纯蒸汽在竖直管内非完全冷凝换热特性的实验研究

为研究纯蒸汽在竖直管内非完全冷凝的换热特性,使用内径为25 mm的换热管进行实验,入口压力为0.1～0.3 MPa,蒸汽质量流速为12～70 kg/(m²·s)。研究了入口压力、质量流速和质量含气率对管内平均和局部冷凝换热系数的影响,判别了冷凝过程中液膜流态,分析了液膜湍流度和液滴夹带对竖直管内冷凝换热的影响。结果表明：冷凝换热系数随着质量流速和质量含气率的增大而增大,竖直管的冷凝换热系数随着入口压力的升高而降低。实验中的液膜流型主要在过渡流区间,液滴夹带的发生使局部冷凝换热系数提高。对比4种环状流冷凝换热关系式计算结果发现,Shah的经验关系式基本偏差在±30%以内,平均绝对偏差(MAD)为18.91%。基于实验数据提出的经验关系式,其计算值和实验值基本偏差在±10%以内。     

竖直管内蒸汽完全冷凝换热特性的理论研究

Nusselt模型是静止蒸汽在竖直平壁上层流膜状冷凝换热的理论模型。蒸汽在竖直管内冷凝时,受管内蒸汽流速的影响,冷凝界面存在剪切应力,导致直接采用Nusselt模型计算冷凝换热系数会引入较大偏差。以非能动余热排出换热器冷凝换热工况为研究背景,考虑界面剪切力的影响,对Nusselt冷凝换热模型进行修正。分别采用Nusselt模型和修正模型对竖直管内蒸汽完全冷凝时的换热特性进行分析并与实验结果比较。研究表明,蒸汽在竖直管内完全冷凝时界面剪切力会改变蒸汽和冷凝液膜的流动状态,其对冷凝换热的影响不能忽略。修正模型合理地考虑了冷凝界面剪切力的影响,计算结果与实验结果吻合较好。     

自然循环条件下竖直管内层流凝结换热特性研究

考虑蒸汽流速的影响,对Nusselt凝结换热模型进行修正,分别采用Nusselt模型和修正模型对自然循环条件下竖直管内层流膜状凝结时的换热特性进行计算并与实验结果比较。研究表明,管内凝结换热受蒸汽流速的影响不能忽略,蒸汽对液膜的剪切作用使液膜减薄,冷凝换热系数增大。由于修正模型合理地考虑了界面剪切力的影响,计算结果与实验相符。     

核态沸腾存在时垂直管内环状流换热数值计算

建立了垂直管内流动沸腾换热与阻力特性的数值计算模型。该模型以环状流为研究对象,认为强制对流与核态沸腾两种换热方式同时存在。通过求解质量守恒、动量守恒、能量守恒方程,获得液膜厚度、速度与温度等参数。由汽泡脱离频率、脱离直径、汽化核心密度及抑制因子等参数计算核态沸腾换热。换热系数根据热流密度叠加原理确定。对一种有机工质在垂直管内向上流动时的沸腾换热进行了数值预测,计算值与实验结果符合良好。随着干度的增加,核态沸腾在总换热系数中的比例由约20％下降至1％。     

垂直管内含不可凝气体蒸汽的冷凝换热MELCOR数值模拟

采用MELCOR程序建模,对垂直管内含有空气的冷凝传热过程进行模拟计算,并将数值模拟结果与Kuhn的实验进行比较。结果表明,MELCOR模拟结果基本与实验结果基本吻合,验证了MELCOR模型的合理性。但是,MELCOR模拟蒸汽传质和液膜累积过程偏大,使得总换热系数偏大。通过对MELCOR模型参数进行修正,调整后计算得到的液膜厚度和换热系数比调整前减小,且结果与实验吻合得很好。     

