Thermal Behavior Characteristics Research Articles

Experimental Study on the Thermal Behavior Characteristics of the Oxidative Spontaneous Combustion Process of Fischer–Tropsch Wax Residue

Coal-to-liquid technology is a key technology to ensuring national energy security, with the Fischer–Tropsch synthesis process at its core. However, in actual production, Fischer–Tropsch wax residue exhibits the characteristics of spontaneous combustion due to heat accumulation, posing a fire hazard when exposed to air for extended periods. This significantly threatens the safe production operations of coal-to-liquid chemical enterprises. This study primarily focuses on the experimental investigation of the oxidative spontaneous combustion process of three typical types of wax residues produced during Fischer–Tropsch synthesis. Differential Scanning Calorimetry (DSC) was used to test the thermal flow curves of the three wax residue samples. Kinetic analysis was performed using the Kissinger–Akahira–Sunose (KAS) and Flynn–Wall–Ozawa (FWO) methods to calculate their apparent activation energy. This study analyzed the thermal behavior characteristics, exothermic properties, and kinetic parameters of three typical wax residue samples, exploring the ease of reaction between wax residues and oxygen and their tendency for spontaneous combustion. The results indicate that Wax Residue 1 is rich in low-carbon chain alkanes and olefins, Wax Residue 2 contains relatively fewer low-carbon chain alkanes and olefins, while Wax Residue 3 primarily consists of high-carbon chain alkanes and olefins. This leads to different thermal behavior characteristics among the three typical wax residue samples, with Wax Residue 1 having the lowest heat release and average apparent activation energy and Wax Residue 3 having the highest heat release and average apparent activation energy. These findings suggest that Wax Residue 1 has a higher tendency for spontaneous combustion. This research provides a scientific basis for the safety management of the coal chemical industry, and further exploration into the storage and handling methods of wax residues could reduce fire risks in the future.

Frequency varying heating strategy for lithium-ion battery rapid preheating under subzero temperature considering the limitation of on-board current

The electrical performance of lithium-ion battery gradually deteriorates with the temperature decrease. Alternating current (AC) heating is an efficient manner to improve the lithium-ion battery (LIB) discharge ability at low temperature. This paper proposes an effective method to quickly preheat battery under low temperature based on sinusoidal AC. An electrothermal coupled model is established to precisely characterize the battery electrical and thermal behavior characteristics. Subsequently, the impedance characteristics of large format prismatic LIB are investigated through electrochemical impedance spectroscopy testing. The amplitude and frequency of sine wave current exploited for battery pack heating are optimized at different temperatures and SOC based on the analysis of AC impedance. Finally, the sinusoidal AC heating for battery pack is achieved leveraging the designed full bridge inverter circuit-based heater and the heating efficiency with respect to different amplitudes and frequencies are comprehensively compared. On this basis, a frequency varying heating strategy with fixed amplitude considering the current limitation of hardware circuit is proposed. The experimental results show that the battery pack can be rapidly heated from −30 °C to 0 °C with the maximum average temperature rise rate of 3.78 °C/min, and the heating energy consumption rate is less than 0.27% SOC/°C with the proposed strategy. On this account, the battery pack discharge capacity under frigid environment can be distinctly enhanced based on the proposed heating strategy.

The suppression of thermal propagation using spray cooling with R410A in overheated lithium battery pack

Currently, the thermal safety control of lithium-ion batteries for electric vehicles has emerged as a prominent research focus in both academia and industry. During the transition from overheating to the initial stage of thermal runaway, lithium batteries undergo an overheating decomposition reaction, which presents an opportunity for proactive prevention of thermal runaway. In this context, this study proposes a spray cooling method and performs numerical simulations to investigate the impact of spray cooling on suppressing overheating propagation in battery packs. Specifically, we examine the suppressor effect of spray cooling on propagating overheating within the battery pack. The cooling effect of R410A spray was investigated at three typical positions prone to overheating. We analyzed changes in thermal behavior characteristics of individual batteries within the pack and evaluated its inhibitory effect on propagating of overheating. The spray strategy is also improved and optimized by increasing the number of spray nozzles and spraying in advance. The results demonstrate that the implementation of the spray cooling method in this study effectively mitigates the average temperature of the overheated battery, thereby preventing the overheating decomposition reaction. Simultaneously, the spray cooling effectively suppresses the heat propagation of excessively heated batteries within the battery pack, thereby preventing and delaying the onset of thermal runaway in the battery pack.

