The operational efficiency of industrial bag filters is strongly dictated by their internal flow distribution and hydraulic resistance; however, the coupled effects of key structural parameters on these aerodynamic characteristics remain insufficiently quantified. This study investigates a small-scale industrial bag filter by combining three-dimensional computational fluid dynamics (CFD) with a three-factor, three-level orthogonal experimental design. A novel multi-index evaluation framework was employed to comprehensively characterize the internal flow field. This framework includes the integrated flow non-uniformity index (assessing bag-to-bag flow allocation), relative root mean square velocity (quantifying cross-sectional velocity fluctuations), and pressure drop. The impacts of baffle perforation ratio, inlet size, and bag spacing on flow redistribution and resistance formation were systematically assessed. Furthermore, experimental measurements were conducted to validate the numerical predictions. Results indicate that inlet size is the dominant structural factor governing both flow uniformity and aerodynamic resistance. The optimal configuration—identified as a baffle perforation ratio of 0.25, an inlet size of 500 mm, and a bag spacing of 170 mm—markedly mitigates inlet jet impingement and suppresses large-scale internal recirculation. At a standard filtration velocity of 1.0 m/min, this optimized design reduces the integrated flow non-uniformity index, relative root mean square velocity, and pressure drop by 47.81%, 60.02%, and 29.84%, respectively, compared to the baseline structure. The simulated trends for both pressure drop and relative root mean square velocity exhibit excellent agreement with experimental measurements across various filtration velocities, demonstrating the reliability of the numerical model. Overall, the proposed multi-index approach provides a robust quantitative basis for the initial flow-field assessment and low-resistance structural design of industrial bag filters.

Liquid nitrogen fracturing is a promising approach for enhancing coalbed methane extraction. However, the optimal temperature for LN2 fracturing under single-interface conditions is yet to be determined. To address this issue, an investigation was conducted into coal cracking across a temperature range of -10 degrees C to -150 degrees C using the Digital Image Correlation (DIC) method. The characteristics of the coal cracking were quantified using metrics including crack width and growth rate, fractal dimension, maximum principal strain and crack opening displacement (COD). The results showed a consistent two-stage process: an initial cracking stage characterized by rapid crack growth (41-108 %), followed by a stable stage with much slower crack growth (8-3 %). Notably, a temperature of -50 degrees C resulted in the most significant crack expansion, with an increase in width of 105 % occurring at a rate of 0.26 mu m/s. This exceeds the growth rates observed at -10 degrees C, -100 degrees C and -150 degrees C. Additionally, the maximum increase in estimated permeability (10.7 %) and the greatest maximum principal strain were observed at this temperature. From a mechanistic perspective, coal cracking is predominantly influenced by frost-heave pressure (FHP) during the eruption and decline stages. Peak cracking at -50 degrees C is the result of the combined effect of confined ice plug space, fluid pressure accumulation and brittle ice plug rupture. A model linking COD and FHP was established to further explain this process. This study provides theoretical support for improving the effectiveness of liquid nitrogen fracturing by optimizing the temperature.

Low-frequency vibration offers an eco-friendly route to enhance permeability in tight coalbed methane (CBM) reservoirs by actively promoting crack propagation in coal. This study systematically examines how independently controlled vibration frequency (200, 300, 400 Hz) and amplitude (3, 6, 9 V) govern fracture evolution. Results reveal a pronounced synergistic effect: coupling high amplitude with high-order resonance (9 V/400 Hz) amplifies the maximum crack opening displacement (CODmax) by 2.6-7.4 times and elevates local strain by 28-64 times relative to single-parameter regimes. Full-field strain analysis and Stress Intensity Factor (SIF) quantification via the J-integral method revealed that the induced fracturing is predominantly Mode I (tensile opening). Under peak excitation (400 Hz, 9 V), the ModeI SIF (KI = 0.198 MPa m1/2) significantly exceeded the Mode II SIF (KII = 0.093 MPa m1/2), identifying tensile-dominated expansion as the fundamental driver for aperture widening. A theoretical model based on multi-degree-of-freedom resonance dynamics was established to quantitatively links crack opening displacement (COD) to vibration amplitude and frequency, providing a framework for field-scale parameter optimization. These findings offer a mechanistic basis for optimizing fluid-free vibration strategies to boost permeability and recovery in low-permeability CBM reservoirs.

