Changes In Temperature Field Research Articles

Study on the mechanism of ultrasonic-assisted water confined laser micromachining of silicon

The ultrasonic-assisted water confined laser micromachining is a novel micromachining method. This paper reports the experimental studies of ultrasonic power and water layer thickness on the laser (1064 nm nanosecond pulse laser) micromachining of silicon. Besides, this reports a systematic discussion on the influence of the acoustic streaming and bubbles (induced by laser) dynamic change on the machining process. The acoustic streaming and flow pattern under different ultrasonic power application and different water layer thickness using Particle Image Velocimetry (PIV). A finite element (FE) heat transfer model was employed to gain a better understanding of the effect of the acoustic streaming velocity on the temperature field change in laser processing. The bubbles (induced by laser) dynamic behavior is observed by the high-speed camera. The results showed that the ultrasonic-assisted laser ablation can yield much higher the material removal rate than laser cutting in water without ultrasonic-assisted. Besides, the increase in the ultrasonic power helps to improve the etching efficiency but is not apparent. When the water layer thickness is 1 mm, the cutting effect is significantly different from the laser ablation in the other three water layers. Through the PIV images and simulate results, it has been found that the influence of acoustic streaming on heat transfer in laser processing is small. Through high-speed camera imaging observations, the dynamic change of bubbles is an essential mechanism for the enhanced material removal rate and affect the machining performance in this study. This study helps understand the mechanism of ultrasonic-assisted water confined laser micromachining better and promoting this technique potential application in the micromachining of hard brittle materials.

Study on the influence law of complex curtain horizontal freezing and freezing on the surrounding environment

Freezing up is one of the problems that are paid close attention to in the construction of artificial freezing method, especially the horizontal freezing up of complex curtain is difficult to be calculated by theoretical formula. The adaptability of numerical calculation is strong. In this paper, numerical calculation method is used to simulate the horizontal freezing and freezing expansion of complex curtain. Thermophysical parameters considered in the simulation change with the change of temperature field. Thermodynamic parameters of each point in soil are given by way of field variables, which provides ideas and methods for accurately simulating the horizontal freezing and freezing expansion displacement field of complex curtain.

An analytical model for vertical-butted geothermal well with different groundwater flow directions

Geothermal has become a popular renewable energy in recent decades due to its properties of non-polluting, clean and large reserves. The vertical-butted geothermal well is a new structure for geothermal utilization. Two vertical boreholes with a certain distance are connected at bottoms by directional drilling to form a U-shape circulation loop. Due to the existence of the aquifers, the movement of underground water extends the heat exchange range and affects the geothermal system performance. This paper aims to develop an analytical method to solve the soil temperature field around the vertical-butted geothermal well with different flow directions. Taking the interacted effect of the two parallel pipes on the surrounding soil into consideration, the temperature distribution in the heat exchange zone is obtained. It is found that the temperature field changes significantly when the groundwater flow exists. The movement of underground water extends the downstream thermal radii from 4.8 m to 10.7 m, 10.6 m and 11.7 m when the flow directions are 0°, 45° and 90° toward the axis of the two pipes, respectively. The upstream thermal radii reduce from 5.4 m to 1.9 m for all the cases with groundwater movement. In addition, the effect of the underground water flow direction on the temperature field around the butted wells is analyzed. The results show that when the groundwater flow direction is perpendicular to the axis of the two pipes, the temperature field is the most beneficial to the performance of the vertical-butted geothermal well.

Study on the influence of horizontal freezing and melting of complex curtain on surrounding environment

In this paper, the 3-D finite element model is used to systematically analyze the displacement field of artificial frozen soil thawing settlement. During the simulation process, the thermophysical parameters change with temperature, such as elastic modulus, density, specific heat and other parameters change with temperature. When calculating the temperature field of melting and settling, the temperature field on which the mechanical parameters are based is given point by point through the field variables. After changing with time, the temperature field changes with the points, and the mechanical parameters also change point by point. To ensure that the simulated melting and settling calculation process is more in line with the actual project. The calculation results of melting and sinking show that the whole displacement field presents nonlinear changes with time and space. The research results of this paper provide reference for the control measures of melting and settling.

