Heat Generation Behavior Research Articles

Magnetic Properties, Heat Generation, and Apatite Formation Ability of Mg‐Ti Ferrite Particles Synthesized by Solid‐State Reaction and Polymerized Complex Methods

Titanium‐doped ferrite has garnered significant interest as thermoseeds for cancer hyperthermia because of its controllable Curie point near body temperature, which prevents overheating and ensures high biological safety. However, few studies examine the effect of the synthesis conditions on microstructure, magnetic properties, and heat generation in an alternating magnetic field. Herein, Mg1+xFe2−2xTixO4 (x = 0.35, 0.45) particles are synthesized by a solid‐state reaction and polymerized complex methods, followed by sintering at various temperatures. Their magnetic properties and heat generation behavior in an alternating magnetic field are investigated. Particles with x = 0.45 generate significantly less heat than those with x = 0.35, despite both being single‐phase ferrite. Particles synthesized by the polymerized complex method at a sintering temperature of 1200 °C exhibit lower saturation magnetization but higher temperature increases compared with the solid‐state reaction method. Additionally, in the sintering temperature range of 800–1000 °C, a temperature increase of more than 10 °C is observed in the polymerized complex method, likely a result of the inclusion of highly crystalline superparamagnetic particles. Furthermore, the ferrite particles form bone‐like apatite on their surface in simulated body fluid, suggesting their potential as a novel material combining hyperthermia and bone integration properties.

Heat Generation Behavior of Lithium-Ion Battery Operated at Low Temperature

The demand for lithium-ion batteries (LIBs) used in electric vehicles (EVs) is rapidly increasing. LIBs face a serious problem of lithium deposition at the anode when the battery is rapidly charged, especially under low temperature conditions. The lithium deposition can cause battery to short-circuit. Self-heating at elevated temperature is also one of the factors of thermal runaway of LIBs. However, there have been few reports on heat generation behavior of LIBs with lithium deposition. In this study, the thermal analysis of battery was conducted to understand heat generation behavior at elevated temperature of LIBs after cycling test under harsh conditions for real applications.The commercial 18650-type LIBs (US18650VTC4, Murata Manufacturing Co.) with a nominal capacity of 2100 mAh were used for thermal analysis. The battery consists of lithium nickel cobalt manganese oxides cathode, graphite anode, and mixed solvent of ethylene carbonate and dimethyl carbonate containing lithium hexafluorophosphate as electrolyte. The capacity of battery was obtained by charge and discharge with 1 C at 25 °C. The degradation test was carried out by cycling at 0 °C with 3 C charge, and 1 C discharge. Here, the ratio of discharge capacity after degradation to initial value before test is referred to as SOHQ. Thermal analysis of battery was carried out using a calvet calorimeter (C80-22, Setaram). The C80-22 is a customized machine based on C80 to measure whole 18650 battery without disassembly. The battery was charged to SOC 100% with 1 C at 25 °C and then enclosed in a stainless steel sample holder under air atmosphere. In the thermal analysis, the temperature was increased from 30 to 130 °C at a rate of 0.025 °C min-1. The pressure in sample holder was also measured during thermal analysis to detect gas evolution from the battery.The capacity of battery decreased during charge-discharge cycle at 0 °C. The degraded batteries with SOHQ 70%, 85%, and 92% were used for thermal analysis. In the thermal analysis of a fresh battery, corresponding to SOHQ 100%, the heat was gradually generated with increase in temperature. Similar trends were observed in the degraded batteries, and the heat flow becomes greater as the battery degrades. In addition, the abrupt pressure increases in the sample holder occurred during measurement, suggesting the opening of the safety vent in the batteries. The heat generation can be attributed to chemical reaction at lithiated graphite anode [1] and degradation due to operation at low temperature. To evaluate heat generation of lithiated graphite, the thermal analysis was performed on a fresh battery with SOC 0%. The difference between the fresh battery with SOC 100% and 0% corresponds to heat flow attributed to lithiated graphite in anode. Based on the assumption that the capacity loss of degraded battery is dominated by graphite anode, the heat generation of lithiated graphite can be evaluated by multiplying SOHQ by the heat flow obtained above for the fresh batteries. The remaining heat flow by subtracting heat flow of lithiated graphite is related to product materials by degradation reaction at low temperature. The result is shown in Figure 1. The heat flows of SOHQ 85% and 92% increase monotonically with increasing temperature. In the result of SOHQ 70%, an additional heat generation is remarkably observed at 70 °C and above. Furthermore, lithium deposition on graphite anode was confirmed by disassembling battery with SOHQ 70%. Therefore, the rapid increase in heat flow after 70 °C with SOHQ 70% may be related to the deposited lithium. The abrupt pressure rise mentioned above corresponds to gas evolution from the battery, which may result from evaporation of electrolyte solvents and decomposition of SEI and electrolyte components. We found that the onset temperature decreases with decreasing SOHQ, as shown in Figure 1. This indicates that thick and unstable SEI was formed in highly degraded battery, resulting in evolution of large amount of gases through SEI decomposition. Thermal analysis was also carried out on batteries degraded by cycling at 50 °C with 1.5 C charge and 1 C discharge as shown in Figure 1. For the battery with SOHQ 80%, the heat flow is similar to that of a fresh battery up to 110 °C. In addition, for the battery with SOHQ 73%, the additional heat generation behavior was not observed at around 70 °C. These results suggest that the heat generation behavior of degraded LIBs at elevated temperature is not simply related to SOHQ, but is largely influenced by the temperature history.

