Adiabatic Heating Research Articles

Subseasonal processes of triple extreme heatwaves over the Yangtze River Valley in 2022

Historical extreme heatwaves struck the Yangtze River Valley (YRV) in the boreal summer of 2022, severely impacting agricultural production, electricity supply, and resident health in China. This study shows that extreme heatwaves recurred over the YRV with distinct subseasonal processes. In early summer, from 14 June to 18 July, two extreme heatwaves were embedded in a mid-latitude 10–25-day intraseasonal oscillation (ISO), and hot-and-wet anomalies persisted over the YRV. A self-sustaining mechanism between the “cold vortex” over Northeast China and the “heat dome” around the YRV maintained this bi-weekly ISO. It fueled the heatwaves by modulating the meridional advection of upper-tropospheric potential vorticity, which firstly warmed the air via adiabatic processes and then later by diabatic heating. In late summer, from 30 July to 29 August, a 30–50-day ISO impacted the heatwave and drought over the YRV. This ISO originated from monsoon convection in the tropics, which regulated the meridional monsoonal circulation and enhanced the heatwave by intensifying the descending air motion and adiabatic heating over the YRV. The alternation of the two ISOs accompanied the northward migration of the subtropical westerly jet over East Asia. The combination of the above-normal 10–25-day ISO and the moderate 30–50-day ISO led to the three consecutive extreme YRV heatwaves in 2022.

Impacts of East Asian winter monsoon circulation on interannual variability of winter haze days in Guangdong Province

Haze days in Guangdong Province (GD) occur mainly in winter, with the highest number of moderate/severe haze days occurring in January. The interannual variability of winter haze days in GD is closely related to the Siberian High, the Aleutian Low, the East Asian Trough, the 850-hPa meridional wind over eastern China, and the 200-hPa East Asian Jet. We construct a winter comprehensive circulation index (WCIDX) to express the joint effects of the above regional-scale circulations on haze days in GD. The positive phase of WCIDX is closely linked to the Eurasian teleconnection pattern, which induces the abnormal southerly winds, high temperatures, and enhanced precipitation over GD by modulating the regional atmospheric circulations, localized meteorological conditions (i.e., enhanced lower specific humidity, reduced planetary boundary layer height, decreased surface wind speed, and enhanced low-level atmospheric inversion) conductive to a higher haze in GD. In addition, the positive phase of the WCIDX favors enhancement of the positive 850-hPa Eady growth rate (EGR) over the mid–high-latitude areas of East Asia, which enhances atmospheric baroclinity and results in a northward shift of the East Asian Jet. Pollutants accumulated over the Indochina Peninsula are advected to GD by the southwesterly airflows. It was found that enhanced horizontal warm advection, adiabatic heating, and diabatic heating provide conditions favorable for low-level atmospheric inversion.

Bidirectional transformation enabled improvement in strength and ductility of metastable Fe50Mn30Co10Cr10 complex concentrated alloy under dynamic deformation

High strain rate compression experiments performed on a non-equiatomic metastable fcc + hcp Fe50Mn30Co10Cr10 high entropy alloy using split Hopkinson pressure bar setup shows improved flow stress and compression ductility compared to quasistatic deformed samples. The deformation response was characterised by the occurrence of hardening and softening stages compared to sustained strain hardening for quasistatic deformation. Detailed EBSD, BSE imaging analysis coupled with TEM shows significant bi-directional transformation (B-TRIP) and increased fcc γ phase stability in high strain rate regime while only forward (fcc to hcp) transformation dominates with increasing fraction of hcp ε phase in the quasistatic regime of deformation. Bidirectional transformation aided by adiabatic heating and heterogeneous deformation in the high strain rate regime leads to optimal stress and strain partitioning between the two phases and delays the initiation of damage at the interface. The presence of concomitant strain rate hardening and improvement in ductility in the dynamic deformation regime opens up avenues for microstructural tunability to achieve simultaneous improvement in strength and ductility using the metastability paradigm in complex concentrated alloys.

