Temperature Gradient Conditions Research Articles

Spatial distribution characterization of the Temperature-induced gradient viscoelasticity inside asphalt pavement

Under the influence of continuous periodic changes of various meteorological factors, there will be an inhomogeneous temperature field inside the asphalt pavement, which will cause a continuous gradient viscoelasticity of asphalt concrete with depth. In order to perform the structural mechanics analysis accurately, the temperature field gradient effect and the temperature-induced gradient viscoelasticity distribution inside the asphalt pavement should be revealed first. In this research, based on the heat conduction theory, a temperature field finite element analysis (FEA) model of a semi-rigid base asphalt pavement was established to investigate the distribution behavior of the temperature gradient along the depth. Dynamic modulus tests were conducted to survey temperature effect on the viscoelastic parameters of asphalt concrete. Eventually, the intrinsic relationship between temperature, depth, and viscoelastic parameters was integrated, and the relaxation time shift method was proposed to quantitatively characterize the temperature-induced gradient viscoelasticity at different depths. It is found that the temperature varies in a cubic parabolic fashion along the depth under the most significant positive and negative temperature gradient conditions. The relaxation time shift method can be effectively used to characterize the distribution of the relaxation modulus and relaxation time spectrum of asphalt concrete under the influence of temperature. It is easy to be programmed to fully consider the inhomogeneous temperature field, and applicable to both traditional and gradient FEA. The change of parameters of generalized Maxwell model for asphalt concrete with temperature is essentially the result of relaxation spectrum shifting along the relaxation time axis at different temperatures. When the temperature is high, the viscosity decreases, the relaxation spectrum shifts to the direction of decreasing relaxation time, the relaxation modulus of asphalt concrete decreases, and vice versa.

Anisotropic Thermal Expansion and Electronic Structure of LiInSe2.

Optical quality cm-sized LiInSe2 crystals were grown using the Bridgman–Stockbarger method, starting from pure element reagents, under the conditions of a low temperature gradient of 5–6 degrees/cm and a slight melt overheating. The phase purity of the grown crystal was verified by the powder XRD analysis. The thermophysical characteristics of LiInSe2 were determined by the XRD measurements in the temperature range of 303–703 K and strong anisotropy of the thermal expansion coefficients was established. The following values of thermal expansion coefficients were determined in LiInSe2: αa = 8.1 (1), αb = 16.1 (2) and αc = 5.64 (6) MK−1. The electronic structure of LiInSe2 was measured by X-ray photoelectron spectroscopy. The band structure of LiInSe2 was calculated by ab initio methods.

Effect of Temperature Gradient on Chloride Ion Diffusion in Nuclear Reactor Containment Building Concrete

Chloride diffusion through concrete is influenced by harsh environmental conditions such as high ambient temperature and relative humidity. This paper examined the influence of temperature gradient on chloride diffusion in concrete under high ambient temperature conditions. Chloride diffusion tests using cylindrical concrete samples were performed in constant temperature and temperature gradient conditions. In a temperature gradient condition, a much higher chloride concentration was measured than at constant temperatures, which could not be explained only by the mass diffusion driven by the concentration gradient. A new analytical model of chloride diffusion with the mass diffusion term including the temperature effect and the thermo-diffusion term including the temperature gradient effect was applied to the results, which showed that the thermo-diffusion contribution was significant. Using the analytical model with the mass diffusion (DCl) and thermo-diffusion (DT) coefficients, the service life of reactor containment buildings (RCBs) in nuclear power plants (NPPs) in the Middle Eastern and North African (MENA) region was estimated. The results showed that the service life of the RCBs could be reduced by the temperature gradient, indicating the possible application of the proposed analytical model.