The spontaneous combustion of sulfide ores (SOSC) is an extremely dangerous mining disaster that directly threatens safety production in mines and causes far-reaching negative impacts on the surrounding ecosystem. In this study, oxidation weight gain experiments, self-heating temperature and ignition temperature tests, and thermogravimetric analysis (TGA) were conducted to detect the spontaneous combustion characteristics of sulfide ores with different sulfur contents (40.29%, 34.56%, 24.81%, and 14.2%). The results show that the sulfur content significantly affects the spontaneous combustion characteristics of sulfide ores. As the sulfur content decreased, the oxidized weight gain rate decreased overall, and the self-heating temperature (135, 152.5, 162.5, and 176.9 °C) and ignition temperature (425.3, 438.6, 455.4, and >500 °C) increased. The three combustion stages of the SOSC were divided based on the TG and DTG curves: low-temperature oxidation stage, combustion decomposition stage, and slow burnout stage. Furthermore, KAS and FWO methods were used to obtain the apparent activation energy in the combustion decomposition stage. The apparent activation energy decreased significantly with the increase in the sulfur content. The results of all experiments and analyses showed that sulfide ores with high sulfur content have a stronger tendency to undergo spontaneous combustion. The research results have important theoretical and practical implications for the prevention of SOSC.

Resistivity is a key method for geophysical exploration of underground coal seams. However, the deep, high geothermal environment poses significant challenges to this approach, mainly due to moisture desorption and matrix contraction effects induced by high temperatures. In this study, experiments were conducted to assess the resistivity of water-bearing coal at varying temperatures between 30 degrees C and 70 degrees C. In addition, Nuclear Magnetic Resonance (NMR) technology was used to analyze the moisture distribution within the coal under high temperature conditions. The results indicate that moisture desorption in coal at elevated temperatures occurs in two distinct stages: a rapid desorption stage from seepage pores and a slower desorption stage from adsorption pores. As the temperature increased from 30 degrees C to 70 degrees C, the amount of moisture desorbed increased by 117 %, while the matrix contraction strain increased by 130 %. Furthermore, the variation of coal resistivity under high temperature conditions can be categorized into three stages: a transient decreasing stage due to the Soret effect, a significant increasing stage caused by moisture desorption, and a continuous decreasing stage due to coal matrix contraction. Finally, a theoretical model was developed to characterize the coupled effects of moisture desorption and matrix contraction on coal resistivity. This model provides a basis for the application of resistivity methods in deep, high-geothermal environments.

Ultrasonic logging technology is an important tool for geophysical exploration in deep coalbed methane (CBM) reservoirs. However, the technology faces significant challenges in the high temperature environment, mainly due to the thermally induced effects of moisture desorption and fissure expansion. This study aims to address these challenges by elucidating the influencing mechanism of moisture desorption and fissure expansion on ultrasonic propagation and developing a theoretical model for ultrasonic wave propagation in high temperature coal reservoirs. Ultrasonic tests were conducted under high temperature conditions based on the temperature range of deep coal reservoirs. The results show that elevated temperature significantly promotes moisture desorption from coal. As the temperature increases from 30 degrees C to 70 degrees C, the amount of moisture desorbed during the rapid stage increases by 60 %, while the desorption time decreases by 56 %. In addition, the moisture desorption process is accompanied by continuous contraction strain and fissure expansion, with the total number of coal fissures increasing by 156 %, and the proportion of small-scale fissures (<100 mu m) growing from 76 % to 90 %. In addition, the ultrasonic wave velocity decreases with moisture desorption, and the ultrasonic attenuation coefficient shows a continuously increasing trend. Finally, the mechanisms of moisture desorption and fissure expansion have been elucidated, and a model for the ultrasonic propagation in high temperature coal reservoirs has been established. The results of this study provide a theoretical basis for addressing the challenges of ultrasonic logging technology encountered in deep, high temperature CBM exploration.