Kinetic analysis on low‐temperature oxidation of wood pellets by isothermal microcalorimetry

AbstractLow‐temperature chemical oxidation is the major driver of self‐heating during storage of wood pellets and its kinetics is essential to describe the heat evolution. In the present work, isothermal microcalorimetry was used to characterize heat generation behavior of three types of wood pellets (pine, fir, and redwood pellets) at 30–70°C. The obtained data were employed to derive the kinetics of low‐temperature oxidation by the peak power, iso‐conversional method, and non‐steady analysis. The consistency and applicability of the kinetics derived by the three methods were evaluated. Kinetic parameters determined by the peak power method were observed to match those from the iso‐conversional method at lower conversions of the oxidation for heat generation. The kinetics derived by the iso‐conversional method indicated the oxidation reactivity generally decreasing and activation energy increasing with the conversion because of O2 consumption and reaction mechanism changing. With the impact of O2 consumption considered separately, the kinetics from the non‐steady analysis is capable of describing the evolution of heat power with the conversion and also consistent with that from the peak power method in describing intrinsic reactivity of pellet materials. The kinetics from the peak power and iso‐conversional methods lump the impact of O2 concentration with the reaction reactivity, suggesting their applications requiring additional models for connecting with O2 consumption.

Anomalously Large Heat Generation of Hydration Water under Microwave Irradiation.

Much attention has been paid to the biological effects of microwave irradiation. The hydration water surrounding a biomolecule is crucial in its biological reactions and functions. Therefore, it is important to know the response of hydration water to microwaves to understand their biological effects; however, the scarcity of studies about it often leads to speculations and debates about that effect. In this study, we have made real-time temperature measurements of reverse micellar solutions with their water droplet size from ∼2.3 to ∼9.5 nm using a waveguide system combined with a microwave generator at 2.45 GHz. The heat generated by water in reverse micelles has been observed to depend on their size. It is about 10 times larger than that of liquid water at their small sizes (<∼3.5 nm) and diminishes with further enlarging the size, approaching the water's value at their large sizes (∼10 nm). These results indicate that the heat generation behavior has an interfacial effect; specifically, the hydration water on the surfactant layer produces heat 10 times larger than bulk water. Moreover, the hydration number per surfactant molecule decreases in a core-shell model with increasing the reverse micelle size. These features are also reflected in the heat generation rate. Our findings may offer a new and fundamental perspective for studies on the biological effects of microwave irradiation.

