Non-uniform Thermal Expansion Research Articles

Thermal buckling behavior of 3D printed foams: Plain, graded, and sandwich variants

The present work focuses on the experimental investigation of the thermal buckling response of 3D printed functionally graded glass micro balloon (GMB) reinforced high density polyethylene (HDPE) composites and their respective sandwiches under non-uniform heating conditions. The influences of GMB loading and its graded composition on temperature distribution are analyzed. The reinforcement of hollow GMB rendered lower thermal conductivity due to enhanced thermal resistance with an increase in filler percentage. An increased thermal buckling strength is also observed. Due to their non-uniform thermal expansion, functionally graded sandwich beams exhibited less deflection than plain beams. Among the cases of three heating conditions (One end heating: case-1, Center heating: case-2, both end heating: case-3), maximum deflection is observed in case 2 while the minimum deflection is noted in case 1. These printed foams can be utilized for lightweight thermal insulating pipes.

Numerical simulation and optimization of In-Vessel primary heat exchangers of NHR200-II

NHR200-II is a multipurpose small integral pressurized water reactor. The primary heat exchangers of NHR200-II are in-vessel single-phase heat exchangers. The primary heat exchangers adopted a tube-in-tube bundle design to improve compactness; however, a significant weakness of the tube-in-tube bundle is the nonuniform thermal expansion between the inner and outer tubes owing to the inhomogeneous tube-temperature distribution. To minimize the thermal stress, the inner and outer tube diameters were optimized using numerical simulations. The nonuniform mass flow rates and temperature fields in each channel and tube were calculated using the optimal tube sizes, and the axially averaged temperatures of the inner and outer tubes were also calculated. The present prediction of nonuniform temperature fields can be used as the input to estimate the magnitude of thermal stress in the assessment of the structural integrity of the primary heat exchangers of NHR200-II.

Phase-field modeling of thermal cracking in hardening mass concrete

The manuscript is concerned with the phase-field modeling of thermal cracking in massive hardening concrete structures. Owing to the exothermic reactions, known as hydration, a considerable amount of heat is generated during the setting and hardening of concrete. Since concrete has relatively low thermal conductivity and fairly high heat capacity, sharp temperature gradients may occur between the interior and exterior parts of massive concrete structures. This uneven temperature distribution results in a non-uniform thermal expansion that, in turn, may lead to thermal cracking in conjunction with restraining external boundary conditions. Hence, it is of key importance to conduct the crack risk assessment of massive concrete structures at various stages of their construction and thereafter where real-size experiments are often unrealizable. To this end, we develop a multi-field computational approach to simulate thermal cracking in hardening concrete. In particular, we propose a novel chemo-thermo-mechanical model developed within the framework of the theory of reactive porous media coupled with a quasi-brittle phase-field regularized cohesive zone model to explicitly account for the initiation and propagation of thermal cracks. In the model, chemical, thermal, mechanical, and phase-field fracture problems are coupled through the constitutive equations. To our best knowledge, this is the first study where a quasi-brittle phase-field fracture model is used to model thermal cracking in hardening massive concrete through a novel incremental formulation. The potential of the proposed approach is demonstrated through the benchmark thermomechanical problems of a normal concrete member and a roller-compacted concrete dam. In the latter, original multi-field interface elements are devised between the lifts.

Reductions in the Laser Welding Deformation of STS304 Cylindrical Structure Using the Pre-Stress Method

Welding deformation occurs due to non-uniform thermal expansion, thermal contraction, restraint, and phase transformation in a metal by a local welding heat source. This causes problems such as low buckling strength and the reduced workability of the production process. Correcting welding deformations in stainless steel using heat—such as by linear heating—causes metal sensitization, which should be avoided. Herein, welding deformation was reduced by applying tension stress instead of correcting the deformation by heating. A deformation-prevention jig was used to reduce welding deformation during the manufacturing of a cylinder made of STS304 by laser welding. The tensile stress was induced by pushing the cylinder shell outward using the deformation-prevention jig. A thermo-elastoplastic analysis was performed to investigate the effects of the magnitude of the tensile stress on welding deformation. Furthermore, the parametric results—which indicated a reduction in welding deformation—were verified through experiments. The thermo-elastoplastic analysis suggested that deformation did not occur when the magnitude of tensile stress was approximately 50% of the yield stress of the base metal. Moreover, the deformation was experimentally reduced by 11–20% when a tensile stress of 30 MPa was applied to the cylinder, compared with that in the absence of tensile stress.