Fluid flow and heat transfer characteristics of three-dimensional slot film cooling in an annular combustor

Film cooling methodologies in air-breathing gas turbines have been evolving for many decades. In the present work, a combined experimental and numerical parametric study is conducted to investigate the three-dimensional slot film cooling of an annular combustor. The experimental investigation is conducted to understand the fluid flow and heat transfer phenomenon of the film cooling and to validate the numerical study under laboratory conditions (low temperature and pressure). Transient infrared thermography is used to estimate both adiabatic film-cooling effectiveness (ηad) and heat transfer coefficient (h) simultaneously using a semi-infinite approximation method. The blowing ratios considered in the study are in the range of 0.5 to 5. The experimental results showed that film-cooling effectiveness (ηad) enhanced with an increase in the blowing ratio from 0.5 to 2 and deteriorated beyond BR = 2 due to the adverse effects of turbulence. A parametric study is conducted numerically to understand the effect of flow and geometrical parameters under actual engine conditions (high temperature and pressure). The parameters considered are slot Reynolds number (Res), slot jet diameter (d), slot jet pitch (p), lip taper angle (α), lip length (L), and slot jet injection angle (β). For the considered parameters, numerical results showed that the slot jet diameter (d) = 2 mm, dimensionless slot jet pitch (p/d) = 2, slot jet injection angle (β)=20o and dimensionless lip length (L/d) = 5.9 outperformed the other configurations due to the low turbulence and entrainment. Finally, an Artificial Neural Network-based mathematical model is developed that correlates the ηlat as a function of flow and geometrical parameters.

A nonlinear and rate-dependent fracture phase field framework for multiple cracking of polymer

Designing durable polymer-based materials and structures requires understanding how the physical processes and failure mechanisms associated with moisture intrusion and loading rate combine to produce the complex damage modes observed in their applications. While numerous experiments have assisted us in gaining general insight into the above issues, in-situ characterization is still lacking, and rational prediction on the failure procedure of polymer in the moisture–mechanical​ coupling environment remains challenging. Here we present a thermodynamically consistent theoretical framework and its computational implementation to reveal how the dependence of epoxy’s mechanical behavior on rate- and moisture dictates the initiation and evolution of highly localized deformation zones and cracks. A multi-physical hydrothermal-viscoelastic–viscoplastic-damage model is first proposed to fully couple the effects of strain rate, moisture degradation, strain softening, and adiabatic heating of the bulk epoxy in a highly humid environment. The constitutive models are augmented by a phase field that enables spontaneous tracing of the nucleation and growth of cracks under a wide range of strain rates (from 4.60 × 10−5/s to 3.80 × 103/s). The theoretical model is implemented into an efficient computational procedure that is used to calculate illustrative examples to demonstrate the influence of the intimate coupling between the multi-physical phenomena. The results highlight significant mechanisms underlying the coupled damage process, including: heat accumulation along the crack propagation path; identification of the energies associated with moisture-induced toughening; prediction of crack deflection in the presence of moisture absorption; and illustration that a portion of the plastic work plays a dominant role in the nucleation of cracks at a wide scale of strain rates.

Distinct characteristics of western Pacific atmospheric rivers affecting Southeast Asia

The dynamic characteristics of atmospheric rivers (ARs) have been researched over the western North Pacific and East Asia due to their close linkage to disastrous precipitation extremes, while very little attention has been paid to the AR features from the western Pacific to Southeast Asia. This study aims to quantify the climatology, long-term trends and variability of different AR properties from the western Pacific to Southeast Asia using an objective identification algorithm, the ERA5 reanalysis dataset and the APHRODITE precipitation dataset for the period 1951-2015. The results indicate a belt of frequent AR activities from the western Pacific to the Andaman Sea during the boreal autumn-winter season. The long-term trend analyses show a significantly increasing trend in AR frequency and an eastward shift of AR plumes. These dynamic changes contribute to the increasing trend of extreme precipitation amounts in the coastal areas surrounding the South China Sea. The intraseasonal variability of the AR associated with the Madden-Julian oscillation (MJO) shows a pronounced enhancement of AR activity in the MJO phase-2 to phase-3 due to the steeper gradient of low-level geopotential height between the Northwestern Pacific and the tropical Indian Ocean. The modulation is partly explained by the enhanced MJO convection and the adiabatic heating in the vicinity of the trough of the 200-500 hPa geopotential thickness of the region. This study shows that ARs are important mechanisms behind the climatology, trends and variability of the regional precipitation in Southeast Asia. This study implies that more attention is required toward the dynamics of these tropical weather systems, particularly for their interactions with other synoptic processes and their response to future climate warming.