Flame dynamics of premixed CH4/H2/air flames in a microchannel with a wall temperature gradient

The effect of hydrogen (H2) addition on the flame dynamics of premixed methane/air mixtures in a microchannel was investigated through two-dimensional numerical computations using a detailed chemistry model. Detailed numerical simulations were performed in a 2 mm diameter tube with 120 mm length and a hyperbolic wall temperature gradient condition. All numerical computations were performed at stoichiometric mixture conditions with a fixed inlet velocity of 15 cm/s. Flame repetitive extinction and ignition (FREI) has been observed to appear at various mixture conditions. The frequency of FREI shows a non-monotonic variation for CH4/air mixtures with H2 addition. The time taken for completion of one FREI cycle increases with H2 addition. The maximum temperature and heat of the reaction were observed to decrease with hydrogen addition. The effect of diameter on the FREI cycle was studied by comparing the numerical results for 1, 1.5, and 2 mm diameter tubes. As the diameter is reduced from 2 mm to 1 mm, the FREI frequency increased, and the maximum temperature decreased owing to increased heat loss through channel walls. The location of the ignition and extinction shifted downstream for 1 mm tube, as compared to a 2 mm diameter tube.

Friction stud riveting (FSR) of thick high-strength aluminum alloy structure

7-series aluminum (Al) alloy is a promising material that can meet the ever-increasing lightweight demand for transportation tools. However, the assembly between Al alloy and steel components brings challenges to the existing stud pre-embedded technology. This study proposes a friction stud riveting (FSR) process to achieve high-performance and high-efficiency embedding of steel studs in Al alloy parts by shank undercut, grooves interlock, and intermetallic compounds bonding. The stud geometry and FSR process were first optimized by evaluating the macro morphology of the joints. Then, the microscopic characterizations were performed to understand the material flow behavior, plastic deformation, and microstructure evolution of the joint induced by the feeding and rotation of the stud. The results indicate that the transient thermo-mechanical coupled FSR process leads to a continuous transition of sliding, mixed sliding-sticking, and sticking contact conditions between the stud and the Al alloy, resulting in a thermo-mechanical affected zone (TMAZ) outside the stud and a trapped Al alloy (TAA) inside the stud with diverse dynamic recrystallization (DRX) states and microstructures. The rotation state evolution and temperature gradients of the material within the TAA create two DRX bands that dominate the fracture behavior of TAA under tensile and shear loads. The strengths of the optimized steel stud-thick Al FSR joints reach 101.3% and 118.5% of the 7A52 Al alloy base material in tensile and shear tests, respectively, which solves the problem of low joining strength between steel stud and Al alloy plate due to the brittle and thick intermetallic compounds layers in conventional stud welding processes.

Towards green energy for sustainable development: Machine learning based MPPT approach for thermoelectric generator

The rapidly increasing demand for electrical energy and the depletion of fossil fuels ignited research in renewable energy generation and management. Thermoelectric generation (TEG) systems as a green energy resource are designed to recover waste heat recovery. Concentrated solar tackles the disadvantages of low power generation efficiency. This paper investigates the feasibility of using machine learning (ML) based MPPT technique, to harvest maximum power of a centralized TEG system under various operating conditions. The environment-dependent issues such as the non-constant distribution of heat, loss to the heat transfer coating between sinks and sources, and mechanical faults create non-uniform current generation and impedance mismatch causing power loss. In this article, we have proposed a feed-forward neural network (FNN) trained by a novel flow direction algorithm (FDA) with a tuned PID controller to harvest the energy under non-uniform temperature gradient conditions. The non-uniformity of physical conditions generates multiple local maxima's (LMs) in electrical characteristics of TEG systems. Common gradient-based MPPT techniques are unlikely to track true GMPP. As a solution to this non-linear problem, novel FNN-FDA is tested under non uniformly distributed temperature (NTUD) over heat source surfaces under varying load and temperature conditions. In this study, certain contributions to the field of TEG systems were made by tackling the issues such as GMPP tracking, low efficiency, and oscillations around GMPP. The results are compared to the particle swarm optimization (PSO), Barnacle mating optimization (BMO), and grey wolf optimization (GWO) algorithm. Five experiments under different weather conditions are performed. Results are validated and proved with experiments and MATLAB/SIMULINK. The experimental results demonstrated that FNN-FDA performs significantly better when compared with other control techniques.

