Coupling Effect Of Temperature Research Articles

On the fast fluid dynamics and fractional step methods to predict the coupled indoor temperature and velocity fields

The two-way coupling of temperature and flow fields in the indoor environment makes the conventional CFD simulation computationally intensive, especially when the transient evolution of temperature and velocity fields is of interest in areas such as unsteady ventilation. This study, by applying different splitting CFD methods (fast fluid dynamics (FFD) and fractional step (FS) method) to solve the momentum equation to decouple velocity and pressure fields, further explored different strategies to tackle the coupled temperature equation, and validated the different sequences of operation based on different combinations of temperature/velocity solution schemes. Each operational sequence of different combined numerical schemes was validated on a mixed convection airflow benchmark case with a heated floor. The results showed that different operational sequences using the numerical schemes which considered the strong coupling effect of temperature and flow fields could predict the final steady-state result well, while for the transient simulation that need to track the physical flow/thermal fields variation process precisely, the operational sequence which introduce the effect of buoyancy into volumetric flux to solve pressure Poisson equation showed better accuracy and owned the capability of predicting the same transient evolution process as conventional CFD method. Based on the comprehensive comparison, several promising numerical schemes under proper operational sequence were recommended and the highest computing efficiency was provided by sequence D of RIPC + Iterative which saved 68% computing time compared to the conventional CFD method.

Effects of hygrothermal ageing and temperature on the mechanical behavior of aluminum-CFRP hybrid (riveted/bonded) joints

Hygrothermal ageing and temperature significantly affect the mechanical properties of joints, but the research on their coupling effect in hybrid joints is insufficient. In this work, the combined effects of the long-term factor of hygrothermal ageing and the short-term factor of temperature on the mechanical properties of Al/CFRP hybrid (riveted/bonded) joints (HJs) are investigated by quasi-static tensile experiments and an advanced simulation method. The mechanical properties of HJs with four kinds of ageing degrees are tested at four temperatures (−40 °C, 20 °C, 50 °C, and 80 °C). Experimental results show that the joint strength is mainly affected by temperature, while the breaking elongation is sensitive to the degree of ageing. Although the joint stiffness and strength decrease significantly under the combined action of the increase in temperature and the deepening of the ageing degree, the three-stage characteristics of failure (first, the adhesive bond and the rivet share the load; and then the adhesive bond gradually fractures and loses its load-bearing capacity; finally, the rivet bears the load alone) do not change. Furthermore, by integrating the change information of moisture absorption and Fourier transform infrared spectrum into the material model, the simulation shows new light on the failure mechanisms of the HJs on the coupling effect of temperature and hygrothermal ageing. In conclusion, this research helps deepen the understanding of the changing laws of mechanical behavior of Al/CFRP hybrid joints under actual service conditions.

Negative corona discharge and flow characteristics of a two-stage needle-to-ring configuration ionic wind pump for temperature and relative humidity

Ionic wind pumps have the advantages of a compact structure, no moving parts, and low power consumption. The effects of temperature and humidity on the current–voltage and flow characteristics of ionic wind pumps are still unclear. This study experimentally investigates the effects of temperature and humidity on the breakdown voltage, discharge current, and velocity of a two-stage needle-to-ring type ionic wind pump with a negative corona discharge. It is found that the coupling effects of temperature, humidity, and water vapor condensation determine the current–voltage and flow characteristics of ionic wind pumps. The temperature and vapor condensation effects can enhance the discharge current and outlet velocity and weaken the breakdown voltage. However, the humidity effect can weaken the discharge current and outlet velocity, and improve the breakdown voltage. Moreover, there exists a competition between humidity and vapor condensation effects on breakdown voltage, current, and velocity. The increase in temperature intensifies the humidity effect and weakens the condensation effect; thus, the temperature changes the contribution of humidity and condensation effects in the competition. A working spectrum of ionic wind is provided in the temperature and humidity coupling environment, including a vapor condensation-controlled zone, a sensitive humidity zone for breakdown voltage and velocity, and an insensitive humidity zone for breakdown voltage and velocity. The spectrum can provide theoretical guidance for designing ionic wind pumps at different temperatures and humidity.

