Heat Transfer and Resistance Characteristics of Conical Spiral Tube Bundle Based on Field Synergy Principle

Conical spiral tube bundle are universally used in heat transfer enhancement in heat exchangers.The heat transfer and resistance of the tube bundle are affected greatly by the conical structure,so the analysis of it is necessary.In order to a further evaluation,the heat transfer and resistance characteristics of conical spiral tube bundle are investigated with regression analysis based on numerical simulation data.The correlations of heat transfer and pressure drop of conical spiral tube bundle are proposed both in laminar and turbulent fluid flow.On the based of the field synergy principle,the synergy of four vectors,the velocity,the velocity gradient,the temperature gradient and the pressure gradient,are calculated and discussed via the user defined function（UDF） program.The synergy angles β and θ,which respectively denote the performance of heat transfer enhancement and pressure drop of the conical spiral tube bundle,are analyzed.Finally,the comprehensive performance of the conical spiral tube is evaluated by the synergy angle γ and all of the three synergy angles of conical spiral tube bundle are compared to both bare tube and thin cylinder-interpolated tube.The analysis of the synergy angles shows that the heat transfer enhancement and pressure drop of conical spiral tube bundle are smaller than that of the thin cylinder-interpolated tube,while the comprehensive performance of conical spiral tube bundle is greater.The analysis of the heat transfer and pressure drop of conical spiral tube is valuable and instructional on the design and optimum of conical spiral tube bundle heat exchangers.

Experimental Study on Cross-Flow Induced Vibrations in Heat Exchanger Tube Bundle

Vibration in heat exchangers is one of the main problems that the industry has faced over last few decades. Vibration phenomenon in heat exchangers is of major concern for designers and process engineers since it can lead to the tube damage, tube leakage, baffle damage, tube collision damage, fatigue, creep etc. In the present study, vibration response is analyzed on single tube located in the centre of the tube bundle having parallel triangular arrangement （60-） with P/D ratio of 1.44. The experiment is performed for two different flow conditions. This kind of experiment has not been reported in the literature. Under the first condition, the tube vibration response is analyzed when there is no internal flow in the tube and under the second condition, the response is analyzed when the internal tube flow is maintained at a constant value of 0.1 rn/s. The free stream shell side velocity ranges from 0.8 rn/s to 1.3 m/s, the reduced gap velocity varies from 1,80 to 2.66 and the Reynolds number varies from 44500 to 66000. It is observed that the internal tube flow results in larger vibration amplitudes for the tube than that without internal tube flow. It is also established that over the current range of shell side flow velocity, the turbulence is the dominant excitation mechanism for producing vibration in the tube since the amplitude varies directly with the increase in the shell side velocity. Damping has no significant effect on the vibration behavior of the tube for the current velocity range.

Pressure Drop of Liquid–Solid Two-Phase Flow in the Vertical Tube Bundle of a Cold-Model Circulating Fluidized Bed Evaporator

A cold-model vertical multi-tube circulating fluidized bed evaporator was designed and built to conduct a visualization study on the pressure drop of a liquid–solid two-phase flow and the corresponding particle distribution.Water and polyformaldehyde particle(POM)were used as the liquid and solid phases,respectively.The effects of operating parameters such as the amount of added particles,circulating flow rate,and particle size were systematically investigated.The results showed that the addition of the particles increased the pressure drop in the vertical tube bundle.The maximum pressure drop ratios were 18.65%,21.15%,18.00%,and 21.15%within the experimental range of the amount of added particles for POM1,POM2,POM3,and POM4,respectively.The pressure drop ratio basically decreased with the increase in the circulating flow rate but fluctuated with the increase in the amount of added particles and particle size.The difference in pressure drop ratio decreased with the increase in the circulating flow rate.As the amount of added particles increased,the difference in pressure drop ratio fluctuated at low circulating flow rate but basically decreased at high circulating flow rate.The pressure drop in the vertical tube bundle accounted for about 70%of the overall pressure drop in the up-flow heating chamber and was the main component of the overall pressure within the experimental range.Three-dimensional phase diagrams were established to display the variation ranges of the pressure drop and pressure drop ratio in the vertical tube bundle corresponding to the operating parameters.The research results can provide some reference for the application of the fluidized bed heat transfer technology in the industry.

