scholarly journals Effects of MgO Nanoparticles on Thermo-Physical Properties of LiNO3-NaNO3-KNO3 for Thermal Energy Storage

Energies ◽  
2021 ◽  
Vol 14 (3) ◽  
pp. 677
Author(s):  
Jianfeng Lu ◽  
Zhan Zhang ◽  
Weilong Wang ◽  
Jing Ding
Keyword(s):  
Heat Transfer ◽  
Heat Capacity ◽  
Thermal Properties ◽  
Heat Transfer Characteristics ◽  
Mgo Nanoparticles ◽  
Storage Media ◽  
Base Salt ◽  
Thermo Physical Properties ◽  
Sem Test ◽  
Scanning Electron

Molten salt LiNO3-NaNO3-KNO3 has been investigated as heat transfer and thermal storage media for its low melting point and good thermal performance. In this paper, nanofluids were synthesized by dispersing MgO nanoparticles into LiNO3-NaNO3-KNO3, and the effects of nanoparticles on thermal properties were studied with different sizes (20–100 nm) and mass percent concentrations (0.5–2.0 wt.%). The addition of nanoparticles had little effect on melting temperature, and led to a slight increase in enthalpy of fusion by 2.0–5.5%. Compared with base salt, the density of nanofluid increased a little by 0.22–1.15%. The scanning electron microscope (SEM) test implied that nubby and punctate microstructures were responsible for larger surface area and interfacial energy, which could lead to the improvement of specific heat capacity reaching 2.6–10.6%. The heat transfer characteristics remarkably increased with the addition of nanoparticles, and the enhancement of average thermal diffusivity and conductivity of salt with 1 wt.% nano-MgO could be 5.3–11.7% and 11.3–21.2%, respectively. Besides, the viscosities of nanofluids slightly increased for 3.3–8.1%. As a conclusion, nano-MgO was positively influential on the thermal properties of LiNO3-NaNO3-KNO3 base salt.

scholarly journals The Effect of In Situ Synthesis of MgO Nanoparticles on the Thermal Properties of Ternary Nitrate

Materials ◽  
2021 ◽  
Vol 14 (19) ◽  
pp. 5737
Author(s):  
Zhiyu Tong ◽  
Linfeng Li ◽  
Yuanyuan Li ◽  
Qingmeng Wang ◽  
Xiaomin Cheng
Keyword(s):  
Heat Transfer ◽  
Heat Capacity ◽  
Thermal Properties ◽  
Specific Heat ◽  
Molten Salt ◽  
Specific Heat Capacity ◽  
Ternary Eutectic ◽  
Mgo Nanoparticles ◽  
Nitrate System

The multiple eutectic nitrates with a low melting point are widely used in the field of solar thermal utilization due to their good thermophysical properties. The addition of nanoparticles can improve the heat transfer and heat storage performance of nitrate. This article explored the effect of MgO nanoparticles on the thermal properties of ternary eutectic nitrates. As a result of the decomposition reaction of the Mg(OH)2 precursor at high temperature, MgO nanoparticles were synthesized in situ in the LiNO3–NaNO3–KNO3 ternary eutectic nitrate system. XRD and Raman results showed that MgO nanoparticles were successfully synthesized in situ in the ternary nitrate system. SEM and EDS results showed no obvious agglomeration. The specific heat capacity of the modified salt is significantly increased. When the content of MgO nanoparticles is 2 wt %, the specific heat of the modified salt in the solid phase and the specific heat in the liquid phase increased by 51.54% and 44.50%, respectively. The heat transfer performance of the modified salt is also significantly improved. When the content of MgO nanoparticles is 5 wt %, the thermal diffusion coefficient of the modified salt is increased by 39.3%. This study also discussed the enhancement mechanism of the specific heat capacity of the molten salt by the nanoparticles mainly due to the higher specific surface energy of MgO and the semi-solid layer that formed between the MgO nanoparticles and the molten salt.

A Numerical Study of Forced Convective Heat Transfer Characteristics of Supercritical Fluid in a Horizontal Circular-Pipe

2020 ◽  
Author(s):  
Alaba Bamido ◽  
V. K. Dhir ◽  
V. Prasad ◽  
Debjyoti Banerjee
Keyword(s):  
Heat Transfer ◽  
Physical Properties ◽  
Convective Heat Transfer ◽  
Supercritical Fluid ◽  
Convective Heat ◽  
Circular Pipe ◽  
Heat Transfer Characteristics ◽  
Forced Convective Heat Transfer ◽  
Transfer Characteristics ◽  
Thermo Physical Properties