Precise prediction of photothermally induced irreversible bending deformation based on non-uniform thermal expansion of layer-structure films

Although photothermally induced self-bending films based on nonuniform thermal expansion are created, heat transfer and shape-deformation procedures are not investigated very well, limiting the understanding of such complicated behavior and the achievement of precise shape control. Here, thermally expanded microspheres (TEMs) were added into polydimethylsiloxane (PDMS) to create active layers as PDMS-TEM single-layer films that were attached onto pure PDMS passive layer to create PDMS/PDMS-TEM bi-layer films subsequently. After heating, TEMs in the film undergo phase transition and present irreversible thermal expansion, driving deformation of films. Combined with steady-state (uniform heating) deformation simulations and experiments, a deformation model was established before a non-steady state (light irradiation) heat transfer model was set up to simulate the heat transfer process of films under light irradiation. Then the temperature distribution was coupled with the deformation model to simulate the photothermally induced deformation of the samples. The PDMS-TEM single-layer films also presented bending deformation under illumination due to the non-uniform thermal expansion caused by temperature gradient. For bi-layer films, different degrees of thermal expansion between two layers lead to bending deformation. The films with TEM concentration of 30 wt% can achieve great deformation, and the bending curvature was 0.07 mm−1. The geometric parameters including thickness, layer thickness ratio and aspect ratio had little effect on deformation degrees of the films. Deformation mode was varied with aspect ratio. A long side bending and diagonal bending were achieved in bi-layer films at aspect ratios of 7:1 and 1:1. In combination with experimental results, the heat transfer model and deformation model were constructed to demonstrate the complex deformation process, which provides guidance for the structural design of the photothermally induced shape-changing films in practical applications.

Impact of circumferential variation in power, neutron flux and spacer grids on structural behavior of SiC-SiC cladding

Silicon carbide (SiC) cladding is being studied for its potential application in light water reactors for improved accident tolerance. SiC-SiC composite material undergoes irradiation-induced, temperature-dependent swelling. The circumferentially non-uniform neutron flux and power generation in the fuel rod, will produce circumferentially non-uniform swelling and thermal expansion, ultimately leading to bending of the cladding. This bending will cause interaction between the cladding and the spacer grids and can be detrimental to the structural integrity of both the cladding and spacer grids. In this study we have analyzed the bending behavior of the cladding, the stress development in the cladding and the effects of spacer grids. The sensitivity of the cladding stress to the spacer grid material, extent of circumferential variation in power have been also evaluated. The results indicate that the spacer grids do not significantly affect the cladding stresses. The stress generated in the spacer grids due to its interaction with the cladding is found to be well below the strength of the spacer grid material. The sensitivity studies showed that changing the spacer grid material have negligible impact on the stresses in both cladding and spacer grid, while the extent of circumferential variation in power can lead to significant increase in the stresses in spacer grid.

Effect of thermal behavior on the grain morphology and dimension of 80-mm-thick Ti6Al4V plates joined by laser melting deposition

As the material experiences non-uniform thermal expansion and contraction under different thermal behavior during laser melting deposition (LMD), the microstructure of the components will be affected, which also causes changes in mechanical properties. It is essential to understand the thermal behavior of the melt pool during LMD to improve the microstructure and joint quality. In this study, two 80-mm-thick Ti6Al4V plates are successfully joined using three different scanning speeds (10, 15, and 20 mm/s). The effects of thermal behavior on the grain morphology and dimension of deposition area, equiaxed crystal zone (EQZ), and the substrate at different scanning speeds are quantitatively analyzed. The results show that the fine equiaxed crystals are formed near the joint boundary due to the high-temperature gradient and cooling rate. The growth direction of fine columnar crystals continuously changes from the joint boundary to the center of the deposition area due to the change of heat-extraction direction. However, the epitaxial growth direction of the coarse columnar crystal is the same as the previous deposition layer at the center of the deposition area. Given the effect of high heat accumulation and low-temperature gradient during LMD, the dimension of columnar crystal is coarsen significantly at the center of the deposition area.