Moisture desorption poses a significant challenge to coalbed methane (CBM) recovery in high-temperature coal reservoirs. This study investigated the effect of moisture desorption on mode I fracture of notched semi-circular bending (NSCB) coal samples using a split Hopkinson pressure bar (SHPB) system. A high-speed camera was used to record the dynamic crack propagation, and image processing methods were used to analyze the crack propagation characteristics. The results show that increasing the moisture desorption rate from 0% to 100% improves the dynamic fracture toughness by 37%. In addition, the crack propagation speed and crack tip opening displacement (CTOD) are increased by 28% and nearly 100%, respectively. The moisture desorption rate is positively correlated with the dynamic fracture toughness, crack propagation speed, and CTOD, which indicates that moisture desorption improves mode I fracture toughness and promotes crack propagation. Furthermore, the mechanisms by which moisture desorption affects coal microstructure were elucidated using an optical microscope, and a theoretical model was proposed to explain the effects of moisture desorption. The model suggests that the matrix contraction force induced by moisture desorption promotes crack propagation, while the surface tension and viscous resistance of the moisture inhibit it. As moisture desorbs, the effects of surface tension and viscous resistance decrease, thereby promoting crack propagation. The results provide theoretical guidance for enhancing CBM recovery in high-temperature coal reservoirs.

Numerous floor water inrush (FWI) disasters have occurred during the roof weighting period in China. Therefore, to clarify why FWI accidents tend to cluster at a specific mining stage, a novel method for evaluating the failure depth of mining floors (FDMF) under dynamic loads induced by roof breakage is proposed in this study. By employing Matlab programming, the stress distribution and failure patterns of the intact floor were analyzed, revealing the dynamic stress response and failure characteristics. In addition, the accuracy of the proposed theoretical model was further verified through numerical simulation and field measurement. The results indicate that dynamic loads significantly impact vertical stress and shear stress, but only have a minor impact on horizontal stress. This leads to an expansion of the stress concentration zone and an increase in the intensity of the mining floor. Moreover, the FDMF is notably enhanced under the dynamic load induced by roof weighting. Besides, both the numerical simulations and field measurement results align closely with the theoretical predictions, which confirm the effectiveness of the proposed method. This study provides a theoretical foundation for understanding FWI mechanisms under the combined influence of dynamic and static loads.

Accurately revealing the spatial distribution law of seismic displacement is significance for revealing the mechanism of dynamic load induced rockburst and guiding the dynamic support of roadway. This paper established the function of seismic displacement based on radiation energy, and compared the influences of fracture type, radiation energy, shear strength, fracture velocity and medium density on the seismic displacement. The results showed that the displacement amplitudes of surrounding rock caused by P-wave, SH-wave and SV-wave increased with the rising of radiation energy, and the rate of displacement amplitude also accelerated. The displacement amplitudes of seismic wave associated with tensile fractures are significantly higher than that with shear fractures. The spatial displacement amplitude of S-wave was significantly higher than that of P-wave by one order of magnitude. The peak value of P-wave displacement of shear fracture was concentrated in two planes at 45° angle to the fracture surface. For SH-wave and SV-wave components, peak values were mainly observed on the fracture surface and its orthogonal plane. The P-wave displacement on the orthogonal plane to the fracture movement was zero, the displacement field of SV-wave was distributed in four quadrants, and the displacement field of SH-wave was symmetrical. The higher the value of medium attribute, the more significant the damage effect of coal-rock seismic wave weakening, and the influence on the S-wave is greater than that of the P-wave. The displacement amplitude caused by seismic wave gradually increased with the rising of fracture velocity of coal- rock mass. The peak value of P-wave displacement increased linearly, and the peak value of S-wave displacement was nonlinear. The research results laid a theoretical foundation for dynamic support design for roadways.