严重事故下混合气体与壁面对流传热模型研究

反应堆严重事故下堆芯熔化发生锆水反应产生大量氢气，若一回路边界破裂，以氢气、水蒸气为主的混合气体进入安全壳内，将与安全壳内壁等结构壁面发生对流换热。本文对Melcor,Gasflow以及Contain三种严重事故模拟软件的对流换热计算模型与通用对流传热模型进行分析对比：Melcor,Contain的单相对流换热模型是通用对流换热模型的简化，其中Melcor的流态划分比Contain更细致，而Gasflow则采用雷诺比拟模型；对于相变对流换热，Melcor采用基于液膜跟踪模型的相变对流换热模型，临界雷诺数不同于通用模型且湍流换热关联式复杂，Contain在通用模型的基础上添加了蒸发修正与不可凝气体修正，Gasflow采用的是雷诺比拟方法。此外，本文还以Conan冷凝对流换热实验为例进行对比分析，模拟发现：Gasflow模拟结果与实验数据的吻合度相对较高；Melcor与Contain模拟结果较为相似，但与实验结果之间存在差异。     

壁面过冷度对水平管内含空气蒸汽冷凝换热影响

为研究壁面过冷度对含不凝性气体蒸汽流动冷凝换热能力的影响,分别进行水冷却与空气冷却条件下空气-蒸汽混合气在水平管内的流动冷凝实验,分析空气入口质量分数,混合气入口流速以及管外冷却剂体积流量变化时,管内局部换热系数随壁面过冷度的变化规律。结果表明:在环状流及波状流范围内,局部换热系数随壁面过冷度的增加而增大;在分层流范围则随壁面过冷度的增加而减小;空气含量与混合气流速的增加,会使得环状流和波状流下壁面过冷度增大对冷凝换热能力的促进作用更为显著。     

竖直通道内下降液膜蒸发换热的数值研究

下降液膜蒸发换热是CAP1400型反应堆非能动安全壳采用的重要换热机理,准确计算下降液膜蒸发换热量对非能动安全壳换热性能的评价有至关重要的影响。本文利用ANSYS FLUENT软件二次开发,实现了两种下降液膜蒸发换热模型的构建,并将两种模型计算结果与实验结果进行了对比分析。计算结果表明：两种模型均可较为准确地计算壁面下降液膜的蒸发换热系数;模型1的计算结果更加可靠,但在靠近壁面处需非常精细的网格;模型2在壁面处可使用较粗网格,但计算结果对对流换热系数的依赖较大。     

非能动余热排出换热器冷凝换热性能研究

以浸没在高位水箱中的竖直管束为研究对象,对不同热负荷条件下竖直管束内冷凝换热特性进行研究,通过对比中心管与周围旁管的凝液增长率以及冷凝换热热阻,分析了中心管与旁管换热特性的差异,解释了低压条件下冷凝换热系数剧烈下降现象。将管束冷凝试验数据与已有单管试验数据对比发现,在相同蒸汽工况下,单管的冷凝换热系数与旁管的冷凝换热系数吻合较好,但远低于中心管的冷凝换热系数,说明中心管的换热性能相对于旁管确实得到了强化。通过对比换热系数的试验值与经典努塞尔理论和努塞尔修正理论的计算值发现,中心管的试验值与努塞尔修正理论计算值吻合较好,但旁管的偏差较大。     

不同管束布置方式下含有空气的蒸汽自然对流冷凝换热特性分析

为研究非能动安全壳冷却系统（PCCS）热交换器管束布置对自然对流条件下含有空气的蒸汽冷凝换热特性的影响,采用气体组分输运方程和冷凝模型耦合,对单管、单排到五排管束通道内冷凝换热过程进行数值研究。研究发现,管束区内存在由于管间高浓度空气层干扰使冷凝换热能力减弱的“抑制效应”,以及由于水蒸气壁面冷凝导致气体横向流动使壁面冷凝能力强化的“抽吸效应”。对不同管束结构下2种效应对冷凝换热的影响进行分析,结果表明,随着管束排数的增加,2种效应对冷凝换热的影响逐渐增强,导致冷凝管周向局部冷凝换热能力不均匀性增加,其中五排管束周向局部冷凝换热系数（HTC）最大值为单管的2.3倍,最小值仅为单管的44.7%。在双排、三排和四排管束中,正四边形布置管束的冷凝换热能力优于正三角形布置,而五排管束中,正三角形布置的冷凝换热能力更强。本研究可对PCCS热交换器管束布置优化提供参考。      

