Changes In Temperature Field Research Articles

Thermal Hall Effect of Spin Excitations in a Kagome Magnet.

At low temperatures, the thermal conductivity of spin excitations in a magnetic insulator can exceed that of phonons. However, because they are charge neutral, the spin waves are not expected to display a thermal Hall effect. However, in the kagome lattice, theory predicts that the Berry curvature leads to a thermal Hall conductivity κ(xy). Here we report observation of a large κ(xy) in the kagome magnet Cu(1-3, bdc) which orders magnetically at 1.8 K. The observed κ(xy) undergoes a remarkable sign reversal with changes in temperature or magnetic field, associated with sign alternation of the Chern flux between magnon bands. The close correlation between κ(xy) and κ(xx) firmly precludes a phonon origin for the thermal Hall effect.

Compositional Dependence of Residual and Interfacial Stresses in Thin Film Systems with Substantial Thermal Mismatch Characteristics

We present an analysis of residual and interface stresses, caused by a change in external temperature field, due to mismatch in thermal and elastic characteristics in a dissimilar system of a thin film and a flexible substrate. A representative volume element of the system is defined as a heterogeneous two-phase layered element bonded at an interface in a sense of coherent bi-layer, where each phase possesses distinct elastic and thermal characteristics. We use a spatial averaging technique with particular form of strain field that satisfies compatibility equations in the bulk and at the interface. Derived special rule of mixtures yields rigorous estimates for residual stress distribution through thickness of the representative volume element. Corresponding distributions of stress fields are calculated for distinct magnitudes of compositional parameter representing the volumetric fraction of the film.

Effects of Flow Ratio of Transverse Jet on Flow and Heat Transfer : A LBE Study

A Lattice Boltzmann Equation (LBE) method is utilized to simulate a transverse jet in cross flow (TJiCF) to investigate the interaction between the transverse jet and the main flow by using the TD2G9 model. Seven cases of different flow ratios (Jr = 0.3, 0.6, 0.9, 1.2, 1.5, 1.8, 2.0) are simulated. The influences of flow ratio (Jr) of the transverse jet to the main flow on vortex streets and temperature fields are studied. The characteristics of fluid vortex, mean axial velocity, mean temperature, fluctuating velocity, etc., are studied in details to show the effects of Jr. Significant changes of velocity and temperature fields are found in TJiCFs for Jr > 1, i.e. the turbulence is augmented significantly and the convective and conductive heat transfer are enhanced greatly too. The turbulence augmentation is especially evident in the recirculation zone after the transverse jet. The conductive heat transfer is enhanced by thinning the thermal boundary layer near the wall, and the convective heat transfer is enhanced by intensive fluid mixing between the transverse jet and main flow.

Analysis of Residual Stress Distribution in Anisotropic Thermo-Elastic Bimorph Systems

We present an analysis of residual stresses in longitudinal and transversal direction of a bimorph element induced by a change in external temperature field due to mismatch in thermal and elastic characteristics in dissimilar two-phase composite material with laminated structure. Representative Volume Element of the system is defined as a heterogeneous two-phase layered element bonded at an interface in a sense of coherent bi-layer, where each phase possesses distinct anisotropic material characteristics. We use a homogenization procedure with particular form of strain field, which satisfies compatibility equations in the bulk and at an interface. Special rule of mixtures derived from a spatial averaging principle yields explicit dependence of through-thickness residual stress on a compositional parameter defined as a volumetric fraction of one phase of the system.

Bubble migration during hydrate formation

A model of the process of migration of methane bubbles in water under thermobaric conditions of hydrate formation is proposed. The peculiarities of the temperature field evolution, migration rate, and changes in the radius and volume fraction of gas hydrate bubbles are studied. It is shown that, with a constant mass flow of gas from the reservoir bottom, for all parameters of the surfacing gas hydrate disperse system, there is a quasistationary pattern in the form of a “step”-like wave. Depending on the relationship of the initial gas bubble density with the average gas density in the hydrate composition determined by the depth from which bubbles rise to the surface, the final radius of hydrate particles may be larger or smaller than the initial gas bubble radii. It is established that the speed at which gas hydrate inclusions rise to the surface decreases by several times due to an increase in their weight during hydrate formation. The influence of the depth of the water reservoir whose bottom is a gas flow source on the dynamics of hydrate formation is studied.

