Effect Of Temperature Gradient Research Articles

Enhanced ocean CO2 uptake due to near-surface temperature gradients

The ocean annually absorbs about a quarter of all anthropogenic carbon dioxide (CO2) emissions. Global estimates of air–sea CO2 fluxes are typically based on bulk measurements of CO2 in air and seawater and neglect the effects of vertical temperature gradients near the ocean surface. Theoretical and laboratory observations indicate that these gradients alter air–sea CO2 fluxes, because the air–sea CO2 concentration difference is highly temperature sensitive. However, in situ field evidence supporting their effect is so far lacking. Here we present independent direct air–sea CO2 fluxes alongside indirect bulk fluxes collected along repeat transects in the Atlantic Ocean (50° N to 50° S) in 2018 and 2019. We find that accounting for vertical temperature gradients reduces the difference between direct and indirect fluxes from 0.19 mmol m−2 d−1 to 0.08 mmol m−2 d−1 (N = 148). This implies an increase in the Atlantic CO2 sink of ~0.03 PgC yr−1 (~7% of the Atlantic Ocean sink). These field results validate theoretical, modelling and observational-based efforts, all of which predicted that accounting for near-surface temperature gradients would increase estimates of global ocean CO2 uptake. Accounting for this increased ocean uptake will probably require some revision to how global carbon budgets are quantified.

Investigating the effects of powder feeding rate on microstructure transformation in linear laser beam additive manufactured thick-walled structures

The coarse columnar crystals that grow through multiple layers are commonly observed in laser additive manufactured structures, with fractures tending to occur in regions where there are abrupt changes in grain morphology. This can lead to a degradation of the mechanical properties of the samples. In this study on laser additive manufacturing, thick-walled structures made of 304 stainless steel were created using a linear beam spot with a rectangular powder feeding nozzle. By adjusting the powder feeding rate to influence the thermal cycling characteristics during the laser additive manufacturing process, a hierarchical grain structure that combines coarse and fine equiaxed grains was achieved, enhancing the forming efficiency and overall mechanical performance of the structure. The results from the thermal cycling characteristics and microstructure analysis indicate that increasing the powder feeding rate during the additive manufacturing process can decrease the hierarchical cooling rate, temperature gradient, and heat accumulation effect. This reduction in turn decreases the grain size and facilitates the transformation of columnar crystals into equiaxed crystals. Furthermore, the transformation of low-angle grain boundaries into high-angle grain boundaries in the interlayer region helps to reduce stress concentration, weaken anisotropic tendencies, and mitigate intergranular fracture tendencies, ultimately improving the mechanical properties of the overall structure. In actual engineering applications, the powder flow can be adjusted to control the temperature gradient and cooling rate of the deposition layer, thereby altering the grain morphology and optimizing the mechanical properties of additive manufacturing parts.

Theoretical Analysis of Landfill Gas Migration in Capillary Barrier Covers Considering Effects of Waste Temperature

The high-temperature and high-humidity conditions arising from the biochemical degradation of landfill waste result in significant temperature gradients within the landfill cover. The effects of waste temperature on landfill gas transport and microbial aerobic methane oxidation are not fully understood. In this study, a fully coupled theoretical model was developed to simulate the interactions of moisture, heat, and gas transport within a capillary barrier cover. A series of parametric studies were carried out to investigate the influence of the combined effects of temperature gradient, initial soil moisture content, and landfill gas generation rate on methane transport, oxidation, and emissions. The simulated results indicated that increasing waste temperature intensified the temperature gradient, leading to higher surface evaporation rates and variations in methane oxidation efficiencies. Additionally, variations in initial soil moisture content and landfill gas generation rates were found to significantly impact gas migration and methane oxidation in the cover. This study demonstrates the critical role of waste temperature in landfill gas migration within landfill cover systems, providing technical methodologies for the optimized design of soil cover systems.

