Temperature Gradient Research Articles

Conflux of spin Nernst and spin Hall effect in ZnCu2SnSe4Topological Insulator.

A comprehensive exploration of the intriguing phenomena known as the spin Nernst effect (SNE) and the spin Hall effect (SHE) within the context of nonmagnetic strong topological insulatorZnCu2SnSe4, has been carried out employing first-principles calculations. Our theoretical calculations unveil significantly large intrinsic spin Nernst conductivity (SNC) and spin Hall conductivity (SHC) in the bulk topological insulatorZnCu2SnSe4. Delving deeper into the intricacies of our findings, we elucidate how the inverted band order in the topological materials drastically influences the spin Berry curvature, consequently exerting a profound impact on SHC and SNC. Detailed analyses reveal that the contribution from the bulk to the generation of pure spin current in a topological insulator is comparable to that of a surface. This underscores the potential role of topological insulators in the development of spin-switching devices. We present compelling evidence thatZnCu2SnSe4holds immense promise as an optimal candidate for the generation of pure spin currents, achieved through the application of both thermal gradients and electric fields. This, in turn, opens up exciting avenues for its utilization in the realms of spin-caloritronics, spin-orbitronics, and spintronics.

A deep-learning-boosted surrogate model of a metal foam based protonic ceramic electrolysis cell stack for uncertainty quantification

Protonic ceramic electrolysis cells (PCECs) are widely considered as an emerging technology that shows capability for enabling environmentally friendly large-scale production of hydrogen. PCEC stacks’ performance is considerably lower compared to smaller, lab-scale button cells. This performance gap is largely attributed to the highly uneven distribution of reactants throughout the larger cell or stack, which presents a significant challenge to the development of PCEC stack. The issue of non-uniform reactant distribution in PCEC stacks can be effectively addressed by incorporating metal foam structures to replace the conventional rib design of the interconnect components. A 3D multiphysical model is developed to train a deep-learning-boosted surrogate model for PCEC with metal foam, which is subsequently used for parameter screening and sensitivity analysis. A collection of 12 inputs that encompass operating/structural/microstructural/material parameters are chosen, in which the operating parameters are identified as influential parameters. Three distribution uniformity indices maintain strong consistence to variations in the inputs, implying the positive role of metal foam. Faradaic efficiency (FE) is primarily influenced by the operating voltage with a total Sobol index of 0.6. The current density and FE are determined as the most stable performance indicators, exhibiting standard deviations of 0.15 and 0.81 respectively. According to a safety threshold of 10 K cm−1 for temperature gradient, the probability of the stack operating below this threshold is 88.61 %. Valuable insights into the design and performance of PCEC stacks that incorporate metal foam structures are provided. The workflow developed in this work can be further leveraged to explore and optimize PCECs.

Quantitative analysis of energy transfer and separation in vortex tubes: Factors and empirical insights

As a device with a simple structure for energy separation, the low efficiency of the vortex tube is the primary obstacle hindering its widespread application. No existing energy separation theory has gained wide acceptance due to inconsistencies with actual processes. Therefore, drawing on prior studies concerning the flow field, the formation process of flow distribution is presented. Then a quantitative analysis of the energy transfer and separation processes in vortex tubes driven by velocity gradient, temperature gradient, and pressure gradient is proposed. The viscous shear work, heat transfer, and turbulent heat transfer processes were analyzed separately. It was found that the main factors of vortex tube energy separation originated from the expansion of the inlet nozzle and the turbulent heat transfer process. At the same time, the viscous shear work and heat transfer processes also have a specific effect on the energy separation, in which the heat transfer process suppressed the energy separation effect of the vortex tube. In addition, its empirical results indicate that interactions among the turbulent heat transfer process, frictional dissipation, angular momentum conservation, and heat transfer should be considered in further studies.

