Thermophysical Properties Research Articles

Synthesis, Characterization and Thermal Studies of Composite Nanofluids and their Comparison with Hybrid Nanofluids

Ternary nanofluids can either be an admixture of three distinct nanoparticles or the dispersion of a ternary nanocomposite in a base fluid. This work focuses on the synthesis, morphological characterization, stability analysis, estimation and optimization of thermophysical parameters of ternary nanofluids consisting of multiwalled carbon nanotubes, graphene oxide and silver (CNT-GO-Ag). Two cases are considered and compared viz. (i) hybrid nanofluids (HNF) prepared from monofluids and (ii) composite nanofluids (CNF) prepared by the dispersion of ternary nanocomposites. The CNF was found to have an enhanced thermal conductivity ratio (knf/kb) of 40% as compared to 30% for HNF at 30 ºC. This enhancement for the CNF and HNF were found to be 45% and 32%, respectively at the electronic cooling exposure temperature of ~40 to 50 ºC. The zeta potential analysis also proved that CNF had superior suspension stability than HNF. The viscosity of CNF was found to be 8% (at 20 ºC) to 20% (at 80 ºC) lower than HNF, much desired for fluid flow characteristics. Overall, the results show that CNF as compared to HNF possesses superior thermophysical properties with good potential for application in electronic cooling studies.

Effect of Flashlamp Heating System Parameters on the Wedge Peel Strength of Thermoplastic Carbon Fiber Tape in the Automated Tape Placement Process

Laser-assisted automated tape placement systems are currently the state of the art regarding thermoplastic tape placement. Flashlamp heating systems are rather new in this field of application and offer high energy density with low safety requirements and moderate costs compared to laser-assisted automated tape placement systems. In this study, the effect of processing parameters on interlaminar bonding of carbon fiber-reinforced polyamide 6 tapes is investigated using a flashlamp heating system. The temperature during placement is monitored using an infrared camera, and the bonding strength is characterized by a wedge peel test. The bonding quality of the tapes placed between 210 °C and 330 °C at a lay-up speed of 50 mm/s is investigated. Thermogravimetric analysis, differential scanning calorimetry, and micrographs are used to investigate the material properties and effects of the processing conditions on the thermophysical properties and geometric properties of the tape. No significant changes in the thermophysical or geometric properties were found. Moisture within the tapes and staining of the quartz guides of the flashlamp system have significant influence on the bonding strength. The highest wedge peel strength of dried tapes was found at around 330 °C.

Predicting thermophysical properties of molten salts in the MgCl2-NaCl-KCl-LiCl system with a shell-model potential

Ternary eutectic salts composed of MgCl2, NaCl, and KCl, referred to as MNK salts, have recently emerged as promising candidates as high-temperature heat transfer fluids and thermal energy storage media. In this study, we performed classical molecular dynamics (MD) simulations to predict the densities, specific heat capacities, viscosities, and ionic self-diffusivities for MNK salts over a wide temperature range. The impact of LiCl additive on their thermophysical properties was also investigated. To capture the electronic polarization of Cl anions by neighboring cations, we developed a novel shell-model potential using the force-matching method and a dataset of ab initio calculated interatomic forces. Our extensive MD simulations predict structure and properties for pure salts and binary/ternary salt mixtures in the MgCl2-NaCl-KCl-LiCl system in overall good agreement with available experimental and theoretical data, which corroborates the accuracy and reliability of our developed potential.

