An experimental study on heat transfer process of multiple mist impinging jets

Mist jet impingement cooling is an enhanced heat transfer method widely used after the continuous galvanizing process.The key of a successful design and operation of the mist jet impingement cooling system lies in mastering heat transfer coefficients.The heat transfer coefficients of high temperature steel plates cooled with multiple mist impinging jets were experimentally investigated,and the effects of gas and water flow rates on heat transfer coefficients were studied.The test results illustrate that the gas flow rate has little effect on the mist heat transfer rate.It is also found that the water flow rate has a great impact on the heat transfer coefficient.When the water flow rate ranges from 0.96m3/h to 1.59 m3/h,an increase in the rate will produce a higher heat transfer coefficient with a maximum of 5650 W/(m2·K).Compared with the conventional gas jet cooling,the heat transfer coefficient of the mist jet cooling will be much higher,which can effectively strengthen the after-pot cooling.     

保护渣晶粒尺寸对传热性能的影响

保护渣在连铸过程中具有重要的作用,其中有效控制钢液向结晶器的传热直接影响了铸坯质量;当保护渣热阻较小、不均匀传热时铸坯容易出现裂纹等缺陷.而保护渣的控热能力主要取决于保护渣的结晶性能,因此,有必要研究保护渣的结晶行为对传热性能的影响.利用双丝热电偶技术通过不同的温度制度,获得不同尺寸的单一结晶相,研究保护渣晶粒尺寸对传...     

多排气雾冲击射流换热过程的试验研究

气雾冷却是带钢连续镀锌后的一种强化冷却方式。气雾冷却装置的设计和运行的关键是掌握气雾换热系数。采用试验方法研究了多排气雾射流冷却高温钢板的换热系数,考察了喷气流量和喷水流量对换热系数的影响。试验结果表明：喷气流量对气雾换热系数影响可以忽略;喷水流量对换热系数影响显著,在喷水流量为0.96～1.59 m^3/h时,换热系数随喷水流量的增加而明显上升,最大可达5 650 W/（m^2.K）;喷雾冷却的换热系数远大于常规喷气冷却,能有效地强化镀后冷却。     

Decision making: the context of nurse prescribing

BACKGROUND: Alterations in body temperature result from changes in tissue heat content. Heat flow is a complex function of vasomotor status and core, peripheral, and ambient temperatures. Consequently it is difficult to quantify specific mechanisms responsible for observed changes in body heat distribution. Therefore the authors developed two mathematical models that independently express regional tissue heat production and the motion of heat through tissues in terms of measurable quantities. METHODS: The equilibrium model expresses the effective regional heat transfer coefficient in terms of cutaneous heat flux, skin temperature, and temperature at the center of the extremity. It applies at steady states and provides a ratio of the heat transfer coefficients before and after an intervention. In contrast, the heat flow model provides a time-dependent estimate of the heat transfer coefficient in terms of ambient temperature, skin temperature, and temperature at the center of the extremity. RESULTS: Each model was applied to data acquired in a previous evaluation of heat balance during anesthesia induction. The relation between the ratio of steady state regional heat transfer coefficients calculated using each model was linear. The effective heat transfer coefficient for the forehead (a core site) decreased approximately 20% after induction of anesthesia. In contrast, heat transfer coefficients in the six tested extremity sites more than doubled. CONCLUSIONS: Effective heat transfer coefficients can be used to evaluate the thermal effects of various clinical interventions, such as induction of regional anesthesia or administration of vasodilating drugs. The heat transfer coefficient for the forehead presumably decreased because general anesthesia reduces brain perfusion. In contrast, increased heat transfer coefficients in the extremity sites indicate that thermoregulatory and anesthetic-induced vasodilation more than doubles the core-to-peripheral flow of heat. This flow of heat causes redistribution hypothermia, which is usually the major cause of core hypothermia during anesthesia.     