Comprehensive analysis of thermo-mechanical responses in collapsible soil under varied water content conditions

AbstractIn this research, the effect of both temperature gradients and varied water content on heat transfer in collapsible soil is investigated. The study based on one-dimensional laboratory setup, soil temperature distribution in proximity to a heat source, was examined across four distinct temperatures (ranging from 50 to 200 °C) under varying water content (0%, 10%, 15%, and 20%). Through steady-state conditions and extended measurements over days, data were collected to compare soil thermal conductivity at 10% water content using two different methods. The first method required some of soil characteristics, such as dry density and optimum water content, while the second method relied on heating parameters and supplied heating content. A robust agreement between thermal conductivity values obtained through these two methods was observed. Correlations from experimental data were analyzed to enrich understanding, and multivariate linear regression was employed to predict the thermal conductivity and resistivity of collapsible soils. Results indicated that the higher soil density, the increasing the thermal conductivity, whereas greater soil porosity exhibited the opposite trend. Elevated temperatures were found to enhance soil density, influencing the spatiotemporal distribution of heat within the soil. This research contributes valuable insights into the dynamic behavior of heat transfer in collapsible soil, emphasizing the complex interaction of temperature gradients and water content variations. The findings of this study can advance the development of efficient and sustainable geothermal systems in regions with collapsible soils, potentially enhancing the design and management of structures built on such soils, especially in arid and semi-arid areas.

Effects of Temperature Gradients on Breakdown Characteristics of Tri-Post Insulator in HVAC GIL

Effects of Temperature Gradients on Breakdown Characteristics of Tri-Post Insulator in HVAC GIL

In situ observation and numerical analysis of temperature gradient effects on growth velocity during directional solidification of silicon

AbstractThe < 110 > directional solidification of silicon under varying overall temperature gradients was investigated using an in situ observation system. The growth velocity of an atomically rough interface was found to decrease with increasing temperature gradient. A theoretical model of the thermal field taking undercooling into account was developed to describe this phenomenon and was demonstrated to be valid. The results of this work indicate that the reported linear relationship between growth velocity (V) and undercooling (ΔT), given by V (mm s−1) = 120ΔT (K), is most accurate in the case of a rough interface. In the case that the overall temperature gradient is small, the melting point isotherm moves rapidly such that it becomes more difficult for the interface to keep pace with the isotherm compared with a large temperature gradient. This effect leads to increased undercooling at the interface and consequently a rapid growth velocity. Thermal field calculations confirm that a rapid increase in the ratio of the temperature gradient in the crystal to that in the melt should increase the latent heat release, again providing a more rapid growth velocity.

Frozen Saline Sand Can Be Highly Permeable

AbstractMass transport in frozen ground is typically regarded slow. However, a highly permeable path can exist in frozen saline sand if the unfrozen water is interconnected at the pore scale. We therefore should consider when the unfrozen water is connected and how permeable can frozen saline sand be, yet there are few studies. This research utilizes in‐situ X‐ray CT to evaluate unfrozen water connectivity and permeability in frozen saline sand considering effects of initial salt content, temperature, freezing rate, and temperature gradient. Results show that higher initial salt content and/or temperature, both of which results in a higher unfrozen water content, easily maintains unfrozen water connectivity. Rapid freezing minimizes the brine expulsion and permits a higher unfrozen water content hence better connectivity. Permeability in frozen saline sand can be several orders higher than the typically reported value, highlighting the potential presence of rapid mass transport through the connected unfrozen water.

Nonlinear static behaviors of nonlocal nanobeams incorporating longitudinal linear temperature gradient

The elastic parameters and the coefficient of thermal expansion (CTE) of nanomaterials change with temperature. If the elastic modulus, the CTE, and the longitudinal linear temperature gradient are coupled, the longitudinal symmetry of the mechanical properties of nanobeams is broken. However, researchers have not yet to examine how this symmetry breaking affects the mechanical properties of nanobeams. This paper provides a new analysis of the modified thermoelastic beam model established by the nonlocal stress gradient theory. The present analysis incorporates the coupling of the longitudinal linear temperature gradient, elastic modulus, thermal expansion, and scale effect. Afterward, we apply the Galerkin method to explore the buckling, post-buckling, and transverse bending of a (10,10) single-walled carbon nanotube (SWCNT). The results show that the linear temperature gradient induces the breaking of the nanobeam's longitudinal symmetry and then results in the coupling of the symmetrical and antisymmetrical weight functions of the deformations. While the linear temperature gradient marginally affects the symmetry of nanobeams, it significantly raises the buckling temperature and introduces the complexity of the post-buckling and transverse force bending. In addition, the integration of the linear longitudinal temperature gradient, elastic modulus, and nonlocal effect more significantly affects nanobeams' mechanical properties than individual factors.

