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Article

Mechanical Damage to Coal and Increased Coal Permeability Caused by Water-Based Ultrasonic Cavitation

by
Xiaoyang Guo
1,2,
Yijia Liu
1,*,
Yanfeng Li
1,
Cunbao Deng
1,
Lemei Zhang
1 and
Yu Zhang
1
1
College of Safety and Emergency Management Engineering, Taiyuan University of Technology, Taiyuan 030024, China
2
Postdoctoral Research Station, Huayang New Material Technology Group Co., Ltd., Yangquan 045000, China
*
Author to whom correspondence should be addressed.
Energies 2024, 17(15), 3626; https://doi.org/10.3390/en17153626
Submission received: 26 June 2024 / Revised: 18 July 2024 / Accepted: 22 July 2024 / Published: 24 July 2024
(This article belongs to the Topic Energy Extraction and Processing Science)
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Abstract

:
Coalbed methane (CBM), recognized as a sustainable and environmentally friendly energy source, plays a crucial role in mitigating global climate change and advancing low-carbon energy solutions. However, the prevalence of low-permeability coal seams poses a significant challenge to effective CBM extraction. Improving coal permeability has emerged as a viable strategy to address the issue of low-permeability coal. Conventional CBM stimulation methods fall short in overcoming this obstacle. In contrast, the enhanced technique of CBM extraction by water-based ultrasonic cavitation holds great promise due to its use of high energy intensity, safety, and efficiency. Nevertheless, the inadequate theoretical framework for managing this technology impedes its widespread adoption for large-scale applications. This study investigated the impact of water-based ultrasonic cavitation treatment on coal’s properties and permeability through mechanical testing and permeability measurements conducted before and after treatment. This study also explored the process by which this technology, known as WUC-ECBM, improves coal’s mechanical properties and permeability. The findings suggest a potential stimulation technique (WUC-ECBM) for use in CBM extraction, and its physical mechanism.

1. Introduction

In the past century, there has been significant advancement in mining engineering technology and related fields, prompting increased focus on the production and utilization of coalbed methane [1]. Coalbed methane is advantageous due to its ease of transport, cleanliness, and lower carbon content compared to coal. As mining technology continues to evolve, it is anticipated that coalbed methane, alongside coal and new energy sources, will form a crucial component of a “three-pillar” energy system aimed at addressing global climate change and promoting green, low-carbon development [2]. China, endowed with abundant CBM resources and substantial growth potential, boasts onshore CBM reserves estimated at approximately 30 × 1012 m3 at a depth of 2000 m, with recoverable resources of around 12.50 × 1012 m3. Additionally, CBM reserves deeper than 2000 m are estimated at about 40 × 1012 m3, with recoverable resources totaling around 10.01 × 1012 m3 [3]. Despite these promising figures, proven geological reserves and annual coalbed methane production during the 11th and 13th Five-Year Plans both failed to meet national targets. In fact, China’s entire coalbed methane output over the past 15 years has fallen short of production goals by more than half [4].
One significant factor influencing the mining efficiency of coalbed methane is the permeability of coal seams. In China, coal seams typically exhibit permeabilities ranging from 1 × 10−7 μm2 to 1.8 × 10−3 μm2, which greatly hinders CBM development effectiveness [5]. Enhancing coal permeability stands out as a critical strategy to improve the efficiency of coalbed methane extraction. Techniques such as protective layer mining [6], hydraulic fracturing [7], hydraulic slitting [8], hydraulic punching [9], and high-energy gas blasting [10] are commonly employed for this purpose. Although these methods perform adequately in practical applications, technological limitations restrict their effectiveness in significantly boosting coalbed methane production. For example, hydraulic fracturing can lead to groundwater pollution, coalbed contamination, and water-locking damage [11], all of which impede increased coalbed methane extraction. In recent years, innovative technologies like thermal displacement [12], pickling [13], electrochemical methods [14], and liquid nitrogen freeze–thaw [15] have emerged to address these challenges. However, each approach has its drawbacks: thermal displacement requires substantial energy input and involves complex operations, while electrochemical and pickling processes can potentially contaminate coal seams. Therefore, there is a pressing need to develop green, safe, and efficient technologies for enhancing CBM production to meet these challenges.
Due to its use of high energy intensity, safety, and efficiency, ultrasonic cavitation-enhanced CBM extraction technology (WUC-ECBM) has gained popularity in recent CBM development (see Figure 1) [16,17]. Using water as a medium, this process generates high-energy cavitation bubbles within coal [18], enhancing coal seam fissures and alleviating water locking to increase gas desorption capacity [19]. The technology offers easy operability, precision management, adaptability to reservoir characteristics, and environmental friendliness. In the late 1990s, scholars attempted to increase coalbed methane production through ultrasound [20,21]. These studies of ultrasonic transformation of coal reservoirs mainly focused on mechanical effects and thermal effects [22,23]. Firstly, the energy attenuation of ultrasound in coal is dissipated in the form of heat, locally increasing the reservoir temperature, and forming a thermal effect [24,25]. In addition, ultrasonic loading reduces the average free path of free methane molecules and enhances the gas diffusion permeation rate [26]. Secondly, the ultrasonic mechanical vibration effect directly changes the local stress field in a coal reservoir, causing damage to the coal and leading to reservoir pressure relief [27,28,29]. However, current research on WUC-ECBM technology predominantly relies on custom-built ultrasonic experimental equipment for direct coal operation [30], neglecting factors such as cavitation effects and the influence of liquid media on ultrasonic propagation distance [31]. Existing experiments on coal cavitation induced by ultrasonic waves lack detailed insight into the process, limiting their practicality for engineering applications. Consequently, there is a scarcity of pertinent research findings, low technical maturity, and inadequate scalability to meet large-scale application demands. Further investigation is essential to understand the mechanical damage and permeability enhancement resulting from ultrasonic cavitation.
Thus, this study examined the impacts of water-based ultrasonic cavitation treatment on the mechanical characteristics and permeability of coal, both before and after treatment [32]. This effort enhanced understanding of how WUC-ECBM technology improves coal’s mechanical properties and permeability. Comprehensive research on WUC-ECBM technology holds the potential to enhance air quality and improve CBM development efficiency [33].

