaching economic competitiveness with fossil fuel based systems and other power technologies, next-generation CSP must increase their operating temperatures and their receiver efficiencies by the substitution of conventional heat transfer fluids (HTFs) with more efficient ones. A more efficient HTF would make possible to enhance the heat transfer process by allowing higher heat flux densities while reducing the thermal losses, a fact which leads to a reduction of the dimensions of the receiver and consequently a reduction in the overall costs of the system. The HTFs which are going to be employed in the next-generation of CSP systems might be based on molten salts and liquid metals. The aim of this work is to focus on the employment of liquid metals as HTF in CSP technologies. For this purpose liquid metal candidates have been chosen by their thermo-physical properties among three main groups: Alkali metals, Heavy metals and Fusible metals. Among these candidates some of them already had operational experience as coolants in other power plants as nuclear power reactors, namely sodium and lead-bismuth, while the others have never been tested in practice. The purpose of this work is to analyse the potential performance of liquid metals as HTF, and the proposal to compare the performance of solar receivers with various coolant candidates. Computational Fluid Dynamics (CFD) tools may be applied to evaluate such performance describing the thermal and fluid-mechanic singularities of each fluid. In addition, the limitation of those tools into its application to low Prandtl HTFs, in which the common Reynolds Analogy is not valid, suggests the utilization of high configurable codes that could be customized to describe accurately heat transfer mechanisms.