Influence Of Thermal Effects Research Articles

Influence of thermal effect on dynamic behavior of high-speed dry hobbing motorized spindle system

Influence of thermal effect on dynamic behavior of high-speed dry hobbing motorized spindle system

Monte Carlo analysis of thermal effects in the DC and AC performance of AlGaN/GaN HEMTs

The influence of thermal effects in AlGaN/GaN HEMTs is studied by means of Monte Carlo simulations. Measured output and transfer characteristics of a transistor are well reproduced using two techniques, a thermal-resistance method and an electrothermal model which solves the steady-state heat-conduction equation. The validity of the model to reproduce the experimental results is checked in two-terminal structures and transistors. Both methods are also employed to investigate in AC regime in terms of the elements of the small-signal equivalent circuit, providing a good agreement with experimental values, with no significant differences between the models. Apart from the expected decrease of transconductance and drain conductance, the gate to source capacitance is also found to be lowered by heating effects.

Tribological properties of a helical gear pair considering interfacial slip between lubricant and tooth surface

AbstractIn this study, an interfacial slip model including the limiting shear stress is proposed and applied to the thermal elastohydrodynamic lubrication (EHL) analysis of a helical gear pair. The main difference between the proposed model and the classical EHL model is that, the term of entrainment velocity in Reynolds equation is modified. The influences of interfacial slip, thermal effect, initial limiting shear stress and operating conditions on the tribological properties are evaluated. Due to the interfacial slip, the pressure distribution moves towards the inlet region, and the fluctuation distributions of entrainment velocity and film thickness are similar to the trigonometric function. The influence of thermal effect on interfacial slip cannot be ignored, especially in the case of high speed and heavy load. As the input torque and input rotational speed increase, the interfacial slip gradually extends to the whole meshing process.

Influence of thermal effect on vacuum electro-osmosis of Taizhou dredged sediment

In recent years, rapid dewatering of dredged sediment has been a key problem in environmental dredging engineering. While vacuum electro-osmosis technology has good application prospects in the treatment of dredged sediment, it has been reported that the thermal effect may improve its efficiency. To further clarify the influence mechanism of the thermal effect of vacuum electro-osmosis, six groups of vacuum electro-osmosis tests under different thermal effects are performed with a homemade test system equipped with a heatable cathode and new electrokinetic geosynthetic (EKG) drainage boards. The obtained results show that the application of a thermal effect at the cathode increases the electro-osmotic flow rate and promotes the drainage process of vacuum electro-osmosis. At the same time, the distribution uniformity of the water content and shear strength after treatment is improved. When the temperature near the cathode is 60 °C, the drainage effect improves. Considering the variation law of the electric permeability coefficient influenced by the thermal effect, the two-dimensional vacuum electro-osmosis consolidation equation is educed. Comparing the observed values with this equation, it is proven that the obtained equation can reasonably reflect the dissipation of excess pore water pressure in vacuum electro-osmosis under the thermal effect.

Laser Induced Thermal Effect on the Polymerization Behavior in Upconversion Particle Assisted Near-Infrared Photopolymerization.

Laser induced thermal effect is inevitable in upconversion particle assisted near-infrared polymerization (UCAP). Herein, the influence of thermal effects on the polymerization behavior are investigated. The effects of up-conversion particles content and NIR laser intensity on the polymerization rate and surface oxygen inhibition were systematically investigated, and the temperature evolution and complex viscosity changes in the polymerization system during the polymerization process were also monitored. In addition, polymerization experiments conducted on a controlled temperature platform were used to study the effect of NIR heating on the polymerization behavior. The results show that the near-infrared thermal effect promotes the polymerization reaction, but also causes severe oxygen inhibition which has an adverse effect on polymerization. Finally, NIR curing materials with enhanced mechanical properties than those of conventional UV curing materials were obtained.

