Numerical simulation and experimental validation of heat transfer enhancement on a loaded heat treatment furnace

Heat transfer simulation within heating furnaces is of great significance for prediction and control of the performance of furnaces. In this paper, a set of models is proposed to solve heat transfer problems in a loaded furnace. Furthermore, a 2-dimensional algorithm based on a finite difference method is presented. The heat transfer models are integrated with a furnace model to simulate the heating process of workpieces. Temperature variation of the workpiece with time is predicted by the system. An experiment is carried out for validation of the system. Themain objective of this work is to evaluate the behavior of a heated enclosure, when variable radiant panels are introduced. Experimental investigation shows that their efficiency depends on their position.     

Experimental and Numerical Investigation of Coil Heating in Hydrogen Annealing Furnace for Optimum Arrangement of Charge

Annealing furnace heat transfer mechanisms were investigated both experimentally and numerically to determine optimum stacking arrangements of coils in one charge. Heating order of the coils in one charge was first determined from experimental conditions in order to interpret temperature differences between coils. A mathematical model and annealing furnace heat transfer relations were used to predict the thermal behavior of coils during the heating process. When the accuracy of the model had been ensured, the heating of the coils was simulated with different stacking arrangements and the best arrangement with the shortest heating time possible was determined. A saving of 1 to 5% was observed in the burning time of furnaces for certain stack arrangements.     

An Experimental Method to Decrease Heating Time in a Commercial Furnace

Abstract

The aim of this article is to present an experimental method to optimize the heating time in a furnace in order to show an example of the progression toward increasingly empirical solutions as the problems become progressively more unwieldy. During this experimental study, different cases are carefully chosen to compare and measure the effects of applying different enhancement methods of the heat transfer processes. It is found that changing the inner geometry by introducing radiant panels inside the heated chamber leads to important time savings in the heating process by increasing the convection rate in the furnace.     

CO2激光加热硅芯光纤预制棒的温场分布

研究了10.6 m CO2激光加热硅芯光纤预制棒的温场分布，在考虑预制棒表面热辐射和空气对流的情况下，用有限元软件COMSOL Multiphysics建立了激光加热预制棒的传热物理模型，比较了激光功率、激光光斑半径和预制棒直径对温场分布的影响，同时提出CO2激光加热与石墨炉加热结合调节温场分布的方法。仿真结果显示，激光参数和预制棒直径都会明显影响预制棒温场分布，且激光光斑半径3 mm，功率达到400 W的激光器可用于直径10 mm内的硅芯光纤预制棒制备硅芯光纤。通过CO2激光加热和石墨炉加热相结合的加热方式，能更加灵活有效地调节预制棒的温场分布，构建适合硅芯光纤拉丝的温场条件。     

The influence of furnace wall emissivity on steel charge heating

Radiation heat transfer is one of the most important heat transfer modes in high-temperature applications. It is a strongly non-linear process, which depends on the temperature and emissivity of heat exchange surfaces, their geometrical configuration and properties of the surrounding atmosphere. Heat exchange intensity between the surfaces depends mainly on their temperature differences. However, their emissivities influence significantly the radiation heat transfer process as well. Emissivity is a function of surface state or atmospheric chemical reactions, temperature and wavelengths. Because of these non-linearities, it is very complicated to evaluate such a real problem by numerical simulation, and experimental work seems to be the most reliable evaluation procedure. We applied special high-temperature coatings of different emissivities on furnace walls to evaluate the dependence between the furnace wall emissivity and steel charge heating. The emissivity analyses of the coatings used and emissivity measurement results in dependence on wavelength are presented in this paper. The dependence of the charge heating on the furnace wall emissivity, the importance of emissivity wavelength dependence and significant differences of the emissivity effect in electrical and gas heated furnaces are shown. The possible consequences and practical benefits are also discussed in this paper.     

Determination of the volumetric heat generation in a furnace chamber from the radiation flux distribution

A thermal model of a furnace chamber involving both a three-dimensional radiation heat transfer equation and an energy equation describing the one-dimensional flow of a combustible mixture is proposed. Convective heat transfer at the walls and shields is taken into account by the approximate standardized method. The model allows one to calculate the temperature and heat flux distributions both in the volume and at the boundaries of the furnace chamber. The problem of finding the specific volumetric heat generation from the radiation fluxes measured at the furnace walls is considered with this model.     

Heat transfer for diode side-pumped YAG slabs

Thermal heating is a major limiting factor in scaling the average power of a solid-state laser. The heat transfer coefficient is affected by the coolant flow rate, the physical properties of the laser slab and the coolant, and the pumping cavity geometry. The relationship between the heating effects and the heat transfer coefficient has been studied by considering the variations of thermal conductivity and expansion coefficient of the laser slab with temperature. It is concluded that different heat transfer coefficients should be adopted according to different heat intensities inside the laser slabs in order to obtain better pumping input as well as to optimize the cooling effects.     