Effects of toolhead size on the heat generation and material flow behaviors in solid state friction rolling additive manufacturing

As a key part of solid-state friction rolling additive Manufacturing (FRAM), the toolhead is used to generate heat and deformation through friction with the feed material to form a deposit, and its geometric size directly affects the formation of the FRAM plastic zone; however, to date, no in-depth studies have been conducted. In this study, the effects of toolhead diameters (25, 50, and 100 mm) on the temperature history, material flow, and mechanical properties of the deposited samples are investigated via thermocouple measurements, optical microscopy, and mechanical property tests. The results indicate that, with the increase in toolhead diameter from 25 mm to 100 mm, the area of the interaction zone between toolhead and strip increases from 138 mm2 to 274 mm2, peak temperature increases from 522.3 °C to 559.8 °C, the material flow distance in the plastic zone increases from 7.03 mm to 16.6 mm, and the deposition height decreases from 2.4 mm to 1.2 mm. Regardless of the chosen toolhead size, defect-free and high-performance deposited materials can be obtained by optimizing the process parameters. The mechanical properties of deposited 6061 via a 100-mm toolhead are optimal, and the microhardness, tensile strength, and elongation of the deposited material are 66 HV, 234.7 MP, and 28.3 %, respectively. This study provides a basis for the selection and optimization of toolhead size in the FRAM process.

Electrochemical reactions coupled multiphysics modeling for lithium ion battery with non-heterogeneous micro-scale electrodes structures

During high-rate discharging process of lithium-ion battery (LIB), the macroscopic models struggle to capture the actual three-dimensional spatial evolutions of physical fields. In this study, an electrochemical-thermal-species coupled microscale homogeneous (MNH) three-dimensional model for LIB is built, with which the electrochemical reaction, lithium-ion concentration, electric potential, and heat generation rate inside the microscale LIB electrodes can be visualized and analyzed. The simulation results show that conventional volume-averaged 1 + 1D Newman models underestimate the influence of the microscopic electrode structure on the diffusion kinetics and reaction kinetics within the electrode. At high multiplicities, the localized pore structure causes insufficient utilization for the electrode material near the collector, leading to the localized hot spots in narrow pores. Additionally, the effects of extreme heat exchange environments on the physical laws within the electrodes are discussed. The results indicate that under an isothermal environment, the mass transfer capability of the electrode decreases. Moreover, the extent of delithiation and heat generation behavior of the particles exhibit stronger spatial nonuniformity, resulting in an increased final cut-off voltage. Furthermore, we conclude that an electrolyte phase potential caused overpotential due to pore structure contributes to the sensitivity of the active polarization heat towards the heat exchange environment.

Analysis on the Thermal Behavior of Lithium-Ion Battery with Nickel-Rich Cathode and Silicon-Carbon Composite Anode

&lt;div&gt;Compared with traditional internal combustion engine vehicles, electric vehicles still have shortfall in driving range and energy replenishment time. In order to continuously improve the driving range of electric vehicles, the high-nickel/silicon-carbon lithium-ion battery with high energy density is a promising industrialized application route. However, with the increase of battery energy density, the heat generation of battery usually increases, which will inevitably bring greater heat dissipation problems to the battery thermal management system. To design a good thermal management system, the first thing is to accurately measure and deeply understand the heat generation characteristics of the battery. In this work, the heat generation behavior of a high-nickel LiNi&lt;sub&gt;0.8&lt;/sub&gt;Co&lt;sub&gt;0.1&lt;/sub&gt;Mn&lt;sub&gt;0.1&lt;/sub&gt;O&lt;sub&gt;2&lt;/sub&gt;/silicon-carbon pouch-type battery under different operating conditions were tested by an isothermal battery calorimeter. The influence of current rate, current direction, and operating temperature on the heat generation characteristics of the battery was systematically analyzed. A comparison between heat generation power of batteries with different cathode/anode materials was provided. The research results of this article can deepen the understanding of the heat generation behavior of LiNi&lt;sub&gt;0.8&lt;/sub&gt;Co&lt;sub&gt;0.1&lt;/sub&gt;Mn&lt;sub&gt;0.1&lt;/sub&gt;O&lt;sub&gt;2&lt;/sub&gt;/silicon-carbon battery and provide guideline for the design of thermal management system.&lt;/div&gt;

A Study of Sustained Heat Generation from Pd-Ni-Zr Alloys in Hydrogen from the Viewpoint of Hydrogen Absorption