Thermal cracking of coal in high-temperature environments poses a significant challenge to the sustainability of deep coal mining. It increases the risk of coal and gas outbursts and spontaneous combustion and also contributes to groundwater pollution and greenhouse gas emissions, ultimately undermining the environmental sustainability of coal mining. This study investigates the coal thermal cracking in such environments and introduces an ultrasonic approach to evaluate the thermal cracking process. The results indicate a positive correlation between crack opening and cumulative moisture desorption, as well as between crack expansion rates and moisture desorption rates. In addition, the ultrasonic P-wave shows a robust response to both moisture desorption and thermal cracking, supported by nonlinear and linear models correlating wave velocity and attenuation coefficient, respectively. In addition, a theoretical model elucidates the driving forces, including surface tension and vapor pressure, that contribute significantly to thermal cracking at high temperatures. The ultrasonic method based on the theoretical model provides an innovative approach for assessing the coal thermal cracking process, contributing to improved environmental sustainability in deep coal mining.

During the deep mining process, coal mass encounter intricate geo-environmental stress, such as periodic weighting loading and repeatedly excavation unloading-reloading cycles, which weakens coal's mechanical integrity and predisposing it to severe coalburst accidents. To investigate the microcracking damage mechanisms and predictive indicators in coal failure under in-situ stress analogs, the multistage step and cyclic loading experiments are conducted on cubic coal specimens. Acoustic emission (AE) technology is employed to track the spatiotemporalenergy evolution of stress-induced damages and discern the microcracking nature through AF/ RA assessments, and the power-law scaling relation of AE activity near the catastrophic failure of coal is investigated. Then the clustering fractal structures of microcracking events in the stressed coal are quantified across temporal, spatial and energetic domains, utilizing correlation integral methodologies and b-value derivations from magnitude-frequency relation. Findings indicate that irrespective of the loading mode (step or cyclic), escalating stress triggers an intensification of irreversible fatigue deformations. AE characteristic parameters manifest a gradual rise, culminating in a precipitous peak coinciding with the critical failure point. This escalation adheres to a power-law correlation between AE occurrence frequency and time to failure, observable in the immediate pre-failure seconds, reflecting a universal attribute of coal fracture. Prior to ultimate failure, a marked increase in shear microcracks is discernible, despite tensile-dominated cracks (constituting about 80 % of total microcracks) prevailing as inferred from the variation of AF/RA values, aligning with an inferred "X" conjugate wedge splitting pattern from AE event density and energy mapping. The microcracking events in the loaded coal exhibit a clustering fractal structure that spans across temporal, spatial, and energetic (or magnitude) domains. Notably, the temporal fractal dimension, spatial fractal dimension, and b-value (i.e., a parameter characterized the energetic fractal dimension) all follow a parallel decrease pattern as the loading stress escalates, with a pronounced diminution becoming especially evident as the specimen approaches its catastrophic failure threshold. This insight offers fresh perspectives for predicting rock/coal dynamic disasters, emphasizing the necessity of concurrently monitoring the shift from diffuse microcracking to localized failure across time, space and energy domains. These research findings contribute to a deeper understanding of microcracking damage evolution and failure mechanism of loaded coal, and provide a foundational basis for early warning of rock failure such as the coalburst disasters.

The digital image correlation (DIC) technology was used to investigate the evolution law of the coal surface strain field under different loading rates and to analyze the influence of loading rate on the evolution of the deformation field, deformation localization, and surface deformation energy density. The experimental results indicate that the higher the loading rate is, the more complete the final failure mode of the coal body, and the failure mode of the coal body also transitions from shear failure to tensile failure; the loading rates of different magnitudes also affect the localization time of coal deformation. The higher the loading rate is, the greater the proportion of the initiation time of coal deformation localization to the overall failure time. The higher the loading rate is, the more obvious the growth trend of deformation energy density before deformation localization, and the more energy accumulates in the surface deformation localization area; the qreater the stress at the start time of deformation localization.