2. Methodology

2.1. Sample Preparation

Two types of coal samples were selected for this study: lignite (YCW) from Yangchangwan Coal Mine and bituminous coal (GH) from Gaohe Coal Mine, each representing different levels of metamorphism. Original coal samples were drilled using a rock-coring machine to create cylindrical samples measuring 50 mm × 100 mm. To ensure uniformity, each sample was extracted from a single coal pillar without visible fissures. Figure 2a illustrates the experimental coal sample, and Table 1 presents industrially relevant analytical parameters.

2.2. Water-Based Ultrasonic Cavitation Treatment

Our team developed a water-based ultrasonic cavitation anti-reflection experimental system aimed at revitalizing the ultrasonic cavitation effect within coal samples immersed in a water environment. The setup operates within a high-pressure, sealed water chamber to induce varying levels of ultrasonic cavitation within the coal, as depicted in Figure 2b. The apparatus consists primarily of an ultrasonic generator, a coal sample fixture, and a high-pressure water injector. The ultrasonic generator, 105 cm in length with a frequency of 28 kHz, supports continuous operation with adjustable power ranging from 600 W to 1100 W, emitting ultrasonic waves in a 360° radius unaffected by temperature differentials or liquid levels [34]. The experimental chamber maintains a pressure capacity of at least 5 MPa, ensuring effective high-pressure sealing. Coal samples were exposed to one-hour sessions of water-based cavitation at power levels of 700 W, 800 W, 900 W, 1000 W, and 1100 W, followed by a full day of drying at 60 °C in an oven.

2.3. Uniaxial Compressive Strength Test

TAJW-3000 triaxial rock experimental equipment (Changchun Chaoyang Test Instrument Co., Ltd., Changchun, China) was employed to conduct compressive uniaxial strength tests on cavitated coal samples, as depicted in Figure 2c. This equipment features a confined pressure loading system capable of reaching up to 120 MPa, with a loading rate ranging from 0.001 to 0.5 MPa/s. The axial loading system can apply a maximum pressure of 3000 KN, with a loading rate of 0.01 to 100 KN/s. The experiment targeted a loading stress of 60 kN, utilizing a constant loading rate of 0.04 kN/s.