Influence of activation energy on charge conduction mechanism and giant dielectric relaxation of sol-gel derived C3H7NH3PbBr3 perovskite; Act as high performing UV photodetector

This work contains an extensive study on temperature dependent complex dielectric behavior over 4 Hz≤ f≤ 8 MHz of a promising hybrid perovskite, propylammonium lead bromide. The structural, as well as morphological property of this sol-gel derived sample have been analyzed with the help of XRD and SEM respectively. The obtained energy band gap and thermal stability study ensure the capability of this material in device fabrication. Possessing a wide band gap, this perovskite fascinatingly serves as a UV photodetector. The individual impact of grain and grain boundary over the entire resistance has been resolved by Maxwell – Wagner Cole–Cole model. This material holds an amazing property; giant dielectric constant near room temperature at low frequency limit which escalates rapidly in the influence of thermal effect. Modified cole – cole plot assures that both space and free charge conductivities ascend with temperature. The asymmetrical nature of the imaginary part of electric modulus is analyzed by Kohlrausch – Williams – Watts which confirms its non – Debye nature diminishes with rising temperature. The thermally triggered AC conductivity follows Jonscher’s power law and is emphasized with the jump relaxation model. The bulk conductivity of the sample depends on temperature and is elucidated with variable range hopping of localized charge carriers. Activation energy plays a key role in the ionic conduction mechanism within the sample, described elaborately. The overall substantial studies on its application as UV detector and different dielectric properties of this sample construct the basis of appreciable acceptability of the sample in energy harvesting.

Oil Film Stiffness of Double Involute Gears Based on Thermal EHL Theory

Lubrication failure is one of the main failure forms of gear failure. Time varying meshing stiffness is an important factor affecting the dynamic behavior of gears. However, the influence of oil film stiffness is usually ignored in the research process. In this paper, according to the meshing characteristics of double involute gears, based on the non-Newtonian thermal EHL theory, a new calculation method of normal and tangential oil film stiffness for double involute gears is established by the idea of subsection method. The oil film stiffness difference between double involute gears and common involute gears is analyzed, and the influence of tooth waist order parameters, working conditions, and thermal effect on the oil film stiffness are studied. The results reveal that there are some differences between normal and tangential oil film stiffness between double involute gears and common involute gears, but there is little difference. Compared with the torque, rotation speed and initial viscosity of the lubricating oil, the tooth waist order parameters have less influence on the oil film stiffness. Thermal effect has a certain influence on normal and tangential oil film stiffness, which indicates that the influence of thermal effect on the oil film can not be ignored. This research proposes a calculation method of normal and tangential oil film stiffness suitable for double involute gears, which provides a theoretical basis for improving the stability of the transmission.

Performance comparison between washcoated and packed-bed monolithic reactors for the low-temperature Fischer-Tropsch synthesis

Washcoating and packing of Co-Re catalyst particles have been employed as structuring methods of parallel channel monoliths used in the low-temperature Fischer-Tropsch synthesis (FTS). These methods were compared with regard to catalyst hold-up, heat transfer properties and pressure drop. Reactors output was assessed in terms of CO conversion, CH4 selectivity and productivity of C5+ hydrocarbons. Washcoating led to much lower pressure drops, but also resulted in considerably lower catalyst inventory. As for the reactors performance (volumetric and per catalyst mass C5+ productivities), the washcoated monoliths were more effective than the packed-bed ones. This has been attributed to their more favorable hydrodynamic behavior that facilitates the drainage of the reaction products (liquids and waxes) through the central hollow of the channels thus reducing the extra-pellet diffusional limitations. For both catalyst configurations, it has been found that the productivity of C5+ per catalyst mass unit increases as the characteristic diffusion length increases within the range of values considered in this study (below 150 µm). This indicates that a moderate level of internal mass transport restrictions is beneficial for the low-temperature FTS, which has been explained in terms of the effects of diffusional limitations on the H2/CO molar ratio, and that of this ratio on the FTS kinetics. The possible influence of thermal effects on these results has been numerically and experimentally discarded.

