Search Results (82)

The accurate computation of the thermophysical properties of gases and gas mixtures is critical for combustion analysis but remains challenging due to the precision and numerical stability required across wide temperature ranges. In this study, we present Thermophy, a computational framework based on Chebyshev polynomial fitting, developed to calculate thermal conductivity, viscosity, and binary diffusion coefficients for pure gases and multicomponent mixtures. Unlike conventional tools that rely on low-order polynomial approximations, Thermophy applies Chebyshev fitting over defined temperature intervals, enabling higher accuracy, improved numerical stability, and computational efficiency. Thermophy is validated through four case studies involving pure gases, binary mixtures, and ternary mixtures relevant to combustion applications. For pure gases and air, deviations in thermal conductivity and viscosity were found to be 1.22–4.25% and 0.11–4.71%, respectively. For ternary mixtures, viscosity deviations ranged from 0.11 to 0.24%, while binary mixtures showed deviations of 2.60% and 0.20% for viscosity and thermal conductivity, respectively. Binary diffusion coefficients exhibited an overall deviation of approximately 3.35%. The combination of flexible input handling, extensibility, and high-fidelity calculations positions Thermophy as a robust and efficient alternative for integration into combustion modeling and other gas-phase simulation frameworks, including gasification, pyrolysis, global carbon cycle analysis, environmental systems, and fire modeling. Full article

This work presents a proof of concept including simulation and experimental validations of acoustic gas sensor prototypes for trace CO₂ detection up to 1 ppm. For the detection of lower gas concentrations especially, the dependency of acoustic resonances on the molecular weights and, consequently, the speed of sound of the gas mixture, is exploited. We explored two resonator types: a cylindrical acoustic resonator and a Helmholtz resonator intrinsic to the MEMS microphone’s geometry. Both systems utilized mass flow controllers (MFCs) for precise gas mixing and were also modeled in COMSOL Multiphysics 6.2 to simulate resonance shifts based on thermodynamic properties of binary gas mixtures, in this case, N₂-CO₂. We performed experimental tracking using Zurich Instruments MFIA, with high-resolution frequency shifts observed in µHz and mHz ranges in both setups. A compact and geometry-independent nature of MEMS-based Helmholtz tracking showed clear potential for scalable sensor designs. Multiple experimental trials confirmed the reproducibility and stability of both configurations, thus providing a robust basis for statistical validation and system reliability assessment. The good simulation experiment agreement, especially in frequency shift trends and gas density, supports the method’s viability for scalable environmental and industrial gas sensing applications. This resonance tracking system offers high sensitivity and flexibility, allowing selective detection of low CO₂ concentrations down to 1 ppm. By further exploiting both external and intrinsic acoustic resonances, the system enables highly sensitive, multi-modal sensing with minimal hardware modifications. At microscopic scales, gas detection is influenced by ambient factors like temperature and humidity, which are monitored here in a laboratory setting via NDIR sensors. A key challenge is that different gas mixtures with similar sound speeds can cause indistinguishable frequency shifts. To address this, machine learning-based multivariate gas analysis can be employed. This would, in addition to the acoustic properties of the gases as one of the variables, also consider other gas-specific variables such as absorption, molecular properties, and spectroscopic signatures, reducing cross-sensitivity and improving selectivity. This multivariate sensing approach holds potential for future application and validation with more critical gas species. Full article

Most existing ultra-deep gas wells are characterized by high temperature, high pressure, and high sulfur content. During development, they face serious challenges such as unclear mechanisms of acid gas-induced blowouts and difficulties in wellbore pressure inversion, posing significant challenges to well control operations. To reveal the reasons behind the tendency of acidic gases to trigger blowouts and to clarify the impact of different concentrations of acidic gases on the flow behavior of annular fluids, this study considers the effects of solubility and phase changes on the physical properties of acidic gases. A method replacing critical parameters with pseudo-critical parameters is used to analyze the variation trends of gas density, solubility, and other properties along the well depth. A mathematical model for the annular flow of acidic gas overflow incorporating solubility phase change effects is established. The model is numerically solved using a four-point difference scheme, exploring the essential characteristics of gas flow in the annulus after overflow, and discussing the distribution patterns of physical properties of acidic gases, as well as dynamic parameters such as wellbore pressure and temperature along the well depth. Numerical simulations show that the physical properties of acidic gases change significantly with well depth: the more acidic gas present in the wellbore, the smaller the deviation factor, and the greater the density and viscosity, with parameter changes exceeding 40% near the pseudo-critical point for binary mixtures with 40% H₂S. Compared to pure methane, mixed fluids containing acidic gas experience more than 20% volume expansion near the wellhead for ternary mixtures with 20% CO₂ and 20% H₂S, and the flow velocity increases by more than 10% for mixtures with ≥30% acidic gas content, leading to a higher risk of a sudden pressure drop during well control. This study clarifies the migration patterns of acidic gas overflow in HPHT (high pressure, high temperature) gas wells, providing valuable guidance for optimizing well control design, improving well control emergency plans, and developing well-killing measures. Full article