Analysis and improvement of local cleavage fracture models at elevated loading rates

Brittle fracture has to be excluded in safety-relevant components such as nuclear reactor pressure vessels. Recent work has indicated that brittle failure under dynamic loading cannot be assessed reliably by macroscopic methods such as the Master Curve concept (ASTM E1921). This finding is strongly connected to adiabatic heating processes and local crack arrest events in the crack tip region. However, a detailed study involving the assessment at elevated loading rates with local cleavage fracture models is not available to this point. The present work deals with the application of a local model to various dynamic loading conditions, as well as a proposed model adjustment to improve the analysis results. It was found that existing local concepts are not capable of describing fracture behavior adequately. Though the explicit numerical consideration of heat generation and conduction at elevated loading rates allows a better estimation of failure compared to the Master Curve concept, this still poor assessment quality can also be obtained by simply utilizing the adjusted “dynamic” Master Curve with an increased exponent of p = 0.030 /°C. It is therefore concluded that this exponent adjustment approximates the impact of heat effects quite well. The shortcomings of the numerical model were observed to correlate strongly with the documented amount of local crack arrest events on the fracture surface. This leads to a micromechanically-motivated adjustment of a local approach model to incorporate this mechanism. This modification ensures a more satisfying physical background of the local approach model. Moreover, it significantly improves model analysis accuracy for all examined testing conditions.

Recycling of date kernel powder (DKP) in mass concrete for mitigating heat generation and risk of cracking at an early age

Mass concrete in many structural and non-structural applications is prone to early age cracking and chemo-damage from the exothermic hydration reactions of the cement binder. Date kernels are a waste product generated in large quantities in the date processing industry in the Middle East, North Africa and other countries worldwide. The use of calcined date kernel powder (DKP) as a mineral admixture in concrete to reduce the heat of hydration and temperature rise in mass concrete is a novel idea for which no prior research has been condcuted. A combined experimental and numerical investigation was conducted to assess the performance of DKP as a heat-reducing material in mass concrete. Concrete mixes with 10%, 20% and 30% DKP replacing cement and similar mixes with fly ash (FA) were investigated for evolution of mechanical and thermal properties and the adiabatic heat of hydration. 3D finite element models of mass concrete blocks 2mx2mx2m in size were validated using the data obtained from similar blocks in field instrumented with thermocouples. The 3D FE model was subsequently used to predict the heat of hydration, temperature rise and cracking index of a mass concrete block with 30% DKP powder. Experimental results showed a significant reduction in the heat of hydration in DKP concrete, with levels comparable to the FA concrete without a significant impact of strength properties. The DKP waste material has a strong potential for reducing heat of hydration in mass concrete structures, thereby promoting waste utilization, recycling and sustainability.

Thermal softening behavior up to fracture initiation during high-rate deformation

This work proposes an innovative method to analyze the softening behavior due to adiabatic heat up to the fracture onset during high-rate deformation of AISI4340 steel at room temperature. To derive the rate- and temperature-dependent constitutive equation considering the post-necking behavior, uniaxial (UT) and notched tension (NT) specimens were tested at three strain rates of 10-3/s, 100/s and 103/s. The full fields of strain and temperature were measured until fracture initiation with high-speed digital and thermal imaging cameras, respectively. In particular, this research focused on observing the abrupt localized temperature increase in the post-necking phase, which was achieved through the use of a newly configured split Hopkinson tension bar (SHTB) system. It enabled an experimental investigation of the effect of adiabatic heat on localized behavior up to fracture at high strain rates (103/s). As the strain rate increased, the strain-localization occurred more quickly, and a higher temperature was experimentally observed at the location where fracture initiated. The experimentally measured thermal field was newly utilized for inverse optimization, to determine the thermal softening effect of the constitutive model considering adiabatic heat up to the onset of fracture including post-necking. Finally, a hybrid experimental-numerical approach was used to investigate the physical quantities of local strain, strain rate, temperature inside the specimen where fracture actually began.