Analytical solutions for hyaluronic acid flow and heat transfer between joints with periodic oscillations under the magnetic field

Osteoarthritis (OA) is a globally prevalent disease that poses significant challenges to the daily work and life of patients. Viscosupplementation is one of the most commonly used drug treatments for OA, which involves injecting hyaluronic acid (HA) into the joint cavity to alleviate synovial inflammation. The current research aims to explore the rheological and thermal behavior of HA between joints by studying the axisymmetric squeezing flow and heat transfer of incompressible Maxwell fluid under the action of static magnetic field between two rigid spheres with partial wall slip. The analytical solutions for velocity and temperature are obtained by using the Laplace integral variational theory. Detailed explanations are provided on the effects of different fluid parameters on velocity and temperature, presented in the form of charts. It can be shown that as the magnetic field intensity increases, the viscosity of HA increases with the increasing of relaxation time, thereby fluid motion is weakened and a strong damping effect is produced. As the frequency of joints motion increases, the velocity distribution becomes more uniform in the central region, and the overall distribution deviates from a parabolic distribution. In addition, as Reynolds number, Prandtl number and squeezing depth increase, the heat transfer capacity of the fluid decreases, resulting in a lower temperature at the top wall and a higher temperature at the bottom wall. This study provides theoretical support for exploring the rheological and thermal behavior characteristics of HA in the treatment of OA.

Apparent activation energy of mineral in open pit mine based upon the evolution of active functional groups

This study aimed to investigate the mechanism of mineral spontaneous combustion in an open pit. On the study of coal and mineral mixture in open pit mines, as well as through the specific surface area and Search Engine Marketing (SEM) experiments, the specific surface area and aperture characteristics of distribution of open pit coal sample and pit mineral mixture samples were analyzed. Thermal analysis experiments were used to divide the oxidation process was divided into three stages, and the thermal behavior characteristics of experimental samples were characterized. On the basis of the stage division, we explored the transfer law of the key active functional groups of the experimental samples. The apparent activation energy calculation of the key active groups, performed by combining the Achar differential method with the Coats–Redfern integral method, microstructural and oxidation kinetic properties were revealed. The resulted showed that the mixed sample had high ash, the fixed carbon content was reduced, the specific surface area was far lower than the raw coal, the large aperture distribution was slightly higher than the medium hole, the micropore was exceptionally low, the gas adsorption capacity was weaker than the raw coal, the pit coal sample had the exceedingly more active functional groups, easy to react with oxygen, more likely to occur naturally, and its harm was relatively large. The mixed sample contained the highest C–O–C functional group absorbance. The functional groups were mainly influenced by the self-OH content, alkyl side chain, and fatty hydrocarbon in the sample. The main functional groups of the four-like mixture had the highest apparent activation energy, and the two reactions were higher in the low-temperature oxidation phase.

Study on Thermal Behavior Characteristics and Microstructure Evolution Mechanism of Residual Coal Combustion Process in Deep High Initial Temperature Environment

