On theoretical modeling of transformer cooling

A theoretical model of the electrohydrodynamic prebreakdown phenomena in the weakly ionized media is proposed. Differential equations and initial conditions for describing the heat transfer in transformers are written. The Nusselt number’s dependence on the high voltage is obtained.     

Heat transfer at electrohydrodynamic pumping through in an evaporator-condensing system

The article considers the hydrodynamic and temperature dependencies of heat and mass transfer in an evaporator-condensing system representing a pulsating heat pipe with a built-in heater used as an evaporator, a vapor condenser, and an electrohydrodynamic pump for forced pumping through of a coolant. The influence of the electric current intensity and voltage on the electrohydrodynamic pump, the applied power, the temperature head, and other factors on the heat transfer has been investigated in order to reveal the physical peculiarities of the processes under investigation and the creation of a background for their calculation. An electric field is used only in the electrohydrodynamic pump, which is situated outside of the evaporator and condenser. The experimental data are treated in the form of “rectified” dependencies having a generalized character between the dependent and governing parameters of the process. The obtained results can be used for in-depth investigations, as well as for the design and fabrication of cooling and compact thermostabilizing electrohydrodynamic devices.     

An investigation of the reduction of oxygen at a rotating disc electrode with heat transfer facilities

The oxygen reduction reaction on a nickel rotating disc electrode has been examined under isothermal conditions and with heat transfer. The results show that although the limiting rate of oxygen mass transfer increases with an increase in the bulk temperature under isothermal conditions, the rate of charge transfer does not increase correspondingly. It is suggested that as the temperature is increased the oxygen reduction reaction on nickel moves from a predominantly 4 electron process to a predominantly 2 electron process. The effect of heat flux is to stimulate the limiting rate of mass transfer. This effect is attributed to the creation of thermal convection by the production of thermal eddies rather than to an increase in the interfacial temperature. It is shown that, notwithstanding the change from a4 to a2 electron process, as the temperature is raised, the effect of heat flux also gives rise to an increase in charge transfer in the oxygen reduction reaction on nickel since the thermal eddies increase mass transfer faster than the change in interfacial temperature decreases z. It is suggested that similar mass transfer effects produced by heat transfer will occur on other metals but that the charge transfer effect associated with oxygen reduction will depend on the mechanism of the reaction on the particular metal.     

Characteristics of an electrohydrodynamic pump

The head and flow rate characteristics—the dependences of the differential head and the fluid flow rate through an electrohydrodynamic pump (EHDP) on the electric field strength and the properties of the working fluid—have been derived. The head characteristics have been determined in hydrostatic and hydrodynamic modes; a linear dependence of the efficiency of the EHDP on the voltage has been found. The theoretical results are in agreement with the experimental data. Formulas for the calculation of the EHDP have been derived. It has been revealed that silicone fluid exhibits the best performance and can be used in EHD heat exchangers.     

Management of materials properties in an electro-thermo-metallurgical simulation of quenching following inductive surface heating

A numerical model for simulating quenching following inductive surface heating is proposed. The metallurgical model, which is based on the superposition principle and uses isothermal data, is integrated within a computerized code for heat exchanges (Flux2D) in order to simulate the thermal kinetics at any point on a test piece. The profile of the zones transformed during a rapid cycle can then be computed. This has been made possible by constructing a coupling scheme that considers the interaction effects among heat transfer, magnetic, and metallurgical phenomena. The coupling is based on a new approach that involves separating the physical laws into equation form to describe the physical phenomena and properties of the material. The latter has been investigated in depth in order to manage the properties in a more representative manner by considering the effect of phase transformations on changes in these properties. An illustrative example compares a coupled thermo- metallurgical numerical simulation with experimental results for treated cylindrical test pieces.     

铝及铝合金型材等温挤压关键技术研究进展

介绍了等温挤压工艺的原理及优点,分析了铝型材挤压过程中的热量变化,指出了挤压制品出口温度的影响因素,并以此为基础介绍了实现铝型材等温挤压工艺的几种方法,包括先进的铝型材挤压技术——温度和速度闭环控制的等温挤压原理及实现方法。     

注射模浇注系统设计中的热平衡分析

介绍了热固性塑料和橡胶注射模浇注系统基本结构和设计要点 ,分析了基于绝热和等温流动模型的流道系统的热平衡条件 ,提出了流道系统设计中实用的热平衡和传热计算方法。     

One-dimensional nonstationary calculation of prebreakdown electrodynamic characteristics of weakly ionized media

A theoretical model of electrohydrodynamic prebreakdown phenomena in a weakly ionized media is proposed. Differential equations and initial conditions for describing it are written. The 1D analytical and numerical solutions of these equations for the calculations of the current time characteristics are given.     