Electron Heating Scales in Collisionless Shocks Measured by MMS

AbstractElectron heating at collisionless shocks in space is a combination of adiabatic heating due to large‐scale electric and magnetic fields and non‐adiabatic scattering by high‐frequency fluctuations. The scales at which heating happens hints to what physical processes are taking place. In this letter, we study electron heating scales with data from the Magnetospheric Multiscale (MMS) spacecraft at Earth's quasi‐perpendicular bow shock. We utilize the tight tetrahedron formation and high‐resolution plasma measurements of MMS to directly measure the electron temperature gradient. From this, we reconstruct the electron temperature profile inside the shock ramp and find that the electron temperature increase takes place on ion or sub‐ion scales. Further, we use Liouville mapping to investigate the electron distributions through the ramp to estimate the deHoffmann‐Teller potential and electric field. We find that electron heating is highly non‐adiabatic at the high‐Mach number shocks studied here.

Cold Spray Coatings of Complex Concentrated Alloys: Critical Assessment of Milestones, Challenges, and Opportunities

Complex concentrated alloys (CCAs) are structural and functional materials of the future with excellent mechanical, physical, and chemical properties. Due to the equiatomic compositions of these alloys, cost can hinder scalability. Thus, the development of CCA-based coatings is critical for low-cost applications. The application of cold spray technology to CCAs is in its infancy with emphasis on transition elements of the periodic table. Current CCA-based cold spray coating systems showed better adhesion, cohesion, and mechanical properties than conventional one-principal element-based alloys. Comprehensive mechanical behavior, microstructural evolution, deformation, and cracking of cold spray CC-based coatings on the same and different substrates are reviewed. Techniques such as analytical models, finite element analysis, and molecular dynamic simulations are reviewed. The implications of the core effects (high configurational entropy and enthalpy of mixing, sluggish diffusion, severe lattice distortion, and cocktail behavior) and interfacial nanoscale oxides on the structural integrity of cold spray CCA-based coatings are discussed. The mechanisms of adiabatic heating, jetting, and mechanical interlocking, characteristics of cold spray, and areas for future research are highlighted.

Superimposed hydration exothermic model of cement slurry considering different reaction rates of various active substances

Cement components usually contain two or more hydration active substances with different hydration reaction rates, and the existing hydration exothermic model of cement-based materials do not consider the difference of reaction rates of active substances. This paper proposes a new exothermic hydration model of cement-based materials, which takes into consideration the different reaction rates of multi-component active substances. Firstly, the hydration heat and the representative temperatures of cement slurry with the water-cement ratio of 0.3, are tested through adiabatic and dissolution heat methods. Secondly, the total hydration reaction process is assumed as the composition of the reaction processes of multi-component active substances. Then, a hydration exothermic model witch is superimposed by several exponential functions is fit according to the exothermic hydration experimental data and the Arrhenius chemical expression. The comparison results show that the proposed model is more accurate than the monomial exponential function model, especiallyat the early age before the initial setting time. In conclusion, the proposed model can better explain the influence of the reaction rate difference of different active substances of cement on the exothermic process, and the accuracy of hydration analysis is more accurate by using it than others.

Electrical resistivity of liquid Fe-8wt%S-4.5wt%Si at high pressures with implications for heat flux through the cores of Io and sub-earth exoplanets

Potentially resulting in magnetic dynamo action, the heat flow through the outer cores of small terrestrial planetary bodies depends on the thermal conductivity of liquid Fe alloys at high pressures. The electrical resistivity of liquid Fe-8wt%S-4.5wt%Si was measured at 2–5 GPa and 295–1800 K in a 1000-ton cubic anvil press with a sample volume of a few cubic millimeters. Resistivity values of 220–270 μΩ·cm were measured, and a range of thermal conductivity values of 15–19 W/m/K were calculated using the Wiedemann-Franz law. The adiabatic heat flux at the top of a terrestrial exoplanet's Fe-8wt%S-4.5wt%Si core as a function of radius is calculated. The core of Io, if liquid, could have a convective heat flow density of a few μW/m2 without generating a magnetic dynamo powered by thermal convection.