Thermo-physical properties estimation of an oil-based hybrid nanofluid: application of a new hybrid neurocomputing approach

Thermo-physical properties estimation of an oil-based hybrid nanofluid: application of a new hybrid neurocomputing approach

An inverse front tracking method for modeling solidification process in a smelting furnace

An inverse process based on the conjugate gradient and adjoint problem is developed for predicting the time-varying bank thickness during the solidification/melting process in a smelting furnace. The direct problem rest on a single-phase moving boundary model to simulate the solid bank and refractory brick, simultaneously. The time-varying heat flux at solid/liquid interface, initial bank thickness and time-varying heat transfer coefficient at outer surface of the furnace are considered as the unknowns. Unlike the methods developed so far based on the enthalpy model, the current method does not require any prior information regarding the thermophysical properties of the liquid-phase and complex physical phenomena that occur in it. This improves the uniqueness of the solution that is inherent in the ill-posed inverse methods. To avoid the so-called “inverse crime”, a two-phase enthalpy method is used to generate the simulated measurement. These measurements are used in the present single-phase method for reconstruction of bank history. The model has shown good performance for non-intrusive temperature obtained from the outer surface of the furnace. The inverse model has been validated through an experiment conducted in a metallurgical reactor. A reasonable agreement between the estimated and measured molten salt bank indicates the existence and convergence of the inverse solution.

Development of coffee bean porosity and thermophysical properties during roasting

The development of coffee bean porosity during roasting was captured for a Kenyan Arabica coffee roasted under different constant inlet air temperature conditions in a pilot-scale spouted bed roaster. Coffee bean porosity was characterised using X-ray Micro Computed Tomography (Micro-CT). These data demonstrated a significant increase in coffee bean porosity of up to 60% during roasting. The coffee's intrinsic physical properties were also analysed to identify the relationship between porosity, thermophysical properties (density, thermal conductivity, specific heat capacity) and common process indicators (colour, mass, moisture, volume). Implications for heat transfer during roasting are also discussed. As Micro-CT, pycnometry and thermal properties analysers are not readily available tools, correlation of costly analytical methods with rapid discriminative tests are presented, allowing developers to utilise more accessible characterisation techniques to inform modulation of their processes and products. The data-driven approach to map coffee's physicochemical development during roasting provides comprehensive data that could be used to calibrate mechanistic or kinetic models. These physics-driven models could then be used as routine equations nested in heat and mass transfer simulations for developers to predict coffee's thermal evolution and subsequent physical transformation during roasting.

Evaluation of nanoparticle shape factor on a laminar forced convective heat transfer characteristics of various nanofluids flow in a tube using single-phase numerical model

Nanotechnology is advantageous in improving thermophysical properties and enhancing heat transfer rate compared with conventional fluids due to their superior thermophysical properties. These properties vary with many parameters such as concentration and shape. In this study, the effect of nanoparticles shape is numerically explored on heat transfer performance under a laminar flow regime (Re=500 and 2000) through the smooth tube. Heat transfer enhancement capability of the nanoparticle shapes with targeted reference to average Nusselt number, average Darcy friction factor, pumping power, and performance evaluation criterion have been investigated. Three types of nanofluids (Fe3O4/water, Al2O3/water, and GO/water) with various nanoparticle shapes (brick, cylindrical, platelet, and spherical) and different nanoparticle volume fractions (φ=1.0, 2.0, 3.0, and 4.0%) have been used as heat transfer fluid in analyzes. Numerical results show that heat transfer performance was greatly influenced by changing nanoparticle shapes. The highest average Nusselt number was obtained for GO/water nanofluid with platelet nanoparticle shape and φ=4.0%. Compared to water, Fe3O4/water, and Al2O3/water, the average Nusselt number in GO/water increased by 64.34%, 54.02%, and 43.41%, respectively. The highest performance evaluaton criterionwas obtained for the GO-water nanofluid with platelet nanoparticle shape at Re=2000. On the other hand, it is found that the Fe3O4/water nanofluid with platelets nanoparticle shape causes the highest pumping power compared with other analyzed nanofluids.