Mechanical response induced by flux jump in a cylindrical superconductor

The flux jump in bulk superconductors is accompanied by a rapid change in temperature and magnetic field, which can induce change in electromagnetic bodyforce and thermal stress. It is well known that bulk superconductors are brittle and have low mechanical strength, and thus, large electromagnetic bodyforce and thermal stress can cause damage of the bulk superconductor. In this paper, an electromagnetic-thermal-mechanical multi-physics model is adopted to compute the mechanical response of a bulk superconductor during flux jump in an external magnetic field. The results indicate that the flux jump in the bulk superconductors can also lead to the jump of the average electromagnetic force, temperature, stress, and strain. Meanwhile, it can be found that the flux jump can occur more easily with a faster change in the magnetic field, a lower ambient temperature, and a large-size superconductor. The results also show that the peak value of thermal strain is much larger than the strain generated by electromagnetic bodyforce during the flux jump. In addition, the change in strain has the same trend as that of the temperature. Thus, the strain may also be used to monitor the flux jump.

High field phase transition of cathode material Li2MnSiO4 for lithium-ion battery

The magnetic properties of the candidate lithium-ion battery cathode materials Li2MnSiO4 have been studied experimentally using static and pulsed high magnetic fields. A field-induced magnetic transition is observed in low temperature region, in which a saturation magnetization is observed above 27 T which confirms that the Mn-ion has a dominant low spin state with a saturated magnetic moment of ∼3.1 μB/Mn. With the change of temperature and magnetic field, the Li2MnSiO4 shows a complex magnetic phase transition. Considering to the coupling between spin, charge and orbital, the field-induced magnetic transition may affect the charge-discharge behavior of the cathode material, thus, the study is expected to explore the possibility and stability of the candidate lithium-ion battery cathode materials used in the low temperature and high magnetic field circumstance and its performance degradation.

A thermal cloak with thermoelectric devices to manipulate a temperature field within a wide range of conductivity ratios

A technology of active thermal cloaks that use thermoelectric (TE) devices to manipulate heat flow is devised, and its powerful adaptive function is studied quantitatively. Determining the distribution of adaptive heat sources is a critical mission in the design of active thermal cloaks. This can be accomplished by directly solving the heat conduction equation for the device being studied. The input electric current of the TE components can then be determined individually according to the heat source distribution. On this basis, the performance of our designed cloak system is tested by finite element analysis. Simulation results show that even if the thermal conductivity ratio m (of object-to-background) and/or the temperature gradient g of the background temperature field change over a very wide range, TE components can pump the heat flow accurately from one side of the cloak to the other side by adjusting the input current, so that the background temperature field can be restored to its original state to good approximation. Design of an active thermal cloak is no longer limited by material properties and can be adjusted freely according to the thermal environment. The feasibility of active thermal cloaks is demonstrated theoretically by this work.

Study on environmental impact of artificial horizontal freezing method in subway connecting passage

When the subway is built in complex urban strata, especially when excavating near buildings, it is necessary to strictly control the freezing amount by adopting artificial freezing method. At present, the theoretical calculation is aimed at the frozen rise under ideal conditions, but for complex geological conditions, the simplified model results are difficult to meet the actual requirements. However, numerical calculation can adapt to complex strata and complex boundary conditions. Therefore, in this paper, the environmental impact of artificial horizontal freezing method in subway connecting passage is studied by numerical simulation, and the change of thermophysical parameters with the change of temperature field is considered in the simulation. The simulation method in this paper provides guidance for actual construction.

The Evolution of Thermal Conductivity and Pore Structure for Coal under Liquid Nitrogen Soaking

An experimental system for liquid nitrogen soaking and real‐time temperature measurement was designed and implemented to investigate the characteristics of temperature field changes in coal under liquid nitrogen soaking. Then, the heat conduction law of the coal in the process of liquid nitrogen soaking and room temperature recovery for dry and water‐saturated coal were examined. The microstructure characteristics of the coal before and after liquid nitrogen soaking were analyzed with nuclear magnetic resonance (NMR) technology. The results showed that, during the liquid nitrogen cold soaking process, the heat transfer law of the dry and water‐saturated coal samples exhibited a notable three‐stage distribution. For the room temperature recovery process, the dry and water‐saturated coal samples exhibited rapid heating characteristics, and the cooling rate gradually decreased to zero. NMR test results indicated that the liquid nitrogen soaking increased the number of micro and small pores in the coal. Thermal stress analysis revealed that the thermal stress generated by the dry coal was larger than that produced by the saturated coal, and the damage was primarily caused by thermal stress. However, the permeability of the saturated coal was better than that of the dry coal. The damage on the saturated coal was caused by the volume expansion of pores and fissures caused by water‐ice phase transition.