ABSTRACT The shallow coal seam resources are gradually reduced, the depth of coal seam mining is increased, and the underground temperature is increased, which makes the risk of residual coal fire increase year by year. In order to explore the transformation path of functional groups during oxidation and the caloric release characteristics of residual coal in deep coal mine, the microcosmic changes of coal oxidation process in deep mine were analyzed by in situ diffuse reflectance (In situ FTIR) and electron spin resonance (EPR) experiments, and macroscopic characteristics such as characteristic temperature of residual coal were tested by synchronous thermal analysis experiment. In FTIR results, it is observed that hydroxyl groups, active aliphatic hydrocarbon structures, and active oxygen-containing groups are key chemical structures involved in the oxidation process of residual coal, displaying a strong correlation transformation phenomenon. This can be described as follows: oxygen absorption led to a negative correlation between aliphatic hydrocarbon structures and hydroxyl groups, while the conversion of aliphatic hydrocarbon structures into carboxyl and aldehyde groups resulted in a negative correlation between aliphatic hydrocarbons, carboxyl groups, and aldehyde groups. Active oxygen-containing functional groups showed a positive correlation. With the increased of free radical concentration, the type of free radicals increased and the linewidth (ΔH) increased. The high-temperature environment intensified thermal behavior tendencies, increased the number of active structures, and raised the risk of spontaneous combustion. The research results provided a theoretical basis for understanding the process of coal spontaneous combustion, and had important reference value for ensuring the safe mining of deep coal seams and implementing effective disaster prevention measures.

Study on the inhibitory effect of DL‐malic acid on the phase structure and combustion characteristics of coal

AbstractDL‐malic acid (DMA), as a recognized antioxidant inhibitor and chelating agent in the food and chemical industries, has good application prospects in coal fire prevention and control. This paper investigates the impact of a DMA solution on the surface properties and phase structure of coal through a range of analytical techniques, including electron microscope scanning, particle size analysis, and x‐ray diffraction. The thermal behavior characteristics of DMA‐treated coal were analyzed using thermogravimetric experiments. The results show that after adding malic acid, the particle size of coal sample is reduced, the sphericity and roundness are reduced, and the pore size is increased. The hydroxyapatite and calcite components in coal were dissolved and consumed, and the calcite components were gradually depleted with the increase of DMA concentration. The flocculent structure produced by the condensation of the crushing residue and broken small particles are attached to the internal pores of coal, which reduced the coal oxygen contact sites and increases the content of the sealed solution, resulting in the increase of the thermal characteristic temperature of the coal and the inhibition of the oxidation heat generation process. DMA has obvious inhibitory effect on fresh coal and oxidized coal, and the inhibitory effect is stronger on high‐temperature oxidized coal. Therefore, DMA can be effectively applied to the prevention and control of spontaneous combustion of residual coal in goaf. The research results provide a reference for the research of coal fire prevention technology and the preparation of environmentally friendly flame retardant materials.

Analysis of the Thermal Behavior Characteristics and Dynamics of Coal Under High Primary Temperature Conditions in Deep Mines

ABSTRACT The exposure to spontaneous combustion of coal subjected to high ground temperatures increases as the depth of mine excavation increases. To research the oxidative heat release characteristics of deep coal, a study was carried out to characterize the oxidation kinetics and thermal effects on coal in deep thermal environments; deep coals (heat-treated coals) in 30°C (T30), 45°C (T45) and 60°C (T60) environments were prepared using a simultaneous thermal analysis, and the thermal weight characteristics (TG) and thermal release characteristics (DSC) of heat-treated coals were tested by simulating coal samples in different deep thermal environments; the thermal effects of heat-treated coals were analyzed by oxidation kinetic theory. The findings indicated that the characteristic point temperature of the coal gradually reduces (T60 has the lowest oxidation characteristic temperature) as the heat treatment temperature increases, and the maximum mass loss (63.76%) during thermal treatment coal oxidation occurs in the combustion stage. The oxidation reaction mechanism function for the low-temperature oxidation phases of the deep coal conforms to the Z-L-T equation with a three-dimensional diffusion reaction mechanism. As the temperature of the thermal environment is increased, the apparent activation energy of the coal decreases and the exothermic heat increases. This increases the tendency for oxidation of the deep coal, making it more amenable to spontaneous combustion as the ambient temperature at depth rises. The results contribute to a theoretical framework for monitoring and preventing coal spontaneous combustion fires in deep mine excavations.