Frequent mining disturbance or periodic rupture of far-field roof in coal seam mining will produce multiple vi-bration loads,which have an important influence on the micro pore-fissure structure and macro mechanical behavior of coal.In order to explore the evolution characteristics of pore-fissure structure of coal under vibration load,the SHPB test system was used to carry out a multiple vibration load impact test on bituminous coal.With the help of low-field nuclear magnetic resonance analyzer,theT2spectrum of coal after each impact was tested,and MRI was performed to analyze the law of pore distribution and evolution,and the damage evolution characteristics of coal pore-fissure structure were studied.The results demonstrate that the peak stress and dynamic elastic modulus of coal show a linear decline trend with the in-crease of vibration load,and the impact effect of vibration load significantly weakens the bearing capacity and deforma-tion resistance of coal,so it is necessary to conduct in-depth analysis on the evolution characteristics of coal pore cracks.According to the T2 spectrum and MRI information,the total pore volume of coal increases greatly under the first action of vibration load,in which the adsorption pores volume increases by 5.0 times.With the increase of the number of vibration loads,the volume of seepage pores begins to increase significantly,while the volume of adsorption pores remains basically unchanged until the sample is completely destroyed.During the multiple action of the vibration load,the internal damage of the coal body gradually accumulates from the initial point distribution to strip distribution until micro-cracks are formed.With the multiple action of the vibration load,the microcracks of the coal sample begin to connect and converge to form macrocracks,which greatly improves the connectivity between the seepage pores,and the overall porosity of the coal sample reaches a peak value,about 6 times higher than the original porosity.During the whole process of coal body being damaged and destroyed by vibration load,the connectivity of seepage pores is gradually increased and improved,and its fractal dimension shows a linear decline trend.The MRI reveals the mechanism of vibration load on coal pore-fissure,and the results show that the central region of the coal first develops and gradually forms microcracks.Under the action of re-flection and stretching of subsequent vibration waves,the damaged areas gradually extend to both sides until penetrating the sample.

Underground coal mining in China has gradually moved into deeper seams in recent years, which results in a higher ambient temperature in the mining space and significantly affects the mechanical behavior of coal. In this study, dehydrated coal samples were obtained at different temperatures ranging from 30[Formula: see text] to 70[Formula: see text], and the mechanical behavior of the dehydrated coal was investigated through compressive loading tests. The digital image correlation (DIC) method was used to acquire the strain field of coal, and a multifractal analysis was conducted to characterize the strain evolution of coal. The findings suggest that the increasing temperatures result in higher moisture desorption rates and greater volumetric contraction strain in coal. Furthermore, coal with higher moisture desorption exhibits higher peak stress and peak strains when subjected to compressive loading. The multifractal analysis of the inhomogeneous strain evolution indicates a gradual decrease in the parameter [Formula: see text] under compressive loading, followed by a sudden increase before reaching the failure point due to strain localization. The multifractal mechanism was further investigated, revealing that the inhomogeneous strain field of coal is inherently affected by the microstructure of coal. In addition, a mathematical model was proposed to elucidate the relationship between the inhomogeneous coal strain and the microstructure of coal. The result indicates that the inhomogeneity of the coal strain is directly associated with the multifractal singularity of the coal microstructure. Finally, the feasibility of using the multifractal parameter [Formula: see text] to identify coal strain localization has been demonstrated, indicating its potential value in aiding engineers to determine the SLZ in deep coal mines.

以综采工作面采空区为研究对象,基于渗流理论及连续性方程,运用三维数值模拟的方法,以Y型通风为例,采用上隅角埋管、预埋立管和高位定向钻孔协同抽采,研究抽采前后采空区在走向、倾向和竖直方向上瓦斯流场分布规律,并通过对比文献中的试验数据来验证数值模拟结果的可靠性.结果表明:抽采前,Y型通风下在综采工作面采空区走向上,距离工作面越远深部瓦斯浓度越高,瓦斯最高体积分数为98.6％,综采工作面采空区倾向上瓦斯浓度较小,瓦斯浓度在1.0％以下;抽采后,综采工作面采空区瓦斯最高体积分数由98.6％降低至4.6％,且采空区3/4区域瓦斯体积分数不足3.0％,综采工作面与上隅角区域瓦斯体积分数也均降低至1.0％以下,未产生上隅角区域瓦斯浓度超限现象,瓦斯浓度大幅度下降.该研究对丰富采空区瓦斯渗流理论、提高瓦斯抽采量、解决上隅角区域瓦斯浓度超限问题、保证矿井安全生产等方面具有一定的理论和现实意义.