The civil construction and infrastructure sectors are known for their high environmental impact. Most of this impact is related to the carbon dioxide (CO₂) emissions from Portland cement. As a sustainable alternative, alkali-activated binders (AABs) are explored for their potential to replace traditional binders. This research focused on AAB formulations using steel industry byproducts, such as Baosteel’s slag short flow (BSSF), coke oven ash (CA), blast furnace sludge (BFS), and centrifuge sludge (CS), as well as fly ash (FA) from a thermoelectric plant. Byproducts were characterized through laser granulometry, Fourier transform infrared spectroscopy (FTIR), X-ray fluorescence (XRF), X-ray diffraction (XRD), and scanning electron microscopy (SEM), followed by the formulation of AABs with different precursor ratios. After 28 days, the compressive strength was obtained for each formulation. Based on the compressive strength tests, two binary mixtures were selected for microstructural and chemical analyses through XRF, FTIR, and SEM. CA demonstrated the greatest potential for use in binary AABs based on BSSF, as it presented a higher source of aluminosilicates and smaller particle sizes. The formulations containing BSSF and CA achieved compressive strengths of up to 9.8 MPa, while the formulations with BSSF and FA reached 23.5 MPa. SEM images revealed a denser, more cohesive matrix in the FA-based AAB, whereas CA-based AABs showed incomplete precursor dissolution and higher porosity, which contributed to the lower mechanical strength of CA-based AABs. These findings highlight the critical role of precursor selection in developing sustainable AABs from industrial byproducts and demonstrate how different formulations can be tailored for specific applications. Full article

Supercritical carbon dioxide (s-CO₂) Brayton cycles have emerged as a promising technology for high-efficiency power generation, owing to their compact architecture and favorable thermophysical properties. However, their performance degrades significantly under cold-climate conditions—such as those encountered in Greenland, Russia, Canada, Scandinavia, and Alaska—due to the proximity to the fluid’s critical point. This study investigates the behavior of the recompression Brayton cycle (RBC) under subzero ambient temperatures through the incorporation of low-critical-temperature additives to create CO₂-based binary mixtures. The working fluids examined include methane (CH₄), tetrafluoromethane (CF₄), nitrogen trifluoride (NF₃), and krypton (Kr). Simulation results show that CH₄- and CF₄-rich mixtures can achieve thermal efficiency improvements of up to 10 percentage points over pure CO₂. NF₃-containing blends yield solid performance in moderately cold environments, while Kr-based mixtures provide modest but consistent efficiency gains. At low compressor inlet temperatures, the high-temperature recuperator (HTR) becomes the dominant performance-limiting component. Optimal distribution of recuperator conductance (UA) favors increased HTR sizing when mixtures are employed, ensuring effective heat recovery across larger temperature differentials. The study concludes with a comparative exergy analysis between pure CO₂ and mixture-based cycles in RBC architecture. The findings highlight the potential of custom-tailored working fluids to enhance thermodynamic performance and operational stability of s-CO₂ power systems under cold-climate conditions. Full article

The rapid growth in lithium-ion battery (LIB) demand has underscored the urgent need for sustainable recycling methods to recover critical metals such as lithium, cobalt, nickel, and manganese. Traditional pyrometallurgical and hydrometallurgical approaches often suffer from high energy consumption, environmental impact, and limited metal selectivity. As an emerging alternative, solvometallurgy, and in particular the use of low-melting mixtures solvents, including deep eutectic solvents, offers a low-temperature, tunable, and potentially more environmentally compatible pathway for black mass processing. This review presents a comprehensive assessment of the recent advances (2020–2025) in the application of LoMMSs for metal recovery from LCO and NCM cathodes, analyzing 71 reported systems across binary, ternary, hydrated, and non-ChCl-based solvent families. Extraction efficiencies, reaction kinetics, coordination mechanisms, and solvent recyclability are critically evaluated, highlighting how solvent structure influences performance and selectivity. Particular attention is given to the challenges of lithium recovery, solvent degradation, and environmental trade-offs such as energy usage, waste generation, and chemical stability. A comparative synthesis identifies the most promising systems based on their mechanistic behavior and industrial relevance. The future outlook emphasizes the need for greener formulations, enhanced lithium selectivity, and life-cycle integration to support circular economy goals in battery recycling. Full article