Optical-thermally actuated graphene mechanical resonator for humidity sensing

This paper demonstrates an optical-thermally actuated multi-layer graphene resonator for humidity sensing. A ∼10-layered graphene resonator with a diameter of 125 µm peripherally clamped on the fiber ferrule end face was actuated to vibrate using the intensity-modulated laser, and the vibration was detected based on the optical fiber Fabry-Perot interference method. The humidity sensing experiment exhibited an up to 350 Hz/%RH humidity sensitivity in the range of 0–100 % RH at 25 °C, which was 10 times higher than those of the previously reported Quartz Crystal Microbalance (QCM)-based humidity sensors. Also, a good repeatability of the frequency-humidity response was observed for the presented graphene resonator. Moreover, in view of the coupling effect of temperature on the graphene resonator, the temperature drift of 0.942 kHz/°C was measured in the range of 25–50 °C, thereby inducing an absolute humidity error of about 0.6 g/(m3·°C).

The anti – Temperature-vibration properties of viscoelastic anticorrosive tape

Viscoelastic anticorrosive tape is extensively used for repairing anticorrosive layers on compressor outlet pipelines in the oil and gas industry. However, there is no relevant research on the coupling effect of temperature and vibration on the performance of viscoelastic anticorrosive tape. In this paper, acceleration tests of temperature and vibration coupling conditions were conducted to investigate the performance of viscoelastic anticorrosive tape. After temperature and vibration treatment, the specimens showed wide variance in thickness, and the adhesion and chemical soaking resistance of the tape was reduced. However, the viscoelastic anticorrosive tape still showed high adhesion. According to theoretical calculations, the tested viscoelastic body can repair pipes with a maximum diameter of 903 mm. Therefore, this viscoelastic anticorrosive tape is suitable for the compressor outlets of buried pipelines with diameters smaller than 903 mm. The research in this paper provides a method and basis for the selection of repairing materials for the anticorrosion coatings of compressor outlet pipelines.

Spatiotemporal Evolution Characteristics and the Climatic Response of Carbon Sources and Sinks in the Chinese Grassland Ecosystem from 2010 to 2020

With the increase in global carbon dioxide emissions, China has put forward the goals of a carbon peak and carbon neutrality (double carbon) and formulated an action plan to consolidate and enhance the carbon sink capacity of the ecosystem. The Chinese grassland ecosystem (CGE) is widely distributed and is the key link for China to achieve the double carbon objectives. However, there is a relative lack of research on carbon sources and sinks in the CGE, so it is urgent to integrate and analyze the carbon sources and sinks in the grassland ecosystem on the national scale. Based on the refined grid data, the net ecosystem productivity (NEP) of the CGE was estimated by coupling the vegetation production model and soil respiration model. The results showed that the cumulative carbon sequestration of the CGE was 14.46 PgC from 2010 to 2020. In terms of spatial distribution, this shows that the differentiation characteristics are high in the northwest of China and low in the southeast of China, which strongly corresponds with the 400 mm isohyet and 0 °C isotherm of China. The results of the correlation analysis showed that the NEP of the CGE was positively correlated with precipitation and negatively correlated with temperature; that is, precipitation mainly promotes the accumulation of NEP, and temperature mainly inhibits it. The coupling effect of temperature and precipitation jointly affects the spatial change of carbon sources and sinks of the CGE. This study can provide a scientific basis for government departments to formulate targeted policies to deal with climate change, which is of great significance for China to improve ecosystem management, ensure ecological security and promote the realization of China’s double carbon goal.