水流量对热轧钢板层流冷却过程对流换热系数的影响

提高带钢层流冷却控制模型的精度,关键是建立精确的对流换热系数与冷却工艺之间的关系.采用有限差分法和反向热传导法,获得了实验条件下钢板表面的对流换热系数及表面温度.研究了不同水流量(0.9~2.1 m3·h-1)对换热系数与表面温度变化规律的影响.在层流冷却过程中,对流换热系数与表面温度呈非线性关系;在距离驻点70 mm内,水流量对换热系数随表面温度变化规律没影响;远离驻点70 mm外,对流换热系数比随远离冲击区驻点距离的增加而减小.采用所确定的换热系数计算得到的温降曲线与实测曲线吻合较好.      

炉缸冷却壁对流换热系数计算及烘炉传热特性

 炉缸冷却壁冷却性能主要体现在冷却水与水管间的对流传热。因为工程上常用计算对流换热系数的经验公式不能满足不同的水流状态从而导致炉缸热应力分析误差较大，所以以某高炉炉缸结构为例，首先利用传热学准数方程推导出冷却水处于不同流动状态时对应的综合对流换热系数表达式，同时探讨了对流换热系数经验公式的适用范围；然后通过迭代计算推导出了冷却水处于层流状态下考虑衰减热阻时的综合对流换热系数表达式；最后对烘炉状态下炉缸侧壁传热模型进行瞬态传热与冷却分析，得到了微水烘炉甚至闭水烘炉的热工依据，可为初步制定高炉烘炉制度进行评估和完善。     

High speed continuous casting of steel billets: Part 1: General overview

Abstract

This paper is the first of a series of two, providing an overview of the results of mould heat transfer analyses conducted over years of industrial trials. The effects of casting speed, carbon content, superheat, water flowrate, electromagnetic stirring, and mould lubricant are discussed in terms of the midface mould heat transfer. Mould corner heat transfer is also discussed. Finally, an overview of mould design is given, as well as an analysis that reveals that both excessively steep and shallow meniscus tapers cause high heat transfer. Alternative designs to the conventional straight tapered moulds are discussed briefly. The focus is on the primary cooling zone, and therefore billet quality issues are not extensively covered.     

金属锂还原罐内化学反应与传热耦合特性

为了分析真空热还原制取金属锂的还原效率和还原率,综合考虑罐内球团传热和化学反应,建立了传热与反应动力学耦合模型.利用该模型对单球团和还原罐内球团还原过程进行数值模拟,得到了球团温度及还原率的时间分布,并分析了罐外换热系数对球团还原过程的影响.结果表明:球团低导热率和反应等效热汇是影响还原过程的主要因素,罐中心区域和罐壁处的温度和反应速率存在较大差值;还原初期传热为还原过程的主要控制因素,而反应后期化学反应为主要控制因素;罐外换热系数对还原过程影响不大,增强罐内传热是提高还原效率的有效途径.      

Effect of Titania Absorption into a Mold Flux on the Heat Transfer Between the Mold and the Slab in the Continuous Casting of Titanium-Stabilized Stainless Steel

The heat transfer behavior between mold and slab changes when titania is absorbed into the mold flux during the continuous casting of titanium-stabilized stainless steel. The trend and the extent of this effect were investigated in the laboratory. Furthermore, to investigate the effect of titania on heat transfer, the effect of titania on the crystallization properties of the mold flux was studied. The results showed that with an increasing titania content of mold fluxes, the heat transfer coefficient and the heat flux of the slag film increases, whereas the heat transfer resistance decreases; the effect is that the growth and crystallization temperature of the cuspidine crystallites in the slag are suppressed by the absorption of titania.     

