Determination of optimal compositions and properties for phase change materials in a solar electric generating station

Abstract

Thermal Energy Storage (TES) systems coupled to thermodynamic power cycles capable of generating electrical work are becoming strategic technologies of the future. The efficiency of TES fluids is a function of several thermodynamic and physical properties such as their heat capacity, latent enthalpy of melting and thermal conductivity. The stored thermal energy in these materials can be delivered to heat transfer fluids either by sensible heat or latent heat interactions. Challenges in the design of TES-based technologies are linked to the thermal stability and corrosivity of the selected heat storage fluid that needs to be encapsulated in metallic tubes/containers as well as the heat transfer efficiency. Latent heat storage materials, also known as Phase Change Materials (PCMs) offer high specific heat storage capacity and can operate at a constant temperature if their chemistry is adjusted so that they represent minima on liquidus surfaces. Working at a constant and minimal temperature is highly desirable from an engineering perspective as it limits corrosion degradation and temperature cycling stresses experienced by the container materials. Up to now, the identification of optimal PCMs has been mostly done via experimental trial-and-error based on limited amounts of thermodynamic data. Being able to theoretically identify PCM candidates and fine-tune their thermo-physical behavior would drastically improve their design. We present here an efficient tool specifically developed for the design of PCMs. This tool was used to identify 30 PCM candidates found in high-order anhydrous chloride-based salt systems that can operate at a temperature of 390±10∘ C.