全氢罩式退火炉退火过程传热的研究

分析了全氢罩式退火炉退火过程各阶段的基本传热形式,着重介绍了影响炉内换热的两个重要参数－对流换热系数和钢卷径向等效导热系数,并对比了氮气和氢气气氛下以上两个参数的不同。最后通过数值模拟计算得到了钢卷退火曲线,并与实测值进行了对比。     

罩式退火炉内罩内加导流翼的强化传热研究

研究了罩式炉内罩强化传热机理,得出通过加强钢卷退火过程中的轴向换热,可以使钢卷中温度场更均匀;在内罩内加导流翼可以增强钢卷的轴向导热,也可以合理地分配内罩内的氢气流量。     

铝材退火炉退火过程的传热分析

根据箱式退火炉退火过程的传热特点,分析了铝箔退火炉退火过程各阶段炉膛内传热形式,建立了铝卷导热的数学模型,着重分析和计算了影响炉内空气与铝材间传热的重要参数——对流换热系数,并模拟计算了铝卷的退火过程和温度变化。结果表明,铝卷退火曲线计算值与实测值结果比较吻合。     

全氢罩式炉钢卷埋偶试验研究

介绍了全氢罩式退火炉埋偶测试的试验原理、装置和方法,分析了某炉台退火试验结果。试验结果表明加热期循环气体温度近似等于钢卷表面温度,冷却期二者差别很大。以循环气体温度是否达到退火温度作为加热期结束的判据是合理的,而冷却期缺乏钢卷的温度信息,有必要通过数学模型计算钢卷温度场。     

全氢炉氢气角度对内罩中气流影响的数值模拟

以国内某钢铁厂常用的全氢炉为例,使用计算机仿真技术对全氢炉炉台氢气进口角度改变后内罩内各处氢气流量的变化进行了仿真研究,研究结果表明氢气入口速度矢量的轴向夹角与切向夹角的变化会主要会引起顶部流通通道、第一、第二层对流板处氢气流量的变化,第三、第四层对流板处氢气流量随着氢气入口速度矢量变化范围不大,且存在"均匀轴向夹角"和"均匀切向夹角",当氢气入口速度矢量的轴向夹角和切向夹角分布在此范围时,顶部流通通道和第一、第二层对流板处氢气流通通道的氢气流量较为均匀,此时有助于内罩内各个钢卷与四周环境的换热。     

耦合法在柴油机传热研究中的应用

利用流固耦合的分析方法,将柴油机气缸盖、气缸垫、气缸体、气缸套等柴油机主要零部件以及缸内气体、冷却介质作为一个耦合体,进行燃烧室部件的传热数值模拟实验。其中,冷却水侧的对流换热系数和温度由CFD软件Star-CD对整个水路进行模拟计算获得;底板火力面侧燃气的对流换热系数和温度由GT-POWER软件对缸内工作过程进行模拟获得;缸套燃气侧温度由活塞组——气缸套耦合传热模拟获得。最终的计算结果与实验数据较吻合,可以为柴油机热负荷分析和柴油机设计提供理论依据。     

300MW循环流化床锅炉稀相区的传热研究

本文针对燃烧煤矸石的循环流化床锅炉的传热情况展开研究,以山西平朔电厂1台300 MW的循环流化床锅炉为实例,采用环核模型和颗粒团更新模型,对稀相区的传热系数分布进行建模计算,本文所建模型考虑炉内床温实际分布特征,根据现场温度实测数据对模型进行修正,研究了对流和辐射换热系数在不同负荷下沿炉膛高度的变化情况。锅炉在较高负荷下运行时,负荷的波动对颗粒团壁面覆盖时均份额影响较小,继而对炉内对流换热影响较小。炉内环形区温度沿床高的偏差随负荷升高略有减小,且对辐射换热影响比对流换热大。随着负荷升高,对流换热系数沿炉高下降增大,而辐射换热系数沿炉高下降减小,高负荷时炉内总换热系数沿炉高下降25%左右,低负荷时沿炉高下降28%左右,高负荷下炉内沿高度温差更小,传热更稳定。     

