Experimental Analysis of Performance of Heat Exchanger with Plate Fins and Parallel Flow of Working Fluids

Heat exchangers are devices in which heat is transferred from one fluid to another fluid as a result of temperature difference. Heat exchanger presented in the current paper in which inside the tubes flows water, but outside the tubes flows air aims to enable cooling of circulating water, which serves to cool the engine of a machine. Such exchangers find application in the automotive industry as well as heating and cooling equipment and HVAC systems etc. The surface of the heat exchanger by the air side always tends to be much larger using surface fins in order to facilitate equalization of thermal resistance for both sides of the heat exchanger, because the rate of transmission of heat from the water side is much greater. Furthermore, the paper will present analytical and experimental studies involved for determination of performance of plate-fin heat exchanger for various flows of working fluids in order to get the highest values of performances i.e.: overall heat transfer coefficient U, efficiency of heat exchanger ε, maximal and real heat transferred, pressure drop, air velocity and Reynolds number from the air side of heat exchanger etc. The present scientific paper is based on the fact that from the experimental model made for laboratory conditions, conclusions are derived that can be used during installation of such heat exchanger on certain machines in order to predict their performance.

NUMERICAL STUDY ON FLOW DISTRIBUTION IN PLATE-FIN HEAT EXCHANGERS

Objective To investigate the flow distribution in plate fin heat exchangers and optimize the design of header configuration for plate fin heat exchangers. Methods A mathematical model of header was proposed. The effects of the header configuration on the flow distribution in plate fin heat exchangers were investigated by CFD. The second header configuration with a two stage distributing structure was brought forward to improve the performance of flow distribution. Results It is found that the flow maldistribution is very serious in the direction of header length for the conventional header used in industry. The numerical predictions indicate that the improved header configurations can effectively improve the performance of flow distribution in plate fin heat exchangers. Conclusion The numerical simulation confirms that CFD should be a suitable tool for predicting the flow distribution. The method has a wide variety of applications in the design of plate fin heat exchangers.

Optimal design of the first stage of the platefin heat exchanger for the EAST cryogenic system

The size of the heat exchanger is an important factor determining the dimensions of the cold box in helium cryogenic systems. In this paper, a counter-flow multi-stream plate-fin heat exchanger is optimized by means of a spatial interpolation method coupled with a hybrid genetic algorithm.Compared with empirical correlations, this spatial interpolation algorithm based on a kriging model can be adopted to more precisely predict the Colburn heat transfer factors and Fanning friction factors of offset-strip fins. Moreover, strict computational fluid dynamics simulations can be carried out to predict the heat transfer and friction performance in the absence of reliable experimental data. Within the constraints of heat exchange requirements, maximum allowable pressure drop, existing manufacturing techniques and structural strength, a mathematical model of an optimized design with discrete and continuous variables based on a hybrid genetic algorithm is established in order to minimize the volume. The results show that for the first-stage heat exchanger in the EAST refrigerator, the structural size could be decreased from the original2.200？×？0.600？×？0.627（m^3） to the optimized 1.854？×？0.420？×？0.340（m3）, with a large reduction in volume. The current work demonstrates that the proposed method could be a useful tool to achieve optimization in an actual engineering project during the practical design process.

Performance Evaluation Methods for Multi-stream Plate-Fin Heat Exchanger

Mathematical model of cross type multi-stream plate-fin heat exchanger is established.Meanwhile,mean square error of accumulative heat load is normalized by dimensionless,and the equations of temperature-difference uniformity factor are improved.Evaluation factors above and performance of heat exchanger are compared and analyzed by taking aircraft three-stream condenser as an example.The results demonstrate that the mean square error of accumulative heat load is common result of total heat load and excess heat load between passages.So it can be influenced by passage arrangement,flow inlet parameters as well as flow patterns.Dimensionless parameter of mean square error of accumulative heat load can reflect the influence of passage arrangement to heat exchange performance and will not change dramatically with the variation of flow inlet parameters and flow patterns.Temperature-difference uniformity factor is influenced by passage arrangement and flow patterns.It remains basically unchanged under a certain range of flow inlet parameters.

Experimental Study on Heat Transfer and Pressure Drop Characteristics of Four Types of Plate Fin－and－TUbe Heat Exchanger Surfaces

In this paper, air side heat transfer and pressure drop characteristics of twelve three-row plate finandtube heat exchanger cores of four types of fin configurations have been experimentally investigated.The heat transfer and friction factor correlations for'the twelve cores are provided in a wide range ofReynolds number. It is found that in the range of Reynolds number tested, the Nusselt number of theslotted fin surface is the largest and that of the plain plate fin is the lowest while the Nusselt numbersof two types of wavy fins are somewhere in between.