Abstract Analytical and computational studies were performed to compare the convective heat transfer characteristics of a supercritical fluid in a circular pipe for horizontal flow configuration. The motivation of this study was to explore the efficacy of heat exchangers involving forced convective heat transfer of supercritical fluids (tube side) integrated with air cooling (i.e., in free convection). The goal of this study was to determine the forced convective heat transfer characteristics of supercritical carbon dioxide (sCO2) in air-cooled tube heat-exchangers. The scope of this study was limited to the values of Reynolds number (Re) varying from 10∼104 (i.e., involving both laminar and turbulent flow correlations for analytical formulations and computational models). The predictions for the forced convection heat transfer characteristics (e.g., heat transfer coefficient, pressure drop, volume flow rate, mass flow rate, pump penalty/ pumping power/ required compressor ratings, Nusselt number (Nu) etc.) were obtained using analytical formulations and compared with that of computational models. The flow configurations involved a horizontal circular pipe of 1 m length and with different diameters (ranging from 1 mm – 10 mm). The supercritical properties of the working fluid were investigated at a fixed value of reduced pressure (Pr = 1.1) and a fixed range of temperatures, i.e., T, varying from 550 to 750 [K]. The fluid properties were gleaned from the NIST property database (available online at the NIST website). For the second part of this study, the forced convective heat transfer characteristics of sCO2 flowing in a horizontal tube with circular cross-section were studied using analytical correlations (e.g., Dittus-Boelter and Gnielinski correlation) and validated using commercial tools for Computational Fluid Dynamics (CFD)/ Computational Heat Transfer (CHT), i.e., using Fluent® (Ansys®). Validation of the analytical predictions using CFD/ CHT tools was performed to ascertain the level of uncertainty in the predicted results due to acute variation of the thermo-physical properties as a function of temperature and pressure (since the thermo-physical properties are expected to oscillate widely in the vicinity of the critical point). In the simulations, the inlet temperature for the supercritical fluid (sCO2) was fixed (at Tin = 700 [K]), and the ambient temperature was also fixed (at Tamb = 300 [K]), for the purpose of determining the values of the natural convection coefficients (external to the tube). Constant values of the thermo-physical properties of sCO2 at the mean film temperature (and corresponding to the inlet pressure values) were assumed for obtaining the analytical predictions. The results from the CFD / CHT simulations helped to quantify the level of uncertainties in the assumption of constant properties (in the analytical model) at different values of Reynolds number (i.e., for both laminar and turbulent flow regimes).

scholarly journals The Variation Mechanism of Thermal Properties of Loess with Different Water Contents during Freezing

2021 ◽  
Vol 2021 ◽  
pp. 1-12
Author(s):  
Xihao Dong ◽  
Shuai Liu ◽  
Yuanxiang Yu
Keyword(s):  
Heat Transfer ◽  
Phase Transition ◽  
Thermal Conductivity ◽  
Heat Capacity ◽  
Thermal Properties ◽  
Water Content ◽  
Volumetric Heat Capacity ◽  
Soil Particles ◽  
Water Ice ◽  
Variation Mechanism

The thermal properties of soils are affected by many factors, such as temperature, water content, and structure. Based on the transient plane source method of thermal physics, the thermal properties of loess with different water content during the freezing process were tested. We analyzed the variation mechanism of thermal properties from the perspective of phase change. Based on the Pore/Particle and Crack Analysis System (PCAS) and theory of heat transfer, we then analyzed the microstructure and heat conduction process of loess. And a calculation model of volumetric heat capacity of frozen soil was presented. The results show that, in the major phase transition zone, the variation of the thermal properties of loess with temperature is the most significant. And the thermal diffusivity increases sharply with the significant increase of thermal conductivity and the rapid decrease of volumetric heat capacity. Moisture content not only increases the thermal conductivity and volume heat capacity of loess but also makes the influence of temperature on the thermophysical parameters more significant. The effect of temperature on thermal properties is mainly due to the change of heat transfer media caused by phase transition of water-ice, followed by the change of thermal properties of heat transfer media such as soil particles, water, ice, and air with temperature. Increasing the water content reduces the contact thermal resistance between soil particles because of the increase in the thickness of the water film on the surface of soil particles and the thermal conductivity of the heat transfer medium between particles, thus changing the thermal properties of soils.

Investigation of High Temperature Nanofluids for Solar Thermal Power Conversion and Storage Applications

2010 ◽  
Author(s):  
Donghyun Shin ◽  
Byeongnam Jo ◽  
Hyun-eun Kwak ◽  
Debjyoti Banerjee
Keyword(s):  
Heat Capacity ◽  
Thermal Properties ◽  
High Temperature ◽  
Energy Storage ◽  
Physical Properties ◽  
Thermal Energy ◽  
Thermal Energy Storage ◽  
Molten Salts ◽  
Solar Thermal ◽  
Thermo Physical Properties

The aim of this study is to investigate the enhancement of thermal properties of various high temperature nanofluids for solar thermal energy storage application. In concentrating solar power (CSP) systems, the thermo-physical properties of the heat transfer fluids (HTF) and the thermal energy storage (TES) materials are key to enhancing the overall system efficiency. Molten salts, such as alkali nitrates, alkali carbonates, or eutectics are considered as alternatives to conventional HTF to extend the capabilities of CSP. However, there is limited usage of molten salt eutectics as the HTF material, since the heat capacity of the molten salts are lower than that of conventional HTF. Nanofluid is a mixture of a solvent and nanoparticles. Well dispersed nanoparticles can be used to enhance thermo-physical properties of HTF. In this study, silica (SiO2) and alumina (Al2O3) nanoparticles as well as carbon nanotubes (CNT) were dispersed into a molten salt and a commercially available HTF. The specific heat capacity of the nanofluids were measured and applicability of such nanofluid materials for solar thermal storage applications were explored. Measurements performed using the carbonate eutectics and commercial HTF that are doped with inorganic and organic nano-particles show specific heat capacity enhancements exceeding 5–20% at concentrations of 0.05% to 2.0% by weight. Dimensional analyses and computer simulations were performed to predict the enhancement of thermal properties of the nanofluids. The computational studies were performed using Molecular Dynamics (MD) simulations.

