Temperature Diffusion Research Articles

Soil Moisture Threshold of Methane Uptake in Alpine Grassland Ecosystems.

Methane (CH4) uptake in alpine ecosystems is an important component of the global CH4 sink. However, large uncertainties remain regarding the magnitude and spatial patterns of CH4 uptake, owing to its extensive spatial variability, diverse controlling factors, and limited regional-scale observations. Here, we investigated field ecosystem CH4 uptake along a 3200-km transect across various alpine grasslands on the Qinghai-Tibetan Plateau (QTP). We found a substantial spatial variation in insitu CH4 uptake among alpine grasslands, with the highest rates in drier regions of the mid-western QTP. Soil moisture was the most important factor controlling CH4 uptake, exhibiting a remarkably low threshold of 6.2 ± 0.1 v/v %. Below this threshold, CH4 uptake was constrained by soil moisture, moisture-induced nitrogen limitation, and high temperatures. Above this threshold, CH4 uptake was mainly limited by gas diffusion and low temperatures. By integrating grid predictors with a random forest model trained on 1851 field measurements encompassing both our observations and a regional synthesis across the QTP, we estimated a regional CH4 uptake of 0.88 ± 0.020 Tg CH4 year-1 from all alpine grasslands on the QTP. This higher estimate, primarily driven by alpine steppes, was significantly greater than current regional estimates from global CH4 models. Our findings highlight the importance of CH4 sink in dry alpine ecosystems characterized by low soil moisture, suggesting that the contribution of CH4 sink in drylands may have been substantially underestimated in the current global CH4 budget.

Diffusion behavior controlled performance enhancement of Nd-Fe-B magnets diffused by Tb-Ni alloy at various temperatures

High coercivity and anti-corrosion properties are required for sintered Nd-Fe-B magnets used in new energy and off-shore wind power industries. Here, we found that both magnetic properties and corrosion resistance of Nd-Fe-B magnets can be significantly improved by grain boundary diffusion (GBD) of Tb69Ni31 alloy. The diffusion temperature is a key factor in determining both the magnetic properties and corrosion resistance. The wettability of Tb69Ni31 alloy with the magnet and the fluidity of Tb69Ni31 alloy gradually increase with increasing temperature above 750 ℃, which facilitates the elements diffusion. Tb and Ni show different diffusion behaviors at different temperatures. The magnet diffused at a relatively high temperature exhibits high coercivity due to the formation of a thick Tb-rich shell in the grain with high magnetocrystalline anisotropy field. However, excessive grain growth leads to a reduction in coercivity as the diffusion temperature further increases. The highest corrosion resistance is achieved by Tb69Ni31 alloy diffusion at a relatively lower temperature. By analyzing the Volta potential distribution using scanning Kelvin probe force microscopy, the Ni-rich phase with high potential formed in grain boundaries is mainly responsible for the improved corrosion resistance. The current results suggested that the performance of Tb-Ni diffused magnets can be controlled by the diffusion behaviors of Tb and Ni.

Hot Spot Offset Variability from Magnetohydrodynamical Thermoresistive Instability in Hot Jupiters

Abstract Hot Jupiter (HJ) atmospheres are possibly subject to a thermoresistive instability (TRI). Such an instability may develop as the ohmic heating increases the electrical conductivity in a positive feedback loop, which ultimately leads to a runaway of the atmospheric temperature. We extend our previous axisymmetric one-dimensional radial model, by representing the temperature and magnetic diffusivity as a first-order Fourier expansion in longitude. This allows us to predict the hot spot offset during the rapid unfolding of the TRI and following Alfvénic oscillations. The instability is periodically triggered and damped within ≈10–40 days, depending on the magnetic field strength, with months of slow buildup between recurring bursts. We show a few representative simulations undergoing TRI, in which the peak flux offset varies between approximately ±60∘ on a timescale of a few days with potentially observable brightness variations. Therefore, this TRI could be an observable feature of HJs, given the right timing of observation and transit and the right planetary parameters.