Enhancing Heat Transfer and Energy Storage Performance of Shell-and-Tube Latent Heat Thermal Energy Storage Unit with Unequal-Length Fins

Previous studies in literatures adequately emphasized that inserting fins into phase change material is among the most promising techniques to augment thermal performance of shell-and-tube latent heat thermal energy storage unit.In this study,the novel unequal-length fins are designed from the perspective of synergistic benefits of heat transfer and energy storage performance,and the effects of arrangement,number and total length of unequal-length fins are numerically investigated.Results show that utilization of fins with ascending length,when short and long fins are located in the inlet and outlet of heat transfer fluid respectively,can further promote the heat transfer and energy storage performance compared with equal length fins,and a maximum 6.17%and 0.43%increment of heat transfer performance and stored energy is achieved in full melting time,respectively.The number of unequal-length fins plays a major role in the energy storage,and 18.95%and 0.91%improvement of heat transfer performance and stored energy is realized when equipped with 2 unequal-length fins.A 21.17%improvement of the heat transfer performance is obtained when the total length of unequal-length fins is 18 mm.The present study is helpful to make further efforts to enhance heat transfer and energy storage of shell-and-tube latent heat thermal energy storage unit with unequal-length fins.

保温时间对钛合金板翅式换热器真空钎焊过程温度场及残余应力的影响

钛合金板翅式换热器成品率较低、残余应力较大,该文针对钛合金板翅结构真空钎焊过程开展热-固耦合建模与仿真研究,阐述了钎焊过程温度均匀性及残余应力分布特征,探明保温时间对钛合金板翅式换热器真空钎焊过程温度场及残余应力的影响机理.结果表明,板翅结构两侧温度较高,中部温度较低,延长保温时间可有效改善板翅结构的温度均匀性.残余应力均主要集中于翅片上表面与隔板背侧中部,在钎缝及夹持点处存在明显的应力集中现象,保温时间越长翅片钎缝的残余应力越小.模拟得到钛合金板翅式换热器真空钎焊中残余应力与试验结果相吻合,相对误差为5.3%,验证了该模型的准确性.

基于响应面法的矿用翅片管空冷器参数优化

矿用空冷器是矿井降温系统常用的末端设备,优化矿用空冷器换热性能对提升矿井降温系统能效具有重要意义。采用Fluent建立了平直翅片管矿用空冷器模型,研究了翅片间距、翅片厚度、横向管间距和纵向管间距对传热因子、阻力因子和综合性能评价指标的影响规律;采用Box-Behnken响应面法,分析了双参数协同作用下传热因子、阻力因子和综合性能评价指标变化规律。结果表明:随着翅片间距、横向管间距的减小,以及翅片厚度增加,传热因子、阻力因子和综合性能评价指标逐渐增加;综合性能评价指标则随纵向管间距的增加而先增加后降低;横向管间距、翅片厚度是影响空冷器传热及流动性能最显著的两个参数,而翅片间距、纵向管间距的影响最小;得到了平直翅片管矿用空冷器的最优参数,传热因子提升16.3%、阻力因子增加26.3%、综合性能评价指标提升8.3%。研究结果可为矿用翅片空冷器设计参数优化提供指导。

低阻叉流板式换热器传热性能与热阻靶向调控研究

用于烟气余热回收的板式换热器存在温度分布不均的问题。为改善烟气温度分布均匀性,有效遏制换热器腐蚀,本文通过实验测试对比碳钢与铸铁材质低阻叉流板式换热器性能差异,运用数值仿真预测局部流动传热特性并开展热阻分析,采用局部热阻调控方法设计了非均匀翅片结构。实验结果表明,在450℃高温时碳钢与铸铁材质的叉流板式换热器总传热系数分别达到32.5 W/(m^(2)·K)与25.1 W/(m^(2)·K)。通过数值仿真研究发现,叉流传热方式导致烟气侧沿程截面温度分布极不均匀,在热侧出口与冷侧入口交叉区、热侧出口与冷侧出口交叉区的热阻大,极易导致局部烟气温度低于露点温度。基于热阻分析法开发非均匀翅片结构,实施局部热阻靶向调控,最终实现维持阻力几乎不变情况下,使出口截面平均温度方差由6.9℃降至1.1℃,换热器内流体温度分布均匀性得到显著提升。

