氟塑料列管换热器的传热系数

由于氟塑料与金属材料在物化性质上差异很大,使得氟塑料换热器的传热系数计算不同于金属换热器。本文通过一设计计算实例叙述了氟塑料列管换热器传热系数的计算过程,介绍了通过用传热因于求得传热膜系数的设计想法,分析了影响氟塑料换热器传热系数的因素,并对如何提高传热系数提出了解决方法。     

基于氟塑料换热器的锅炉余热回收影响研究

采用氟塑料设计了一种U型管换热器结构,通过有限元方法计算了氟塑料换热器换热性能,分析了冷媒水流速对换热器性能的影响。实验结果表明:换热器的等效传热系数可以达到40.168 W/(m~2·K)。冷媒水在内管出口的温度比入口处的温度上升了9.045℃,吸收了烟气中的锅炉余热。烟气在外管出口的温度比入口处的温度下降了6.97℃,余热得以散失。此外,氟塑料换热器的冷媒水压降、烟气压降、烟气降低温度和等效传热系数都会随着冷媒水流速的增大而增大,因而氟塑料换热器的性能随着冷媒水的流速增大而提高。     

F_(-46)列管式稀酸冷却器若干问题探讨

随着化学工业的迅速发展,对强腐蚀介质的热交换设备提出越来越高的要求。具有很好的化学稳定性、低摩擦系数的氟塑料对制造、使用耐腐蚀性能良好的热交换器则开辟了一条新的途径。氟塑料热交换器的总传热系数,目前基本都是按照金属换热器的传热系数计算进行;或将氟塑料热交换器投入使用后,再进行现场实     

氟塑料换热器的研究及应用进展

从氟塑料换热器在强腐蚀工作环境中运行,相比于金属换热器具有耐腐蚀、抗积灰结垢、传热系数大的优势出发,详细阐述了氟塑料换热器在国内外的研究进展及工程应用。其在电厂锅炉余热利用及烟气余热利用领域应用广泛,并发现PFA与PTFE相比,除有更好的热塑性和力学性能外,其他性质相似,对PFA耐腐蚀换热器今后的研究与应用进行了展望。     

氟塑料换热器的研究及应用进展

从氟塑料换热器在强腐蚀工作环境中运行,相比于金属换热器具有耐腐蚀、抗积灰结垢、传热系数大的优势出发,详细阐述了氟塑料换热器在国内外的研究进展及工程应用。其在电厂锅炉余热利用及烟气余热利用领域应用广泛,并发现PFA与PTFE相比,除有更好的热塑性和力学性能外,其他性质相似,对PFA耐腐蚀换热器今后的研究与应用进行了展望。     

氟塑料换热器在低温气水换热领域的应用

氟塑料换热器具有耐腐蚀、耐高温、耐老化、不粘灰、不结垢、重量轻、传热系数高等特点,在低温烟气换热中,比传统金属换热器更有优势。氟塑料换热器结构采用大量小直径、薄壁的氟塑料柔性软管密集排列的方式制作而成,换热管采用U型布置,换热器垂直悬挂安装,模块化布置,可实现单独隔离,方便检修。分析了管径对换热器安全性及水侧阻力的影响。目前,氟塑料换热器已在低温烟气余热回收、烟气冷凝、MGGH系统上得到了大量应用,随着材料改性技术的进一步提高及环保政策的推进,氟塑料换热器成本将大幅降低,其将在电力、钢铁、煤化工等行业得到更广泛的应用。     

氟塑料换热器可以推广使用

锦西化工厂试制的氟塑料换热器(F-46换热器),通过技术鉴定,认为可在工业生产中推广使用。氟塑料换热器是用国产聚全氟乙丙烯树脂制成的。其主要特点是:换热管和花板都用氟塑料制造。它与金属换热器比较,具有耐腐蚀、不结垢、体积小、重量轻、适应性强、传     

氟塑料换热器的研制(三)

本刊在1975年2期刊载了郑州工学院《氟塑料换热器的研制(一)》,在1977年第1期又刊载了《氟塑料换热器的研制(二)》,在以上两篇文章中,已介绍了氟塑料换热器的意义、特点和研制工作,本文介绍它的研制小结及试用等情况。     