In this work, the phenomenon of long-term heat generation from Pd-Ni-Zr (PNZ) alloy samples in hydrogen was investigated using differential scanning calorimetry (DSC). As a result, we succeeded in observing sustained heat generation when the PNZ sample was maintained at temperatures in the 300–500◦C range. The fact that the DSC confirmed sustained heat generation over a short period of time is very significant. This is because repeated measurements over a short period of time provide more information about sustained heat generation. The relationship between sustained heat generation and hydrogen absorption behavior was examined in detail. No sustained heat generation occurred at temperatures at which the hydrogen was absorbed, while sustained heat generation occurred at the temperatures at which hydrogen was desorbed. The output of sustained heat generation decreased as the hydrogen pressure was increased. These results indicate that sustained heat generation is different from the heat of hydrogen storage. It was also found that sustained heat generation can be observed when the temperature is kept constant in the temperature range where hydrogen is being desorbed. In addition, the results of the alloy phase changes of PNZs when heat-treated in hydrogen suggested that the contribution of the alloy phase transition heat to sustained heat generation was small. Thus, it became clear that sustained heat generation in PNZs was not due to the heat of hydrogen storage, and it was suggested that the contribution of the alloy phase transition heat was small.

Elucidating the process mechanism in Mg-to-Al friction stir lap welding enhanced by ultrasonic vibration

The composite structures/components made by friction stir lap welding (FSLW) of Mg alloy sheet and Al alloy sheet are of wide application potentials in the manufacturing sector of transportation vehicles. To further improve the joint quality, the ultrasonic vibration (UV) is exerted in FSLW, and the UV enhanced FSLW (UVeFSLW) was developed for making Mg-to-Al dissimilar joints. The numerical analysis and experimental investigation were combined to study the process mechanism in Mg/Al UVeFSLW. An equation related to the temperature and strain rate was derived to calculate the grain size at different locations of the weld nugget zone, and the effect of grain size distribution on the threshold thermal stress was included, so that the prediction accuracy of flow stress was further improved. With such modified constitutive equation, the numerical simulation was conducted to compare the heat generation, temperature profiles and material flow behaviors in Mg/Al UVeFSLW/FSLW processes. It was found that the exerted UV decreased the temperature at two checking points on the tool/workpiece interface from 707/671 K in FSLW to 689/660 K in UVeFSLW, which suppressed the IMCs thickness at Mg-Al interface from 1.7 µm in FSLW to 1.1 µm in UVeFSLW. The exerted UV increased the horizontal materials flow ability, and decreased the upward flow ability, which resulted in the increase of effective sheet thickness/effective lap width from 2.01/3.70 mm in FSLW to 2.04/4.84 mm in UVeFSLW. Therefore, the ultrasonic vibration improved the tensile shear strength of Mg-to-Al lap joints by 18 %.

Regulation of electrically responsive shape recovery behavior of 4D printed polymers for application in actuators

Four-dimensional (4D) printing, an additive manufacturing technology for intelligent materials and structures, has received increasing scholarly attention for its ability to achieve variable shapes, properties and functions. However, recent research has primarily focused on developing new materials and structures, neglecting the regulation of deformation behavior. We hereby propose a novel photocuring 4D printing strategy for electrically responsive shape memory polymers (E-SMPs) actuators embedded with a dual-layered electrothermal layer (ETL) and channel. One way to achieve tunable shape recovery behavior in E-SMPs is to regulate the heat generation behavior of ETL by introducing a coolant into the channel. The electric heating and water cooling were sequentially and simultaneously activated to achieve suspension of the shape recovery process and reduction in the shape recovery rate, respectively. E-SMPs embedded with single and double ETLs were utilized to evaluate their electrically-induced heating behavior, electrically responsive shape recovery behavior, and shape recovery force. Additionally, sequential shape recovery behavior was achieved by serially interconnecting three (3) ETLs with varying thicknesses. Furthermore, the channel integrated within the SMPs were employed to realize remote thermally responsive shape recovery (T-SMPs), for which the shape recovery rate was regulated by adjusting the flow rate of hot water and channel dimensions. This strategy was successfully demonstrated for manufacturing E-SMPs actuators with adjustable shape recovery rate, sequential recovery behavior, and high-load deformation capability.

