Analysis Of Thermal Effects Research Articles

Pinning of domain walls in thin ferromagnetic films

We present a quantitative investigation of magnetic domain wall pinning in thin magnets with perpendicular anisotropy. A self-consistent description exploiting the universal features of the depinning and thermally activated sub-threshold creep regimes observed in the field driven domain wall velocity, is used to determine the effective pinning parameters controlling the domain wall dynamics: the effective height of pinning barriers, the depinning threshold, and the velocity at depinning. Within this framework, the analysis of results published in the literature allows for a quantitative comparison of pinning properties for a set of magnetic materials in a wide temperature range. On the basis of scaling arguments, the microscopic parameters controlling the pinning: the correlation length of pinning, the collectively pinned domain wall length (Larkin length) and the strength of pinning disorder, are estimated from the effective pinning and the micromagnetic parameters. The analysis of thermal effects reveals a crossover between different pinning length scales and strengths at low reduced temperature.

Interpretation of Thermal Effects in Differential Scanning Calorimetry Study of Asphalts

The structural and thermal properties of petroleum asphalt and its components have been analyzed using temperature-modulated differential scanning calorimetry (DSC). This technique makes it possible to distinguish processes, such as “order–disorder” and glass transition, ensuring identification of structural- phase transitions that are undetectable or overlapping on conventional DSC curves. The analysis of thermal effects for macro- and microcrystalline paraffins; mono-, bi-, and polycyclic aromatic hydrocarbons; asphaltenes; and benzene and alcohol–benzene resins allows identifying and interpreting effects on DSC thermograms of test asphalts.

Buckling enhancement of laminated composite structures partially covered by piezoelectric actuators

The buckling (eigenvalue) problem of biaxially compressed laminated plates and shallow cylindrical panels having two symmetric piezoelectrical (PZT) patches on the top and the bottom of laminates is considered. The analysis is carried out with the use of the classical laminate theory and of the first order shear deformation theory. The variable thickness of structures (the local positions of PZT patches) is described by piecewise constant step functions in one direction or in both directions due. Three different methods of the solution of the linear eigenvalue problem are proposed: the exact analytical solution, the approximate solution based on the definition of the Rayleigh quotient and the numerical 3D finite element analysis. For the approximate Donnell's theory of shallow panels two variational formulations of the eigenvalue problem are derived in the form of the Hu-Washizu functional (the Airy stress functions and transverse normal displacements) and in the form of the Legendre functional (displacements). The influence of geometric parameters of composite panels and PZT patches, piezoelectric effect, external electric voltage and laminate configurations (symmetric angle-ply and cross-ply laminates) on buckling characteristics are discussed in detail. The analysis demonstrates evidently that the use of the local piezopatches should be considered as the buckling problem for structures with the non-uniform thickness distribution. The appropriate use of the local PZT patches should be always combined with the appropriate choice of the best (optimal) laminate configuration. The formulation system developed is suitable to other shell theories and to account for the analysis of thermal effects or the imperfection sensitivity.

An Experimental Study on LT-GaAs Photoconductive Antenna Breakdown Mechanism

In this paper, an experimental study on the low-temperature-grown gallium arsenide (LT-GaAs) photoconductive antenna (PCA) breakdown mechanism is presented. A terahertz (THz) PCA is an important device for the THz wave generation. Due to that the typical LT-GaAs PCA breakdown scenarios, different trigger positions and different bias voltages, have been studied. Breakdown mechanism analysis has shown that when the trigger position was on the antenna electrode edge, the PCA breakdown was more probable to happen, because the electrode edge electric field was nearly 3 times greater than the electric field of the electrode center. Moreover, it has been shown that the thermal effect was the main cause of the LT-GaAs PCA breakdown. Last, the PCA lifetime has been calculated using the current waveform and the thermal effect analysis.

Model-based analysis of thermal and geometrical effects in a microscale methanol fuel cell

This paper reports the development of a mathematical model to predict the performance of a microscale methanol fuel cell with a single fuel/electrolyte channel. Performance of the cell is investigated as a function of fuel stream inlet temperature and catalyst deposition geometry. The model is fit to experimental data by maximizing the coefficient of determination, R2. Results show that peak power density with regard to total exposed catalyst surface area is inversely proportional to catalyst deposition width and proportional to fuel stream temperature. For both parameters, the mathematical model was found to compare well with experimental results in the operating regime preceding and including maximum power density. The model presented here can be used to optimize these parameters during the design phase.

