分体管壳式余热锅炉内摩擦及局部压降

通过搭建可视化分体管壳式余热锅炉实验平台,对其下部管壳内汽液两相横向冲刷水平管束时摩擦及局部压降的计算进行了研究。在测量竖直上升管内截面含汽率时,将粒子图像测速(PIV)技术与传统压差法相结合,针对上升管中出现的泡状流型,给出了计算截面含汽率的新方法;在竖直上升管内定义了一种泡状-段塞流的新流型,并分析得出将质量含汽率x=10?4作为区分泡状流与泡状-段塞流的边界。根据汽液两相横向冲刷管束时摩擦压降与局部压降类似的产生规律,将两者作为整体分析,通过借鉴Chisholm计算方法对实验数据进行处理,重点对汽液两相横向冲刷管束时摩擦及局部压降的计算进行研究,得到了可用于计算摩擦及局部压降的关联式。对所得实验数据验证计算后发现,误差在±20%以内,能够较好地满足工程计算需要。     

分体管壳式余热锅炉内摩擦及局部压降

通过搭建可视化分体管壳式余热锅炉实验平台,对其下部管壳内汽液两相横向冲刷水平管束时摩擦及局部压降的计算进行了研究。在测量竖直上升管内截面含汽率时,将粒子图像测速（PIV）技术与传统压差法相结合,针对上升管中出现的泡状流型,给出了计算截面含汽率的新方法;在竖直上升管内定义了一种泡状-段塞流的新流型,并分析得出将质量含汽率x=10^-4作为区分泡状流与泡状-段塞流的边界。根据汽液两相横向冲刷管束时摩擦压降与局部压降类似的产生规律,将两者作为整体分析,通过借鉴Chisholm计算方法对实验数据进行处理,重点对汽液两相横向冲刷管束时摩擦及局部压降的计算进行研究,得到了可用于计算摩擦及局部压降的关联式。对所得实验数据验证计算后发现,误差在±20%以内,能够较好地满足工程计算需要。     

管壳式换热器管束流致振动实例分析

阐述管壳式换热器管束流致振动的机理,基于HTRI软件的Xist和Xvib模块,进行管壳式换热器管束流致振动实例的分析与研究,并比较了HTRI-Xist与HTRI-Xvib分析方法的优缺点及适应性。     

纵流式管束支撑物的结构及性能对比

纵流式管束支撑物使管壳式换热器壳程流体呈纵向流动，因而该类换热器具有传热效率高、压降小，有效消除了流体诱导振动等特点。本文阐述了纵流管束支撑物的结构变化对换热器综合性能的影响，为改进和优化管壳式换热器提供参考。     

管壳式换热器壳程传热强化研究进展

对比分析了管壳式换热器壳程传热强化的主要方式和壳程管束支撑结构的研究进展。大多数管壳式换热器壳程强化结构兼具管束支撑的功能,主要以不同形式的折流杆、整圆形孔板、空心环、管束自支撑和螺旋折流板等代替传统的弓形折流档板,结构的优化提高了换热器壳程传热系数,且有效降低了壳程的流动阻力,缓减了换热器壳侧管束的振动和结垢,从而提高了换热器的传热性能。     

浅谈管壳式换热器的振动及预防措施

对管壳式换热器在换热过程中管束振动的原因进行分析,并阐述了相应观点,文中对如何防止管壳式换热器管束振动提出了一些切实和具体的解决方法。预防振动对换热器设计者来说值得共同探讨。     

换热器的振动与折流

介绍了折流板式换热器与折流杆式管壳式换热器的区别,折流杆式换热器在介质流动速度大及振动工况下的应用,并根据设计实例介绍了折流杆式换热器的管束结构。     

钢制管壳式换热器管束失效原因浅析

针对钢制管壳式换热器管束的失效原因.着重从腐蚀、热膨胀和收缩、结垢、冲刷及磨损、堵 塞、内漏、振动等几方面进行分析探讨.并提出相应对策。     

管壳式换热器强化传热技术的研究与进展

综述了管壳式换热器壳程内管束支撑结构的发展概况,管束支撑由传统的弓形折流板到各种形式的折流杆、整圆形孔板、空心环、管束自支撑和螺旋折流板等,不但提高了换热器的整体传热性能,同时还大大降低了壳程流动阻力。     

