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.

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 study of shell side flow-induced vibration of conical spiral tube bundle

Conical spiral tube bundles are widely used in enhancing the heat transfer via the flow-induced vibration in heat exchangers. The shell side flow-induced vibration of the conical spiral tube bundle is experimentally investigated in this paper. The experi- ment table was built and the operational modes, the vibration parameters of the tube bundle were analyzed. The results show that, the operational mode frequencies of the conical spiral tube are decreased as the shell-side fluid flow velocity increases, especially for the first order frequency. Within the parameter range of this experiment, the real working frequency of the conical spiral tube is between the 1 st and the 2nd operational modes, and the free end vibration amplitude of the tube bundle increases greatly when the shell side fluid flow velocity exceeds a critical value.

MATHEMATICAL ANALYSIS OF TRANSVERSE VIBRATION OF CONICAL SPIRAL TUBE BUNDLE WITH EXTERNAL FLUID FLOW

The conical spiral tube bundle is a new type of heat transfer elements used to enhance heat transfer through flow-induced vibration. The effect of the external fluid flow on the transverse vibration of the conical spiral tube bundle is investigated with a mathematical method proposed in this article. Firstly, the natural vibration of the tube bundle is obtained by the hammering excitation method and the mode shapes of the transverse vibration are discussed. Then the effect of the external fluid flow on the transverse vibration of tube bundle is analyzed by a combination of experimental data, empirical correlations and FEM. The results show that in the frequency range from 0 Hz to 50 Hz, there exist six transverse vibrations. The external fluid flow has a significant effect on the frequency of the tube＇s transverse vibration, which are decreased by about 18% to 24% when the external fluid flow speed is 0.3 m/s.

折流板对锥形螺旋管束壳程传热性能的影响

以锥形螺旋弹性管束(conical spiral elastic tube bundle,CSETB)换热器为研究对象,通过在换热器内增设脉动/引流折流板,以期获得具有更高传热性能的弹性管束换热设备。通过采用双向流固耦合计算方法,研究了不同壳程入口流速和不同结构方案下CSETB换热器的振动强化传热性能。研究表明,CSETB的振幅随流速的增加而增加,仅增设脉动折流板可使CSETB表现为相对大幅高频振动,同时增设脉动、引流折流板可使CSETB表现为相对大幅低频振动。增设折流板可使流体流动的规律性和温度场分布的层次性增强,且能使换热器的壳程传热能力获得大幅提高。振动能够实现强化传热,这种强化传热的程度在高流速时更明显,且增设折流板能明显提高CSETB的振动强化传热性能。此外,引流折流板的存在使换热器的综合传热性能降低。

空间锥螺旋管束流体诱导振动换热器及性能分析

基于动态子结构理论、利用固定界面模态坐标变换及超单元技术,分析了空间锥螺旋管束的振动特性和脉动元件诱发管束振动的频率条件,计算了0.1m/s壳程流速、横向脉动流激励条件下空间螺旋管束的振动特性,研究了空间锥螺旋管束管内二次流及其换热特性.结果表明:单排空间锥螺旋管束的振动分为横向和纵向振动,以纵向振动为主;在横向脉动流激励作用下,管束的振动与其横向固有振型近似,空间锥螺旋管束的低阶模态频率较低,易于诱发振动;管内截面二次流分为4个涡区,强烈的管内二次流致使管束换热性能提高,空间锥螺旋管束单位面积的换热量是传统平面管束的1.4倍以上.

铅铋流体作用下螺旋管束的流致振动机理研究

流体外掠螺旋管束引起的流致振动在工程实际中广泛存在,传统研究的流体介质多为水和空气,而近年来铅铋流体正逐渐成为一种新兴的热交换介质。针对铅铋流体作用下的单排螺旋管束流致振动问题,利用计算流体动力学方法和有限元方法,对单排螺旋管束流致振动进行了数值建模与仿真计算,揭示了不同来流速度下管束的流致振动机理。结果表明:铅铋流体作用下单排管束周围会产生漩涡脱落,其频率随着来流速度的升高逐渐增大;管束各管道之间的漩涡脱落存在干涉现象,中间管道的振动响应以漩涡脱落频率的二倍频振动为主,而两侧管道的振动响应主要频率分量为漩涡脱落频率,且伴随有倍频振动响应出现;随着来流速度升高,管道之间的流动干涉对管道振动的倍频振动响应影响逐渐减弱;当铅铋来流速度超过一定值后,管道振幅突然增大,管道发生流弹失稳现象。

管内流体诱导锥螺旋弹性管束振动分析

弹性管束换热器通过流体诱导弹性管束振动实现强化换热。弹性管束设计时,需兼顾强化换热和疲劳寿命。对管内流体诱导锥螺旋弹性管束的振动响应进行了研究。通过ANSYS CFX软件仿真分析了锥螺旋弹性管束的固有模态和管内流体流速对弹性管束振幅的影响,并搭建管内流体诱导锥螺旋弹性管束振动试验台。利用加速度传感器,测试了锥螺旋弹性管束监测点的振动加速度信号,对其进行快速傅里叶变换并分析了锥螺旋弹性管束的振动位移响应特性,将数值分析结果与试验值进行了对比分析,验证了数值分析结果的正确性。分析结果表明:锥螺旋弹性管束的振动形式主要表现为纵向振动;管内流体在0.05~0.6 m/s流速范围内,随着流速的增加,管束的振动主频保持不变;振幅随流速增加而增大且振幅增加值逐渐减小。该研究结果为锥螺旋弹性管束的设计提供了依据。