Numerical Investigation of Crude Oil Diffusion Dynamics and Temperature Field Evolution in Heterogeneous Porous Media Surrounding Buried Pipelines

Numerical Investigation of Crude Oil Diffusion Dynamics and Temperature Field Evolution in Heterogeneous Porous Media Surrounding Buried Pipelines

Involvement of temperature dependent thermal conductivity and diffusion coefficient on bio-convective flow partial differential equations of Williamson model with radiation phenomenon

The Williamson nanofluid flow via a nonlinear stretching plate is examined in this work. Unlike the literature analysis for a linear stretching situation, which focuses on the local impact of Williamson parameter, this analysis will examine the global influence of λ. Furthermore, the characteristics of activation energy are also considered in this review. It is still unclear how the proposed model and ensuing similarity transformation are viewed. Analytical solutions are found for the altered partial differential equations. Figures illustrate the effects of embedding factors on the temperature, concentration, density microorganisms, and velocity curves. Tables are also used to illustrate how embedded characteristics affect mass transfer, heat transfer, and skin friction.

Comparison of Particle Image Velocimetry and Planar Laser-Induced Fluorescence Experimental Measurements and Numerical Simulation of Underwater Thermal Jet Characteristics

During the underwater movement of a submarine, cooling water at a specific temperature is discharged into the surrounding water through nuclear reactor secondary loop circulation, creating a thermal jet. Thermal jets are characterized by initial velocity and temperature properties that allow for complete mixing with the surrounding water through a combination of mixing and heat transfer processes. This paper aims to investigate the movement and diffusion of underwater thermal jets, specifically examining the temperature stratification of the ambient water, the initial velocity of the jet, and the effect of temperature on the velocity field and temperature field of the underwater thermal jet. This study utilizes particle velocity measurements and the laser-induced fluorescence method to measure the velocity field and temperature field of the thermal jet, as well as simulation methods to validate conclusions. The experimental and simulation conditions in this paper are mainly categorized into two types: uniform water body and thermally-stratified water body. Upon analysis and comparison of the experimental and simulation results, it has been observed that an increase in jet velocity will hinder the upward diffusion of jet temperature, decrease the floating height of the jet, and slow down the rate at which the jet temperature decays. Furthermore, as the difference between the jet temperature and the ambient water temperature increases, the upward diffusion of the jet temperature becomes predominant, resulting in a 40–50% increase in its floating rate. It is evident that the stratification conditions of the background environment have a significant impact on the jet temperature diffusion. When the jet temperature diffuses to the thermally-stratified interface of water in the tank, it ceases to float due to density differences; consequently, its temperature cannot diffuse further towards or reach the water surface.

Impact of cold fluid injection on caprock integrity

In Brazilian pre-salt fields, the extracted carbon dioxide (CO2) is reinjected with lower temperatures into the reservoirs to maintain reservoir pressure, improve oil recovery and reduce greenhouse gas emissions. The cold CO2 injection can alter the mechanical and hydraulic properties of the subsurface and induce variations in formation stresses. Stress changes can be sufficiently high to generate undesirable fracture propagation, damage the caprock, and activate natural fractures or geological faults. Consequently, they can induce seismicity, leaks, and contamination of shallower aquifers and CO2 release into the atmosphere. This work investigates the thermo-hydro-mechanical effect of cold fluid injection on caprock integrity. To this end, a fully coupled thermo-hydro-mechanical (THM) finite element model governs the rock formation behavior. The proposed model considers poroelasticity, fluid flow, and convection/diffusion heat transfer within the permeable rock formation under single-phase fluid flow conditions. The temperature diffusion, pore-pressure buildup, and stress variation under isothermal or non-isothermal injection scenarios are investigated. The results show reservoir expansion in the isothermal scenario due to fluid injection, which is expected in the pressurization process. In the non-isothermal scenario, the thermally disturbed region throughout the reservoir resulted in compaction rather than expansion, even though it was subjected to injection. The instantaneous drop in temperature induces a hard drop in pore pressure and plastic deformations in the reservoir. The lower interval of the caprock presents critical horizontal tension stresses compromising its integrity. Finally, the study adds valuable insight to better understand the complex cold fluid injection process, considering hydraulic, mechanical, and thermal coupling.