The effect of thermal radiation on singularities in the dark universe

Cosmological models with an inhomogeneous viscous dark fluid, coupled with dark matter in the Friedmann–Robertson–Walker (FRW) flat universe, are considered. The influence of thermal effects caused by Hawking radiation on the visible horizon is studied, in connection with the classified Types I and III singularities which are known to occur within a finite amount of time. Allowance of thermal effects implies that a transition to a Type II singularity can take place, in a finite time. We take into account a bulk viscosity of the dark fluid, observing the equation of state in the case of radiation, and find that there is a qualitative change in the singular universe of Type I: it may pass into a singularity of Type III, or it may avoid the singularity at all.

Influences of thermal effects on residual stress fields of an aluminium-lithium alloy induced by shot peening

In this paper, the thermal effects and the corresponding influences on the residual stress fields of a 2060-T8 aluminium-lithium alloy induced by shot peening are investigated both theoretically and numerically. Based on the Hertz contact theory, a theoretical analysis is conducted by considering energy transformation during the shot peening process. Moreover, in the numerical simulation, explicit methods for the coupled thermomechanical problem and the purely mechanical case are employed to compute the dynamic process. The static method is adopted for the spring-back process to acquire the residual stress fields. Then, the numerical model is verified by comparing the predicted temperature with the theoretical results and comparing the residual stress fields with the experimental results. The results indicate that shots with a higher velocity or a larger radius possess greater kinetic energy so that more frictional heat can be obtained from the energy transformation, and the temperature on the contact surface is definitely higher. The compressive residual stresses in the surface layers will decrease after considering the thermal effects. This can be ascribed to the comprehensive influences of thermal relaxation and the decrease in yield strength at high temperatures. As a result, a modified empirical equation is established to describe the distributions of residual stresses considering and neglecting the thermal effects. The proposed models considering the thermal effects can help predict the residual stress distributions under different processing parameters and provide a better understanding of the shot peening process.

Влияние теплового излучения на сингулярное поведение Вселенной

Cosmological models with inhomogeneous viscous fluids with a logarithmic equation of state in the Friedmann-Lemaitre-Robertson-Walker universe are considered. The influence of thermal effects caused by Hawking radiation on the visible horizon of the Universe on the change in the type of singularity of the dark Universe is investigated. It is shown that under the influence of thermal radiation, taking into account the viscosity property of a dark fluid, a qualitative change in the type of the Big Rip singularity is possible, which can lead to the absence of a singularity in the Universe at all.

Influence of Thermal Effects on the Transport Characteristics of Cellulose Acetate Porous Films

Experimental data have been obtained, and the characteristics of the moisture content and permeability of cellulose acetate porous materials were analyzed via thermal action. Dynamic thermogravimetric analysis found that the destruction process in an air-dry sample of the membrane begins at 21°C. It is accompanied by a 2% weight loss and an endothermic effect. The destruction ends at 50°C. With a subsequent increase in temperature, the manifestation of endothermic effect continues a temperature of 120–175°C with the maximum rate of mass loss at 146°C. The weight loss ends at about 190°C and is 6.5%. The study of MGA-80 and MGA-95 porous cellulose acetate films at transmembrane pressure upon temperature exposure showed that the permeability and specific output flow to water increase as the temperature rises to 50°C. Analysis of dependences of the specific output flow on temperature revealed that the specific output flow to water increases by ~18% upon an initial temperature rise of 10°C. This is due to structural changes in the cellulose acetate layer. A further increase in temperature by 15°C leads to an increase in permeability by ~10%. These phenomena are associated with the process of structural transformation in the active layer and the polymer substrate of the MGA-95 and MGA-80P membranes, respectively.