Interlaminar thermal effect analysis of steel bridge deck pavement during gussasphalt mixture paving

ABSTRACTIn this research, the effect of high-temperature asphalt concrete paving on the interlaminar shear behaviour between the steel bridge deck pavement (SBDP) and the orthotropic steel bridge deck (OSBD) is the main objective. A thermal field model of steel box-girder was established based on the transient thermal field theory, and the element deletion method was used to simulate the dynamic paving process of gussasphalt mixture (GAM). The thermal field model was validated by the field monitoring data of Taizhou Yangtze River Highway Bridge in China, and the temperature variations in OSBD during the paving was summarised. Applying the most unfavourable temperature load during GAM paving to the steel box-girder mechanical model, the interlaminar shear stress distribution was calculated, and combined with the shear strength variation of waterproof bonding material during GAM paving, the interlaminar thermal effect of SBDP was evaluated. Results show that the thermal field of steel bridge presents temporal and spatial variation characteristic. The interlaminar shear stress during GAM paving in the low-temperature season is much larger than that in the high-temperature season, but the interlaminar thermal effect is more severe in the high-temperature construction season due to the more inferior shear performance of waterproof bonding material.

Experimental characterization of concrete removal by high-power quasicontinuous wave fiber laser irradiation

The performance of high-power quasicontinuous wave fiber laser irradiation on concrete has been investigated in the downward (along the gravitational direction) and the upward laser directions (against it). Mechanism of material removal without an assist gas is dominated by vaporization and melts expulsion induced by recoil pressure evaporation. Also, the melt concrete ejection is greatly enhanced by expansion via gaseous bubbles and breakup. The performance of laser irradiation on concrete is significantly enhanced in the upward direction by the assistance of gravity. In addition, the laser parameters can control the quality and performance of laser drilling and cutting of concrete. Furthermore, the thermal effect analysis determines the impact of laser power on the concrete surface, which may help to consider the heat affected zone coupled with the analyses of material property around the laser treated region.

Monitoring and analysis of thermal effect on tower displacement in cable-stayed bridge

Thermal actions greatly influence the mechanical behavior of cable-stayed bridges. The objective of this research is to investigate the characteristics of the thermal field and the variability of the quasi-static responses of the bridge towers. Based on the monitoring temperature and displacement data, the distribution of the thermal field for the bridge was studied and the time variability of the tower displacement was investigated. The correlation was analyzed to study the relationship between the temperature and the tower displacements and the tower-girder distances. The temperature-induced cable force increments were calculated and a linear regression between the cable force increments and the structural temperatures was performed. A strong linear relationship between the temperature and quasi-static responses of the tower was observed. It is concluded that thermal actions have substantial effects on the quasi-static displacement. Moreover, the temperature-induced cable forces should be fully considered in the safety design of the bridge cables.

Mathematical modeling of laser linear thermal effects on the anterior layer of the human eye

In this paper, mathematical analysis of thermal effects of excimer lasers on the anterior side of the human eye is presented, where linear effect of absorption by the human eye is considered. To this end, Argon Fluoride (ArF) and Holmium:Yttrium-Aluminum-Garent (Ho:YAG) lasers are utilized in this investigation. A three-dimensional model of the human eye with actual dimensions is employed and finite element method (FEM) is utilized to numerically solve the governing (Penne) heat transfer equation. The simulation results suggest the corneal temperature of 263°C and 83.4°C for ArF and Ho:YAG laser radiations, respectively, and show less heat penetration depth in comparison to the previous reports. Moreover, the heat transfer equation is solved semi-analytically in one-dimension. It is shown that the exploited simulation results are also consistent with those derived from the semi-analytical solution of the Penne heat transfer equation for both types of laser radiations.

Thermal effect analysis of silicon microring optical switch for on-chip interconnect**Project supported by the Natural National Science Foundation of China (Nos. 61235001, 61575187, 61535002).

