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Melting in a finite slab with a second kind boundary condition is studied numerically in order to simulate the charging process of a thermal energy storage system. A dimensionless model is given, from which it is concluded that the main factors that influence the melting process are the dimensionless heating flux, the modified Stefan number, the relative thermal diffusivity and the relative thermal conductivity. The influence of preheating or solid subcooling is studied. It is found that though preheating does not have very important effects on the melting time, it does influence the interface marching velocity significantly. The melt fraction and the melting time are calculated extensively for various dimensionless numbers. The numerical results show that the ratio of the thermal conductivity of the solid to that of the liquid has little effect on the melting time, and the time for finishing melting can be expressed as a function of the dimensionless heating flux, the modified Stefan number and the relative thermal diffusivity, and the possible function form is suggested. [Copyright &y& Elsevier]

Based on the single-screw compressor (SSC) structure, a new type of composite slide valve (CSV) has been proposed and designed, featuring internal volume ratios of 2.8, 3.9, and 5.6 and operating under a partial load of 35%. The theoretical model describing the dynamic features and thermodynamic performance of the SSC with CSV has also been built. The pressure ratio of the experimental system can be adjusted from 3.3 to 7.8, and the experimental results demonstrate the CSV's effective performance. The deviations between the calculated and measured results for volume ratio and input power are 3.33–9.08% and 0.32–8.03%, and the deviations for heating capacity and adiabatic efficiency range from 0.92–8.73% to 2.09–9.67%, respectively. The introduction of the CSV offers a novel approach to enhancing SSC efficiency. Both the theoretical and experimental findings lay a foundation for future optimization and design improvements in variable load and internal volumetric ratio single-screw compressors. [ABSTRACT FROM AUTHOR]

• Single screw expanders (SSE) can achieve 92.7% volumetric efficiency. • The effect of oil with six viscosities on the performance of SSE was studied. • This research investigates the effect of lubrication oil on irreversible loss. • This research analyzes the optimum operating conditions of lubrication oil. • The maximum increment of shaft power reached 26% in the experiment. A single screw expander (SSE) is a small to medium-sized volumetric expander of high performance, which can be used for energy recovery in vapor compression refrigeration (VCR) systems and expansion refrigeration in air compression refrigeration (ACR) systems. As an energy recovery device, expander operation improvement is helpful to improve the efficiency of the system. The expander, however, suffers from gas leakage losses and friction losses due to the viscosity of lubrication oil, where greater viscosity results in lesser gas leakage and more viscous friction. This study undertook an experiment to investigate six different viscosity lubrication oils (oil viscosity type from small to large: 10#, 22#, 32#, 46#, 68#, and 80#) under different inlet pressures (0.5–1.1 MPa) for clarifying the influence of lubrication oil viscosity on the operation of SSE. The results showed that increasing the kinematic viscosity of the lubrication oil could reduce leakage loss, which results in a maximum increment of volumetric efficiency of 23.06%, and with the use of 68# and 80# lubrication oils, volumetric efficiency was the highest at 92.7%. In contrast, reducing the kinematic viscosity of the lubrication oil could improve the shaft power. The maximum difference in shaft power between 10# and 80# lubrication oil was greater than 26%. The SSE had a superior shaft efficiency and a lower gas consumption rate by using 10# lubrication oil at an inlet pressure <0.55 MPa, 46# lubrication oil at an inlet pressure of 0.55–0.9 MPa, and 80# lubrication oil at an inlet pressure of 0.9–1.1 MPa. [ABSTRACT FROM AUTHOR]

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]

Vapor compression refrigeration is considered as ideal miniature cooling system for miniature electronic systems and portable cooling systems. Many applications of the miniature refrigeration system are working under the situations (such as aviation field, individual combat system and automobile air conditioning, etc.) that exist bump, tilt, and even flip, which will severely degrade the performance of the miniature refrigeration system. In order to study the influence of compressor's tilt angle on refrigeration system, a test bench was built and the performance experiments were made. The results show that the compressor's tilt angle has a great impact on the refrigeration system performance. When the compressor worked at the maximum tilt angle of 60°, COP-c and COP-h of the system change periodically. When the compressor works in full load, the maximum tilt angle for compressor is 20°. When the compressor tilt angle is 15°, there is an optimal amount of refrigerant charge, and corresponding COP-c and COP-h reach the maximum of 2.9 and 3.9, respectively. [ABSTRACT FROM AUTHOR]

In this paper, a prediction model for the crystallization fouling was proposed on the basis of the Kern-Seaton model for the heat transfer and fouling process in circulated cooling water. The fouling deposition and removal process were analyzed, respectively, for the fouling process, on which the coupling effects of the scale layer, temperature and ions concentration were considered. The model calculation may predict the fouling resistance variations in fouling process, which were in good agreement with experimental data from references within a range of given conditions especially for the turbulent flow, indicating the model applicability for actual process. Since the model can be used without requirement of a large amount of measured data for fitting, it gives a more convenient way for predicting fouling process of heat exchangers in industry. • A prediction model for CaCO 3 crystallization fouling in circulating cooling water was established. • The fouling deposition and removal processes were all analyzed in the model respectively. • The coupling effects of fouling layer, temperature and concentration of fouling ions were considered. • The calculation of model may provide a fouling prediction without requirement of a number of experimental data for fitting. [ABSTRACT FROM AUTHOR]

