Search Results (83)

Routine model-based diagnosis of sulfuric acid converters can attribute performance loss to catalyst deactivation, fouling, bypass, or maldistribution before establishing whether routine measurements distinguish these causes. This study develops the Converter Condition Inference Framework (CCIF) for four-bed double-contact SO₂ converters, placing a practical identifiability gate before mechanism-specific interpretation. A reported-parameter reaction and energy balance kernel using published feed, kinetics, and physical reaction enthalpy reproduces the industrial benchmark only approximately. An energy balance check indicates that the reported first-bed conversion and temperature require an effective enthalpy of about 1.6 times the physical value under the adopted thermochemical basis. At the reference condition, the uncertainty-scaled local sensitivity matrix has rank 1 for a six-state vector; this result persists across the tested inlet temperature range and rate and heat release perturbations. In the equilibrium-limited reduced model, catalyst activity loss and fouling down to 40% of fresh activity produce no resolvable change in conversion, outlet SO₂ slip, or bed temperatures, whereas bypass alters the temperature signature. Even idealized bed-resolved catalyst condition observations raise the rank only to 5. CCIF therefore reports the evidence-supported state class and required measurement upgrades rather than a validated diagnosis. Unit-specific calibration and catalyst-side evidence remain necessary before mechanism-specific maintenance decisions. Full article

Paraffin-rich organic deposits in the near-wellbore zone reduce pore space, increase the skin factor, and impair oil-well productivity, and frequently recur after conventional treatment. This study develops a coupled one-dimensional radial model of thermochemical treatment in which an activated aluminum alloy reacts with formation water in the wellbore, releasing heat that propagates into the formation and melts and dissolves paraffin deposits. The model combines two-phase oil–water flow; heat transfer with latent-heat effects; eight paraffin pseudo-components in dissolved, suspended, and deposited states; temperature-dependent solid–liquid equilibrium; and wax deposition, dissolution, melting, and redistribution coupled to porosity–permeability recovery. Hydrogen is treated as a wellbore reaction byproduct that segregates upward and accumulates below the closed packer, rather than as a mobile reservoir phase, and the reaction kinetics are based on experimental hydrogen-evolution data for three activated aluminum alloys of differing reactivity. Simulations show a rapid skin-factor reduction during the reaction, followed by partial recovery to approximately 80–90% of the initial value during prolonged shut-in because of cooling, recrystallization, and redeposition. Increasing reagent amount or reactivity, initial wax-induced damage, or oil saturation enhances the predicted treatment effect, whereas reservoir type has a comparatively minor influence. Full article

High-speed turbulent boundary layers govern the transport of momentum, mass, and energy in compressible flows and play a central role in determining aerodynamic performance, skin-friction drag, aerodynamic heating, flow stability, and thermal protection requirements of advanced aerospace vehicles. Over the past three decades, direct numerical simulation (DNS) has revolutionized the study of compressible wall-bounded turbulence by resolving all dynamically relevant turbulent scales without turbulence-model assumptions, providing benchmark-quality databases and unprecedented physical insight into flow phenomena that remain difficult or impossible to measure experimentally. Together with complementary high-fidelity approaches, DNS has substantially advanced the understanding of turbulence dynamics across a broad range of supersonic and hypersonic flow conditions. This review presents a critical assessment of advances in the high-fidelity simulation of compressible turbulent boundary layers under non-reacting conditions. Particular emphasis is placed on the flow physics of canonical zero-pressure-gradient boundary layers, shock-wave/turbulent-boundary-layer interactions (SWTBLIs), pressure-gradient-driven flows, streamline-curvature effects, and thermochemical non-equilibrium phenomena. Recent developments in numerical methodologies are also briefly examined, including high-order discretization techniques, turbulence inflow generation methods, hybrid continuum-kinetic formulations, and advances in high-performance computing that have enabled DNS at increasingly high Reynolds and Mach numbers. The review highlights the major physical insights emerging from DNS studies, demonstrating that many fundamental characteristics of compressible wall turbulence remain closely related to their incompressible counterparts when appropriate compressibility transformations are employed. At the same time, DNS has revealed the critical influence of wall temperature, pressure gradients, streamline curvature, shock interactions, and finite-rate thermochemistry on turbulence structure, coherent motions, interscale energy transfer, boundary-layer separation, and aerodynamic heating. Full article

