Adiabatic Heating Research Articles

The influence of the adiabatic heating coefficient on the near solidus forming process

The Near Solidus Forming (NSF) process represents a critical method for shaping metallic components under extreme temperature conditions. When metals deform plastically, significant amounts of heat can be generated, which is due to the conversion of plastic deformation energy in the material often known is adiabatic heating. In this study, the influence of the adiabatic heating coefficient (AHC) on temperature distribution and plastic strain during NSF process is investigated. For this purpose, three industrial benchmarks previously fabricated using NSF techniques are selected to serve as representative cases for analysis. To conduct the analysis, sensitivity studies is performed at two key temperatures: 1360 °C and 1370 °C. These temperatures are chosen to capture the range of operating conditions typically encountered in industrial NSF applications. The simulation tool FORGE NXT® is utilized to investigate the potential effect of AHC on equivalent plastic strain (EPS). The range of potential AHC values considered is between 85% and 100%, as determined from a comprehensive literature survey. The study suggests that the AHC has a minimal effect on the deformation behaviour of 42CrMo4 steel at NSF condition for the studied benchmarks. The findings of this study provide the inside to the importance of AHC in the developing of a reliable Digital Twin (DT) for industrial NSF application.

The influence mechanism of thermal invasion on spontaneous combustion of different coals using continuous adiabatic heating and non-isothermal oxidation method

Within deep coal mines, the elevated ground temperature has the potential to induce thermal invasion, thereby exacerbating coal spontaneous combustion (CSC). To investigate the influence mechanism of thermal invasion on CSC, experiments were conducted using coals of different metamorphic degrees (lignite, bitumite, and anthracite) with a continuous adiabatic heating and non-isothermal oxidation method in an oxidation furnace and an in-situ ESR spectrometer. Thermal invasion markedly enhanced the inherent susceptibility of spontaneous combustion of coals by increasing the oxygen consumption rate and lowering the apparent activation energy. This enhancement results from active free radicals generated during thermal invasion which accelerated coal-oxygen reactions during non-isothermal oxidation. These free radicals were found to be mainly carbon-centred radicals adjacent to an oxygen atom (alkyl radicals). An increase in both the g-factor value and free radical concentration was observed with thermal invasion temperature and invasion duration, especially in lignite, leading to a surge of free radical concentration during non-isothermal oxidation. The active free radicals generated during thermal invasion can easily react with oxygen, providing heat for coal-oxygen reactions and enabling rapid free radical generation. These findings offer insights for developing CSC evaluation and prevention strategies in deep mines where high ground temperatures are encountered.

Simultaneous Eruption and Shrinkage of Preexisting Flare Loops during a Subsequent Solar Eruption

We investigated two consecutive solar eruption events in the solar active region 12994 at the solar eastern limb on 2022 April 15. We found that the flare loops formed by the first eruption were involved in the second eruption. During the initial stage of the second flare, the middle part of these flare loops (E-loops) erupted outward along with the flux ropes below, while the parts of the flare loops (I-loops1 and I-loops2) on either side of the E-loops first rose and then contracted. Approximately 1 hr after the eruption, the heights of I-loops1 and I-loops2 decreased by 9 Mm and 45 Mm, respectively, compared to before the eruption. Their maximum descent velocities were 30 km s−1 and 130 km s−1, respectively. The differential emission measure results indicate that the plasma above I-loops1 and I-loops2 began to be heated about 23 minutes and 44 minutes after the start of the second flare, respectively. Within ∼20 minutes, the plasma temperature in these regions increased from ∼3 MK to ∼6 MK. We proposed an adiabatic heating mechanism where magnetic energy would be converted into thermal and kinetic energy when the prestretched loops contract. Our calculations show that the magnetic energy required to heat the two high-temperature regions are 1029–1030 erg, which correspond to a loss of field strength of 2–3 G.