Revealing the mechanism of tool tilting on suppressing the formation of void defects in friction stir welding

Experiments have proven tool tilting in friction stir welding (FSW) can effectively suppress the formation of void defects. However, the mechanism of tool tilting on suppressing the formation of void defects has not been revealed. In this study, a CFD model considering the influence of tool tilting is established. A non-uniform distribution of normal pressure at the tool-workpiece contact interfaces is proposed to relate to the tool tilt angle. The discrete particle tracing method is used to characterize the formation of void defects in FSW. The heat generation, temperature distribution and plastic flow behaviors between the case without (i.e. 0° tool tilt angle) and with (i.e. 2.5° tool tilt angle) tool tilting are quantitatively compared and analyzed. The results show the tool tilting in FSW leads to higher heat flux and temperature near the pin side in the middle and low parts of the workpiece. Moreover, the frictional shear stress at the pin side/workpiece contact interface significantly increases when the tool is tilting, leading to a higher driving force for the plastic material to flow. As a result, the material flows farther to the advancing side of the workpiece after bypassing the tool when the tool is tilting at 2.5°, which helps to heal the voids on the advancing side of the FSW joints. The higher temperature with higher frictional shear stress enhances the plastic material flow in the middle and low part of the joints when the tool is tilting, which is attributed to suppressing the void defects. The model is validated by experimental results.

Experimental and numerical studies on lithium-ion battery heat generation behaviors

Current predictions of battery HGR (heat generation rate) mainly rely on Bernardi’s empirical equations, which suffer from limitations of adaptability for thermal use. A novel scheme based on experiments and BPNN (BP (back propagation) neural network is a multilayer feedforward neural network trained according to the error back propagation algorithm) is proposed in this paper. In the experiments, the thermal generation behavior of 18650 batteries under 108 different operating conditions was investigated, and the Ta (ambient temperature) as well as ID (discharge current) were extracted as inputs to the BPNN model. The experimental results show that the heat generation performance of the battery is strongly influenced by Ta and ID. The higher Ta and ID, the more obvious this effect is. The maximum error of the battery HGR obtained by using Bernardi’s empirical equations can reach 45.2 %. The predicted battery HGR using BPNN has good accuracy with error control within 5%. Accordingly, this paper provides the technical basis for proposing a promising thermal management solution.

In-depth understanding of rotating toolhead-induced heat generation and material flow behavior in friction-rolling additive manufacturing

In-depth understanding of rotating toolhead-induced heat generation and material flow behavior in friction-rolling additive manufacturing

Lifetime of photoexcited carriers in space-controlled Si nanopillar/SiGe composite films investigated by a laser heterodyne photothermal displacement method

Thermal management has become more critical as semiconductor devices are miniaturized. In metal–oxide–semiconductor field-effect transistors, the problem is the reduction in electron mobility in the channel layer owing to the temperature rise caused by heat generation near the channel-drain region. Focusing on the mean free paths of phonons and electrons in Si, nanostructures of a few 10 nm may only hinder heat propagation without affecting electron transportation. Therefore, inserting nanostructures into the channel layer may prevent a temperature rise and maintain a higher electron mobility. To discuss the relationship between the spacing between the nanopillars (NPs) and the heat generation and carrier behavior of the Si-NP/SiGe composite film, samples with NP spacings of 13, 27, or 47 nm were prepared. We previously confirmed that the thermal conductivity of the Si-NP/SiGe composite film decreased as NP spacing narrowed. The NPs scattered phonon propagation and suppressed heat propagation. However, carrier transport properties such as electrical conductivity, carrier mobility, and carrier lifetime have never been discussed. The laser heterodyne photothermal displacement method was used to examine the effect of nanostructures on carrier mobility and carrier lifetime of Si-NP/SiGe composite films. We observed that the carrier lifetime became longer when the NP spacing was comparable to the electron mean-free path of approximately 27 nm.