Hydrogen sulfide (H₂S), a high-volume by-product of the hydrodesulfurization of fossil fuels, can be valorized by thermolysis to recover both molecular hydrogen and elemental sulfur, rather than being oxidized as in the conventional Claus process. The viability of this route depends on quantitative knowledge of the reaction mechanism and of the energy costs of dissociation, which are difficult to obtain experimentally at the temperatures involved. Here we study H₂S thermolysis by reactive molecular dynamics (RMD) with the ReaxFF potential for systems of 1000 H₂S molecules at 1 atm, addressing three coupled questions: the simulation parameters required for dilute gases, the energetics of dissociation, and the elementary reaction mechanism. The interaction cutoff radius proved critical: the original 10 Å value, parametrized for condensed systems, misses about 23 eV of attractive non-bonded interaction energy in the gaseous system at 298.15 K (≈0.023 eV per molecule) and fails to capture dissociation at 3000 K within 20 ns, whereas radii of 30–40 Å converge. Using a 40 Å cutoff at 2500, 3000 and 3500 K, atom-resolved species-transition records reveal a free-radical chain mechanism built from the same set of elementary steps at the three temperatures, whose relative contributions shift with temperature: S–H homolysis initiates the chain, hydrogen abstraction (H• + H₂S → H₂ + HS•) is essentially the exclusive source of H₂ (persistent H• + H• recombination contributed only 1, 13 and 17 events, below 0.5% of the abstraction count), and a slow sulfur-condensation stage (S₂ → S₃ → S₄) limits the net conversion, which reached 9.3 ± 0.9%, 26.3 ± 1.4% and 46.7 ± 1.6% within the simulated windows (single-trajectory counting resolution)—kinetically limited values, not equilibrium conversions. The enthalpy of the system rises linearly with the number of H₂S molecules consumed (R² ≥ 0.99), defining energy costs of 2.46 ± 0.04, 3.10 ± 0.08 and 3.95 ± 0.18 eV per molecule that increase with temperature by ≈1.48 eV per 1000 K; at 3500 K the cost lies between the 0 K complete-dissociation limit D₀ = 3.90 eV derived from the experimental H–SH bond energy and the Kirchhoff-corrected complete-dissociation enthalpy at that temperature (4.11–4.12 eV), statistically indistinguishable from the latter (a 0.9σ difference). These results provide a thermochemically validated, molecular-level basis for engineering the valorization of residual H₂S as a source of green hydrogen. Full article

Acrylonitrile butadiene styrene (ABS) has emerged as a widely adopted solid fuel for hybrid rocket propulsion due to its compatibility with fused deposition modeling and favorable regression characteristics. As a terpolymer, however, ABS monomer mass fractions vary across commercial sources, introducing thermochemical variability that is rarely accounted for in propulsion modeling. This study presents a sensitivity analysis examining how compositional variability among ten commercially available ABS feedstock propagates into hybrid rocket performance predictions. Each source was characterized using bomb calorimetry and Fourier-transform infrared spectroscopy to derive source-specific constituent mass fractions and enthalpies of formation, which were supplied to NASA’s Chemical Equilibrium with Applications code to evaluate characteristic velocity under gaseous oxygen combustion. The second objective of this work is to determine which characterization and modeling workflow is sufficient for that purpose by quantifying the sensitivity of characteristic velocity predictions to the enthalpy of formation values derived from bomb calorimetry versus Fourier-transform infrared spectroscopy combined with the Van Krevelen group-contribution method. The two pathways yield enthalpy estimates that differ by 2.4–25.9 kJ/mol, but these differences propagate to less than 0.5% in predicted characteristic velocity across all 3D-printed filaments, indicating that the simpler group-contribution approach is adequate for routine performance prediction while direct calorimetry retains independent values for material qualification. The results demonstrate that assuming a single canonical ABS formulation introduces meaningful uncertainty in predicted characteristic velocity and that experimental feedstock characterization should be considered standard practice in hybrid propellant development. Full article