On the energy release in an oil heat carrier during transformer cooling

A theoretical model of the electrohydrodynamic prebreakdown phenomena in a weakly conductive media is proposed. Differential equations and the initial conditions for describing this model are written. The analytical and numerical solutions of these equations are given. The breakdown energy value for the oil in a transformer is calculated.     

Optimising Gas Quenching Technology through Modelling of Heat Transfer

AMONG the carburising and quenching technologieslow-pressure carburising in line with high pressure gasquenching knows a strong development[1],[2],[3].Thisprocess offers indeed an environmentally-friendlyalternative to standard atmosphere carburisingassociated to oil quenching.Gas quenching allows toeliminate parts washing and oil residues processingsteps.Besides low pressure carburising and quenchingprocesses allow more automation of the processFinally gas quenching offers process controopp…     

Effects of Temperature Gradients and Heat Fluxes on High-Temperature Oxidation

The effects of a temperature gradient and heat flux on point defect diffusion in protective oxide scales were examined. Irreversible thermodynamics were used to expand Fick’s first law of diffusion to include a heat-flux term—a Soret effect. Oxidation kinetics were developed for the oxidation of cobalt and of nickel doped with chromium. Research is described to verify the effects of a heat flux by oxidizing pure cobalt in a temperature gradient at 900 °C, and comparing the kinetics to isothermal oxidation. No evidence of a heat flux effect was found.     

Research on Transient Liquid Phase Diffusion Bonding of Steel Sandwich Panels Under Small Plastic Deformation

Plastic deformation was newly introduced in transient liquid phase (TLP) diffusion bonding of steel sandwich panels. The effect of plastic deformation on bonding strength was investigated through lab experiments. It was assumed that three factors, including newly generated metal surface area, deformation heat, and lattice distortion, contribute to the acceleration of interface atoms diffusion and increase of diffusion coefficients. A numerical model of isothermal solidification time was developed for TLP bonding process under plastic deformation and applied to carbon steel sandwich panels bonding with copper interlayer. A reasonable isothermal solidification time was obtained when an effective diffusion coefficient was used. Based on lab experiments, the effects of plastic deformation on interlayer film thickness and isothermal solidification time were studied through theoretical calculation with the new model. The evolution of interlayer film thickness indicates a good agreement between the calculation and experimental measurement. The results show that the isothermal solidification time is obviously reduced due to the effect of plastic deformation. Furthermore, a new steel sandwich cooling panel for heat exchanger was fabricated by TLP diffusion bonding under 13.1% plastic deformation. The test results suggest that a steel sandwich panel of inequidistant fin structure can provide enhanced heat transfer efficiency.     

Theoretical grounds for the calculation of the electroconvective heat and mass transfer

A brief analysis of the state-of-the-art in the area of heat and mass transfer from the point of view of its intensification, as well as the design of heat exchangers based on the use of strongly nonuniform electric fields and the presence of a corona discharge, is presented. With an electric filter as an example, there are considered the peculiarities of the electroconvective heat and mass exchange based on the principle of corona discharges. The main problems that arise at the design of heat and mass transfer exchangers, such as how to determine the output characteristics—the temperature as a function of time in the case of heat transfer and the dispersed phase concentration in the case of mass transfer—are formulated. A working equation describing the above mentioned problems is obtained and the corresponding partial solutions are found.     

