A new heat transfer correlation for flow boiling in helically coiled tubes

Based on the superposition principle of the nucleate boiling and convective heat transfer terms,a new correlation is developed for flow boiling heat transfer characteristics in helically coiled tubes.The effects of the geometric and system parameters on heat transfer characteristics in helically coiled tubes are investigated by collecting large amounts of experimental data and analyzing the heat transfer mechanisms. The existing correlations are divided into two categories,and they are calculated with the experimental data.The Dn factor is introduced to take into account the effect of a complex geometrical structure on flow boiling heat transfer.A new correlation is developed for predicting the flow boiling heat transfer coefficients in the helically coiled tubes,which is validated by the experimental data of R134a flow boiling heat transfer in them;and the average relative error and root mean square error of the new correlation are calculated.The results show that the new correlation agrees well with the experimental data,indicating that the new correlation can be used for predicting flow boiling heat transfer characteristics in the helically coiled tubes.

Forced Convection Boiling Heat Transfer and Dryout Characteristics in Helical Coiled Tubes with Various Axial Angles

对水和水蒸汽汽液两相流体在螺旋轴呈各种倾角放置的螺旋管内强制对流沸腾传热与烧毁特性进行了系统地试验研究，试验中系统及结构参数范围如下：压力：Ｐ＝０．４～３．０ＭＰａ质量流速：Ｇ＝１００～２４００ｋｇ／ｍ２·ｓ进口水温：Ｔ＝３０～８０℃出口干度：ｘ＝－０．０５～１．２管内壁面热负荷：ｑ＝０～５４０ｋＥ／ｍ２试验段结构参数：总长Ｌ＝６４４８ｍｍ，管内径ｄ＝１１ｍｍ，螺旋直径Ｄ＝２５６ｍｍ，螺旋升角β＝４．２７°螺旋管轴向放置倾角：水平位置（０°）、向上倾斜４５°（＋４５°）、垂直向上（＋９０°）、向下倾斜４５°（－４５°）．共进行了１０５０个工况的试验．试验结果表明，螺旋管内汽液两相流强制对流沸腾传热可以划分为核态沸腾区、两相流强制对流区、烧毁及烧毁后传热区等３种区域．通过数据处理和分析总结，给出了３区域间转变的边界方程，和３个区域内两相流传热系数的计算公式．根据试验观察和数据结果，对烧毁现象及烧毁点或区域发生的条件及机理进行了深入的分析研究，发现一系列有关现象的规律和特点，指出了其主要影响因素，并给出了烧毁点临界质量干度的预报公式．

Efficiency and Effectiveness Thermal Analysis of the Shell and Helical Coil Tube Heat Exchanger Used in an Aqueous Solution of Ammonium Nitrate Solubility (<i>ANSOL</i>) with 20% H₂O and 80% <i>AN</i>

The case study is about obtaining the flow rate and saturation temperature of steam that makes it possible to heat a solution of water and ammonia nitrate (ANSOL) in a shell and helical coil tube heat exchanger, within a time interval, without that the crystallization of the ANSOL solution occurs. The desired production per batch of the solution is 5750 kg in 80 minutes. The analysis uses the concepts of efficiency and effectiveness to determine the heat transfer rate and temperature profiles that satisfy the imposed condition within a certain degree of safety and with the lowest possible cost in steam generation. Intermediate quantities necessary to reach the objective are the Reynolds number, Nusselt number, and global heat transfer coefficient for the shell and helical coil tube heat exchanger. Initially, the water is heated for a specified period and, subsequently, the ammonium nitrate is added to a given flow in a fixed mass flow rate.