2.4. Gas Permeability Test

Figure 2d illustrates the results of the gas permeability test conducted on cavitated coal samples using the HBCDS-14/70 ultra-low permeability tester (Nantong Huaxing Petroleum Instrument Co., Ltd., Nantong, China). This equipment was designed to measure coal sample permeability under various coaxial, confining, and gas-injection pressures. The apparatus includes an air source pressurization system, sample installation system, data measurement system, and shaft confining pressure control system. To ensure air-tightness, the experimental system was initially pressurized with 0.6 MPa of nitrogen. Subsequently, the pressure vessel was charged with 0.5 MPa of methane, followed by increasing the pressure to 1 MPa once adsorption equilibrium was achieved. The permeability measurement experiment commenced by gradually applying axial and confining pressures under hydrostatic conditions (σ1 = σ2 = 2 MPa). The test was halted when the pressure differential reached one-third of the initial pressure value. Confining pressures of 3~5 MPa and the appropriate corresponding experimental axial pressures were employed.

3. Analysis and Discussion

3.1. Characteristics of Coal Mechanical Damage

Figure 3 depicts stress–strain curves of GH bituminous coal under uniaxial compression before and after water-based ultrasonic cavitation treatment. Post-treatment, as shown in Figure 3a, the stress–strain curve of GH bituminous coal exhibited distinct changes in the compaction and yield stages. Initially, the GH bituminous coal sample demonstrated an ability to absorb energy elastically. However, after water-based ultrasonic cavitation treatment, its compression resistance noticeably decreased, likely due to increased pores and cracks. Coal deformation typically began during initial loading. With cracks induced by ultrasonic cavitation, the treated coal sample more readily transitioned to the yield state, resulting in an overall reduction in compressive strength. In Figure 3b, stress–strain curves of GH bituminous coal and YCW lignite exhibit similar shifting tendencies, with the former being more susceptible to failure and deformation. The extent of damage varied significantly depending on the strength of ultrasonic cavitation, correlating with the energy received. At 1100 W, the yield region of the YCW lignite stress–strain curve shows an increasing trend post-attenuation, suggesting a delayed reaction of coal strain to stress after crack formation due to the heat-shrinkable tube covering the coal sample. Figure 3c displays the uniaxial compressive strength of coal samples treated with various powers of water-based ultrasonic cavitation. The results indicate a progressive decline in the compressive strength of GH bituminous coal by 21.44%, 23.67%, 25.67%, 27.79%, and 31.02%, following treatments of increasing ultrasonic power. Similarly, YCW lignite experienced reductions of 22.84%, 26.32%, 30.53%, 34.02%, and 37.03%. This demonstrates a strong negative exponential relationship between compressive strength and ultrasonic power, characterized by both a rapid and gradual decline phase. According to Griffith’s theory, damage to pore and fissure structures of coal contributed to this decrease [35]. Water-based ultrasonic cavitation widens pore fissures, thereby diminishing coal’s strength [36]. As ultrasonic power increases, the structural damage to coal intensified, suggesting potential improvements in permeability.

