Numerical Study on Heat Transfer Enhancement for Use of Corrugated, Nodal and Horizontal Grain Tubes

With isopentane as working fluid, the heat transfer performances for corrugated, nodal and horizontal grain tubes are simulated. The structural parameters of the three kinds of tubes are compared with those of the plain tube. The numerical results using computational fluid dynamics are validated with theoretical values. For the corrugated, nodal and horizontal grain tubes, the heat transfer enhancements(HTEs) are 2.31—2.53, 1.18—1.86 and 1.02—1.31 times of those of the plain tube, respectively. However, the improved HTEs are at the expense of pressure losses. The drag coefficients are 6.10—7.09, 2.06—11.03 and 0.53—1.83 higher, respectively. From the viewpoint of comprehensive heat transfer factor, the corrugated tube is recommended for engineering applications, followed by the horizontal grain tube.

Experimental study on pressure fluctuation characteristics of slug flow in horizontal curved tubes

In order to study the pressure characteristics of slug flow in horizontal curved tubes,two kinds of curved tubes with central angle 45° and 90° respectively are studied,of which are with 0. 5m circumference and 26 mm inner diameter are used. When the superficial liquid velocity or the superficial gas velocity is constant,the pressure fluctuations and the probability distribution of the average velocity of slug flow are clear for all of the five experimental conditions. The results of experiment show that the pressure characteristics of slug flow in curved tubes have periodic fluctuations. With the rise of central angle,the period of pressure fluctuation is more obvious. The system pressure of the slug flow increases with the increasing of superficial liquid/gas velocity. Meanwhile,the probability distribution of pressure signal shows regularity,such as unimodal,bimodal or multimodal.

Theoretical Research on R245fa Condensation Heat Transfer inside a Horizontal Tube

Numerical simulation on R245fa condensation inside an inner diameter of 8 mm horizontal tube is researched in this paper. The effect of variation in velocity, condensation temperature and superheat of inlet steam and variation in cooling water temperature on heat transfer coefficient are investigated as a parametric study. Condensation process of steam has been successfully modeled by applying a user defined function (UDF) added to the commercial computational fluid dynamics (CFD) package. By analyzing the corresponding condensate contours and the curves of local heat transfer coefficient, the relationships between condensation heat transfer coefficient and various parameters of R245fa inside horizontal tube are obtained. It shows that the heat transfer coefficient increases by the increase in velocity, condensation temperature and superheat of inlet steam and the decrease in cooling water temperature. The errors between the heat transfer coefficient of simulation result and model of Wang and Shah are within ±30%. The parametric study will provide the basis for designing efficient heat exchangers of R245fa.

Heat Transfer in Horizontal Copper Tube Heated by Electric Heating Process

Heat transfer from electrical and electronics component is essential for better performance of that electrical system,The maximum heat transfer from that system results long period durability.In most of the system base provided for equipments are very small and placed in a very complicated position.so heat transfer by forced convection is not easy for that purpose.The heat transfer by natural convection is the familiar technique used in electronics cooling;there is huge group of apparatus that lends itself to natural convection.This category consist of stand-alone correspondence such as modems and small computers having an array of printed circuit boards(PCB)accumulate within an area.Natural convection heat transfer in heated horizontal duct drive away heat from the interior surface is offered.The duct is open-ended and round in cross section.The test section is heated by provision of heating coils,where constant wall heat flux mentioned.Heat transfer experiment is carried out for channel of 50 mm.internal diameter and 4 mm thickness with length 600 mm.Ratios of length to diameter of the channel are taken as L/D=12.Wall heat fluxes maintained at q//=300 W/m2 to 3150 W/m2.A methodical investigational record for the local steady state natural convection heat transfer activities is obtained.The wall heating condition on local steady-state heat transfer phenomena are studied.The present experimental data is compared with the existing theoretical and experimental results for the cases of vertical smooth tubes.

Test on methane flame velocity in horizontal tube with obstacles

To test flame propagation velocity of gas explosion in a horizontal tube,a set of flame velocity testing system is designed.The system is composed of two parts:a horizontal tube used for methane burning and a flame detection system.The effect of obstacles on flame propagation velocity of methane explosion is tested.Methane volume density is 10% in the tube.The obstacle is the circular ring,2 mm thick.Its blockage ratios are 40%,50% and 60%,respectively.The number of obstacles put in the tube is 1,3,5 and 7.Experimental results show that the obstacle has obviously accelerating effect on flame wave of gas explosion.As the number and blockage ratios of the obstacles increase,flame accelerating became more obviously.When there are seven obstacles,the maximum average flame velocity reaches over 351.2 m/s.When the blockage ratio of three obstacles is 60%,the maximum average flame velocity is 238.9 m/s.

Convective Boiling of Near-Azeotropic Refrigerant R410A in the Horizontal Micro-fin Tube

Using near-azeotropic refrigerant R410A as the working fluid, the experimental studies on the horizontal micro-fin tubes were conducted. Several factors affecting heat transfer coefficients were analyzed, and the characteristics of flow boiling of the refrigerant in the horizontal micro-fin tubes were discussed. The local heat transfer coefficients increase with mass flux, heat flux and quality. And the heat transfer enhancement factor of those testing tubes is about 1.6 to 2.2.