The silicon microring resonator plays an important role in large-scale, high-integrability modern switching matrixes and optical networks, as silicon photonics enables ring resonators of an unprecedented compact size. But as the nature of resonators is their sensitivity to temperature, their performances are vulnerable to being affected by thermal effect. In this paper, we analyze the dominant thermal effects to the application of silicon microring optical switch. On the one hand we theoretically analyze and experimentally measure the thermal crosstalk among adjacent microring optical switches with different distances, and give possible solutions to minimize the affect of thermal crosstalk. On the other hand we analyze and measure the thermooptic dynamic response of microring switch; the experiment shows for the thermal-tuning that the rising edge is around 2 μs, and the falling edge is around 35 μs. We give the explanation of the asymmetric rise-time and fall-time.

Theoretical analysis of Casimir and thermal Casimir effect in stationary space–time

We investigate Casimir effect as well as thermal Casimir effect for a pair of parallel perfectly plates placed in general stationary space–time background. It is found that the Casimir energy is influenced by the 00-component of metric and the corresponding quantity in dragging frame. We give a scheme to renormalize thermal correction to free energy in curved space–time. It is shown that the thermal corrections to Casimir thermodynamic quantities not only depend on the proper temperature and proper geometrical parameters of the plates, but also on the determinant of space–time metric.

Thermal effect analysis on crosstalk and performance of optoelectronic transmitter modules for optical interconnects

This paper presents thermal analysis on crosstalk and performance of optoelectronic transmitter modules and also demonstrates the thermal analysis for efficient heat dissipation for the transmitter modules. The thermal crosstalk model for analysis is based on interconnects parameters for vertically stacked and horizontally packaged optoelectronic transmitter modules. While the analytical expression is used to estimate the thermal critical frequency, f crit_th , above which signals become severely deteriorated, a Teflon-based thermal printed circuit board (PCB) has been designed for packaging the optoelectronic transmitter modules to ensure efficient heat dissipation. The thermal and performance analysis of the packaged modules show that the chips operate at temperatures below the f crit_th , which is apt for reliable data and signal transmission.

Analysis of thermal history effects on mechanical anisotropy of 3D-printed polymer matrix composites via in situ X-ray tomography

The tensile behavior of an additively manufactured (AM) polymer matrix composite (PMC) is studied with in situ X-ray computed microtomography (CT) and digital volume correlation (DVC). In this experiment, the effects of recycled material content and print direction on the selective laser-sintered (SLS) material’s mechanical response are explored. The PMC samples are printed in a tensile specimen geometry with gage lengths parallel to all three orthogonal, primary sintering directions. In situ tensile-CT experiments are conducted at Argonne National Laboratory’s Advanced Photon Source 2-BM beamline. Analysis of the AM PMC’s tensile response, failure, and strain evolution is analyzed both from a conventional standpoint, using the load–displacement data recorded by the loading fixture, and from a microstructural standpoint by applying DVC analysis to the reconstructed volumes. Significant variations on both strength and ductility are observed from both vantages with respect to print direction and the recycled material content in the printed parts. It is found that the addition of recycled source material with a thermal history reduces the tensile strength of the SLS composite for all directions, but the effect is drastic on the strength in the layering direction.

Thermal Effect Analysis of Hot flow Manifold Made for Industrial Automated Washing Machine

Thermal Effect Analysis of Hot flow Manifold Made for Industrial Automated Washing Machine

Analysis of magnetohydrodynamics (MHD) natural convection in 2D cavity and 3D cavity with thermal radiation effects

In this work, the thermal radiation effects on magnetohydrodynamics (MHD) natural convection in 2D cavity and 3D cavity are investigated numerically with different Plank number Pl and Hartmann number Ha. The radiative flux is obtained by solving radiative transfer equation (RTE) instead of widely used approximation methods. A combined method SCM-ACM (spectral collocation method-artificial compressibility method) is developed to solve the N-S equations. Comparative analysis of thermal radiation effects on MHD flow and heat transfer in 2D cavity and 3D cavity is conducted with same parameters. The results show that the thermal radiation strengthens the flow and heat transfer on the spanwise direction in 3D cavity, while the magnetic field plays opposite effects. The differences on flow and temperature distribution between 2D cavity and 3D cavity (on the middle XY-plane in the spanwise direction) are remarkable for high level thermal radiation and weak magnetic flied, and become smaller for weaker thermal radiation and stronger magnetic flied.