Electron heating mechanisms at quasi-perpendicular shocks – revisited with magnetospheric multiscale measurements

ABSTRACTWe demonstrate that measurements obtained from NASA’s magnetospheric multiscale (MMS) mission support quasi-adiabatic electron heating in quasi-perpendicular shocks with temperature Te⊥ ∝ B1 + α, where B is the magnetic field strength and α represents departure from adiabaticity. Adiabatic heating (α = 0) results from the conservation of magnetic moment on spatially increasing magnetic field inside the shock ramp. Negative α < 0 is observed in most situations, where perpendicular energy gain from adiabatic heating is redistributed by interactions with waves to the parallel direction leading to a lower isotropic temperature increase. Positive α is observed when the stochastic heating of electrons is activated by the E × B wave acceleration mechanism by electrostatic waves leading to a higher temperature increase. By using test-particle simulations in a realistic shock model we have elucidated the process of stochastic wave acceleration. We have also shown the equivalence of adiabatic heating and acceleration by gradient B drift at shocks with low Mach numbers and demonstrated that the cross-shock potential does not contribute to the electron heating. Signatures of quasi-adiabatic heating and/or stochastic heating of electrons are observed in all shocks analysed with measurements by the MMS.

The Influence of Adiabatic Heat and Combined Blast Load and Fire Loading on the Response of Mild Steel Plates

This paper study the influence of adiabatic heat and fire loading on the behaviour of unstiffened mild steel plates subjected to close-in blast loads using finite element (FE) analysis. A quarter-symmetry 3D FE model consists of the steel plate, clamps and bolts was developed using Abaqus/CAE. Classical plasticity model was used as the material model in the steel plate and bolts. The clamps were assumed as an elastic material. Temperature-material properties relationship according to Eurocode 3 and Masui model was assigned to the steel plate. Conwep function was used to simulate the blast loads. The influence of strain rates was considered in the steel plate using the Cowper-Symonds equation. The FE model of the unstiffened plates was verified and validated against experimental data from literature, where a good agreement was achieved. The results suggest the adiabatic heat in the steel plates does not significantly influence the behaviour of the steel plates in both temperature-material properties models. The study then investigated the effect of combined blast loads and fire loading on the response of steel plates. The fire loading was applied by increasing the temperature in the steel from 200 °C to 1000 °C. Excessive deformation and thinning of the plate at the central area of the plate was observed. The thinning at the central area is pronounce than the thinning of the plate at the boundary between the clamp and the steel plate. Hence, the FE analysis suggests that the failure might occur at the central area of the plate, which could suggest a tearing type of failure. This type of failure is common in plates subjected to close-in blast loads. Therefore, this study has shown that the effect of adiabatic heat is insignificant, and the combined blast-fire loading might cause a similar type of failure as in plates subjected to blast loads only.

Electron‐Scale Front of Magnetic Pile‐Up Region in Reconnection Exhaust

AbstractThe magnetic pile‐up region and its front, which plays a crucial role in electron energization during magnetic reconnection, has been widely studied at fluid and ion scales. However, there have been few studies on electron‐scale front of magnetic pile‐up regions so far. Here, we present detailed observations of electron‐scale front in a tailward reconnection exhaust. With a thickness of ∼5.5 de (electron inertial length), the front propagated along its normal direction, mainly along the reconnection outflow direction. At this front, the strong energy conversion observed was mainly driven by the perpendicular electron current. The front can lead to adiabatic electron heating and acceleration. The front hosts an intense and highly structured electric field, reaching up to ∼120 mV/m and predominantly attributed to the electron convection term. Electrostatic waves with frequencies higher than the electron gyrofrequency and parallel normal angles (WRT background magnetic field) were detected adjacent to the front. Our study can provide insight into the roles of fronts and electron‐scale physics in magnetic reconnection.

