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This work examines formate salts as potential phase change materials (PCMs) for middle-high temperature (≤250 °C) latent heat thermal energy storage applications. The thermophysical properties of three formate salts were characterized: pure sodium formate and binary blends of sodium/potassium formate and sodium/calcium formate. The stability of for...
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... formates followed this same trend. Table 3 lists the measured density of solid and liquid phases for the formate salts near their melting points. Containment and heat exchanger systems must be designed to accommodate the volume of the PCMs liquid phase, as melting the PCM will result in a volumetric increase. ...Similar publications
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... . Solid alkali metal and alkaline earth formates (KOOCH, NaOOCH, Ca(OOCH)2, etc.) are non-toxic, stable, non-corrosive and suitable for safe long-term storage, over many years if necessary38,39 . In terms of energy density, solid formate fuels are comparable volumetrically to 350-bar hydrogen tanks [Supplementary Note 1]. ...
CO2 electroreduction (CO2ER) is a promising route to carbon-neutral production of various chemicals and fuels. Carbon efficiency is one of the most pressing problems for CO2ER today. While there have been studies on anion exchange membrane (AEM) electrolyzers with CO2(gas) and bipolar membrane (BPM) electrolyzers with HCO3–(aq) feedstock, both suffer from significant carbon efficiency loss. In AEM electrolyzers, this is due to carbonate anion crossover, whereas in BPM electrolyzers, the exsolution of CO2(gas) from the bicarbonate solution is the culprit. Here, we first elucidate the root cause of the low carbon efficiency of liquid bicarbonate electrolyzers with thermodynamic calculations, then achieve carbon-efficient CO2ER by adopting a near-neutral-pH cation exchange membrane (CEM) and CO2(gas) partial pressure management, with tin nanoparticle catalysts. We have converted highly concentrated bicarbonate solution to solid formate fuel with a yield (carbon efficiency) of > 96%. The device test was demonstrated at 100 mA cm–2 with a full-cell voltage of 3.1 V for over 100 h. This strategy enables full conversion of HCO3–(aq) feedstock to energy-dense solid formate fuel at ambient pressure and temperature with renewable electricity. Importantly, it can power direct formate fuel cells (DFFCs) which exhibit promising power density for seasonal energy storage.
... In the solid phase, the density value of the powder, obtained after having melted and solidified again the PCM, was around 1.94 g/cm 3 . This value represents an "apparent" behavior; in fact, the stable phase of solid salts presents, as a rule, a higher density than the one in the molten form [44]. ...
Molten salts eutectics are promising candidates as phase change materials (PCMs) for thermal storage applications, especially considering the possibility to store and release heat at high temperatures. Although many compounds have been proposed for this purpose in the scientific literature, very few data are available regarding actual applications. In particular, there is a lack of information concerning thermal storage at temperatures around 600 °C, necessary for the coupling with a highly efficient Rankine cycle powered by concentrated solar power (CSP) plants. In this contest, the present work deals with a thermophysical behavior investigation of a storage heat exchanger containing a cost-effective and safe ternary eutectic, consisting of sodium chloride, potassium chloride, and sodium carbonate. This material was preliminarily and properly selected and characterized to comply with the necessary melting temperature and latent enthalpy. Then, an indirect heat exchanger was considered for the simulation, assuming aluminum capsules to confine the PCM, thus obtaining the maximum possible heat exchange surface and air at 5 bar as heat transfer fluid (HTF). The modelling was carried out setting the inlet and outlet air temperatures at, respectively, 290 °C and 550 °C, obtaining a realistic storage efficiency of around 0.6. Finally, a conservative investment cost was estimated for the storage system, demonstrating a real possible economic benefit in using these types of materials and heat exchange geometries, with the results varying, according to possible manufacturing prices, in a range from 25 to 40 EUR/kWh.
... The heat capacity may be increased by phase change of the heat storage material. In this case, the heat capacity is elevated by the value of latent heat [9][10][11]. In most cases, liquid to solid phase transformation (or vice versa) is used. ...
The paper presents an innovative method for smoothing fluctuations of heat flux, using the thermal energy storage unit (TES Unit) with phase change material and Artificial Neural Networks (ANN) control. The research was carried out on a pilot large-scale installation, of which the main component was the TES Unit with a heat capacity of 500 MJ. The main challenge was to smooth the heat flux fluctuations, resulting from variable heat source operation. For this purpose, a molten salt phase change material was used, for which melting occurs at nearly constant temperature. To enhance the smoothing effect, a classical control system based on PID controllers was supported by ANN. The TES Unit was supplied with steam at a constant temperature and variable mass flow rate, while a discharging side was cooled with water at constant mass flow rate. It was indicated that the operation of the TES Unit in the phase change temperature range allows to smooth the heat flux fluctuations by 56%. The tests have also shown that the application of artificial neural networks increases the smoothing effect by 84%.