Investigating Optimum Hot Working Window of 2205 Duplex Stainless Steel Using Modified Dynamic Material Modeling

AbstractThis paper uses a modified dynamic material modeling (MDMM) suggested by Murty and Rao to develop processing maps (PM) of 2205 duplex stainless steels (DSS). Gleeble 1500D, a thermo-mechanical simulator was used to conduct single hit compression tests at a temperature between 850 and 1050 °C and strain rates of 0.001-5 s−1. Additionally hot compression tests at a strain rate of 15 s−1 and same temperature range were also conducted on a Bahr 805 dilatometer. As per general procedure acquired stress-strain data were corrected for friction and adiabatic heating, before constructing PMs at true strains of 0.1, 0.3, 0.5 and 0.8. Microstructures to validate the PM were prepared from safe domains and instability regimes belonging to PM of 0.8 true strain. Results showed that hot processing at intermediate to high strain rates and temperature leads to formation of flow instabilities such as mechanical twins and adiabatic shear bands. Safe domain located within the temperature range of (850-925) °C, strain rates of (2.6-15) s−1 and peak η = 35% gave an inhomogeneous microstructure with presumably non-uniform mechanical properties. This region was considered ideal for hot processing of 2205 DSS provided that deformation conditions are carefully controlled to optimise DRX. Low Z conditions also provided an optimum hot working for hot processing.

Hot Deformation Behavior and Microstructure Evolution of the Maraging Stainless Steel

Hot deformation behavior of the maraging stainless steel is studied in temperature range from 900 to 1150 °C and strain rate from 0.1 to 10 s−1. When the deformation temperature is 900−950 °C, the abnormal stress increase is observed at the end of the flow curves. Transmission electron micrographs reveal that the Laves phase at the interface between prior austenitic (γ) and high‐temperature ferrite (δ) impedes hot deformation. The microstructure analysis shows that the dynamic recrystallization (DRX) mechanism of γ and δ is discontinuous DRX and continuous DRX, respectively. When the specimens are deformed at 950 °C, the extent of DRX at a strain rate of 5 s−1 is higher than at 0.1 s−1. This anomaly is due to adiabatic heating causing the actual deformation temperature at high strain rate () to be higher than at low , indicating that DRX is more influenced by temperature compared to . The influences of adiabatic heating and friction are corrected. Strain‐dependent constitutive equation is developed based on the revised flow curves, yielding an average absolute relative error of 4.69% and a correlation coefficient of 0.99; the prediction accuracy exceeds 90% when the relative error is within 10%.

Thermal reflectance of fabric in color temperature spectral domain

PurposeThis study aims to explore the thermal reflectance of fabrics under sunlight or other thermal radiation sources at various color temperatures.Design/methodology/approachThis study analyzed the spectral distribution of sunlight at different solar altitude angles as well as the spectral distribution characteristics of other light and thermal radiation sources, pointing out that their color temperatures can be used to identify their spectral distribution domains. Reflectance, transmittance, absorptance and color temperature domain reflectance of 35 different fibers and color fabrics were tested in a wide spectral range. The different behavior of these optical parameters in the segmented spectrum is discussed. The temperature rise tests demonstrate that the reflectance corresponding to the color temperature of the radiation sources is highly correlated with the temperature rise results.FindingsThe reflectance in the color temperature domain shows a strong correlation with the radiation source at same color temperature. The correlation coefficients for the 6,000 K xenon lamp test are −0.96 and −0.90 in two groups, and for the 3,200 K tungsten iodine lamp test are −0.87 and −0.90 as well.Originality/valueThe concept of fabric thermal reflectance in the color temperature domain was first introduced to match different thermal radiation sources. Validation of temperature rise is conducted through a self-constructed tester with unidirectional adiabatic heating. This new discovery could serve as a basis for developing functional fabric or clothing, such as sun-proof clothing, fire protection clothing, etc.

Thermal quench modeling of REBCO racetrack coils under either alternating current or short-circuit voltage