High-speed synchrotron X-ray imaging of melt pool dynamics during ultrasonic melt processing of Al6061

Ultrasonic processing of solidifying metals in additive manufacturing can provide grain refinement and advantageous mechanical properties. However, the specific physical mechanisms of microstructural refinement relevant to laser-based additive manufacturing have not been directly observed because of sub-millimeter length scales and rapid solidification rates associated with melt pools. Here, high-speed synchrotron X-ray imaging is used to observe the effect of ultrasonic vibration directly on melt pool dynamics and solidification of Al6061 alloy. The high temporal and spatial resolution enabled direct observation of cavitation effects driven by a 20.2 kHz ultrasonic source. We utilized multiphysics simulations to validate the postulated connection between ultrasonic treatment and solidification. The X-ray results show a decrease in melt pool and keyhole depth fluctuations during melting and promotion of pore migration toward the melt pool surface with applied sonication. Additionally, the simulation results reveal increased localized melt pool flow velocity, cooling rates, and thermal gradients with applied sonication. This work shows how ultrasonic treatment can impact melt pools and its potential for improving part quality.

Magnetohydrodynamics Marangoni boundary-layer Copper/water nanofluid flow driven by surface temperature gradient over a rotating disk

Abstract Marangoni driving problem is very important in many practical science engineering, such as semiconductor industry, crystal growth, aerospace, material synthesis. Consider these applications, this work we investigate Marangoni boundary-layer Copper/Water nanofluid driven by the surface temperature gradient over a rotating disk in the presence of magnetic field. Buongiorno model of nanofluids, which contains two important terms, thermophoresis and Brownian motion, are taken into account. Rotating disk model is established, also a suitable Kármán transformation and the multi-shooting technique are applied. Graphical discussion include free stream concentration, rotating speed, magnetic field, Marangoni driving, thermophoresis, Brownian diffusion, Prandtl number, and Schmidt number. The results show that rotating speed inertia and Marangoni driving force tend to reduce temperature/concentration and thickness of thermal/mass boundary layer, while free stream concentration and magnetic field raise up. Meanwhile, Prandtl number tends to reduce temperature, while thermophoresis and Brownian diffusion raise up, and Schmidt number has little influence on temperature, and Schmidt number and Brownian diffusion tend to reduce concentration, while thermophoresis raises up, and Prandtl number has an important influence on concentration. For most selected values of physical parameters, as the nanofluid far away from the disk, the local temperature decreases directly, and the local concentration firstly increases to a peak and then decreases to zero.

Novel high-throughput oxygen saturation measurements for quantifying the physiological performance of macroalgal early life stages.

Understanding how macroalgal forests will respond to environmental change is critical for predicting future impacts on coastal ecosystems. Although measures of adult macroalgae physiological responses to environmental stress are advancing, measures of early life-stage physiology are rare, in part due to the methodological difficulties associated with their small size. Here we tested a novel, high-throughput method (rate of oxygen consumption and production; ) via a sensor dish reader microplate system to rapidly measure physiological rates of the early life stages of three habitat-forming macroalgae, the kelp Ecklonia radiata and the fucoids Hormosira banksii and Phyllospora comosa. We measured the rate of O2 consumption (respiration) and O2 production (net primary production) to then calculate gross primary production (GPP) under temperatures representing their natural thermal range. The microplate system was suitable for rapidly measuring physiological rates over a temperature gradient to establish thermal performance curves for all species. The microplate system proved efficient for measures of early life stages of macroalgae ranging in size from approximately 50 μm up to 150 mm. This method has the potential for measuring responses of early life stages across a range of environmental factors, species, populations, and developmental stages, vastly increasing the speed, precision, and efficacy of macroalgal physiological measures under future ocean change scenarios.

Preparation of thermally conductive polyimide/aluminum oxide/boehmite composite separators for enhancing lithium‐ion battery safety and performance

AbstractThis study endeavors to enhance the safety of lithium‐ion batteries (LIBs) by synthesizing a polyamide acid (PAA)/Al2O3 composite spinning solution using 4,4′‐diaminodiphenyl ether (ODA) and pyromellitic anhydride (PMDA) as monomers, and nano‐Al2O3 as a thermal conductivity filler. Subsequently, the PAA/Al2O3 fiber membrane is fabricated via electrostatic spinning, followed by gradient heating imidization to produce a polyimide (PI)/Al2O3 composite membrane. This membrane is then dipped into a boron nitride (BM) slurry to ultimately yield an organic–inorganic PI/Al2O3/BM composite separator with superior flame‐retardant and thermal conductivity properties. The thermal stability, flame retardancy, electrolyte wettability, mechanical integrity, and cycle rate performance of the composite membranes are rigorously evaluated. The results demonstrate that the PI/5% Al2O3/BM composite membrane exhibits the most favorable overall performance, with no shrinkage observed at 200°C and no significant changes after sustained ignition for 10 s. The incorporation of the thermal conductivity Al2O3 filler significantly enhances the heat transfer properties of the composite separator. The room temperature ionic conductivity reaches 2.786 mS cm−1 after electrolyte absorption, and the initial discharge capacity of the assembled battery is 156.28 mAhg−1. Following 100 charge/discharge cycles at 0.2C, the capacity retention rate is 97.7%, and at a discharge rate of 5C, the capacity retention rate is 74.9%.

