共查询到20条相似文献,搜索用时 15 毫秒
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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. 相似文献
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LIUZheng-dong IVSamarasekera 《钢铁研究学报(英文版)》2004,11(3):15-23
The controlled runout table cooling is essential in determining the final mechanical properties and flatness of steel strip. The heat of a hot steel strip is mainly extracted by cooling water during runout. In order to study the heat transfer by water jet impingement boiling during runout, a pilot facility was constructed at the University of British Columbia. On this pilotfacility, the water jet impingement tests were carried out under various cooling conditions to investigate the effect of processing parameters, such as cooling water temperature, water jet impingement velocity, initial strip temperature, water flow rate, water nozzle diameter and array of water nozzles, on the heat transfer of heated strip. The results obtained contribute to the optimization of cooling water during runout. 相似文献
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采用数值方法研究了狭缝射流冲击柱状凸形表面的流动换热特性,通过四种湍流模型计算结果与实验数据对比,确定了湍流模型适用性.以压力梯度分布为依据,重点分析了狭缝射流沿柱状凸形表面的流动结构和边界层分离特点及柱状凸形表面的强化换热特性.结果表明:RNG k-ε和Realizable k-ε模型具有预测适应性;狭缝射流冲击至柱状凸形表面,气体沿表面运动,速度降低,并在流动下游发生边界层分离;量纲一的逆压梯度随量纲一的曲率半径(D/B)的减小而增大,使得边界层分离更早出现;驻点区域换热Nu随量纲一的曲率半径(D/B)的减小而获得增强,但流动进入下游后,D/B对换热基本无影响;压力梯度是影响狭缝射流冲击柱状凸形表面换热分布的重要因素. 相似文献
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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。 相似文献
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The influence of running water on spray water cooling is experimentally looked at with the aid of a stationary working experimental plant. The running water was fed separately to the sample from above as a defined water film by using a slot nozzle. In addition to the spray nozzle pre-pressure, the velocity of the running water at the slot nozzle exit and the temperature of the running water, the angle of inclination of the sample plane was also varied. By employing three different full cone spray nozzles and setting different nozzle distances, a range of 450 to 2000 l/(m2·min) of the water impingement density was covered. To estimate the marginal influences, samples of 20 × 20 mm as well as 30 × 30 mm were used. Studies of initially pure spray water cooling without the additional running water film revealed a dependency of the heat transfer on the spray water impingement density, the spray water velocity and also the angle of inclination of the sample plane. For nozzles with a low water impingement density, a superimposing of a running water film on the spray water revealed a sharp increase in the heat transfer coefficients compared to pure spray water cooling. For nozzles with a high water impingement density and, therefore, with a high heat transfer already even for pure spray water cooling, the increase of the heat transfer coefficient is minor. 相似文献
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Using a unique pilot facility a series of tests were conducted using three top jets to simulate the heat transfer that occurs during run‐out table (ROT) cooling. Steel samples instrumented with internal thermocouples were tested on this facility and the effect of top jet configuration (nozzle spacing of 40 to 115mm), and water flow rate (15 and 30 1/min) were quantified using moving plate samples. The multiple top jet work indicated that heat transfer across the plate width varies significantly and is high directly under the nozzle but decreases rapidly away from the nozzle in the interaction region. As cooling progresses a much larger wetted region occurs and more uniform cooling is experienced across the plate. Multiple jet cooling experiments have also confirmed that nozzle spacing does have an effect on heat transfer. This effect is predominate in the interaction region where closer nozzle spacing leads to enhanced and more uniform heat transfer in the lateral direction across the plate width away from the nozzle. As expected higher water flow rates led to higher heat transfer both under the nozzle and in the interaction region. 相似文献