A generalized methodology for lithium-ion cells characterization and lumped electro-thermal modelling

This paper deals with the experimental characterization and electro-thermal modelling of lithium-ion batteries. This aspect is of considerable importance to be able to understand the phenomena of heat generation and thermal behavior of a lithium-ion battery. Electrical parameters need to be characterized to properly estimate the electrical losses inside the battery and, thus, the total heat generation. The testing methodology is based on capacity test, open circuit voltage tests, and hybrid power pulse characterization tests. It highlights the dependency of each parameter on state of charge, current and temperature. A first order equivalent circuit model is used to simulate the electric behavior of the cell. Extrapolation physical models are used to accurately estimate capacity (Peukert model) and resistive parameters (Arrhenius model) for points outside the considered test matrix. The thermal behavior of the cell is modeled using a nodal network, assigning volume, heat capacity and heat generation to the nodes. The main output of the research is the development of a completely generalized methodology that can be adapted to any other chemistry, format, or capacity; furthermore, this methodology can be applied also in case of limited test matrix points, due to the implementation of extrapolation physical models for electrical parameters. The model is validated with a scaled real driving emission cycle. Finally, a case study for the fast charging of a battery module is presented, to highlight the great potential of the model, not only for on-line estimation, but also for off-line studies, being the charging operation one of the most critical from the thermal management point of view. From this analysis, it is found that a stand-alone cell can be charged for a longer time at 6C – a 5.42% more time -, with respect to the hottest cell in the considered battery module configuration.

Experimental study on thermal management of lithium-ion battery with graphite powder based composite phase change materials covering the whole climatic range

In order to ensure the normal operation of lithium-ion battery in any climate environment, it is necessary to explore the temperature dependence of lithium-ion battery performance, and adopt an effective and low energy thermal management system to maintain the temperature of lithium-ion battery within the normal operating temperature range. In this paper, the temperature dependence of heat generation behavior and charge–discharge performance of lithium-ion battery was studied, and the critical temperature of heat preservation and preheating process was determined. On this basis, graphite powder/paraffin composite phase change material and graphite powder/paraffin/nickel foam ternary composite phase change material with optimized composition were prepared. The thermal management experiment of large-capacity rectangular lithium iron phosphate battery covering the whole climatic range was carried out. The performance of the following thermal management modes was compared: air natural convection, paraffin, graphite powder/paraffin composite, graphite powder/paraffin/nickel foam ternary composite. The experiment showed that the necessary heat dissipation of lithium-ion battery was needed at 20℃ and 40℃ to avoid exceeding the upper limit of normal working temperature. The charge–discharge performance of lithium-ion battery was very sensitive to low temperature environment, especially the battery endurance and charge–discharge capacity. Both graphite powder/paraffin and graphite powder/paraffin/nickel foam composites can effectively control the surface temperature rise of lithium-ion battery, and keep the surface temperature above 0℃ for at least 40 min in the extremely cold environment of −20℃. They also had similar heating efficiency. However, the ternary composite had better temperature homogeneity in both the high temperature environment of 40℃ and the extremely cold environment of −20℃. The maximum temperature difference of ternary composite in the preheating process was 21.43% lower than that of binary composite.

Numerical study of moving fin with thermal properties

AbstractIn the present study, the influence of numerical analysis involves the transfer of heat for moving fin under convection and radiation with fluid properties depending on internal heat generation is considered. The temperature field for the fin is derived based on the defined geometry. This is transformed into a linear model as per the boundary conditions. The dimensionless analysis is performed, and the equations obtained are solved by Runge–Kutta Fehlberg fourth‐order method coupled with the shooting method. The effects of the relative parameters are studied and depicted graphically. Finally, the computational observation indicates that there is an enhancement of temperature variation under the influence of thermal conductivity gradient, heat generation, and opposite behavior results. In understanding the thermal characteristics of various effects, it was seen that thermo geometric film, radiation conduction, and Peclet number were very useful for many industrial applications. To validate the numerical scheme, a comparative study has been done with an earlier result on a few nondimensional parameters and was found in good agreement.