Abstract Racetrack coils in REBCO High-Temperature Superconductor (HTS) motors help to increase the power-over-weight ratio by raising the magnetic flux density and output power. Nevertheless, HTS motors face thermal quench due to self-heating effects when subjected to alternating or short-circuit onset DC voltage. Additionally, thermal events have been observed due to screening currents when motors operate at high frequencies. Therefore, for the safe operation of HTS motors, quench research is crucial. To accurately simulate and analyze quench events in different scenarios, it is imperative to employ fast and precise software to numerically model the electrothermal behavior in racetrack coils. Our contribution involves the development of a novel and efficient model implemented in C++ that takes screening currents into account. This model is designed to conduct coupled electromagnetic and electrothermal analyses, utilizing variational methods. Specifically, the model incorporates both Minimum Electro-Magnetic Entropy Production and the Finite Difference Method. In this article, we explore the phenomenon of temperature rise within a racetrack coil subjected to either alternating or DC voltages of magnitudes ranging from 0.1 V to 1000 V. The study encompasses conditions of adiabatic operation and heat exchange with liquid nitrogen (LN2). Among other results, we found that in moderate DC voltages like 10 V, non-uniformity in the AC loss causes highly localized quench at the central turns. Then, screening currents play a key role also for DC voltages. The developed model exhibits the potential to comprehensively and swiftly analyze the electromagnetic and electrothermal characteristics of real-world superconducting applications, including high-field rotating machines, such as motors for aviation.

Role of North Atlantic warming in the extremely hot summer of 2023 in North China

Abstract A deadly heatwave hit North China in the summer of 2023, causing severe damage to human health and public infrastructure. However, the underlying physical mechanism is still unknown completely. In this study, we explore the causative role of anomalous sea surface temperatures in three oceans using observation and reanalysis data, as well as partial regression and correlation methods. This heatwave exhibited the longest maximum duration of the past 50 years. According to the probability density function, the maximum temperature also reached an unprecedented high. A long-lived anticyclone dominated North China, causing persistent downward motion and adiabatic heating, enabling the heatwave to form and continue for more than 20 d. The Indian, Pacific, and North Atlantic oceans all experienced extreme warming. However, our results indicate that North Atlantic warming played a decisive role in the occurrence of this heatwave by exciting a Rossby wave train that propagated eastward, generating the long-lived anomalous anticyclone and inducing heatwaves. In comparison, the other two oceans exhibited weak or negative contributions to the heatwave. As the North Atlantic shows an obvious warming trend with increasing global warming, more attention should be paid to its relationship with heatwaves in North China.

High strain-rate fracture behavior of a hollow projectile

In this paper, a hollow projectile made of AISI4340 steel was fabricated based on an arbitrary warhead shape, and high-speed impact tests were performed according to various target encounter conditions including velocity and angle. In order to characterize the dynamic fracture behavior, tensile tests were performed on various notch specimens under three strain rates (10–3 s-1, 100 s-1, 103 s-1), and the stress state histories of the specimens were calibrated through a hybrid experimental-numerical analysis. In particular, for the intermediate (100 s-1) and high (103 s-1) strain rate conditions, the local temperature rose due to adiabatic heating until fracture was experimentally measured, and the thermal softening behavior determined from the inverse optimization technique was considered for the dynamic constitutive model. For the comparison with the high-speed impact test results, a rate-dependent ductile fracture model was utilized for numerical simulation. Considering that the model parameters were calibrated with the thermal softening effect, the proposed fracture model implicitly takes temperature into account. The deformation and fracture modes of the projectile from experimental and numerical study showed very good agreement under all impact conditions. It was confirmed that the softening of a material by adiabatic heating should be considered along with strain rate hardening in dynamic fracture simulation.

Deformation behavior of aluminum alloy rivets for aerospace applications

For many decades, solid rivets made of high-strength aluminum alloys have been used for mechanical joining of aircraft structures. For numerical modeling of riveting processes the detailed description of the deformation behavior of the rivets is of utmost importance; however, only very little reliable material data are available. Therefore, this study reviews and investigates the deformation behavior of commercial MS20426AD3-5 countersunk rivets made of aluminum alloy AA-2117-T4 as typically used in aerospace applications. The self-consistent procedure for determining the material-specific flow curve includes (i) the exact preparation of cylindrical samples, (ii) compression testing of the samples at testing speeds of 0.05 mm/s, 0.5 mm/s and 5 mm/s, and (iii) inverse numerical modeling of the testing procedure. In general, the compliance of the testing setup must be considered for obtaining reliable flow curves, especially when testing small samples. The determined flow curve of aluminum alloy AA-2117-T4 showed higher yield stress and more distinct initial strain hardening than most of the flow curves published in literature. Although the flow curve did not show any significant strain rate dependency, notable softening due to deformation-induced adiabatic heating of the compressed sample was observed at the highest testing speed. However, the fracture strain seems to be strain rate-dependent, because samples deformed at the low testing speed did not show any signs of macroscopic fracture, whereas local fracture occurred in samples deformed at the medium and high testing speeds.

