Abstract
A binary carbonate salt eutectic (Li2CO3-K2CO3)-based nanofluid was in situ synthesized by mixing with a precursor material, aluminum nitrate nonahydrate (Al(NO3)3·9H2O). Thermal decomposition of the precursor was successfully carried out to synthesize alumina (Al2O3) nanoparticles at 1 wt.% concentration. A thermogravimetric analysis (TGA) confirmed a complete thermal decomposition of aluminum nitrate nonahydrate to alumina nanoparticles. A transmission electron microscope (TEM) was employed to confirm the size and shape of the in situ formed nanoparticles; the result showed that they are spherical in shape and the average size was 28.7 nm with a standard deviation of 11.7 nm. Electron dispersive X-ray spectroscopy (EDS) confirmed the observed nanoparticles are alumina nanoparticles. A scanning electron microscope (SEM) was employed to study microstructural changes in the salt. A differential scanning calorimeter (DSC) was employed to study the heat capacity of the in situ synthesized nanofluid. The result showed that the heat capacity was enhanced by 21% at 550 °C in comparison with pure carbonate salt eutectic. About 10–11 °C decrease of the onset melting point of the binary carbonate salt eutectic was observed for the in situ synthesized nanofluids.
Highlights
Molten salts such as nitrate salts, carbonate salts, chloride salts, and their mixtures are known for promising thermal energy storage media at high-temperature applications
Enhancing the heat capacity of molten salts can significantly improve their performance as thermal energy storage because it can reduce the material to store heat and minimize associated heat transfer systems
Since heat capacity enhancements were first reported for carbonate salt-based and chloride salt-based nanofluids in 2011, many studies have reported showing enhanced heat capacity of various molten salt-based nanofluids such as nitrate salts [6], carbonate salts [7], and chloride salts [8]
Summary
Molten salts such as nitrate salts, carbonate salts, chloride salts, and their mixtures are known for promising thermal energy storage media at high-temperature applications. Various synthesis techniques were studied for enhancing the heat capacity of molten salt nanofluids. Lasfargues et al [18] proposed a one-step method using a precursor material to create nanoparticles instead of dispersing commercial nanoparticles This method can reduce potential nanoparticle aggregations by eliminating the evaporation step in the liquid solution method. Alumina (Al2O3) nanoparticles (at 1 wt.% concentration) were in situ synthesized in a binary eutectic mixture of lithium carbonate and potassium carbonate (62:38 by molar ratio) This carbonate salt eutectic is stable up to very high temperatures and reported for their large enhancement in heat capacity after being mixed with nanoparticles [22,23]. A scanning electron microscope (SEM) was used to investigate micro-structural changes in the nanofluids
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