Effect of free radicals and electric field on preparation of coal pitch-derived graphene using flash Joule heating

Most of the traditional graphene production processes were not only solvent-intensive but also time-and-energy-consuming. Flash Joule heating (FJH) is an efficient approach to green and scalable large-scale production of graphene. However, its reaction mechanism is not clear during the process of electric field and free radical on graphene generation. In this work, synthesis of coal pitch-based graphene by FJH under the coupling effect of temperature and electric field, and Raman spectroscopy and electron transient magnetic resonance were studied at different input energies. The results show that the input energy is positively correlated with the generated radicals and is beneficial for the quality improvement of graphene. In addition, the mechanism is explained using ReaxFF molecular dynamics and DFT calculations: Joule heat provides energy for the kinetics and thermodynamics of the reaction. High temperature (3000 K) can dissociate branch chains in coal tar molecules to generate highly reactive alkane and alkene radicals. Different cooling rates affect the quality of graphene generation. When the cooling rate is slow, the graphite microplates will grow in layers, and a multi-layer phenomenon will appear; when the cooling rate is fast, the generated graphene will be in a turbostratic order. At the same time, the DFT calculation shows that the coal tar molecules are ionized under the action of the electric field and are oriented and arranged to reduce the reaction potential barrier.

Modeling of temperature- and stress state-dependent yield and fracture behaviors for Mg-Gd-Y alloy

The research aims at characterizing and modeling the influence of temperature and stress state on the yield and fracture behaviors of an Mg-Gd-Y alloy. The mechanical experiments at 25∼300 ℃ were carried out by various designed specimens, including tension, compression and shear. The experimental result indicates that the strength of the Mg-Gd-Y alloy presents a monotonous and non-uniform downward trend as the temperature increases. The mechanical behavior at 100 ℃ and 150 ℃ are very similar, and the strength rapidly declines when the temperature is higher than 250 ℃. The tension-compression asymmetry presents the obvious nonlinear variation with the temperature and strain, which is weakened at elevated temperature. The fracture behavior belongs to the ductile fracture with tension and shear mechanisms, showing a coupling effect of temperature and stress state. A modified Zerilli-Armstrong model is proposed to characterize the plastic flow behavior with the coefficient of determination about 0.99, which is prior to the Johnson-Cook and Zerilli-Armstrong models. The Cazacu-Barlat2004 yield function is established to describe the temperature- and strain-related non-uniform evolution characteristic, and capture the fracture-related variables of all fracture tests with the acceptable prediction accuracy. The temperature-dependent parameter is introduced into the DF2016 fracture criterion to predict the onset of fracture under various temperatures and stress states with a small prediction error. The numerical simulation is conducted to validate the reliability and practicability of the established model.

Load–Temperature Coupling Effect on the Base Plate End of the Whole Tram Road

Although trams have been widely recognized, systematic and comprehensive research on their design and construction is lacking. Based on the ABAQUS finite element software, we constructed a three-dimensional finite element analysis model of the overall track bed of the tram. Taking the most unfavorable working condition of load and temperature coupling as the research object, that is from 5:30 to 6:00 a.m., the load was applied to the plate end position. The simulation experiments were carried out by selecting different thicknesses of the track bed slab, support layer thickness, contact conditions between the track bed slab and the support layer, the modulus of the track bed slab, the modulus of the support layer and the soil foundation strength, and the stress and deflection of the subgrade were calculated. The most unfavorable load–temperature coupling condition was taken as the research object, that is, applying a load of 5.5–6 points on the plate end. Different track bed slab thicknesses, support layer thicknesses, contact conditions between track bed slab and support layer, track bed slab moduli, support layer moduli, and foundation strengths were utilized to conduct simulation tests for calculating the stress and deflection of the subgrade. Under the coupling effect of load on the end of the slab and the effect of temperature, changing the thickness of the track bed slab and the coefficient of friction between layers can improve the lateral force and deflection of the track bed slab. The effect of deflection is small. Changing the thickness of the support layer has an insignificant effect on the stress on the top surface of the soil foundation and the deflection of the top surface of the subgrade. The modulus of the track bed slab can affect the lateral force and deflection of the track bed slab, but it only slightly affects the longitudinal force and deflection of the track bed slab and the longitudinal and lateral force and deflection of the soil foundation. The modulus of the supporting layer only slightly affects the vertical and horizontal force and deflection of the track bed slab and soil foundation. The soil foundation modulus has the greatest influence on the vertical and horizontal forces and deflection of the track bed slab and soil foundation.