Signature of Vertical Mixing in Hydrogen-dominated Exoplanet Atmospheres

Vertical mixing is a crucial disequilibrium process in exoplanet atmospheres, significantly impacting chemical abundance and observed spectra. While current state-of-the-art observations have detected its signatures, the effect of vertical mixing on atmospheric spectra varies widely based on planetary parameters. In this study, we explore the influence of disequilibrium chemistry across a parameter space that includes eddy diffusion, surface gravity, internal and equilibrium temperature, and metallicity. We also assess the effectiveness of retrieval models in constraining the eddy diffusion coefficient. By running numerous 1D chemical kinetics models, we investigate the impact of vertical mixing on the transmission spectrum. We also built a custom fast-forward disequilibrium model, which includes vertical mixing using the quenching approximation and calculates the model abundance orders of magnitude faster than the chemical kinetics model. We coupled this forward model with an open-source atmospheric retrieval code, used it on the JWST simulated output data of our chemical kinetics model, and retrieved eddy diffusion coefficient, internal temperature, and atmospheric metallicity. We find that there is a narrow region in the parameter space in which vertical mixing has a large effect on the atmospheric transmission spectrum. In this region of the parameter space, the retrieval model can put high constraints on the transport strength and provide optimal exoplanets to study vertical mixing. In addition, the NH3 abundance can be used to constrain the internal temperature for equilibrium temperature T equi > 1400 K.

Heat conduction applied in ‘River Pollutant Diffusion’

Environment problems are a highly valued topic in today’s society, where water pollution issue is one of the most significant that could threaten human’s safety. Sources such as industrial wastewater and agricultural runoff are affecting the water quality. Rivers around the world suffer from varying degrees of pollution. In this paper, we investigate river heat pollution and employ a numerical model to investigate its evolution and impacts downstream by adapting the heat advection-diffusion equation. We explore the stability of our numerical solutions using von Neumann stability analysis of the forward and backward differencing method of discretization of the analytical equations. We further consider a setting where there are multiple sources of pollutant in the river to explore interaction of the two pollution sources. We use python to develop the model and plot temperature diffusion in the river as a function of time and location. Our model reflects the relationship between the speed of diffusion and thermal diffusivity, and how advection enhances pollutant. Our results show that heat pollution is very quickly transported to other locations and can affect water and food quality in many locations along the river. Additionally, pollution in rivers with fast currents will be more readily transported downstream, therefore both proximity to cities and speed of river water needs to be taken into account when addressing the problem of heat pollution in rivers near cities.

U-Shaped Dimeric Acceptors for Balancing Efficiency and Stability in Organic Solar Cells.

Despite significant improvements in power conversion efficiencies (PCEs) of organic solar cells (OSCs), achieving excellent stability remains a great challenge to their commercial feasibility. Here, U-shaped dimeric acceptors (5-IDT and 6-IDT) with different molecular lengths are introduced into the binary OSCs as a third component, respectively. The introduction of the third component effectively reduces the energetic disorder and non-radiative voltage losses and improves the exciton dissociation and charge transport of the devices. Consequently, the PCEs of the 6-IDT- and 5-IDT-treated OSCs are significantly improved to 19.32% and 19.96%, respectively, which is the highest PCE for oligomeric acceptors-based ternary OSCs to date. Meanwhile, the thermal stability of the treated devices is dramatically improved, with the initial efficiency retention of the 6-IDT- and 5-IDT-treated devices increasing from 18% to 32% and 75%, respectively, after 1000h of thermal stress. This is mainly attributed to the ability of the smaller molecular length of 5-IDT to stabilize the phase-separated morphology of the polymeric donor and small molecular acceptor, rather than the high glass transition temperature and low diffusion coefficient.

Performance of Crumb Rubber Tire-Modified Bitumen for Malaysian Climate Regions.