Analysis of End-Winding Thermal Effects in a Totally Enclosed Fan-Cooled Induction Motor With a Die Cast Copper Rotor

Thermal overload protection techniques commonly use a simplified 1st order thermal model, which does not provide accurate stator winding temperature prediction and causes frequent undesirable stoppage of the motor in the processes. This paper proposes a higher order lumped parameter thermal network model to accurately predict stator winding temperature. First, the comparison of the predicted stator winding temperature from a 1st order thermal model with a higher order thermal model is performed. Second, a comparison between the actual and the predicted stator winding temperature rise is verified for a 20 hp totally enclosed fan-cooled copper rotor induction motor that has no rotor fins on its short-circuit ring to enhance heat dissipation compared with an aluminum rotor induction motor.

A dynamic stiffness method for analysis of thermal effect on vibration and buckling of a laminated composite beam

Thermal effects on vibration and buckling behaviors of generally layered composite beams with arbitrary boundary conditions are dealt with in this paper. The composite beam is modeled using third-order shear deformation beam theory in which the Poisson effect is incorporated. A constant temperature change through the beam thickness is assumed. An exact dynamic stiffness matrix is formulated by directly solving the differential equations of motion governing the natural vibration of the composite beams subjected to uniform temperature changes along the beam thickness. Application of the derived dynamic stiffness matrix together with the Wittrick–Williams algorithm to compute the natural frequencies and buckling temperature changes of two particular composite beams is discussed. The correctness and accuracy of the derived dynamic stiffness matrix is evaluated by comparing the present results with the available solutions in literature. The influences of Poisson effect, boundary condition, temperature change, thermal expansion coefficient and material anisotropy on the natural frequencies of the composite beams are studied.

Finite Element Analysis of Thermal Effects in Diode End-Pumped Solid-State Lasers

Thermal effects are the main obstacle to getting high power and good beam quality in diode end-pumped solid-state lasers. In this work, a theoretical investigation of thermal effects in single and dual end-pumped solid-state lasers is carried out using finite element analysis (FEA) for a selected number of widely used laser producing materials, namely, Nd:YAG, Yb:YAG, and Nd:KGW. Crystals with different dimensions are also investigated both in single and in dual end-pumped configuration. Finally, the effect of using composite crystals on thermal lensing is investigated. An experiment to measure the thermal focal length for two different crystals was carried out and a comparison with FEA computed focal length of the thermal lens is made. In all cases studied in this work, results show clear effects of thermal lensing with some differences depending on crystal type, pump power, and size.

Analysis and Modeling of Thermal Effect and Optical Characteristic of LED Systems With Parallel Plate-Fin Heatsink

Based on the photoelectrothermal (PET) theory, prediction methods for the thermal effect and optical properties of the light-emitting diode (LED) systems mounted on a given parallel plate-fin heatsink are proposed in this paper. With the PET theory and the heatsink characteristics (heat transfer coefficient, equivalent radius for heat source, fins efficiency), it is possible to accurately quantify junction temperature, heat dissipation coefficient, optical power, and luminous flux of the LED systems. The prediction model consists of a series of optical and thermal evaluation, with which it is simple for LED system designers to comply. The proposed model has been validated using LED sources, which shows good agreement between the calculated and experimental results.

Analysis of Thermal Effects in a Long Porous Rough Slider Bearing

This paper analyses the thermal and roughness effects on different characteristics of long porous slider bearings numerically. The roughness is assumed to be stochastic, Gaussian randomly distributed, and viscosity is assumed to be temperature dependent. The cases of one-dimensional longitudinal and transverse roughness are considered. The irregular domain of the fluid due to roughness is mapped to a regular domain so that the numerical method can be easily applied. It is shown that the combined effect has a significant influence on the performance of the bearing. The impact of the influence depends on the type of roughness and the permeability of the porous matrix. For transverse roughness model it is seen that the combined effect enhanced the load carrying capacity when compared to that of thermal effect on smooth surface, and the opposite is true for longitudinal roughness. However, the load capacity of the bearing is decreased due to the combined effect compared to that of roughness effect for both types of roughness models.