Thickness and temperature dependences of the degradation and the breakdown for MgO-based magnetic tunnel junctions

The reliability of a magnetic tunnel junction (MTJ) with an MgO tunnel barrier was evaluated. In particular, various voltage tests were used to investigate the effects of the barrier thickness and the temperature on the resistance drift. We compared the resistance change during a constant voltage stress (CVS) test and confirmed a trap/detrap phenomenon during the interval stress for different barrier thicknesses and temperatures. The resistance drift representing degradation and the time to breakdown (TBD) representing the breakdown characteristic were better for a thicker barrier and lower temperature, but were worse for a thinner barrier and a higher temperature. The results suggest that breakdown and degradation due to trap generation strongly depend on both the barrier thickness and the temperature. Furthermore, as the TBD varies at steady rates with changing barrier thickness, temperature, and electric field, we assume that a MTJ with an adnormal thin layer of MgO can be screened effectively based on the predicted TBD. As a result, the barrier thickness and the temperature are very important in determining the reliability of a MTJ, and this study is expected to be helpful in understanding the degradation and the breakdown of a MTJ.

Two-phase flow and thermal transients in proton exchange membrane fuel cells – A critical review

The start-up and varying load conditions encountered during a drive cycle introduce transient behavior in electrochemical performance as well as two phase flow and temperature of PEM fuel cells. The electrochemical transients have been extensively studied in literature, while the effects of two-phase flow transients and temperature transients have not been studied to any great detail. These two transients affect the electrochemical and mass transport performance in an automotive PEM fuel cell. Changes in load result in changes in flow rates and electrochemical reaction rates. These in turn result in changes in temperature field, two-phase flow patterns, area coverage ratio, and pressure drop. Transient operation leads to uneven power generation and loss in reliability. Transient changes in two-phase flow result in increased pressure drop, thereby increasing the auxiliary power consumption and the parasitic power losses. Thermal transients may result in flooding or dry-out of the GDL and membrane and lead to performance deterioration. Understanding transient behavior is thus critical for the reliable and predictable performance from the cell. A detailed review of the existing literature is presented along with the research needs in this area.

Numerical Analysis of Hot Stamping Mold Cooling System Based on FLUENT

Cooling is very important in the process of hot stamping process of a link, directly affect the mechanical properties and service life of the forming parts. Mold cooling system is effective and reasonable, therefore, is the important indicators of the hot stamping process performance. This paper deeply analyzes the hot stamping process and heat transfer theory, summarizes the main factors affecting mold cooling system performance. At the same time, the fluid analysis software FLUENT is adopted to U artifacts a numerical simulation of the hot stamping process analysis of mold during the cooling process, the work piece temperature field change, for the hot stamping mold cooling system design to provide theoretical reference.

Sensitivity of transient temperature field in the casting domain with respect to latent heat perturbations

The mathematical model of thermal processes in the casting domain can be formulated using the fixed domain approach. The energy equation corresponding to this model contains the parameter called a substitute thermal capacity (STC), in which the alloy latent heat appears. The aim of considerations is the application of sensitivity analysis methods for estimation of temperature field changes due to the perturbations of alloy latent heat. In this the analytical form of STC results from the consideration concerning the lever arm model and the Scheil model. The equations determining the sensitivity function are found using the so-called direct approach. At the stage of numerical modeling the finite difference method is used. In the final part of the paper the example of computations is shown.

Overall stability analysis of oversized steel‐framed buildings in a fire

SummaryOur present paper summarizes the shortcomings in the current fire‐resistant design of oversized steel structures and proposes a method for overall stability analysis of steel structures in the event of fire. The Fire Dynamics Simulator (FDS) software platform–based large‐eddy simulation technology can accurately reflect the environment in a fire scenario and correctly predict the spatial–temporal change in the smoke temperature field within an oversized space. Adopting the FDS software and finite element structural analysis (ANSYS) coupling can fundamentally overcome the natural defect of adopting the International Organization for Standardization (ISO) standard curve (or other indoor homogeneous temperature increase curves) that substitutes a point for the overview of a field. They reflect the structural additional internal force and internal force redistribution incurred by the gradient temperature difference of the spatial–temporal changing nonhomogeneous temperature field and both theoretically and technically realize the analysis of structural heat transfer and mechanical properties in a natural fire. Furthermore, a modified model to predict the steel temperature curve in localized fire is also proposed. The localized fire in large spaces can be treated as a point fire source to evaluate the flame thermal radiation to steel members in the modified model. Copyright © 2014 John Wiley & Sons, Ltd.