High temperature structure and vibrational properties of ScXO4 (X= V5+ and P5+): A comparative study

ScVO4 and ScPO4 represent the zircon (xenotime) type structures with smallest trivalent cations, and that enable them to host both transition metal and rare-earth ions for applied optical materials. Thus, their crystal chemistry and thermophysical properties becomes relevance for their application in non-ambient conditions. In this report, high temperature crystal chemistry and vibrational properties of ScVO4 and ScPO4, as observed from in situ high temperature powder XRD and Raman spectroscopic studies, are reported. The comparative analyses of the results indicate that, though both are isostructural, they show drastically different thermal expansion behavior. In case of ScVO4, the c-axis shows significantly larger expansion compared to a-axis, while in ScPO4 the thermal expansion along and a and c-axes are more or less similar. At ambient condition, the thermal expansion anisotropy in ScPO4 and ScVO4 are 1.02 and 3.97, respectively. Additionally, ScPO4 shows relatively lower coefficient of volume thermal expansion compared to ScVO4, (αv = 23.64 × 10−6 K−1 for ScPO4 and 26.09 × 10−6 K−1 for ScVO4), and is contributed by the expansion of ScO8 units in their structures. The thermal expansion coefficients of ScO8 unit in ScPO4 and ScVO4 are 36.3 × 10−6 K−1 and 39.1 × 10−6 K−1, respectively. Temperature evolution of Raman modes indicates weakening of all the modes, except a symmetric stretching mode, with increasing temperature. The anharmonic analyses of the Raman modes indicate that implicit contributions in ScVO4 and ScPO4 are appreciably higher than the explicit contributions, and hence the changes in mode wavenumbers with volume play dominating role in governing their thermal expansion behaviors. Further, it is concluded that ScPO4 is characterized by more or less like rigid unit cell compared to ScVO4.

Thermophysical Properties of Compressed Earth Blocks Incorporating Natural Materials

Building materials are responsible for significant CO2 emissions and energy consumption, both during production and operational phases. Earth as a building material offers a valuable alternative to conventional materials, as it naturally provides high hygrothermal comfort and air quality even with passive conditioning systems. However, disadvantages related to high density, conductivity, and wall thickness prevent its effective inclusion in the mainstream. This research explores enhancing the thermophysical properties of compressed earth blocks (CEBs) by using locally sourced natural materials. The study is framed in the Portuguese context and the natural materials involved are wheat straw (WS) as a by-product of wheat harvesting, cork granules (CGs) from bottle caps, and ground olive stone (GOSs) residues from olive oil production. Blocks were produced with different mixtures of these materials and the thermal response was examined in a hot box apparatus. Best results include a 20 and 26% reduction in thermal conductivity for mixtures with 5v.% CG and 10v.% GOS, respectively, and an associated reduction in bulk density of 3.8 and 5.4%. The proposed approach therefore proves to be effective in improving the key thermophysical characteristics of CEBs. The article includes a comparative analysis of the experimental data from this study with those from the literature. The study contributes to the growing knowledge of sustainable materials, providing insights for researchers and practitioners looking for innovative solutions for low-carbon and energy-efficient materials.

Numerical investigation of the thermal-hydraulic performance of a novel parabolic trough wavy tubular receiver by using FMWNCT/oil-nanofluid coupled with fins

This study employs a computational fluid dynamics (CFD) approach to assess the performance of a novel wavy profile tube receiver. It integrates rectangular fins and an Oil-based nanofluid, specifically utilizing Thermodyne GG-03 synthetic oil combined with Functionalized Multi-Wall Carbon Tubes (FMWNCT). The synthesis involves rigorous experimental procedures to characterize the thermophysical properties of the oil and nanofluid. Empirical correlations, validated against Bitam et al.'s model [1], guide the numerical analysis. The investigation, utilizing a steady-state κ - ω SST turbulence model with a non-uniform Gaussian thermal flux distribution, explores thermohydraulic performance in fully developed turbulent flow (Reynolds number range: 2 × 104 – 5 × 104). Comparative analysis with Bitam et al.'s work, employing Syltherm 800 oil as a reference, reveals a 25.76% average Nusselt number enhancement with Thermodyne GG-03. Additional improvements are observed: 124.69% with FMWNCT/oil-nanofluid, 137.04% with fins, and 236.54% with combined FMWNCT/oil-nanofluid and fins. These enhancements lead to increased heat transfer coefficients and rates. The friction coefficient rises by less than 60%, mainly attributed to the Nusselt number improvement. At RE = 20000, the Maximum Performance Evaluation Criteria (PEC) is 5.5, signifying significant improvement. Notably, a 300% PEC enhancement is observed compared to Roger and Mayhew's curved tube model [1]. In conclusion, these findings offer valuable insights for efficiently designing wavy tubular receivers in PTR collectors.