Unsteady Heat Flux Measurement and Predictions Using Long Short-Term Memory Networks

Energy consumption modeling has evolved along with building technology. Modeling techniques can be largely classified into white box, gray box, and black box. In this study, the thermal behavior characteristics of building components were identified through time-series data analysis using LSTM neural networks. Sensors were installed inside and outside the test room to measure physical quantities. As a result of calculating the overall heat transfer coefficient according to the international standard ISO 9869-1, the U value of the multi-window with antireflection coating was 1.84 W/(m2∙K). To understand the thermal behavior of multiple windows, we constructed a neural network using an LSTM architecture and used the measured data-set to predict and evaluate the heat flux through deep learning. From the measurement data, a wavelet transform was used to extract features and to find appropriate control time-step intervals. Performance was evaluated according to multistep measurement intervals using the error metric method. The multistep time interval for control monitoring is preferably no more than 240 s. In addition, multivariate analysis with several input variables was performed. In particular, the thermal behavior of building components can be analyzed through heat flux and temperature measurements in the transient state of physical properties of pre-installed building components, which were difficult to access with conventional steady-state measurement methods.

Self-Heating and Thermal Network Model for Complementary FET

In this article, we investigate the self-heating effect (SHE) of the Complementary FET (CFET) device and propose a cross-coupled thermal network model. For the investigation of thermal behavior, the intra- and inter-device crosstalk of CFET is evaluated qualitatively through the defined crosstalk coefficient. The results indicate that CFETs have more severe intra-device thermal crosstalk, almost twice that of CMOS. Moreover, the vertical structure makes the heat dissipation path of CFET devices significantly different in the two transition states (inputs “1” and “0”). Based on the thermal behavior characteristics of CFET and the necessity of high-precision and rapid prediction of thermal characteristics of the devices, a thermal network model is proposed, which can quickly respond to the heat source and be extended at the array level. In the last part, we analyze the influence of load capacitance and operating frequency on the self-heating of CFET, and SHE-related reliability lifetime is predicted based on the lattice temperature obtained from the thermal network. The prediction results show that the bias temperature instability (BTI) lifetime of CFET degrades by 84% compared with standard CMOS.

Numerical Simulations of Heat Transfer Phenomena through a Baffled Rectangular Channel

In presence of baffle, the turbulent airflow phenomena as well as forced convective heat exchange characteristics in two-dimensional rectangular channel have been analyzed in this work. For variations in Reynolds number (Re), we have studied the variations in characteristics of thermal behavior due to the change in the shape of baffle. Computations have been done using finite volume method (FVM) and FLUENT software and the SIMPLE algorithm has been employed for solving the governing equations. Finally, the flow and thermal exchange characteristics viz., streamline flow, turbulence intensity (TE), axial velocity, turbulence kinetic energy (TKE), normalized friction factor (F), normalized average Nusselt number (Nuavg) and thermal enhancement factor (TEF) have been studied in details from numerical standpoint. It has been found that the triangular shaped baffle provides highest value of F at Re = 30,000 and at Re = 46, 000, the maximum value of the TEF is found for the same baffle implying that triangular shaped baffle is more suitable for overall purposes.

Pyrolysis of corn cob: physico-chemical characterization, thermal decomposition behavior and kinetic analysis

Abstract Bioenergy out of lignocellulosic biomass, especially from agricultural crop residues, is making massive inroads in our quest for sustainable environment. In the present study, detailed physico-chemical characterization, thermal degradation characteristics, and kinetics of pyrolysis of corn cob are reported. Thermogravimetric experiments were performed at different heating rates, such as, 10, 20, and 30 °C/min in an inert atmosphere. Thermogravimetric (TG) and derivative thermogravimetric (DTG) curves inferred the thermal behavior characteristics of corn cob. Significant content of cellulose and hemicellulose put together (76.23%) suggested tremendous potential of corn cob to give enhanced yield of bio-oil through pyrolysis. Maximum mass loss of 61.92% for corn cob was observed in the temperature range of 180–360 °C. The kinetic parameters for pyrolysis of corn cob were determined by employing model-free isoconversional methods like, Kissinger-Akahira-Sunose, Flynn-Wall-Ozawa, and Starink. Activation energy from FWO (62.44 kJ/mol) and Starink (61.74 kJ/mol) method for pyrolysis of corn cob was found to be in close proximity. The results revealed prospective bioenergy potential of corn cob as a feedstock for pyrolysis process.