3.2. Changes in Coal Strain Energy

Elastic deformation stores energy within the coal body as strain energy when subjected to external forces. As the coal approaches the critical point of fracture, a part of this energy is released as elastic potential energy, facilitating fissure expansion and the onset of fractures that progressively widen. Concurrently, another portion of the energy transforms into heat energy, dissipated due to interaction and friction among particles within the coal body. This complex interaction defines coal’s energy dynamics:
U = ∫ 0 ε 1 σ 1 d ε 1
U e = 1 2 σ 1 ε e 1 = σ 1 2 2 E u
U d = U − U e = U = ∫ 0 ε 1 σ 1 d ε 1 − σ 1 2 2 E u
Here, Eu represents the elastic modulus in MPa, U denotes the total strain energy in kJ/m3, Ue stands for the elastic potential energy kJ/m3, and Ud represents the dissipated energy in kJ/m3. σi, σj, and σk denote major stresses in the three respective directions in MPa, while εi indicates the total strain in direction i as a percentage, and εei represents the elastic strain in direction i as a percentage. vi denotes the Poisson’s ratio. In this study, only axial stress and uniaxial compression were utilized, hence σ2 and σ3 are both 0.
The total strain energy, elastic potential energy, and dissipated energy of coal samples under different water-based ultrasonic conditions were determined using Equations (1)~(3), respectively. Consequently, relationship curves depicting the total strain energy, elastic strain energy, and dissipated energy as functions of strain for GH bituminous coal and YCW lignite were generated under various water-based ultrasonic power settings, as illustrated in Figure 4 and Figure 5. These curves reflect initial and subsequent levels of damage to the coal induced by water-based ultrasonography.
Figure 4 illustrates that following water-based ultrasonic cavitation treatment of GH bituminous coal, dissipative energy increased at a slower rate, while total strain energy and elastic potential energy both showed an upward trend. This indicates that the coal absorbed and retained energy primarily through elastic forms under uniaxial compression, rather than releasing energy through plastic deformation or fracture processes. After applying 1100 W cavitation, the coal sample’s total strain energy decreased from 178.3 kJ/m3 to 126.2 kJ/m3, its elastic potential energy decreased from 142.4 kJ/m3 to 95.01 kJ/m3, and its dissipative energy from 35.9 kJ/m3 to 31.19 kJ/m3. This pattern highlights the structural impact of ultrasonic cavitation on coal. Notably, the most significant decrease was observed in elastic potential energy, underscoring the substantial influence of ultrasonic waves on coal’s elastic deformation capabilities.
Figure 5 shows that as ultrasonic cavitation intensity increased, the energy evolution process of YCW lignite began to resemble that of GH bituminous coal. The key difference lies in YCW lignite’s higher sensitivity to ultrasonic cavitation, particularly in terms of dissipated energy, owing to its unique high-porosity structure. Cavitation treatment reduced total strain energy, elastic potential energy, and dissipative energy from 129.5 kJ/m3 to 66.1 kJ/m3, from 100.41 kJ/m3 to 60.41 kJ/m3, and from 29.09 kJ/m3 to 5.69 kJ/m3, respectively. This indicates that water-based ultrasonic cavitation is more effective in improving the structure of YCW lignite.
Figure 6 illustrates curves showing changes in total strain energy, elastic potential energy, and dissipative energy for GH bituminous coal and YCW lignite under ultrasonic power. Following cavitation treatment, GH coal’s total strain energy decreased by 17.78%, 22.99%, and 29.22%, while its elastic potential energy decreased by 23.82%, 28.45%, and 33.28%, respectively. YCW lignite exhibited reductions in total strain energy of 28.57%, 42.39%, and 48.96%, and in elastic potential energy of 21.05%, 32.52%, and 39.85%. These results indicate that as ultrasonic power increased, the strain energy, elastic potential energy, and dissipative energy of the coal samples decreased. The impact of ultrasonic cavitation damaged the pore and fissure structure of coal, thereby reducing energy storage and conversion efficiency during compression. This led to decreased energy absorption and elastic storage energy fraction. Consequently, less energy was required for rupture and deformation, which was particularly evident in YCW lignite. Coal becomes more prone to fracturing under external stress, resulting in reduced dissipative energy and increased fracture resistance. Ultrasonic cavitation promotes the formation and interconnection of fractures [37].

3.3. The Influence of Gas Pressure on Permeability

Figure 7 illustrates the permeability enhancement of YCW lignite and GH bituminous coal under various gas injection pressures. It was observed that the increase in permeability of both GH bituminous coal and YCW lignite after cavitation treatment decreased as gas injection pressure rose. Moreover, the effect of ultrasonic cavitation on coal permeability varied with different gas injection pressures. The highest improvement in coal permeability occurred at a gas injection pressure of 0.6 MPa. Specifically, with 1100 W of ultrasonic power, the permeability increased by 0.332 mD for YCW lignite and 0.285 mD for GH bituminous coal. The rate of permeability enhancement slowed steadily as gas injection pressure increased above 0.6 MPa. Additionally, under the same gas injection pressure, the permeability increment of both types of coal increased with higher ultrasonic power. This occurred because increased ultrasonic power introduced more energy into the coal body, significantly altering its structure and creating a more intricate network of pores and fissures, thereby facilitating more gas pathways.
This section utilizing the permeability change rate to analyze the evolution of permeability in coal samples subjected to water-based ultrasound. This approach aimed to investigate how the degree of permeability enhancement varied with different ultrasound powers. The permeability change rate is calculated as follows:
β = Δ K K 0 × 100 % = K 1 − K 0 K 0 × 100 %
where β represents the permeability change rate, %; ∆K is the permeability increment, mD; K0 is the permeability before water-based ultrasonic treatment, mD; and K1 is the permeability after water-based ultrasonic treatment, mD.
Figure 8 illustrates the coal permeability change rate under various gas injection pressures. It was observed that as ultrasonic power increased, the rate of coal permeability change accelerated significantly. This acceleration is attributed to smoother primary seepage channels, increased total gas flow, and heightened structural damage to coal as ultrasonic power rose, leading to larger interconnected pore networks and fissures [38]. The highest permeability fluctuation rates for GH bituminous and YCW lignite coal were 377.45–431.98% and 274.23–314.33%, respectively, with an ultrasonic power of 1100 W. An appropriate increase in ultrasonic power should be considered in practical applications of WUC-ECBM technology to enhance coalbed methane production efficiency [39].

