Effect Of Temperature Gradient Research Articles

Assessment of thermo-mechanical fatigue in a nickel-based single-crystal superalloy CMSX-4 accounting for temperature gradient effects

Turbine blades are working under complex thermal gradient mechanical loading conditions. In the present study, a nickel-based single-crystal superalloy CMSX-4 is experimentally and computationally investigated under the thermo-mechanical fatigue (TMF) and thermal gradient mechanical fatigue (TGMF) loading conditions of the in-phase and out-of-phase thermal-mechanical angel. The fatigue life of TGMF with and without the thermal barrier coating was studied. It was confirmed that the lifetime of TGMF is affected by the temperature gradient significantly and substantially differs from conventional isothermal high temperature fatigue and thermo-mechanical fatigue. Since conventional fatigue models fail to characterize the TGMF, a modified model considers temperature gradient effects and thermal-mechanical phase angle and can describe the TGMF lifetime of the single-crystal superalloy reasonably.

A transient heat and moisture transfer model for building materials based on phase change criterion under isothermal and non-isothermal conditions

In this paper, a transient model for coupled heat and moisture transfer in building materials based on phase change criterion (PCC) was built. The PCC was introduced in both the energy conservation equation and the moisture conservation equation to simplify the model. The relations between PCC and usual material hygrothermal properties under isothermal and non-isothermal conditions were both derived to evaluate the effects of relative humidity, temperature and temperature gradient on the PCC. These relations enabled solving the problems that the empirical determination of the PCC was difficult and the existing models with a constant empirical value of PCC were inaccurate. The numerical results showed that the PCC was significantly affected by the sorption capacity. The effects of relative humidity, temperature and temperature gradient on the PCC could be ignored when the relative humidity in the cellulose insulation was less than 60%, and the PCC could be taken as a constant value of 1.0 within this relative humidity range. When the relative humidity in the cellulose insulation was larger than 60%, the model with the proposed expressions of PCC was more accurate than that with an empirical value of PCC for the hygrothermal performance analysis of the material.

A Study on Plume Dispersion Characteristics of Two Discrete Plume Stacks for Negative Temperature Gradient Conditions

The dispersion of air pollutants emitted from industries has been studied ever since the dawn of industrialisation. The present work focuses on investigating the effect of negative atmospheric temperature gradient and the plume stack orientation of two individual equal-height stacks on the vertical rise and dispersion of the plume. The study carried out upon three-stack layout configurations namely inline, 45° and non-inline, separated by an inter-stack distance of 12 times the exit chimney diameter (12 D) and 22 times the exit chimney diameter (22 D) in each case over the two temperature gradients of −0.2 K/100 m and −0.5 K/100 m. The turbulence is modelled using realisable k-ε model, a model used in the FLUENT flow solver. In the case of the inline configuration, the upwind plume shields its downwind counterpart, which in turn allows for higher plume rise at a given temperature gradient. The plume oscillates more in the case of inline than 45° and non-inline cases. Also, for a temperature gradient of −0.5 K/100 m, the plumes oscillate violently in the vertical direction, mainly because, with the initial rise of the plume, cold air from higher altitudes moves down and forms a layer of lower temperature closer to the ground. The present study is important to highlight the plume dispersion characteristics under negative temperature gradient conditions.

Vibrational frequencies of FG-GPLRC viscoelastic rectangular plate subjected to different temperature loadings based on higher-order shear deformation theory and utilizing GDQ procedure

In this study, the effect of nonlinear temperature gradient on the natural frequencies of functionally graded graphene platelets reinforced composite (FG-GPLRC) viscoelastic plate embedded in the visco-Pasternak foundation is examined on the basis of higher-order shear deformation theory (HSDT) numerically and analytically. By performing Hamilton’s principle, the governing equations of the system are obtained. And also, the viscoelastic properties of the structure are modeled based on the appropriate Kelvin–Voigt viscoelasticity model. Afterward, the deflection problem of the system as a function of time is solved according to the fourth-order Runge–Kutta numerical manner. Also, in order to obtain the numerical results, the generalized differential quadrature method (GDQM) is applied as a high accuracy numerical method. For validation, the calculated numerical results are compared with those reported in the engineering literature. Furthermore, to demonstrate the effects of various parameters on the response of the system, such as various patterns of temperature rise, the stiffness of the foundation, damper, and viscoelasticity constants, weight fraction, and distribution patterns of GPLs, a comprehensive parametric study is done. According to the results, an increment in the temperature difference leads to an increase in the absolute value of sensitivity for various distributions of temperature. Ascending the nonlinearity of the temperature distribution soars the rigidity of the system; consequently, contrary to the dimensionless vibrational frequency lessens the transverse displacement of the structure.