高温空气电阻炉内强化传热性能实验研究

本文对基于碳化硅泡沫陶瓷的高温空气电阻炉内的传热性能进行了实验研究。通过在高温空气电阻炉内插入不同数量的泡沫陶瓷片,研究陶瓷片数量对空气出口温度的影响。同时研究了泡沫陶瓷片的位置对空气出口温度的影响。实验结果表明:当炉膛内不插入泡沫陶瓷片时,在空气流量为200 m~3/h时,空气出口温度为650℃,当炉膛内插入五块泡沫陶瓷片时,空气出口温度达到980℃。本文从实验方面验证了将碳化硅泡沫陶瓷应用到太阳能热发电的吸收器中,强化空气与吸热材料之间的换热的可行性。     

An Infrared Image Synthesis Model for High-Speed Targets

Although a number of infrared models are available for synthesizing the infrared image of static objects, they fail to simulate the infrared signature of targets flying at high speed. This paper presents an infrared image synthesis model for such kind of targets. Within this model, we account for not only all forms of heat transfer inside the targets but also the dynamic interaction between the target's surface and the surrounding air-flow. The heat transfer process between the target's surface and the air-flow is carefully analyzed based on the principles of infrared physics, aerodynamics and heat transfer, and a term due to aerodynamic heating is incorporated into our new model. Experimental results illustrate the potential of the model     

Modeling the Water Droplet Evaporation Processes with Regard to Convection,Conduction and Thermal Radiation

A predictive model was developed for investigation of high-temperature heating and evaporation of water droplets. The model takes into account the basic interrelated processes of heat transfer and phase transitions. Typical velocity and temperature profiles were found in the high-temperature gas–water droplet system with external gas medium temperature varied from 100 to 800°C. Various formulations of the problem, significantly different in the type of considered processes and factors, are considered.We analyzed temperature conditions of heating and evaporation of water droplets, which allow the use of simplified models and which need consideration of all complex interrelated processes of heat and mass transfer (including convection, conduction and radiant heat transfer in droplets, and also in the surface vapor–gas layer).     

Recent research on magnetic properties of glass-coated microwires

In this paper, we report and analyse the results of tailoring the GMI effect of glass-coated amorphous thin microwires (with the metallic nucleus diameter about 10–22 μm) by choosing the sample chemical composition, geometry (thickness of glass coating) and conditions of heat treatment by Joule heating and furnace annealing. The observed dependencies have been interpreted in terms of stress relaxation and changes of the magneto-elastic anisotropy induced by the Joule heating.     

Phenomenological models of microwave heating of a flat coal mass with release of absorbed heat by the convection law

Phenomenological models of electrodynamics and heat transfer in application to microwave heating are constructed. Analytically rigorous solutions to problems of heating a flat coal mass under microwave radiation are obtained. The boundary conditions correspond to convection mechanism of absorbed heat release to the ambient medium. Mathematical models of dielectric heating for homogeneous boundary conditions are solved by a method of dual integral Laplace and Fourier transform. In the presence of inhomogeneities in the boundary conditions, a quite universal method of Green functions is used. The obtained formulas have a constraint associated with constancy of electro- and thermophysical characteristics of coal fuel, or when their piecewise constant approximation is admissible. The obtained dependences form the basis for scientific support of the microwave heating technology.     

Development of a finite element model for coupled radiative and conductive heat transfer in participating media

Considering the geometrical applicability, a finite element model (FEM) for coupled radiative-conductive heat transfer has been developed which is applicable to enclosures of arbitrary geometry in present research. The present work provides a solution of coupled heat transfer in a rectangular, cylindrical or annulus enclosure with black or gray walls containing an absorbing-emitting-scattering medium. It is also applied to study the influence of conductive/radiation coefficient, albedo and wall emissivity on the temperature distribution in the medium. Compared with the results available in other references, the present FEM has no limitation with respect to geometry and can predict the coupled radiative-conductive heat transfer in participating media accurately.     

Optimization of fin geometry in heat convection with entransy theory

The entransy theory developed in recent years is used to optimize the aspect ratio of a plate fin in heat convection.Based on a two-dimensional model,the theoretical analysis shows that the minimum thermal resistance defined with the concept of entransy dissipation corresponds to the maximum heat transfer rate when the temperature of the heating surface is fixed.On the other hand,when the heat flux of the heating surface is fixed,the minimum thermal resistance corresponds to the minimum average temperature of the heating surface.The entropy optimization is also given for the heat transfer processes.It is observed that the minimum entropy generation,the minimum entropy generation number,and the minimum revised entropy generation number do not always correspond to the best heat transfer performance.In addition,the influence factors on the optimized aspect ratio of the plate fin are also discussed.The optimized ratio decreases with the enhancement of heat convection,while it increases with fin thermal conductivity increasing.     