Modeling and Calculating of Residual Stress and Strain of Butt Welded Joint

The non-uniform thermal expansion and contraction resulting from welding processes cause residual stresses and strains. Experimental studies on measuring welding residual stresses and strains of structure are costly and sometimes they are not possible. Previously, analytical methods with idealized models were developed to determine the welding residual stresses and strain. Recently, numerical methods are constructed to analyze the stresses and the strains in welded structures. This paper presents the calculation results of residual stress and welding strain in butt welded joint of S355J2G3 carbon steel of 5 mm thickness made by MAG welding process with a single pass. The calculation is performed by two methods: the imaginary force method and the finite element method. In the finite element method, the SYSWELD software is used to simulate and to determine residual stresses and strain of this welded joint. The results of finite element method are compared with those of imaginary force method to show the rationality and the advantages of finite element method. The study results have shown that in this welded joint, only the longitudinal and transverse stress components are important and the other stress components are negligible.

Flexural-torsional buckling of shear deformable steel circular arches under a central concentrated load in a thermal environment

When subjected to a constant temperature gradient, a steel circular arch will experiences non-uniform thermal expansion in its axial direction. This expansion will produces complex internal forces in the arch, which in turn will affect its flexural–torsional buckling behavior under a central concentrated radial load. Hitherto, research studies of the flexural–torsional buckling of such arches are scarce. The position of the effective centroid and shear center do not coincide with the geometric centroid of the section in a temperature gradient field, and this influences the flexural–torsional buckling response. In this paper, the flexural–torsional buckling of shear deformable circular arches with in-plane elastic rotational end restraints subjected to a central concentrated radial load at a constant temperature gradient field is studied. The theoretical solutions for the buckling load of the arch including the effect of the temperature gradient field are obtained and validated by ANSYS simulations. It is found that the buckling load decreases with an increase of the temperature differential when the included angle is small and increases with an increase of the temperature differential in case the included angle is larger than a certain value. The buckling loads including shear deformations are higher than those ignoring shear deformations at a bigger temperature differential. The influences of shear deformations on the buckling load are more significant at a bigger temperature differential.

Microstructural Changes in Concrete: Postfire Scenario

The thermal and mechanical properties of coarse aggregates, cement mortar, and cement concrete specimens of varying mix proportions were studied after exposure to a range of high temperatures. For the tests, 70.6-mm mortar cubes, concrete cubes of 100 and 150 mm, and concrete cylinders of 100 and 150 mm diameters and 200 and 300 mm heights, respectively, were cast. The water to binder ratio was varied from 0.35 to 0.5. These specimens were exposed to a wide range of temperatures varying from room temperature (24°C±2°C) to 1,000°C and tested to understand the degradation in strength and spalling behavior of normal-strength concrete (NSC) and high-strength concrete (HSC). The crack initiation and propagation was studied using micrographs obtained from scanning electron microscopy (SEM). Changes in the porosity of coarse aggregates and concrete at elevated temperatures is quantified by incorporating digital image processing on the SEM micrographs. The influence of high temperature on the physical and chemical properties of concrete and concrete constituents at the macroscale and microscale are discussed. Simple empirical relationships to compute residual compressive strength of NSC and HSC at elevated temperatures are proposed. It is concluded from the results that the degradation in the concrete strength at high temperatures is primarily a result of nonuniform thermal expansion of concrete and its individual constituents leading to porosity changes in the cement–sand matrix, coarse aggregates, and interface between the two.

Coastal sea level anomalies and associated trends from Jason satellite altimetry over 2002\u20132018

Climate-related sea level changes in the world coastal zones result from the superposition of the global mean rise due to ocean warming and land ice melt, regional changes caused by non-uniform ocean thermal expansion and salinity changes, and by the solid Earth response to current water mass redistribution and associated gravity change, plus small-scale coastal processes (e.g., shelf currents, wind & waves changes, fresh water input from rivers, etc.). So far, satellite altimetry has provided global gridded sea level time series up to 10–15 km to the coast only, preventing estimation of sea level changes very close to the coast. Here we present a 16-year-long (June 2002 to May 2018), high-resolution (20-Hz), along-track sea level dataset at monthly interval, together with associated sea level trends, at 429 coastal sites in six regions (Northeast Atlantic, Mediterranean Sea, Western Africa, North Indian Ocean, Southeast Asia and Australia). This new coastal sea level product is based on complete reprocessing of raw radar altimetry waveforms from the Jason-1, Jason-2 and Jason-3 missions.