Hydrothermal liquefaction of municipal sludge: Coupling effects of temperature and time on nitrogen migration

Biocrude derived from hydrothermal liquefaction of municipal sludge has a high nitrogen content, which limits its direct use. This work explored coupling effects of reaction temperature and residence time on N transformation during hydrothermal liquefaction of municipal sludge. The results showed that 350 ℃ and 40 min were the optimal conditions, which led to the highest biocrude yield, HHV, energy recovery, and N removal efficiency after hydrothermal liquefaction of municipal sludge within 200–350 ℃ for 10–50 min. More than 60 wt% N in municipal sludge was distributed in the aqueous phase and NH4+ was the richest substance after hydrothermal liquefaction. Also, N transformation pathways were clarified by correlating the effects of reaction temperature and residence time on N distribution.

Hot Deformation Behavior of the 25CrMo4 Steel Using a Modified Arrhenius Model.

25CrMo4 steel is widely used in the manufacturing of high-speed train axles due to its excellent mechanical properties. The purpose of this study is to develop an accurate modified constitutive model to describe the hot deformation behavior of the steel. Isothermal compression experiments were performed at different strain rates (0.01, 0.1, 0.5, and 1 s−1) and different temperatures (950, 1000, 1050, and 1100 °C) using a Gleeble-3800 thermal simulator. The microstructure after hot deformation was observed by the electron backscatter diffraction (EBSD), and the effects of temperature and strain rate were analyzed. The results showed that the coupling effect of temperature and strain rate on the dislocation density led to the change in the shape of the true stress–strain curve and that dynamic recovery (DRV) and dynamic recrystallization (DRX) caused the macroscopic softening phenomenon, with DRX being the main mechanism. Based on the true stress–strain curves, the strain-compensated Arrhenius constitutive model was calibrated. To improve prediction ability, a modified Arrhenius constitutive model was proposed, in which the temperature and strain rate coupling correction functions were incorporated. The original, modified Arrhenius models were evaluated according to the absolute relative error (ARE), the average absolute relative error (AARE), and the correlation coefficient (R2). Compared with the original model, the modified Arrhenius model has a higher prediction accuracy, with the ARE value mostly below 4%, the AARE value of 1.91%, and the R2 value of 0.9958.

Numerical evaluation of the coupled/uncoupled effectiveness of a fluid-solid-thermal multi-field model for a long-distance energy transmission pipeline

As the main component of energy transmission, long-distance energy transmission pipeline (LETP), whose safety problem is becoming more and more prominent with the development of the oil and gas transportation industry, is susceptible to the traffic loading, temperature loading, pressure loading and other loadings. In this paper, the mechanical characteristics of LETP under the interaction of temperature loading and pressure loading are investigated. Based on the theory of multi-field coupling, the mathematical model of fluid-solid-thermal coupling of fluid-filled pipelines under the combined effect of temperature and pressure loadings is established and verified. Meanwhile, an equivalent model is proposed to accurately calculate the stress of any pipeline segment in LETP. The results show that the coupling of temperature loading and the pressure loading is significantly affected by the end-side constraints of the pipelines. For strong end-side constraint, the coupling effect of temperature and pressure loadings has a significant effect on the calculated equivalent stress. The difference between the stress solution under coupling effect and decoupling effect is above 30 MPa. However, for weak end-side constraints, the error is within 10 MPa. The equivalent stress can be approximated by the decoupling solution instead of the coupling solution.

Temperature Dependence of Interfacial Bonding and Configuration Transition in Graphene/Hexagonal Boron Nitride Containing Grain Boundaries and Functional Groups.

