Search Results (3,425)

A rigorous rate-based absorption model integrated with an improved thermodynamic framework was developed to simulate natural gas desulfurization using TMS–MDEA (Tetramethylene Sulfone–Methyldiethanolamine) aqueous solutions. The model was validated against 50 sets of industrial and experimental data, achieving R² values above 0.98 and average deviations within 5%. The model was formulated for steady-state operation of a trayed absorber integrated with flash and packed-bed regeneration and applicable over industrially relevant ranges (absorber pressure 3–6.4 MPa; gas–liquid ratio 350–720; flash pressure 0.3–0.6 MPa; packing height ≥ 3 m). The results indicate that H₂S can be removed almost completely (>99.9%); CO₂ and COS achieve 70–85% and 75–83% removal, respectively; and CH₃SH removal exceeds 90% under typical conditions. Parametric analysis revealed that higher tray numbers, weir heights, and pressures enhance absorption efficiency, whereas hydrocarbon solubility increases with carbon number and is strongly affected by pressure and the gas–liquid ratio. In the desorption section, flash regeneration efficiently strips light hydrocarbons, with decreasing desorption efficiency from CH₄ to C₆H₁₄. This study provides quantitative insights into the coupled absorption–desorption process and offers practical guidance for process design, solvent selection, and energy-efficient operation in natural gas purification. Full article

Materials that allow the storage of a significant amount of heat in a narrow temperature range by a solid–liquid or a solid–solid phase change are called Phase Change Materials (PCMs). Understanding the thermodynamics of PCMs is crucial in PCM R&D for identifying candidate materials, developing new PCMs, and optimizing known PCMs. In this work, a review of the use of entropy to understand the thermodynamics of pure substances as PCMs is performed. Among pure substances, water, alkanes, alkanols, and fatty acids are well-known. Because they give valuable information, elements are also included. While phase change enthalpy and temperature are easy to comprehend and are directly used for application, the opposite holds for entropy. Thus, entropy usually receives little attention. However, as this review shows, entropy is of central importance, and even if it is not analyzed explicitly, then it is implicitly included in the data. If explicitly used, it can reveal crucial information. This is shown by a review of analysis tools and their results from analyzing typical PCMs. The review shows that if entropy is used systematically, a significant improvement in the understanding of the thermodynamics of PCMs is possible. Full article

We present a comprehensive quantum field theoretical analysis of graviton self-energy and mass generation in 3+1 dimensional BTZ black hole spacetime, incorporating axion interactions within the framework of dark matter theory. Using a novel mathematical approach based on ultrahyperfunctions, generalizations of Schwartz tempered distributions to the complex plane, we derive exact quantum relativistic expressions for graviton and axion self-energies without requiring ad hoc regularization procedures. Our approach extends the Gupta–Feynman quantization framework to BTZ gravity while introducing a new constraint that eliminates unitarity violations inherent in previous formulations, thereby avoiding the need for ghost fields. Through systematic application of generalized Feynman parameters, we evaluate both bradyonic and tachyonic graviton modes, revealing distinct quantum correction patterns that depend critically on momentum, energy, and mass parameters. Key findings include (1) natural graviton mass generation through cosmological constant interactions, yielding $m^2=2\left|\Lambda \right|/\kappa (1-\kappa )$; (2) qualitatively different quantum behaviors between bradyonic and tachyonic modes, with bradyonic corrections reaching amplitudes 6 times larger than their tachyonic counterparts; (3) the discovery of momentum-dependent quantum dissipation effects that provide natural ultraviolet regulation; and (4) the first explicit analytical expressions and graphical representations for 17 distinct graviton self-energy contributions. The ultrahyperfunction formalism proves essential for handling the non-renormalizable nature of the theory, providing mathematically rigorous treatment of highly singular integrals while maintaining Lorentz invariance. Our results suggest observable consequences in gravitational wave propagation through frequency-dependent dispersive effects and modifications to black hole thermodynamics, potentially bridging theoretical quantum gravity with experimental constraints. Full article

Promising photophysical properties and the enhanced sensitivity to molecular oxygen of porphyrins metalated with Gd(III) generate a need for their detailed description on an atomic level with the account of coordinated ligands, which also influence the properties. Herein, the complexation of tetraphenylporphyrin with gadolinium chloride in imidazole medium was analyzed using density functional theory in the framework of ωB97XD functional with hybrid diffused polarization-consistent basis sets. The complexes with different number of coordinated imidazole ligands (k = 0–2) were calculated to compare their structural parameters, electrostatic potential distribution, and interaction with molecular oxygen. Thermodynamic functions of complex formation were estimated for a set of possible reactions, including various side products (hydrogen chloride or imidazole hydrochloride) and different number of imidazole molecules involved. Weak interactions in the coordination sphere of chlorogadolinium tetraphenylporphyrin with attached imidazole ligands were also assessed. Performed analysis proved the presence of imidazole protection against the molecular oxygen attack. Full article