Study of structural, elastic, thermal, electronic and magnetic properties of heusler Mn2NiGe: An Ab initio calculations and Monte Carlo simulations

In this work, we have focused on the study of heusler Mn2NiGe alloys. Various compositions of those materials exist but few of them exhibit magnetic characteristics. Augmented plane wave method which is based on the density functional theory using Wien2k code combined with the generalized gradient approximation was proposed to examine the structural, electronic, mechanical, magnetic and thermal properties and magnetocaloric effect of heusler Mn2NiGe compound. The magnetocaloric effect for the material was studied using Monte Carlo simulation. Further, thermal magnetization dM/dT, magnetic specific heat, magnetic entropy and relative cooling power are obtained for several magnetic field. The magnetic hysteresis of this system was obtained for several temperature values. The investigation indicated that heusler material Mn2NiGe shows a magnetic character. Paramagnetic to ferromagnetic transition was well established around the transition temperature. The influence of thermal effects on the lattice parameter, compression modulus, volume, heat capacity, thermal expansion coefficient and total magnetic moment at several pressures was studied.

Numerical approximation of a two-dimensional non-equilibrium model of non-isothermal liquid chromatography considering core-shell particles

A nonlinear and non-isothermal two-dimensional lumped kinetic model (2D LKM) is solved numerically to simulate the transport of multi-component mixtures in fixed-bed liquid chromatographic columns of cylindrical geometry packed with core-shell particles. The model considers axial and radial dispersions, interfacial mass, and heat transfers, nonlinear adsorption, and rectangular pulse injections. It is formed by a nonlinear system of partial differential equations coupled with differential and algebraic equations. A semi-discrete high-resolution finite volume scheme (HR-FVS) is extended and applied to approximate the model equations. A few case studies related to single and multi-component elution are considered to illustrate the effects of important parameters, such as core radius fraction, enthalpy of adsorption, radial and axial-dispersion coefficients, equilibrium constant, as well as film mass and heat transfer coefficients. A typical performance criterion is adopted to quantify the influence of thermal effects on the process performance and to evaluate the optimum value of inert core radius. The results obtained in various case studies are useful for understanding and upgrading liquid chromatographic processes considering non-isothermal conditions and core-shell particles.

Influence of thermal effects in turn-rolling

The part life span significantly depends on microstructure and the residual stress state. The current state of research shows that the mechanical surface strengthening process deep-rolling is a suitable method for alteration of surface and subsurface properties to increase strength and life span of highly stressed components. A further increase in the life span can be reached by using the process temperature of the turning process to enhance the influences of deep rolling. For this purpose, a turn-rolling tool was developed. Especially concerning soft machining operations, the induced process temperatures can lead to higher compressive residual stresses, and finally, to higher part life spans. For this, it is necessary to consider the influence of heat on the component caused by the turning process. Therefore, a novel approach to the design of process parameters and tool geometries for turn-rolling based on 3D FEM simulations was developed in this work. Based on this approach, it was shown that depending on process parameters and tool microgeometry, the component temperature can be specifically influenced near the surface.

Thermohydrodynamic (THD) Analysis of Journal Bearing Operating with Bio-based Nanolubricants

The objective of current research is to study the adiabatic solutions of a plain journal bearing operating with bio-based lubricants containing nanoparticles. Estimation of pressure and temperature fields has been accomplished by simultaneous numerical solutions of the modified Reynolds equation and the adiabatic energy equation. These equations have been solved by adopting the finite difference method with suitable iterative scheme. The analysis has been carried out taking into account the heating effects and non-Newtonian rheology of bio-based nanolubricant following the power law model. The results have been investigated for temperature and pressure fields and the static performance parameters for a broad range of eccentricity ratio e and different power law index values. The calculated results present that the involvement of nanoparticles in bio-based lubricant significantly enhances the pressure, load carrying capacity and friction force. Moreover, the influence of thermal effects on performance parameters is seen to be maximum at higher values of power law index.