Analytical solution of elastic–plastic stress for double-layer FGM spherical shell subjected to pressure and temperature load

Elastic–plastic analysis of thick homogenous sphere which was coated internally with functionally graded materials (FGMs) subjected to the temperature gradient and pressure under the assumption of axisymmetric deformation is presented in this paper. As a novel idea, the elastic material properties of the composite at the inner and external radius of the FGM sphere are calculated based on the Mori–Tanaka method and the yield stress is varied according to the rule of mixture. Hence, the effective material properties of FGM coating as the power function of the radius are calculated based on the Mori–Tanaka method. Analytical equations for radial and circumferential stresses, radial displacement, and temperature are obtained. According to the analytical solution, the results of the numerical solution were examined which shows good agreement between the simulation and analysis results. Effects of internal pressure and temperature gradient on radial stress, circumferential stress, and radial displacement are investigated. Results show that as internal pressure increases, the maximum circumferential stress moves from the inner towards the external radius. It is also turned out that for low-temperature quantities, the sign of both radial and circumferential stresses is changed somewhere in the wall thickness of the sphere.

Pure thermal spin current and perfect spin-filtering with negative differential thermoelectric resistance induced by proximity effect in graphene/silicene junctions

The spin-dependent Seebeck effect (SDSE) and thermal spin-filtering effect (SFE) are now considered as the essential aspects of the spin caloritronics, which can efficiently explore the relationships between the spin and heat transport in the materials. However, there is still a challenge to get a thermally-induced spin current with no thermal electron current. This paper aims to numerically investigate the spin-dependent transport properties in hybrid graphene/silicene nanoribbons (GSNRs), using the nonequilibrium Green’s function method. The effects of temperature gradient between the left and right leads, the ferromagnetic exchange field, and the local external electric fields are also included. The results showed that the spin-up and spin-down currents are produced and flow in opposite directions with almost equal magnitudes. This evidently shows that the carrier transport is dominated by the thermal spin current, whereas the thermal electron current is almost disappeared. A pure thermal spin current with the finite threshold temperatures can be obtained by modulating the temperature, and a negative differential thermoelectric resistance is obtained for the thermal electron current. A nearly zero charge thermopower is also obtained, which further demonstrates the emergence of the SDSE. The response of the hybrid system is then varied by changing the magnitudes of the ferromagnetic exchange field and local external electric fields. Thus, a nearly perfect SFE can be observed at room temperature, whereas the spin polarization efficiency is reached up to 99%. It is believed that the results obtained from this study can be useful to well understand the inspiring thermospin phenomena, and to enhance the spin caloritronics material with lower energy consumption.

Investigation of Thermal Gradient Mechanical Fatigue Test Methods for Nickel-based Superalloys

Temperature gradients significantly affect the material fatigue process. A reliable and robust test procedure is needed for quantifying the effects of temperature gradients on the evolution of fatigue damage in nickel-based superalloys. The present study aims to develop a radiation heating system for universal material testing machine for simulating thermal gradient mechanical fatigue in turbines. The developed heating system mainly consists of halogen lamps, reflectors, cooling subsystems, and control units. Based on extensive experimental and computational investigations, a thermal model is developed for accurate thermo-mechanical fatigue testing under given temperature gradients in the heating system, and it is applied to variable temperature fatigue tests. The detail procedure for determining heat transfer coefficients is presented based on experimental and computational results. TGMF tests are successfully performed with the developed radiation heating system. The temperature gradients are found to reduce the TGMF life significantly in comparison to that of the TMF life. It is confirmed that the developed thermal gradient mechanical fatigue methodology can be applied to different thermo-mechanical fatigue tests with various temperature gradients.