A Meshless Method of Radial Basis Function-Finite Difference Approach to 3-Dimensional Numerical Simulation on Selective Laser Melting Process

Selective laser melting (SLM) is a rapidly evolving technology that requires extensive knowledge and management for broader industrial adoption due to the complexity of phenomena involved. The selection of parameters and numerical analysis for the SLM process are both costly and time-consuming. In this paper, a three-dimensional radial basis function-finite difference (RBF-FD) meshless model is introduced to accurately and efficiently simulate the molten pool size and temperature distribution during the SLM process for austenitic stainless steel (AISI 316L). Two different volumetric moving heat source models were presented, namely the ray-tracing method heat source model and the double-ellipsoidal shape heat source model. The temperature-dependent material properties and phase change process were also considered, based on experiments and effective models. Results of the model for the molten pool size were validated with those of the literature. The proposed approach can be used to predict the effect of different laser power and scan speed on the molten pool size and temperature gradient along the depth direction. The result reveals that the depth of the molten pool is more sensitive to laser power than scan speed. Under the same scan speed, a 22% change in laser power (45 ± 10 W) affects the maximum temperature proportionally by about 9%. The developed algorithm is computationally efficient and suitable for industrial applications.

Interpretive modeling of tungsten divertor leakage during experiments with neon gas seeding

Many existing and future tokamaks with tungsten divertors operate, or will operate, with low-Z impurity seeding, but the direct effect of these seeded impurities on tungsten Scrape-off-Layer (SOL) transport has not been explored in detail. This paper reports on a DIII-D experiment designed to test how tungsten divertor leakage from the Small-Angle Slot V-Shaped, tungsten-coated divertor is impacted by neon seeding at a variety of injection rates and poloidal injection locations. Measurements from the experiment show an inverse relationship between the neon injection rate and the tungsten core penetration factor. Interpretive modeling is performed with a combination of the SOLPS-ITER and DIVIMP codes to assess the underlying tungsten behavior. The modeling results show that the reduction in tungsten divertor leakage is driven by both an increase in the divertor collisionality as well as a reduction in the ion temperature gradient near the divertor target. Collisions between low-Z impurities and tungsten impurities are found to have a significant impact on the tungsten SOL transport, such that ignoring the low-Z impurity collisional effects on the tungsten transport can result in an overestimate of the divertor leakage by an order-of-magnitude. Given the importance of these localized interactions, neon seeding from the closed, slot-like divertor has a clear advantage in being able to reduce tungsten divertor leakage without the high levels of neon core contamination that occur when seeding from other poloidal locations.

MAGNETIC SHAPING EFFECTS ON TURBULENCE IN ADITYA-U TOKAMAK

Abstract The work reported in this paper addresses two aspects. In the first part, numerical simulations are conducted to examine
the impact of magnetic equilibrium shaping (elongation and triangularity), on both conventional Ion Temperature Gradient
(ITG) modes and Short Wavelength Ion Temperature Gradient (SWITG) modes. This analysis is performed considering the
experimental profiles and parameters of the ADITYA-U tokamak, employing the nonlinear global gyrokinetic Particle-in-Cell
(PIC) code ORB5. The linear and nonlinear collisionless electrostatic simulation of these modes are carried out with kinetic
ions and adiabatic electrons. From the linear results, it has been observed that the magnetic equilibrium shaping slighty reduced
the growth rates and widened the spectrum, and the maxima of growth rate curve is shifted to higher toroidal wave number.
We find that the heat flux is reduced by a significant ≃ 35% for the true circular MHD magnetic equilibrium as compared
to ad hoc concentric circular equilibrium reported in [1]. A further ≃ 10% reduction in the heat flux is seen with magnetic equilibrium
shaping. In the second part, linear collisionless electrostatic simulation studies of ITG coupled with fully kinetic electrons
(both trapped and passing electrons are treated kinetically) using a drift-kinetic ordering is performed. It can be seen from
the linear results that, in presence of kinetic electrons, the growth rate and real frequency of the ITG mode are increased
significantly for ADITYA-U parameters and a mode propagating in the electron diamagnetic direction is identified at high
toroidal wavenumbers.