基于非接触测量的圆柱相界面对流传热系数计算方法研究

为发挥非接触测量实验方法在相变对流换热研究中的优点,充分考虑显热传热在整个相变传热中的作用,以长圆柱对流融化过程为研究对象,建立圆柱内部导热控制方程及定解条件,采用三次多项式热平衡积分方法进行近似求解,构建基于非接触测量的圆柱相界面对流换热系数计算方法。建立水流顺掠冰柱实验台,通过对实验例题的分析与讨论得到结论如下:圆柱相界面对流换热系数与相界面位置、圆柱半径融化速率、融化时间、圆柱初始温度及圆柱中心温度等参数有关,该计算方法能够较好的反映出显热变化对于对流换热系数的影响;相界面位置是影响对流换热系数计算准确性的主要因素,提高其测量准确性是减小计算误差的主要努力方向。     

全氢罩式退火炉内罩温度数值分析

利用CFD软件对全氢罩式炉退火热过程进行了模拟计算,得到了不同工况下罩式炉内罩的表面温度分布,根据得到的模拟结果研究了罩式炉内罩温度和热流密度的变化情况,并对退火生产中钢卷表面碳黑缺陷的产生原因进行了分析。     

水平单管外混合气体对流冷凝换热的理论研究

采用修正的膜模型与Nusselt凝结理论结合的方法,对含湿混合气体自上而下横掠水平管外时的对流冷凝换热机理进行研究,建立了液膜流动和传热模型,进行数值求解并分析了雷诺数、壁面温度及水蒸汽浓度等因素对混合气体冷凝换热的影响。计算结果表明:水管外壁液膜厚度分布很大程度上受气体边界层对液膜剪切力的影响。而局部努谢尔数不同于纯蒸气的的冷凝换热,它受气相热阻的影响很大,其分布状况类似于单相气体管外的对流换热。     

Mathematical Model and Its Application of Radial Effective Thermal Conductivity for Coil Heat Transfer in HPH Furnace

Temperature uniformity of steel coils in High Performance Hydrogen bell-type annealing furnace has a significant effect on their quality and production. The hot rolled coil can be considered as a periodically laminated material composed of steel layers and interface layers in radial direction. A new formula for the radial effective thermal conductivity has been proposed, which is based on surface characteristic, strip thickness and compressive stress of the rolled coil. Furthermore, it has been used to develop a heat transfer mathematical model for steel coils in the HPH furnace. The calculated annealing curves using this mathematical model are in good agreement with the experimental data.     

钢丝盘条退火用的批式炉的退火质量和气氛控制

通常被人们称为STC炉的半连续辊底式炉,主要用作冷镦用钢丝盘条的退火处理,与罩式炉比较,退火质量好,单位燃料消耗降低。例如,炉内温度分布、炉的气密性和炉内保护气体控制方法的基本概念,对于热处理的质量有很大的影响。     

Numerical studies on flow and heat transfer in membrane helical-coil heat exchanger and membrane serpentine-tube heat exchanger

The flow and heat transfer characteristics of synthesis gas (syngas) in membrane helical-coil heat exchanger and membrane serpentine-tube heat exchanger under different operating pressures, inlet velocities and pitches are investigated numerically. The three-dimensional governing equations for mass, momentum and heat transfer are solved using a control volume finite difference method. The realizable k-ε model is adopted to simulate the turbulent flow and heat transfer in heat exchangers. There flows syngas in the channels consisting of the membrane helical coils or membrane serpentine tubes, where the operating pressure varies from 0.5 to 3.0 MPa. The numerically obtained heat transfer coefficients for heat exchangers are in good agreement with experimental values. The results show that the syngas tangential flow in the channel consisting of membrane helical coils is significant to the heat transfer enhancement to lead to the higher average heat transfer coefficient of membrane helical-coil heat exchanger compared to membrane serpentine-tube heat exchanger. The syngas tangential velocity in the membrane helical-coil heat exchanger increases along the axial direction, and it is independent of the gas pressure, increasing with the axial velocity and axial pitch rise and decreasing with the radial pitch rise.     