用于低温余热回收系统热管换热器传热性能的数值模拟

采用CFX软件Fluent模拟了用于低温余热回收的重力热管内的相变情况及充液率、热管长度比、管中心距对热管换热器传热性能的影响。模拟结果显示,水量一定时,加热段与冷凝段长度相同的热管在不同充液率条件下的传热特性,高充液率的传热能力优于低充液率的传热能力,适宜的充液率为60%~70%。当充液率一定时,加热段的长度小于冷凝段的长度有利于热管传热。当充液率及管长一定时,热管换热器的传热系数随管中心距的增大而减小。将热管换热器数值模拟的总传热系数与理论计算的结果进行对比,实现了特定体系热管换热器的结构优化。     

传热系数取决于管程的流量

<正> 众所周知,在管壳式换热器中热传递取决于总传热系数和管内的质量流量。但是,人们通常不知道总传热系数和管内质量流量两者的相互关系及它们影响工艺流体出口温度的准确程度。 在下面三个例子中,我们从选定的管壳式换热器开始,分析流量如何影响工艺流体的出口温度。每当流量减少,一个新的总传热系数被计算出来。根据这个新的总传热系数和变化的流量从下面能量平衡式计算出一个新的出口温度:     

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.     

Thermal model validation of plate heat exchangers with generalized configurations

Thermal models of plate heat exchangers rely on correlations for the evaluation of the convective heat transfer coefficients inside the channels. It is usual to configure the exchanger with one countercurrent single-pass arrangement for acquiring heat transfer experimental data. This type of configuration approaches the ideal case of pure countercurrent flow conditions, and therefore a simplified mathematical model can be used for parameter estimation. However, it is known that the results of parameter estimation depend on the selected exchanger configuration because the effects of flow maldistribution inside its channels are incorporated into the heat transfer coefficients. This work presents a parameter estimation procedure for plate heat exchangers that handles experimental data from multiple configurations. The procedure is tested with an Armfield FT-43 heat exchanger with flat plates and the parameter estimation results are compared to those obtained from the usual method of single-pass arrangements. It can be observed that the heat transfer correlations obtained for plate heat exchangers are intimately associated with the configuration(s) experimentally tested and the corresponding flow distribution pattern(s).     

单螺旋和双螺旋折流板换热器性能的研究

为了研究双螺旋结构对螺旋折流板换热器性能的影响及其与单螺旋结构的比较,利用热态试验和数值模拟方法,研究了四分之一扇形和三分之一扇形螺旋折流板换热器单、双螺旋结构的壳程传热和阻力性能.热态试验结果表明,单、双螺旋结构的壳程传热系数和压力损失均随流量的增大而提高.在相同流量下,双螺旋结构的壳程传热系数高于单螺旋结构,同时其壳程压力损失也有所增大.但随着流量的增加,双螺旋结构对应的单位压降下的传热性能与单螺旋基本一致.这说明双螺旋结构可以提高壳程传热性能,同时不会影响换热器的综合性能.因此在流体输送动力允许的条件下,双螺旋结构有利于设备处理能力的提高.数值模拟结果表明,由于折流板数量是单螺旋结构的两倍,因此双螺旋结构对壳程流体具有更强的导流作用,流体的分布更加均匀,且呈现出更加强烈的旋转运动.     

交错螺旋折流板管壳式换热器壳侧传热与阻力性能

对交错搭接螺旋折流板换热器壳侧的流动与传热性能进行了实验研究,着重研究了内插假管及不同螺旋角度对壳程传热和阻力的影响,并与传统弓形折流板换热器进行了对比.结果表明,假管的存在反而使传热综合性能下降,同时,在相同的壳侧流量下,螺旋折流板换热器的壳程阻力和壳侧传热系数均随螺旋角的增大而减少,且小于同样条件下弓形折流板换热器的相应值.与弓形折流板换热器相比,螺旋折流板换热器的特点是单位压降下的壳侧传热系数高.     