ИССЛЕДОВАНИЕ ТЕМПЕРАТУРНОГО СОСТОЯНИЯ ГАЗОГЕНЕРАТОРА ТВЕРДОГО ТОПЛИВА ПРИ СТЕНДОВОМ ИСПЫТАНИИ МЕТОДОМ ТЕПЛОВИЗИОННОЙ СЪЕМКИ

In this article, the authors described in detail the methodology for conducting fire bench tests for the reusable experimental design of a solid propellant (SP) gas generator, specially designed to study the complex laws of heat and mass transfer under conditions of unsteady combustion of SP during operation of the installation and in the after-treatment mode. The developed technique allows us to study the nonlinear dynamics of temperature field changes, fuel and generator gas consumption, as well as its composition. The paper presents the chronology of the research, describes the used measuring equipment. Based on the carried out thermodynamic analysis of working processes in the combustion chamber of the gas generator under study, an algorithm for the optimal determination of its operating characteristics is proposed. The methodology of experimental studies of the thermal state of the design of the TT gas generator is universal and can be successfully used in working out other gas generating solid fuels with various energy characteristics during the optimal design of special technical systems such as solid propellant rocket motors (the approbation of the methodology is given on the example of an experimental design with a rotating nozzle), emergency rescue systems and aircraft engines. The results of studies of the thermal state of the elements of the TT gas generator by thermal imaging are well verified with the readings of temperature field sensors.

Climate Change Assessment Using Negative Extreme Deviations of Surface Temperature Field (Case Study: Tbilisi)

To conduct regional climate change assessment for the selected location (Tbilisi) more than century period hydrometeorological observation data of day-night minimal temperature is used. In the presented paper only temperature negative values of whole winter season are used. The temperature field change is characterized by the following four parameters: the minimal temperature sum (winter-day temperature is less than zero) of winter frost days; frost day number; season minimal temperature and the occurrence date of season minimal temperature. The modular structure of the above listed parameters has been studied and the mathematical expressions for temporal changes of those parameters have been obtained considering dynamical norms and cyclical changes. The intensity of this change in terms of global warming has been determined. One of the main parameters determining climate change is the variations of temperature field. Despite the fact that this parameter has been modified in the large range due to numerous impacts, they kept stable and provide sustainable equilibrium of the Earth’s energy potential during long-term (several decades) period. This was the reason why the Earth climate remained unchained. As it is known, the anthropogenic impact on the environment has breached the sustainable balance of the Earth energy potential, the potential has been gradually grown almost for more than a century and is known by the name of global warming. The above-mentioned process has already created the greatest threat to the existence of Earth’s biosphere and if it still continues the catastrophic results eventually have to be expected. This led that the problem solving has been set as an urgent task. The numerous fundamental studies for all regions of the world have been carried out to assess the intensity of this process.

Effect of Hydration Heat Inhibitor on Thermal Stress of Hydraulic Structures with Different Thicknesses

Concrete hydration heat inhibitor can inhibit the early hydration reaction of concrete and reduce the initial heat release of concrete. However, there is no in‐depth research on the effect of hydration heat inhibitor on hydraulic structures with different thicknesses and constraints. In this paper, numerical simulation is used to study the change of temperature and stress field after adding hydration heat inhibitor by establishing the finite element models of tunnel lining, sluice, and gravity dam. The results show that the effect of the hydration heat inhibitors on reducing the temperature peak is inversely proportional to the thickness of the structure. A formula is put forward to evaluate their relation in this paper. When the thickness of the structure is about 6 m, there is no peak cutting effect. For the stress field, hydration heat inhibitor can greatly reduce the thermal stress of the thin‐walled structure and make the structure meet the temperature control requirements; for the medium wall thickness structure, it can reduce the internal tensile stress about 50% and the surface tensile stress about 20%, and other temperature control measures are still needed to ensure that the surface tensile stress of the structure meets the requirements; for hydraulic structures with large volume and thickness, the application effect of the inhibitor has limitations, which can reduce the internal tensile stress about 30%, but the tensile stress in the surface area will increase about 7% due to the increase of the internal and external temperature difference; therefore, other temperature control measures such as arranging cooling water pipe, strengthening surface insulation, and so on are needed to ensure that temperature cracks do not occur. This paper provides references and suggestions for the research and engineering application of hydration heat inhibitor.