Solidification Effect on the Microstructure and Mechanism of Laser‐Solid‐Forming‐Produced Flame‐Resistant Ti–35V–15Cr Alloy

Ti–35V–15Cr alloy has become an indispensable material in aerospace industry due to its excellent flame‐resistance properties. Herein, the block and thin‐wall Ti–35V–15Cr samples are built by laser solid forming (LSF) under the same processing parameters, and the evolution of solidification microstructure is investigated. This work focused on the effect of molten pool solidification parameters and complex thermal cycling conditions on the morphology of β grains and the substructure in the grains. The microstructure of LSF‐produced Ti–35V–15Cr block sample mainly consists of epitaxial columnar dendritic grains, whereas that of the deposited thin‐wall sample is mainly composed of near‐equiaxed grains together with subgrains formed in the near‐equiaxed grains. Such different microstructure results from extremely sensitive thermal behavior condition in LSF process. The simulated thermal behavior characteristics using finite element method illustrate that the thermal cycles during block deposition are very complex and the temperature gradient at the last solidification in block deposition is much higher than that in the deposition of thin‐wall samples, resulting in significantly different solidification microstructure between thin‐wall and block samples.

Alkali metals association in biomass and their impact on ash melting behaviour

Selected agricultural and energy crop biomass ashes represented by two mixed cereal straws, corn straw, Miscanthus × Gigantus and Salix Viminalis were chosen for ash behaviour investigation and prediction of operating problems during biomass combustion. The presence of aggressive species in the ash generate operational problems of heat exchanging surfaces in power boilers connected with slagging and fouling processes, limiting the use of biomass direct combustion for energy production. In this work, thermal behaviour characteristics, transformation properties of the inorganic components and ash fusion temperatures of biomass ashes were investigated using thermal analysis (STA), X-ray diffraction (XRD) and high-temperature microscope. The special attention was focused on the evaluation of potassium compounds presented in ashes. Potassium was detected as KCl, K2SO4, K2CO3 and K3PO4. It was noted, that presence and concentration of alkali metals, silicon and calcium compounds has the major impact on fusion temperatures of studied ashes. Leaching process of ash elements using water, ammonium acetate and hydrochloric acid solutions was performed to determine the association of alkali metals in the raw material. Based on the results, a mineral matter composition recalculation model was proposed to predict alkali compounds concentration in the fuel. The model might be also used to determine the risk of eutectics formation, which have the strongest influence on ash melting behaviour.

플랜지 케이스의 입구온도 경계조건에 따른 케이스 내부의 열적거동에 관한 연구

In this study, the thermal behavior characteristics of flange case interior were analyzed by the numerical method. The boundary conditions at the inlet port of flange case were the heat flux and heat flux time. As the heat flux time at inlet of case increased, the temperature values gradually increased, and the degree of increase was very small. If the heat flux of the melted iron increases to 2,000,000 W/m2, the temperature change at the case interior will occur largely, causing heat deformation. As a result, in order to reduce thermal defects at the case interior, the heat flux and heat flux time of the melted iron should be set within 500,000 W/m2 and 5 seconds, respectively.

Thermal Behavior During the Selective Laser Melting Process of Ti-6Al-4V Powder in the Point Exposure Scan Pattern

Currently, there are two main scan patterns, including the continuous exposure scan pattern and the point exposure scan pattern, during the selective laser melting (SLM) process. The point exposure scan pattern allows a three-dimensional (3-D) printer to build finer detail features as a static molten pool that is more stable than a dynamic one. However, there has been limited theoretical research on the thermal behavior characteristics during the process in the point exposure scan pattern. Therefore, in this study, the simulation of thermal behavior during SLM of Ti-6Al-4V powder in the point exposure scan pattern was performed. The temperature evolution behavior of different positions and the effects of exposure time on the temperature evolution behavior of different positions, temperature distributions, and dimensions of the molten pool were investigated. The results showed that the direct exposure position and unexposed position had significantly different temperature evolution behaviors under a given condition, and the changed exposure time had the greatest influence on the direct exposure position compared with unexposed position. Moreover, the thermal accumulation effect of a former exposure point on a later one decreased with increasing exposure time. In addition, with the increase of exposure time, the maximum temperature of the molten pool was enhanced and the surface morphology of the molten pool changed from an approximate ellipse to an approximate circle. Besides, the molten pool dimensions were found to increase with exposure time, which indicated that the exposure time played an important role in the stability of the molten pool and the metallurgical bonding in the process. Furthermore, the dimensions of the molten pool and metallurgical bonding in the cross-sectional view were obtained through experiments. Good agreement was obtained when comparing the simulated results with the experimental ones.