New borehole heat exchanger thermal enhanced grout formulations

2021 ◽  
Author(s):  
Eloisa Di Sipio ◽  
Enrico Garbin ◽  
Laura Fedele ◽  
Davide Menegazzo ◽  
Ludovico Mascarin ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Heat Capacity ◽  
Thermal Properties ◽  
Heat Exchange ◽  
Specific Heat ◽  
Specific Heat Capacity ◽  
Operation Mode ◽  
Silica Sand ◽  
Geothermal Systems

<p>In shallow geothermal systems, especially ground source heat pumps (GSHP), cementitious grouts play a decisive role in guaranteeing an efficient heat transfer between the probe and the surrounding ground. Several studies have been devoted to understand the effect of different additives (silica sand, graphite, fluorspar, glass and fly ash …) in improving especially the thermal conductivity of such mixtures, maintaining at the same time physical properties as viscosity and workability suitable for in situ application. In fact, when continuous operation mode is running, thermal conductivity shows a positive effect on the mean heat exchange rate of vertical borehole heat exchangers (BHE). However, when an intermittent operation mode is selected, the BHE performance improves when a high thermal conductivity is coupled with a high specific heat capacity.</p><p>This research focus on assessing the contribution of two specific thermal additives (silica sand and molybdenum disulphide powder) to the thermal properties’ improvements of a specific commercial cementitious grout. These components are added in different proportion to the grout, up to the creation of 6 different mixtures. For each mixture 3 specimens are prepared, in order to perform the thermo-physical analyses. In addition, other 3 commercial grouts are considered. A total of 10 mixtures, leading to the creation of 30 specimens, have been analyzed. Then, thermal conductivity, thermal diffusivity and specific heat capacity of each specimen measured in anhydrous and saturated conditions are considered.</p><p>The commercial grouts prepared as stated by the producers show, as expected, a minimum variation of their thermal properties in wet and anhydrous conditions. Instead, when the additives are used, a noticeable improvement of the thermal properties is observed in saturated conditions, where the effect of silica sand seems dominant. The best thermal properties improvement obtained by combining the two additives is also considered.</p><p>However, the grouts suitability to be easily managed on site must be considered because, even if the new mixtures show a general gain of the thermal properties, these can be difficult to apply going from laboratory to full scale.</p><p>Anyway, the characterization of the grouts thermal properties based on composition and saturation variations is important not only in numerical simulations, but also in analytical approaches, typical of the heat exchange probe fields sizing processes. In fact, the cementitious grouts play a key role in determining the shallow geothermal systems efficiency in transient mode operation, often neglected by sizing programs. In fact, those characterized by better thermal performances will contribute to the reduction of the borehole thermal resistances, interposed in the heat exchange processes between the heat transfer fluid and the ground. Finally, this research contributes to fill the gap between numerical simulation and experimental data, providing real data to be used as database for further numerical modelling analysis improvement.</p><p> </p><p>GEO4CIVHIC project has received funding from the European Union’s Horizon 2020 research and innovation program under grant agreement No. 792355.</p>

Enhanced Sensible Heat Capacity of Molten Salt and Conventional Heat Transfer Fluid Based Nanofluid for Solar Thermal Energy Storage Application

2010 ◽  
Author(s):  
Hyun-eun Kwak ◽  
Donghyun Shin ◽  
Debjyoti Banerjee
Keyword(s):  
Heat Transfer ◽  
Heat Capacity ◽  
Physical Properties ◽  
Molten Salt ◽  
Solar Thermal ◽  
Heat Transfer Fluid ◽  
Solar Thermal Energy ◽  
Silicon Dioxide Nanoparticles ◽  
Operational Capabilities ◽  
Thermo Physical Properties

In concentrating solar power (CSP) systems, the thermo-physical properties of the heat transfer fluid (HTF) are key parameters for enhancing the overall system efficiencies. Molten salts, such as alkali nitrates, chlorides or carbonates, and their eutectics, are considered as alternatives to conventional HTF (such as water or oil) to extend the operational capabilities of CSPS. However, the usage of the molten salt as the HTF is limited, since the heat capacity of the molten salt is relatively lower than that of conventional HTF. Nanofluid is a mixture of a fluid and nanoparticles. Well dispersed nanoparticles can be used to enhance the thermo-physical properties of HTF. In this study, silicon dioxide nanoparticles were dispersed into a molten salt and into a conventional HTF (Therminol VP-1, Solutia Inc). The specific heat enhancement of each nanofluid was studied and the applicability of such nanofluid materials for solar thermal storage applications was explored.

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