Measurement bias in self-heating x-ray free electron laser experiments from diffraction studies of phase transformation in titanium

X-ray self-heating is a common by-product of X-ray Free Electron Laser (XFEL) techniques that can affect targets, optics, and other irradiated materials. Diagnosis of heating and induced changes in samples may be performed using the x-ray beam itself as a probe. However, the relationship between conditions created by and inferred from x-ray irradiation is unclear and may be highly dependent on the material system under consideration. Here, we report on a simple case study of a titanium foil irradiated, heated, and probed by a MHz XFEL pulse train at 18.1 keV delivered by the European XFEL using measured x-ray diffraction to determine temperature and finite element analysis to interpret the experimental data. We find a complex relationship between apparent temperatures and sample temperature distributions that must be accounted for to adequately interpret the data, including beam averaging effects, multivalued temperatures due to sample phase transitions, and jumps and gaps in the observable temperature near phase transformations. The results have implications for studies employing x-ray probing of systems with large temperature gradients, particularly where these gradients are produced by the beam itself. Finally, this study shows the potential complexity of studying nonlinear sample behavior, such as phase transformations, where biasing effects of temperature gradients can become paramount, precluding clear observation of true transformation conditions.

Split of the pseudocritical temperatures of chiral and confinement-deconfinement transitions by a temperature gradient

Searching of the critical endpoint (CEP) of the phase transition of quantum chromodynamics (QCD) matter in experiments is of great interest. The temperature in the fireball at a collider is location dependent, however, most theoretical studies address the scenario of uniform temperature. In this work, the effect of temperature gradients is investigated using lattice QCD approach. We find that the temperature gradient catalyzes chiral symmetry breaking, meanwhile the temperature gradient increases the Polyakov loop in the confined phase but suppresses the Polyakov loop in the deconfined phase. Furthermore, the temperature gradient decreases the pseudocritical temperature of chiral transition but increases the pseudocritical temperature of the confine-deconfine transition. It is also found that the temperature gradient can drive the system away from the singularity, implying that the CEP in the T−μ plane may move in the direction of the first-order phase transition in the phase diagram due to the temperature gradient. Published by the American Physical Society 2024

Theoretical study on the effect of temperature gradient on contact-free scanning for scanning ion conductance microscopy

Scanning ion-conductance microscopy (SICM) is a non-contact, high-resolution, and in-situ scanning probe microscope technique, it can be operated in probing the physical and chemical properties of biological samples such as living cells. Recently, using SICM to study the effects of microenvironment changes such as temperature changes on response of the biological samples has attracted significant attention. However, in this temperature gradient condition, one of the crucial but still unclear issues is the scanning feedback types and safe threshold. In this paper, a theoretical study of effect of the temperature gradient in electrolyte or sample surface on the SICM safe ion-current threshold is conducted using three-dimensional Poisson-Nernst-Planck, Navier-Stokes and energy equations. Two temperature gradient types, sample surface and two types of pipettes with different ratio of inner and outer radii are included, respectively. The results demonstrate that the local temperature of the electrolyte and then sample surface significantly affect the ion flow, shape of the approach curves and thus safe threshold in SICM pipette probe for contact-free scanning. There is a current-increased and decreased phases for approaching the surface with higher temperature and two current-decreased phases for surface with lower temperature. Based on this shape feature of approach curves, the change rate of current is analysis to illustrate the possibility for contact-free scanning of slope object. The results indicate that with the decrease of the normalized tip-surface distance, the coupling effect of large slope angle and local high temperature makes the increase in change rate of ion current not significant and then it challenging to realize contact-free scanning especially for higher surface temperature.