An experimental study was carried out to examine the antifouling effect of compound treatment with ultrasonic and magnetic fields simultaneously in convection heat transfer process. The ultrasonic was provided with a frequency of 20 kHz and powers up to 240 W, and the magnetic field was applied with field intensity of 0.25 T and 0.4 T, respectively. The results showed that the ultrasonic treatment presented a good antifouling effect in flow and heat transfer of hard water, and further the combined treatment of the ultrasonic and magnetic displayed much better performance in scale inhibition of convection heat transfer, in which the scale-inhibition efficiency got up to a maximum of 93.9%. The water treatment not only presented the good scale-inhibition effect but also had the morphology of fouling crystal changed. The crystal of calcium carbonate was mainly comprised of the dense calcite with a cubic shape for the case untreated but transformed to the slender aragonite branchlike after the treatment, and the aragonite became longer with the compound treatment. The experimental phenomenon was also discussed for understanding of the mechanism of the technical treatment, which may be referenced to the antifouling application in heat exchanger. [ABSTRACT FROM AUTHOR]

The performance of a heat exchanger is directly related to the energy conversion efficiency of the thermal storage system, and its optimal design is an important method to improve the performance of the heat exchanger. This paper uses the distributed parameter method to analyze the effect of the structural parameters and operating parameters of a heat exchanger on the entransy dissipation rate, the entransy dissipation number, the entransy dissipation heat resistance, entropy production rate, and entropy production number in a molten salt–supercritical CO2 concentric tube heat exchanger. The results show that the entransy dissipation rate and entropy production rate have the same trend, with the structural parameters and operating parameters, as well as the changes in the entransy dissipation number and entransy dissipation thermal resistance, jointly affected by the entransy dissipation rate and the heat exchange. Based on the above indicators, single-objective and multi-objective optimization calculations were carried out. The results show that taking the minimum entropy dissipation number, entransy dissipation heat resistance, and improved entropy production number as the objective functions, and using the heat transfer effectiveness as the evaluation index, the optimization effect is better. The ε value is increased by 41.2%, 39.5%, and 40.3% compared with the reference individual. In the multi-objective optimization, taking the minimum number of entransy dissipation and entropy production as the objective function, and using the efficiency of heat transfer and the pressure drop of the working fluid as the evaluation indicators, the optimization effect is better. Compared with the reference individual, the ε value increased by 23.5%, and Δ P h and Δ P c decreased by 51.9% and 32.5%, respectively. This study provides a reference for the optimization of supercritical CO2 heat exchangers by utilizing parameters such as entransy and entropy, which reflect the irreversible loss of the heat transfer process. [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]

An experimental study on the antifouling performance of ultrasonic and/or electronic treatment was carried out in a convective heat transfer process by using a fouling monitor system. An ultrasonic device was used in a frequency of 28 kHz and a power of 80 W, and a low-voltage electronic processor also used with a maximum current of 0.8 A for water treatment. The experimental results showed that both of the ultrasonic and the electronic treatment, all displayed good scale-inhibition effects for hard water in convective heat transfer, and further the compound treatment of them gave much better antifouling performance at the same conditions. The fouling inhibition efficiency got up to a maximum of 100% by the treatments. The technical treatment may change not only the amount of deposition on heat transfer surface, but also the morphology of crystals formed in microscale. The fouling crystal displayed a clear type of aragonite of calcium carbonate but varied obviously with the treatments. It can be sure that the technical treatments are effective and applicable in real heat transfer application with hard water as a working fluid. [ABSTRACT FROM AUTHOR]

An innovative physical method to control fouling in heat transfer equipment—low voltage electrolysis anti-fouling (LVEAF) technology—is introduced. The objective of the present study is to testify the effect of LVEAF treatment in forced convective system and identify the operating mechanism. A series of fouling tests were carried out with and without LVEAF treatment. During the experiments fouling resistance was monitored, and the properties of test liquid were measured, including hardness, alkalinity, electrical conductivity, and pH. The main results were as follows: (1) The fouling was effectively restrained to form on the heat exchanger surface if the circulating water was treated with LVEAF. The scale inhibition ratios exceeded 90% in most cases. (2) The LVEAF technology is an active anti-fouling technology with lower energy consumption. The properties of treated test liquid were changed. (3) Electrochemical reactions occur near the electrode due to the low current existence in the water when the LVEAF device is working. A lot of fouling deposits formed in the test liquid near the cathode or on the inner surface of the treatment unit, but did not deposit on the heat exchanger surface. [ABSTRACT FROM AUTHOR]