Effects of Temperature Gradient on Electrical Tree Initiation and Breakdown Phenomenon in XLPE Under Harmonic Superimposed DC Voltage

In this article, the temperature of the needle tip and the ground electrode were changed to obtain different temperature gradients. The harmonic superimposed DC voltage was also simultaneously applied to study the electrical tree initiation, growth and breakdown characteristics in cross-linked polyethylene (XLPE) under the temperature gradient. The tree inception voltage, tree structure, tree length, accumulated damage (AD) and breakdown time were used to analyze the electrical tree degradation process. It was found that the greater the temperature gradient, the easier it is for electrical trees to be initialed which is related to the different charge behaviors affected by the trap distribution indicated by surface potential decay (SPD) results at different temperatures. With the temperature gradient increasing, the electrical tree length increases firstly but then decreases slightly when the temperature of the ground electrode is fixed, but the electrical tree length and AD increase linearly with the temperature gradient increasing when the temperature of the needle tip is fixed. The temperature rise of the ground electrode has a more serious impact on the safety of the insulation compared with the temperature rise of the needle tip. Positive DC bias voltage is more likely to cause damage and breakdown than negative DC bias voltage under the temperature gradient. These results indicate that the temperature gradient and harmonic superimposed DC voltage will promote the electrical growth in cable insulation, so special attention should be paid to the safety of electrical equipment under such special conditions.

Effects of gas temperature gradient on the accuracy of single-particle inductively coupled plasma (SP-ICP) measurements

A sheath gas device was used to show that the measured intensity of single particles depends on the radial position of the particles in the ICP central channel, which may result in inaccurate particle size determination at low observation positions.

The effect of urban temperature gradients on grassland microclimate amelioration in Los Angeles, USA

AbstractAimMicroclimate amelioration between neighboring plants may be more common in environments with greater abiotic stress. This pattern has been shown in deserts, alpine systems, and forests, but has not been explored along urban severity gradients. In this study we hypothesized that strong temperature gradients in the greater Los Angeles area might be driving changes in microclimate amelioration in annual grasslands.LocationTwenty‐seven sites along a 100‐km latitudinal, 72‐km longitudinal urban gradient across the greater Los Angeles area in California, USA.MethodsWe measured macro‐ and microclimate variables during the 2019 growing season. We took measurements of temperature, humidity, and vapor pressure deficit (VPD) at the site level as well as under grass canopies.ResultsWe found strong cooling effects of the vegetation during the day and warming effects from vegetation at night. We found that these effects were strongest on the hottest/driest days and at the hottest (and often most urban) sites.ConclusionsOur microclimate amelioration data suggest that positive interactions might become stronger along urban temperature gradients and may be determining plant interactions in these areas in a way that was not previously considered.

Investigation of the Battery Temperature Gradient and its Influence on Battery Aging from Different Thermal Management Methods Under the Application of Electric Tools

Due to its spatial efficiency, phase-change materials (PCMs) are particularly welcomed in the application of the electric tools where extremely high current at 10~15 C-rate is needed. With the Samsung 18650 20R Nickel-Cobalt-Manganese batteries, this study explores the temperature distribution from battery core to surface at extreme working current (15 C) with thermal conductive or storage wrapping materials including HDPE, thermal conductive sheet, thermal conductive adhesive, and PCMs. The proposed temperature distribution prediction model is validated with experimental data. The results indicate that the best battery surface temperature decrease is 18.60 ℃ when 2mm PCMs are applied. The discharge capacity of batteries is thus prolonged by 80-100 % compared to the naked battery cell. On the other hand, the battery core temperature reduction is much lower, only by 6.40 ℃ (from 139.70 ℃ to 133.29 ℃). Accordingly, the internal temperature gradient rises from 35.92 ℃ to 48.12 ℃. This is due to the heat generation exceeded the heat exported from the core to the outside under the 15C working condition of the electric tool. The study further evaluates the effects of high temperature gradient and finds that the capacity fade 90-250 % times faster with 2mm PCMs wrapping.

Temperature Field and Gradient Effect of a Steel‐Concrete Composite Box Girder Bridge

To study the effect of the temperature field and gradient of a steel‐concrete composite box girder bridge, a 5 × 35 continuous composite box girder bridge is used as the research object. The temperature measuring point is set by selecting a typical cross section, and the temperature change data are measured. The temperature field of the different positions in the composite box girder bridge is studied, the global and local temperature differences are compared, and the law of temperature distribution and the main factors affecting the temperature field are formulated. The most unfavourable expression function of the vertical temperature gradient of the section is simulated using the measured data, the existing standard temperature gradient mode is compared, the finite element model of the bridge is established, and the influence of the actual temperature gradient mode on the stress and deformation of the composite girder is further analysed. The conclusions show that the temperature differences of different azimuth sections and the local temperature differences between the steel and concrete joint parts of the steel‐concrete composite box girder bridge are not significant. The temperature gradient heating and cooling model fitted by the measured temperature field can be used as a reference for the structural design of similar local bridges.