The thermodynamic properties of di-2-ethylhexylphosphoric acid (D2EHPA) in organic solvents are critical for optimizing metal extraction processes in hydrometallurgy, necessitating precise determination of activity coefficients in binary systems such as D2EHPA–n-hexane. This study was devoted to the determination of n-hexane’s concentrations in the vapor phase over D2EHPA solutions at 293.0 K using gas chromatography (GC) and isopiestic (IP) methods. Comparison with literature data confirmed the superior reliability of GC measurements at low n-hexane concentrations. The experimentally determined activity coefficients of hexane, obtained via GC, served as the initial input parameters for UNIFAC modeling. The optimized interaction parameters were 1144 ± 25 (CH₂-HPO₄) and 228 ± 50 (HPO₄-CH₂), with the infinite dilution activity coefficient for D2EHPA ${\gamma }_{\infty }=22.1$. These results experimentally clarify the non-ideal behavior of D2EHPA–n-hexane mixtures, establishing a validated thermodynamic modeling framework for organophosphorus extractant systems. This work establishes a fundamental basis for investigating ternary systems, such as D2EHPA–aliphatic solvent–aromatic solvent and D2EHPA–metal complex–solvent systems, paving the way for enhanced liquid–liquid extraction efficiency. Full article

Cuboid packed-bed devices developed for chromatographic separation typically have shorter bed heights and larger cross-sectional areas than their equivalent cylindrical columns. These devices can be operated at low back pressures and give comparable or even better resolution than their equivalent columns. However, the bed height of a cuboid packed-bed device could potentially affect its separation performance. To examine this, three devices having 5, 10 and 19.5 mm bed heights were fabricated and packed with the same resin media. A mathematical model was first developed to predict the effect of bed height on the performance of these cuboid devices. This prediction was performed based on the residence time heterogeneity (RTH) in these devices, which increased slightly as the bed height was decreased. However, this was not likely to affect the separation efficiency very significantly. The relative performances of these three cuboid devices were then compared based on the resolution obtained during ion-exchange chromatography of multi-protein mixtures. As predicted by the mathematical model, the loss in resolution due to the decrease in bed height was relatively small (0.83 to 0.73 in binary protein separation). Also, this loss could easily be compensated for by slightly lowering the flow rate or by extending the elution gradient. The results discussed in this paper demonstrate that with cuboid packed-bed devices, the dimensions could be altered in a reasonably flexible manner without adversely affecting separation performance. Such flexibility is advantageous from the point of view of process design and optimization, which is critically important for developing large-scale processes for the purification of biologics. Full article

Controlling the stability of colloidal nanoparticles in multicomponent systems is crucial for advancing formulations and separation processes. This study investigates the selective agglomeration approach for binary colloidal mixtures, providing both fundamental insights into stability/agglomeration mechanisms and a scalable separation strategy. First, we established a binary model system comprising gold nanoparticles (Au NPs) and ZnS quantum dots (QDs) to assess interparticle interactions. UV-visible spectroscopy revealed that impurities released from ZnS QDs, particularly thiol-based ligands and unbound Zn ions, triggered the aggregation of Au NPs depending on their surface stabilizers. Functionalization of Au NPs with bis(p-sulfonatophenyl) phenylphosphine (BSPP) significantly enhanced colloidal stability, with unpurified BSPP-functionalized Au NPs exhibiting superior resistance to agglomeration. Building on these insights, we applied selective agglomeration to separate a complex colloidal system consisting of InP/ZnS core–shell QDs and ZnS byproducts, a critical challenge in QD synthesis that is particularly relevant for post-processing of samples that originate from large-scale flow synthesis. By systematically tuning the ethanol concentration as a poor solvent, we successfully achieved composition-dependent fractionation. Optical and spectroscopic analyses confirmed that coarse fractions were enriched in InP/ZnS QDs, while fines fractions mainly contained pure ZnS QDs, with absorption peaks at 605 nm and 290 nm, respectively. Photoluminescence spectra further demonstrated a redshift in the coarse fractions, correlating with an increase in particle size. These results underscore the potential of selective agglomeration as a scalable, post-synthesis classification method, offering a framework for controlling stability and advancing post-synthesis separation strategies in colloidal multicomponent systems. Full article