Study on the Arc Motion Characteristics of Multi-Chamber Arrester Based on 3D Model

In ultra HVDC transmission system, arcing horn gap breakdown makes the arc hard to extinguish, threatening transmission safety. Multi-chamber arrester (MCA) is applied in extinguishing the arc to ensure safety. Here, we investigated the arc motion characteristics of the MCA to analyze its arc extinguishing ability. First, a three-dimensional model of the arc plasma in a single chamber was established based on magneto-hydrodynamic (MHD) theory, and the arc motion inside and outside the chamber were analyzed. Next, changes of temperature, velocity and pressure field were simulated. The results showed that the time required for arc totally exiting the chamber is approximately $96~\mu \text{s}$ , the airflow maximun velocity is about 865 m/s, and the highest pressure is more than 4 atm. Particularly, there is a flow reflux at the outlet, as the air flows inward from the outside and form an “oscillation”. Moreover, the arc motion characteristics of different discharge currents within different chamber structure were analyzed. It was found that the spacing between anode and cathode, the radius of electrodes and the outlet radius are the key factors regulating the airflow velocity, and the outlet radius of the chamber has the greatest influence. At last, the accuracy of our model was validated with experimental data.

Numerical analysis of the forming process of the bearing capacity of the auxiliary pile foundation in Permafrost area

Bore Cast-in-place Piles broke the original water and heat balance state of the stratum in the bridge construction of Qinghai Tibet railway. The settlement of a bridge pile foundation was relatively large after more than ten years of operation. It was found that there is confined water in the foundation soil after investigation. Engineers planned to add auxiliary piles at the original pile side to reduce the settlement of the pile foundation.This paper studied the temperature change, bearing capacity formation rule and long-term bearing capacity change trend of the new pile-soil system after adding auxiliary piles on the original foundation, which provides certain theoretical basis and reference basis for engineering practice. A three-dimensional model of a bridge pile foundation was established by numerical method. Considering the influence of atmospheric temperature, hydrogeological conditions, concrete temperature into the mold, and the temperature of underground confined water, based on the heat transfer theory, the boundary conditions and initial conditions are given. The influence of the change of ground temperature field and the change of pile-soil interface temperature on the bearing capacity of the foundation was studied after the auxiliary pile was poured. The analysis shows that the measure to increase the bearing capacity by adding auxiliary piles is a double-edged sword. On the one hand, the auxiliary piles themselves constitute the bearing capacity together with the original pile foundation after thawing, on the other hand, the auxiliary piles are constructed by the method of pouring concrete in the field. The hydration heat of concrete makes the temperature of the original foundation soil rise, and reduces its bearing capacity. The whole bearing capacity will not be increased at the initial stage, but also will be temporarily reduced, and the whole bearing capacity will be formed after the frozen soil is frozen back in the later stage.

Effect of the Landau Levels on the Super Hyperfine Structure of ESR Spectra of Fe3+ Precipitates in Dirac 3D Semimetal Cd3As2

The influence of d-metal impurities on the magnetic and transport properties of 3D topological semimetal Cd3As2 has been experimentally studied. It is found that alloying with iron does not change the sign of magnetoresistance (in contrast to Eu). Amplification of oscillations of the parameters (magnetic susceptibility, contact potential difference, and conductivity) related to oscillations of the density of states at the Fermi level is observed with a change in temperature and magnetic field. ESR signals from Fe2+ ions (which are most likely the main type of Fe impurity in Cd3As2) have not been detected in the temperature range of 10–300 K. Weak ESR signals with a super hyperfine structure, which is obviously affected by the Landau levels, have been observed from Fe3+ ions.

Modeling of the plywood making process glued with thermoplastic polymer

A promising variety of the wood composite materials is plywood glued with thermoplastic polymers. However, making such a wood composite requires adjustment of the pressing modes, because there is a slightly difference between the hot method of the veneer packages pressing glued with thermoplastic films and the method of the veneer packages pressing glued with thermosetting adhesives. Among the main processes that occur in the gluing plywood process are heat and mass transfer. The availability of the thermoplastic film between the veneer sheets is going to change the thermal conductivity of the package, and therefore will affect the pressing duration. If suppose, that the package has a plate appearance, which is located between heated to the certain temperature pressed plates, then the known Fourier-Kirchhoff thermal differential equation can be applied. The basis for the model development of the warming package veneer process glued with thermoplastic film are laid methods of nonlinear programming, uniform search and conjugate gradient. On the offered mathematical model basis, the temperature field change in the package thickness during the plywood gluing with plastic film is calculated, the calculation of the warming duration indicators of the package veneer is done and this indicator dependence on the thermoplastic film flow rate and the pressing temperature is established. The duration of the warming package veneer glued with thermoplastic film depends on the temperature at which the thermoplastic polymer will change from a highly elastic to the viscous state. The transition of the thermoplastic film LDPE to the viscous state begins at 125оС and lasts up to 240 оС. With increasing of the press temperature plates from 140 to 180оС the duration of warming up the middle of the package to 125оС decreases by 89% for all investigated polymer costs is established. Changing the polymer content in the package does not significantly affect the duration of its warming. With increasing of the thermoplastic film flow rate from 130 g/m2 to 190 g/m2, the duration of warming up the middle of the veneer package to 125оС increases slightly from 3,8 to 4,2% depending on the pressing temperature. Suggested mathematical model allows to set the material parameters and plywood pressing mode influence on the duration of the warming package veneer while plywood making glued with the thermoplastic film LDPE.