Toward Material Property Extraction from Dynamic Spherical Indentation Experiments on Hardening Polycrystalline Metals

Static indentation and dynamic indentation are reviewed, with a focus on extraction of material properties of isotropic strain-hardening polycrystalline metals that may be rate- and temperature-sensitive. Static indentation is reviewed first, followed by dynamic indentation, since the former is regarded as a specialization of the latter with inertia, rate dependence, and adiabatic heating excluded. Extending concepts from the literature review, a treatment of dynamic indentation using dimensional analysis is forwarded, and a general framework for extraction of material property information (i.e., constitutive model parameters) from instrumented dynamic spherical indentation experiments is set forth. In an example application of the methodology, experimental data obtained from instrumented spherical indentation in a miniature Kolsky bar apparatus are evaluated via dimensional analysis. The substrate material is aluminum alloy Al 6061-T6. Several definitions of indentation strain proposed for static indentation are assessed for dynamic indentation, as are indentation strain rates. While the fidelity of the experimental method and inertial effects could inhibit extraction of elastic properties, extraction of certain plastic constitutive properties may be feasible. Current data are insufficient to enable determination of a complete and unique set of all physical properties. Motivated by the present review and analysis, new experiments and simulations are proposed that would identify influences of material properties, facilitating their extraction from data.

Analysis of step-heating thermography methods for defect depth prediction

In this study, five theoretical equations of specific characteristic peak times are proposed to predict the defect depth for step-heating thermography. These equations were derived for test samples with surfaces under adiabatic and convective heat transfer conditions, where, as demonstrated from experiments, the effect of convection on depth prediction can be significant for materials with low thermal conductivities. Two glass fiber reinforced plastic (GFRP) samples with flat-bottom holes at various depths were inspected by step-heating thermography, and the defect depths were predicted by these five methods. Based on the experimental results, the prediction accuracy and the performance of these depth prediction methods are discussed.

Hot Deformation Behavior and Microstructure Evolution of Ti–6Cr–5Mo–5V–4Al–1Nb Alloy

This study looked into the thermo-mechanical properties and the recrystallization mechanisms of the Ti–5.5Cr–5Mo–5V-4Al–1Nb alloy (wt.%, Ti−65541). Hot compression experiments were conducted at two phase regions (740~950 °C) and strain rates from 0.001 to 1 s−1. The compressive strain–stress curves were corrected by the adiabatic heating effect. The Arrhenius model was established and provided a reliable prediction of the value of stress with a 0.992 correlation coefficient. The constructed processing map demonstrated that when the temperature rose and the strain rate fell, the power dissipation efficiency (η) showed a rising trend. By utilizing electron backscattered diffraction (EBSD), the microstructural evolution and deformation process were analyzed. It was possible to witness both continuous dynamic recrystallization (cDRX) and discontinuous dynamic recrystallization (dDRX). The dynamic recovery (DRV) and dDRX eventually replaced dDRX while η decreased. Moreover, the deformation band (DB) impeded re-crystallization in the low η area. This study can supply a relatively reliable processing interval for the new Ti−65541 alloy.

Effects of strain rate and adiabatic heating on mechanical behavior of medium manganese Q&P steels

In this work, the mechanical behavior and properties of four different multiphase steels was studied in tension at strain rates of 10−4, 10−2, 0.5 and 800 s−1. The four materials include a medium manganese (3%) steel grade overcritically and intercritically annealed and Q&P heat treated and two industrially produced TRIP-assisted steels, DH800 and TRIP700 steels, which have different retained austenite morphology. The temperature and strain of the specimens were studied using high speed infrared thermography (IRT) and digital image correlation (DIC). The mechanical response of the Q&P steels had considerably higher tensile strength than the two industrially produced steels. The Q&P steel with a higher austenite volume fraction strain hardened significantly more than the other steels. The DH800 steel and the intercritically annealed Q&P steel heated less with ΔT of 25 °C during uniform deformation than the TRIP700 steel and the overcritically annealed Q&P steel with ΔT of 35 °C. However, the industrially produced steels DH800 and TRIP700 had higher uniform elongation of 0.12 mm/mm and 0.14 mm/mm whereas the Q&P steels reached only 0.09 mm/mm, meaning that the heating rate of the Q&P steels was considerably steeper. In addition, the stronger necking of the DH800 and TRIP700 steels led to much higher maximum temperatures before failure (max. 260 °C) than those observed for the Q&P steels (max. 140 °C). The Taylor-Quinney coefficients of the Q&P steels were large in the beginning of the plastic deformation (0.65–0.95) but decreased as a function of plastic deformation, whereas the Taylor–Quinney Coefficients of the DH800 and TRIP700 steels were lower (0.5–0.6) but increased gradually as a function of plastic deformation.