The quasi-three-dimensional effect induced by functional groups (FGo) and the in-plane stress and structural deformation induced by grain boundaries (GBs) may produce more novel physical effects. These physical effects are particularly significant in high-temperature environments and are different from the behavior in bulk materials, so its physical mechanism is worth exploring. Considering the external field (strain and temperature field), the internal field (FGo and GBs) and the effect of distance between FGs and GBs on the bonding energy, configuration transition, and stress distribution of graphene/h-BN with FGo and GBs (GrO-BN-GBs) in the interface region were studied by molecular dynamics (MD). The results show that the regions linked by hydroxyl + epoxy groups gradually change from honeycomb to diamond-like structures as a result of a hybridization transition from sp2 to sp3. The built-in distortion stress field generated by the coupling effect of temperature and tension loading induces the local geometric buckling of two-dimensional materials, according the von Mises stresses and deflection theory. In addition, the internal (FGo and GBs) and external field (strain and temperature field) have a negative chain reaction on the mechanical properties of GrO-BN-GBs, and the negative chain reaction increases gradually with the increase in the distance between FGo and GBs. These physical effects are particularly obvious in high-temperature environments, and the behavior of physical effects in two-dimensional materials is different from that in bulk materials, so its physical mechanism is worth exploring.

Reflective Optical Fiber Sensor Based on Dual Fabry Perot Cavities for Simultaneous Measurement of Salinity and Temperature

A reflective optical fiber sensor that is composed of two Fabry Perot cavities is proposed for temperature and salinity measurement. One of the Fabry Perot cavity which is fabricated by offset splicing is exposed to the ambient directly to sense the ambient salinity, the other is employed to compensate for the temperature coupling effect. A thin layer of the gold film is coated on the refractive index change interface, which makes the spectrum quality is no longer limited by the refractive index difference between the two sides of the interface. By applying the frequency division multiplexing (FDM) technique and cavity length demodulation technology, the measurement range is no longer restricted to the free spectrum range (FSR), which can realize salinity measurement in the full measurement range. The proposed sensor can realize the salinity sensitivity better than 50 nm/‰ and temperature sensitivity of 6.85 nm/°C in the cavity length domain. It is promising for salinity measurement application for its merits of low cost, easy fabrication, and long sensing distance.

Study on Damage Statistical Constitutive Model of Triaxial Compression of Acid-Etched Rock under Coupling Effect of Temperature and Confining Pressure.

Based on Lemaitre’s strain equivalence hypothesis theory, it is assumed that the strength of acid-etching rock microelements under the coupling effect of temperature and confining pressure follows the Weibull distribution. Under the hypothesis that micro-element damage meets the D-P criterion and based on continuum damage mechanics and statistical theory, chemical damage variables, thermal damage variables and mechanical damage variables were introduced in the construction of damage evolution equations and constitutive models for acid-etching rocks considering the coupled effects of temperature and confining pressure. The required model parameters were obtained by theoretical derivation, and the model was verified based on the triaxial compression test data of granite. Comparing the experimental stress-strain curve with the theoretical stress-strain curve, the results show that they were in good agreement. By selecting reasonable model parameters, the damage statistical constitutive model can accurately reflect the stress-strain curve characteristics of rock in the process of triaxial compression. The comparison between the experimental and theoretical results also verifies the reasonableness and reliability of the model. This model provides a new rock damage statistical constitutive equation for the study of rock mechanics and its application in engineering, and has certain reference significance for rock underground engineering.

Transient thermomechanical analysis of micro cylindrical asperity sliding contact of SnSbCu alloy

A transient thermomechanical sliding model for the contact between elastic-plastic asperities is established to analyze the contact behaviors of micro asperity in the sliding process. During the process, the coupling effect of temperature and strain rate on material properties is considered. The SnSbCu alloy is focused as it is a common journal bearing material in marine engine. The results show that the effect of temperature and strain rate on the material properties should be considered in the asperity sliding process at the micro scale, which could make the contact model more practical and accurate. Based on the sliding contact model, the influence of sliding conditions and mechanical properties of material on contact behaviors is studied.