Steam-assisted gravity drainage (SAGD) makes a significant contribution to Canada’s heavy oil production. Yet, it faces notable efficiency challenges during late-life stages, characterized by increased Steam–Oil Ratios and environmental concerns. Non-condensable gas (NCG) injection has emerged as a promising strategy to address these issues, particularly in late-life and post-steam SAGD phases. This review systematically examines the mechanisms, phase behavior, thermochemical interactions, field applications, and operational impacts of injecting NCGs such as methane, nitrogen, and carbon dioxide. This work exclusively synthesizes the application of NCG injections in mature SAGD reservoirs while outlining existing challenges. It delivers a unified perspective on this domain, introducing practical insights to improve NCG injection efficiency. Critical analysis of the existing literature reveals key benefits, including reservoir pressure maintenance, steam chamber stabilization, and viscosity reduction. However, literature gaps persist regarding long-term field-scale validation, complex drive mechanisms at the steam chamber flanks, thermochemical reactions, interactions with geological heterogeneity, and detailed thermodynamic modeling under non-equilibrium conditions. Emphasizing these gaps underscores the importance of further research and integrated modeling to optimize NCG utilization, thus enhancing recovery efficiency, reducing environmental footprints, and extending reservoir life. Full article

This study investigates the thermochemical reaction behaviour of scheelite–millscale aluminothermy for direct tungsten alloying in steel production. Experimental mixtures of aluminium, millscale, and scheelite concentrate were simulated using gas–slag–metal (g-s-m) equilibrium calculations in FactSage 8.3 at 2200 °C, and compared with previously reported experimental results. The simulations reproduced metal yields accurately with 0.901 to 0.940 correlation coefficients and predicted tungsten levels consistent with measured steel compositions. However, significant discrepancies were observed in predicted silicon levels, with simulations overestimating steel %Si by up to 3.5%, despite negligible gas-phase losses. Oxygen partial pressure calculations indicate that the Fe/FeO reaction equilibrium controls process reduction conditions. Backcalculation of activity coefficients revealed that FactSage minimisation routines understated silicon activity coefficient values. SiO₂ mass transfer may play a role in low %Si in steel, but this is not clear due to differences in expected mass transfer regimes in aluminothermy under ASR and SHS conditions. Overall, the simulations demonstrate adequate predictive capability for alloying trends and metal yields while highlighting limitations in predicting silicon partitioning. These findings confirm the utility of thermochemical simulation for designing aluminothermic feed mixtures, reducing the number of experiments needed to optimise the aluminothermic feed mixture ratios. Full article