水平管降膜换热器性能规律研究进展

水平管降膜换热器具有热质传递效率高、阻力小、结构简单等优点,被广泛应用于化工等传统领域及能源利用的节能减排领域。降膜换热器内部发生复杂的流动及传热传质相互耦合过程。介绍了实验及模拟研究手段的进展,综述了不同操作参数(气体温度、流向及流量,溶液流量、温度及浓度,内部媒介流量及温度等)与结构参数(管径、管间距等)对水平管降膜管间流型、液膜厚度与润湿性等流动特性的影响规律,以及对蒸发传热特性、吸收传热传质特性等换热器性能的影响规律,包括整体性能和局部微细特征,为水平管降膜换热器的性能优化提供理论支撑。指出在不同气流特征以及多因素相互作用下多维度的局部流动与传热传质性能的耦合影响规律以及强化换热手段会是水平管降膜换热器未来研究的重点方向。

水平井段连续管多形态流域可溶桥塞碎屑运移规律

随着油田大规模的开发,连续管钻磨桥塞技术得到广泛应用。然而该技术在现场应用中会由于桥塞碎屑的堆积而造成钻磨时效低、井下故障频发等一系列工程难题。为此,探究在水平井眼多形态流域桥塞碎屑的运移规律很有必要。运用CFD数值模拟方法,对水平井段连续管不同形态时的桥塞碎屑进行运移规律研究,探究当边界条件不同(钻磨液黏度、钻磨液流量、固相初始体积分数)时各个截面上桥塞碎屑的体积分数的变化规律。研究结果表明:钻磨液黏度的增加、钻磨液流量的减少、固相初始体积分数的降低都有利于桥塞碎屑的运移;并且当连续管在中心时出口处的桥塞碎屑体积分数比连续管螺旋屈曲时的要高26.5%;碎屑初始体积分数对碎屑运移的影响最大。所得结论可有效预防井下卡钻等风险。

基于有限元模拟的水平连铸TP2铜管坯一次冷却结构优化研究

对比多种结晶器结构下温度场、速度场等分布状态及石墨模具内部温度变化趋势,探究其对铜套、石墨模具等易损件及铜管铸坯温度变化的影响。结果表明,在一次冷却结构增设12道Φ10 mm且倾斜角度为30°的流槽,可使冷却水流态平稳均衡,铜套受热均匀,有利于铸坯周向同时凝固。本文通过有限元软件模拟铜管水平连铸过程一次冷却结构优化对温度的影响,为生产企业改善产线冷却效果,提高产品质量,降低模具成本和延长使用寿命,提供了实验参照和理论指导。

铜管坯水平连铸水冷调控与实验分析

为实现传统铜管坯水平连铸水冷控制系统在线自动化精准控制,提高生产质量与精度,改善管坯组织性能,对现有铜管坯水平连铸一冷水控制进行分析。采用程序设计和物理实验验证的方法,开展了基于可编程逻辑控制器(PLC)闭环策略下石墨结晶器冷却水量自动控制的相关研究。实验结果表明,基于闭环控制逻辑的自动水冷控制系统可以将流量波动控制在±0.5 L/min范围内,离散系数为2.68×10^(-3),明显小于传统水冷控制系统,铜管坯水平连铸一次冷却水闭环控制系统可以实现连铸过程的精确控制。

圆钢管型钢再生混凝土组合柱水平承载力计算方法研究

通过对11个圆钢管型钢再生混凝土组合柱进行低周反复荷载试验,分析再生粗骨料取代率、型钢截面形式、轴压比、型钢配钢率及圆钢管壁厚参数对组合柱水平承载力的影响规律;观察了组合柱的破坏形态及特征,研究了圆钢管、型钢翼缘及腹板应变的发展规律,分析了组合柱的地震破坏特征。研究表明,在水平地震作用下组合柱发生典型的压弯塑性铰破坏。在此基础上,结合现有规范提出了基于叠加原理的圆钢管型钢再生混凝土组合柱水平承载力计算方法。计算结果表明,其水平承载力计算值与试验值吻合度较好,能较为准确地预测组合柱的水平承载力。

页岩油水平井连续管底封拖动压裂难点与对策

连续管拖动压裂作为页岩油藏压裂增产的主体工艺之一,为了解决长水平段水平井压裂改造过程中面临的连续管下入自锁、压裂封隔器坐封困难、喷射阶段封隔器频繁解封等难点。文章通过对连续管拖动压裂作业中摩擦系数实验测试、软件模拟工具受力分析和射孔过程套管回压精确计算等方法,针对连续管下入自锁问题提出了利用金属降阻剂和环空泵送压裂工具延长连续管下深的方法,针对压裂封隔器坐封困难问题采用环空泵送辅助封隔器坐封,通过精确计算射孔阶段需要控制的套管回压,有针对性地预防封隔器频繁解封的问题。现场实践表明,上述措施能有效解决水平段2 000 m以内的底封拖动压裂过程连续管技术难题,为后续鄂尔多斯页岩油规模化开发提供技术支撑。

