The development of energy saving technologies is very actual issue of present day. One of perspective directions in developing these technologies is the thermal energy storage in various industry branches. The review considers the modern state of art in investigations and developments of high-temperature phase change materials perspective for storage thermal and a solar energy in the range of temperatures from 120 to 1000 °C. The considerable quantity of mixes and compositions on the basis of fluorides, chlorides, hydroxides, nitrates, carbonates, vanadates, molybdates and other salts, and also metal alloys is given. Thermophysical properties of potential heat storage salt compositions and metal alloys are presented. Compatibility of heat storage materials (HSM) and constructional materials have found its reflection in the present work. Data on long-term characteristics of some HSMs in the course of repeated cycles of fusion and solidification are analyzed. Article considers also other problems which should be solved for creation of commercial high-temperature heat storage devices with use of phase change materials.

High-temperature phase change materials for thermal energy storage

United States. Advanced Research Projects Agency-Energy (Awards DE-AR0000471 and DE-AR0000181)

Concentrating Solar Power.

The growing interest in energy applications of molten salts is justified by several of their properties. Their possibilities of usage as a coolant, heat transfer fluid or heat storage substrate, require thermo-hydrodynamic refined calculations. Many researchers are using simulation techniques, such as Computational Fluid Dynamics (CFD) for their projects or conceptual designs. The aim of this work is providing a review of basic properties (density, viscosity, thermal conductivity and heat capacity) of the most common and referred salt mixtures. After checking data, tabulated and graphical outputs are given in order to offer the most suitable available values to be used as input parameters for other calculations or simulations. The reviewed values show a general scattering in characterization, mainly in thermal properties. This disagreement suggests that, in several cases, new studies must be started (and even new measurement techniques should be developed) to obtain accurate values.

Molten salts database for energy applications

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Assessment of Candidate Molten Salt Coolants for the NGNP/NHI Heat-Transfer Loop

Phase change thermal energy storage (TES) is a promising technology due to the large heat capacity of phase change materials (PCM) during the phase change process and their potential thermal energy storage at nearly constant temperature. Although a considerable amount of research has been conducted on medium and low temperature PCMs in recent years, there has been a lack of a similar systematic and integrated study on high temperature PCMs and high temperature thermal energy storage processes. Analyzing the available literature, this review evaluates the selection principles of PCMs and introduces and compares the available popular material selection software options. The thermophysical property data of high temperature PCMs is comprehensively summarized, including high temperature molten salts and metal alloys. Several heat transfer and performance enhancement techniques are summarized and discussed as potential alternative methods to overcome poor thermal conductivity when using high temperature molten salt as the PCM. The common thermophysical property measurement methods used in literature are also summarized and compared. This review gives a broad overview of material selection, innovation and investigation of thermophysical properties for high temperature PCM development, and will be a helpful reference for the design of high temperature phase change TES systems.

Selection principles and thermophysical properties of high temperature phase change materials for thermal energy storage: A review

The thermal conductivity of some molten salts was measured at atmospheric pressure, using the coaxial cylinder method. The pure compounds NaCO3, KNO3, and NaNO2, the equimolar mixture NaNO3-KNO3, and HITEC, which is a three-component mixture, NaNO3-NaNO2-KNO3 (0.07-0.40-0.53 in weight), were investigated. For mixtures, it was found that the experimental thermal conductivity coefficients are in agreement with calculated values using a simple linear mixing law. The thermal diffusivity was calculated and compared with experimental data.

Experimental determination of the thermal conductivity of molten pure salts and salt mixtures

We report experimental measurements of the critical thermal-conductivity enhancement along the critical isochore for a number of fluids. The data are analyzed in terms of a corresponding-states treatment which can be used as a predictive method to calculate the thermal-conductivity enhancement along the critical isochore for any fluid. The quantities which are needed are the coordinates of the critical point, the slope of the critical isochore, and the viscosity along the critical isochore.

The critical thermal-conductivity enhancement along the critical isochore

New measurements of the thermal conductivity of H2O and D2O have been performed from critical temperature up to 510°C and from atmospheric pressure up to 100 MPA. As these measurements have been made with the same cell, a precise analysis of the isotopic effect as a function of temperature and density is possible. Our analysis is presented in terms of corresponding states. It is shown that the critical thermal conductivity excesses for H2O and D2O reduced by their respective background thermal conductivity terms are represented by single reduced isotherms.

R. Tufeu

Papers

Experimental determination of the thermal conductivity of molten pure salts and salt mixtures

The critical thermal-conductivity enhancement along the critical isochore

Comparison of the thermal conductivities of water and heavy water