Relationship between the Intensity of Secondary Flow and Convection Heat Transfer in a Helically Coiled Circular Tube with Uniform Wall Temperature

Numerical method is used to investigate fully developed laminar flow in helically coiled circular tube in this paper.The non-dimensional parameter(secondary flow Reynolds number Se)based on absolute vorticity flux along the mainstream is used to indicate the intensity of secondary flow caused by the centrifugal effect in helically coiled circular tube.The relationship between the intensity of secondary flow and the intensity of laminar convective heat transfer is studied.The effects of curvature and torsion on the enhancement of heat transfer are also considered.The results reveal that the absolute vorticity flux along the mainstream can be used to indicate the local or averaged intensity of secondary flow;the non-dimensional parameter of the absolute vortex along the main flow determines the convective heat transfer and friction factor.The relationships of Nusselt number and friction factor with the Se are obtained.The effect of curvature on Nusselt number is obvious,but the effect of torsion on Nusselt number is less obvious.

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

An experimental investigation is described for the characteristics of convective boiling flow instabilities in horizontally helically coiled tubes using a steam-water two-phase closed circulation test loop at pressure from 0.5 MPa to 3.5 MPa. Three kinds of oscillation are reported: density waves; pressure drop excursions; thermal fluctuations. We describe their dependence on main system parameters such as system pressure, mass flowrate, inlet subcooling, compressible volume and heat flux. Utilizing the experimental data together with conservation constraints, a dimensionless correlation is proposed for the occurrence of density waves.

CONDENSATION HEAT TRANSFER OF R-134A IN HORIZONTAL STRAIGHT AND HELICALLY COILED TUBE-IN-TUBE HEAT EXCHANGERS

This article presents an experimental investigation on condensation heat transfer of R-134a in horizontal straight and helically coiled tube-in-tube heat exchangers. The experiments were carried out at three saturation temperatures（35 ℃ , 40 ℃ and 45 ℃ ） with the refrigerant mass flux varying from 100 kg/m2 s to 400 kg/m2 s and the vapor quality ranging from 0.1 to 0.8. The effects of vapor quality and mass flux of R-134a on the condensation heat transfer coefficient were investigated. The results indicate that the condensation heat transfer coefficients of the helical section are 4%-13.8% higher than that of the straight section. The experimental results were compared with the data available in literature for helical and straight pipes.

螺旋套管换热器大变形与热应力分析

采用“流-固”共轭传热与“热-固”单向耦合的方法,分析了螺旋套管换热器对流换热特性、热膨胀大变形以及对热应力计算的影响。结果表明:受离心力影响,螺旋管及夹层流体质点形成二次流混合强化螺旋外侧换热,螺旋内管外侧比同一截面内侧点温度更低;在高温换热工况下,在螺旋管因热膨胀而出现显著的变形,其变形量与管壁厚度处于同一数量级,高温工况下螺旋套管换热器热应力计算属于大变形问题,采用大变形有限单元非线性计算结果比小位移线性计算的热应力更大、更加符合实际。最后,以减小热应力为优化目标,对螺旋套管T型接头布置方位进行了优化,当接管径向布置时热应力比轴向布置减小约1/3。

基于多孔介质方法的铅铋螺旋管式直流蒸汽发生器设计优化研究

本文提出了基于多孔介质方法,铅铋螺旋管式直流蒸汽发生器开展数值模拟,并通过与三维数值模拟结果的对比验证了多孔介质模拟方法的正确性。基于此方法,对给定工况条件的铅铋螺旋管蒸汽发生器开展了设计研究。在1.5 MW功率目标下,发现四层螺旋管的布置方式具有最优综合性能。在此基础上,通过综合性能评价指标对不同工况条件下不同几何参数的螺旋管蒸汽发生器开展性能评价,并运用多元线性拟合探究在工况以及几何范围内综合性能最佳的几何模型,最高性能提升达到3.37%。本研究为铅铋螺旋管式直流蒸汽发生器数值模拟及设计优化提供新的方法参考。