Experimental and Numerical Investigation on Erosion Corrosion of the Air Cooler Tube Bundle in a Residue Hydrotreating Unit

Corrosion leakage occurred in the 14th tube bundle in the first row of a residual oil hydrotreating air cooler after operating for two years.The failure location was 0.5 m from the outlet header box.In this paper,the erosion corrosion of the air cooler tube bundle was investigated by experimental and numerical methods.Visual inspection,scanning electron microscopy(SEM),and X-ray diffraction(XRD)experiments were performed,and the failure morphology and material composition confirmed that the damage was caused by erosion corrosion.The shear stress transport k–ωturbulence model(SST-k–ω)was then used to investigate the flow and erosion corrosion characteristics,combined with mass transfer,corrosion rate,and ionization equilibrium models.The numerical simulation results revealed that the water phase volume fraction increased with flow and heat transfer in the fluid,which increased the mass flow rate and concentration of hydrogen sulfide.The mass transfer coefficient and corrosion rate were proposed as important parameters to characterize erosion corrosion.Moreover,the local concentration of wall shear stress was found to increase the risk of erosion corrosion.The predicted high-risk area was consistent with the actual failure area,which verified that this failure incident was attributable to erosion corrosion by the water phase.

A comprehensive comparison on vibration and heat transfer of two elastic heat transfer tube bundles

Elastic heat transfer tube bundles are widely used in the field of flow-induced vibration heat transfer enhancement. Two types of mainly used tube bundles, the planar elastic tube bundle and the conical spiral tube bundle were comprehensively compared in the condition of the same shell side diameter. The natural mode characteristics, the effect of fluid-structure interaction, the stress distribution, the comprehensive heat transfer performance and the secondary fluid flow of the two elastic tube bundles were all concluded and compared. The results show that the natural frequency and the critical velocity of vibration buckling of the planar elastic tube bundle are larger than those of the conical spiral tube bundle, while the stress distribution and the comprehensive heat transfer performance of the conical spiral tube bundle are relatively better.

Experimental Research on Resistance Characteristics of H-type Elliptical Finned Tube Bundles

阻力特性是换热器的基本特性之一，流体横掠换热管产生的绕流扰动是换热器阻力恶化的主要因素。为分析前排绕流对后排阻力的影响规律，分别对管排数2-10不等的换热管进行阻力特性试验研究，同时为定量分析管排数对阻力特性的影响规律，定义了管排阻力修正系数，并根据实验数据给出了其在不同管排数下的取值，具有重要的工程意义；同时基于冷态阻力特性试验台进行实验研究，得到κ=1及κ=1.6的经典椭圆管的阻力特性公式Eu，并研究不同管型及布置方式对其的影响规律。

Heat transfer characteristics of air cross-flow for in-line arrangement of spirally corrugated tube and smooth tube bundles

An experimental study on heat transfer and resistance coefficients of linearly arranged smooth and spirally corrugated tube bundles in cross-flow was performed. The heat transfer and resistance coefficients are presented in this paper with transverse and longitudinal tube-pitch and tube geometries taken into account. The experiment's results can provide technical guidelines for application to horizontal air preheater with arranged in-line spirally corrugated tube bundles, especially to the air preheater for CFBCBs (Circulating Fluidized Bed Combustion Boilers).

Heat transfer model of two-phase flow across tube bundle in submerged combustion vaporizer

In order to optimize the design of the submerged combustion vaporizer(SCV), an experimental apparatus was set up to investigate the heat transfer character outside the tube bundle in SCV. Several experiments were conducted using water and CO_2 as the heat transfer media in the tubes, respectively. The results indicated that hot air flux, the initial liquid level height and the tube pitch ratio had great influence on the heat transfer coefficient outside the tube bundle(ho). Finally, the air flux associated factor β and height associated factor γ were introduced to propose a new hocorrelation. After verified by experiments using cold water, high pressure CO_2 and liquid N_2 as heat transfer media, respectively, it was found that the biggest deviation between the predicted and the experimental values was less than 25%.