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Liquid jet impingement has many industrial cooling applications such as metal manufacturing and steel cooling on run‐out tables (ROT). The development of the wetting front around the impingement point of a jet is central in jet impingement cooling. In this paper, the effects of moving target surface and jet Reynolds number on wetted zone and on the formation and location of hydraulic jump (HJ) are explored through a series of industrial‐scale experiments of an impinging circular free surface long water jet with high Reynolds number of 11 000–50 000 and industrial jet parameters. The moving test surface impacts the radial evolution of circular wetted zone in all directions and alter the circular HJ at the wetting front into a non‐circular contour that depends on the jet Re number. The limited relations in the literature do not represent these measured shapes and do not appropriately predict radii of HJ in industrial scale. A new correlation for radius of non‐circular HJ has been derived in this study that compared more accurately to the experimental data. Numerical simulations of radial impingement flow on moving surface were performed using a variant of k–ε turbulent model and results are compared to the experimental data. The computational results for the wetting front were found to be close to the experimental data indicating the appropriate performance of the turbulent model. 相似文献
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根据低温钢筋穿水冷却工艺特点,利用现场实测数据并结合理论分析得到不同规格低温钢筋穿水冷却过程中的对流换热系数。采用MSC Marc有限元软件与现场试制结果对低温钢筋穿水冷却过程进行了研究。研究了冷却水流量、终轧温度、穿水时间等工艺参数对低温钢筋温度场和组织演变的影响。模拟结果表明:当冷却水流量为120 m3/h时,钢筋芯部开始有珠光体转变;当冷却水流量为400 m3/h时,钢筋芯部无铁素体转变;冷却水流量为160~200 m3/h时,所获得的组织为针状铁素体与贝氏体。终轧温度增加50 ℃,出水冷装置后钢筋表面温度约增加10 ℃,返红温度约增加30 ℃;在200 m3/h水流量下冷却1.2 s,终轧温度为1 050 ℃时,其芯部组织为针状铁素体与细小的贝氏体。在相同水压与水流量条件下,随着穿水速度的增加,淬透层深度减小,返红温度增加。 相似文献
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A transient three-dimensional mathematical model has been developed to analyze the three-phase flow in a 150 t EAF (electric arc furnace) using oxygen. VOF (multiphase volume of fluid) method is used to simulate the behaviors of molten steel and slag. Numerical simulation was conducted to clarify the transient phenomena of oxygen impingement on molten bath. When oxygen jet impinges on the surface of molten bath, the slag layer is broken and the penetrated cavity in molten steel is created. Simultaneously, the wave is formed at the surface of uncovered steel on which the slag layer is pushed away by jet. The result of numerical simulations shows that the area and velocity of uncovered steel created by impingement, jet penetration depth change from 0.10 m2, 0.0125 m/s, 3.58 cm to 0.72 m2, 0.1445 m/s, 11.21 cm, when the flow rate of an oxygen lance varies from 500 to 2000 m3/h. The results have been validated against water model experiments. More specially, the relation between the penetration depth and oxygen flow rate predicted by numerical simulation has been found to agree well with that concluded by water model. 相似文献
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利用热传系数测试装置,系统地对攀钢板坯连铸机上使用的喷嘴进行了热态性能的测定,获得了这些喷嘴在不同水量和气量下传热系数随铸坯表面温度的变化关系。测试结果为喷嘴的选择以及进一步研究二冷传热机理和设计合理的二冷工艺制度打下了基础。 相似文献
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In this paper results of systematic FE-calculations about the influence of characteristic points of the temperature dependent heat transfer coefficient, especially the Leidenfrost point and the point of maximum heat transfer coefficient on the development of residual stresses are discussed. The numerical investigations were carried out for SAE 1045 and 4140 steel cylinders with 10 and 20 mm 0 quenched in water and oil, respectively. In this work experimentally determined h, T-curves are linearly approximated in the successive stages of heat transfer. Changes of the Leidenfrost-temperature do not influence the middle plane residual stresses of the cylinders investigated. Increasing maximum heat transfer coefficients and low temperatures of maximum heat transfer coefficient, respectively, cause higher magnitudes of residual stress. The development of residual stresses is determined by the temperature dependent gradient of the heat flux density δq/δT in the temperature range of martensitic transformation. Increasing Leidenfrost-temperatures cause more homogeneous stress and residual stress states at the surface of quenched cylinders due to the symmetrical cooling of the sample in axial as well as in radial direction. In particular, it was shown that during immersion cooling of cylindrical parts the heat transfer is locally dependent. Simulating immersion cooling this dependence has to be considered using effective local heat transfer coefficients. 相似文献