格子气自动机法模拟冶金多孔介质传输现象

在评述冶金多孔介质传输现象模拟方法的基础上,介绍了近年来以流体离散运动认继背景而发发展真情淡的格子气自动机和格子Ｌａｔｔｉｃｅ Ｂｏｌｔｚｍａｎｎ模型方法及其发展历程,用１３－Ｂｉｔ多速正六边形ＬＧＡ模型和单速多能ＬＧＡ模型对冶金多孔介质传输现象模拟的实例表明：ＬＧＡ模型可模拟多孔介人流体流动的速度场的传热场,也能得到渗和率等宏观特征参量,为冶金多孔介质传输现象的模拟提供了新方法。     

Dynamics of charge transfer in molecular switches

With impurity molecules working as switches, the charge transfer on a single conducting polymer chain is studied. The chain is modeled by a modified tight-binding Hamiltonian extended to include the effects of an external field and the parameters of the switching molecules. The charge transfer through the sites that work like a switch is analyzed by the numerical integration of the equations of motion. Two basic types of molecular switches are studied: single and pairs of donor—acceptor molecules bonded to the chain. The main differences between these two models of switches are determined. We have found that the single radical switch has an anisotropic character and only works for solitons with the same parity of bonding site. For the donor—acceptor pair we have encountered that the chain offers a wider range of devices, from simple switches to perfect molecular rectifiers. The influence of the parameters of the molecules on the charge transfer and the changes they must undergo to characterize the molecular switch are obtained. The role of the length of separation between the sites where the donor and acceptor molecules bond is clarified. The optimum switch configuration is determined.     

Experimental study of heat transfer coefficient on hot steel plate during water jet impingement cooling

Experiments were performed, under transient conditions, to investigate the heat transfer phenomena of stationary hot steel plate under multiple top circular jets on run-out table. Based on inverse heat conduction model, a two-dimensional finite difference program was developed to calculate the local surface convective heat transfer coefficients and corresponding temperatures. The cooling water jet flow rate was varied from 15 L/min to 35 L/min and its effect on the convective heat transfer coefficient and surface temperature was analyzed. The results show that heat transfer coefficients are nonlinear functions of surface temperature. The cooling flow rate has no effect on heat transfer coefficient and surface temperature at stagnation point. Within 70 mm distance from stagnation line, heat transfer coefficient ratio changes slightly from 0.87 to 0.97. Beyond surface temperature of 350 °C, heat transfer coefficient ratio decreases with increasing distance from stagnation line.     

The influence of heat transfer on the kinetics of cathode processes with limiting diffusion stages

Cathode reduction of oxygen has been investigated on a rotating heat emitting amalgamated disk electrode in limiting diffusion current regime in aerated 0.05 N H₂SO₄. Under natural aeration, the rate of oxygen diffusion to the heat emitting disk is essentially higher than that under isothermal conditions at the same temperature of the disk surface, which is due to the change in oxygen solubility with temperature. At constant concentration of the oxidizer in liquid the diffusion rate under laminar flow and heat transfer is equal to that under isothermal conditions at a temperature corresponding to that of the middle of the diffusion layer.For temperature drop higher than some critical value (Δt_eri = 15–20°C) heat emission from the rotating disk has a high destabilizing effect on stability of the liquid laminar flow.     

薄板坯在二冷区内温度场的数值模拟

研究了薄板坯在二冷区冷却的不同计算方法对传热现象的影响。采用两种完全不同计算方法即monotonic cooling approach MCA和fluctuated cooling approach FCA计算换热系数和温度。计算中采用二维传热模型对温度分布进行计算。对不同冷却方式的结果进行了比较和讨论。结果显示,FCA比MCA的计算结果准确,能更好地反映每对辊之间的换热系数。     

Heat transfer of an evaporator–condensing system with electrohydrodynamic coolant circulation and different spatial orientation

The influence of the spatial orientation of an evaporator–condensing system (ECS) on the heat transfer coefficient is considered. As found, it varies according to the cosine law, which implies that it is at its minimum when the evaporator is in the top position, and it is at its maximum when the heater is in the bottom position. This is consistent with the physical considerations about the effect of buoyancy forces on heat transfer. The average velocity of coolant circulation through the ECS loop is found, and on this basis, the “electric” Reynolds number and heat transfer coefficient are estimated. The influence of pressure on heat transfer in the ECS has been analyzed. The considered phenomena have been physically interpreted; they agree well with the experimental data.     

Peculiar features of heat transfer under conditions of electric convection

The criterion dependencies of the Nusselt number on determining the similarity numbers for two types of electrothermoconvection (in ideal and poor conducting liquid dielectrics) for two types of electromechanical convection (in emulsions and suspensions) and for three types of electroisothermal convection (electric wind, electrization at generalized unipolar convection, and at a diffusion model) are presented. The main peculiarities of the heat transfer allowing us to calculate the heat transfer process, as well as to understand the mechanisms and regularities of the EHD phenomena, are revealed.