New coal-charging method: analysis of force characteristics and velocity distribution of coal particles with dense phase continuous flow in cylinder

ABSTRACT Low-moisture coal used in coking has the advantages of increasing production capacity and reducing power consumption but produce a lot of dust during coal charging. A new method of coking coal charged into top-charge coke oven was built, in which the cylinder with telescopic and high-temperature resistant was used to realize the coal flow as dense phase continuous. Based on the 400 kg top-charged coke oven, theoretical analysis, calculation, and numerical simulation were used to study the forces and motion of coal particles under the conditions of temperature gradient. The temperature distribution and particle motion characteristics were simulated by FLUENT when the distance between the coal outlet and the bottom of the coking chamber is 0 mm, 0.5 m, 0.7 m, and 0.9 m. The results show that the dust formed by coal particles was mainly affected by thermophoretic force and air resistance. In the non-uniform temperature field, the radiative heat transfer drop reduces the deposition rate of coal particles. The initial thermal migration velocity of particles in the lower part of the coking chamber is 0.4 m/s, and that of particles in the upper is only 0.1 m/s. As the temperature gradient of coking chamber tends to be uniform, the thermal velocity of particles gradually stabilizes. After the time of particles in the furnace exceeds 0.5 ~1s, the thermophoretic velocity of each part tends to be the same. There was no dust escapes from the coal charging hole during the cylinder lifting process, the escape velocity of dust was controlled below 0.4 m/s by new method. Through simulation and experiment, the simulation results were similar to the experimental when the distance between coal outlet and the bottom of coking chamber is 0 m and 0.7 m, and the maximum error is less than 0.1.

Regularities of Martensitic Transformations of Fe–Ni Alloys Rapidly Quenched from Melt

The regularities of formation of the grain structure of metastable iron–nickel alloys formed in conditions of high temperature gradients during the melt hardening (spinning) and its effect on the characteristics of martensitic transformations (MT) in local areas of thin ribbons are reviewed and studied. A comparison of the texture of the austenitic and martensitic phases on different sides of thin ribbons is carried out. The consequences of influence of relaxation processes in hardening of thin ribbons on regularities of formation of the grain structure are investigated. The proposed x-ray method of measuring the amount of martensite allows solving the problem of measuring the amount of martensite in the local areas of textured alloys. As established, the completeness of MT is different for the contact and free sides of the ribbon. The main factors, which determine the heterogeneous distribution of the martensitic phase in the local areas of the ribbon, are analysed. The size effects at MP, residual stresses, and changes in the chemical composition of the austenitic phase on the distribution of the martensitic phase in local sections of the ribbon are analysed. The influence of size effect on the direct γ–α- and reverse α–γ-MT in thin ribbons is studied. The role of ultradispersed component of austenitic grains in the stabilization of austenite of rapidly quenched alloys with cyclic γ–α–γ MT is revealed.

Distribution Characteristics of the Plasma Irregularities Inside the Mid‐Latitude Ionospheric Trough Based on Swarm In Situ Measurements

AbstractA large number of studies have confirmed the frequent occurrence of mid‐latitude trough irregularities (MTI), but the distribution characteristics of these irregularities are still pending. Based on the Swarm in situ plasma measurements from 2014 to 2020, the dependences of MTI on magnetic local time, season, solar flux, and geomagnetic activities are analyzed. The results show that for the irregularities with scale‐size of about 7.5–75 km. (a) Geomagnetic activity has an obvious inhibitory effect on the formation of MTI, regardless on the dayside or nightside. (b) The daytime MTI occurrence rate is significantly higher than that at nighttime, and the difference between the poleward wall and equatorward wall during daytime is higher than that at nighttime. (c) The dayside MTI occurrence rate appears highest in winter and lowest in summer, but the nightside MTI occurrence rate appears highest in equinoxes and lowest in winter. (d) The nightside MTI show lower occurrence rate under high solar activity conditions, but no obvious solar activity influence is shown on the dayside. It is suggested that the temperature gradient instability plays an important role in causing the seasonal effect of the nightside MTI, but cannot directly support the solar activity effect. The relatively low nightside MTI occurrence rate in high solar activity years probably results from the relatively small electron temperature gradient. It is speculated that the formation of nightside MTI not only requires the antiparallel conditions of density gradient and temperature gradient, but may also needs to meet the enough large magnitude of the two gradients.