Impact of blending of phase change material for performance enhancement of solar energy storage

The contemporary challenge of energy scarcity underscores the vital necessity for effective energy storage solutions. Addressing this concern becomes particularly crucial given the abundance of solar energy available for harnessing. Thermal energy storage emerges as a pivotal approach in this context, with phase change materials serving as valuable components due to their affordability and widespread accessibility. Specifically, various inorganic salts find application as phase change materials, contributing to the development of cost-effective and readily available solutions for storing the ample energy derived from solar sources. This research assesses the impact of varying Sodium chloride (NaCl) proportions on the thermophysical properties of nitrate-based salts, specifically Sodium nitrate (NaNO3) and Potassium Nitrate (KNO3). The investigation reveals significant influences on latent heat, specific heat, and thermal conductivity. High levels of NaCl adversely impact the thermal properties, leading to a decrease in the latent heat of NaNO3 and KNO3 by 7.3 % and 4.4 %, respectively. This reduction resulted due to the disruption of the crystal structure caused by blending, which results in the initiation of melting at lower energy levels. Conversely, lower NaCl quantities, particularly 7.5 %, positively influence latent heat for both salts. Thermal conductivity and specific heat show enhancement with 7.5 % and 10 % NaCl, but further increases mitigate these properties. Microstructure analysis indicates that limited NaCl promotes a compact structure with strong bonding forces, while exceeding a threshold increases lattice vibration frequency. A network structure between NaNO3 and NaCl forms, becoming more compact and complex with increased NaCl content, impacting melting and solidification points. X-ray diffraction (XRD) analysis confirms the stability of both mixtures. The NaNO3–NaCl combination exhibits superior thermophysical properties compared to KNO3–NaCl, underscoring the importance of fine-tuning NaCl proportions for optimal performance in these salt mixtures.

Ascending Performance of Scientific Balloons with Buoyant Gas–Air Mixture Inflation for Designated Ceiling Height

This paper aims to investigate a new method that uses buoyant gas mixed with air to control the floating height of scientific balloons. Firstly, the static characteristics and thermophysical properties of mixed-gas balloons are analyzed. Subsequently, the inflation model and the thermal-dynamic coupled model are established. Furthermore, based on theoretical research, a GUI program is compiled to simulate the ascent of mixed-gas balloons. Finally, flight tests are conducted. As the balloon volume expands to the maximum, the vertical velocity begins to decay and eventually oscillates around 0 m/s, which is consistent with the simulation. In addition, there is a noticeable shift in which the balloon starts to float after climbing to the target altitude, and the difference values between the test and the simulation are less than 350 m. Moreover, the trajectory results are similar to the prediction, and the errors of the end position are less than 2.5 km in horizontal distance. Consequently, this paper provides guidance for balloon-designated ceiling height technology which can allow a single balloon system to be used for tests at multiple heights.

Enhancing concrete sustainability using crushed peanut shells: An analysis of thermophysical properties, durability, and application potential in construction

This study explored the integration of crushed peanut shells (PS) into concrete with an emphasis on sustainable construction. Uniquely, it examines the impact of PS morphologies at low incorporation rates (0–6%) on the thermophysical properties and durability of concrete through rigorous experimental analysis and computational simulations. Our findings reveal that PS significantly enhances insulation properties and reduces thermal metrics and density while maintaining structural viability despite a slight increase in water absorption and a reduction in compressive strength with higher PS content. This investigation not only highlights the potential of PS-concrete to improve the thermal efficiency of building envelopes but also introduces it as an innovative approach to using agricultural by-products in eco-friendly construction. The results indicate significant advancement in the development of sustainable building materials, contributing to enhanced construction practices with environmental benefits.