Влияние термического воздействия на микромеханические свойства хромоникелевого покрытия, полученного газопорошковой лазерной наплавкой

Влияние термического воздействия на микромеханические свойства хромоникелевого покрытия, полученного газопорошковой лазерной наплавкой

Thermal influence on surface layer of carbon fiber reinforced plastic (CFRP) in grinding

In this study, we investigated thermal influence on surface layer of CFRP in grinding with heat conduction analysis using grinding temperature at wheel contact area on dry and wet condition. Moreover, the thermal affected layer was analyzed through an experiment to examine the temperature of glass transition and thermal decomposition of the matrix resin that composes the CFRP used in this study. The influence of thermal effect on grinding of CFRP was verified based on observation of ground surface finish after grinding using SEM and the measurement of surface roughness. From the measurement result of DSC (Differential Scanning Calorimetry)，TG-DTA (Thermogravimetry-Differential Thermal Analysis), It was found that the thermal affected layer of CFRP includes a layer in which the matrix resin is changed in quality by exceeding the glass transition temperature and a layer in which the matrix resin is thermally decomposed by exceeding the thermal decomposition temperature. In addition, it was found that the surface roughness was significantly reduced if the thermal affected layer with thermal decomposition was generated. In each grinding atmosphere, it tended to increase of grinding temperature at wheel contact area with increasing in the setting depth of cut. In the case of dry grinding, grinding temperature at wheel contact area increased up to t thermal decomposition temperature of the matrix resin. However, in the case of the wet grinding, grinding temperature at wheel contact area did not increase until thermally decomposition temperature. From the result of simulation about thermal affected layer, influence of grinding heat increased with increasing in the setting depth of cut. Ultimately, the thermal affected layer with thermal decomposition was generated in dry grinding. Moreover, from the results of SEM observation, it was confirmed that the surface finish properties deteriorated significantly due to thermal decomposition of the matrix resin in the case of Δ = 400 μm in the setting depth of cut at fiber angle θ = 0°. On the other hand, it was confirmed that the micro damage of carbon fiber was occurred in wet grinding at each setting depth of cut.

Propagation of Rayleigh waves in unsaturated porothermoelastic media

SummaryBased on the frame of elastic theory for unsaturated porous medium, considering the influence of thermal effect, the propagation characteristics of Rayleigh wave in unsaturated porous media are studied. Firstly, the thermoelastic wave equations for three‐phase porous media are established, in which the mass balance equations, generalized Darcy law, momentum balance equations, and generalized non‐Fourier heat conduction law are taken into account. Secondly, through theoretical derivation, the dispersion equation of Rayleigh wave for unsaturated porothermoelastic media is given by introducing the potential functions. Finally, the variations of the phase velocity of Rayleigh wave are analyzed with numerical examples. The results show that the thermal conductivity has little effect on the phase velocity of Rayleigh wave. The phase velocity of Rayleigh wave increase with increasing of the thermal expansion coefficient and media temperature.

Analysis of mechanical power loss of a helical gear pair based on the starved thermal-elastohydrodynamic lubrication model

PurposePower loss is an important index to evaluate the transmission performance of a gear pair. In some cases, the starved lubrication exists on the gear contact interface. The purpose of this paper is to reveal the mechanical power loss of a helical gear pair under starved lubrication.Design/methodology/approachA starved thermal-elastohydrodynamic lubrication (EHL) model is proposed to evaluate the tribological properties of a helical gear pair. The numerical result has been validated against the published simulation data. Based on the proposed model, the influence of thermal effect, working conditions, inlet oil-supply layer and surface roughness on the mechanical power loss and lubrication performance has been discussed.FindingsResults show that the thermal effect has a significant effect on the tribological properties of helical gear pair, especially on mechanical power loss. For a specified working condition, there is an optimal oil supply for gear lubrication to obtain the state of full film lubrication. Meanwhile, it reveals that the mechanical power loss increases with the increase of the surface roughness amplitude.Originality/valueIn this paper, a starved thermal-EHL model has been developed for the helical gear pair based on the finite line contact theory. This model can be used to analyze the tribological properties of gear pair from full film lubrication to mixed lubrication. The results can provide the tribological guidance for design of a helical gear pair.