扭曲椭圆管换热的壳程强化传热特性

通过搭建扭曲椭圆管换热器壳程传热与压降性能测试平台,对扭曲椭圆管换热器壳程传热与压降性能进行了实验测试,以实验数据为基础对前人得到的壳程传热与压降性能计算准则关系式的应用范围进行了分析,同时拟合得到了测试用扭曲椭圆管换热器壳程传热与压降性能计算准则关系式,设计了与测试扭曲椭圆管换热器结构类似的折流板换热器以及折流杆换热器,采用相关计算方法对换热器的传热与压降性能进行了计算和比较,并分析了3台换热器的综合性能,结果显示扭曲椭圆管换热器传热效果好、压降低,具有很好的工业应用前景。     

Design and optimization of heat exchangers with helical baffles

The hydrodynamics and heat transfer characteristics of a heat exchanger with single-helical baffles are studied experimentally as well as numerically. A heat exchanger with two-layer helical baffles is designed by using computational fluid dynamics (CFD) method. The comparisons of the performance of three heat exchangers with single-segment baffles, single-helical baffles and two-layer helical baffles, respectively, are presented in the paper. The experiment is carried out in counter-current flow pattern with hot oil in shell side and cold water in tube side. Overall heat transfer coefficients are calculated and heat transfer coefficients of shell side are determined by Wilson plots technique. It shows that the heat exchangers with helical baffles have higher heat transfer coefficient to the same pressure drop than that of the heat exchanger with segmental baffles based on the present numerical results, and the configuration of the two-layer helical baffles has better integrated performance than that of the single-helical baffles.     

Heizen und Kühlen –- verfahrenstechnische Aspekte

Heating and cooling-chemical engineering aspects. This paper reviews the commonest types of heat exchangers and their applications. They are classified in the following types: tube bundle heat exchangers, plate heat exchangers, spiral heat exchangers, lamella heat exchangers, and heat exchangers for special purposes. Most of these apparatus can be used for heat exchange between single phases or for condensation or boiling of substances. The different criteria determining the choice of heat exchanger are explained.     

制氢体系中催化燃烧换热器

催化燃烧换热器具有高效、经济和环境友好等特点。本文详细阐述了催化燃烧换热器在制氢体系中的重要意义,以及国内外对于催化燃烧换热器的研究现状。通过对制氢系统中不同结构的燃烧换热器的比较,指出了它们各自的优缺点。结合本实验室在75kW甲醇水蒸气重整制氢和5kW甲烷重整制氢体系开发过程中催化燃烧换热器的设计所涉及到的一些相关问题,指出现阶段对于催化燃烧换热器的研究还存在很大的欠缺。同时,指出开展催化燃烧换热器相关领域的研究在进一步优化制氢体系过程中的必要性。最后提出了研究的着眼点和解决问题的措施。     

Heat Exchanger Network synthesis with Detailed Heat Exchanger Design

Pressure drop and fouling are important issues in heat exchanger network synthesis, which are usually neglected. Heat exchangers were designed in detail during the heat exchanger network synthesis, and pressure drop and fouling effects were taken into account. Pinch analysis combined with exergoeconomic analysis was used for determining optimal minimum approach temperature (ΔT_min) for heat exchanger network synthesis. Exergy consumption of heat transfer in HENs was calculated using a subsection integral on balanced composite curves. The heat transfer coefficients of all heat exchangers in the network were calculated iteratively to meet the requirements of optimal area and allowable pressure drops. The proposed method was applied to an industrial case. Numerical results indicate the importance of the detailed design of heat exchangers in HENs synthesis.     

Dynamische Simulation von Wärmeübertragern

Simulation of the Dynamic Behaviour of Heat Exchangers . Four models for heat exchangers under transient conditions are presented. Three of them describe a single phase heat exchanger, and the forth one is used for the simulation of a condenser. All models are of intermediate complexity and valid for simulation of both single heat exchangers and chemical processes. They use distributed variables and incorporate the calculation of local heat transfer coefficients so that temperature profiles over the apparatus can be determined in addition to the transient behaviour of the outlet variables.