DATABASES AND MODELS TO SUPPORT THE ACCEPTANCE OF TECHNOLOGICAL DECISIONS IN THE PROOFING OF STEEL AT THE LADLE FURNACE INSTALLATION

The need to develop the databases of the «Metallurgy» industry data bank in order to preserve unique industrial and laboratory experimental data, which can be the basis of licensed profile computer programs, is substantiated. Emphasis is placed on the importance of the development of calculation methods for determining the primary properties of ferroalloys, which will ensure that industrial metallurgists receive adequate data for further operational decision-making in the production of competitive and high-quality steel and their introduction into automated technological process control systems. Based on the concept of directional chemical bonding, models have been developed that allow predicting important physicochemical and thermophysical properties that are the limiting factors in the efficiency of interphase interaction processes, in particular, of manganese-containing ferroalloys with sufficient accuracy for industrial use.

Dynamics of magnetized viscous dissipative material of hybrid nanofluid with irregular thermal generation/absorption

The intriguing thermophysical properties of nanoparticles have considerable potential in thermal transportation for engineering applications. The inclusion of solid nanoparticles in the base fluid raises the fluid's thermal conductivity, which improves thermal transfer characteristics. Thus, an analysis is performed by assuming the Tiwari and Das model, for the flow and energy transportation aspects of hybrid nanoparticles in a shrinkable porous medium. The current study focuses on the thermal heat transfer performance on the dynamic of ethylene glycol-based titania and alumina nanoparticles. The flow-controlling system of PDEs is transformed into a system of non-linear ODEs by using similarity transformations, and the resulting equations are then solved numerically through the solver bvp4c in Matlab function with a limit of tolerance 10−6. The multiple branches of solutions are noted for distinct values of suction and shrinking parameters. The outcomes reveal that the inclusion of titania and alumina nanocomposites improves the thermophysical properties of the base fluid significantly. The findings indicate that hybrid nanofluids are more effective for increasing the thermal transport rate. Further, in the upper branch solution, the friction drags, and energy transportation rate raises for the higher influence of suction strength while it declines for the lower branch.

Synthesis of silica-encapsulated myristic acid phase-change-assisted nanocapsules for thermal management applications

AbstractMyristic acid-based silica (MA/SiO2) nano-encapsulated phase change materials (NePCMs) were synthesized by the sol–gel process. Five different samples of the MA/SiO2 nanocapsules were prepared by varying the mass of the myristic acid. The nanocapsules were characterized by Fourier transform infrared spectrophotometer (FTIR), X-Ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM), energy dispersive X-ray (EDX), and dynamic light scattering (DLS). These characterization techniques confirmed the successful encapsulation of the myristic acid inside the silica shell. The maximum latent heat was found to be 114.46 J/g for the sample which was prepared with 25 g myristic acid and 20 ml tetraethyl orthosilicate precursor material. The highest encapsulation ratio of approximately 62% was obtained in the same sample and the mean size of the nanocapsules was 597 nm. The thermal stability of these nanocapsules was assessed using the thermogravimetric analyzer (TGA) and differential scanning calorimetry (DSC) results exhibited that the thermophysical properties remained consistent after 50 heating/cooling thermal cycles indicating excellent durability of the NePCMs.

Molecular dynamics simulations for the prediction of thermophysical properties of plutonium-based molten salts

Molten salt nuclear reactors are promising technologies for sustainable energy sources. In this context, understanding the physicochemical properties of molten salts is essential to the development, usage, and maintenance of reactors. Classical molecular simulations allow estimating the macroscopic properties of molten salts at a relatively low computational cost. In this work, we develop a new force field for plutonium-based molten salts. We validate our classical model by comparing molecular dynamics results with experimental measurements, obtaining a quantitative agreement. Our work demonstrates the reliability and transferability of classical force fields to represent the physicochemical properties of molten salts.