B30波槽管水平管外蒸汽凝结换热的实验研究

在常压条件下对水平波槽管管外凝结换热及流阻特性进行了实验研究实验结果表明．波槽管具有良好的强化传热效果在实验参数范围内．波槽管的总传热系数比光管提高48％以上,通过对实验数据的回归分析．得到了管内对流换热、管外凝结换热及阻力系数的实验关联式。     

Forced convection condensation in the presence of noncondensable gas in a horizontal tube; experimental and theoretical study

To have a better understanding on forced convection condensation with noncondensable gas inside a horizontal tube, an experimental research and theoretical investigation were conducted under annular and wavy flow. The effects of noncondensable gas mass concentration, mixture gases velocity, pressure and inner wall sub-cooling on the condensation heat transfer have been analyzed. The results indicate that the local heat transfer coefficient increases with the increase of the mixture inlet velocity and pressure while decreases with the increase of the noncondensable mass fraction and wall sub-cooling. Based on the above conclusions, an empirical correlation for predicting the local heat transfer coefficient was proposed which showed a good agreement with the experimental data with an error of ±20%. Furthermore, a theoretical model using the heat and mass transfer (HMT) analogy method was developed including the suction effect. The heat transfer capacity for the film, gaseous boundary and convective heat transfer of the bulk gases were compared along the tube. Besides, the axial distribution of the bulk gases and liquid–gas interface temperatures inside the tube were analyzed. The present theoretical model fits better with the experimental data compared with Lee's and Caruso's models for stratified flow.     

Simple heat transfer model for laminar film condensation in a vertical tube

A new physical model for estimating the liquid film thickness and condensation heat transfer coefficient in a vertical tube, considering the effects of gravity, liquid viscosity, and vapor flow in the core region, is proposed. In particular, for calculating the velocity profile in the liquid film, the liquid is assumed to be in Couette flow forced by the interfacial velocity at the liquid-vapor interface. The interfacial velocity is calculated using an empirical power-law velocity profile. The film thickness and heat transfer coefficient from the new model are compared with existing experimental data and the original Nusslet condensation theory. The new model describes the liquid film thinning effect due to the vapor shear flow and predicts the condensation heat transfer coefficient from experiments reasonably well.     

Reflux condensation of flowing vapor and non-condensable gases counter-current to laminar liquid film in a vertical tube

An analytical model using the heat and mass transfer analogy approach was developed for local heat transfer in reflux condensation of flowing vapor and non-condensable gases counter-current to laminar liquid film in a vertical tube. The liquid film model was derived from the two-phase integral momentum equations for counter-current flow. The non-condensable gas effect was accounted for using the diffusion layer theory. The momentum, heat and mass transfer for the liquid and gas phases are coupled together by the shear stress, temperature and gas mass fraction at the two-phase interface, which together with the unknown vapor flow conditions at the outlet of the tube were solved iteratively. The model anticipates that vapor might not necessarily condense completely inside the tube. The root mean square of the theory's relative error is 30% compared with available experimental data. The model provides a mechanism for the safety analysis codes to evaluate reflux condensation in the presence of non-condensable gases.     

Pool boiling heat transfer enhancement on porous surface tube

The passive residual heat removal exchanger (PRHR HX),which is a key equipment of the passive residual heat removal system,is installed in an elevated pool.Its heat transfer performance affects security and economics of the reactor,and boiling heat transfer in the liquid surrounding the exchanger occurs when the liquid saturation temperature exceeded.The smooth tubes,which are widely used as heat transfer tubes in PRHR HX,can be replaced by some enhanced tubes to improve the boiling heat transfer capability.In this paper,the pool boiling heat transfer characteristics of smooth tube and a machined porous surface tube are investigated by using high-pressure steam condensing inside tube as heating source.Compared with smooth tube,the porous surface tube considerably enhances the boiling heat transfer,and shortens the time significantly before reaching the liquid saturation temperature.Its boiling heat transfer coefficient increases from 68% to 75%,and the wall superheat decreases by 1.5oC.Combining effect of condensation inside tube with boiling outside tube,the axial wall temperatures of heat transfer tube are neither uniform nor linear distribution.Based on these investigations,enhance mechanism of the porous surface tube is analyzed.     