The study of solid–liquid equilibria offers critical insights into the molecular interactions between constituents in binary mixtures. Predicting these equilibria often requires comprehensive thermodynamic models, yet simplified approaches can provide valuable perspectives. In this work, we explore the application of the Bragg–Williams model to solid–liquid equilibria in binary mixtures leading to the formation of eutectic solvents. This model relies on a single parameter—the molar energy change upon mixing compounds—and demonstrates noteworthy features: the parameter can be estimated from a few (in principle, from a single) experimental melting points, and it correlates strongly with interaction energy parameters from more complex models, such as the PC-SAFT molecular-based equation of state. By using the Bragg–Williams model, we provide a straightforward and informative framework for characterizing solid–liquid equilibria, enabling insights into molecular interactions while requiring few data points as input. Despite its simplicity, the model effectively captures the essence of binary mixture energetics, positioning it as a practical tool for advancing the understanding of phase behavior in eutectic solvent systems. Full article

Global warming is a critical issue driven largely by the extensive release of greenhouse gases, with the cement industry being one of the biggest contributors to CO₂ emissions. A sustainable solution involves the integration of supplementary cementitious materials (SCMs) into cement production, which can mitigate environmental impacts. This study focuses on the effects of binary SCMs, composed of calcined expanded clay kiln dust and opoka, on the hardening and hydration behavior of Portland cement. The analysis used methods such as X-ray diffraction, thermal analysis, calorimetry, and compressive strength testing. The tested dust was thermally activated at 600 °C and the opoka was dried and milled to evaluate its combined influence on the cement properties. Portland cement was substituted with a combination of these two additives. The findings revealed that the two-component mixture exerts a multifaceted impact on the hydration process of Portland cement. The activated expanded clay kiln dust triggers a pozzolanic reaction because of its high reactivity, while the opoka component promotes the development of monocarboaluminates. This binary supplementary cementitious material, derived from opoka and expanded clay kiln dust, proves to be a highly effective substitute, allowing up to 25 wt.% replacement of Portland cement without reducing its compressive strength. Full article

Concentrated Solar Power (CSP) plants integrated with Thermal Energy Storage (TES) represent a promising renewable energy source for generating heat and power. Binary molten salt mixtures, commonly referred to as Solar Salts, are utilized as effective heat transfer fluids and storage media due to their thermal stability and favorable thermophysical properties. However, these mixtures pose significant challenges due to their high solidification temperatures, around 240 °C, which can compromise the longevity and reliability of critical system components such as pressure sensors and bellows seal globe valves. Thus, it is essential to characterize their performance, assess their reliability under various conditions, and understand their failure mechanisms, particularly in relation to temperature fluctuations affecting the fluid’s viscosity. This article discusses experimental tests conducted on a pressure sensor and a bellows seal globe valve, both designed for direct contact with molten salts in CSP environments, at the ENEA Casaccia Research Center laboratory in Rome. The methodology for conducting these experimental tests is detailed, and guidelines are outlined to optimize plant operation. The findings provide essential insights for improving component design and maintenance to minimize unplanned plant downtime. They also offer methodologies for installing measurement instruments and electrical heating systems on the components. Full article

As a renewable energy source and potential substitute for fossil fuels, biodiesel plays an increasingly important role in both energy security and environmental protection. Accurate thermal conductivity data of biodiesels and their mixture with diesel are critical to engine design to achieve high combustion efficiency. This study measured the thermal conductivity of binary mixtures of heptane and biodiesel components, specifically methyl myristate, methyl laurate, and methyl caprate, over a temperature range of 298.15–328.15 K, using the two-wire 3ω method. Based on the experimental data, the effect of mass fraction, temperature, and carbon chain length of the fatty acid ester on the thermal conductivity was analyzed. The second-order Scheffé polynomial model, Flippov equation, Jamieson equation, and Chen equation were used to correlate the experimental data and compare to find a better one. The Flippov equation shows the lowest absolute average relative deviation of 0.80% for the binary mixtures of heptane with methyl myristate, methyl laurate, and methyl caprate. Full article

