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A numerical heat transfer analysis of the phase change material (PCM) in a high temperature vertical triplex tube thermal energy storage system (TTTESS) was performed, using ANSYS FLUENT 15.0. The model has been validated against experimental data using a low temperature PCM in a TTTESS. The numerical results agree well with experiment. The validated model was used to analyse a high temperature PCM in a TTTESS. Supercritical CO2 was assumed for the heat transfer fluid (HTF) which flows in the inside and outside tubes, whereas the lithium and potassium carbonate (Li2CO3-K2CO3) (35%-65%) PCM with a melting temperature of 505°C was enclosed between them. This study provides a comprehensive parametric analysis to demonstrate the effect of adding more fins relative to the case of no fins on the melting and solidification processes to find the optimum design of the TTTESS. The TTTESS with eight fins is the design that has substantial performance and is cost competitive compared with two-tank system [ABSTRACT FROM AUTHOR]

In the current study the feasibility of using concentrated solar power (CSP) coupled with thermal energy storage (TES) to displace gas for heating was explored. To assess the feasibility, a numerical model of an air-based encapsulated phase change storage system was developed, validated, optimised, and economically costed. The optimised air-based EPCM system utilised a high and low melting temperature PCM with a sensible filler. It was found that a capsule radius of 10 mm and PCM volume of 13 % resulted in the lowest cost of discharged energy of $25.55/kWht. This system was then coupled to typical meteorological year (TMY) solar data for Adelaide, South Australia, to simulate performance of a 1 MWt heat load over a year. By solving an hourly system generation and demand profile, it was found that the system could provide an economical alternative to gas when the gas price was $20/GJ for a variety of demand profiles. [ABSTRACT FROM AUTHOR]

Lithium sulphate (Li2SO4) was evaluated as a solid-solid PCM material to be coupled with concentrated solar power (CSP) technologies. The energy is stored in a cubic crystalline phase that is formed at temperatures above 576°C and can potentially be discharged at temperatures as low as 150°C, providing both sensible and latent thermal energy storage in a hybrid sensible-latent system. These operational conditions are appropriate for current CSP technologies based on subcritical steam Rankine power cycles. Results from thermal cycling experiments in air showed no change in energy storage capacity after 15 cycles. There was up to a 5% reduction in latent thermal capacity and 0.95% in total thermal capacity after 150 cycles in air. In our paper, we evaluate a hybrid sensible-latent thermal energy storage system based on lithium sulphate from an economic and technical performance point of view, demonstrating its potential as a high temperature thermal energy storage material. [ABSTRACT FROM AUTHOR]

This paper presents the stability and corrosion testing results of a candidate high temperature phase change material (PCM) for potential use in concentrating solar power applications. The investigated PCM is a eutectic mixture of NaCl and Na2CO3 and both are low cost materials. This PCM has a melting temperature of 635℃ and a relatively high latent heat of fusion of 308.1 J/g. The testing was performed by means of an electric furnace subjected to 150 melt-freeze cycles between 600℃ and 650℃. The results showed that this PCM candidate has no obvious decomposition up to 650℃ after 150 cycles and stainless steel 316 potentially can be used as the containment material under the minimized oxygen atmosphere. [ABSTRACT FROM AUTHOR]