This paper presents a one-dimensional (1-D) thermodynamic engine simulation validated through testbench measurements. The objective was to evaluate the accuracy of the 1-D model by comparing simulated results with experimental data from a modern 2-L turbocharged gasoline direct injection (DI) internal combustion engine featuring variable valve timing. Key parameters such as engine speed, air–fuel ratio, temperature, and pressure were measured under controlled conditions. Using AVL BOOST, simulation modeled combustion, valve timing, and thermodynamic processes across intake and exhaust systems. Simulation results were compared with experimental data across various steady-state operating points. The model demonstrated strong agreement with experimental results in steady-state operation. A few differences highlight the need for further refinement of the model. The study confirms the effectiveness of 1-D simulations as a reliable and cost-efficient tool for engine analysis and optimization. Future work will focus on enhancing the accuracy of the simulation. Full article

Municipal solid waste incineration (MSWI) fly ash, classified as hazardous waste (HW18) due to the presence of heavy metals and dioxins, necessitates both harmless treatment and resource utilization. In this study, a Na-P1 zeolite adsorbent was synthesised from MSW incineration fly ash using its intrinsic Si and Al sources, supplemented by silica sol and sodium aluminate solution. The synthesised zeolite was employed for the adsorption removal of tetracycline hydrochloride (TCH) from wastewater. Under the optimised conditions (initial TCH concentration of 10 mg·L⁻¹, adsorbent dosage of 0.4 g·L⁻¹, pH 5.0, temperature 45 °C, and contact time 60 min), a maximum adsorption capacity of 14.8 mg·g⁻¹ and a removal efficiency of 59.1% were achieved. Kinetic analysis revealed that the adsorption process followed the pseudo-first-order model (R² = 0.975). The Langmuir isotherm provided a better fit than the Freundlich model (R² = 0.988), indicating monolayer adsorption on homogeneous sites. Thermodynamic parameters (ΔG < 0, ΔH > 0) confirmed that the adsorption was spontaneous and endothermic, with higher temperatures favoring enhanced TCH adsorption. This work demonstrates the feasibility of converting hazardous MSW incineration fly ash into a value-added Na-P1 zeolite adsorbent with excellent performance for antibiotic wastewater treatment, thereby offering a sustainable strategy for fly ash resource recovery and environmental remediation. Full article

Bedding-parallel fractures represent a crucial flow-path network in shale oil reservoirs, yet their timing of opening and driving mechanisms remain subjects of long-standing debate. This study investigates the origin and opening mechanisms of bedding-parallel fractures within the Paleogene Funing shale oil reservoir of the Huazhuang area, Subei Basin, eastern China. A combination of petrography, fluid-inclusion analysis, PVTx paleo-pressure modeling, hydrocarbon generation history modeling, and reflectance measurements was employed. The results reveal the presence of abundant oil inclusions and bitumen within the bedding-parallel veins, indicating that the initiation of fracture was essentially synchronous with the oil emplacement. The studied Funing shale, with vitrinite reflectance values of 0.85% to 1.04%, is mature, identifying it as an effective oil-prone source rock. Thermal maturity of bitumen is comparable to that of the host shale, suggesting a local oil source. Homogenization temperatures (T_h) of coeval aqueous inclusions record fracture opening temperatures of approximately 100–150 °C, consistent with oil-window conditions. By integrating T_h data with burial history modeling, the timing of fracture formation and coeval oil injection is constrained to the peak period of local hydrocarbon generation, rather than the Oligocene Sanduo tectonic event. This indicates that fracture opening was primarily associated with hydrocarbon generation rather than tectonic compression. Petroleum-inclusion thermodynamic modeling demonstrates that the bedding-parallel fracture opening occurred under moderate to strong overpressure conditions, with calculated paleo-pressure coefficients of ~1.35–2.36. This finding provides direct paleo-pressure evidence supporting the mechanism of bedding-parallel fracture opening driven by fluid overpressure created during oil generation. These oil-bearing, overpressured fluids facilitated the initial opening and subsequent propagation of fractures along the bedding planes of shales. Concurrently, the precipitation of the calcite veins may have been triggered by pressure drop associated with the expulsion of some coexisting aqueous fluids. This study provides evidence addressing the debated mechanisms of bedding-parallel fracture opening in organic-rich shales, highlighting the critical role of oil generation-induced overpressure. Full article