3.4. The Influence of Stress on Permeability

Figure 9 and Figure 10 depict changes in coal sample permeability under various circumferential strains and how this permeability increased in proportion to ultrasonic power. These figures show that following ultrasonic cavitation treatments ranging from 800 to 1100 W, the permeability of GH bituminous coal increased by 0.267 mD, 0.305 mD, 0.361 mD, and 0.406 mD, respectively, at a circumferential tension of 2 MPa. Similarly, YCW lignite exhibited increases of 0.310 mD, 0.356 mD, 0.423 mD, and 0.505 mD, respectively, under the same conditions. Under a circumferential stress of 5 MPa, GH bituminous coal’s permeability increased by 0.091 mD, 0.155 mD, 0.232 mD, and 0.318 mD after a series of ultrasonic cavitation treatments, while YCW lignite saw increases of 0.138 mD, 0.196 mD, 0.245 mD, and 0.284 mD, respectively. As circumferential stress increased, the permeability of both GH bituminous coal and YCW lignite decreased following a series of ultrasonic cavitation treatments. The high-power ultrasonic cavitation effect efficiently enhanced coal’s permeability, thereby improving the permeability of coalbed methane reservoirs [40]. This enhancement was achieved through water-based ultrasonic cavitation, which induced the formation, expansion, and interconnection of internal pores and fissures within the coal [41]. Moreover, by exacerbating topological degradation and structural damage, ultrasonic cavitation promoted gas migration and diffusion in coal [42]. Additionally, this effect can remove minor obstructions within coal fissures, thereby clearing and enhancing the seepage channels and overall permeability of coal.

4. Conclusions

This study examined the impact mechanism of water-based ultrasonic cavitation on coal’s mechanical properties and seepage characteristics using WUC-ECBM technology. The main findings are as follows:
(1)
Water-based ultrasonic cavitation has the potential to significantly weaken coal’s structure and mechanical properties. For example, after 1100 W ultrasonic cavitation treatment, GH bituminous coal and YCW lignite exhibited reductions in their uniaxial compressive strengths by 31.02% and 37.03%, respectively. There was a negative exponential relationship between compressive strength and ultrasonic power, following a pattern of significant decrease, which is attributed to damage to the coal’s pore and fissure structure.
(2)
The damage to pores and fissures caused by ultrasonic cavitation profoundly impacts coal’s energy storage and conversion efficiency during compression. As ultrasonic power increased, dissipative energy, elastic potential energy, and total strain energy evidently decreased, particularly in YCW lignite. The possible reason is that ultrasonic cavitation altered the microstructure of coal. In an environment of 1100 W ultrasonic cavitation, the total strain energy and elastic potential energy of GH bituminous coal decreased by 29.22% and 48.96%, respectively, while those of YCW lignite decreased by 42.39% and 39.85%, respectively.
(3)
The ultrasonic cavitation effect effectively enhanced coal’s permeability, with GH bituminous coal’s and YCW lignite’s permeability increasing by 4.32 and 3.14 times, respectively, in a 1000 W ultrasonic cavitation environment. This enhancement resulted from seepage structural damage, topological degradation, and throat dredging, which facilitate gas diffusion and migration within coal. Additionally, with increasing ultrasonic power, coal permeability and its rate of change also increased. However, as circumferential stress intensified, the permeability and its increment gradually declined. As gas injection pressure rose, permeability initially decreased but eventually stabilized. Therefore, in practical applications of WUC-ECBM, increasing ultrasonic power is a potential optimization method, but the impact of ground stress on this approach should be carefully analyzed.

Author Contributions

X.G.: conceptualization, methodology, funding acquisition, and writing—original draft. Y.L. (Yijia Liu): investigation, software, visualization, and writing—original draft. Y.L. (Yanfeng Li): formal analysis, visualization, and writing—review and editing. C.D.: resources, supervision, funding acquisition, and investigation. L.Z.: funding acquisition, investigation, and resources. Y.Z.: software and visualization. All authors have read and agreed to the published version of this manuscript.