Thermally Induced Moisture Flow in a Silty Sand under a 1-D Thermal Gradient

Thermally induced moisture flow in unsaturated soils involves complex coupled thermal–hydro processes with the moisture flow in both the vapor and liquid phases. The accurate measurement of the moisture flow in unsaturated sands remains a challenging task due to low moisture migration, the temperature effect on moisture sensors, and the gravity effect on moisture flow. This study aims to accurately measure transient moisture flow, heat transfer, and thermal conductivity in a silty sand with 35% non-plastic fines in a closed heat cell with a controlled 1-D temperature gradient. The heat cell consists of two temperature-controlled heat exchanger plates, heat flux sensors, moisture sensors, thermocouples, and thermal conductivity sensors. The soil moisture sensors were calibrated in the test soil at room temperature and then at elevated incremental temperatures. Soil samples compacted at various initial moisture contents were tested under a constant 1-D temperature gradient of 4 °C/cm. Soil moisture redistribution, temperature, and thermal conductivity profiles were determined from the test results. Transient temperature responses indicated that a lower initial moisture content led to a higher temperature drop after reaching the peak, or a more concaved temperature profile in a steady state due to enhanced moisture migration driven by the temperature gradients. Dry soils exhibited uniform thermal properties, while moist soils showed varying thermal conductivity profiles. A critical moisture content was identified when the maximum moisture migration occurred. Thermal conductivity in soils increased with the distance from the heat source due to thermally induced moisture migration. These findings provide valuable insights into coupled moisture–heat flow dynamics in unsaturated sands.

Exothermic Characteristics Evaluation of the Pt coated α-Al2O3 catalyst in Bed for Passive Airborne Radioactive Material Reduction System under Forced Flow Conditions

After the severe accident at the Fukushima nuclear power plant, there has been heightened interest in the development of severe accident countermeasures. As part of these efforts, a passive filtration system capable of passive operation during power loss is under development.This paper focuses on evaluating the performance of a catalyst-filled bed designed to create a temperature gradient through exothermic reactions between combustible gases generated during accidents and a catalyst. The temperature gradient facilitates the formation of natural convection within the system, enabling passive operation. The catalytic bed is designed in a bed-type configuration filled with exothermic catalysts. To ensure physical and chemical stability under severe accident conditions, heat resistance tests were conducted using inorganic materials as a base to select an optimized exothermic catalyst. A test apparatus was designed for unit evaluation testing of the catalyst-filled bed equipped with the catalytic bed. Exothermic characteristics evaluation tests were conducted by varying the hydrogen volume fraction and face velocity, measuring heat generation in the catalytic bed under each condition. The correlation between these variables and the heat generation performance of the catalytic bed was determined. These findings will be utilized to inform the design parameters of the passive airborne radioactive material reduction system.

Efficient low-grade heat harvesting with flexible paper-based thermoelectric generators fabricated by facile process

The study presents the fabrication and characterization of paper-based thermoelectric generators (PTGs) using p-type Bi0.5Sb1.5Te3 (BST) and n-type Bi2Te2.7Se0.3 (BTS) thermoelectric (TE) materials, deposited via a novel cotton swab powder deposition technique. This method eliminates the need for complex equipment or high-temperature processes, reducing fabrication complexity and enabling large-scale production. The key advancements of this method are its simplicity, cost-effectiveness, and practical applicability, ensuring uniform coating and good material adherence to the paper substrate. The PTGs, consisting of five p-n pairs interconnected with various materials, were laminated for enhanced stability and humidity protection. Experimental measurements under temperature gradients(ΔTs) of 5–30 °C revealed an optimal configuration achieving an open-circuit voltage(Voc) of 42.60 mV, internal resistance(Rint) of 42.50kΩ, short-circuit current(Isc) of 1.00µA, and maximum power output(Pmax) of 10.65nW for the carbon paste/copper sheet interconnected PTG at ΔT of 30 °C. The obtained normalized power density is 5.68nWcm-2K-1pair-1, which is one of the best among the reported Bi2Te3-based PTGs. A preliminary demonstration on an arm showed the PTG generating an 11.95 mV output voltage in hot weather conditions (ΔT ≈ 8 °C), effectively harnessing body heat for wearable electronics. This work highlights a simple, cost-effective, and scalable method for fabricating PTGs for sustainable energy harvesting in low-power wearable applications. Future efforts will focus on optimizing materials, fabrication techniques, and novel designs to enhance efficiency and scalability.