This study investigates an integrated solar-driven single-effect H₂O–LiBr absorption chiller powered by low-grade thermal energy. A detailed thermodynamic model, comprising a solar collector, a thermal storage tank, and an absorption cycle, was developed using the Engineering Equation Solver (EES) software V10.561. A comprehensive parametric analysis and multi-objective optimization were then conducted to enhance both the energy and exergy performance of the system. The Response Surface Methodology (RSM), based on the Box–Behnken Design, was employed to develop regression models validated through analysis of variance (ANOVA). The generator temperature (78–86 °C), evaporator temperature (2.5–6.5 °C), and absorber/condenser temperature (30–40 °C) were selected as key variables. According to the results, the single-objective analyses revealed maximum values of COP = 0.8065, cooling capacity = 20.72 kW, and exergy efficiency = 39.29%. Subsequently, the multi-objective RSM optimization produced a balanced global optimum with COP = 0.797, cooling capacity = 20.68 kW, and exergy efficiency = 36.93%, achieved under optimal operating conditions of 78 °C generator temperature, 6.5 °C evaporator temperature, and 30 °C absorber/condenser temperature. The obtained results confirm the significance of the proposed low-grade solar absorption chiller, demonstrating comparable or superior performance to recent studies (e.g., COP ≈ 0.75–0.80 and ≈35–37%). This agreement validates the RSM-based optimization approach and confirms the system’s suitability for sustainable cooling applications in low-temperature solar environments. Full article

Aluminum doping can improve the phase stability of metastable compound Sm₂Fe₁₇C_x with a high carbon content (x > 1.5). We investigated the preferential site substitution of Al, chemical bonding, and structural stability in Sm₂(Fe,Al)₁₇C₃ using first-principle calculations. Our results reveal a strong correlation between the preferential substitution of Fe by Al and the atomic site chemical environment, which affects the overall phase stability. Specifically, Al preferentially occupies the 9d site in Sm₂(Fe,Al)₁₇C₃. At the same time, Al prefers the site 6c in its parent phase Sm₂(Fe,Al)₁₇. Partial replacement of Fe with Al leads to a more negative formation energy, indicating enhanced thermodynamic stability. Crystal Orbital Hamilton Population (COHP) and Crystal Orbital Bond Index (COBI) analysis suggest that insertion of carbon weakens the bonding strength of Sm-Fe (18f) and Sm-Fe (18h), resulting in metastability of Sm₂Fe₁₇C_x. Doping Al strengthens Al-Fe, Al-Sm, Sm-Fe (18f, 18h) and Fe–C bonding in Sm₂(Fe,Al)₁₇C₃, as revealed by calculated COHP and COBI. These effects contribute to improved phase stability in the Al-doped 2:17 interstitial compound. Full article

Injecting carbon dioxide (CO₂) into underground geo-structures, such as depleted oil and gas reservoirs, reduces man-made CO₂ emissions into the atmosphere or removes what is already there. Studies have identified the risks of CO₂ leaks from these underground geo-structures through wellbores back into the atmosphere due to the high mobility of CO₂ in gaseous and supercritical states. This work aims at proposing a novel method of CO₂ storage using the Joule–Thomson cooling effect to effectively produce CO₂ hydrates on seafloors, with an objective to avoid the leakage risks of storage in depleted oil and gas reservoirs. Through the combination of thermodynamic data, analysis of hydrate stability, and engineering design with established working parameters, this study proposes an innovative concept and an enabling process for CO₂ placement onto seafloors for safe storage. The results of case analysis of typical seawater conditions reveal that the appropriate seafloor depth ranges for different applications (>1900 m for liquid CO₂ and 700–1900 m for CO₂ hydrate). An engineering design procedure for real applications is outlined. Full article

Exergy efficiency is a measure of thermodynamic perfection. A device that operates reversibly has an exergy efficiency of 100 percent and is said to be thermodynamically perfect. A reversible process involves zero entropy generation and thus zero exergy destruction since X_destroyed = T₀S_gen. Exergy efficiency is generally defined as the ratio of exergy output to exergy input η_ex = X_output/X_input = 1 − (X_destroyed + X_loss)/X_input or the ratio of exergy recovered to exergy expended η_ex = X_recovered/X_expended = 1 − X_destroyed/X_expended. In this paper, exergy efficiency relations are obtained first for a general steady-flow system using both approaches. Then, explicit general relations are obtained for common steady-flow devices, such as turbines, compressors, pumps, nozzles, diffusers, valves and heat exchangers, as well as heat engines, refrigerators, and heat pumps. For power and refrigeration cycles, five different forms of exergy efficiency relations are developed, and their equivalence is demonstrated. With the unified approach presented here and the insights provided, the controversy and confusion associated with different exergy efficiency definitions are largely alleviated. Full article