Coupling Effect of Temperature, Gas, and Viscoelastic Surfactant Fracturing Fluid on the Microstructure and its Fractal Characteristics of Deep Coal

The study of the microstructure evolution law of coal in a natural reservoir environment for the extraction of coalbed methane mining (ECBM), especially deep ECBM, is of major significance. We treated coal samples from Qinshui Basin under combined temperature–gas–fracturing fluid conditions and analyzed the evolution of the microstructure and its fractal characteristics to study the microstructural evolution of coal under natural hydraulic fracturing conditions. In the temperature range of 303.15 to 343.15 K and the gas-pressure range of 0.5–4.5 MPa, our data demonstrate that the pore structure is more susceptible to the temperature influence, compared with microfracture. The treatment of viscoelastic surfactant fracturing fluid (VES-FF) can effectively increase the permeation pore and fracture ratio by more than 300% and reduce the adsorption pore by more than 200% through dissolution, gas wedge, and other effects, which is favorable to ECBM. At the same temperature, as the gas pressure increases, the pore decreases, whereas the fracture ratio increases. The pore fractal dimension ranges from 2.90 to 2.99, which is significantly higher than that of microfractures. The temperature has a minor effect on the fracture fractal dimension, but it causes a decrease in the pore fractal dimension. The treatment of VES-FF induces an increase in the fracture fractal dimension, implying an increase in the fractal complexity. In contrast, the pore fractal characteristics show a contrary trend. At a gas pressure of 4.5 MPa, the negative effect of VES-FF on the pore structure reaches its maximum, whereas the effect on the fracture drops to its minimum. The results document that high temperature and high gas pressure can severely limit the penetration enhancement effect of VES-FF.

Desorption and Transport of Temperature-Pressure Effect on Adsorbed Gas in Coal Samples from Zhangxiaolou Mine, China

Abstract The development of coal seam fissures and gas migration process caused by mining disturbance has an extremely important influence on gas control and roadway stability. In this study, the desorption, diffusion, and migration tests of adsorbed gas under the coupling effect of temperature and uniaxial compression were conducted on four coal samples from Zhangxiaolou mine, using the temperature and pressure coupling test system of deep coal rocks. The test confirms that the higher the temperature, the faster the desorption and emission of the adsorbed gases in the coal, and the larger the volume of the emitted gases. Meanwhile, it is found that the adsorbed gases in the coal samples of Zhangxiaolou mine are carbon dioxide and methane in the order of content. It is found that during the uniaxial compression process, several large negative values of the pressure of the emitted gas occur during the stable growth stage of the crack. This indicates that the crack expansion makes a new negative pressure space inside the coal sample, and the negative pressure values increase continuously during the unstable growth phase of the crack until the coal sample is destroyed. And after the axial pressure is removed, the escaped gas pressure shows a large positive value due to the rebound of the coal matrix and the continuous desorption of a large amount of adsorbed gas from the new crack location, which has a significant hysteresis with respect to the occurrence of the peak stress. Meanwhile, the SEM images of the coal samples before and after the test are analyzed to confirm the cause of the negative pressure generation.

Mechanical Properties of Shale under the Coupling Effect of Temperature and Confining Pressure

Mechanical Properties of Shale under the Coupling Effect of Temperature and Confining Pressure

Coupling effect of temperature and Cr content on the steam oxidation of Ni-Fe-Cr alloys

Excellent resistance to steam oxidation is a key required property for heat-resistant alloys used in next-generation fossil power plants. In order to clarify the degradation mechanism of Ni-Fe-Cr alloys in high temperature steam, four kinds of Ni-Fe-Cr model alloys with various Cr content were prepared and their long-term steam oxidation were investigated at 650 °C and 700 °C. The microstructure and composition of oxide scales were characterized by SEM equipped with EDS, and the oxide phases were identified by XRD. The results showed significant dependence of temperature and Cr content in alloys on the oxidation kinetics, cross-section morphology and elemental section-distribution. For Ni-Fe-Cr alloys with low Cr contents (12∼16 wt.%), the increase of temperature made the oxide scale change from breakaway scale morphology (nodule-crater microstructure with external exfoliation) to protective scale morphology (uniform layer and internal oxidation). For Ni-Fe-Cr alloy with 18wt.% Cr, the effect of temperature was greatly reduced. The oxidation mechanism was discussed from the perspectives of selective oxidation and the effect of alloying elements.