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To enhance the field applicability, based on enthalpy differences black box method was proposed to estimate the cooling load on mining face in this paper.The cooling load of mining face is composed of basic and increased cooling load. The former is considered with enthalpy difference between airflow in hottest period of summer and air flow under the cooling control at the target temperature, while the latter comes from the increased heat dissipation relative heat source after the implementation of cooling measures.Then taken above estimated results as a reference, theoretical analysis (i-d chart) and numerical simulation (Fluent software) were conducted on heat and moisture treatment process and distribution characteristics of air in tunnel after mixture cooling modes.The results show that the mixed air cooling process can be divided into three parts:cooling, mixing and warming, in which the most important is cooling process. Cooling process mainly depends on system refrigeration capacity and heat exchange equipment performance, which has great influence on the following two processes.During the mixing, air temperature (18℃~20℃ to 24℃~25℃,30℃~31℃ to 25℃~26℃) and wind speed (15~17 m/s to 1~2 m/s) change dramatically, showing a negative correlations between them.In addition, the length of mixing process should be controlled in less than 10 m (3~6 m) tunnel.At last, the warming stage should be reduced to release mining face heat and moisture source at the present stage, along with the system and parameter optimization, mine cooling should be made a scientific decision according to the concrete situation and diminish mine heat hazard during coal mining.

The findings of the major strategic consulting project of Chinese Academy of Engineering 'Research on the strategy of coal mine safety and abandoned mine resources development and utilization in China' suggest that almost 13,000 discarded collieries in China will provide abundant surface lands and massive underground heritages to not only develop but also store renewable energy within the Earth's Critical Zone, thus helping attain its net-zero energy goal. [ABSTRACT FROM AUTHOR]

This letter introduces the founding of a new Deep Underground Science and Engineering Laboratory-DUSEL in China, the distinguishing feature of which is focusing on the key scientific issue on the law of fluid matter migration within the Earth's Critical Zone in geoscience. Various technical, economic, and social challenges were elucidated. The achievements of this facility and thereby ambitious research may provide essential solutions to both energy transition and climate security, and then bolster support for decarbonization of China's energy sector, finally helping attain its double carbon' goal. [ABSTRACT FROM AUTHOR]

Cretaceous sandstones have weak cementation and high porosity while exhibit a high apparent brittleness. Compression and torsion (C-T) fractures are widely distributed in Cretaceous sandstones due to asymmetric tectonic convergence action. However, studies on C-T fracture formation and the mechanisms causing variability in Cretaceous sandstones containing no oil or gas are rare due to the challenges in sampling intact sandstone cores, despite their significance to mine shaft sinking. Therefore, this study used binder jetting-based 3D printing to prepare artificial Cretaceous sandstone and developed a real-time X-ray computed tomography- (CT-) aided torsion shear apparatus to test them. The test results showed that the 3D printed (3DP) sandstone had characteristic indexes that approached and even exceeded the lower limits of Cretaceous sandstone cores, thereby accurately representing the unavailable cores. Furthermore, the 3DP sandstones had anisotropic properties comparable to the sandstone cores. Under C-T action, the 3DP sandstone exhibited a pronounced strain gradient of 2.0 %/mm perpendicular to fracture inclination. The inclination angles of fractures formed under C-T action tended to increase as the cell pressure increased, and that approached the orientation angles of maximal principal stress. The maximal and minimal principal stresses exerted inclination-slip and width-stretching effects, respectively, on C-T fractures. But the effect of inclination-slip on the C-T fractures was stronger than that of width-stretching. This insight into C-T fracture formation will guide future studies on the fracture evolution and its disaster-dominating mechanisms arisen from disturbances by shaft sinking. [ABSTRACT FROM AUTHOR]

Efficient fracturing is the key issue for the exploitation of geothermal energy in a Hot Dry Rock reservoir. By using the laser irradiation cracking method, this study investigates the changes in uniaxial compressive strength, ultrasonic characteristics and crack distributions of granite specimens by applying a laser beam under various irradiation conditions, including different powers, diameters and moving speeds of the laser beam. The results indicate that the uniaxial compressive strength is considerably dependent on the power, diameter and moving speed of the laser beam. The ultrasonic-wave velocity and amplitude of the first wave both increase with a decreased laser power, increased diameter or moving speed of the laser beam. The wave form of irradiated graphite is flattened by laser irradiation comparing with that of the original specimen without laser irradiation. The crack angle and the ratio of the cracked area at both ends are also related to the irradiation parameters. The interior cracks are observed to be well-developed around the bottom of the grooving kerf generated by the laser beam. The results indicate that laser irradiation is a new economical and practical method that can efficiently fracture graphite. [ABSTRACT FROM AUTHOR]