Tailoring the Coefficient of Chemical Expansion in Perovskite Oxides through A Vs. B-Site Multivalent Cation Placement

Chemical expansion is a strain induced by a change in stoichiometry, such as oxygen loss. It can enable a material to actuate when exposed to different gas environments, and it can significantly impact device longevity when there are large concentration gradients across small material dimensions in multilayer devices. The desired magnitude of chemical expansion depends on the application; typically, the goal is a large expansion in the former and a small expansion in the latter, where compatibility with neighboring materials is of concern. Therefore, design rules for tailoring expansion from oxygen exchange are needed for the multitude of applications in which it is a contributing factor.As oxygen leaves an oxide lattice during reduction, electrons are generated to preserve charge neutrality, which may move to multivalent cations; this process results in significant expansion of the multivalent cation, and the surrounding lattice, as the oxidation state of the multivalent cation decreases. Recently, an empirical formula describing the pseudo-cubic lattice constant of perovskite materials was developed [1], which relates the lattice parameter to the ionic radii of each cationic and anionic component. This equation predicts that changes in the B-site cation size will have a larger effect on the lattice parameter than an equal change at the A-site. If the multivalent cation is the only one changing size during redox processes, this equation suggests that its placement on the A or B site will have a significant effect on the magnitude of the overall lattice strain during oxygen loss or gain.To test this theory, model perovskite bulk ceramic compositions with multivalent Pr(3+,4+) on the A site and on the B site were fabricated: PrGa0.9Mg0.1O2.95+ δ and BaPr0.9Y0.1O2.95- δ, respectively. Strain values from dilatometry and defect concentrations from thermogravimetric analysis were used to calculate the coefficients of chemical expansion (CCE) in both materials, to determine the effect of multivalent cation placement. These measurements were performed under isothermal conditions while varying the pO2 to avoid effects from nonuniform thermal expansion at different stoichiometries. Multiple temperatures were analyzed to observe any temperature-related trends in CCEs and to determine any effects from crystal structure changes. The resulting CCEs will be interpreted not only in terms of multivalent A vs. B site placement but also considering other factors that may impact CCEs: crystallographic distortions, temperature, and charge localization.[1] Marrocchelli, D., Perry, N. H., & Bishop, S. R. (2015). Understanding chemical expansion in perovskite-structured oxides. Physical Chemistry Chemical Physics, 17(15), 10028-10039.

Thermal expansion property and anisotropy of columnar-grained Cu71.5Al18.5Mn10 shape memory alloy under pre-deformation

Columnar-grained Cu-Al-Mn shape memory alloy (SMA) is a kind of obvious anisotropic structure alloy due to its axial high aspect ratio grain structure and axial strong 〈001〉 orientation texture along the solidification direction (SD). Based on the application potential of non-uniform thermal expansion characteristics owing to the martensite transformation characteristics of alloys, in this paper, the anisotropy of thermal expansion property and the effect of pre-deformation on the anisotropy of columnar-grained Cu71.5Al18.5Mn10 shape memory alloy were investigated. The results show that the alloy has obvious thermal expansion anisotropy in different directions and low thermal expansion behavior at certain temperature range. The regulation from positive thermal expansion to negative thermal expansion is achieved in 0° direction along the SD. Furthermore cold rolled pre-deformation treatment can achieve near-zero thermal expansion property with a temperature range of 155.5 K, undergoing a cold rolling deformation of ~12%.

Microscopic characterization of structural relaxation and cryogenic rejuvenation in metallic glasses

Plasticity improvement in metallic glasses resulting from cycling treatment between room and liquid nitrogen temperature has been reported and attributed to rejuvenation due to a non-uniform thermal expansion coefficient. However, the detailed microscopic effect is still unclear. The present study focuses on the microscopic effect of room-temperature ageing and cryogenic cycling. La70Cu15Al15 and La70Ni15Al15 metallic glasses were subjected to varying ageing times, after which some were also cryogenically cycled. Quasi-static anelastic relaxation measurements were then employed to characterize the time-constant spectra over seven orders of magnitude. The overall anelastic strain decreases with increasing ageing time, but is not noticeably affected by cryogenic cycling. On the other hand, while ageing also causes an increase in characteristic time constants, cycling reverses this effect. The new details shed light on the effect of structural relaxation and rejuvenation on the properties of shear transformation zones.