Researchers are increasingly concerned about the vast amounts of waste rubber tires produced globally, which contribute significantly to environmental pollution. The potential of incorporating waste rubber tires to modify bitumen has garnered considerable interest. This study assesses pavement design temperatures according to SUPERPAVE standards for representative Malaysian regions. The assessment is based on hourly air temperature data and simulates temperature diffusion in typical Malaysian road pavements using the finite difference method (FDM). Tests on neat bitumen (PEN 60/70) and crumb rubber-modified bitumen (CR-TMB) samples evaluated their physical and rheological properties across various temperatures and aging stages. These tests were conducted using the dynamic shear rheometer, rotational viscometer, and bending beam rheometer. The attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) analysis provided insights into the aging processes of both PEN 60/70 and CR-TMB. The findings indicate that adding 15% crumb rubber to produce CR-TMB enhances the physical and rheological properties of bitumen. Additionally, this modification significantly improves aging behavior, highlighting its potential for more resilient and sustainable road construction materials. Therefore, the use of crumb rubber in road construction should be considered to improve pavement durability and strength. Furthermore, utilizing crumb rubber as an alternative material can reduce costs by recycling waste materials.

Experimental Investigation of the Influence of Different Thermal Aging Conditions on the Thermal Conductivity of Battery Electrodes

A thermal management system is required to ensure the safe and optimized operation of a lithium-ion battery systems in electric vehicles. The design of the thermal management systems is thereby commonly based on the respective cell behavior only at the Begin of Life (BoL). During operation, various aging mechanisms occur on both the anode and cathode side, depending on the cell chemistry. These mechanisms change the properties of the battery cells. For a more profound understanding and design of thermal management systems the dependency of the thermal cell behavior on the State of Health (SoH) until the End of Life (EoL) is crucial.The aging mechanisms themselves depend on the temperature during aging. The changes in the microstructure at the electrode level lead to changes in the effective thermal material properties, resulting in reduced heat transfer among other changes. Alterations of the thermal cell behavior will influence the electrical and electrochemical behavior. In literature, few studies have been carried out investigating the changes in the integral thermal conductivity of pouch cells on cell level, which have shown an influence of the SoH on the thermal conductivity (for example Tendera et al. 2023). However, from these studies it is not directly possible to assign the individual aging effects and the observed changes in thermal conductivity to the individual processes at the anode and cathode.Therefore, in this work, the influence of different thermal aging conditions on the thermal conductivity of cathode and anode stacks is investigated on electrode level to gain more insight on the individual underlying mechanisms. An experimental method for the thermal characterization at electrode level (electrode stack, current collector and coating) was developed. In combination with measurements of the specific heat capacity with differential scanning calorimetry, the density with gas pycnometer and the temperature diffusivity with laser flash analysis, regarding the microstructure, the effective thermal conductivity can be determined.The thermal aging conditions for the investigated cell were chosen over a wide temperature range (from 0 °C to 50 °C) to trigger different aging mechanisms within the cells. The investigated cell consists of a graphite anode and a NCA/LCO blend cathode. For lower temperatures, for example, lithium plating occurs increasingly on the anode side. At higher temperatures, particle cracks can occur in the cathode particles and side reactions resulting in cover layers are enhanced. In addition, various inhomogeneous temperature distributions were considered, such as the change in temperature during charging / discharging and inhomogeneous temperature fields over the geometric dimensions of the cell.The main focus of this contribution is the influence of the inhomogeneous temperature distribution during aging and the comparison to homogenous aging conditions. The aging mechanisms are investigated through various post-mortem analysis methods and compared to the effective thermal conductivity for the different samples. Several samples are taken from aged cells of each aging condition and the corresponding effective thermal material properties are determined using the described methodology. Through comparison with the results of the post-mortem analysis and the homogenously aged samples the aging effects responsible for the changes of the thermal properties are investigated.

Phase and thermal diffusivity variation of saline water diagnosed by visual and temperature method during freezing process

Freezing step is a fundamental physical phenomenon of cooling a liquid formulation for guaranteeing product quality. In this study, freezing process of saline water under various concentrations was monitored through the visual and temperature methods. The formation of the ice crystal nuclei at the supercooling stage, and the increase of ice and ice/water layers were observed. The formation of the ice crystal nuclei and ice layer was affected by the location of vials placed on a shelf and the concentration of saline water. A saline water solution at a higher concentration had a lower ice layer height under the same freezing settings. The location of vial on the shelf affects the stability and efficiency of thermal transmission. Moreover, the concentration of saline water has the relationship with the thermal diffusivity, and ice layer is an indicator of variation of temperature and thermal diffusivity for saline water during freezing process. This study was able to replicate and observe the physical phenomena of the formation of ice crystal nuclei and the ice layer during the freezing process under laboratory conditions; as well as show how the specific concentration of the saline water solution affected the developmental speed of the ice layer.