Statistical and computational analysis for state-of-health and heat generation behavior of long-term cycled LiNi0.8Co0.15Al0.05O2/Graphite cylindrical lithium-ion cells for energy storage applications

The heat management of lithium-ion cells under ceaseless high-current operation plays a pivotal role in preventing an internal short-circuit, which is generally caused by separator meltdown at high temperatures and rapid cell deterioration. However, the simple specification sheets provided by battery manufacturers do not provide explanations nor supporting data on why or how permitted C-rates for charging or discharging at different temperatures can be guaranteed. Thus, the long-term degradation behavior of commercial 18650 cylindrical lithium-ion cells (LiNi0.8Co0.15Al0.05O2/graphite, 2.85 Ah) is systematically and statistically studied to determine the key degradation factors. Specifically, the capacity and power retention as well as the temperature changes of each cylindrical cell are gathered during 1,000 cycles at three C-rates, 0.5C, 1C, and 2C, for both charging and discharging (i.e., nine cases in total). The analysis of variance method shows that the capacity degradation is mainly governed by the charging C-rate, while power degradation and cell temperature behavior are affected by both the charging and discharging C-rates. Also, a thermo-electrochemical model is used to predict how quickly the cells reached the critical temperature under catastrophic conditions, like an adiabatic condition. Thus, this systematic approach can be an indispensable to ensuring the reliability of lithium-ion cells.

Properties of Surface Heating Textile for Functional Warm Clothing Based on a Composite Heating Element with a Positive Temperature Coefficient.

A high-stretch positive temperature coefficient (PTC) surface heating textile (PTC-SHT) was fabricated using a composite of PTC powder and multiwall carbon nanotubes (MWCNTs). The PTC-SHT (heating area = 100 × 100 mm2) was produced by screen-printing the PTC-MWCNT composite paste onto a high-stretch textile with embroidered electrodes. Overall, the temperature increased to 56.1 °C with a power consumption of 5 W over 7 min. Subsequently, the surface temperature of the PTC-SHT remained constant despite the continued decrease in power consumption. This indicated that heating was accompanied by an increase in resistance of the PTC-SHT, which is typical of this process—i.e., heating to a constant temperature under a constant voltage over an extended period of time. In addition, 4.63 W power was required to heat the PTC-SHT surface from an external temperature of 5 to 45 °C in 10 min, after which stable low-temperature heat generation behavior was observed at a constant temperature of 50 °C, which was maintained over 40 min. In contrast, negative temperature coefficient (NTC) behavior has been observed in an NTC-SHT consisting of only MWCNTs, where a slow heating rate in the initial stage of power application and a continuous increase in surface temperature and power consumption were noted. The PTC-SHT consumed less power for heat generation than the NTC-SHT and exhibited rapid heating behavior in the initial stage of power application. The heat generation characteristics of the PTC-SHT were maintained at 95% after 100,000 cycles of 20% stretch–contraction testing, and the heating temperature remained uniformly distributed within ± 2 °C across the entire heating element. These findings demonstrated that an SHT with PTC characteristics is highly suitable for functional warm clothing applications that require low power consumption, rapid heating, stable warmth, and high durability.

Development of New Particle Method Based on MPS and its Applicability for Friction Stir Welding of Dissimilar Joint

Friction stir welding (FSW) is one of the solid-state welding and it has been widely employed for joining aluminum alloys. In addition, as a result of R&amp;D efforts about FSW tool, this method is expected to join the steels and/or various dissimilar materials. In order to examine the thermal and mechanical behavior in FSW, many numerical studies have been conducted and the heat generation behavior near FSW tool is precisely demonstrated by using the moving particle semi-implicit (MPS) method which is one of the particle method. In this research, in order to reduce the computational time, a new parcel method based on MPS is developed and its applicability is examined for simulating the friction stir welded dissimilar joint between V-ally and austenite stainless steel SUS316L. From the serial computational results, it is revealed that the influence of rotational speed on the heat generation during FSW seems to be larger than that of traveling speed. Moreover, the numerical result indicates that the sound dissimilar joint might be fabricated when V-alloy is set to be the retreating side (RS), the FSW tool is inserted in RS and the rotational speed increased appropriately although the two materials have not been joined in this welding condition of FSW experimentally.