Growth of BPO4 Crystals in Low Temperature Gradients

AbstractThe method of synthesis of a monophase boron phosphate (BPO4) powder has been refined. Single crystals of BPO4 free from solvent inclusions and cracks have been obtained by the top‐seeded solution growth technique with the seed orientation [010]. The growth is carried out under conditions of a low axial temperature gradient in the melt‐solution, which is varied in the range of 1–4°C cm−1. The value of the temperature gradient that promotes the growth of defective crystals is determined. The absorption spectra and optical homogeneity of crystals are studied. The chemical composition of polycrystalline BPO4 is studied using inductively coupled plasma mass spectrometry. The purity of the synthesized powder is better than 4 N.

Interpreting Observed Temperature Probability Distributions Using a Relationship between Temperature and Temperature Advection

Abstract The nonnormality of temperature probability distributions and the physics that drive it are important due to their relationships to the frequency of extreme warm and cold events. Here we use a conditional mean framework to explore how horizontal temperature advection and other physical processes work together to control the shape of daily temperature distributions during 1979–2019 in the ERA5 dataset for both JJA and DJF. We demonstrate that the temperature distribution in the middle and high latitudes can largely be linearly explained by the conditional mean horizontal temperature advection with the simple treatment of other processes as a Newtonian relaxation with a spatially variant relaxation time scale and equilibrium temperature. We analyze the role of different transient and stationary components of the horizontal temperature advection in affecting the shape of temperature distributions. The anomalous advection of the stationary temperature gradient has a dominant effect in influencing temperature variance, while both that term and the covariance between anomalous wind and anomalous temperature have significant effects on temperature skewness. While this simple method works well over most of the ocean, the advection–temperature relationship is more complicated over land. We classify land regions with different advection–temperature relationships under our framework, and find that for both seasons the aforementioned linear relationship can explain ∼30% of land area, and can explain either the lower or the upper half of temperature distributions in an additional ∼30% of land area. Identifying the regions where temperature advection explains shapes of temperature distributions well will help us gain more confidence in understanding the future change of temperature distributions and extreme events.

Effects of temperature gradient on the granite’s mechanical properties

Temperature gradient significantly affects the production of surrounding rock stress in mining engineering. The mechanics and deformation characteristics of the rock will change under the temperature gradient, thereby increasing the probability of accidents in the roadway. This paper conducts uniaxial compression tests on granite at different temperatures from room temperature to 250∘C, and analyzes in detail the changes in the stress-strain curve, peak stress, peak strain and tangent modulus of granite under high temperature and different temperature gradient conditions. The results of this study are as follows: (1) Under high temperature conditions, the granite’s peak stress and tangent elastic modulus increased with temperature from 17 to 100∘C, then decreased from 100∘C to 250∘C, whereas the granite’s peak strain increased steadily with increasing temperature; (2) under temperature gradient, the granite’s peak stress and tangent modulus first decreased and then increased with increasing temperature gradient, while the granite’s peak strain first decreased and then increased at 100∘C, but first increased and then decreased from 150∘C to 250∘C.

Diagnosis and modelling of two destructive derecho events in European Russia in the summer of 2010

In the summer of 2010, European Russia experienced an unprecedented high air temperature, catastrophic wildfires, heavy air pollution, but also several severe convective storms. Two of them occurring on June 27 and July 29 had a particularly high intensity and resulted in unprecedented forest damage. In this study, we estimate storm-related forest damage using Landsat images and analyse the synoptic-scale and mesoscale peculiarities of these storms formation and evolution using satellite and reanalyses data, surface observations, and mesoscale numerical simulation. The total area of stand-replacing windthrow caused by these two storms amounts to 1250 km2. We found for both events that dark-coniferous and pine forests were more impacted than deciduous and re-grown forests. Damage track length exceeds 500 km for one storm and 600 km for another; therefore, we classify them as derecho events, which are documented for the first time in Russia. Formation of both derecho-producing mesoscale convective systems (MCSs) was triggered by fast-moving waves formed on the polar front under conditions of substantial temperature gradients on a western flank of long-lived blocking anticyclones in their termination dates. Backward trajectories analysis shows that advection from the Caspian Sea was one of the sources of high atmospheric water content during the MCSs formation. Both MCSs developed within environments of moderate to strong convective instability and extremely high wind shear due to strong midlevel jet stream. We performed convection-permitting simulation of storms using the WRF model started with the initial data of CFSR and ERA5 reanalysis. For the event of June 27, the simulations with both initial conditions underestimate the maximum wind gusts since the model reproduces only a squall line without dominating derecho-producing storm. For the event of July 29, the ERA5 based simulation successfully reproduced the main features of the storm life cycle, while the CFS-based simulation substantially underestimated the wind gusts and the storm-affected area. Our results highlight the importance of the atmospheric blocking influence on the convective severe storms formation and development, which deserves further research.