Abstract: Knowledge of the temperature distribution on the membrane electrode assembly (MEA) surface and heat transfer processes inside a proton exchange membrane fuel cell (PEMFC) is helpful to improvement of cell reliability, durability and performance. The temperature fields on the surface of MEA fixed inside a proton exchange membrane fuel cell with a serpentine channel flow bed were measured by infrared imaging technology under non-humidification conditions. The temperature distributions over the MEA surface under whole channel region were achieved. The experimental results show that the downstream temperatures are higher than the upstream. The hot region on the MEA surface is easy to locate from the infrared temperature image. The mean temperature on the MEA surface and the cell temperature both increase with the current density. Higher current density makes the non-uniformity of temperature distribution on the MEA surface worse. The loading time significantly affects the temperature distribution. Compared with the electrical performance of the cell, the MEA''s temperatures need much more time to reach stable. The results indicate that isothermal assumption is not appropriate for a modeling of PEMFCs, and monitoring the temperature of external surface of the flow field plate or end plate cannot supply accurate reference to control the temperatures on MEA surface. [Copyright &y& Elsevier]

Abstract: The water flooding and two-phase flow of reactants and products in cathode flow channels (0.8mm in width, 1.0mm in depth) were studied by means of transparent proton exchange membrane fuel cells. Three transparent proton exchange membrane fuel cells with different flow fields including parallel flow field, interdigitated flow field and cascade flow field were used. The effects of flow field, cell temperature, cathode gas flow rate and operation time on water build-up and cell performance were studied, respectively. Experimental results indicate that the liquid water columns accumulating in the cathode flow channels can reduce the effective electrochemical reaction area; it makes mass transfer limitation resulting in the cell performance loss. The water in flow channels at high temperature is much less than that at low temperature. When the water flooding appears, increasing cathode flow rate can remove excess water and lead to good cell performance. The water and gas transfer can be enhanced and the water removal is easier in the interdigitated channels and cascade channels than in the parallel channels. The cell performances of the fuel cells that installed interdigitated flow field or cascade flow field are better than that installed with parallel flow field. The images of liquid water in the cathode channels at different operating time were recorded. The evolution of liquid water removing out of channels was also recorded by high-speed video. [Copyright &y& Elsevier]

Abstract: A new thermal storage system, a heat pipe heat exchanger with latent heat storage, is reported. The new system may operate in three basic different operation modes, the charging only, the discharging only and the simultaneous charging/discharging modes, which makes the system suitable for various time and/or weather dependent energy systems. In this part of the paper, the basic structure, the working principle and the design concept are briefly introduced. Extensive experimental results are presented of the charging only and discharging only operations, and the effects of the inlet temperature and the flow rate of the cold/hot water were also investigated. The results show that the heat exchanger performs the designed functions very well and can both store and release the thermal energy efficiently. [Copyright &y& Elsevier]

Abstract: In this part of the paper, the performance of the simultaneous charging/discharging operation modes of the heat pipe heat exchanger with latent heat storage is experimentally studied. The experimental results show that the device may operate under either the fluid to fluid heat transfer with charging heat to the phase change material (PCM) or the fluid to fluid heat transfer with discharging heat from the PCM modes according to the initial temperature of the PCM. The melting/solidification curves, the performances of the heat pipes and the device, the influences of the inlet temperature and the mass flow rate of the cold water on the operation performance are investigated by extensive experiments. The experimental results also disclose that under the simultaneous charging/discharging operation mode, although the heat transfer from the hot water directly to the cold water may vary, it always takes up a major part of the total heat recovered by the cold water due to the very small thermal resistance compared with the thermal resistance of the PCM side. The melting/solidification processes taking place in the simultaneous charging/discharging operation are compared with those in the charging only and discharging only processes. By applying a simplified thermal resistance analysis, a criterion for predicting the exact operation modes was derived and used to explain the observed experimental phenomena. [Copyright &y& Elsevier]

Abstract: An experimental rig was set up to study the performance of a thermal storage unit using stearic acid as the heat storage medium. The unit mainly consists of an electrical heating rod and an outer tube, and the space between is an annulus that is filled with stearic acid. The thermal performance of the unit is measured, and the heat transfer characteristics of the melting processes of stearic acid are studied under different heat flux conditions to determine the influence of heat flux on the melting processes. A new type of fin is designed and fixed to the electrical heating rod to enhance the thermal response of the stearic acid. The experimental results show that the fin can improve the heat transfer of the melting process of the thermal storage unit greatly. The equivalent thermal conductivity of the PCM can be augmented by a factor up to 3. The analysis of the experimental results shows that the enhancement mechanism of the fin is attributed to its ability to improve both heat conduction and natural convection very effectively. The influences of the fin size and pitch on the enhancement are also studied and analyzed and it is found that these two parameters can both affect the thermal conductivity enhancement significantly. [Copyright &y& Elsevier]