Experimental Study of Condensation Heat Transfer on Tube Bundles in Large Power Plant Condensers

In order to clarify the effect of condensate inundation on steam condensation in a large tube bundle, condensation heat transfer and the condensate flow pattern in the tube bundle have been experimentally investigated. Test tube bundle consists of 36 cooling tubes, 12 condensate supply tubes and 24 un-cooled dummy tubes. Cooling test tubes are made of copper and have an outer diameter of 19.1 mm and condensing length of 150 mm, Steam flows horizontally through the test tube bundle at gap velocities 15-27 m/s at pressures of 8.8 kPa. In this study, experimental data about condensate flow pattern and condensation heat transfer in a tube bundle were collected for the optimization of tube arrangement in large power plant condensers.

Vibration Response and Stress Analysis of Planar Elastic Tube Bundle Induced by Fluid Flow

Flow?induced vibration plays a positive role on heat transfer enhancement. Meanwhile, it is also a negative factor for fatigue strength. Satisfying the fatigue strength is the primary prerequisite for heat transfer enhancement. This paper numerically studied the flow?induced vibration of planar elastic tube bundle based on a two?way fluid–structure interaction(FSI) calculation. The numerical calculation involved the unsteady, three?dimensional incompressible governing equations solved with finite volume approach and the dynamic balance equation of planar elastic tube bundle solved with finite element method combined with dynamic mesh scheme. The numerical approach was verified by comparing with the published experimental results. Then the vibration trajectory, deformation and stress contour of planar elastic tube bundle were all studied. Results show that the combined movement of planar elastic tube bundle represents the agitation from inside to outside. The vibration of out?of?plane is the main vibration form with the typically sinusoidal behavior because the magnitude of displacement along the out?of?plane direction is the 100 times than the value of in?plane direction. The dangerous point locates in the innermost tube where the equivalent stress can be utilized to study the multiaxial fatigue of planar elastic tube bundle due to the alternating stress concentration. In the velocity range of 0.2-3 m/s, it is inferred that the vibration amplitude plays a role on the stress response and the stress amplitude is susceptible to the fluid velocity. This research paves a way for studying the fatigue strength of planar elastic tube bundle by flow?induced vibration.

Numerical Study of Fluid Flow over Bundle Tubes

In this paper, a bank of tubes containing a flowing fluid which is immersed in a cross flow second medium of fluid with different temperature has been studied numerically using computational fluid dynamics. Laminar steady flow with a low Reynolds number has been studied in this work. Inlet mass flow rate and the bulk temperature are known and numerical method has been implemented to study the convective heat transfer to investigate the temperature and flow fields. Effects of different inlet bulk temperatures and mass flow rates have been investigated on temperature and pressure variations.

十字形钢管束自密实混凝土短肢剪力墙轴压性能研究

为研究十字形钢管束自密实混凝土短肢剪力墙的轴压受力性能,通过模型试验研究和ABAQUS数值模拟相结合的方法,对不同腔体数十字形钢管束自密实混凝土短肢剪力墙的轴压性能进行分析。首先,根据轴压试验结果对剪力墙的破坏形态和轴向荷载-应变曲线等轴压受力性能进行分析,提出轴压承载力计算公式。其次,建立剪力墙轴压有限元计算模型,将试验结果和模型计算结果进行对比以验证有限元模型的准确性。最后,根据有限元参数化分析结果验证并修正剪力墙轴压承载力计算公式。研究发现,剪力墙的轴向荷载-应变曲线在不同腔体数下具有相似的特征,表明其变形能力良好。在破坏过程中,钢管束对核心混凝土的约束作用显著,提高了试件的延性和承载能力,其中钢管束的破坏主要表现为多波鼓曲和焊缝开裂,尤其是在钢管束中部的1/4区域。此外,随着腔体数增加,剪力墙极限承载力提升,但其延性系数有所下降。本研究提出的简化公式与有限元分析结果的误差控制在10%以内,该公式可为工程设计应用提供理论借鉴。