Providing Energy Self-Sufficiency to LoRaWAN Nodes by Means of Thermoelectric Generators (TEGs)-Based Energy Harvesting

The aim of this paper is to present the viability of an energy-harvesting system prototype, based on thermoelectric generators (TEGs), to be embedded in a Long-Range Wide Area Network (LoRaWAN)-based wireless sensor node, allowing continuous quasi-real-time data transmission even for low temperature gradients and for frequent transmissions. To this end, an RFM95x LoRa module is used in the system. The energy management of the entire node is achieved by exploiting a nano power boost charger buck converter integrated circuit, which allows power extraction from the energy-harvesting source and, at the same time, regulates the charging/discharging process of a Li-Po battery that supplies the wireless node. The first phase of the project was dedicated to understanding the electrical characteristics of the TEG. A series of tests were performed to study the open circuit voltage, the current and the power generated by the TEG at different temperature gradients. Following this first phase, tests were then set up to study the charging/discharging process of the battery by changing two crucial parameters: the temperature between the faces of the TEG and the frequency of the transmissions performed by the transceiver. Experimental results show a positive balance for the battery charging at different conditions, which suggests two important conclusions: first of all, with high temperature gradients, it is possible to set relatively high transmission frequencies for the LoRaWAN module without discharging the battery. The second important consideration concerns the operation of the system at extremely low temperature gradients, with a minimum of 5 °C reached during one of the measurements. This suggests the usability of thermoelectric energy-harvesting systems in a wide range of possible applications even in conditions of low temperature gradients.

Thermo-chemo-mechanical stress analysis in a thin-electrolyte plate of all-solid-state battery

Stress fields of the electrolytes of all-solid-state batteries can be induced by several factors, such as temperature variations, lithium-ion distributions, and mechanical constraints. In this study, the thermo-chemo-mechanical stress field in an electrolyte was formulated using plate theory, assuming an infinite thin-electrolyte plate in a planar battery system. The stress fields were successfully calculated with consideration of property variations with temperature and lithium concentration under various conditions of temperature gradients, lithium concentration profiles, and mechanical boundary constraints. The extent to which the property variations affected the stress fields was also demonstrated. From these calculated stress distributions, an estimation method of the critical conditions for safe operation was proposed to limit maximum stress induced in electrolytes.

Effects of Climatic Conditions and Temperature Gradient on Jointed Plain Concrete Pavement Slabs

Abstract: A long lasting, reliable and economical transportation system is a critical component for the continuous movement of goods and services. Rigid pavements are widely used in construction world due to its high performance and serviceability. Traditional bituminous pavements and their needs for continuous maintenance and rehabilitation operations point towards the scope for cement concrete pavements. Cement concrete slab in a rigid pavement structure are exposed to different conditions at the surface in comparison to the bottom due to daily temperature fluctuations and results in the formation of temperature gradients in the slab. Transient gradients are due to the seasonal changes to which the slabs are subjected whereas permanent gradients are due to the slab condition during the setting of slab. The objective of this study is to determine the effect of temperature gradient and climatic conditions on a jointed plain concrete (JPC) pavement slab and to establish a proper temperature gradient chart which can be referred to depending on the climatic conditions existing in Kerala. A properly designed slab can reduce the formation of cracks and hence increase the life of slab. A detailed study in this area, can help in forming some codal provisions for the design of pavement slab depending upon the climatic conditions of Kerala. Keywords: Rigid Pavements, Bituminous pavements, Jointed Plain Concrete (JPC), Permanent gradients, Temperature Gradient

Thermodynamic test of Li2WO4 single crystals with low molybdenum doping: Enthalpy, interconnections, heat capacity