环路型脉动热管的稳态运行机制

建立了环路型脉动热管稳态自激循环流动运行机制的物理模型和数学模型。潜热传递决定了运行的驱动力和循环流动的速度;显热传递和循环流动速度决定了净换热量的大小。通过关联加热段和冷却段的传热、进出口汽液容积流率、密度、运行驱动力和阻力,对传热和流动进行了耦合求解。结果表明,潜热传热量占总传热量的比例在30％以内;工质循环流动的速度决定了壁面温度波动,温度波动取决于显热传热和循环流动速度。     

Numerical modelling of heat transfer in plasma shaft electric furnace at utilization of anthropogenic waste

The mathematical model of heat transfer between the counter flows of gas and porous batch of anthropogenic wastes in the working area of a shaft furnace is presented. This model considers chemical transformations in separate batch components and radiation heat transfer between the gas and solid phases. Results of calculations are presented.     

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Based on the computational fluid dynamic code ANSYS CFX, the inhomogeneous Eulerian- Eulerian multiphase model coupled with RPI (Rensselaer Polytechnic Institute) boiling model is adopted to simulate the subcooled boiling two-phase flow of hypervapotron structure, and the effects of different fin structures on the heat transfer performance of hypervapotron structures are compared. The results show that under high heat flux conditions, the heat transfer performance of the triangular fin structure is better than the rectangular fin structure. Triangular 4×3 to the flow geometry has the best heat transfer performance. Rectangular 4×3 geometry is greatly affected by the flow rate due to the obstruction of the fins making the flow rate to be lower and the heat transfer performance will be getting worse. Triangular 4×3 against the flow geometry make the fluid in the cavity to maintain a large degree of turbulence due to the small cavity between the fins and the adverse effects of counter-flow fins on the mainstream, so the fin area has a good heat transfer performance, but due to the impeding effect of the counter-flow fin on the fluid, the fluid velocity in the slot is getting lower and lower, as the result, the heat transfer performance on the sidewall far away from the fin area is getting worse.     

质子交换膜燃料电池及其发电系统模拟

本文通过质子交换膜燃料电池单电池子模型、布气管子模型、流场子模型相互耦合,对电池堆传热传质过程加以数值模拟,得到单电池及电池堆的流场、温场、当地电流密度分布、过电位分布;给定平均电流密度下单电池及电池堆输出电压等参数;并比较了平均电流密度、布气管尺寸对电池输出电压、堆内反应物分配的影响;在此基础上,对整个ＰＥＭＦＣ发电系统进行流程模拟和参数分析,得到平均电流密度、重整器Ｓ／Ｃ等主要参数对系统性能影响．     

翅片结构对超汽化结构换热性能影响的研究

基于计算流体动力学软件ANSYS CFX，利用非均相流欧拉-欧拉模型耦合RPI(伦斯勒理工大学)沸腾模型开展超汽化冷却结构的过冷沸腾两相流模拟，比较不同翅片结构对超汽化结构换热性能的影响。研究发现在高热流量条件下三角形翅片结构的换热性能优于矩形翅片结构：其中顺流4×3 三角形翅片结构总体换热性能最好；矩形4×3 翅片结构受流速影响较大，由于翅片的阻碍作用使得流速越来越低，换热性能越来越差；逆流4×3 三角形翅片结构由于其翅片间的腔小，并且逆流翅片对主流的破坏使得腔内流体保持着很大的湍度，所以翅片区有很好的换热性能，但由于逆流翅片对流体阻碍作用大，小槽内流体速度越来越低，使得远离翅片区的侧边换热性能逐渐变差。     

自激振荡流热管脉冲加热强化传热实验研究

自激振荡流热管也称为脉动热管,是一种新型高效的传热元件。本文提出了采用脉冲加热代替常规连续热源加热强化自激振荡流热管传热的方法,并对其进行了实验研究。实验结果显示,脉冲加热时热管冷、热端壁面温度的振荡频率明显大于连续加热热管的壁面温度振荡频率。在相同的加热功率下,当脉冲宽度在200-1000 ms时,脉冲加热热管的传输热流量与当量导热系数均大于连续加热热管的传输功率和当量导热系数．这表明脉冲加热强化自激振荡流热管传热的方法是可行的．