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Molten salt is an excellent medium for heat transfer and storage. The unique microstructure of carbon nanomaterials leads to good mechanical stability, low density, high thermal conductivity, and high strength, etc. The addition of carbon nanomaterials to molten salt to form molten salt nanofluid can remarkably enhance the specific heat capacity and thermal conductivity of molten salt and reduce the molten salt viscosity, which is of great importance to increase the heat storage density and reduce the heat storage cost. Nevertheless, some challenges remain in the study of such nanofluids. The main challenge is the dispersion stability of carbon nanomaterials. Therefore, to improve research on carbon nanofluids, this paper summarizes the progress of carbon-based molten salt nanofluid research worldwide including the preparation methods of molten salt nanofluids, the improvement of heat transfer performance, and the improvement of heat storage performance. The effects of carbon nanoparticle concentration, size, and type on the heat transfer and storage performance of molten salt are derived, and the effects of nanoparticle shape on the heat transfer performance of molten salt are analyzed while more promising preparation methods for carbon-based molten salt nanofluids are proposed. In addition, the future problems that need to be solved for high-temperature molten salt-based carbon nanofluids are briefly discussed. [ABSTRACT FROM AUTHOR]

The corrosivity of molten salt can be detrimental to the safe operation and longevity of concentrated solar thermal power generation equipment. Additionally, the presence of impurity Cl− can increase corrosion on metal materials, leading to mechanical property degradation. To assess the extent of this effect, the corrosion behaviour of three types of stainless steel (304, 316L, and 347H) in molten salt at high temperatures was studied using the loss-in-weight method and tensile tests. According to the findings, the Rdepths of 304, 316L, and 347H stainless steels are 0.0018 mm/a, 0.0016 mm/a, and 0.0019 mm/a, respectively, resulting in a decrease in elongation of 12.2%, 7.0%, and 3.7% after 720 h of corrosion at 600°C. Furthermore, at a higher temperature of 680°C, the Rdepths of all stainless steels increased, and the elongation decreased by 25.4%, 18.9%, and 13.5%, respectively. Similar corrosion behaviour was observed in 347H stainless steel with increased chloride ion concentration. However, the yield strength and tensile strength of stainless steel did not exhibit significant changes under different experimental conditions. The corrosion mechanism of metal alloys in molten salt is mainly due to the selective corrosion of Cr and its dissolution into molten salt in the form of ions. [ABSTRACT FROM AUTHOR]

Summary: Dispersing nanomaterials can effectively improve the thermal energy storage performance of molten salts. However, research on such improvement mechanism is still immature, as the understanding of the performance improvement levels induced by different nanoparticles has not been consistent. Using silica nanoparticles as additives, this work prepares nine molten salt nanofluids by aqueous solution method with the use of potassium nitrate, sodium nitrate, and their binary mixture as base salts. The key thermal performance of these nanofluids are evaluated through different characterization approaches, such as differential scanning calorimetry, thermal gravimetric analysis, laser flash analysis, and scanning electron microscopy for microstructural characteristics. The possible performance enhancement mechanism caused by silica nanoparticle is also explored. Results show that, for these nine molten salt nanofluids containing silica nanoparticles, the change in the melting point is negligible. The potassium nitrate salt dispersed with 20‐nm silica nanoparticles achieve the highest performance improvement not only in latent heat but in specific heat and thermal conductivity, while sodium nitrate salt nanofluids reach maximum improvement at their decomposing temperature. The improvement level can be associated with the electronegativity of alkali ions. Cloud nuclei cause microstructure differences among molten salt nanofluids and may be the main reason for the thermal performance enhancement of the molten salt nanofluids. [ABSTRACT FROM AUTHOR]

Summary: Molten salts as thermal energy storage (TES) material have been numerously studied. The annular baffle immersed in single tank can improve the heat discharging performance (HDP) of the TES system. The different annular baffle conditions are experimentally studied in single tank TES system, the working conditions are set as atmospheric pressure, vacuum and filled with solar salt in the annular baffle. The results present that the effective heat discharging time (HDT) of working condition C (filling the solar salt in the annular baffle) and working condition B (the vacuum treatment of the annular baffle) is increased by 21.1% and 6.1%, respectively compared with the working condition A (the atmospheric pressure in the annular baffle). The highest heat discharging efficiency (HDE) is 93.93% obtained by working condition C, while the HDE of working condition B and A is 91.16% and 83.2%, respectively. This research provides a significance guide for the design and application of single tank TES system. [ABSTRACT FROM AUTHOR]