管束结构的阻尼控制型流弹失稳特性研究

尽管自2012年SONGS事故以来,流弹失稳对管束结构的危害性和重要性再次引起了重点关注,但对导致这种不稳定现象的根本因素仍未确定。为进一步研究流弹失稳的基本物理机制,以压水堆蒸汽发生器通常采用的平行三角形管束为对象,基于开源CFD(computational fluid dynamics)工具OpenFOAM,同时耦合管的动力学方程,求解具有移动边界的非定常Navier-Stokes(uRANS)方程,建立了研究阻尼控制型不稳定机制的数值模型,进而预测管束的流固耦合振动,揭示影响阻尼控制型不稳定机制的关键参数和流动响应;重点讨论了不同质量阻尼参数下,系统的响应特性、能量输入与耗散,升力与位移间的相干性、相位差、相关系数,升力的频谱特性,主导激励机理。进一步揭示了管束流弹系统中占主导地位的激励机理和关键流动现象,有助于理解管束与流体之间的相互作用机理,同时为工程中使用开源CFD工具OpenFOAM预测流弹失稳行为提供了参考。

管壳式换热器管束的搪瓷涂层防腐技术研究

随着生产工艺水平的提高,换热器工作环境的温度、压力和流体高速流动所产生的应力都随之提高,同时介质的腐蚀性也随之提高,因此防腐性能较强的换热器成为刚性需求。文中对换热器管束进行防腐技术研究,选用搪瓷涂层对管束进行腐蚀防护;研究了管束表面搪瓷涂层的加工工艺,验证了搪瓷涂层的防腐性能及热震性能,结果良好;提出搪瓷管束与管板新连接加工工艺,取代了原有的先胀后焊的加工工艺,并加以验证,效果良好。

采用叉排管束模型的刷式密封刷丝束变形特性研究

采用刷式密封三维叉排管束泄漏流动数值模拟与有限元分析模型相结合的流固耦合方法,研究了刷丝束在气动载荷作用下的变形特性。通过数值求解三维雷诺时均Navier-Stokes(RANS)方程组和SSTk-ω湍流模型,获得了刷丝束气动载荷,刷丝束有限元接触模型综合考虑了刷丝束内部存在的摩擦接触力。研究表明:随着压比的增大(1.5~3.0),刷式密封泄漏流量系数增大的趋势逐渐减缓,第5~9排刷丝承受压差占比从60%增长至70%,转速对刷式密封泄漏流场影响微弱。刷丝所受周向和径向气流力大小相当,二者合力方向与刷丝垂直,轴向气流力则是周向、径向气流力的13.6~18倍。较大轴向气流力使刷丝在围栏高度区域向下游发生轴向弯曲,压比为1.5、2.0、2.5和3.0时,刷丝束最大轴向变形量分别为0.077、0.096、0.114和0.130mm。较小周向、径向力以及后排刷丝与后夹板之间较大摩擦接触力,使刷丝周向和径向变形量很小。刷丝束所受轴向气流力与法向气流力的比值可用于分析刷丝周向变形滑移。所建立的基于刷式密封叉排管束模型的流固耦合方法为分析刷丝束变形特性提供了研究途径。

基于刷丝束叉排管束模型的透平机械刷式密封泄漏流动特性和封严机理研究

【目的】为获得刷式密封的精细化泄漏流动特性,并揭示其封严机理,建立基于刷丝束叉排管束模型的刷式密封泄漏流动特性数学模型。【方法】数值求解三维雷诺平均纳维-斯托克斯(Reynolds-averaged Navier-Stokes,RANS)方程和剪切应力输运(shear stress transport,SST) k-ω湍流模型,研究刷式密封泄漏量和刷丝束间隙的流动特性。数值模拟获得的泄漏量和压力分布与实验数据吻合一致,验证了数值方法的可靠性。获得了4种压比和转速下的刷式密封泄漏量和刷丝束间的泄漏流动曲线。【结果】随着进出口总静压比的增大,刷丝束内部开始出现细小漩涡并逐渐发展,对泄漏流的阻碍作用变大,刷式密封泄漏量增大的趋势逐渐减缓,最后一排刷丝承受的压差占比从13.1%增加至26.3%。【结论】在所研究的转速范围内,转速对刷式密封的泄漏量的影响可以忽略。压比不同时,泄漏流在末排刷丝与后夹板间隙处的径向流动与围栏高度处轴向流动强度存在差异,导致后夹板下方涡系结构不同,通过刷丝束间精细化泄漏流动分析,揭示了刷式密封的封严机理。研究结果可为三维叉排管束模型在刷式密封泄漏流动研究中的应用提供参考。