"双碳"战略是我国应对极端气候变化的重要决策,要达成这一战略目标首先要提高热能转换效率、减少化石燃料的消耗、降低热量传递的损失,这与热工学课程教学主题高度契合.文章以"双碳"战略下我国电力能源行业节能减排为切入点,探索将"双碳"战略融入热工学课程思政的教学模式,通过问卷调查收集学生对热工学课程思政的教学评价和意见,分析热工学课程思政教学模式成效及影响因素,提出有针对性的改进措施,为进一步提高热工学课程思政教学效果提供参考.

混合式教学模式是当前高等教育领域的一种创新教学方法,它将疫情期间建立的线上课程资源与疫情常态化后课堂讲授有效结合,为当前教育发展提供了新的思路.以安全工程专业热工学课程为例,以疫情常态化后线上线下混合式教学数据为基础,调查分析混合式教学方法在热工学课程的影响因素及应用效果,根据调查结果提出了具有针对性的改进措施,为进一步提升混合式教学效果提供参考.

Brittleness has a significant influence on rock failure under compression; however, the mechanism is rarely comprehensively discussed. This study numerically investigates the brittleness effect on microcracking behavior of crystalline rock using a grain-based model implemented into a two-dimensional particle flow code, with a focus on the discussion of how rock brittleness affects the failure mechanism. The simulated failure mode changes from tension to shear with decreasing rock brittleness, which is consistent with previous laboratory test results. As the brittleness gradually decreases in the model, the grain boundary (GB) tensile crack to shear crack ratio increases, and the corresponding fractures change from vertical or subvertical to an angle about 45 degrees along the vertical direction. The propagation and coalescence of generated microcracks result in a transition of failure pattern from splitting to shear under uniaxial compression with a decreasing brittleness level in the rock. A transition from GB tensile crack to shear crack is also observed under direct tension when the brittleness index gradually decreases. The tension to shear transition mechanism is closely related to the relative strength of the mineral grain and mineral bonding. The relative strength of mineral and mineral bonding could be used as a parameter to characterize rock brittleness from a microscale viewpoint.

Basic friction angle is an important input parameter in many peak shear strength criteria of rock joint. Reliable estimation of joint basic friction angle is essential for accurate determination of the corresponding peak shear strength. In this study, the basic friction angles of planar joint surface of three rocks (i.e., granite, marble, and sandstone) are studied using two commonly used methods, including tilt test and direct shear test. Although the basic friction angles determined from tilt test are about 4 to 5° smaller than those determined from direct shear test, the marble is found to have the largest basic friction angle in both tilt test and direct shear test. In direct shear test, there is about 2° difference of basic friction angles determined under low and high normal stress conditions, which is mainly associated with the shearing mechanism of joint surface. Friction generally occurs under low normal stress. On the other hand, shear-off is observed when the applied normal stress is high. To obtain a reliable basic friction angle using direct shear test, the test data under low normal stresses are suggested to be used. It is also seen from the results that the shear strength of planar joint surface is negligibly influenced by the cyclic shearing when the applied normal stress is low. The data in this study replenish the test data of basic friction angle of different rock types and are useful for establishing a database for the estimation of basic friction angle in future.

Coal failure behavior under dynamic loading is significant for dealing with the failure issues encountered in underground coal mines. In this study, the crack propagation and internal fracture process of coal under dynamic loading were investigated by a split Hopkinson pressure bar (SHPB) experimental system and numerical approach, respectively. The experimental and numerical results show that the coal crack propagation and internal fracture surface manifest significant multifractal features. Further, multifractal analysis suggests that the multifractal feature becomes more and more significant during the dynamic loading. The formation mechanism of the multifractal features was further discussed, and the result demonstrates that the crack propagation path within coal is essentially a multifractal structure, thus causing the total fracture behavior of coal to show multifractal features under dynamic loading. Moreover, the multifractal spectrum parameter [Formula: see text] was proved to be closely related to the brittle fracture property of coal, which transpires that the multifractal feature is feasible to evaluate the coal brittleness under dynamic loading and also applicable to predict the coal failure risk in underground coal mines.