Investigation on the Effect of Thermo-Mechanical Tensioning on Weld Induced Out-of-Plane Distortions

Fabrication of ship structures involving welding of thin plates, poses a real challenge in limiting the out-of-plane distortion due to buckling. In this study, the effect of thermo-mechanical tensioning (TMT) on minimizing out-of-plane distortion due to buckling in fabrication of stiffened panels has been investigated through experimental and numerical studies. Experiments were conducted using 3-mm-thick plates. The pretensioning of the plates was done along the stiffener welding lines using the shrinkage forces of the tensioning lugs. The lug width was decided based on the possible width of the tensile stress zone due to the welding of stiffener. The tensioning lugs were heated to a temperature so that the plastic deformation of the lugs are minimized thereby required tensioning of the plate could be achieved. Through the implementation of TMT, a noticeable reduction in the out-of-plane distortions were observed. The influence of the sequence of lug removal on the buckling distortions was studied numerically. Fairly good agreement was obtained between experimental and numerical results. The process of TMT was found to be quite effective as an active in-process distortion mitigation technique for fabrication of thin stiffened panels. 1. Introduction Fusion welding is one of the widely used processes of joining. It is extensively used in heavy fabrication industries such as railways, shipbuilding. Fusion welding being a thermal process, it may lead to structural distortions and residual stresses due to nonuniform thermal expansion and contraction of the weld metal and the adjoining the base material. Welding distortions adversely affect the dimensional accuracy of the welded structures and as a consequence act negatively on productivity because of the postweld corrective work that becomes necessary. On the other hand, residual stresses due to fusion welding are the major contributors in crack generation and impairing the fatigue life of the structure. Therefore instead of postweld treatments, in-process active distortion and residual stress mitigation techniques are more beneficial to enhance product quality and productivity. in ship building industry, thin plates are widely used to reduce the weight and thereby cost of fuel (Huang et al. 2004). Welding of these thin plates are more prone to buckling because of their lesser buckling strength. Masubuchi was the first to report about the weld-induced buckling distortions caused by compressive residual stresses in thin plates (Masubuchi 1953). Further Watanabe and Satoh (1958) made an attempt to find out the minimum half wavelength, below which a plate does not buckle, and maximum radius of curvature after buckling for bead welding of thin steel plates. The effect of thermal tensioning on the mitigation of weld-induced buckling distortions was studied by Michaleris and Sun (1997). They employed both finite element analysis and experimental technique in their study. Thermal tensioning was done by simultaneous cooling the bottom of the weld zone by water spraying and heating of the adjacent areas with resistive heating blankets. it was observed that too high a temperature gradient had a detrimental effect on the weld-induced buckling distortions and too low a value of the same resulted in insufficient tensioning. Also it was concluded that the cooling time should be as low as possible for the process to be effective and economic (Michaleris & Sun 1997). Deo and Michaleris (2003) evaluated experimentally the influence of transient thermal tensioning on the reduction of buckling distortions. They also compared the case of Time Temperature Transformation (TTT) at 200 and 250°C with the case of plates welded with only mechanical restraints. It was observed that the buckling distortions cannot be mitigated only with the use of mechanical restraints. The introduction of tensile stresses in the direction of welding through the side heating reduced the compressive residual stresses at the free edges of the plate to a value below the critical buckling stress.

Computational performance of beam-column elements in modelling structural members subjected to localised fire

In the past decades, increasing attention has been directed to understanding the structural response to various scenario fires, which is stimulated by the trend of considering localised burning in large open plan compartments. Beam-column elements as widely used in modelling steel frames have been extended to account for the thermal impact in OpenSees, the development of which is undertaken to formulate the displacement and force-based beam elements. After including the non-uniform thermal expansion along the element length caused by localised heating, the force-based beam-column element has shown greater efficiency compared to the displacement-based element. A detailed discussion regarding the computational performance of both beam-column elements has been presented in this paper, which concludes that force-based beam-column elements can better represent the localised plasticity of fibres caused by non-uniform heating. A generic simply supported steel beam can be modelled even with two force-based elements to reproduce accurate mid-span deflection under localised heating. A steel beam subjected to a localised fire is presented as a case study in this paper, experiencing run-away collapse after 15 min of exposure when the load ratio reaches 50%. Using a 12 element force-based beam-column model and shows equivalent accuracy against 48 element displacement-based beam-column model.