Consolidation of Saturated Kaolin Subjected to Intermittent Thermal Loading with Temperature Gradient

Consolidation of Saturated Kaolin Subjected to Intermittent Thermal Loading with Temperature Gradient

Release of Contaminants from Polymer Surfaces under Condition of Organized Fluid Flows

The use of polymers for water storage or distribution is closely monitored, especially with regard to the possible contamination with substances coming from the material's surfaces. Different standards are practiced across countries according to type of applied materials and such test methods are prevalently based on constant temperature conditions. However, these polymers systems could be located in diverse environment which does not necessarily provide constant conditions. Experimental findings show that exposure of liquid inside polymeric materials to specific temperature gradients, and consequently to emerging organized flows, can result in an accelerated leaching of undesirable substances from the solid surface. In presented work model steady-state and organized flow conditions are used to compare release of contaminates from polyethylene by measuring of surface tension, UV-Vis spectroscopy, FTIR, scanning electron microscopy and elemental analysis of polymer surfaces and water leachates. The pilot study shows that convective flow generated via temperature gradient significantly affects contaminant release in comparison to a steady state and mixing flow conditions.

Association between cytokines, nitric oxide, hemodynamic and microcirculation in a porcine model of sepsis

Systemic inflammation and hemodynamic or microvascular alterations are a hallmark of sepsis and play a role in organs hypoperfusion and dysfunction. Pimobendan, an inodilator agent, could be an interesting option for inotropic support and microcirculation preservation during shock. The objectives of this study were to evaluate effect of pimobendan on cytokine and nitric oxide (NO) release and investigate whether changes of macro and microcirculation parameters are associated with the release of cytokines and NO in pigs sepsis model. After circulatory failure, induced by intravenous inoculation of live Pseudomonas aeruginosa, eight animals were treated with pimobendan and eight with placebo.Pimobendan did not affect cytokines secretion (TNF-α, IL-6 and IL-10), but decreased time-dependently NO release. Data of macro and microcirculation parameters, NO and TNF- α recorded at the time of circulatory failure (Thypotension) and the time maximum of production cytokines was used for analyses. A positive correlation was observed between TNF-α and cardiac index (r = 0.55, p = 0.03) and a negative with systemic vascular resistance (r = −0.52, p = 0.04). Positive correlations were seen both between IL-10, 30 min after resuscitation (T30min), and systolic arterial pressure (r = 0.57, p = 0.03) and cardiac index (r = 0.67, p = 0.01), and also between IL-6, taken 2 h after resuscitation and systolic arterial pressure (r = 0.53, p = 0.04). Negative correlations were found between IL-10 and lactate, measured resuscitation time (r = −0.58, p = 0.03). Regarding microcirculation parameters, we observed a positive correlation between IL-6 and IL-10 with the microvascular flow index (r = 0.52, p = 0.05; r = 0.84, p = 0.0003) and a negative correlation with the heterogeneity index with TNF-α and IL-10 (r = −0.51, p = 0.05; r = −0.74, p = 0.003) respectively. NO derivatives showed a positive correlation with temperature gradient (r = 0.54, p = 0.04).Pimobendan did not show anti-inflammatory effects in cytokines release. Our results also, suggest changes of macro- and microcirculation are associated mainly with low levels of IL-10 in sepsis.