Abstract: The thermal and heat transfer characteristics of stearic acid during the solidification processes were investigated experimentally in a vertical annulus energy storage system. The temperature distribution and temperature variations with time at different radial positions during the freezing processes were obtained. The thermal characteristics of the stearic acid, including movement of the solid–liquid interface in the radial direction, and the effects of Reynolds number on the heat transfer parameters were studied. The heat flux was estimated by using a simple approximate model. A new copper fin was designed and fixed to the electrical heating rod to enhance the thermal conductivity of the stearic acid. The results show that the new fin can enhance both the conduction and the natural convection heat transfer of the PCM, and the enhancement factor during solidification is estimated to be as high as 250%. The effect of the fin width on the enhancement was also examined experimentally, and it is found that the fine fin usually produce more effective enhancement. [Copyright &y& Elsevier]

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]

Summary: The single thermal energy storage tank (STEST) has been extensively investigated because of the advantage of cost and efficiency. This research presents heat discharging performance of STEST using coil heat exchanger (CHE) with annular baffle at different working conditions. The heat discharging performance, flow field and temperature distribution of different parameters of the annular baffle are presented and discussed. The results show that the heat discharging time decreases with an increase inlet air velocity of the CHE. The heat discharging efficiency is up to 95.7% in this study, and the heat discharging time can reach to 18.7 hours. In addition, optimal dimensionless diameters of annular baffle are Db/Dt = 0.6, Hs/Ht = 0.075 and Hx/Ht = 0.050 (Hs is the height from the top of baffle to the top of tank. Ht is the height of the tank. Hx is the height from bottom of the baffle to the bottom of the tank). The efficiency of heat discharging process can be enhanced with optimal dimensions of the annular baffle. This study presents a direct practicable guide to design the STEST. [ABSTRACT FROM AUTHOR]

Summary: Specific heat and thermal conductivity are important thermal properties of high‐temperature heat transfer fluids and thermal storage materials for supercritical solar power plants. In the present work, nanofluids composed of ternary carbonate Li2CO3‐K2CO3‐Na2CO3 (4:4:2, mass ratio) and 1.0 wt.% carbon nanotubes (CNT) were prepared to obtain high‐temperature heat transfer and storage media with enhanced specific heat and thermal conductivity. The dispersion of CNTs in the nanofluids was tuned by changing the evaporation temperature (100, 140, 180 and 220 °C) and adding surfactants such as sodium dodecyl benzene sulfonate (SDBS), sodium dodecyl sulfate (SDS), or gum Arabic (GA). The results showed that GA and SDS facilitate good dispersion of CNT in nanofluids at the evaporation temperatures of 140 °C and 180 °C, resulting in the formation of more needle‐like nanostructures. The higher increase in the specific heat and thermal conductivity of the nanofluids with SDS at 500 °C was 78.3% and 149.2%, respectively. Additionally, the specific heat of as‐prepared ternary carbonate nanofluids exhibits a good thermal stability after 30 cycles of thermal shock experiments. [ABSTRACT FROM AUTHOR]

To recover pressure energy effectively during the gas pressure regulation, innovatively, this work proposed a sole expander for gas pressure regulation and energy recovery: By detecting the outlet gas pressure, the PID controller to control the speed of the expander through the magnetic brake, which adjusts the gas flow, and the outlet gas pressure of the expander reaches stable in this way. By establishing an experimental platform, the pressure regulation and energy recovery performance was investigated in detail. Results showed that three PID parameters P , I and D exerted different influence on pressure regulation, and an optimal pressure regulation accuracy of 1.0% was observed at the optimal PID parameters (P = 15%, I = 50 and D = 2). The gas flow has a certain influence on the pressure regulation while the target pressure has no obvious impact on pressure regulation. The pressure regulation accuracy at maximum flow and minimum flow is limited to the allowable speed and inter leakage of expander. The output power was influenced greatly by gas flow, and a maximum output power 145 W was obtained. The method proposed in this work is proved to be feasible and reliable and has good prospect in gas pressure regulation and energy recovery area. • Proposed a method for pressure regulation and energy recovery by a sole expander. • Investigated operation and control performance under variable working conditions. • PID algorithm for pressure regulation is feasible and reliable. • Achieved a pressure regulation accuracy of 1.0% by a sole vane expander. • Achieved a maximum output power of 146.7 Wat during the pressure regulation. [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]

Molten salt is one of the most promising heat transfer and thermal energy storage medium for the third-generation solar thermal power generation, and the spiral-wound tube heat exchanger can improve the heat transfer performance of molten salt. In this paper, the flow and heat transfer characteristics of molten salt nanofluids in spiral-wound tubes are experimentally and numerically studied. Molten salt nanofluids and synthetic oil as the heat transfer fluids, the heat transfer performance of them in the spiral-wound tube heat exchanger were studied. The Wilson separation method was used to process the experimental data, and the heat transfer correlation of molten salt nanofluids is obtained through experiments. The heat transfer correlation can be in good agreement with the experimental data, the heat transfer correlation on the molten salt nanofluids side is N u = 0.3897 R e 0.4370 Pr 1 / 3 , Re = 4296–8348, Pr = 13–23, and the maximum error is 17.9%. A three-dimensional model of the spiral-wound tube heat exchanger is used to explore the distribution of the pressure, temperature and velocity fields of the molten salt nanofluids. The friction factor correlation on the molten salt nanofluids side is f = 4.6729 R e − 0.4855 , Re = 3536–17684, Pr = 13–23 and the maximum error is 12.65%. The heat transfer correlation and resistance correlation of molten salt nanofluids obtained in this paper can contribute to the design of heat exchanger for the third-generation solar thermal power. [ABSTRACT FROM AUTHOR]