Microstructure and Physico-Mechanical Properties of Biocompatible Titanium Alloy Ti-39Nb-7Zr after Rotary Forging

The evolution of microstructure, phase composition and physico-mechanical properties of the biocompatible Ti-39Nb-7Zr alloy (wt.%) after severe plastic deformation by rotary forging (RF) was studied using various methods including light optical microscopy, scanning and transmission electron microscopies, X-ray diffraction, microindentation, tensile testing and investigation of thermophysical properties during continuous heating. The hot-rolled Ti-39Nb-7Zr with initial single β-phase structure is subjected to multi-pass RF at 450 °C with an accumulated degree of true deformation of 1.2, resulting in the formation of a fibrous β-grain structure with imperfect 500 nm subgrains characterized by an increased dislocation density. Additionally, nano-sized α-precipitates formed in the body and along the β-grain boundaries. These structural changes resulted in an increase in microhardness from 215 HV to 280 HV and contact modulus of elasticity from 70 GPa to 76 GPa. The combination of strength and ductility of Ti-39Nb-7Zr after RF approaches that of the widely used Ti-6Al-4V ELI alloy in medicine, however, Ti-39Nb-7Zr does not contain elements with limited biocompatibility and has a modulus of elasticity 1.5 times lower than Ti-6Al-4V ELI. The temperature dependences of physical properties (elastic modulus, heat capacity, thermal diffusivity) of the Ti-39Nb-7Zr alloy after RF are considered and sufficient thermal stability of the alloy up to 450 °C is demonstrated.

Influence of reduced pressure on arc and weld pool properties in TIG welding

In this article, transient transport phenomena in the arc and weld pool for different ambient pressures during tungsten inert gas welding were reported. Arc plasma and weld pool behaviour vary with ambient pressure because of changes in arc thermophysical properties. The maximum arc temperature decreases with decreasing ambient pressure because of reduced plasma electrical conductivity. Decreased arc mass density results in a lower maximum weld pool surface temperature and a decrease in maximum metal vapour content as ambient pressure decreases. Arc pressure decreases with decrease in ambient pressure, resulting in shallower penetration. Calculated arc temperature distribution and weld cross-section are compared with experiments to validate the modeling method for simulating heat and mass transfer phenomena in low ambient pressure welding.

Enhancement effects of hydrolysable/soluble Al-type dopants on the efficiency of CaO/CaCO3 thermochemical energy storage

Modification of CaO-based materials using Al-type dopants has been considered a promising method to enhance energy storage performance. The synergistic multi-doping effects of different Al-type dopants (soluble, hydrolysable and insoluble) on the energy storage performances, thermophysical and mechanical properties of CaO-based materials have never been reported. The hydrolysable/soluble Al-type supports co-doped CaO-based pellets were prepared, which exhibited superior energy storage density, multi-cycle stability, reaction rate, thermal conductivity and crushing strength compared to undoped CaO pellets. The regulation mechanisms of hydrolysable/soluble Al-type dopants (AlN/Al(NO3)3) on the reaction kinetics, multi-cycle stability, thermophysical properties and mechanical properties of CaO-based pellets were revealed. The addition of different Al-type dopants results in different dispersions of the formed Ca12Al14O33, which leads to different micro-morphologies and pore structures of CaO-based pellets. Hydrolysable Al-type dopants exhibit a more concentrated distribution in CaO-based pellets and the pellets have smaller crystallite sizes of CaO and predominantly microporous pores, which results in the high CO2 reactivity. Soluble Al-type dopants exhibit a more uniform dispersion in CaO-based pellets and the pellets have larger crystallite sizes of CaO and obvious pore channels, which results in the improved cyclic stability and decomposition kinetics. The optimized CaO-based pellets combine the advantages of the two Al-type dopants and present an increasing trend of energy storage density during the cyclic process. Its energy storage density remains 1571 kJ/kg after 50 cycles, and the value for CaO is only 569 kJ/kg. In addition, the optimal synthesized material has excellent thermal conductivity and crushing strength, which are 1.36 and 9.75 times those of CaO, respectively.