The Growth of V5S8 Single Crystals by Chemical Vapour Transport

Single crystals of the d-electron antiferromagnetic metal V5S8 can be prepared by chemical vapour transport with gaseous iodine as a transport agent. We present the outcomes of an endeavour to synthesise high-purity single crystals of V5S8 with reduced crystalline disorder, important to the formation of novel quantum orders. We report results on the residual resistivity ratio of the single crystals as growth parameters are varied including growth temperature, temperature gradient and pre-growth processing of the initial apparatus and reagents. We demonstrate that single crystals of at least a few mm in size can be successfully grown at relatively low temperatures in the range 550–600 °C. The optimisation of this method may imply a better crystallographic organisation, reducing sulphur vacancies and increasing vanadium positional order. The resulting longer electron mean free paths may enhance the probability of finding exotic quantum states of matter at low temperatures. The results presented here may also be of relevance to the development of vanadium sulphide-based energy storage and spintronic devices.

Lid-driven effect on convective heat transfer with heated rods in a modified equilateral triangular cavity

This article presents heat transfer analysis at the walls of a circular heated obstacle under the influence of force and natural convection in a triangular domain. The circular obstacle is fixed at the center of triangular domain. The circular obstacle and the inclined walls differ in temperature (Th>Tc). The flow and heat transfer in the computational domain are caused by lid movement and temperature gradient. The triangular cavity is filled with air. The physical setup is described in terms of a system of differential equations. The dimensionless equations are solved using the Finite Volume Method (FVM). The results are computed for various flow controlling variables and presented in the form of isotherms, contours, tabular values and curves. The finding reveals that larger Reynolds number and Grashof number tend to higher heat transfer at the surfaces of heated obstacle. The average Nusselt number is noted to be maximum at w1 in the third quadrant when compared with the other walls of the heated obstacle. The results are compared with literature results in the limiting case.

Multi-decadal warming alters predator's effect on prey community composition.

Predator responses to warming can occur via phenotypic plasticity, evolutionary adaptation or a combination of both, changing their top-down effects on prey communities. However, we lack evidence of how warming-induced evolutionary changes in predators may influence natural food webs. Here, we ask whether wild fish subject to warming across multiple generations differ in their impacts on prey communities compared with their nearby conspecifics experiencing a natural thermal regime. We carried out a common garden mesocosm experiment with larval perch (Perca fluviatilis), originating from a heated or reference coastal environment, feeding on zooplankton communities under a gradient of experimental temperatures. Overall, in the presence of fish of heated origin, zooplankton abundance was higher and did not change with experimental warming, whereas in the presence of fish of unheated origin, it declined with experimental temperature. Responses in zooplankton taxonomic and size composition suggest that larvae of heated origin consume more large-sized taxa as the temperature increases. Our findings show that differences between fish populations, potentially representing adaptation to their long-term thermal environments, can affect the abundance, biomass, size and species composition of their prey communities. This suggests that rapid microevolution in predators to ongoing climate warming might have indirect cross-generational ecological consequences propagating through food webs.

The Influence of ENSO Diversity on Future Atlantic Tropical Cyclone Activity

Abstract El Niño–Southern Oscillation (ENSO) influences seasonal Atlantic tropical cyclone (TC) activity by impacting environmental conditions important for TC genesis. However, the influence of future climate change on the teleconnection between ENSO and Atlantic TCs is uncertain, as climate change is expected to impact both ENSO and the mean climate state. We used the Weather Research and Forecasting Model on a tropical channel domain to simulate 5-member ensembles of Atlantic TC seasons in historical and future climates under different ENSO conditions. Experiments were forced with idealized sea surface temperature configurations based on the Community Earth System Model (CESM) Large Ensemble representing: a monthly varying climatology, eastern Pacific El Niño, central Pacific El Niño, and La Niña. The historical simulations produced fewer Atlantic TCs during eastern Pacific El Niño compared to central Pacific El Niño, consistent with observations and other modeling studies. For each ENSO state, the future simulations produced a similar teleconnection with Atlantic TCs as in the historical simulations. Specifically, La Niña continues to enhance Atlantic TC activity, and El Niño continues to suppress Atlantic TCs, with greater suppression during eastern Pacific El Niño compared to central Pacific El Niño. In addition, we found a decrease in the Atlantic TC frequency in the future relative to historical regardless of ENSO state, which was associated with a future increase in northern tropical Atlantic vertical wind shear and a future decrease in the zonal tropical Pacific sea surface temperature (SST) gradient, corresponding to a more El Niño–like mean climate state. Our results indicate that ENSO will remain useful for seasonal Atlantic TC prediction in the future.