Surface temperature modulations induced by Rossby Wave Breaking over Indian region

Abstract Upper-level Rossby Wave Breaking (RWB) significantly affects surface weather patterns in the subtropical Indian region through influencing wind circulation often resulting in extremes in rainfall and surface temperatures. While the impact of RWB on rainfall is relatively well understood, its role in modulating surface temperatures within the Indian subcontinent is less explored. This study examines the link between pre-monsoon (March to May) RWB events and the occurrence of extreme surface temperatures and heatwaves by considering long-term data of 43 years between 1979 and 2021. We identify 139 RWB events using a potential vorticity (PV) contour searching algorithm over the Indian sub-continent. Our analysis reveals a significant amplification in temperature both to the west and east of the breaking PV streamers. These temperature anomalies, which last for 3–4 days during the breaking events, strongly correlate with the maximum day of breaking. Further, regression analyses explain the reasons behind the temperature enhancement mainly on the western and eastern flank of RWB. It indicates a positive association between upper-level PV anomalies and anticyclonic circulations at 250 hPa, along with subsidence at 500 hPa, leading to drier conditions in the western and eastern regions of the PV streamers. Additionally, the decomposition of temperature anomalies during RWB events reveals that surface warming is primarily driven by diabatic heating on both sides of the centroid, with stronger adiabatic heating in regions of upper-level anticyclonic circulation and significant temperature advection predominantly on the western side of the centroid, resulting in dry weather and the poleward movement of warm air toward the ridges near the PV streamers.

Analytical temperature model for spindle speed selection in additive friction stir deposition

This paper describes a physics-based, analytical model for additive friction stir deposition (AFSD) spindle speed selection to achieve a desired deposition temperature. In the model, power input to the feedstock, which enables plastic flow and deposition, is related to the material temperature rise and subsequent flow stress reduction using Fourier’s conduction rate equation. Power input is modeled as frictional heating at the deposit-surface interface and adiabatic heating due to plastic deformation. The flow stress is predicted using the strain, strain rate, and temperature-dependent Johnson-Cook constitutive model for the selected feedstock alloy. Model predictions are compared to AFSD numerical simulation results available in the literature and experiments for aluminum alloys.

Thermal effect of the Southeast Asian low-latitude highlands on interannual variability in the date of the Bay of Bengal summer monsoon onset

The timing of the Bay of Bengal summer monsoon (BOBSM) onset has implications for the evolution of the Asian summer monsoon and associated precipitation. This study employs Japanese 55-year Reanalysis and NOAA's Gridded Precipitation Reconstruction over Land data to explore the spatiotemporal variation in the thermal influence of the Southeast Asian low-latitude highlands (SEALLH) and its effect on the BOBSM onset date. There is a significant correlation between pre-monsoon season (February–April) shortwave radiative heating (SWH) in the SEALLH and BOBSM onset in the interannual time scale. During the enhanced SWH, an anomalous vertical circulation, which converges and ascends in the lower troposphere over the SEALLH and converges and descends in the upper troposphere north of the Bay of Bengal (BOB), develops over the SEALLH–north of BOB during the pre-monsoon season with anticlockwise rotation. The warmer air mass resulting from the adiabatic heating is accumulated around the north of BOB by the insulation effect related to the anomalous vertical circulation. By facilitating the reversal of the land-sea thermal contrast, the warmer upper troposphere over the north of the BOB causes a 16-day earlier onset of the BOBSM than the case of weakened SWH. The findings shed light on subsequent research into the thermal effects of the SEALLH on Asian summer monsoon variability.