管程流体诱导锥螺旋管束振动的实验研究

为了研究换热器内锥螺旋管束在管程流体诱导下的振动特性,搭建了管束振动测试实验台,在管程流速为0.106~0.446 m/s的范围内,利用加速度传感器实测了管束的振动加速度,分析了管束的振动加速度频谱图和振动位移幅值的变化。实验结果表明:在管程流体的作用下,流速为0.106~0.361 m/s时各排管束的振动主频不变,流速继续增大时主频改变;管束振动主频的加速度幅值随流速增加整体上呈现先增大后减小的趋势;管程流体对顶排管束振动的影响最大,自上而下对管束的激励作用逐渐减小。

空间螺旋式弹性传热管束模态与应力特性分析

弹性管束换热器利用流体诱导振动实现强化传热,弹性管束的结构优化、模态及应力特性等对弹性管束的使用寿命具有重要影响。基于此,提出一种新型空间螺旋式弹性传热元件,通过ANSYS有限元模拟技术,分析了空间螺旋管束的固有模态特性以及在一定振幅条件下管束的应力分布特性,并与现有的平面弹性管束进行比较。结果表明,在相同尺寸下,空间螺旋式弹性管束固有频率较低,以纵向振动为主;管束的应力分布均匀,最大应力发生在管程流体进出口固定端,其最大应力仅为平面弹性管束的1/4左右。

两类弹性传热管束管内流固耦合振动特性研究

弹性传热元件是由多根弯曲管束组成,通过连接体胀接后悬臂支撑,由于结构复杂,难以直接求解其管内流固耦合振动方程。建立了平面弹性管束和空间螺旋管束2类弹性管束的振动状态方程,对比分析了管内流速对2类弹性管束振动特性的影响。在相同的管内流动条件下,空间螺旋管束的频率较低,其振动失稳的临界流速比平面弹性管束的小,但远大于弹性管束换热器在石化工程中的实际管程流速,保证了设备运行的可靠性。

锥螺旋弹性管束及其振动控制的研究

管束振动的诱导与控制是弹性管束换热器在一定疲劳寿命前提下实现强化换热的重要保证。设计锥螺旋弹性管束和脉动流发生装置并对考虑流固耦合情况下锥螺旋管束的固有模态进行研究;通过谐响应分析,得到锥螺旋管束的频率响应;通过仿真分析脉动流发生装置中绕流体纵向尺寸对各分支管脉动流的影响,确定了工况流速下的绕流体纵向尺寸。结果表明:锥螺旋管束在流固耦合作用下固有频率有所下降;在相同入口流速条件下,随着绕流体纵向尺寸增大,脉动流发生装置同一分支管脉动流强度先增大后减小,而其频率先减小后增大。研究工作对锥螺旋弹性管束换热器设计具有重要意义。

基于不同截面形状的螺旋弹性管束换热器传热特性分析

为探究截面形状对螺旋弹性管束(spiral elastic tube bundle,SETB)换热器传热性能的影响,基于四种截面形状(四边形、六边形、椭圆形和圆形),采用双向流固耦合计算方法,对单层四螺旋弹性管束在不同入口速度条件下的振动和传热特性进行了研究。结果表明:不同截面形状的螺旋弹性管束在换热器内不同安装位置的振动响应有明显的不同。截面为椭圆形的螺旋弹性管束在振动和不振动条件下的传热系数最高,管束圆周上的局部传热系数最大,说明管束截面形状为椭圆时的传热性能最佳。振动能够实现强化传热,但振动剧烈的螺旋弹性管束其传热性能并不一定最佳,在进行螺旋弹性管束换热器设计时,并不是要一味追求高强度的振动,还要综合考虑螺旋弹性管束的安装位置和截面形状。

换热器内锥螺旋弹性管束振动强化传热研究

为分析换热器内锥螺旋弹性管束的流致振动强化换热情况,采用双向流固耦合的数值方法,分别研究入口流速和管排间距对其在壳程流体诱导下的振动响应及传热特性的影响。结果表明当入口流速由0.5m/s增大到0.9m/s,锥螺旋弹性管束的振动强度明显提高,管束的传热性能提高,流致振动使得管束的传热性能分别提高了5.2%、4.3%和3.5%,管束流致振动强化传热性能增强。随着管排间距从30mm增加到40mm,锥螺旋弹性管束的振动强度增大,流致振动使得管束的传热性能分别提高了2.5%、4.9%和3.1%,且管排间距为35mm时锥螺旋弹性管束的传热性能最佳,管束流致振动强化传热性能也最佳。