液相物性对壳侧不互溶双组分两相流流型的影响及通用流型图

在用空气-水,空气-0~＃柴油研究的基础上,用空气与质量浓度为30%的甘油水溶液研究了理想管壳式换热器壳侧两相流型,以期进一步考察液相物性对壳侧两相流动流型的影响。研究表明,液相物性对某些流型的转变有明显影响,而对另外一些流型转变的影响并不明显,提出了考虑液相物性影响的通用流型图。     

Experimental investigation of heat transfer in shell- and- tube heat exchangers without baffles

The influences of geometrical parameters on the shell side heat transfer in shell-and-tube heat exchangers are investigated by experiments using 32 different test heat exchangers. The test heat exchangers differ by number of tubes, length, shell and tube diameter, nozzle diameter and tube pitch. From the experimental results it can be confirmed that the influence of the tube pitch is small enough to be neglected in shell-and-tube heat exchangers used in real processes. The heat transfer rate of the longitudinal flow can be calculated from the correlation for turbulent flow in concentric annular ducts by inserting the porosity instead of the ratio of tube to shell diameter. The influence of the cross flow in the nozzle region increases with decreasing length of the heat exchangers. The heat transfer coefficients in the nozzle region are determined by comparing the overall heat transfer coefficients of the heat exchangers with that calculated from the correlation for the longitudinal flow. The results show that the heat transfer coefficient in the nozzle region is 40 % greater than that in the parallel region, if the length of the apparatuses is about 30 times the hydraulic diameter. A new correlation suitable for predicting the heat transfer coefficient is presented, which consists of a superposition of the Nusselt number for the flow in the nozzle region and that for the longitudinal flow.     

管壳式换热器流体流动与耦合传热的数值模拟

结合化工行业中使用的某型号管壳式换热器的结构图和工艺参数,对换热器的结构进行了合理的简化,利用ANSYS参数化建模方法建立了管壳式换热器的参数化模型。在ANSYS FLUENT14.0数值模拟软件中对换热器的流体流动以及耦合传热进行了数值模拟,得到管程和壳程流体的流速分布、压降情况、温度场变化的细节信息。该工作对于设计传热效率高、流体阻力小的换热器进行了有益探索。     

釜式再沸器循环流动计算模型评述

对釜式再沸器壳侧循环流动进行了理论分析，对计算模型进行了评述，阐述了确定循环流率的方法，比较了计算横掠管束两相流压降及空泡份额的几种算法     

扭曲三叶管传热与流阻性能的数值研究

扭曲管换热器是一种新型高效换热器。在扭曲管强化传热机理研究的基础上,提出了一种新的扭曲管管型--三叶管。验证了标准k-ω湍流模型在圆管及扭曲椭圆管计算中的精确度,并采用该湍流模型对扭曲三叶管Re在4000～20000范围内的传热和流阻性能进行了研究。计算结果表明,扭曲三叶管的Nusselt数比扭曲椭圆管大,虽然压差增大较多但综合传热性能比扭曲椭圆管高。这是由于扭曲三叶管特殊的三叶区结构以及过渡区曲率的变化,使得三叶管内的螺旋流动比椭圆管更为复杂,速度场与温度梯度场的协同程度更好。随着Reynolds数的增大扭曲三叶管的压差及Nusselt数都逐渐增大,但综合性能逐渐降低,在低Reynolds数下扭曲三叶管的强化传热效果较为明显。内切圆直径及过渡圆弧直径越小,扭曲三叶管的综合性能越好,其中内切圆直径的影响更为显著。     