Differentiated influences of anomalous subtropical high on extreme persistent precipitation and heatwave events in the Yangtze River Valley

AbstractIn the summers of 2020 and 2022, the Western Pacific Subtropical High (WPSH) intensified extremely and extended westward. However, in summer 2020, the Yangtze River Valley (YRV) witnessed record‐breaking floods, while in 2022, an unprecedented and prolonged heatwave occurred. Distinctly, these two extreme events were caused by different effects of the WPSH: one is enhancement of the transportation of water vapor and the other is adiabatic heating caused by the descending airflow. In June–July 2020, the stable extension of the WPSH ridge line to South China directed a southwesterly airflow along its northwest flank, leading to sustained precipitation in the YRV. Additionally, the midlatitude circulation pattern featured two troughs and two ridges. Such a circulation configuration, combined with the strong and westward WPSH, enabled the continuous southward intrusion of cold air and northward transport of warm moist air, converging over the YRV, and thus influenced extreme persistent precipitation. In contrast, the WPSH covered the YRV almost entirely during summer 2022. Under this influence, the clear‐sky condition and descending airflow through adiabatic warming directly resulted in the heatwave. In addition, local land–atmosphere feedback was crucial in its development and persistence. The soil moisture deficit induced by high temperatures increased the sensible heat flux between the soil and atmosphere upward, further enhanced the surface air temperature and strengthened the heat dry condition.

Thermodynamic analysis of the air separation unit and CO2 purification unit in the semi-closed supercritical CO2 cycle with nearly zero emission

The natural gas-fired semi-closed supercritical CO2 cycle is an efficient oxyfuel combustion power generation technology featuring nearly zero emissions. This study investigated the interaction of the semi-closed supercritical CO2 power unit with the air separation unit (ASU), which supplies O2 for combustion and adiabatic compression heat for the heat recovery process in the power unit, and the CO2 purification unit (CPU), which refines the CO2 in the exhaust gas to 99.97% for enhanced oil recovery (EOR) applications. The detailed thermodynamic models of the power unit, ASU, and CPU have been constructed to explore the impact of variations in oxygen purity and excess oxygen coefficient on the overall thermodynamic performance of the system. The results demonstrate that the net electric efficiency peaks at an oxygen purity of 98%, and a one percent decrease in oxygen purity reduces the net electrical efficiency by approximately 0.36% to 0.97% points. Moreover, the net electric efficiency decreased by 0.10% points when the excess oxygen coefficient increased from 3.00% to 13.67%. These findings may offer valuable guidance for developing oxyfuel combustion power generation technologies.

Stress and Strain Characterization for Evaluating Mechanical Safety of Lithium-Ion Pouch Batteries under Static and Dynamic Loadings

The crashworthiness of electric vehicles depends on the response of lithium-ion cells to significant deformation and high strain rates. This study thoroughly explores the mechanical behavior due to damage of lithium-ion battery (LIB) cells, focusing on Lithium Nickel Manganese Cobalt Oxide (NMC) and Lithium Iron Phosphate (LFP) types during both quasi-static indentation and dynamic high-velocity penetration tests. Employing a novel approach, a hemispherical indenter addresses gaps in stress–strain data for pouch cells, considering crucial factors like strain rate/load rate and battery cell type. In the finite element method (FEM) analysis, the mechanical response is investigated in two stages. First, a viscoplastic model is developed in Abaqus/Standard to predict the indentation test. Subsequently, a thermomechanical model is formulated to predict the high-speed-impact penetration test. Considering the high plastic strain rate of the LIB cell, adiabatic heating effects are incorporated into this model, eliminating heat conduction between elements. Addressing a notable discrepancy from prior research, this work explores the substantial reduction in force observed when transitioning from a single cell to a stack of two cells. The study aims to unveil the underlying reasons and provide insights into the mechanical behavior of stacked cells.

Research on the division of heat dissipation spaces for multiple heat sources based on the adiabatic characteristic of heat flow lines