This study focuses on a 155 mm 32CrNi3MoV steel barrel and presents a thermochemically coupled phase transformation and diffusion dynamics model. The model leverages the significant disparity between radial and axial temperature gradients to simplify the heat conduction problem to a one-dimensional transient formulation. The temperature field distribution during firing sequences is solved analytically, accounting for the dynamic shift in critical phase transformation temperatures under high heating rates. The evolution of the martensitic layer thickness under repeated thermal shock is subsequently calculated. A numerical model for the pulsed diffusion of C and N is established based on Fick’s second law, incorporating the competitive diffusion–phase transformation mechanisms that govern martensite/austenite interface migration. To quantitatively evaluate the synergistic contribution of C and N to austenite stabilization, a carbon equivalent (Ceq) model is introduced, with the weight coefficient of N relative to C determined to be 0.68 and the critical Ceq required to lower the martensite start temperature below 25 °C calculated as 1.15 wt%. Concurrently, the microstructure and elemental distribution within the austenite layer of the retired barrel are systematically characterized using multi-scale techniques. The results indicate that the austenite layer on the inner bore surface arises from the synergistic effects of cyclic thermal-shock-induced phase transformation and elemental diffusion. Based on the Ceq criterion, the austenite layer thickness increases rapidly during the initial ~100 firing cycles, after which the growth rate slows significantly: it reaches approximately 1.27 μm after the first cycle and 2.94 μm after 1000 cycles, with only 0.2 μm of additional thickening between 100 and 1000 cycles—consistent with the experimentally observed range of 1.52–4.16 μm. The martensitic layer formed during the first firing cycle exhibits low thermal conductivity, which impedes subsequent heat transfer and leads to stabilization of its thickness at a characteristic depth. Grain refinement induced by repeated thermal shock provide short-circuit diffusion paths for elemental diffusion, accelerating compositional homogenization within the austenite layer and resulting in a stepped concentration profile at the interface. This study provides a representative example of non-equilibrium coupled phase transformation–diffusion phenomena under extreme transient loading. The established thickness prediction model can provide guidance for service life assessment of large-caliber barrels, offering both theoretical foundations and practical engineering guidance for their material design and performance optimization. Full article

To address the erosion-induced failure of large-caliber gun barrels under extreme thermochemical coupling, this study systematically investigates the microstructural evolution of multi-layered gradient regions along the radial direction of 32CrNi3MoV steel under extreme thermochemical cycling. Leveraging SEM, EBSD, TKD, and double-beam aberration-corrected TEM, combined with JMatPro thermodynamic simulations, the phase transitions, crystallographic characteristics, and substructural evolution spanning from the bore surface to the matrix are elucidated. The results demonstrate that a three-layer gradient structure forms along the radial direction. The topmost layer is a chemically stabilized metastable austenite diffusion layer with a thickness of 1.5–4.0 μm. which is attributed to the suppression of martensitic transformation due to C/N interstitial diffusion lowering the MS temperature. The observed high-density dislocation tangles and stacking faults within this austenite diffusion layer result from thermal mismatch stresses during rapid thermal cycling. The subsurface region is a martensitic transformation layer with a thickness of 70–97 μm, exhibiting a substructural gradient from nanostructured high-density twinned martensite to refined lath martensite. Thermodynamic analysis indicates that rapid heating (≈10⁵ °C/s) facilitates significant austenite nucleation and growth during the reverse phase transformation, subsequently forming nanostructured martensitic grains via non-equilibrium transformation during rapid cooling. Adjacent to this is a matrix tempering layer extending approximately 160 μm. Nanoindentation hardness profiling reveals that the peak radial hardness (≈1000 HV) occurs within the fine-grained martensitic zone approximately 40 μm from the surface. In contrast, the tempered layer exhibits reduced hardness (≈400 HV) compared to the original matrix (≈500 HV). This is primarily attributed to transient high-temperature over-tempering effects, which induces carbide coarsening and the loss of solid solution strengthening, alongside the softening of prior austenite grain boundaries. This study clarifies the micro-to-nanoscale evolution of the barrel microstructure, providing critical theoretical insights for understanding erosion mechanisms and improving lifetime predictions. Full article