A vertically non-uniform temperature approach for the friction term computation in depth-averaged viscoplastic lava flows

Recently, depth-averaged shallow flow models have been adapted to modelling liquefied lava flows, generally characterized by a marked temperature-dependent non-Newtonian rheology. Modelling these complex flows requires to include the effects of the depth-averaged temperature gradients in the governing equations. The most significant term to correctly predict the lava mobility is the flow resistance term, which is widely estimated using the linear viscoplastic Bingham model. This non-Newtonian model allows to relate the bed shear stress to the depth-averaged lava flow features by means of a cubic equation with analytical solution when assuming a uniform temperature distribution along the vertical profile. Nevertheless, the lava temperature is non-uniform along the vertical due to the heat transfer at the bottom and the free surface, and hence the classical cubic Bingham model is not valid anymore. In this work, a depth-averaged shallow flow model is adapted for realistic lava flows considering influence of the non-uniform vertical temperature profile in the non-Newtonian resistance. This requires to modify the rheological viscoplastic models for ensuring the coupling between flow dynamics and temperature evolution. Three non-uniform temperature vertical distributions are considered: linear, piece-wise and diffusion profiles. Synthetic tests are used to show the influence of the temperature vertical profile on the numerical results. Furthermore, laboratory experimental data are used to validate this novel viscoplastic resistance formulation and to show that the calibration of its parameters is possible.

Integrated transcriptomic and epigenomic analyses to disclose the transcriptional regulatory mechanisms of lipid and energy metabolism under cold stress in grass carp

Cold-induced injuries significantly restrict the potential and efficacy of suivival and growth, necessitating a deeper understanding of cold response in ectothermic fish. Understanding the mechanisms by which fish respond to low-temperature stress has thus become a critical research focus in aquaculture. This study aims to investigate the effects of different temperature gradients (28 °C, 10 °C, and 2 °C) on global gene transcription in grass carp Ctenopharyngodon idellus. Additionally, the study examines cold-induced chromatin accessibility and transcriptional regulation through an integration of RNA sequencing (RNA-seq) and assay for transposase-accessible chromatin using sequencing (ATAC-seq) analyses. Transcriptome analysis revealed that mitochondrial damage and endoplasmic reticulum stress are major factors contributing to grass carp mortality under cold stress. The dataset also disclosed hepatocyte nuclear factor 1 beta (Hnf1b) and peroxisome proliferator-activated receptor alpha (PPARa) as key transcription factors for lipid and energy metabolism in grass carp under cold stress. Notably, Hnf1b and PPARa form a complex transcriptional regulatory network with other transcription factors, decreasd binding activity inactivates the expression of genes related to lipid and energy metabolism under cold stress. These results highlight the transcriptional regulation of lipid and energy metabolism in response to cold stress in grass carp. Overall, this study enhances our understanding of low-temperature response mechanisms in grass carp, providing valuable insights for further investigations.

The effect of vertical temperature gradient on the equivalent depth in thin atmospheric layers

AbstractThe equivalent depth of an atmospheric layer is of importance in determining the phase speed of gravity waves and characterizing wave phenomena. The value of the equivalent depth can be obtained from the eigenvalues of the vertical structure equation (the vertical part of the primitive equations) where the mean temperature profile is a coefficient. Both numerical solutions of the vertical structure equation and analytical considerations are employed to calculate the equivalent depth, , as a function of the atmospheric layer's thickness, . Our solutions for layers of thickness 100 2000 m show that for baroclinic modes, can be over two orders of magnitudes smaller than . Analytic expressions are derived for in layers of uniform temperature and numerical solutions are derived for layers in which the temperature changes linearly with height. A comparison between the two cases shows that a slight temperature gradient (of say 0.65 K across a 100 m layer) decreases by a factor of 3 (but can reach a factor of 10 for larger gradients) compared with its value in a layer of uniform temperature, while a change of 10 K in the layer's uniform temperature hardly changes . The baroclinic mode exists in all combinations of boundary conditions top and bottom while the barotropic mode only exists when the vertical velocity vanishes at both boundaries of the layer.