Funding

This study was supported by the National Natural Science Foundation of China (grant number 52204231), the Fundamental Research Program of Shanxi Province (grant number 20210302124483), the Science and Technology Innovation Program for colleges and universities of Shanxi Province (grant number 2021L052), and the Natural Science Foundation Project of Taiyuan University of Technology (grant number 2022QN132).

Data Availability Statement

Data are available on request due to privacy reasons.

Conflicts of Interest

Author Xiaoyang Guo was employed by the company Postdoctoral Research Station, Huayang New Material Technology Group Co., Ltd. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Abbreviations

CBMCoalbed methane;
WUC-ECBMWater-based ultrasonic cavitation-enhanced coalbed methane recovery.

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Figure 1. Schematic diagram of the WUC-ECBM system.
Figure 1. Schematic diagram of the WUC-ECBM system.
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Figure 2. Experimental samples and instruments. (a) indicates the coal samples. (b) indicates the experimental instrument of ultrasonic cavitation used for coal treatment. (c) indicates the triaxial rock experimental equipment. (d) indicates the ultra-low permeability tester.
Figure 2. Experimental samples and instruments. (a) indicates the coal samples. (b) indicates the experimental instrument of ultrasonic cavitation used for coal treatment. (c) indicates the triaxial rock experimental equipment. (d) indicates the ultra-low permeability tester.
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Figure 3. Stress–strain curves of coal before and after water-based ultrasonic cavitation treatment. (a,b) indicate the stress–strain curves of GH bituminous coal and YCW lignite, respectively. (c) indicate the uniaxial compressive strength of coal samples.
Figure 3. Stress–strain curves of coal before and after water-based ultrasonic cavitation treatment. (a,b) indicate the stress–strain curves of GH bituminous coal and YCW lignite, respectively. (c) indicate the uniaxial compressive strength of coal samples.
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Figure 4. Relationship curves between energy change and strain of GH bituminous coal.
Figure 4. Relationship curves between energy change and strain of GH bituminous coal.
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Figure 5. Relationship curves between energy change and strain of YCW lignite.
Figure 5. Relationship curves between energy change and strain of YCW lignite.
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Figure 6. The variation in energy with ultrasonic power.
Figure 6. The variation in energy with ultrasonic power.
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Figure 7. Coal permeability increments under different injection pressure conditions.
Figure 7. Coal permeability increments under different injection pressure conditions.
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Figure 8. Permeability change rates of coal samples under different injection pressures.
Figure 8. Permeability change rates of coal samples under different injection pressures.
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Figure 9. Permeability and its increments in GH bituminous coal under different circumferential stresses.
Figure 9. Permeability and its increments in GH bituminous coal under different circumferential stresses.
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Figure 10. Permeability and its increments in YCW lignite under increasing circumferential stresses.
Figure 10. Permeability and its increments in YCW lignite under increasing circumferential stresses.
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Table 1. Basic physical parameters of coal samples.
Table 1. Basic physical parameters of coal samples.
Coal SamplesTypeMaceral Proportion (%)Ro,max (%)Mad (%)Aad (%)Vdaf (%)FCad (%)
VitriniteInertiniteExiniteMineral
GHBituminous coal57.8132.192.507.501.183.0913.7222.6560.54
YCWLignite42.6755.680.001.650.738.083.2630.0658.60
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MDPI and ACS Style

Guo, X.; Liu, Y.; Li, Y.; Deng, C.; Zhang, L.; Zhang, Y. Mechanical Damage to Coal and Increased Coal Permeability Caused by Water-Based Ultrasonic Cavitation. Energies 2024, 17, 3626. https://doi.org/10.3390/en17153626

AMA Style

Guo X, Liu Y, Li Y, Deng C, Zhang L, Zhang Y. Mechanical Damage to Coal and Increased Coal Permeability Caused by Water-Based Ultrasonic Cavitation. Energies. 2024; 17(15):3626. https://doi.org/10.3390/en17153626

Chicago/Turabian Style

Guo, Xiaoyang, Yijia Liu, Yanfeng Li, Cunbao Deng, Lemei Zhang, and Yu Zhang. 2024. "Mechanical Damage to Coal and Increased Coal Permeability Caused by Water-Based Ultrasonic Cavitation" Energies 17, no. 15: 3626. https://doi.org/10.3390/en17153626

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