Suppression of ice nucleation in supercooled water under temperature gradients

Understanding the behaviours of ice nucleation in non-isothermal conditions is of great importance for the preparation and retention of supercooled water. Here ice nucleation in supercooled water under temperature gradients is analyzed thermodynamically based on classical nucleation theory (CNT). Given that the free energy barrier for nucleation is dependent on temperature, different from a uniform temperature usually used in CNT, an assumption of linear temperature distribution in the ice nucleus was made and taken into consideration in analysis. The critical radius of the ice nucleus for nucleation and the corresponding nucleation model in the presence of a temperature gradient were obtained. It is observed that the critical radius is determined not only by the degree of supercooling, the only dependence in CNT, but also by the temperature gradient and even the Young’s contact angle. Effects of temperature gradient on the change in free energy, critical radius, nucleation barrier and nucleation rate with different contact angles and degrees of supercooling are illustrated successively. The results show that a temperature gradient will increase the nucleation barrier and decrease the nucleation rate, particularly in the cases of large contact angle and low degree of supercooling. In addition, there is a critical temperature gradient for a given degree of supercooling and contact angle, at the higher of which the nucleation can be suppressed completely.

The effect of temperature gradient on the heavy quark–antiquark potential using a gravity dual model

Abstract Thermal systems have traditionally been modeled via Euclideanized space by analytical continuation of time to an imaginary time. We extend the concept to static thermal gradients by recasting the temperature variation as a variation in the Euclidean metric. We apply this prescription to determine the quark–antiquark potential in a system with a thermal gradient. A naturally occurring QCD medium with thermal gradients is a quark–gluon plasma (QGP). However, the QGP evolves in time. Hence, we use a quasi-stationary approximation, which is applicable only if the rate of time evolution is slow. The application of our proposal to a quark–antiquark potential in QGP can be seen as a step towards a more exact theory that would incorporate time-varying thermal gradients. The effect of a static temperature gradient on the quark–antiquark potential is analyzed using a gravity dual model. A non-uniform black string metric is developed by perturbing the Schwarzschild metric, which allows us to incorporate the temperature gradient in the dual anti-de Sitter space. Finally, an expression for the quark–antiquark potential in the presence of a static temperature gradient is derived.

From thin films to shaped platelets: effects of temperature gradient on SnS synthesis

In this work, we studied the synthesis and properties of SnS thin films and platelets obtained by vapor phase deposition under controlled pressure. Two morphological types are obtained in the same process depending on the absolute temperature and the temperature gradient inside the reactor. The growth of isolated platelets is favored by a small temperature gradient between the sublimation and deposition regions of the deposition chamber. Films are formed when there is a large temperature gradient. Raman spectroscopy and energy dispersive spectroscopy analysis were used to identify the phase of the synthesized samples, and polarized Raman spectroscopy and X-ray diffraction analysis helped us confirm the crystallographic orientation of the isolated platelets. We have carried out studies on the crystallographic shape and orientation of orthorhombic isolated platelets using optical microscopy, scanning electron microscopy and surface energies of the crystalline planes of SnS.

Fabrication and Thermal Degradation Kinetics of PBT/BEO/Nano-Sb2O3 Composites

Developing polybutylene terephthalate (PBT) with high thermal stability and flame-retardant properties is crucial for automotive, biomedical devices, electronics, and other fields. Herein, we focus on a PBT/brominated epoxy resin (BEO)/nano-Sb2O3 composites by a melt-blending method. The effects of heating rate and nano-Sb2O3 content on the thermal stability and thermal degradation kinetics of PBT composites were studied by TG-DSC. With the increasing of heating rate, the thermal hysteresis effect of temperature gradient is produced, which is eliminated when the temperature exceeds 400°C. With the increase of nano-Sb2O3 content, the E a of PBT/BEO/nano-Sb2O3 composites increases at first and then decreases. When the content of nano-Sb2O3 is 3 wt%, the E a of PBT/BEO/nano-Sb2O3 is the highest, which is 66.18 kJ/mol (31.43%) higher than that of neat PBT. Also, the exploration of the thermal degradation kinetics of PBT/BEO/nano-Sb2O3 composites is expected to provide research ideas for new high flame-retardant materials.