Investigation on the thermal behavior characteristics and products composition of four pulverized coals: Its potential applications in coal cleaning

Although the thermochemical conversion of coal has dominated the research concerning the primary chemical production in the coal chemical industry utilization field, obtaining higher tar yield and lighter tar quality remain as challenges. The pyrolysis and its product distribution were studied using a thermogravimetric analyzer and a fixed bed reactor. A gas chromatograph (GC) and a gas chromatograph−mass spectrometer (GC-MS) were employed to test the properties and composition of the pyrolytic products. Here, we demonstrated that the tar yield only fluctuates when the carbon content is approximately 80%. The ratios of aliphatic hydrogen to all the functional groups (Ib1) are the largest in HM2 coal, while the change of the ratios of aromatic hydrogen to all of the functional groups (Ib2) is the same as that of the tar yield. With the increase of coalification, the ratio of CH2 to CH3 in the aliphatic structure (Ic1) decreases. The oxygen containing functional groups in YL coal were mostly converted into tar products, but the corresponding functional groups in ZC3 coal decompose to form more water. When the final pyrolysis temperature is below 550 °C, there was a higher yield of gaseous products containing carbon and oxygen than of gaseous products containing hydrogen. With the decrease of the H/C ratio, the relative content of the aliphatic hydrocarbon and phenolic compounds in tar increased, while the benzene series and polycyclic aromatic hydrocarbons decreased.

Thermal behavior characteristics of casein under acidic conditions

Thermal behavior characteristics of casein under acidic conditions

Thermal Behaviors of Bisazocalix[4]arene Derivatives

ABSTRACTIn this article, calix[4]arene (4) was prepared by debutylation and hydrolyses reacting from 25,27-dibenzoyl-26,28-dihydroxy-5,11,17,23-tetra(tert-butyl)calix[4]arene (2). Azocalix[4]arenes (6a-c) were coupled by linking 4-methoxy, 4-ethyl, and 4-nitroaniline to calix[4]arene (4) through a diazo-coupling reaction. Thermal behavior characteristics and decomposition routes of 25,26,27,28-tetrahydroxy-11,23-di(tert-butyl)-5,17-(p-substitue phenyl)azocalix[4]arene (6a-c) were investigated in air atmosphere by means of thermogravimetry (TG), differential thermogravimetry (DTG), and differential thermal analysis (DTA) analyses. It was found that the decomposition of all compounds complete with two exothermic stages which corresponded to removal of substitute groups (methoxy-, ethyl-, nitro-) and second stage rest of structure decomposition.

Characteristics of thermal behavior of photoluminescent copolymers studied by the TG/DTG/FTIR coupled method

Thermal properties of the photoluminescent copolymers, naphthalene-2,7-diol dimethacrylate derivatives, are presented in this paper. The materials were synthesized by bulk copolymerization of 2,7-(2-hydroxy-3-methacryloyloxypropoxy)naphthalene (2,7-NAF.DM) with four popular vinyl monomers: 2-hydroxyethyl methacrylate (HEMA), butyl acrylate (BA), divinylbenzene (DVB) and styrene (ST). As an initiator, the α,α′-azoiso-bis-butyronitrile was used. Thermal stabilities and degradation behaviors of the obtained copolymers were studied by means of the differential scanning calorimetry and thermogravimetric (TG/DTG, in air and in helium atmosphere) analyses. Gases evolved during the thermal treatment were monitored using the TG-FTIR coupled method. The presented copolymers can have potential application as luminophores, protective coatings or fiber-optical sensors.