Constitutive analysis of electrically-assisted tensile deformation of CP-Ti based on non-uniform thermal expansion, plastic softening and dynamic strain aging

Electrically-assisted (EA) deformation has shown promising effects in increasing formability and reducing springback in sheet metal forming. This work experimentally and analytically investigated the influence of non-uniform and transient Joule heating on the plastic flow stress of titanium which evolved nonlinearity with time and deformation. Three-stage constitutive analysis was carried out in the present study. First, the pure influence of non-uniform Joule heating was investigated in terms of linear elastic thermal expansion, which then explained the measured drops in stress. Second, the Johnson-Cook model was adopted to interpret a plastic thermal-mechanical behavior of the material loaded at a constant quasi-static deformation rate under the uniaxial tension combined with a single pulse of electric current. Finally, it was revealed that the sudden change in strain rate and rapid heating rate due to an electric current pulse could give rise to the transient occurrence of dynamic strain aging (DSA) in materials. This resulted in an accumulated plastic strain as well as transient high-temperature strain hardening, which estimated the experimentally measured data well. The DSA contribution revealed in this work could help to explain many observations in the past studies in the field of EA deformation.

Structural integrity analyses of two gas turbines exhaust systems used for naval propulsion

Heating and cooling cycles, as well as accelerations and decelerations, to which naval gas turbine's exhaust systems under study are submitted to, could lead to the nucleation and propagation of cracks, and result in the reduction of its expected fatigue life. The paper herein presented refers to the numerical simulations of the mechanical and thermal behaviours of two different gas turbine's exhaust systems used in naval propulsion. In addition, some experimental values that were collected, namely temperature and pressure, served as input values for the finite element analyses carried out. The analyses made to the exhaust systems revealed the existence of high stresses near the lower support flanges, which are mainly caused by the non-uniform thermal expansion that the exhaust systems are subjected to. Additionally, redesigned exhaust systems were studied in order to enhance the thermal behaviour of the exhaust systems and, therefore, increasing its fatigue life. The modifications introduced in the exhaust systems resulted in the reduction of the induced stresses. However, frequent surveys should be performed to the critical welds of the exhaust systems, in order to prevent crack propagation from the weld toes. Moreover, high quality fabrication is required in order to avoid the presence of initial defects in the structure.

3D Nondestructive Visualization and Evaluation of TRISO Particles Distribution in HTGR Fuel Pebbles Using Cone-Beam Computed Tomography

A nonuniform distribution of tristructural isotropic (TRISO) particles within a high-temperature gas-cooled reactor (HTGR) pebble may lead to excessive thermal gradients and nonuniform thermal expansion during operation. If the particles are closely clustered, local hotspots may form, leading to excessive stresses on particle layers and an increased probability of particle failure. Although X-ray digital radiography (DR) is currently used to evaluate the TRISO distributions in pebbles, X-ray DR projection images are two-dimensional in nature, which would potentially miss some details for 3D evaluation. This paper proposes a method of 3D visualization and evaluation of the TRISO distribution in HTGR pebbles using cone-beam computed tomography (CBCT): first, a pebble is scanned on our high-resolution CBCT, and 2D cross-sectional images are reconstructed; secondly, all cross-sectional images are restructured to form the 3D model of the pebble; then, volume rendering is applied to segment and display the TRISO particles in 3D for visualization and distribution evaluation. For method validation, several pebbles were scanned and the 3D distributions of the TRISO particles within the pebbles were produced. Experiment results show that the proposed method provides more 3D than DR, which will facilitate pebble fabrication research and production quality control.

Uniformity of temperature variation in coal during methane adsorption

Uniformity of methane adsorption by coal is important for assessing both the maximum storage capacity and damage caused by nonuniform thermal expansion. Therefore, this study examines the structural characteristics and temperature variation on the surface of coal during methane adsorption at 1 and 1.5 MPa. The results showed that the temperature increase in different surface regions associated with methane adsorption obeys the normal distribution law, and it is closely related to its meso-structure characteristics. That is, the vitrinite of the coal matrix has a fast adsorption rate and a better developed microscopic structure, resulting in a higher adsorption capacity and more pronounced temperature rise. In contrast, clay minerals present in coal have a lower methane adsorption capacity and slow adsorption rate, resulting in a smaller temperature rise.