• Binary nitrate molten salt nanofluids were prepared and developed. • Specific heat of the binary nitrate can be enhanced by adding SiO 2 nanoparticles. • Specific heat of molten salt nanofluid with mass fraction of 1% is the highest. • Optimal size of nanoparticles to improve the specific heat is 20 nm. • Thermophysical properties of the binary nitrate molten salt nanofluids is good. Molten salts, good heat transfer and thermal storage media, show potential for various applications, particularly solar thermal power. Nanofluid technology has been applied to molten salts to improve specific heat. In this study, molten salt nanofluids with a base solution of binary molten salt and SiO 2 nanoparticles were prepared through high-temperature melting. The specific heat of the molten salt nanofluids was examined with different diameters and mass fractions of nanoparticles, and their optimal diameter and mass fraction were determined. The thermophysical properties of the optimized molten salt nanofluids were experimentally tested and compared with those of pure molten salt. Results reveal that the specific heat of the molten salt nanofluids is higher than that of the pure molten salt. The optimal mass fraction and size of SiO 2 nanoparticles at the improved specific heat of the molten salt nanofluids are 1% and 20 nm, respectively. The optimal specific heat of the molten salt nanofluids is 17.8% more than that of the pure molten salt. The density of the optimized molten salt nanofluids is similar to that of the pure molten salt, and the average thermal conductivity is 20.2% more than that of the pure molten salt. [ABSTRACT FROM AUTHOR]

Highlights • Nano-bromides were examined for heat pipes in concentrated solar power plants. • Heat of fusion and decomposing point were improved by 99.19% and 68.4 °C respectively. • Inapparent effect on melting point was observed. • Interaction between nanoparticle and salt molecule account for the enhancement. • Dense dendritic-like structure networks were observed by microstructure analysis. Abstract Thermal performance of molten salts can be enhanced by nanostructured materials, which can enhance the heat transfer capacity of heat pipes and further improve the global efficiency of Concentrated Solar Power plants. In this work, a eutectic mixture of sodium bromide, potassium bromide, lithium bromide and calcium bromide acted as the base salt, into which nine SiO 2 nanoparticles in three diameters were dispersed to form twenty-two nano-bromides in total. The thermodynamic properties of the base salt and nano-bromides, e.g. the thermal stability and the phase change performance were investigated experimentally and analytically. It was observed that the size and the mass concentration of the SiO 2 nanoparticles exhibited significant influence on the heat of fusion and the decomposing temperature but little on the melting point. By adding 0.7 wt% of 10 nm SiO 2 particles, the heat of fusion and the decomposing point of the base salt were increased by maximum 99.19% and 68.4 °C respectively. In addition, densely dendritic-like networks were observed with Scanning Electron Microscopy in the nano-bromides and considered to be responsible for the improvement of the heat of fusion and the decomposing point. The authors believed these findings would contribute to enhance the heat transfer performance of heat pipes furtherly. [ABSTRACT FROM AUTHOR]

To analyze the natural convection heat transfer of molten salt nanofluids around vertical array of horizontal cylinders, a numerical simulation is performed with cylinder numbers in the range of N = 2-8 and pitches in the range of S/D = 5-10. The results show that the heat transfer of nanofluids around each cylinder is affected by the position in the tube row and its distance from the adjacent cylinder. The average Nusselt number (Nua) of the natural convection heat transfer over the whole array of cylinders is determined by cylinder spacing S/D, cylinder number N, and Ra. When S/D = 5, Nua decreases as the cylinder number increases. When S/D = 10, Nua increases as the cylinder number increases. Compared with the molten salts, the natural convection heat transfer of nanofluids is enhanced. This study provides a theoretical basis for the design of a single-tank energy storage system. [ABSTRACT FROM AUTHOR]

In order to investigate the heat transfer characteristics of mixed molten salt, an experimental setup for the submerged jet impingement has been established in this paper. Firstly, an experimental investigation on heat transfer of submerged jet impingement with water as working fluid was carried out to verify reliability of experimental method. A good consistence was found between experimental results and those classical correlations from references for stagnation heat transfer, which indicate the reliability and accuracy of experimental method. On the basic of ensuring the reliability of experiment, a series of studies on jet impingement experiments were carried out with new mixed molten salt. The results indicated that effect of submerged jet impingement heat transfer enhanced gradually with the increase Reynolds number and the heat transfer characteristics at the stagnation are analogous with the water in the scope of experimental investigations. Further, a correlation about quaternary mixed molten salt was proposed based on experimental data. At same Reynolds number, the Nusselt number of mixed molten salt is obviously higher than that of water at stagnation zone because of its higher Prandtl number and becomes lower than water at larger radial distance due to its higher viscosity. The results indicated that thermophysical properties of working fluid have an enormous influence on the Heat transfer performance. The experimental results in this paper provide a necessary technical guarantee for the study of heat transfer of the high temperature fluid. [ABSTRACT FROM AUTHOR]