A fixed-parameter ETC predictive model was proposed using simple combinatory rules, based on which the tri-weighted means (arithmetic, geometric and harmonic) of tri-upper and lower ETC bounds (Series-Parallel, two forms of Maxwell-Eucken, and Co-Continuous-Effective Medium Theory) can be unified. Theoretical analyses firstly explain the relative success of the weighted arithmetic combination between series and parallel models in the literature so far. Experimental validation was then conducted and the results indicate that the presented combinatory models can be well fitted to most ETC data of internal porosity geomaterials by adjusted values of weighting parameter f. However, this type of combinatorial model would give more uncertainty when applied to external porosity geomaterials such as granular sands. Finally, some meaningful analyses, conclusions and research perspectives were obtained, drawn and opened for future investigations in this field. [ABSTRACT FROM AUTHOR]

[Display omitted] • The extended unit divided method can capture heat and moisture sources in tunnel. • Airflow enthalpy augment per one meter tunnel represents the heat hazard degree. • Phenomenon of return heat easily occurs in underground long development tunnel. • Production activities have an impact on the thermal inertia of airflow parameters. The unit divided method, which initially enables zones of methane emission, distribution and concentration in long-wall coal mining face to be manually identified, was analogously utilized in this study to capture distribution characteristics and variations of the airflow thermodynamic parameters in an underground long distance development tunnel. Field observations and thereby analyses preliminarily provide a definition of the airflow 'return or turn back heat' phenomenon that commonly occurred in deep underground long distance cul-de-sac development tunnels. Furthermore, the cooling performance in heading face was illustrated and some regression relations among cooling parameters associated with the heading face were developed simultaneously to maintain the climatic condition within the design limit. Finally, the influence of production activities on the thermal inertia of airflow in horizontal development tunnel was analyzed, which is similar to that near the mine vertical shaft. These findings may provide beneficial guidance for existing practical applications of deep mine heat hazard control. [ABSTRACT FROM AUTHOR]

This letter is a comment to the published paper entitled, "Soil thermal conductivity estimated using a semi-analytical approach" (by Rubin and Ho, Geothermics, 2021, 92: 102051). In the reviewed article, an enhanced semi-analytical model was proposed to evaluate the effective thermal conductivity of three-phase (solid-liquid-gas) soils by changing the assumption of 1D monodirectional to 2D quasi-uniaxial parallel heat fluxes in pore-scale soil heat conduction process. The significant innovation, some shortcomings and further research directions were discussed in this comment. In addition, some statements, conclusions and misprints occurred in the published version were also mentioned, indicating that more careful proof, necessary corrigendum and some supplementary materials are required to avoid confused presentation and improve the reliability. [ABSTRACT FROM AUTHOR]

Abstract: By analyzing the definition, mechanism of action, determination methods and damage degree of mine gas and heat, a conclusion can be reached that these two types of object (or be known as physical quantity) have similarities to a large extent. First, both of the mine gas and the mine heat are caused by field changes that respond to the mining activities. Second, we can use relative equipments and the element method to do quantitative determination and analysis. Third, the phenomenon which gas and temperature exceed the limit occurrs frequently in the return corner and other specified place. According to the above similarities, we proposed that the exploitation of mine heat should be brought into the mine green mining technology system, to form the mining technology of extracting coal, gas and heat together, which can enrich and perfect the green mining technology system. [Copyright &y& Elsevier]

This comment concerns a rightful doubt involved in the above paper. In the reviewed article, a novel model without empirical constants was proposed to evaluate the effective thermal conductivity of three-phase soils, and such a model was claimed to be workable for soils with porosity ranging from 0.0349 to 0.4764 at all saturation degrees. However, sufficient reasons and pictorial explanations were given in this comment to prove its inapplicability for high degrees of saturation. Besides, the inapplicable range is constantly changing, depending on the porosity, i.e. the larger the porosity, the smaller the inapplicable saturation region. Similar issues were further discussed due to its great influence on the follow-up research in this field, i.e. whether can achieve a full coverage of the applicable saturation range [0,1] for a given porosity. [ABSTRACT FROM AUTHOR]

A good knowledge of the effective thermal conductivity (ETC) of geomaterials is required to achieve accurate study on heat transfer in a variety of earth-contact engineering applications. On account of composite-porous characteristic of geomaterials, the thermal conductivity of each component is the foundation while the porous structure is the key influence factor. Accordingly, a fractal capillary bundle model at pore scale is proposed in this paper to predict the ETC of saturated/unsaturated composite-porous geomaterials. The combination of fractal theory and capillary bundle model hypothesis is used to describe the random, disordered and extremely complicated microstructure of geomaterials. The analytical solution of the ETC is obtained by using the thermal-electrical analogy technique, which demonstrates that the proposed model is a function of variety of composition and microstructure parameters. Both the effects of these two types of parameters on the ETC of geomaterials are analyzed theoretically. Compared with other models, the present model represents specific physical meaning and shows acceptable accuracy and performance. The model predictions are further compared with the available experimental data for three types of concrete, and a good agreement between them can be found in most of saturation degrees (0.2 < S r < 0.8). [ABSTRACT FROM AUTHOR]