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《钢铁冶炼》2013,40(8):598-604
AbstractThe aim of the paper is to design the new wide plate mill. The work on the new cooling technology was supported by extensive laboratory testing while a simulator with full scale testing of cooling units was used. The principal objective of the investigation was to establish the design specification of equipment for accelerated cooling, particularly with respect to the product dimensions and steel grades. The possibilities of accelerated cooling are limited by technical parameters of cooling equipment such as thickness of water layer, flowrate, spray height, position of cooled surface to the nozzles and water or plate speed. These parameters were studied for different product temperatures and water impingement densities from 50 to 110 l s?1 m?2. The heat transfer coefficient was determined and compared for each case. There were three recognised significant cooling regions: water layer region, impinging jet region without water layer and impinging region with water layer, which must be taken into account. The application of the new cooling technology showed better flatness product and productivity higher than previous accelerated cooling system, even shorter cooling length. The rejection ratio by flatness problem of new mill was nearly half of the previous one. 相似文献
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连铸二冷区铸坯表面温度通常高于900 ℃,此时喷淋液滴接触高温铸坯时不会湿润铸坯表面,仅在其上形成一层蒸汽膜,阻碍了液滴与铸坯表面接触传热。针对以上问题,以国内某钢厂连铸二冷区的扁平型水喷嘴为原型,建立了喷嘴射流仿真计算模型,并对所建模型进行了理论和实验室验证;采用数值模拟的方法研究了喷嘴自由射流区的流场分布,运用连铸喷嘴冷却检测系统测量获得了射流液滴粒径演变规律;结合数值模拟和实验室测定结果,定量分析了喷嘴在不同水流量下射流液滴冲击铸坯表面蒸汽膜深度的变化规律。结果表明,该喷嘴的最大射流速度在喷嘴出口处,射流在喷嘴出口附近出能维持较大的射流速度,且随着水量的增加,射流保持高射流速度的距离也增长;整体射流的轴向速度占比均在80%以上。当喷淋水量越大时,射流液滴粒径变得越小;随着距喷嘴出口距离的增加,射流中心处的液滴粒径逐渐增大并达到最大值;当水流量为9和12 L/min时,液滴粒径基本相同,这表明当水流量增加到一定值时,冷却水量的增加不影响液滴粒径分布。在不同水流量下,随着喷淋距离的增加,液滴穿透铸坯表面蒸汽膜深度呈先增大后略微减小的变化规律,在喷射距离为100~200 mm范围内时,液滴穿透深度最大,这表明喷射高度在该范围时,喷淋冷却效果最好。 相似文献
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An analysis of mould, spray and radiation zones of a continuous billet caster has been done by a three‐dimensional turbulent fluid flow and heat transfer mathematical model. The aim was to reduce crack susceptibility of the billets and enhance productivity of the billet caster. Enthalpy‐porosity technique is used for the solidification. Turbulence is modelled by a realizable k‐ε model. The three‐dimensional mesh of the billet is generated by Gambit software, and Fluent software is used for the solution of equations. In various zones, different standard boundary conditions are applied. Enhanced wall treatment is used for the turbulence near the wall. In the mould region, Savage and Prichard expression for heat flux is applied. In the spray cooling zone, the heat transfer coefficient for surface cooling of the billet is calculated by knowing the water flow rate and the nozzle configuration of the plant. The model predicts the velocities in the molten pool of a billet, the temperature in the entire volume of billet, the heat transfer coefficient in the mould region, the heat flux in the cooling zone and radiation cooling zone, and the shell thickness at various zones. The model forecasts that the billet surface temperature up to the cutting region is above the austenite‐ferrite transformation temperature (which is accompanied by large volume change). The model predicts a temperature difference of maximum 700 K between the centre and surface of the billet. The entire solidification takes place at 11.0 m length at 3.0 m/min. For the same casting arrangement, increasing the casting speed up to 4.0 m/min has been explored. Based on the simulation results, recommendations to alter the spray water flow rate and spray nozzle diameter are presented to avoid a sudden change of temperature. 相似文献