High-entropy MAX (HE-MAX) phases represent a new class of layered ceramics that combine the multi-principal-element chemistry of high-entropy materials with intrinsic damage tolerance, electrical conductivity, and multifunctionality of conventional MAX phases. Despite their promise, the synthesis of HE-MAX phases remains fundamentally constrained by sluggish multicomponent diffusion, narrow thermodynamic stability windows, and strong competition from thermodynamically favored binary and ternary carbides, borides, and nitrides. These challenges are further exacerbated by the volatility of A-site elements under near-equilibrium processing conditions. This review positions self-propagating high-temperature synthesis (SHS) as an energy-efficient, non-equilibrium processing route capable of stabilizing selected entropy-driven MAX chemistries through ultrafast thermal excursions and rapid quenching. A unified thermodynamic–kinetic framework is developed to elucidate the interplay among reaction enthalpy, configurational entropy, combustion wave sustainability, and phase evolution in HE-MAX systems. Predictions of thermochemical adiabatic temperature are systematically correlated with experimental SHS studies to delineate phase stability boundaries, stoichiometric sensitivity, and the roles of diluents and transient liquid formation. Finally, practical design principles for scalable SHS synthesis of HE-MAX phases are outlined, alongside strategies for their selective exfoliation into high-entropy MXenes and a critical assessment of their emerging functional applications. Full article

Hybrid rocket engines offer a compromise between safety, controllability, and performance, making them attractive for small-scale propulsion systems. However, oxidizer selection remains a critical early-stage design decision that cannot be determined solely from ideal thermodynamic metrics. This study presents a comparative analysis of three oxidizers—nitrous oxide (N₂O), gaseous oxygen (GOX), and liquid oxygen (LOX)—for a 1 kN-class hybrid rocket engine using HDPE fuel under identical operating conditions. Equilibrium combustion performance was first evaluated using NASA Chemical Equilibrium with Applications (CEA) to determine optimal oxidizer-to-fuel ratios and theoretical specific impulse. These results were subsequently refined using Rocket Propulsion Analysis (RPA) to incorporate finite combustion chamber geometry and non-ideal nozzle expansion effects. The equilibrium analysis predicts maximum specific impulses of approximately 260 s for N₂O/HDPE and nearly 300 s for oxygen-based systems. However, finite-geometry modelling indicates that practical performance is reduced by approximately 5–8%, yielding delivered specific impulses of about 275 s for GOX and 272 s for LOX. The results demonstrate that although oxygen (GOX and LOX) provides higher thermodynamic performance, the practical advantage of LOX over GOX becomes marginal at the kilonewton scale. Consequently, oxidizer selection for small hybrid engines should be treated as a system-level trade-off involving performance, infrastructure complexity, and operational safety. Full article

Waste tyres, with their high carbon content and heating value that is greater than that of coal and biomass, present a potential feedstock for energy recovery. Similarly, automotive paint sludge (APS) is a hazardous waste rich in volatile and inorganics compounds, making it difficult to dispose of safely, but it also has potential for thermochemical conversion. Gasification is a thermochemical process which can turn such wastes into syngas, a mixture mainly composed of carbon monoxide and hydrogen that can be utilized to generate power and produce liquid fuels. To deal with challenges of single feedstock gasification, co-gasification combines two or more feedstocks, taking advantage of synergistic interactions to enhance syngas yield and overall efficiency. In this work, Aspen Plus simulation software is used to develop a model for the co-gasification of waste tyres and automotive paint sludge. Sensitivity analysis was performed with the aim of investigating and optimizing the overall process conditions of waste tyre and APS co-gasification. This study investigated the effect of air (ER) and water feed (SFR) and blend ratios on the adiabatic reaction temperature, product gas composition and heat value of the product syngas. Optimal operating ranges were identified as ER = 0.35–0.40 and SFR = 1.0–1.2 for tyre gasification, ER ≈ 0.50–0.55 for APS-only gasification, and ER = 0.40–0.48 with SFR = 0.8–1.0 for co-gasification blends. Adiabatic temperatures under recommended conditions were typically 700–800 °C. The LHV of syngas decreased with increasing ER, SFR, and APS fraction, falling from ~13 MJ/kg for tyre gasification to below 10 MJ/kg for APS-rich cases due to oxidation and dilution by CO₂ and ash. No positive synergistic effect in syngas quality was observed under thermodynamic equilibrium conditions. APS primarily acted as an ash-rich, low-carbon diluent, reducing CO concentration, heating value and adiabatic temperature. However, potential catalytic interactions from APS mineral matter, which are not represented in the equilibrium model, may produce synergistic effects in practical gasifiers. Full article