Magnetic Structure of Nanosized Ferrimagnetic Particle Depending on External Parameters

In this work we performed analysis of the magnetic order of nanosized ferrimagnetic particle at the temperature and magnetic field changes, using Monte-Carlo method. The calculations take into account real mechanisms of exchange and magnetocrystalline anisotropy of ferrospinels.

Changes to the Canadian Arctic Archipelago Sea Ice and Freshwater Fluxes in the Twenty-First Century under the Intergovernmental Panel on Climate Change A1B Climate Scenario

A coupled ocean and sea-ice pan-Arctic model forced by the Intergovernmental Panel on Climate Change A1B climate scenario is used to study the evolution of ice and ocean surface conditions within the Canadian Arctic Archipelago (CAA) during the twenty-first century. A summer ice-free CAA is likely by the end of our simulation. Sea ice undergoes significant changes from the mid-2020s to the mid-2060s in both concentration and thickness. The simulation shows a shrinking of 65% and a thinning of 75% in summer over the 40 years, resulting in a partially open Northwest Passage by the 2050s. However, ice in central Parry Channel might increase due to a decrease in export from April to June, linked to a reduced cross-channel sea surface height (SSH) gradient, before melting thermodynamically. On a larger scale, the central CAA throughflow will experience a significant decrease in both volume and freshwater transport after 2020, which is related to the change in the SSH difference between the two ends of Parry Channel, particularly the lifting of SSH in Baffin Bay. With a lower albedo, a warmer ocean is simulated, particularly in summer. The sea surface salinity within the CAA demonstrates a strong decadal oscillation without a clear trend over the entire simulation. A north–south pattern, separated by Parry Channel, is also found in the changes of ocean temperature and salinity fields due to different ice conditions.

A comprehensive study on the equivalent electrical conductivity tensor validity for thin multidirectional carbon fibre reinforced plastics

The electrical conductivity of the dry carbon fibre multidirectional thin layers (without resin matrix material) can be expressed by an equivalent EC tensor. The flow of the electric current inside the material is depended, mainly, upon the material’s microstructure and specifically upon the interlaminar microstructure. In the case of the multidirectional carbon fibre composites, two different methodologies were used in order to elucidate the EC behaviour of the multidirectional laminates both quantitatively and qualitatively. The first experimental setup was used in order to compare the measured electrical resistance to the calculated equivalent EC tensor. Also, the temperature field changes according to the equivalent EC tensor of each laminate and the second methodology was utilized in order to elucidate the validity of equivalent EC tensor indirectly, comparing the temperature field of the electro-thermal numerical models and the measured temperature field.

Application of Biomass Burning Stove in the Greenhouse Environment

According to the demands of greenhouse environmental conditions, this paper examines a solid fuel burning stove applied to compression molding of biomass in order to solve the issues which temperature is too low in greenhouses in winter north of China and carbon dioxide concentration is too low caused by insufficient ventilation number. The burning stove designed with big furnace, no grate and recalculated secondary air. Fuel utilization was improved in the largest degree in this design. Feed amount, feed rate and time are controlled by the PLC system which is adopted to make fuel fully burning, low pollution emissions and more automation. The temperature field and gas flow field changes is simulated by the FLUENT. The temperature of various sections and the formation of nitrogen oxides is reduced by the special design when burning. Experiment shows that sulfur dioxide concentration is about 0.41mg/m3, nitrogen dioxide is about 0.498mg/m3 which have no effect in growth and development of crops. This paper provides theoretic guidance for improving greenhouse conditions.

Joint Resistance Characteristics of Mechanical Lap Joint of a GdBCO Tape With a Change in Temperature and Magnetic Field

Mechanical joints of a high-temperature superconducting (HTS) conductor has been investigated for a “remountable” (demountable) HTS magnet. In a previous study, prediction method of joint resistance for a large-scale conductor was proposed using experimental data and current distribution analysis. However, the data were obtained by tests conducted at 77 K under self field. The joint resistance consists of contact resistance and resistance of constituted materials of HTS tapes, which depend on temperature and magnetic field. In this paper, therefore, we experimentally and numerically evaluated joint resistance characteristics with changing temperature and magnetic field using mechanical lap joint of a GdBCO tape. The experimentally evaluated joint resistance varied with the temperature and magnetic field as predicted. The joint resistance characteristic also depended on contact materials. The numerically evaluated contact resistance included in the joint resistance depending on temperature shows a tendency similar to the calculated value of the constriction resistance based on the Holm's contact theory.