钢的连铸过程结晶器与铸坯之间的传热分析

针对连铸过程中的结晶器传热模型，分析总结了结晶器与坯壳之间的热阻构成，并研究了结晶器壁和坯壳界面热流的影响因素，为传热模型的求解和结晶器锥度的优化设计提供了理论依据。     

Combination of inverse problem and neural network for thermal behaviour calculation of mould process based on temperature measurements in plant trial

Abstract

Heat transfer between mould and strand has a critical influence on billet quality, caster productivity and operating safety. It is very important to obtain the correct distributions of temperature and heat flux, and many studies are made on the calculation methods of heat transfer between strand and mould, aiming to reduce the computation time and improve the calculation accuracy. In the present paper, based on measured data of temperature and heat flux during round billet continuous casting, the calculation method which combines the online measurement data and numerical simulation was investigated. Through identifying the local thermal resistance and its distribution between the mould and the strand by an inverse heat transfer model, the heat flux and shell thickness profiles were calculated. To avoid the iterative solution by inverse model, a faster alternative model using an artificial neural network was developed to predict the thermal resistance from the measured temperature. After training, there is an exact correspondence between the observed temperature values and the thermal resistance. The calculation results obtained by the combination of neural network and numerical simulation can correctly reflect the characteristics of non-uniform heat transfer around the mould circumference, which provides a worthwhile and applicable method for online calculation and visual technology of heat transfer and solidification in continuous casting mould.     

Investigation of non-uniform slag films and air gap during slab continuous casting

Based on an inverse algorithm and a full-scale heat transfer model of slab/mould, the non-uniform temperature fields of mould and slab are obtained. Considering the formation mechanism and heat transfer characteristics of the slag films and air gap, a mathematical model of the heat transfer between the liquid/solid slag films and air gap is further developed. According to the model, the non-uniform distributions and evolution of liquid/solid slag films and air gap are comprehensively revealed, which proposes a theoretical foundation for exploring the complex heat transfer of mould/slab and provides a helpful tool for further improving the casting parameters and operations.     

Heat transfer in an iron bath of a two-stage smelting reduction process

Mechanisms of the heat transfer by means of iron and slag drops in smelting reduction are discussed. The quantity of slag on the molten iron exists in two forms depending on the different processes: either a thin slag layer or a voluminous slag layer. In the case of a small amount of slag, iron and slag drops are spattered in the free space above the bath furnace. By smelting reduction with a high post-combustion degree, the spattered iron drops are quickly oxidized in the free space. The spattered slag drops transfer heat from the free space to the molten iron. A definition for the heat transfer efficiency in the iron bath of a two-stage smelting reduction process is presented. Experiments on heat transfer were made in an experimental EOF-furnace with 100 kg iron. The post-combustion degree and the heat transfer efficiency were on a high level, because inleaked air was used.     

煤气换热器损坏原因分析及解决方案

针对鞍钢1700 ASP生产线加热炉煤气换热器损坏问题,从煤气换热器本身构造及外部环境进行系统分析,并采用化学检测等方法确定了换热器损坏的直接原因,具体为煤气管道中的水进入换热器内造成温度应力、内部煤气分流不均、空气换热器换热效果不佳等,并提出了改进煤气换热器结构、加大煤气管道排水能力、增加空气换热器换热而积的策略.     

Study of the Effects of the Mold Surface and Solid Mold Flux Crystallization on Radiative Heat Transfer Rates in Continuous Casting

Radiative heat transfer plays a crucial role in the meniscus area of a steel continuous casting machine. However, the study of radiation across the mold flux and copper molds is very difficult due to the harsh environment and highly transient nature of the phenomena in continuous casting molds. By using an infrared radiation emitter, a radiative heat flux was able to be applied to a copper mold with different top surfaces to observe their effects on the radiative heat transfer. The mold surface was covered with solid slag disk subjected to the radiative heat flux to simulate the radiative heat transfer phenomena in continuous casting. The solid slag disk could either be glass or a mixture of glass and precipitated crystals. The effect of full crystallization of a slag disk was to reduce the heat transfer rate by 20.5%, as compared with a completely glassy sample.     