Summary: Molten salts as thermal energy storage (TES) material have been numerously studied. The annular baffle immersed in single tank can improve the heat discharging performance (HDP) of the TES system. The different annular baffle conditions are experimentally studied in single tank TES system, the working conditions are set as atmospheric pressure, vacuum and filled with solar salt in the annular baffle. The results present that the effective heat discharging time (HDT) of working condition C (filling the solar salt in the annular baffle) and working condition B (the vacuum treatment of the annular baffle) is increased by 21.1% and 6.1%, respectively compared with the working condition A (the atmospheric pressure in the annular baffle). The highest heat discharging efficiency (HDE) is 93.93% obtained by working condition C, while the HDE of working condition B and A is 91.16% and 83.2%, respectively. This research provides a significance guide for the design and application of single tank TES system. [ABSTRACT FROM AUTHOR]

Based on a modification of a magnetohydrodynamic turbulence model, a numerical study was performed to investigate the effects of transverse uniform and gradient magnetic field on the turbulent flow and heat transfer characteristics of a low melting point molten salt in a stainless steel pipe. With the Hartmann number from 0 to 80, the numerical results showed that the fluid flow displayed anisotropic distributions under the magnetic field with decrease of velocity in the mainstream region, and decrease of turbulent intensity, whereas the flow velocity increased in the boundary layer near the Hartmann and Roberts wall. Especially, a velocity jet phenomenon was observed in the Roberts boundary layers at higher Hartmann number in the uniform magnetic field or the positive gradient magnetic field. Under the gradient magnetic field, the flow and heat transfer of molten salt displayed much more variations than under the uniform magnetic field. The magnetohydrodynamic calculation results proposed here might be helpful to the design of the composite heat transfer system for molten salt in actual industrial applications. • Both the uniform and non-uniform magnetic field were applied in pipe flow of molten salt for comparison. • A modified MHD turbulence model was established for turbulent flow of molten salt. • The characteristics of flow and heat transfer were numerically studied for a low melting point molten salt. • The complex influence of magnetic field to flow and heat transfer of molten salt was observed. [ABSTRACT FROM AUTHOR]

In order to evaluate the effect of nanoparticles on the specific heat capacity of a low-melting-point eutectic quaternary nitrate salt, 1.0 wt% SiO 2 nanoparticles with an average size of 20 nm was doped into the mixed salt Ca(NO 3 ) 2 ·4H 2 O-KNO 3 -NaNO 3 -LiNO 3 . A mechanical dispersion mixer was developed to prepare molten salt nanofluids. The effects of the mixing time (15, 45, 90, 120, and 150 min) and stirring rate (600, 750, and 1000 rpm) on the specific heat capacity of the nanofluids were analyzed using a differential scanning calorimeter. The results showed that the specific heat capacity of the nanofluids varied with the mixing time and stirring rate. It increased by ~ 17.0% at a mixing time of 15 min and stirring rate of 750 rpm. Microstructural characterization of the molten salt nanocomposites was performed using scanning electron microscopy, which showed that special nanostructures, which resemble chain-like nanostructures, were formed on the surface of the solid nanofluids. The special nanostructures with a large specific surface area and high surface energy could increase the specific heat capacity of the molten salt nanofluids. [ABSTRACT FROM AUTHOR]

Molten salt is an important working fluid in the field of solar energy. However, the mixed convection heat transfer of molten salts has not been investigated. In this study, the performance of the mixed convection heat transfer of molten salt in horizontal square tubes under different side heating conditions is experimentally and numerically examined. The bottom side heating is experimentally studied, and a correlation is fitted on the basis of the experimental data. A good agreement between the correlations and the experimental data is achieved. The experimental results show that the mass flow rate of molten salt and the Reynolds number ( Re ) increase with the increase in the pump frequency. Moreover, the Nusselt number ( Nu ) increases with the increase in Re . The maximum enhancement of Nu in the mixed convection heat transfer compared with the forced convection heat transfer is approximately 50%. The experimental results and previous simulation results of the mixed convection heat transfer of molten salt with bottom surface heating are also compared. The comparison results also show a good agreement. The two-side heating condition (bottom and lateral side) is numerically examined. The simulation results of the two-side heating show that the vortexes caused by the buoyancy effect change the shape of the mainstream core area and strengthen the performance of heat transfer. [ABSTRACT FROM AUTHOR]