Due to the pressing need for compact layouts, the spacing between high-power devices is gradually decreasing, making the mutual influence between multiple heat sources unavoidable. Therefore, this paper proposes a method based on the adiabatic characteristics of heat flow lines and their convergence positions to evaluate the rationality of the thermal space design of each heat source. This method has been validated for applicability in one-dimensional, two-dimensional, and three-dimensional multi-heat-source conjugate convection heat transfer. Heat flow lines have significant advantages in describing energy flow, as they align with the direction of the temperature gradient. In thermal spaces with adiabatic boundaries or mutual influences between multiple heat sources, heat flow lines converge at certain positions. The relationship between adiabatic boundaries and heat flow line convergence positions has been studied, and a more interpretative decoupling scheme for multi-heat-source systems has been proposed. The main feature of this scheme is the separation of each heat source in the same steady-state thermal space and assigning adiabatic boundaries to the solid partition surfaces, allowing efficient observation of the thermal conditions of individual heat sources and targeted layout optimization. Results indicate that this method can utilize changes in heat flow line convergence positions to assess current thermal conditions and can be used to compare the thermal performance of different shaped heat sinks. Simulation results show that under the same mass conditions, thin-fin heat sinks perform 47 % better than thick-fin heat sinks, providing a more comprehensive and intuitive assessment compared to metrics such as thermal resistance and average temperature. The proposed method offers new ideas for multi-heat-source layout optimization, heat flow control, multi-heat-source partitioned simulation, and abnormal heating detection in multiple heat sources.

Determination of Local Heat Transfer Coefficients and Friction Factors at Variable Temperature and Velocity Boundary Conditions for Complex Flows

Transient conjugate heat transfer measurements under varying temperature and velocity inlet boundary conditions at incompressible flow conditions were performed for flat plate and ribbed channel geometries. Therefrom, local adiabatic wall temperatures and heat transfer coefficients were determined. The data were analyzed using typical heat transfer correlations, e.g., Nu=CRemPrn, determining the local distributions of C and m. It is shown that they are closely linked. A relationship lnC=A−mB is observed, with A and B as modeling parameters. They could be related to parameters in log-law or power-law representations for turbulent boundary layer flows. The parameter m is shown to have a close link to local pressure gradients and, therewith, near wall streamlines as well as friction factor distributions. A normalization of the C parameter allows one to derive a Reynolds analogy factor and, therefrom, local wall shear stresses.

Obvious difference of dominant circulation patterns between dry‐type and humid‐type heatwaves in North China

AbstractBased on the observed maximum temperature (Tmax), relative humidity (RH) and NCEP/NCAR reanalysis data during 1981–2021, basic temporal features and dominant atmospheric circulation patterns of dry‐type and humid‐type heatwaves in North China are investigated and compared. Statistical results indicate the dry heatwaves occur mainly in early summer (from early June to early July), that is, before the rainy season of North China, while the humid heatwaves have a high frequency in mid‐July to mid‐August. During the research period, the increasing trend of dry heatwaves is 0.67 days·decade−1, while the humid heatwaves increase at a greatly higher rate of 1.85 days·decade−1. For the dry heatwave, a high ridge in the subtropical westerlies plays the main role, and the northerly wind in the east of the ridge reduces the air moisture convergence over the region. However, for the humid heatwave, the westward and northward propagations of the western Pacific subtropical high (WPSH) may make the major contribution, and the southerly wind anomalies in the west of the WPSH enlarge the water vapour to the region. The adiabatic heating in subsiding air at all levels and horizontal temperature advection at lower troposphere are stronger for dry heatwaves than for humid heatwaves, which cause a higher Tmax for the former type. These results highlight the diversity of the heatwaves in North China, which suggests that multiple local and large‐scale subseasonal circulations should be considered to improve the subseasonal to seasonal forecast skills for heat extremes.

Finite Element Ductile Fracture Simulation of Charpy and Drop Weight Tear Tests for API X52

This paper presents a systematic procedure for performing finite element (FE) impact ductile fracture simulation of Charpy (CVN) and Drop Weight Tear Tests (DWTT) with validation using test data of API X52. For deformation and fracture models, the Johnson-Cook (J-C) model is used, of which seven parameters are determined by analyzing (1) round bar tensile test data at three different temperatures (two parameters), (2) tensile test and fracture toughness test at room temperature (three parameters) and (3) instrumented Charpy test (load–displacement) data at room temperature (two parameters). FE impact fracture simulation results with the determined parameters show good agreement with instrumented CVN test data at three different temperatures (0 °C, −30 °C and −60 °C) and DWTT data at temperatures of RT and −30 °C. For DWTT simulation, an analysis of the pre-strain due to flattening is included. Additionally, sensitivity analyses for the effect of adiabatic heating and strain rate on simulation results show that, although both phenomena should be considered in simulation, the strain rate effect is more significant than the adiabatic heating effect.