Air liquefaction systems are essential in cryogenic engineering and energy storage, yet their performance is often constrained by significant exergy destruction. This study develops an exergy-based assessment of the Linde–Hampson air liquefaction cycle to identify dominant sources of inefficiency and explore strategies for improvement. The analysis shows that throttling (≈41%) and compression (≈40%) represent the major contributions to exergy losses, followed by finite-temperature heat transfer (≈15%) in the recuperative heat exchanger. To mitigate these losses, fractional throttling and optimized inlet conditions are proposed, leading to reduced compressor work and improved overall efficiency. A comparative study of a two-stage throttling configuration demonstrates a decrease in throttling-related exergy destruction to approximately 30%. Reverse Pinch analysis is employed to verify the thermal coupling of hot and cold streams and to determine the minimum feasible temperature difference. The design optimization of the recuperative heat exchanger identifies an optimal velocity ratio that minimizes pressure losses and quantifies how compression pressure affects the required heat transfer surface area. The results provide a systematic framework for improving the thermodynamic performance of air liquefaction cycles, highlighting exergy analysis as a powerful tool for guiding structural modifications and functional optimization. Full article

Surface energy is involved in various thermodynamic processes, providing a driving force for thermodynamic reactions. However, surface energies applied in current engineering calculations are generally measured in J/m², which is unsuitable for thermodynamic analysis. To solve this problem, the calculation formula for surface energies was modified to convert the unit of measurement, transforming the non-thermodynamic measurement unit J/m² into the thermodynamically characterized kJ/mol. The calculated surface energy values measured in kJ/mol are unstable due to the influence of the number of atomic layers (t) in the constructed models. Meanwhile, the problem of determining the surface layer thickness, i.e., the number of atomic layers with surface characteristics (t₀), remains unresolved in surface science. Therefore, the extended Finnis Sinclair (EFS) potential was improved by extending the nearest neighbor range and utilized in analyzing the energy per atom, resulting in the determined number of t₀. These results suggest that selecting the surface layer number corresponding to the first to third nearest-neighbor atoms could be appropriate, and the resulting surface energies in kJ/mol appear reasonable. The validity of this computational method and the origin of nanoporous W activity were confirmed by analyzing the changes in total surface energy before and after nano-treatment using the novel nanosized approach. Full article

Polar patterns and topological defects are ubiquitous in active matter. In this paper, we study a paradigmatic polar active dumbbell system through numerical simulations, to clarify how polar patterns and defects emerge and shape evolution. We focus on the interplay between these patterns and morphology, domain growth, irreversibility, and compressibility, tuned by dumbbell rigidity and interaction strength. Our results show that, when separated through MIPS, dumbbells with softer interactions can slide one relative to each other and compress more easily, producing blurred hexatic patterns, polarization patterns extended across entire hexatically varied domains, and stronger compression effects. Analysis of isolated domains reveals the consistent presence of inward-pointing topological defects that drive cluster compression and generate non-trivial density profiles, whose magnitude and extension are ruled by the rigidity of the pairwise potential. Investigation of entropy production reveals instead that clusters hosting an aster/spiral defect are characterized by a flat/increasing entropy profile mirroring the underlying polarization structure, thus suggesting an alternative avenue to distinguish topological defects on thermodynamical grounds. Overall, our study highlights how interaction strength and defect–compression interplay affect cluster evolution in particle-based active models, and also provides connections with recent studies of continuum polar active field models. Full article

A comprehensive analysis of key findings derived from density functional theory (DFT) studies reveals that current theoretical data on curcumin remain incomplete, underscoring the need for further computational investigation to achieve a more thorough understanding of its chemical and biological reactivity. This study addresses these gaps through four primary objectives: (i) determination of a complete set of thermodynamic descriptors and elucidation of the multi-step anti-radical mechanisms of the neutral, radical, anionic, and radical–anionic forms of curcumin; (ii) calculation of global chemical reactivity descriptors of curcumin in various solvent environments; (iii) theoretical reproduction of experimentally determined pK_a values for all active sites within the molecule; and (iv) examination of the effects of dispersion interactions and solvent polarity on the reactivity descriptors of keto–enol forms of curcumin. The results obtained provide enhanced insight into the molecular behavior of curcumin, facilitating improved predictions of its reactivity under diverse conditions. Moreover, the findings indicate a potential structural modification of the keto form of curcumin, involving the attachment of two 4-hydroxy-3-methoxyphenyl-prop-1-en-2-one moieties to the methylene group. The resulting modeled compound, referred to as di-curcumin, exhibits enhanced chemical reactivity and increased anti-radical potential. Full article