The Dynamic Characteristics Research of Compact Heat Regenerator used in Regenerative Burners for Metallurgical Heating Furnaces

Abstract The gas burner is a device which the main aim is delivering the right number of gas fuel and oxidizing agent and it also has to ensure flame stabilization. The difficult controlling problem appears when the modern and compact high temperature regenerative burners are used. The controlling difficulties in those systems are related to the large number of burners and a periodic change (with high frequency) of temperature field which depends on such parameter as reversion time. The knowledge of the dynamic and static regenerator characteristics makes easier the programming of automatic control and regulation process and helps in creating the new regenerator filling construction in order to improve the heat transfer intensification and the furnaces efficiency. Based on research results the paper presents the selected data research dealing with the dynamic and static regenerator characteristic. The measurement of quick-changing fluctuating thermal field and the way of the temperature sensors selection have been indicated. The regenerator starting state and pseudo-steady state characteristics have also been presented. Finally the qualities of the regenerator and the economic income have been expressed.

Study on the influence of airflow on the temperature of the surrounding rock in a cold region tunnel and its application to insulation layer design

To show the influence of airflow on the temperature of the surrounding rock in a cold region tunnel, a temperature field model was developed. The model includes temperature control equations of the surrounding rock, air temperature field control equations in the tunnel and wind flow control equations of the turbulence field. On this basis, a numerical analysis method is used to discuss the temperature field change law of the surrounding rock and the thermal insulation measures of the Galongla tunnel in Tibet under the condition of ventilation. The study results show that (1) the air temperature and air speed are two important factors that significantly affect the temperature distribution of the surrounding rock in the tunnel and (2) because of the ventilation effect, the temperature of the surrounding rock falls below 0 °C, and adverse conditions appear at the inlet and outlet sections of the tunnel during the coldest month (January). Further research shows that heat preservation material, such as a phenolic layer with a thickness of 6 cm laid on the secondary lining surface, could effectively protect the Galongla tunnel and rock from freeze and thaw damage if placed for 600 m into the inlet section and 400 m from the outlet section of the Galongla tunnel.

Numerical Study of Steady Natural Convection Flow in A Prismatic Enclosure with Strip Heater on Bottom Wall Using Flexpde

Laminar natural convection in two-dimensional Prismatic enclosure is studied and analysis numerically. For the enclosure top inclined walls are considered at low temperature, two vertical walls are adiabatic and strip heater at constant high temperature mounted on the bottom enclosure, while the reminder bottom wall kept at low known temperature. The partial differential equations for two dimensional conservation of mass, momentum and energy are solved using finite element software package (FLEXPDE.5). For Rayleigh number varying from 103 to 105 and for constant Prandtal number Pr=0.7 the change in temperature and flow fields (stream functions) were investigated for different heater locations and for different number of heaters. The effect of the number and locations of the strip heaters on local and mean Nusslet number were examined. Results were presented by streamlines, isotherms and Nusselt number and it indicates that the Nusselt number is significantly affected by increasing both Ra and number of heaters. A comparison of the streamlines, isotherms curves and average Nusselt at the same boundary conditions was made with that obtained by Tanmay et al.(7), and showed a good agreement.

The Numerical Simulation of Composite Explosive Energy Coupling in Underwater Explosion

This paper choose three kinds of explosives and two kinds of charge structure, the inner and outer layer, the left and the right structure. It studies the energy coupling between the two parts of explosives and the influence of charging way of energy output structure. Ls-dyna is used to numerically simulate the process, analyze this kind of composite explosive shock wave overpressure - time history curve and the change of temperature field with time when the explosive blast in deep water. Their energy outputs were compared with single formula of explosive. Simulation results show that: Using the same chemical composition, Different dual charging structure of explosives has an impact on the explosion of the same point load and the heat loss. The energy couples between two parts of explosive.

Multi-Point Temperature Monitoring System for the LNG Storage Tank

Liquefied natural gas (LNG) is obtained by reducing the gas temperature to-162 degree, Fault of the inside steel cans, the insulation layer or the concrete outer tank of the LNG storage tank can lead to changes of the temperature field, local temperature decreases, and the outer concrete tank safety is threatened. Infrared thermal imagers are used to monitor the temperature of the LNG storage tank, get the overall temperature distribution image of the outside concrete tank, establish the communication between the thermal imagers and the computer, and analyze the heat image of tank by the compute, find out the failure structure of the LNG storage tank according to the temperature field changes. Multi-point temperature monitoring system for the LNG storage tank can provide powerful guarantee for the safe storage of the liquefied natural gas.