Effect of texture and temperature gradient on anisotropic plastic deformation of commercially pure titanium at room and low temperatures

This paper describes a study of deformation anisotropy of rolled grade 1 commercially pure titanium (CP-Ti) in the temperature range -115–20 °C. The tensile experiments combined with DIC technique were performed with samples dipped in liquid nitrogen for ~15 min. Electron backscatter diffraction (EBSD) was effectively used to characterise the microstructure evolution with respect to the extent of deformation. The experimental results and DIC-based analysis presented the texture-dependent plastic anisotropy showing the uniform cross-section reduction and strain localisation. The twinning-induced hardening was responsible for the anisotropic plastic behaviours. The low deformation temperature and increasing temperature gradient during deformation intensified the plastic anisotropy and twinning activity, and possibly increased the activation rate of slips. Consequently, the improvement and deterioration of ductility was observed under the two different crystallographic textures with the plastic anisotropy intensified by the temperature-related effects. These findings are important for understanding the deformation mechanisms of titanium at low temperature, and potentially could lead to improve its formability by conducting low temperature processing (e.g., cryorolling).

The combined kinetic effects of the ion temperature gradient and the velocity shear of a plasma flow parallel to the magnetic field on the drift-Alfven instabilities

The drift-Alfvén instabilities of the sheared flow along the magnetic field of a finite beta (1>β≫me/mi) plasma with comparable inhomogeneous ion temperature and homogeneous electron temperature are examined by the numerical analysis of the derived linear dispersion equation. Accounting for the electromagnetic ion kinetic response, which has been neglected in conventional discussions of the drift-Alfvén instabilities of a steady plasma, a new kinetic drift-Alfvén instability has been found. It develops in a plasma shear flow due to the coupled action of the ion temperature gradient, the flow velocity shear, and the inverse ion Landau damping.

Effect of the temperature gradient on hot cracking susceptibility for electron beam welding Alloy 247 LC

Abstract Conventionally cast Alloy 247 LC is characterized by good creep rupture strength and corrosion resistance at high temperatures and is therefore frequently used for cast components in the aero-engine and power generation industries. From a welding technology point of view, the precipitation- hardening nickel-based alloy has an increased susceptibility to hot cracking. Due to its high segregation tendency and its γ’ precipitation formation, the material is even classified as non-weldable. However, electron beam welding in a vacuum as the method of choice for joining and repairing nickel-based components in industrial practice, provides a variable beam welding process with high energy density. This allows varied temperature gradients to be implemented. In this paper, results of welding parameter optimization with regard to hot crack reduction are presented. For this purpose, a comprehensive crack analysis was carried out using scanning electron microscopy, metallography and X-ray microtomography and was then compared with the temperature gradient along the fusion line. Two hot cracking phenomena were identified and differentiated. Thereby, a clear dependence between temperature gradient and crack reduction becomes obvious.

Investigating the vapour transport phenomena inside the cathode gas diffusion layer media by controlling local temperature gradient inside an operating proton exchange membrane fuel cell

Water management is critical for the function of the proton exchange membrane fuel cell (PEMFC). The local through-thickness temperature gradient of the cathode gas diffusion layer (GDL) affect water management for a PEMFC. That has been known and been targeted for the discussion for several years. In this study, the effects of temperature gradient inside PEMFC was investigated by controlling it externally with a fine (testing diameter about 30 μm) and thin (thickness about 6 μm) thin-film thermocouple (TFTC), which has been developed using micro electromechanical system (MEMS) technology. In addition, X-ray computed tomography (CT) has been chosen as a method to visualise inside of an operating PEMFC. The simultaneously measurement of temperature gradient and liquid water distribution was firstly accomplished. In conclusion, in the case where the temperature of the cathode catalyst coated membrane (CCM) side is higher than that of the channel side, the PEMFC performance drastically decreased. The difference in PEMFC performance was caused by a difference the preferential sites for water condensation.