不同螺旋缠绕异形管换热器壳程性能数值研究

缠绕管的形状对螺旋缠绕管换热器的传热能力有重要影响,本文建立了具有不同截面形状的螺旋缠绕管换热器模型,数值研究了八种不同截面形状的缠绕管对螺旋缠绕管换热器壳程流动与传热性能的影响。相比于传统圆管,三叶管和水滴管对壳程流体造成的扰动较大,增强了螺旋缠绕管换热器的综合换热性能,而三叶管则具有最大换热能力。进一步分析了不同冲刷方式对螺旋三叶管换热器和螺旋水滴管换热器壳程性能的影响,结果表明:在相同的进口工况下,螺旋三叶管换热器壳程努塞尔数相比于传统圆管提高了11.8%~15.5%,阻力系数增大了41.9%~49.6%;螺旋水滴管换热器壳程努塞尔数相比于传统圆管提高了2.8%~4.3%,阻力系数增大了3.2%~6.8%;在雷诺数为2 603~5 206的工况条件下,管截面与流动方向夹角为0°的三叶管换热器综合换热性能最好,而管截面与流动方向呈逆流形式的水滴管换热器综合换热性能优于顺流形式。

液态金属快堆螺旋管蒸汽发生器一、二次侧耦合传热数值研究

螺旋管蒸汽发生器是液态金属快堆中能量传递的核心设备,其运行的稳定性、安全性对核电站的运行有至关重要的影响。为此,本文构建了液态金属快堆螺旋管蒸汽发生器一次侧、二次侧耦合传热的三维数值模型,分别基于经济合作与发展组织核能署(The Organisation for Economic Co-operation and Development,OECD/NEA)物性手册和美国国家标准与技术研究院(National Institute of Standards and Technology,NIST)数据库建立液态金属和水-水蒸气变物性计算关联式,采用Lee相变模型计算二次侧水-水蒸气蒸发过程中两相间的质量传递。基于实验数据,分别对本文模型一次侧传热以及二次侧传热的计算可靠性进行了验证。最后以铅铋快堆为例,研究了不同一次侧进口参数下蒸汽发生器一、二次侧之间的耦合传热特性,并与传统水冷堆进行了对比。结果表明:在同等条件下,相比于传统水冷堆,一次侧采用铅铋液态金属时,一、二次侧之间的壁面热流密度明显提升,热流密度峰值可达1439.97 kW·m^(-2),比水冷堆相应数值提升5~6倍,这导致二次侧管内气相蒸发过程明显加剧,体积含气率急剧上升;同时,一、二次侧之间的沿程热流密度分布更加不均匀,沿程热流密度分布相对偏差值比水冷堆相应数值增大3~4倍。随着一次侧进口铅铋温度从350℃增大到450℃,一、二次侧之间的壁面热流密度随之增大,对应的热流密度峰值从950.7 kW·m^(-2)增大到1439.97 kW·m^(-2),提升约1.5倍,同时一、二次侧之间的沿程热流密度分布更加不均匀,不均匀度增大20%。

Turbulent Convective Heat Transfer of Methane at Supercritical Pressure in a Helical Coiled Tube

The heat transfer of methane at supercritical pressure in a helically coiled tube was numerically investigated using the Reynolds Stress Model under constant wall temperature. The effects of mass flux （G）, inlet pressure （Pin） and buoyancy force on the heat transfer behaviors were discussed in detail. Results show that the light fluid with higher temperature appears near the inner wall of the helically coiled tube. When the bulk temperature is less than or approach to the pscudocritical temperature （Tpc）, the combined effects of buoyancy force and centrifugal force make heavy fluid with lower temperature appear near the outer-right of the helically coiled tube. Beyond the Tpc, the heavy fluid with lower temperature moves from the outer-right region to the outer region owing to the centrifugal force. The buoyancy force caused by density variation, which can be characterized by Gr/Re3 and Gr/Re2.7, enhances the heat transfer coefficient （h） when the bulk temperature is less than or near the T~, and the h expe- riences oscillation due to the buoyancy force. The oscillation is reduced progressively with the increase of G. Moreover, h reaches its peak value near the Tpv. Higher G could improve the heat transfer performance in the whole temperature range. The peak value ofh depends on Pin. A new correlation was proposed for methane at su- percritical pressure convective heat transfer in the helical tube, which shows a good agreement with the present simulated results.