Mechanical properties of hcp Fe at high pressures and temperatures from large-scale molecular dynamics simulations

We study the elastic behavior of hexagonal close-packed (hcp) Fe at the high temperature and pressure conditions of the Earth Core, using an embedded-atom method interatomic potential adjusted to those conditions. We calculate diffusivity, elastic constants, density, bulk modulus, shear modulus, and sound velocities vs temperature. We obtain reasonable agreement with ab initio simulations and with other empirical potential simulations. Our densities and shear modulus are slightly higher than those in the preliminary reference earth model for the core. Phase stability is discussed in terms of the Born criteria and free energies, finding that hcp is mechanically stable and that the free energy difference between hcp and body-centered cubic (bcc) is very small compared to the thermal energy. We compare our simulated shear modulus G to several analytical models, obtaining excellent agreement with the Atom in Jelium model by Swift and co-workers. Assuming that the yield strength Y is equal to the shear modulus G, Y=G/30, we find reasonable agreement with a recent parametrization of the Steinberg–Guinan model. These results can lead to future large-scale, multi-million simulations of Fe under core conditions for samples with microstructure like grain boundaries and twins, which might be present under those conditions.

Numerical Study of Hydrogen-Rich Fuel Coherent Jet in Blast Furnace Tuyere

Injecting hydrogen-rich fuel into blast furnaces is an effective strategy to reduce carbon dioxide (CO2) emissions. The present study established a three-dimensional (3D) model based on a coherent jet of hydrogen-rich fuel. The combustion characteristics and the flow, heat, and mass transfer behaviors in the reaction region were simulated by the Computational Fluid Dynamics (CFD) method. The effects of fuel jet velocity on the distributions of gas velocity, temperature, and species in the reaction region were systematically analyzed. The results show that hydrogen-rich fuel burned around the main jet, generating a high-temperature, low-density flame. As flame length increased, the main jet experienced less decay. The outward expansion of the jet caused continuous diffusion of gas temperature and its components. As the fuel jet velocity increased, the temperature along the main jet centerline rose sharply, while the length of the high-concentration gas region extended. Doubling the jet velocity increased its centerline velocity by 11% and raised the average reaction region temperature by 4.12%. The obtained highlighted results are of paramount importance for optimizing hydrogen-rich smelting in blast furnaces.

Optoelectronic and photoacoustic waves in rotating excited semiconductor subjected to thermal shock

In this study, the impact of rotation on the transmission of optical acoustic waves, arising from the movement of the optical carrier within an elastic thermal environment, is examined through theoretical analysis. The theoretical framework incorporates the interaction between acoustic waves and thermomechanics to formulate governing equations specific to a semiconductor medium. The fundamental equations of the physical model, influenced by photothermal and thermoelastic principles, are deduced mathematically while considering the presence of rotation. The model studied the medium under a thermal shock wave from thermal stress resulting from light-induced temperature elevation that is not fixed but decaying over time. The mathematical model is solvable using the normal mode method. The model’s numerical solutions provide access to all physical fields within the physical domain, encompassing displacement, temperature, acoustic pressure, mechanical stress, and carrier density diffusion. Utilizing the harmonic wave method, a two-dimensional graphical representation of the rotation parameter with and without the influence of the decay parameter is obtained. The theoretical analysis involves comparison, analysis, and discussion of the effects of these parameters investigated.