The fluidized bed is a critical reactor in the energy and chemical industries, where the mixing and agglomeration behaviors of binary particles significantly influence both the efficiency of reaction processes and the uniformity of final products. However, the selection of appropriate drag force models remains a subject of debate due to the variability in particle properties and operating conditions. In this study, we investigated the fluidization behavior of binary mixtures composed of two different sizes of Geldart-D particles within a fluidized bed, evaluating nine distinct drag force models, including Wen and Yu; Schiller and Naumann; Ergun; Gidaspow, Bezburuah, and Ding; Huilin and Gidaspow; De Felice; Syamlal and O’Brien; and Hill, Koch, and Ladd. We focused on four key parameters: particle mixing degree, migration characteristics, temperature variation, and mean pressure drop. Simulation results revealed that the choice of drag model markedly affected mixing behavior, migration dynamics, and temperature distribution. Notably, the Ergun; Gidaspow, Bezburuah, and Ding; and Hill, Koch, and Ladd models exhibited superior particle mixing uniformity. While the drag model had a relatively minor impact on particle temperature changes, its selection became critical in simulations requiring high-temperature precision. Regarding pressure drop, the Huilin and Gidaspow and Gidaspow, Bezburuah, and Ding models demonstrated smaller and more stable pressure drop fluctuations. These findings offer valuable theoretical insights into gas–solid two-phase flow under binary particle mixing and provide practical guidance for the design and operation of fluidized bed reactors. Full article

C-based XC binary materials and their (XC)_m/(YC)_n (X, Y ≡ Si, Ge and Sn) superlattices (SLs) have recently gained considerable interest as valuable alternatives to Si for designing and/or exploiting nanostructured electronic devices (NEDs) in the growing high-power application needs. In commercial NEDs, heat dissipation and thermal management have been and still are crucial issues. The concept of phonon engineering is important for manipulating thermal transport in low-dimensional heterostructures to study their lattice dynamical features. By adopting a realistic rigid-ion-model, we reported results of phonon dispersions ${\mathsf{\omega }}_{\mathrm{j}}^{\mathrm{S}\mathrm{L}}\left(\overrightarrow{\mathrm{k}}\right) \mathrm{o}\mathrm{f} \mathrm{n}\mathrm{o}\mathrm{v}\mathrm{e}\mathrm{l} \mathrm{s}\mathrm{h}\mathrm{o}\mathrm{r}\mathrm{t}-\mathrm{p}\mathrm{e}\mathrm{r}\mathrm{i}\mathrm{o}\mathrm{d} {\left(\mathrm{X}\mathrm{C}\right)}_{\mathrm{m}}/{(\mathrm{Y}\mathrm{C})}_{\mathrm{n}}\left[001\right] \mathrm{S}\mathrm{L}\mathrm{s}$, for m, n = 2, 3, 4 by varying phonon wavevectors $\left|{\overrightarrow{\mathrm{k}}}_{\mathrm{S}\mathrm{L}}\right|$ along the growth ${\mathrm{k}}_{||}$ ([001]), and in-plane ${\mathrm{k}}_{\perp }$ ([100], [010]) directions. The SL phonon dispersions displayed flattening of modes, especially at high-symmetry critical points Γ, Z and M. Miniband formation and anti-crossings in ${\mathsf{\omega }}_{\mathrm{j}}^{\mathrm{S}\mathrm{L}}\left(\overrightarrow{\mathrm{k}}\right)$ lead to the reduction in phonon conductivity ${\mathsf{\kappa }}_{\mathrm{z}}$ along the growth direction by an order of magnitude relative to the bulk materials. Due to zone-folding effects, the in-plane phonons in SLs exhibited a strong mixture of XC-like and YC-like low-energy ${\mathsf{\omega }}_{\mathrm{T}\mathrm{A}}$, ${\mathsf{\omega }}_{\mathrm{L}\mathrm{A}}$ modes with the emergence of stop bands at certain $\left|{\overrightarrow{\mathrm{k}}}_{\mathrm{S}\mathrm{L}}\right|$. For thermal transport applications, the results demonstrate modifications in thermal conductivities via changes in group velocities, specific heat, and density of states. Full article