Deep neural networks (DNNs) have demonstrated remarkable capability in accurately predicting equilibrium combustion products and thermodynamic properties of diesel combustion. However, the lack of awareness of uncertainty and interpretability has limited their scientific credibility and practical application. In this work, an enhanced DNN framework with uncertainty quantification and explainability is developed. The model achieves high accuracy across all outputs, with R² values exceeding 0.99 for major thermodynamic variables. In this model, Monte Carlo dropout sampling is used to estimate epistemic uncertainty, and prediction confidence intervals are analyzed across all species and thermodynamic outputs, revealing strong correlations for major components. Model explainability is further explored using Shapley additive explanations (SHAP), which attribute the influence of equivalence ratio, temperature, and pressure on each predicted species and combustion characteristics. The combined uncertainty quantification and explainability framework not only enhances confidence in DNN combustion models but also provides physical insight into the relationships between input conditions and equilibrium thermochemistry that are learned by the DNN. Full article

Thermochemical conversion of plastic waste to hydrogen and synthesis gas represents a potential pathway for energy recovery from heterogeneous waste streams. The feasibility and performance of such systems are fundamentally governed by thermodynamic constraints and heat-management requirements. This review critically examines the thermodynamic and heat-integration aspects of plastic waste conversion to hydrogen and syngas, with emphasis on pyrolysis, steam reforming, gasification, and system-level behaviour. Key thermodynamic features of plastic pyrolysis, reforming, and gasification are discussed, including reaction endothermicity, equilibrium limitations, temperature effects, and product distribution trends. The role of steam reforming and water–gas shift reactions in enhancing hydrogen yield is assessed from equilibrium and energy-demand perspectives. Heat integration emerges as a critical determinant of overall efficiency, with recoverable waste heat present at multiple process stages offering opportunities for internal heat recovery. Energy and exergy analyses identify dominant sources of irreversibility and enable comparison of plastic-derived hydrogen systems with conventional thermochemical hydrogen production routes. Quantitatively, conventional steam methane reforming achieves energy efficiencies of 65–75% and exergy efficiencies of 60–70%, whilst plastic-derived systems without extensive heat integration report 45–60% and 40–55%, respectively. Key challenges include limited thermodynamic property data for real plastic-derived mixtures, insufficient reconciliation of equilibrium and kinetic behaviour, incomplete system-level heat-integration analysis, and scarcity of comprehensive exergy-based evaluations. This review provides a thermodynamic framework for assessing the opportunities and limitations of hydrogen production from plastic waste. Full article

This study investigates the reaction thermodynamics of the sodium oxide-fluxed aluminothermic reduction of pyrolusite-based manganese ore under self-propagating high-temperature synthesis (SHS) conditions, using Si, Cr, and Cu as collector metals. The experimental results are compared with thermochemical equilibrium calculations using FactSage 7.3 thermochemistry software. Experimental mixtures were prepared with controlled additions of aluminium, sodium silicate, calcium oxide, and collector metals and heated to the ignition temperature in a muffle furnace preheated to 1350 °C. The resulting alloys and slags were analysed for bulk composition. Collector metals significantly influence alloy carbon saturation and manganese recovery. The individual reaction’s Gibbs free energy values and the gas–slag–metal equilibrium were calculated. Discrepancies between the experimental and equilibrium-predicted results highlight the kinetic factors of SHS processes, particularly with respect to aluminium uptake and manganese volatilisation. The main difference is the alloy’s aluminium uptake. The difference between the calculated and experimental aluminium levels is, in part, due to the higher partial oxygen pressure predicted in the gas–slag–metal equilibrium calculations, compared with that of the likely Al–Al₂O₃ governing reaction equilibrium. Short-circuiting of aluminium to the alloy is also a possible contributing factor. The findings provide insights into optimising feed formulations and process parameters for improved manganese recovery. Full article