三维翅片管外螺旋流动传热强化

流体在螺旋隔板换热器的壳程类似于塞状流流动,几乎没有返混和流动死区.在相同压降下,其传热系数比普通的弓形隔板换热器高得多.以润滑油作为实验介质,研究了润滑油在螺旋隔板单管换热器的壳程传热和压降性能,并与光滑管进行了性能对比.采用Wilson图解法分别分离出了螺旋隔板花瓣管和光滑管单管换热器的管程传热系数,并计算出各自的壳程传热系数,壳程传热系数相对误差为±3％.实验结果表明,在相同Reynolds数下,螺旋隔板花瓣管单管换热器的Nusselt数和压降Δp分别是螺旋隔板光滑管单管换热器的2～2.7倍和1.3～1.4倍.与螺旋隔板光滑管单管换热器相比,螺旋隔板花瓣管单管换热器的传热性能的提高远高于压降的提高,证明在螺旋流条件下,花瓣管具有很好的传热强化性能.     

Effect of reynolds and prandtl number on the frequency response of concentric tube heat exchangers

An analytical and experimental investigation was made of the frequency response of both the shell and tube fluid outlet temperatures of a six foot concentric tube exchanger to disturbances in either flow rate. The fluid Reynolds and Prandtl numbers were varied from 4,000 to 20,000 and 3 to 40 respectively. The effect of increasing either the tube fluid Reynolds or Prandtl number, for both shell and tube flow disturbances, was to increase the attenuation and phase shift of the tube outlet temperature and decrease it for the shell outlet temperature. The “resonance effect”, was observed experimentally.     

小尺度管壳式换热器流场的数值分析

针对小尺度管壳式换热器的管间距选取问题,建立三维模型,基于Simple算法,采用SST k-ω湍流模型,结合有限体积法对控制方程进行离散,在管径d不变的情况下,分别针对管间距a=1.2d,a=1.4d和a=2.0d 3种不同的管间距工况对壳侧流场的分布及阻力变化进行了研究。由于管路附近的速度梯度较大,为了提高计算的精度,进行局部的网格细化,最终对比了不同模型的流场模拟效果。结果表明:阻力和湍流强度随着管间距的增大而减小,应按照压降的减小比例小于平均湍流强度的减小比例为原则来选取a的值。对于这种小尺度的流场模拟,采取实验的方法将受到极大的限制,通过大型商用流体仿真软件来模拟计算,为工程实际设计提供参考的依据。     

Rayleigh–Benard convection in vertical shell and tube heat exchangers

Large scale recirculation due to unwanted free convection currents of the fluids in a vertical countercurrent shell-and-tube heat exchanger in industry obviously was the reason of severe reductions in heat transfer performance by up to 40% against the design expectations. The apparatus was operated with the cold end on top. Applying a simple one dimensional calculation of flow and heat ransfer, with backflow of the tube side fluid in some of the tubes, shows that the reductions predicted from the model are not too far from the observed ones. In comparing experimental plant data to the predictions of the model, it became obvious, that the influence of free convection on the shell side heat transfer needs to be taken into account additionally to fully explain the experimental observations. An effective remedy, as earlier suggessted is to change flow directions in shell and tubes, i.e. to operate the heat exchanger with the hot side on top. In case of the industrial heat exchanger presented in the paper, the change of flow directions in shell and tube side has been carried out in the meantime. This change actually solved the problem, and resulted in the designed performance with efficiencies around 95%.     

Transient behaviour of shell and tube heat exchangers

Based on the dispersion model rather than on the conventional pluf-flow model, a method of predicting the transient behaviour of parallel and counterflow heat exchangers is developed, whereby the effects of shell-side flow maldistribution and the finite heat capacities of both fluids, tube bundle and shell are considered. The final solution has been obtained by numerical inversion of the Laplace transform, to determine the transient responses to arbitrary inlet temperature variations. The experiment was carried out in a one pass tube heat exchanger. The comparison between therotical and experimental results is presented and the feasibility of this method is discussed.