表面张力模型对水平椭圆管外降膜流动传热数值计算结果的影响

采用VOF方法对水平椭圆管外降膜流动和换热进行了二维数值分析。研究了4种椭圆管管型在不同表面张力模型下的降膜流动和换热问题。结果表明,在椭圆管近壁处存在极薄的层流底层,对换热影响很大;在滞止区,流体涡流导致壁面换热系数波动较大。同时发现在椭圆管外降膜流动计算中,表面张力不可忽略,连续表面力(CSF)模型和连续表面应力(CSS)模型均能较好地体现椭圆管的壁面流动和换热情况,但CSF模型在上下滞止区的计算更为准确。此外,椭圆度对壁面传热系数影响也较为显著。椭圆度增大,换热增强,特别是当周向角θ=20°~180°时,换热增强尤为明显。

深层煤层气水平井连续油管解卡工艺研究

针对深层煤层水平井连续油管较卡问题,从地质因素、工程因素两方面分析垢卡原因,并系统性总结解深层煤水平井连续油管煤垢卡的解卡过程及技术要点,为今后同类作业提供指导性建议。

Numerical simulation of liquid falling film on horizontal circular tubes

这研究的目的是数字地在水平圆形的试管上调查掉落的电影的流动特征。数字模拟被执行用为有一个和二柱体的 2D 配置流畅。液体方法的卷被用来追踪液体掉落电影和煤气液体的接口的运动。热和转移系数上的流动特征的效果可能是显著的，尽管它在以前的研究被忽视了。最高的试管，底部试管上的一些特殊流动特征， intertube 流动模式和流动特征上的液体 feeder 高度的效果上的速度分发和电影厚度特征被学习了。我们的模拟显示那 1 )试管的上面、更低的部分的速度分布不严格地对称、不一致， 2 )电影厚度取决于流动率和尖分布， 3 )最高的试管的流动特征与底部试管的那些不同， 4 )三位校长和二个中间的转变模式被区分，并且 5 )液体喂高度戏掉落的形成上的一个重要角色电影。数字结果在与由 Nusselt 模型和报导结果的理论价值的一个好协议。

Experimental Investigation of Forced Convective Boiling Flow Instabilities in Horizontal Helically Coiled Tubes

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Experimental Study of Falling-film Mode Transitions between Horizontal Tubes in CaCl_2/Water Absorber

It is important to accurately predict the flow mode especially intertube falling-film mode of absorbent for its great impact on the heat and mass transfer in a horizontal tube absorber. In this paper, a test facility used to study falling-film outside horizontal tubes was built, and experiments were conducted to explore the intertube mode transitions with water-calcium chloride(CaCl2/water) solution in quiescent surroundings. The correlations which are more suitable for predicting CaCl2/water solution intertube mode transitions were developed. In general, the transitional Re will decrease with the solution concentration increasing, and its effects increase with the transitions from droplet mode to sheet mode. Hysteresis exists in all the mode transitions, and it is more obvious for low concentration solutions. The results may be an important support for modeling, designing and operating of CaCl2/water falling-film absorber.

低产液量水平井快速找水技术研究与试验

找水控水是水平井见水后的开发政策调整、综合治理的重要手段。低渗透油田注水开发水平井单井液量低、水平井段长、改造段数多,常规生产测井找水受井筒低流量限制无法适应,现有封隔器分段生产找水技术作业效率低、周期长,无法满足现场快速制定调控措施的需求。为了实现低渗透油田见水水平井精细找水目的,采用技术集成思路,提出了连续油管起下钻作业、井筒电潜泵排液增大流量、拖动MAPS测井仪对产层段连续监测为核心的快速找水新方法,设计了内穿复合电缆连续油管+电潜泵+MAPS测井仪的快速找水工艺管柱,研制了配套的复合电缆、撬装滚筒、高压滑环、穿越接头、测井仪器连接接头等工具和装置,系统具备了电潜泵供电和数据传输功能,形成了低渗透油田水平井快速找水技术。在对工艺系统运行安全性评价的基础上,开展了现场先导试验2口井,实现找水周期由25 d缩短至1 d,为低产液量水平井高效找水开拓了新的技术途径。

三角形核心筒在超高层建筑结构中的应用研究

三角形核心筒能提供的抗侧刚度和楼层平面利用率都不如矩形核心筒,因此在超高层建筑中应用较少。结合实际工程,介绍了三角形核心筒在超高层建筑结构中的应用,采取了相应加强措施,并进行了风洞试验。通过方案比选和计算分析可知,为有效抵抗水平荷载,结构布置时利用避难层设置加强层,以增强整体结构的抗侧刚度。风洞试验结果表明,体型系数在裙房以下个别风向角大于1.4,大部分结果都小于1.4,不同风向角风荷载作用下的层间位移角均小于规范风荷载结果。前两阶周期接近7s,塔楼抗侧刚度相对较弱,但前两阶振型均为平动,扭转周期比为0.5,整体抗扭刚度较好。在进行构件截面设计时,应考虑不同方向水平力的作用,且地震作用方向应与墙肢长度方向一致,风荷载方向应与墙肢垂直。