Desulfurization Behavior of Magnetite Pellets Reduced by Isothermal Pure Hydrogen

The desulfurization behavior of magnetite pellets reduced by pure hydrogen at isothermal temperature is studied, the mechanism of self‐oxidation desulfurization is put forward, and the thermodynamic theoretical calculation and experimental verification of this mechanism are carried out. The feasibility of the reaction between iron sulfide and Fe3O4 is analyzed by HSC Chemistry 6.0 software. Additionally, a thermal gravimetric analyzer is used to further study the thermal behavior of pellet material under Ar atmosphere from 400 to 1400 K. The results show that the removal of sulfur in the isothermal reduction process of pure hydrogen does not depend on hydrogen phase diffusion and reduction temperature. During the heating process, self‐oxidation desulfurization occurs in the system, and the self‐desulfurization reaction is more inclined to Fe3O4 + FexSy → FeS + SO2. Under the experimental conditions, the temperature range of self‐oxidation desulfurization under conventional thermal field and microwave field is 700–1100 and 370–1140 K, respectively, and the desulfurization rate is 92.9% and 95.8%, respectively. The key to improving desulfurization by microwave radiation is that iron sulfide has good wave‐absorbing characteristics.

On the Origin of the 107 K Hot Emitting Gas in the Circumgalactic Medium of the Milky Way

The presence of the ≈106 K gas in the circumgalactic medium of the Milky Way (MW) has been well established. However, the location and the origin of the newly discovered hot gas at “supervirial (SV)” temperatures of ≈107 K have been puzzling. This hot gas has been detected in both absorption and emission; here, we focus on the emitting gas only. We show that both the “virial” and the SV temperature gas, as observed in emission, occupy disk-like extraplanar regions, in addition to the diffuse virial temperature gas filling the halo of the MW. We perform idealized hydrodynamical simulations to show that the ≈107 K emitting gas is likely to be produced by stellar feedback in and around the Galactic disk. We further show that the emitting gas at both SV and virial temperatures in the extraplanar regions is metal enriched and is not in hydrostatic equilibrium with the halo but is continuously evolving.

Rethinking Porosity-Based Diffusivity Estimates for Sorptive Gas Transport at Variable Temperatures.

The detection of noble gas radioisotopes following a suspected underground nuclear explosion is the surest indicator that nuclear detonation has occurred. However, the accurate interpretation and attribution of radioisotopic signatures is only possible with a complete understanding of transport processes occurring between the nuclear cavity and surface. In the far-field, diffusive forces contributing to gas transport are impacted by temperature gradients and subsurface lithology. In the current study, we investigate diffusive transport of xenon (Xe), krypton (Kr), and sulfur hexafluoride (SF6) through intact Bandelier tuff at elevated temperatures using a newly developed high temperature diffusion cell. Diffusion coefficients determined using Finite Element Heat and Mass transfer code simulations and the Parameter ESTimation tool range from 2.6-3.1 × 10-6 m2/s at 20 °C, 3.4-5.1 × 10-6 m2/s at 40 °C, and 4.3-7.0 × 10-6 m2/s at 70 °C. Sorption was found to be an important transport mechanism at ambient temperatures (20 °C). Most critically, our study shows that empirical porosity-based diffusion estimates for these gases through tuff captured neither the magnitude nor trends relative to a nonsorbing sandstone. These new insights highlight the importance of experimental transport investigations and will be used to improve models for subsurface gas propagation relevant to proliferation detection and environmental contamination.

Experimental verification of a common assumption in the use of concentration-dependent interdiffusion coefficient

There has generally been a view that concentration-dependent interdiffusion coefficient, D(C), obtained at any diffusion temperature and time is a material constant and can be reliably used to predict diffusion effects at all other isothermal diffusion times. This notion which is implicitly predicated on the assumption that diffusion-induced stress (DIS) rapidly and completely relaxes once formed and does not influence D(C) is experimentally verified in the present work. The results of the study show that reliably computed D(C) from concentration profile obtained at long diffusion time fails to correctly predict concentration profiles at shorter diffusion periods, due to isothermal variation of the D(C) with time. Accordingly, instead of continuing to assume that D(C) is time-independent and can be reliably used to predict diffusion effects at any isothermal diffusion time, without appropriate experimental support, proper experimental verification of this crucial concept in other alloy systems, as done in the present work, is imperative.