A single-screw expander (SSE) is a type of volumetric expander that can be applied to low-grade heat and waste heat recovery utilizing the organic Rankine cycle system. In this paper, a new thermodynamic modeling of SSEs considering the friction power consumption is carried out to examine the performance. The mathematical model was verified by experimental results, and the calculation results have a good agreement with the experimental results. The clearance height has great influence on the expander performance. The influence of clearance height on the leakage flow rate, friction power consumption, volumetric and isentropic efficiency were investigated. Results show that path L 8 , L 7 and L 2+4 are the three main leakage paths, and path L 8 , L 7 and L 9 are the three main friction power consumption. Compared with the meshing clearance height, the fitting clearance has a more significant effect on the performance of SSEs. Setting a higher fitting clearance and meshing clearance is an effective measure to reduce friction power consumption and prevent gaterotor wear, respectively. It would be favorable if the fitting and meshing clearance height is no less than 0.04 mm and 0.02 mm, respectively. [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]

To recover high pressure energy in a letdown station, a high pressure single screw expander (HPSSE) with 117 mm diameter is developed in our laboratory recently. This study presents the results of an experimental survey on the performance of HPSSE under varied inlet pressure and rotational speed. The inlet pressure of HPSSE ranges from 1.0 MPa to 5.0 MPa and the rotational speed is from 1500 rpm to 3000 rpm. The experimental results show that when the inlet pressure is 5.0 MPa, the maximum power output, volumetric efficiency, isentropic efficiency and shaft efficiency of HPSSE are 56.55 kW, 80.57%, 62.55% and 50.96%, respectively. The volumetric efficiency is immensely affected by inlet pressure under fairly slow rotational speed and a slight change in volumetric efficiency is observed under considerably high rotational speed. A high rotational speed is an effective method to reduce leakage in large pressure difference working conditions. [ABSTRACT FROM AUTHOR]

A single-screw expander (SSE) is a type of volumetric expander that can be applied to power generation, which is beneficial for energy conservation and environment protection. Investigating the SSE leakage characteristics is necessary because leakage has a significant influence on the SSE performance. This study provides theoretical and experimental analyses of the SSE internal leakage with compressed air as the working fluid. Both mathematical model of different leakage paths and leakage model have been established. The simulation model was verified by experimental data at internal volume ratios of 2.95 and shows a maximum deviation of 3.63%. Results show that fitting clearance height and rotational speed could clearly influence the volumetric efficiency and power output. The diameters of both the screw and the gate rotor could also significantly influence the volumetric efficiency. The volumetric efficiency decreased with the increase in internal volume ratio. [ABSTRACT FROM AUTHOR]

Direct particle receiver of the concentrated solar power (CSP) with a supercritical CO 2 (sCO 2) Brayton cycle is based on the solid particles to achieve high efficiency at high temperature. Among all kinds of solid particles, desert sand is abundant and cheap, however its solar weighted absorptance and thermal stability remain to be improved. In this work, the dark desert sands were obtained by in-situ coating transition metal oxides via sol-gel combustion process. The thermal stability of the resultant samples was analyzed according to the changes in composition, morphology and optical properties before and after thermal treatment at 800 °C for 200 h. Based on the characterization of UV–Vis–NIR diffuse reflectance spectroscopy, the solar weighted absorptance of each sample was calculated. Compared with the original particles, all of dark desert sands have the improved solar weighted absorptance, and the highest value of 0.8635 belongs to desert sand coated with spinel CuMn 2 O 4. Moreover, compared to the original desert sand, each dark desert sand has superior thermal stability. In addition, the specific heat of particles was measured at different temperatures, and it is found that the coating has lesser effects on the specific heat of desert sand. The solar weighted absorptance of dark desert sand nearly unchanged after attrition and the coating remained well maintained on the surface of the sample. This work provides a practical and feasible way to enhance the solar weighted absorptance and thermal stability of desert sand, making it possible to apply in sCO 2 CSP. • Desert sand was in-situ coated with transition metal oxides via sol-gel combustion method. • The optical properties and specific heat of desert sand before and after coating were evaluated. • The solar weighted absorptance of desert sand coated spinel CuMn 2 O 4 is as high as 0.8635. • The coating of transition metal oxides can improve the thermal stability of desert sand. [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]