The thermodynamic test of Li2WO4 single crystals doping by low molybdenum content with special emphasis on investigation of interconnections, enthalpy, heat capacity to improve device portfolio was performed. We reduced doping content in 7 times for Li2W1-xMoxO4 in this investigation. The formation enthalpy of Li2WO4 was estimated using interconnections. The heat capacity was measured for Li2W1-0.025Mo0.025O4 single crystal (T = 320–997 K) by differential scanning calorimetry. There were no phase transitions of Li2W1-0.025Mo0.025O4 single crystal that made single crystals with low doping by molybdenum promising for application. The single crystal of lithium tungstate doped by 1.25% molybdenum (content was Li2W0.9875Mo0.0125O4) was grown by LTG CZ for the first time. The reaction enthalpies of Li2W0.9875Mo0.0125O4 single crystal were investigated by reaction calorimetry. The interconnections of formation enthalpies and lattice enthalpies of Li2W1-xMoxO4 in the range (x = 1–0.0125) from x were established. It indicated the growth of phenakite structure in the range. It was shown that under conditions of low temperature gradients it was possible to grow perfect single crystals of lithium tungstate with low doping of molybdenum.

Fabrication and Application of Single Crystal Fiber: Review and Prospective

AbstractThe state of the art of single crystal fiber (SCF) fabrication has evolved and improved over the last five decades. Nowadays, edge‐defined film‐feed growth, micro‐pulling down, and laser heated pedestal growth are three major techniques for the fabrication of SCF. Solid state crystal growth and temperature gradient technology are also very active recently making small size SCF. These optical fiber growth techniques are powerful material research tools employed globally for both scientific inquiry and practical applications. This article introduces the development of SCF growth techniques, with particular emphasis on recent practical applications including temperature sensing, radiation environment sensing, fiber laser and power delivery, chemical and medical application, imaging application, and piezoelectric application. In all cases, the application‐oriented point of view provides the reader with an up‐to‐date panorama of the vast possibilities offered by SCF. In the end, perspectives on the trends and future development of single crystal fibers are discussed.

Wind- and Wave-driven Ocean Surface Boundary Layer in a Frontal Zone: Roles of Submesoscale Eddies and Ekman-Stokes Transport

AbstractLarge-eddy simulations are used to investigate the influence of a horizontal frontal zone, represented by a stationary uniform background horizontal temperature gradient, on the wind- and wave-driven ocean surface boundary layers. In a frontal zone, the temperature structure, the ageostrophic mean horizontal current, and the turbulence in the ocean surface boundary layer all change with the relative angle among the wind and the front. The net heating and cooling of the boundary layer could be explained by the depth-integrated horizontal advective buoyancy flux, called the Ekman Buoyancy Flux (or the Ekman-Stokes Buoyancy Flux if wave effects are included). However, the detailed temperature profiles are also modulated by the depth-dependent advective buoyancy flux and submesoscale eddies. The surface current is deflected less (more) to the right of the wind and wave when the depth-integrated advective buoyancy flux cools (warms) the ocean surface boundary layer. Horizontal mixing is greatly enhanced by submesoscale eddies. The eddy-induced horizontal mixing is anisotropic and is stronger to the right of the wind direction. Vertical turbulent mixing depends on the superposition of the geostrophic and ageostrophic current, the depth-dependent advective buoyancy flux, and submesoscale eddies.

Iterative Finite Element Method Applied to the Nonlinear Electric Field of ±400kV Converter Transformer Barrier System

The DC steady-state and the polarity reversal (PR) are typical states of composite insulation in converter transformer barrier system, and the insulation medium has the strong E-field and temperature nonlinear characteristic, so the DC steady-state and polarity reversal E-field will be affected by the variation of electric parameters under temperature gradient. The FEM was applied to the quantitative E-field analysis considering electric and temperature nonlinear factors simultaneously. First, the nonlinear relationship between conductivity with E-field and temperature of medium has been obtained by experiments. Then, the iterative FEM was proposed and verified by coaxial insulation with analytical solution. Finally, the full-scale model of ±400kV converter transformer barrier system has been established, the DC steady-state and polarity reversal E-field has been calculated with the proposed method. The results show that under linear and nonlinear conditions the E-field is quite different, and E-field non-linearity can inhibit the local high electric spot, temperature non-linearity can reduce the E-field in the high temperature area and increase that in the lower temperature area. Under the temperature gradient condition, the local high E-field spot is easy to occur in the PR process. The iterative FEM and calculation results can provide references for the design of converter transformer barrier system.