THE FRICTIONAL RESISTANCE CHARACTERISTICS OF GAS LIQUID TWO PHASE FLOW IN HELICAL COILED TUBES

This paper deal with the frictional resistance characteristics of gas liquid two phase flow in vertical upward helical coiled tubes under the system pressure 0.1 0.6MPa. By means of dimension analysis and π theorem, the correlation formulas were obtained for calculating the frictional resistance coefficients of gas liquid two phase flow in helical coiled tubes. The calculated results agree well with the experimental results.

压断连续油管落鱼打捞技术实践

连续油管在油田井下作业领域已得到广泛应用,但不可避免的出现连续油管断裂等不同类型井下事故。目前国内外对拉断和剪断连续油管落鱼打捞研究较多,但对压断连续油管打捞的研究较少。压断连续油管鱼顶复杂,本体在井内呈螺旋屈曲状态,打捞难度极大,文章通过一口井案例研究与实践,分析压断连续油管螺旋屈曲状态并建立穿心引入模型,针对性研制打捞工具并制定打捞工艺方案,形成了一种压断连续油管落鱼打捞技术,并通过现场试验得到验证。研究表明:压断连续油管在井内处于螺旋屈曲状态,处置的关键在于解除螺旋造成的摩擦阻力;采用特制的螺旋屈曲释放工具和管柱组合能够分段释放螺旋状态,设计的打捞工具简单可靠;过油管修整鱼顶可降低井径比,防止二次弯折,减少晃动,同时能够有效重建循环通道,防止偏磨套管。文章所涉及的研究方法和技术措施,能够为打捞压断连续油管落鱼提供一定的借鉴和指导。

炼焦荒煤气上升管显热回收换热过程动态特性

煤焦油结焦是制约炼焦荒煤气上升管显热回收换热器长期高效安全运行的主要因素。通过调控荒煤气及上升管管壁温度抑制煤焦油析出是防止结焦的有效措施。基于多孔介质非热平衡模型,建立了内嵌螺旋盘管及多孔填料的荒煤气显热回收套管换热器的一维非稳态热传递模型。结合炼焦周期内荒煤气流量与温度瞬时数据计算得到荒煤气、上升管管壁、填料层、熔融盐温度动态变化,分析了填料层热容、填料层有效导热系数及熔融盐流量对其动态变化的影响,并提出了有效控制荒煤气及上升管管壁温度的方法。结果表明:荒煤气中煤焦油析出及结焦主要发生在炼焦后期荒煤气流量减小时;填料层导热系数是上升管换热器设计时考虑的重要参数,增大填料层导热系数可显著提高余热回收效率,但会使荒煤气与上升管管壁温降增大,设计时应在保证焦油蒸汽不发生冷凝的前提下尽可能增大填料层导热系数;炼焦后期,通过切断熔融盐取热,并合理设计填料层导热系数、填料层热容及熔融盐入口温度等可实现上升管管壁温度调控,从而避免荒煤气中煤焦油析出及结焦。

内置双螺旋结构换热管金属氢化物反应器的传热性能

针对金属氢化物反应器传热性能较差的问题,提出了更紧凑高效的单进–出口的双螺旋结构换热管。建立了内置螺旋管的金属氢化物反应器的3维数学模型,并采用COMSOL Multiphysics 5.2a软件进行求解。首先,通过热阻分析发现,在不同换热流体入口平均流速(0.5~3.0 m/s)下,导程为15 mm的单螺旋换热管管内对流传热热阻占总热阻的百分比为8.5%~45.2%,这表明管内对流传热热阻对反应器的传热性能有很大影响。然后,研究了换热流体入口平均流速对反应器传热性能的影响,确定了模拟中换热流体入口平均流速的范围,对比分析了单、双螺旋结构对反应器性能的影响。结果表明:当换热流体入口平均流速大于0.5 m/s时,能达到较好的换热效果,换热流体的平均真实温升趋于稳定。减小螺旋导程可以明显提高换热流体的平均真实温升及反应器的传热和输出性能。对于导程为60 mm的单、双螺旋结构管,床层平均温度降至300 K所用时间分别为7000 s和3000 s。导程为30 mm的双螺旋结构管的单位重量输出㶲功率比导程为15 mm的单螺旋结构管更高,可见双螺旋结构管反应器的传热和输出性能均优于单螺旋结构管反应器。双螺旋结构管具有更大的换热面积,在反应器床层内的位置分布更加均匀,从而提升了反应器的传热和输出性能。