This paper presents a mathematical model of torque for Single screw expanders (SSEs). Instantaneous torque and torque ratio were analyzed and discussed. The periodic variation of instantaneous torque is the same for different inlet pressure levels. The torque ratio, with its value close to 1, is independent of the inlet pressure of SSE. An experimental system was established to measure the torque, power and shaft efficiency of the self-developed SSE prototype, and results were used to validate the model. Comparison shows that the difference between calculated and experimental torque values is small (6.58 N.m to 7.55 N.m). The calculated and experimental output power is similar, with a difference of 2.07 kW to 2.37 kW. Therefore, the proposed model can be used to estimate the torque and output power of SSEs. [ABSTRACT FROM AUTHOR]

In order to improve the unsteady high temperature heat transfer performance of receivers in solar thermal power stations the receivers should be optimized further. High temperature could help to optimize heat transfer of the receiver. Based the selection of heat pipes and bromides this work prepared six samples of quaternary bromides with different composition ratios of KBr, LiBr, NaBr, and CaBr 2 and their density and surface tension were measured and analyzed. Experimental results show that density of quaternary bromides shows very good linearity with salt temperature, and density of quaternary bromides is higher than that of Solar salt at a same temperature. Also, quaternary bromide NO.2 has maximum density, and quaternary bromide NO.3 has minimum thermal expansion coefficient while quaternary bromide NO.6 has the minimum density and maximum thermal expansion coefficient at the same temperature. In addition, quaternary bromide NO.1 has a maximum surface tension and fitting curve slope at a same temperature among the six samples of quaternary bromides. Their density and surface tension were fitted with linear fit with their temperature respectively. Furthermore, that the composition ratio has evident influence on the density and surface tension of quaternary bromides has been concluded. [ABSTRACT FROM AUTHOR]

A miniature vapor compression refrigeration system included two heat sinks connected in series (indicated as series system) or in parallel (indicated as parallel system) was built. The performance of the series system was studied and compared with that of the parallel system. The results indicate that the largest cooling capacity of the two systems is about 160 W and the optimal refrigerant charge is about 0.6 M total in the miniature vapor compress refrigeration (VCR) system. There is no relation between the optimal refrigerant charge and the arrangement of the heat sinks. The coefficient of performance (COP) of the series system ranged from 1.81 to 3.22, while the COP of the parallel system was in the range of 1.51–2.92 under the cooling capacity of 100 W. The cooling of the heat sink 2 lag behind that of the heat sink 1 in the serial system, while the refrigerant is difficult to equally distribute in the parallel system. [ABSTRACT FROM AUTHOR]

In order to meet the requirements of high temperature solar thermal power generation better, the melting point of mixed carbonates should be further reduced. Starting with ternary carbonates, we modified their composition ratios and added NaNO3 or NaOH as additives. Their new melting points, initial crystallization points, decomposition temperatures, specific heats and thermal stabilities were analyzed. While the melting points of the mixed nitrate/carbonate salts were maintained at 394.7°C, the melting points of the mixed hydroxide/carbonate salts were reduced to 323.2°C. Also the initial crystallization temperature of the mixed hydroxide/carbonate salts was dependent on their composition. Among the hydroxide-mixed molten salts, there are six samples with lower initial crystallization temperature. The decomposition temperature of the selected six samples was nearly 800°C. Their specific heats were fitted with the quadratic polynomial of the temperature and their thermal stability was shown by the excellent repeatability of five heating curves. Only the very first heating curves showed that the initial measured value of a melting point was higher than all the later values of the molten salts due to starting with the powder. Furthermore, possible issues that arise with the addition of NaOH are discussed. [ABSTRACT FROM AUTHOR]

Abstract: A new kind of expanders, called as single screw expander, has been developed by our team and applied to refrigeration systems. The present paper is to determine experimentally the refrigeration performance of a compressed air refrigeration system which is based on a single screw expander with 175 mm diameter rotor. Results indicate that the single screw expander has good refrigeration performances with a 70 °C odd temperature drop and an adiabatic efficiency above 65%. A high refrigerating output can be obtained at high intake pressure and high rotational speed. The coefficient of performance (COP) varies a little with increasing intake pressure at low rotational speed, but has an obvious increase with increasing intake pressure at high rotational speed; and the higher the rotational speed, the higher the COP. The maximum COP of 0.9 can be achieved. This preliminary study shows that the compressed air refrigeration system based on single screw expanders exhibits good refrigeration performances. [Copyright &y& Elsevier]

Abstract: Solar reforming of natural gas has been considered as the promising conversion route of solar fuels with the concentrated solar heat. The present work focuses on investigating the catalytic reforming reaction over metal foam based monolithic catalysts. The 2 wt.%Ru/Al2O3/AISI 316 foam and 5 wt.%Ni/Al2O3/AISI 316 foam were prepared via the process of coating and impregnation. The catalytic properties of 5 wt.%Ni/Al2O3/AISI 316 foam and 2 wt.%Ru/Al2O3/AISI 316 foam for the methane reforming with carbon dioxide were tested in a continuous-flow fixed-bed reaction system. The results showed that the 2 wt.%Ru/Al2O3/AISI 316 foam exhibited higher catalytic activity and long-term stability for CO2 reforming of methane. The 316 stainless steel metal foam matrix had the very low catalytic performance for methane reforming with CO2 and the Al2O3 coating played a key role on the reactivity of the resulting catalysts. [Copyright &y& Elsevier]