Development of heat transfer coefficient correlation for concentric helical coil heat exchanger

The present study deals with developing a Correlation for heat transfer coefficient for flow between concentric helical coils. Existing Correlation is found to result in large discrepancies with the increase in gap between the concentric coils when compared with the experimental results. In the present study experimental data and CFD simulations using Fluent 6.3.26 are used to develop improved heat transfer coefficient correlation for the flue gas side of heat exchanger. Mathematical model is developed to analyze the data obtained from CFD and experimental results to account for the effects of different functional dependent variables such as gap between the concentric coil, tube diameter and coil diameter which affects the heat transfer. Optimization is done using Numerical Technique and it is found that the new correlation for heat transfer coefficient developed in this investigation provides an accurate fit to the experimental results within an error band of 3–4%.     

Convective heat transfer in helical coils for constant-property and variable-property flows with high Reynolds numbers

Forced convection heat transfer of single-phase water in helical coils was experimentally studied. The testing section was constructed from a stainless steel round tube with an inner diameter of 10 mm, coil diameter of 300 mm, and pitch of 50 mm. The experiments were conducted over a wide Reynolds number range of 40000 to 500000. Both constant-property flows at normal pressure and variable-property flows at supercritical pressure were investigated. The contribution of secondary flow in the helical coil to heat transfer was gradually suppressed with increasing Reynolds number. Hence, heat transfer coefficients of the helical tube were close to those of the straight tube under the same flow conditions when the Reynolds number is large enough. Based on the experimental data, heat transfer correlations for both incompressible flows and supercritical fluid flows through helical coils were proposed.     

JM-600型导热胶泥在改性沥青反应釜上的应用

某石化公司改性沥青装置中,反应釜外形尺寸为准7408mm×2600mm×8mm,需要加热的面积约为20m2。反应釜内加热盘管,管径为准76mm×4mm的流体无缝钢管,管内介质为270℃高温导热油,反应釜外为保温层。混合液温度从190℃加热到240～245℃,通过顶置搅拌器进行搅拌,使其充分混合,增强反应的效果。由于反应釜内加热盘管与内壁有很大的空隙,且盘管之间约有50mm的间隙;另外,升温过程中由于混合液中的SBS改性剂与270℃高温导热油盘管壁直接接触,导致含有SBS改性剂的沥青混合液在釜内加热盘管外壁和加热盘管间隙内结焦,罐内介质升温速度变慢。选择外加热盘管+导热胶泥的加热方式对现有加热方式进行改造。JM-600型导热胶泥以石墨为基料,具有极高的传热效率、优异的传热稳定性和受热均匀性。外加热盘管+导热胶泥,是将加热盘管与反应釜的接触方式由线接触改变为面接触。改造后应用效果表明,外加热盘管+导热胶泥相结合的方式,施工简单,热效率高,解决了反应釜内介质结焦和升温慢的问题。此方法也可推广到其他受温度影响较大的易凝、易结晶的管道介质输送上。     

Modeling cooling coils

Finned-tube heat exchangers commonly used as cooling coils in air conditioning systems undergo complex heat transfer and dehumidification. Due to the presence of water film on the outside surface of the coils, the general approach for an analysis of dry surface is not adequate to predict the performance of such coils. This paper presents a modeling procedure for cooling coils with dehumidification based on the approach of Threlkeld. In order to verify the calculational results of the model, experiments were conducted with an aim to determine the outlet air conditions as well as some other parameters required as the inputs to the model. Comparison between the simulation and experimental results reveals that the model is accurate and suitable for predicting the performance of cooling coils with dehumidification.     

罩式退火炉加热罩改造

针对罩式退火炉加热罩存在助燃空气的换热效果不理想、煤气和空气混合不均匀、煤气燃烧不充分、煤气消耗高等系列问题,对换热器进行了改造,即将“单一箱型集中换热方式”改为“顶部环形对称换热方式”,空气预热温度由改造前的最高350℃增至430℃,换热效率提高明显.同时对烧嘴结构进行改进,在煤气管路内部靠近出口端处增设上、下空气导入支管,将原单一集中的煤气出口通道改为5路分散布置的煤气出口通道,使一次点火成功率由82％提高到91％,吨钢煤气消耗由104m3减少到81m3.