雷诺数关系式对膜状凝结湍流区传热计算的影响

膜状凝结现象广泛存在于核电站安全壳和稳压器中。关于膜状凝结液膜湍流区的传热模型,目前未明确辨析基于质量和能量关系的两种雷诺数关系式的差别。本文针对管外纯蒸汽自然对流膜状冷凝传热,定量地分析雷诺数关系式对膜状凝结液膜湍流区传热计算的影响。基于液膜湍流区修正项的一般性假设,推导了膜状凝结湍流区传热系数的表达式。同时,分别与雷诺数关系式Remass和Reenergy联立,求解得到不同雷诺数关系式之间以及对应的膜状凝结传热系数之间的关系。分析表明:受普朗特数Pr的影响,在膜状凝结液膜湍流区,雷诺数关系式Remass和Reenergy差别明显,并存在关于Pr的分界点。基于Remass和Reenergy得到的膜状凝结平均传热系数及其相对偏差是Re和Pr的非线性函数。当0.1Pr4.0且Re1 600时,基于Reenergy和Remass得到的膜状凝结平均传热系数相对偏差在-60%和+60%之间。通过实验和理论验证,在膜状凝结液膜湍流区基于Reenergy得到的膜状凝结传热系数更加准确。     

Investigation on condensation in presence of a noncondensable gas for a wide range of Reynolds number

A theoretical model has been developed to study the local heat transfer coefficient of a condensing vapour in the presence of a noncondensable gas, where the gas/vapour mixture is flowing downward inside a vertical tube. The two-phase heat transfer is analysed using an annular flow pattern with a liquid film at the tube wall and a turbulent gas/vapour core. The gas/vapour core is modeled using the analogy between heat and mass transfer. The model incorporates Nusselt equation with McAdams modifier and Blangetti model for calculating the film heat transfer coefficient, Moody and Wallis correlations to account for film waviness effect on gas/vapour boundary layer. The suction effect due to condensation, developing flow and property variation of the gas phase is also considered. A comparative study of heat transfer coefficient and vapour mass flow rate has been made with various models to account for condensate film resistance and condensate film roughness. Results show that for very high Reynolds number, the condensation heat transfer coefficient is higher than the film heat transfer coefficient.     

竖直管束外含空气蒸汽冷凝的实验研究

本文对竖直管束及单管的管外冷凝换热进行了实验研究,分析了管壁面过冷度、混合气体压力和不凝性气体含量对管束外冷凝传热性能的影响,对比了管束与单管的传热特性,给出了管束外冷凝传热系数的计算关联式。研究结果表明,管束的平均冷凝传热系数随过冷度的增大而减小,随混合气体压力的增大而增大,随不凝性气体质量分数的增加而减小。在混合气体高压力、低不凝性气体含量时管束的传热效果明显优于单管。关联式计算值与实验值误差范围小于±10%。     

钛波槽管垂直管外凝结换热的实验研究

对钛波槽管进行了垂直管外凝结换热的实验研究通过实验得出结论：钛波槽管具有良好的强化传热效果;在实验范围内,最佳钛波槽管的总传热系数是钛光管的1．12～1．36倍通过对实验数据的回归分析,得到了管内对流换热、管外凝结换热及流动阻力系数的实验关联式     

高温钾热管稳态运行传热特性研究

本文采用钾金属作为热管工质，对热管的传热性能展开理论和实验研究。首先，对不同加热功率和倾角下热管传热性能影响规律进行实验研究。结果表明，热管加热功率的提升有利于传热性能的改善，加热功率升高导致蒸发加剧，蒸气密度增加，进而强化蒸气传热。倾角对传热性能有正反两方面的作用。一方面，随倾角的增加冷凝段液膜不稳定性加剧，导致传热恶化；另一方面，倾角的增加导致重力加速液体工质回流并减薄冷凝段液膜，传热增强。在二者的共同作用下，随倾角的增加，热管等效热阻逐步增加且超过某一限值后趋于平稳。其次，以热阻网络法为指导，建立了钾热管的数学物理模型，并基于模块化程序思想，开发了热管设计分析程序。通过与实验数据对比，二者整体误差在2.7%以内，验证了热管模型的合理性。本文对碱金属高温热管的设计优化提供了数据及理论支持。