Abstract: The photocatalyst TiO2 with a wormhole-like mesoporous structure and narrow pore distribution were successfully synthesized using triethanolamine as template. The complex oxides InVO4 with a relatively high surface area, a visible light active hydrogen-evolving photocatalyst, were obtained by means of the templating hydrothermal method with a variety of surfactants. InVO4 with wormhole-like structure were fabricated by templating of cetyltrimethylammonium bromide. By comparing with the non-mesoporous samples, the mesoporous photocatalysts exhibited higher photocatlytic hydrogen evolution activity for water splitting in the absence and in the presence of oxalic acid. [Copyright &y& Elsevier]

The influence of direct current (DC) electric field on the thickness and mass of frost on a cold vertical plate was investigated. The photos of frost layer growth were taken with and without the presence of electric field, and results showed that the electric field has a strong influence on the frost thickness. The influences of cold plate temperature and ambient temperature on frost thickness and frost mass were also investigated under the natural convection condition with electric field. Experimental results demonstrated that the cold plate temperature has very strong effect on the frost layer thickness, but its influence on frost mass is minor; the influence of ambient temperature on the frost mass is more obvious than that on the frost thickness. [ABSTRACT FROM AUTHOR]

Abstract: In this part of study, the comparative observations of the structure and the surface temperature of the frost layer of both the coated and uncoated surfaces ware carried out and a preliminary analysis was presented. A series of the repeated cycling tests were completed that lasted for more than 2 months, and the influences of the coating thickness were also investigated. The results show that the frost layer deposited on the coating surface has a very fragile structure and can be removed easily by external force. The coating thickness has an important effect on the anti-frosting performance of the paint. The results also show that the coating of the paint on the copper surface is durable and presents a very good repeated cycling performance. [Copyright &y& Elsevier]

Abstract: In this study, an experimental investigation is made of the anti-frosting performance of our newly developed anti-frosting paint. By coating the paint on a cold metal surface the onset of the frost formation may be delayed at least 15min and the thickness of the deposited frost layer may be reduced by at least 40% and thus the weight of the deposited frost may be reduced by more than 40% compared with that on the uncoated copper surface. Under some preferable conditions (air relative humidity <60%, cold plate surface temperature >−10°C), the coating surface can be kept free of frost at least for 3h. [Copyright &y& Elsevier]

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]

The organic Rankine cycle (ORC) is a popular and promising technology that has been widely studied and adopted in renewable and sustainable energy utilization and low-grade waste heat recovery. The use of zeotropic mixtures in ORC has been attracting more and more attention because of the possibility to match the temperature profile of the heat source by non-isothermal phase change, which reduces the irreversibility in the evaporator and the condenser. The selection of working fluid and expander is strongly interconnected. As a novel expander, a single screw expander was selected and used in this paper for efficient utilization of the wet zeotropic mixtures listed in REFPROP 9.1 in a low-temperature subcritical ORC system. Five indicators, namely net work, thermal efficiency, heat exchange load of condenser, temperature glide in evaporator, and temperature glide in condenser, were used to analyze the performance of an ORC system with wet and isentropic zeotropic mixtures as working fluids. The calculation and analysis results indicate that R441A with an expander outlet temperature of 320 K may be the suitable zeotropic mixture used for both open and close type heat source. R436B may be selected with an expander outlet temperature of 315 K. R432A may be selected with an expander outlet temperature from 295 K to 310 K. [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]

Ternary carbonate (K 2 CO 3 –Li 2 CO 3 –Na 2 CO 3 , 4:4:2 mass ratio) can be used as a high-temperature heat transfer and thermal storage medium in concentrated solar power systems. Ternary carbonate nanofluids with 1.0 wt% SiO 2 nanoparticles were prepared by mechanical mixing at high temperatures in order to enhance the specific heat capacity and the thermal conductivity. The effects of stirring rate (500 rpm, 750 rpm, and 1000 rpm) and stirring time (15 min, 30 min, and 60 min) on the thermal properties of the as-prepared nanofluids were analyzed. The results showed that the dispersion homogeneity of the nanoparticles in the nanofluids varied with the stirring rate and the mixing time, thereby affecting the formation of special nanostructures. The maximum enhancements in specific heat capacity and thermal conductivity at a temperature of 540 °C, stirring rate of 750 rpm and stirring time of 30 min were 38.5% and 50%, respectively. The specific heat capacity of the optimal nanofluids had no significant deterioration after the thermostatic (at 600 °C for 150 h) and thermal shock (50 cycles) experiments were conducted. • High temperature mixing method is used to prepare ternary carbonate nanofluids. • Enhancement in C p of nanofluids prepared at 750 rpm with 30 min is 38.5%. • Enhancement in λ of nanofluids prepared at 750 rpm with 30 min is 50.0%. • C p of nanofluids has no great deterioration after 50 cycles of thermal shock. [ABSTRACT FROM AUTHOR]