Effect of Membrane Thickness and Operating Conditions on PEMFC Limiting Current Analysis

Hydrogen powered proton exchange membrane fuel cells (PEMFC) have great potentials to replace the traditional internal combustion engines due to its inherent advantages of zero greenhouse gas emissions, better fuel efficiency, quick startup, silent operation, less required maintenance, etc. In a PEMFC, oxygen transport is a critical performance limiting factor because of the sluggish oxygen reduction reaction kinetics. Limiting current method is a well-established in-situ diagnostic tool to measure the oxygen transport resistance in a PEMFC. To obtain accurate oxygen transport resistances, a few key assumptions need to be made including: (1) the effect of temperature gradient in the diffusion media is negligible, (2) no convective flow in the porous media, (3) oxygen is diluted in a gas mixture of nitrogen and water vapor, (4) the total oxygen transport resistance combines gas diffusion layer, microporous layer, and catalyst layer, (5) the effect of membrane thickness has negligible effect, and (6) the anode side does not affect the measurement results due to fast hydrogen oxidation reaction. In this study, we perform a systematic study of the effect of membrane thickness and operating conditions on obtaining robust and reliable limiting current measurement. Standard Nafion membranes of three different thicknesses (25, 50, and 85 µm) are tested with Toray 060 and Freudenberg H23C8 diffusion media. In addition, we further study the interaction between membrane thickness and asymmetric pressure and relative humidity and their effects on limiting current results. Our results show that membrane thickness and relative humidity are critical factors in obtaining reliable oxygen transport resistance due to their effect on overall water balance in the cell. Lastly, the experimental data are compared with the simulation results to establish fundamental understanding. Detailed experimental and analytical results will be presented at the conference.

Influence of packing height on the pyrolysis products of Jimsar (China) oil shale

AbstractThe effect of particle packing height (10, 30, 50, 70 mm) on the yield and composition of oil shale pyrolysis products is investigated. The results show that the oil yield could decrease 1.0% and the noncondensable gases yield could increase 0.5% as the oil shale packing height increased from 10 to 70 mm. The main hydrocarbon gases are C1–C6 gases, and the increase of packing bed height could decrease the relative content ratio of alkanes to alkenes in hydrocarbon gases. The primary components of the derived oil are aliphatic compounds, aromatic compounds, and compounds containing heteroatoms in the carbon atoms range of C6–C28. And the hydrogen type of shale oil is mainly composed of methylene groups (about 70%) with longer alkyl chains, and CH3 in aromatics, cycloalkanes, and alkanes. The chemical composition and hydrogen type have certain regularity changes with the changing of packing height, attributing to the effect of temperature gradients between surface and center of packing bed, and the diffusing time of products through the packing bed.

Investigation of temperature gradient effects and effective thermal inertia during adiabatic decomposition of substances with varying exothermic characteristics

To further study adiabatic parameters distortion, the adiabatic decomposition of 2,4-DNT, 20%DTBP, and 45%Glucose was systematically analyzed using thermal analysis calorimetry and numerical simulation methods. The study revealed the variation laws and influence mechanisms of the temperature gradient effects and thermal inertia in adiabatic systems. A numerical model for decomposition in a closed adiabatic system was developed by integrating the apparent kinetics into the CFD code. The results show that the temperature gradient effects during adiabatic decomposition initially increase and then decrease until reaching zero. The temperature gradient effects become more pronounced as the exothermic characteristics of substances increase. They are the most significant at the peak self-heating rate, with gradients of 182.4 °C·cm−1, 21.6 °C·cm−1, and 0.78 °C·cm−1, respectively. Specific data segments for adiabatic analysis should maintain α values below 0.138 for 2,4-DNT, 0.484 for 20%DTBP, and should utilize complete 100 % adiabatic data for 45%Glucose, aiming to mitigate potential distortion in adiabatic parameters. Furthermore, Фeff varies with the reaction, initially increasing and then decreasing in deviation from the theoretical value, with peak deviations of 60 %, 20 %, and 0.3 % for three substances, respectively. These findings lay the foundation for further optimizing the temperature gradient effects and establishing a dynamic Фeff correction model.