This paper reports a fundamental experimental investigation of the start-up characteristics of heat pipes using a dedicated molten-salt mixture as the working fluid. Based on four single salt, i.e. NaNO 3 (AR), KNO 3 (AR), LiNO 3 (AR) and Ca(NO 3 ) 2 (AR), a quaternary molten-salt working fluid was developed and charged at different masses into four heat pipes with the same dimensions of 980 mm in length and 22 mm in diameter. A parallel comparison on the start-up performance of these heat pipes was then conducted to observe the influence of the charging mass and the inclination angle under the consistent lab-controlled conditions. The experimental results showed the heat pipe with molten-salt charge of 40 g responded much quicker than those with molten salt charge of 60 g, 70 g and 80 g respectively; meanwhile, the molten-salt heat pipe achieved the maximum condensation temperature at inclination angle of 50°. Comparing to the conventional naphthalene heat pipe, the dedicated molten-salt heat pipe had a much shorter start-up time when they were charged with the same amount of 40 g. The overall research result is expected to provide certain guidance for further design and operation of molten-salt heat pipe in high-and-medium-temperature heat transfer and storage scenarios. [ABSTRACT FROM AUTHOR]

Nitrate salts have been applied as heat transfer and heat storage medium in the Concentrating Solar Power (CSP) plants. Corrosion is critical to the long-time safe operation of the CSP system. This experimental study was conducted to research the dynamic corrosion behaviors of 316 L stainless steel in high-temperature quaternary nitrate nitrite mixture. The effects of corrosion on 316 L stainless steel were investigated under the varied flow rates of 0.6 m/s, 1.3 m/s and 2 m/s with 565 °C constant temperature for 1000 h. The results showed that oxidation corrosion occurred in 316 L stainless steel at all working conditions. The dynamic corrosion curves were parabolic, and the value corrosion weight loss (m mass) increased with the increase of the flow rate. Meantime, when the products flow rates were 0.6 m/s, 1.3 m/s and 2 m/s, the values of m mass were 3.6 mg cm−2, 3.77 mg cm−2 and 4.36 mg cm−2. The values of corrosion depth (R depths) were 0.039 mm/a, 0.041 mm/a and 0.048 mm/a, respectively. Besides, the corrosion products were consisted of hematite (Fe 2 O 3), magnetite (Fe 3 O 4), trace amounts of MgFe 2 O 4 and NaFeO 2 with the structure of lamellar. Furthermore, the corrosion products gradually transformed into FeCr 2 O 4 with structures of dense and massive, and the increase of the flow rate deepened the degree of corrosion, but it had little effect on the types of corrosion products. • Dynamic corrosion behavior of 316 L steel are experimentally studied in quaternary nitrate-nitrite mixed salt at 565 °C. • The corrosion rates of 316 L steel are obtained at different flow velocities. • The analysis of dynamic corrosion mechanism is comparatively discussed by SEM, XRD and EDS method. [ABSTRACT FROM AUTHOR]

• An experimental setup for free-surface jet impingement heat transfer of molten salt. • A new correlation of stagnation heat transfer with molten salt proposed. • Heat transfer characteristics of molten salt along heat transfer surface obtained. An experimental study of free-surface jet impingement was carried out with compound molten salt to understand its characteristics of heat transfer. Based on pre-experimental verification on the reliability of experimental method by water as working fluid, a compound molten salt was chosen as a new working fluid to conduct experiment of free-surface jet impingement. The heat transfer of molten salt at stagnation point was investigated in detail, and the Nusselt number of molten salt increased with increasing of the Reynolds number and the Prandtl number, and was nearly constant with increasing of nozzle-to-plate spacing at present ranges. The data was correlated by an empirical formula, which was compared with those classical correlations from references. Next, the variation of the Nusselt number of molten salt was also verified along heated surface. It was shown that the local Nusselt number decreased monotonously with increasing of lateral distances from stagnation point, and increased with increasing of the Reynolds number. The profiles of the Nusselt number were nearly unchanged for different nozzle-to-plate spacing, which can be well correlated by a normalized formula. This work focused on the heat transfer characteristics of the molten salt in free-surface jet impingement, which may be recognized as a reference for promoting the application of molten salt in heat transfer process, especially in high temperature situations. [ABSTRACT FROM AUTHOR]