Alterations in the coal matrix pore structure caused by gas adsorption are a critical factor affecting the efficiency of coalbed methane (CBM) extraction. This study investigates the adsorption behaviors of CH4, CO2, and N2. The evolution characteristics of micropore structure and permeability in a coal matrix under different pressures are discussed using molecular simulation methods. The alterations in the coal matrix pore structure are controlled by pore-filling and structural reconfiguration effects. CO2 shows the most pronounced effects on both processes, leading to increased complexity in pore morphology and a 35.7% decrease in the number of transport pores. CH4 exerts a moderate impact, which reduces both the porosity and surface area of the coal matrix. The number of pore throats displays a nonlinear variation characteristic. In contrast, N2 adsorption has a minimal influence on the pore structure, exerting only a weak filling effect. A permeability model established in this study, which accounts for adsorption-induced pore structure evolution, reveals that although CO2 exhibits strong adsorption and displacement effects, the gas transport capacity of coal post-adsorption declines by more than 90%. Meanwhile, N2 exhibits limited CH4 displacement efficiency and has a negligible effect on coal matrix permeability.
This study investigates the suppression mechanism and microkinetic evolution of heptafluoropropane (HFC227ea) in methane-air premixed combustion with a low ammonia fraction. Experimental results show that HFC227ea reduces the maximum explosion overpressure (Pmax) and the maximum pressure rise rate ((dP/dt)max), with strong dependence on the overall equivalence ratio ((p). Suppression is most pronounced under stoichiometric ((p = 1.0) and fuel-rich ((p = 1.4) conditions, whereas inhibition weakens under fuel-lean conditions ((p = 0.6) because of excessive O2 that promotes chain-branching reactions. Microkinetic analysis shows that suppression is governed by an oxygen-dependent kinetic competition mechanism. Suppression efficiency is controlled by competition between fluorinated radicals that scavenge H/OH/O radicals and the dominant chainbranching reaction (H + O2 = O + OH). Inhibition arises from nonlinear coupling between the initial endothermic decomposition of HFC-227ea and subsequent radical-scavenging reactions, which chemically terminate combustion chains by depleting H/OH/O radicals. This coupled process disrupts the energy-radical balance required to sustain combustion. Reaction flux analysis shows that this mechanism remains consistent across different ammonia-methane blending ratios, indicating the chemical stability of fluorinated intermediates such as CF3CHF and CF3 in complex fuel systems. These findings provide a theoretical basis for the safe application of ammonia-methane blended fuels.
The chemical state of silver was found to affect the catalytic activity of ethanol-SCR reaction. The hydroxyl (OH) groups on the surface of Al2O3 support as anchor sites for Ag species, were benefit for the dispersion of silver and the formation of active sites. The surface OH contents of the Al2O3 support were synergistically regulated by varying the calcination temperature and hydrothermal treatment, to control the coordination environment of silver and optimize the catalytic performance. The result showed that the OH contents of Al2O3 mainly govern the dispersion of Ag species. The decrease in OH groups led to increased proportion of metallic Ag species, resulting in significant decrease in the NOx reduction activity. Additionally, hydrothermal treatment of support promoted the formation of well dispersed oxidized Ag species, significantly enhancing the NOx reduction performance in the high-temperature range of 400-500 degrees C. Cycling tests revealed that the Ag species on the catalyst surface would migrate and redisperse under conditions of oxygen-rich at temperatures above the Tammann temperature of silver (344 degrees C). The transformation causes hysteresis in the catalytic activity during heating and cooling, further revealing the dynamic evolution of Ag species under reaction conditions. The results reveal the mechanism through which OH contents in the support govern the structure and performance of Ag/Al2O3 catalysts, providing a theoretical basis and novel insights for the development of high-efficiency diesel vehicle exhaust purification catalysts.