失重和重力条件液态金属绕流管束对流传热特性对比

液态金属绕流管束对流换热能力强,其应用有助于换热设备小型化,是空间动力反应堆主换热器设计的较好选择。失重是空间环境的典型特征,失重和重力条件下液态金属绕流管束流动传热特性的异同尚不清楚,阻碍了液态金属用于空间反应堆的发展进程。为此,通过雷诺时均数值模拟方法,对比研究了失重和重力条件下液态金属绕流管束湍流传热特性,获得了局部温度与速度分布,得到了流动传热性能变化规律。结果表明:竖直向下流动时,液态金属对流传热性能在失重和重力条件下表现不同;重力条件下浮力影响了流场和温度场,相比失重条件,阻力和换热性能最大偏差约10%。

基于换热管束优化布置的固态储氢反应器储氢性能模拟研究

为探究固态储氢反应器内的热质传递过程,建立了反应器的二维数值计算模型,分析了反应器内固态储氢材料的径向反应分率分布特性,以及储氢材料床层厚度与换热管径对饱和半径的影响规律,进而开展了换热管束优化布置研究。结果表明:换热管存在对应的最大饱和半径,且随管径增加而增大;当管半径为1.00~6.00 mm的单管布置时,最大饱和半径分别为2.60、3.30、3.50、3.70、3.80、3.90 mm,其中半径为1.00、2.00、3.00 mm的换热管体积分数较小,分别为7.72%、14.24%、21.30%,当这3种换热管以管束布置时,较优的管间床层厚度分别为4.86、6.09、6.38 mm;此外,增设换热管束可有效改善反应器内反应死区的储氢性能。在半径2.00 mm换热管束的反应器内,与未增设换热管束相比,在反应死区增设12根半径1.00 mm换热管后储氢时间减少了40.00%,为267 s,而换热管束体积分数仅增加了1.92%,储氢量仅减少2.17%。该研究成果可为固态储氢反应器的优化设计奠定基础,并为后续的工程应用提供指导。

矩形钢管混凝土束风机塔筒风振特性研究

随着风电资源优势区开发逐渐饱和,风电开发的重心开始向风资源条件相对恶劣的低风速地区转移,分布式、大功率、高塔筒和长叶片已经成为风电行业发展趋势。基于此提出了一种新型的矩形钢管混凝土束风机塔筒,该塔筒由矩形钢管混凝土束拼接而成,具有强度高、刚度大和耗能能力强的优点。为研究该塔筒结构的风振响应特性,选用Kaimal脉动风速功率谱,采用谐波合成法模拟风荷载时程曲线,对其进行了动力时程分析,并计算了风振系数及等效静力风荷载。结果表明:该新型塔筒在额定风速下位移塔顶位移最大值为911.84 mm,对应的水平位移角为1/154,符合规范要求。塔筒各构件的强度较好,且具有较大的安全富余度。基于位移等效的阵风荷载因子法计算得到的风振系数值较低;在惯性风荷载法计算得到的等效静力风荷载作用下,结构位移、基底剪力与结构随机振动分析得到的基本一致。

连续重整装置再接触空冷器管束泄漏分析

以某炼化企业连续重整装置再接触空冷器为研究对象,通过实际分析和模拟计算,对连续重整装置再接触空冷器管束泄漏原因进行分析并提出腐蚀防护措施。结果表明:连续重整装置再接触空冷器中的NH_(4)Cl结晶温度为80~100℃,处于再接触空冷器出入口温度区间内,NH_(4)Cl在再接触空冷器中间及出口部位会结晶沉积于管束内壁,停工期间会发生吸水潮解腐蚀。因此,停工期间可通过碳酸氢钠水溶液水洗、再接触空冷器管束充氮气保护等措施来防止产生NH_(4)Cl垢下腐蚀,同时还需对再接触空冷器管束进行打压,确保管束无泄漏。