空调器冷凝器结构参数对其制冷剂积存量及系统性能的影响

在保持R290空调器系统性能的前提下,为降低冷凝器中制冷剂积存量,建立冷凝器性能综合评价模型,对冷凝器不同支路数流程的结构参数进行优化研究。结果表明:管径减小使得制冷剂积存量下降、COP下降;管间距和翅片厚度增大以及翅片间距减小均使得制冷剂积存量下降、COP升高;对冷凝器的制冷剂积存量和系统COP进行多目标优化,得到最优设计结构参数为四支路流程,管径5.74 mm,管间距19.67mm,翅片间距1.43mm,翅片厚度0.092mm。本研究可为R290房间空调器减少制冷剂充注量提供参考。

房间空调器小管径室外换热器流路优化

随着空调器的快速发展和国际铜价的持续升高,制冷空调行业采用的换热器在向着小体积、低成本发展的过程中往往面临着性能衰减的技术瓶颈。为突破此瓶颈,以一款冷暖型房间空调器翅片管式室外换热器为研究对象,将其换热管外径由7 mm减小至5 mm并在此基础上优化其流路,最终实现Φ5 mm换热器性能达到初始样机水平并有效降低换热器成本。首先,分别在5种标准工况下测试初始样机性能;然后,利用CoilDesigner软件来分析小管径化对换热器性能的影响,仿真结果表明,在不改变流路布置的情况下,Φ5 mm换热器的换热能力略有提升,但制冷剂侧压降增大4~7倍;进一步地,有针对性地设计了5种流路布置方案来探究分路数、分路汇合位置等因素对换热器传热及压降特性的影响规律,总结了小管径翅片管式换热器流路优化的思路,并设计了3种Φ5 mm管径室外换热器流路优化方案。仿真评估3种方案的可行性后制作样机进行性能测试,实验结果表明:方案(3)性能与原换热器相当,同时其材料成本可降低34.6%。

扁平纵向翅片管换热器的传热特性分析及结构优化

为进一步优化传统纵向翅片管换热器的传热性能,提出了一种扁平纵向翅片管换热器。基于传热流动基础理论,建立扁平纵向翅片管的物理模型,给出相关传热计算公式,优化扁平管和翅片的结构参数。进一步将扁平翅片管和圆管翅片管以及组成换热器的换热性能进行比较分析,结果表明,等截面同翅片结构参数下单位体积内气侧换热面积增加1.5倍,同质热负荷下换热器的体积减少50%以上,结构紧凑,具有较好的综合优势,为该换热器的推广应用提供参考。

水平微肋管内R513A冷凝换热特性研究

采用实验方法研究了R513A在光管和不同齿密度微肋管内的冷凝换热性能,并通过对比冷凝换热系数实验值与关联式的预测值,探究了现有关联式对R513A的适用性,实验在冷凝温度33、35、38℃,质量流速50~150 kg/(m^(2)·s)的工况范围内进行。实验结果表明:冷凝换热系数随质量流速的增大而增大,在低质量流速区域,微肋管的冷凝换热系数增长幅度更大;随着齿密度的增加,管内换热面积增大,但管内表面张力作用增强,相应的流动阻力增强,强化传热作用被削弱;与R134a相比,微肋管对R513A的强化传热效果更优;对于光管,Bashar关联式的预测效果最佳,Cavallini关联式与Dobson关联式在低质量流速区域的预测误差偏大;对于微肋管,Yu关联式的预测效果最理想,Cavallini关联式与Kedzierski关联式均低估了管内冷凝换热特性。以Kedzierski关联式为基础,拟合了新的修正关联式,修正关联式的预测值与实验值的一致性较好,其平均绝对误差与标准差分别为7.8%、8.5%。

鱼鳍型涡发生器强化管翅式换热器传热

提出了一种鱼鳍型涡发生器,并将其应用在管翅式换热器中强化传热。采用数值模拟方法研究了鱼鳍型涡发生器安装方式对换热器中流体流动和传热的影响,分析了流体流经涡发生器前后的压力变化。结果表明:涡发生器以common-flow-up方式安装在圆管下游时传热j因子提高了46.6%,摩擦因子提高了24.4%,与以common-flow-down方式安装于圆管上游相比,圆管后方的负压区更小,流动阻力更小,冷热流体的混合效果更好,因而具有更好的强化传热效果。