螺旋管外空气-蒸汽冷凝强化传热实验研究

管外含空气蒸汽冷凝是非能动安全壳热量导出系统工作的重要环节,为了提高系统的传热效率需要对空气-蒸汽冷凝强化传热进行研究。本文在压力0.2~1.3 MPa,壁面过冷度50~120℃,对管外径为19、25、38 mm的螺旋管外含空气蒸汽冷凝进行了实验研究。实验结果表明:螺旋管管径越小,换热系数越大,19 mm管的换热效果可达38 mm管的1.55倍;与竖直管相比,螺旋管强化换热效果受压力影响较大,压力越高,强化换热效果越好,0.2 MPa时换热系数较竖直管低3%左右,而1.3 MPa时比竖直管可强化65%左右。螺旋管有较好的强化换热效果,可对非能动安全壳热量导出系统的优化设计提供支持。

盘管式核主泵高压冷却器的流致振动分析

采用计算流体动力学方法对单个盘管进行了流场分析,并将分析结果应用于盘管的流致振动评定。采用有限元软件Ansys Workbench进行盘管的模态和振型分析,根据盘管管束的固有频率、运行参数和评定依据,对高压冷却器的流致振动特性进行了评定。结果表明:盘管式高压冷却器管束的固有频率、振动幅值均处于安全范围内,可避免由漩涡脱落产生的振动;盘管式换热管外侧的横向流速小于流体弹性失稳临界流速,不会发生流体弹性失稳;湍流抖振的频率及其产生的峰值振幅均远小于限值,不会因湍流抖振导致设备失效。

超临界压力下CO_2在螺旋管内的混合对流换热

在恒热流条件下,对超临界压力CO2在内径为9 mm,绕径为283 mm,节距为32 mm的螺旋管内垂直上升混合对流的传热特性进行了实验研究,实验参数范围为：进口压力8 MPa、质量流速0～650 kg·m-2·s-1、内壁热负荷0～50 kW·m-2。研究发现：受热螺旋管内超临界压力CO2的壁温及传热特性由变物性、浮升力及离心力的耦合作用共同支配,变物性及浮升力影响的相对大小可用Buoyancy数定性表征,当Bo〉8×10-7时,自然对流占主导作用,浮升力作用引起强烈的二次流效应,显著强化传热;在浮升力和离心力共同作用下,截面周向温度最低点出现在外下侧区域,且当浮升力作用占优时,底部区域的传热系数大于外侧,当离心力作用占优时,底部区域的传热系数小于外侧。基于本实验获取的2346个数据点,得出了计算Nu实验关联式,90%以上的实验值与拟合公式计算值偏差在±20%以内。

螺旋管内油-水液液两相流流型

在两种不同放置位置螺旋管内进行了油 -水液液两相流流型的实验研究 ,定义了各种不同流动条件下油-水两相流的流型 ,给出了螺旋管内液液两相流的流型图 .进而讨论了各流型之间转变的机理 ,并考察了螺旋管结构尺寸及放置方式对油水两相流流型及相转变特性的影响 .

多头螺旋管式换热器换热与压降计算

从实际工程设计出发,对多头螺旋管式换热器的设计进行了研究,提出了多头螺旋管束受热面结构的设计方法,推荐了螺旋管内外的传热系数和压降的计算关系式。并对200MW蒸汽发生器进行了实例设计计算。