Effect of temperature gradient on the chemical structure and physical morphology of polyacrylonitrile fibers during thermal stabilization process

The thermal stabilization process is a crucial stage for microstructure transformation and quality of carbon fibers, which is determined by the stabilization temperature gradient. In this work, the effect of the temperature gradient on the evolution of both chemical structures and physical morphology of polyacrylonitrile (PAN) fibers at multistage of thermal stabilization process was investigated. Combined with functional groups, oxygen element content, and aromatization index, increasing temperature reasonably shifted oxidation and cyclization reaction into early stage and the corresponding samples possessed relatively large degree of cyclization. It was worth noting that high stabilization temperature gradient could accelerate the formation of the conjugated structures at early stage and facilitate the cyclization reaction in the stabilized fibers. As for morphologies, there were aligned microfibrils and transvers lamellae in stabilized fibers. Their radial structure difference increased firstly and then decreased in the later stage. The tensile strength and tensile modulus decreased during the thermal stabilization process. Moreover, increasing temperature resulted in reduction of tensile strength and tensile modulus, which was mainly resulted by the high degree of cyclization instead of structural defects. These results guide the design and optimization of temperature program and adjusting the processing parameters for all commercially PAN fibers without any additional conditions.

Combined effect of Ag element and temperature gradient on the formation of highly orientated Sn grains in micro solder joints

Sn–Ag solders are widely used for advanced electronic packaging. The combined effect of Ag element and temperature gradient (TG) on the formation of Sn grains in Cu/Sn-xAg/Cu micro solder joints was elucidated systematically. Numerous small-sized β-Sn grains were formed in both Cu/Sn/Cu and Cu/Sn-0.5Ag/Cu micro solder joints after reflow with or without TG. The Cu/Sn-0.5Ag/Cu joint was found to have more twinning β-Sn structures. The formation of the multiple β-Sn grains in these two joints was attributed to the presence of multiple tetrahedral metastable short-range order (SRO) structures which acted as nuclei for the nucleation and growth of β-Sn. The existence of TG slightly enhanced the preferred orientation characteristics of Sn grains. For the joints with Ag content was or higher than 2 wt%, several Sn grains were formed without TG, while a single or highly oriented Sn grains were observed with TG. The number and orientation of Sn grains were affected by the combined effect of Ag element and TG significantly. The β-Sn grains formed without TG were based on the {101} type cyclic twinning configuration clusters that stabilized by Ag atoms and acted as nuclei. The formation of a single or highly preferred β-Sn grains was benefit from the combined effect of Ag element and TG. The results provide theoretical guidance for optimizing the composition of Sn–Ag solders and controlling the microstructure of the joints, thereby contributing to the advancement of electronic packaging technologies.

METHODS OF REDUCING THE INFLUENCE OF TEMPERATURE GRADIENTS ON THE SENSITIVITY OF FIBER-OPTIC GYROSCOPE

Thermally induced error is one of the main limitations of the sensitivity of fiber-optic gyroscopes (FOGs). The analysis of thermal sensitivity of FOG is based on the study of the Shupe effect and the elastic-optical effect in the fiber circuit. The main requirement in this case is to preserve the principle of reciprocity for rays propagating in opposite directions of the fiber circuit. It was determined that the thermally induced phase difference of these rays should not exceed ∆φ(t) ≈ 10-7 rad. To reduce the thermal sensitivity of FOG, various methods are used, including quadrupole methods of winding the fiber circuit, using frameless coils, as well as coils made of special materials. Considerable attention is paid to improving the properties of fiber and adhesive compounds to minimize the effect of temperature on the optical-physical characteristics of these components of the fiber circuit. The article examines the advantages and disadvantages of each of the methods of compensating the thermally induced error of FOG. Analytical relations characterizing the effect of temperature gradients on the sensitivity of measuring angular velocity and Sagnac phase when using FOG are given. Part of the methods for solving this problem are discussed in this article. However, the elemental base and FOG signal processing tools are constantly being improved, the transition to integrated optical technologies is being carried out, which opens up new ways to increase the sensitivity of the FOG with minimal costs. On the basis of the conducted research, practical recommendations are given to reduce the influence of temperature gradients on the sensitivity of FOG. The work can be useful for specialists working in the field of FOG design.