Understanding the synergistic effects of inorganic minerals and pore structure on coal pore wettability remains a critical knowledge gap. This study investigates the pore-scale wettability mechanism of five high-rank coals by integrating quantitative inorganic mineral analysis, pore morphological characterization, and low-field nuclear magnetic resonance (LF-NMR) T 2 relaxation spectroscopy. A series of water-droplet-coal wetting experiments, organized into three groups, was conducted to establish a cross-scale framework linking physical pore structure, mineral composition and wetting response. The results indicate that the dual mechanism of strong adsorption on hydrophilic mineral surfaces and capillary forces in micropores drives the wetting process. In terms of mineral aspect, clay minerals exhibit significantly higher wettability than non-clay minerals, and clay content shows a significant negative correlation with wetting parameters R g,24h measured by LF-NMR. Notable, when clay content ranges from 2% to 10%, its regulatory effect on pore wettability is particularly sensitive. In terms of pore structure, an exponential saturation model was employed to fit the pore wetting kinetics. The derived kinetic parameters, including the rate constant k and equilibrium pore diameter R eq are consistent with the trends observed in R g,24h . And the 24 h observation is confirmed to represent quasi-steady state for all samples. Additionaly, Pore wettability is governed by absolute pore capacity when pore volume differences exceed approximately two-fold, whereas at smaller differences, micropore complexity and connectivity dominate. Micropores play a critical role due to capillary force-driven physical contributions. Furthermore, a critical pore diameter of 42.16 nm is identified, above which wetting transitions from capillary-driven to surface-spreading or gravity-dominated regimes. A two-dimensional pore-wet coupling model is proposed, and five representative wettability types were defined. Among them, samples C4 and C5 exhibit synergistic enhancement (type A), while C1 shows mutual inhibition (type B). These results provide a new multidimensional coupling paradigm for understanding wettability in heterogeneous porous media.
This article presents a new second-law theoretical framework for heat exchangers to evaluate the entropy transfer efficiency and two irreversibility indicators from the finite-time thermodynamic perspective. A general second-law efficiency model based on two equivalent reversible heat engines (one reversible heat engine and one reversible heat pump) coupled through an intermediate reference reservoir between a source at the hot inlet temperature T1 infinity and a sink at the cold inlet temperature T2 infinity is reformulated for the parallel-flow (counterflow) heat exchangers, and the entropy transfer efficiency nS with the parallel-flow (counterflow) arrangement is recovered when the reference temperature is equal to the cold outlet temperature T2 (cold inlet temerature T2 infinity). New expressions for entropy generation rate and entropy transfer efficiency dependent on the flow arrangement are obtained, where nS with parallel-flow (counterflow) arrangements is simply represented by T2/T1 (T2 infinity/T1) with the hot outlet temperature T1 under the condition of no heat leakage. We consider the heat exchanger as a conjugated machine to an endoreversible heat engine and find that the critical entropy transfer efficiency at maximum entropy generation rate Sg,max for both parallel-flow and counterflow configurations as well as that at maximum lost available power Wlost,max for counterflow is identical to z0.5 = 1 - nCA, where z = T2 infinity/T1 infinity is the inlet temperature ratio, and nCA = 1 - z0.5 represents the CA efficiency in the Curzon and Ahlborn's heat engine. Magnitudes of Sg, nS, effectiveness e and their extrema are pinpointed using a temperature-entropy diagram and a heat flow-temperature diagram. We obtain novel expressions for Sg/Sg,max and Wlost/Wlost,max and find that Sg/ Sg,max with both parallel-flow and counterflow arrangements is the same and identical to Wlost/Wlost,max with counterflow. An ideal heat exchanger with T1 = T2 for parallel-flow or T1 = T2 infinity for counterflow is achieved when nS reaches its maximum value of unity and Sg = 0, which corresponds to the quasi-static transformation implying infinitely slow heat exchange cycles causing a zero heat load, so seeking the operation condition avoiding the most disadvantageous case of Sg/Sg,max = 1 or Wlost/Wlost,max = 1 is among the rational criteria for the heat exchanger design. The nS was compared to previous second-law efficiencies and shows its superiority in its ability to predict the effect of heat exchanger parameter changes on the energy utilization quality. The present entropy transfer efficiency model was verified by comparing with the Pitchandi's experimental data with the maximum relative error of 0.87 %. A novel Sg/Sg,max-nS-e-transfer unit number method is developed as an alternative design and evaluation criterion for heat exchangers from both the first- and second-law viewpoints, whose usefulness is demonstrated through two practical heat exchanger cases.