Research of Heat Exchange in the Concentration of Vegetable Juice

The purpose of the article is to improve the heat transfer equipment for the production of concentrates from vegetable raw materials, namely a vacuum-evaporator apparatus with a mixing device. System analysis, namely simulation modeling, has been chosen as a tool to determine the advantages of the proposed technical solutions.Research methods. The main heat exchange process of the proposed method for the production of concentrated products from vegetable raw materials is the boiling of the juice in a vacuum evaporator apparatus of periodic action with an improved design of a steam mixer. The mixer is a spiral metal tubular constructor with the possibility of supplying steam into its cavity. As a result of the experiments the dependence of the heat transfer coefficient on the rotation frequency of the developed mixer was investigated, the analysis of which allowed to determine the efficiency of using the new design of the mixing device. This became a practical basis for system-dynamic modeling of temperature field changes during vegetable juice boiling.Results. A new method of processing of vegetable raw materials has been proposed. For its implementation, a vacuum-evaporator apparatus with advanced mixing device was developed. Experimental studies were conducted to determine the heat transfer coefficient during juice concentration. The simulation of changes in the temperature field in the apparatus and the overall working cycle of the evaporator are carried out. Simulation results were obtained using the Vensim system analysis software package. The duration of real steadystate heating was controlled experimentally with the use of a vacuum-evaporator apparatus.Conclusions. The dependence of the heat transfer coefficient on the number of revolutions of the stirrer during the boiling of vegetable juice in the developed vacuum-evaporator apparatus is determined. A system-dynamic model of the heat transfer process has been created, namely the changes in the temperature field in the apparatus are determined, and that makes it possible for further computer experimentation on the basis of the practical studies of the complex heat transfer system relations.

Numerical Simulation Study on T-tape Welding of Mild Steel

Welding technology as an important technology of industrial production is widely used in production practice, T-type welding joint, as the main form of welding space joint, is widely used in daily production. The article mainly uses software ANSYS, the T-type welding of Q345 low carbon steel was analyzed by numerical simulation. Calculating the changes of temperature field and stress field, the results can effectively predict the problems related to welding quality, improve production efficiency and save production cost.

Experimental and numerical study of a passive thermal management system using flat heat pipes for lithium-ion batteries

Effective thermal management is essential for lithium-ion batteries to reduce the battery surface temperatures and the temperature differences within the battery packs. In this study, a battery thermal management (BTM) system containing flat heat pipes was established to improve the temperature uniformity during high discharge rate operations, thereby ensuring battery performances, long lifetimes, and safety. A numerical model was developed, and the modeling results agreed with the experimental data. Through the simulation analysis, we discuss the change in the battery temperature fields, which were compared to two other cooling systems: air natural convection and aluminum plate cooling. The results indicated that the use of flat heat pipes could effectively decrease the maximum temperature and temperature difference with minimum energy costs.

Study on Thermal Erosion Process of SiCp/Al Composite Material in EDM

SiCp/Al composites are composed of two different material properties of aluminium matrix and SiC particles. In order to deeply study the erosion process of SiCp/Al composite in EDM, a single pulse discharge model of SiCp/Al composites was established. The melting and solidification model and the volume of fluid (VOF) model in Fluent software were used to simulate the thermal erosion process of EDM. The change of temperature field and the formation of molten pool in the heating process of SiC particles and Al matrix are analysed. The number of SiC particles in molten pool is counted and analysed, and the number of SiC particles in molten pool was counted, the simulation results were verified by the single pulse EDM experiments. The results show that the depth-diameter ratio of the molten pool increases with the increase of the pulse width, and decreases with the increase of the peak current. The number of melted particles in molten pool is basically unchanged.