钛合金板翅式换热器钎焊工艺仿真分析

针对钛合金板翅式换热器结构特点,确定了加压钎焊的工艺方法,开展了单层钛合金板翅式换热器钎焊仿真分析,并进行了工艺验证。根据换热器结构的受力特点,设计了加压后挡板变形和波纹板变形两种钎焊方式,并设置了不同变形下压量,采用ABAQUS有限元仿真软件对焊接过程进行了分析。结果表明,在单层挡板下压量为0.1 mm时,换热器整体受力均匀,最大应力为170MPa;在单层波纹板下压量为0.3 mm时,波纹板变形均匀,未出现畸变扭曲等缺陷,最大应力为165.8 MPa。设计了单层挡板总高度低于波纹板总高度0.3 mm,先将波纹板下压0.3 mm,再将挡板下压0.1 mm的工艺方案,并进行了验证,制备得到了质量良好、焊接紧密的换热器样件。

锯齿型翅片内不同温区氦气流动与传热性能对比及节距对翅片性能影响的研究

为分析板翅式换热器在低温工况下的流动换热性能与常温工况下的差异和翅片节距对其性能影响,建立氦气在锯齿翅片通道内流动与传热的数值模型,开展数值模拟分析。结果表明:低温氦气在锯齿型翅片通道内的传热性能优于常温氦气。在氦气入口温度为20 K时,j因子比300 K时提升1.1%~55.9%,比77 K时提升0.41%~13.01%;在氦气入口温度为77 K时,j因子比300 K时提升0.53%~38.47%。低温氦气在锯齿型翅片通道内的流动性能比常温氦气差。在氦气入口温度为20 K时,f因子比300 K时高16.84%~28.87%,比77 K时高3.98%~23.19%。翅片节距大小在不同温区下对翅片流动与传热性能均有显著影响。在不同温区下,j因子随着翅片节距增大而减小,f因子随着翅片节距减小而增大。低雷诺数时,JF因子随着翅片节距减小而增大,而高雷诺数时则出现相反的趋势。

管壳式换热器换热管强化传热研究

研究了油库夏季高温导致的油气回收工艺中吸附罐回收率低、吸收塔解吸效率低、油气回收系统能耗过高以及安全隐患较多等问题。将温度较低的地下水作为冷却水,从实践的角度构建多种强化传热结构的管壳式换热器并采用CFD的方法对其热力学与水力学性能进行多方面探究。结果表明当油气在管壳式换热器壳程中流动时,热流可以获得更好的冷却效果;油气在壳程流动时,CIRF型换热管具有最佳的热力学性能,RAW型换热管具有最佳的水力学性能。综合油气回收工况与计算结果配置CIRF型换热管的管壳式换热器在油气回收工艺中有着较强的适用性,其可以在有效提高油气的冷却效果的同时兼顾换热器的水力学性能。

翅片管式换热器翅片结构对空气侧性能的影响

建立5mm管径翅片管式换热器百叶窗翅片的物理模型和数学模型,模拟分析百叶窗翅片开窗角度和换热器管间距对空气侧性能的影响,结果表明:在相同迎面风速下,空气侧的换热量及表面传热系数均随百叶窗开窗角度的增大而增大,风机功率随之大幅增加;空气侧的换热量及表面传热系数均随管间距的减小而增大;综合考虑换热量、风机功率及空气侧表面传热系数,开窗角度20°、管间距17.1 mm时换热器空气侧性能更优。

基于翅片管的固-液相变储热型换热器的模拟研究

针对现有的余热回收技术在低温余热回收方面较为落后的问题,以90℃水为输入热流体、60号石蜡为相变材料对低温蓄热换热器进行设计。采用Fluent进行仿真模拟,针对翅片管的翅片大小和数目进行储热放热仿真,并针对换热管数量进行了研究。结果表明,大翅片储热500 s时相变材料平均液态分数比小翅片和无翅片分别提升45.5%和81.3%,更能促进相变材料的储热放热效率;放热500 s时大翅片、小翅片、无翅片出口水温分别升高0.5℃、0.4℃和0.2℃,其中大翅片温度最高、最稳定;增加翅片层数的模拟结果可见,随着翅片层数增加,储热1000 s时,采用1、2、3个翅片平均液态分数分别为0.36、0.47和0.58,储热放热效果增强,相变材料熔化、冷凝平均速率增快;放热600 s时,采用1、2、3个翅片出口水温分别升高0.21℃、0.26℃和0.36℃,稳定性增强,可为余热回收中的低温余热回收提供技术指导。

管壳式换热器折流板开孔流场特征及场协同分析

折流板是管壳式换热器最主要的结构之一,但流体介质容易在折流板背风侧产生一个相对静止的“流动死区”,影响换热器壳程的换热效果。因此,本文利用Fluent对换热器壳程折流板进行开孔研究,分析流体流动特征,同时利用场协同分析的方法对其进行了验证分析。结果表明:折流板开孔可有效减小换热器壳程背风区的“流动死区”,达到强化传热的效果。