Determination of interfacial heat transfer coefficients in casting and quenching using a solution technique for inverse problems based on the boundary element method

Both casting and quenching are processes during which several physical phenomena like heat transfer, fluid flow, phase transformation,etc. interact in a complex manner. To obtain a nu-merical model which is capable of accurately simulating the actual process, one has to be able to quantify all the parameters affecting the process. One parameter which substantially influ-ences heat transfer in these processes is the heat transfer coefficient at the interface between the mold and the metal in casting and that between the metal and the quenchant in quenching. The heat transfer coefficient could vary on the surface of a casting or a quench metal both spatially and with time. Its accurate determination is imperative for a realistic simulation of these processes. In this work, an algorithm based on the boundary element technique is proposed to solve for the interface heat transfer coefficient. The problem is cast as one of inverse heat conduction in two dimensions where some of the boundary conditions, namely, the previously mentioned heat transfer coefficients, are unknowns. Since it is the boundary properties that are being determined, the boundary element method (BEM) is the most suitable technique to use. The algorithm uses experimentally measured temperature data inside the domain to determine the interface heat transfer coefficient. The technique is outlined in detail and some casting and quenching examples are presented to demonstrate its capability.     

分形微通道换热过程强化研究进展

随着微纳制造技术的快速发展,微电子芯片、微反应器和微燃料电池等微型器件受到了研究者越来越多的关注。微型器件的应用不仅对加工工艺和材料具有较高的要求,而且需要高效的热管理来维持其性能。特别是对于高集成度和高频化的高性能微电子芯片而言,超高的热流密度不仅会严重制约芯片的性能,而且会显著影响芯片的寿命和可靠性。鉴于传统的风冷和液体单相对流换热冷却方式无法满足散热需求,具有高换热系数的微通道换热技术成为解决微型器件散热问题的重要途径。然而,常规的微通道换热技术普遍存在着高流动阻力和非均温性的难题,限制了该技术的实际规模化应用。近年来,研究者开发出一系列新型的分形微通道技术用于换热过程强化。本文系统总结了不同类型的分形换热微通道（包括Y、H、T、Ψ、康托、科赫等分形结构）,并对各分形微通道的原理和性能进行了着重介绍,最后对分形微通道换热的现存挑战和未来发展方向分别进行了分析和展望,以期为换热过程强化的发展提供新的研究思路。      

Numerical simulation of fluid flow and solidification in continuous slab casting mould based on inverse heat transfer calculation

Abstract

A mathematical model based on an inverse heat transfer calculation was built to determine the heat flux between the mould and slab based on the measured mould temperatures. With K–? turbulence model, a mathematical model of three-dimensional heat transfer and solidification of molten steel in continuous slab casting mould is developed. Solidification has been taken into consideration, and flow in the mushy zone is modelled according to Darcy’s law as is the case of flow in the porous media. The heat flux prescribed on the boundaries is obtained in the inverse heat conduction calculation; thus, the effect of heat transfer in the mould has been taken into consideration. Results show that the calculated values of mould temperature coincide with the measured ones. Results also reveal that the temperature distribution and shell thickness are affected by the fluid flow and heat transfer of slab which is governed by the heat flux on the mould/slab interface.     

热烧结矿竖式冷却过程传热特性

 与传统环冷相比,烧结竖冷拥有漏风率低、换热效率高的优势。为此利用竖冷试验装置,在某烧结厂取热风与热烧结矿研究了竖式冷却过程气固对流换热特性。研究表明,烧结矿竖式冷却过程中影响传热特性的主要因素为冷却风的流量及温度。烧结矿和冷却风对流换热系数随着烧结矿温度的升高而增大,且随着冷却风流量的增大以及冷却风温度的降低,对流换热系数也随之增大。基于白金汉定理,结合试验数据拟合得出了描述烧结矿与冷却风传热特性的准数关联式,其模拟性较好且平均相对误差为7.25%。     

内翅片管换热器传热性能实验研究

以内翅片管作为换热器传热元件，通过实验方法对其传热性能进行研究。在考虑了内翅片使管内传热面积增大，传热性能提高这一特点，经过反复实验，回归出了内翅片管传热的准则方程式。并对与内翅片管结构和特点相近的内插管，在外型尺寸相同、实验条件相同的前提下，进行了传热性能实验研究和比较。