沸腾换热强化特性实验研究

沸腾换热具有传热温差低、换热系数高等优点,对提高设备的紧凑性、经济性和安全性具有重要意义.目前,核动力装置中主要以光管作为沸腾换热元件,沸腾换热强化的空间很大.本文针对核动力装置非能动余热排出换热器沸腾换热工况,以水为工质,对光管及3种强化管的管外沸腾换热特性进行实验研究,得出了4种管型的沸腾换热强化特性,并分析了各强化管的强化机理.整体针翅管表面大量螺旋排列的三维翅片增大了换热面积、延缓了汽泡在壁面附近聚合形成大汽膜,使沸腾换热得到强化;多孔管采用机械方法在壁面加工出大量微细小孔,汽化核心数量和汽泡脱离频率均大幅提高,因此,沸腾换热强化效果显著;绕丝针翅管是一种复合强化手段,兼有整体针翅管和多孔管的优点,沸腾换热强化效果也较好.     

多孔壁面管强化大容积沸腾换热特性研究

针对非能动余热换热器大容积沸腾换热工况,采用高温饱和蒸汽作为加热热源,对机械加工多孔壁面管和光管的大容积沸腾换热特性进行实验研究.结果表明,多孔壁面管对大容积沸腾换热具有很好的强化能力,多孔壁面管可使沸腾换热系数较光管提高68%～75%,壁面过热度降低约1.5℃;受管外沸腾和管内凝结之间传热耦合的影响,换热管轴向壁面温...     

复合换热管过冷沸腾换热实验与关联式评价

以去离子水为实验介质,在单面受热流密度条件下,开展了聚变装置偏滤器的过冷流动沸腾强化换热特性实验研究,将内肋强化换热技术与内插扭带结构相结合,利用两者的协同强化传热效应,设计出一种复合换热管。实验参数为：质量流速,992～4 960 kg/(m2·s);压力,04～2 MPa;入口过冷度,8701～11921 ℃;热流密度,1～163 MW/m2。对4种强化换热管（光管、内插扭带管、内螺纹肋管和复合换热管）的管内过冷流动沸腾换热特性和综合性能评价指标（PEC）进行了对比实验。结果表明：与其他3种管道相比,复合换热管的对流换热系数和PEC最高,传热特性最好。研究了复合换热管的扭带扰动比、螺距、压力和质量流速对管内两相流动对流换热系数的影响规律,发现对流换热系数与螺距、质量流速呈正比,与扭带扰动比、压力呈反比。最后对比了4个现有的过冷流动沸腾换热经验公式,并在无量纲模型基础上,增加了扰动比和螺径比（t/Dh）进行修正,利用非线性拟合方法提出了适合复合换热管过冷流动沸腾的努塞尔数新公式。     

低压低流速条件下的过冷沸腾换热特性

为探究低压低流速条件下的过冷沸腾换热特性，开展本实验研究。通过分析实验中采集的热工参数和可视化图像，探究了沸腾滞后现象、沸腾失稳现象以及沸腾换热特性。实验发现沸腾起始点壁面过热度较高，而沸腾的发生大幅提高了换热系数，因此出现了显著的沸腾滞后现象。实验中较为光滑的加热面可达到较高的过热度，而低压下快速产生的气泡尺寸较大，在较低的热流密度下气液界面发生剧烈变化，使气泡破裂为多个小气泡并成为核化点。在过冷沸腾换热系数的预测中，Dittus-Boelter对流换热关系式不再适用，采用Hallman关系式和Gnielinski关系式计算对流换热系数，并引入壁面过热度对池式沸腾换热系数进行修正，可使过冷沸腾换热系数的预测精度大幅提高。     

套管式蒸汽发生器沸腾传热实验研究

用氟里昂Ｆ－１１３作为沸腾换热介质来模拟套管式蒸汽发生器沸腾传热过程，对环形、狭空间的沸腾换热情况进行了实验研究。将环形空间又分为单面加热、双面加热两种情况，并和一般尺寸圆管进行了比较，对狭空间沸腾换热的流型变化也进行了观察研究。     

朝下针翅结构表面稳态临界沸腾换热实验研究

针对商用压水堆核电站堆内熔融物滞留(IVR)策略对提高压力容器外表面沸腾换热临界热流密度(CHF)的迫切需求，本文采用冷喷涂技术在铜基体表面制备了一种由针翅凸起结构与多孔涂层相结合的毫米-微米双尺度结构表面，运用稳态池沸腾实验研究了铜光表面和针翅涂层结构表面在朝下不同倾角下的沸腾换热性能。结果表明：朝下表面的CHF随倾角的增加而增大，与铜光表面相比，针翅涂层结构表面CHF至少提高了63%，具有较好的工程应用前景。     

螺旋管内单相及沸腾的强化换热与阻力特性实验

实验研究了三维内肋螺旋管内单相及沸腾的强化换热与阻力性能。单相对流换热实验采用光滑螺旋管和两种不同结构尺寸的三维内肋螺旋管。与光滑螺旋管相比,在测试的流动范围内．两种三维内肋管的平均换热系数增加了71％和103％．平均阻力增加了90％和140％;曲率δ=0．0605、测试段长0．58m的三维内微肋螺旋管内流动沸腾换热实验结果表明：在不同质量流速、热流密度工况下,三维内微肋螺旋管的平均换热系数比光滑螺旋管增加40％到120％．阻力增加18％到119％。     

腐蚀对微结构金属试样表面沸腾换热特性的影响研究

大量现有研究表明，使用合适的表面改性方法能够强化沸腾换热效果，使其在压水堆内有着广阔的潜在应用前景。但对于堆内高温高压碱性环境，这种强化换热效果能否长时间维持却鲜有研究。使用激光加工的方式，在不锈钢板状试样表面分别加工微槽、微孔、微柱三种微结构，将试样置于模拟实际堆内工况的高温高压反应釜中开展长达200 d的腐蚀实验，并对腐蚀前后试样进行池式沸腾实验与可视化研究。结果表明：三种微结构试样表面临界热流密度（Critical Heat Flux,CHF）均随腐蚀时间的增加先升高后降低，其中微孔试样在核态沸腾起始有着最大的气泡生成速率，微槽试样有着最高的CHF。     

竖直窄矩形通道内沸腾换热系数的预测模型

对窄矩形通道内流动沸腾换热特性进行实验研究,拟合出沸腾换热系数计算关系式。使用不同的沸腾换热预测模型计算窄矩形通道的沸腾换热系数并将预测值与实验值进行对比,结果表明:各关系式预测窄矩形通道的沸腾换热系数,预测效果都不同程度地存在一些问题。根据Schrock-Grossman模型并以强迫对流沸腾换热原理为基础,建立了窄矩形通道沸腾换热系数的预测模型,与实验数据符合良好。     

环形狭缝通道内沸腾换热传热特性的实验研究

对环形狭缝间隙为 1 0mm ,低质量流量下 ,狭缝内流动沸腾换热的传热特性进行了实验研究。实验以去离子水为工质 ,实验压力范围为 :1 5 5～ 3 72MPa,质量流量的范围是 :9 5 3～ 1 9 65kg/h。实验研究结果表明 :1 以Jens lottes公式对实验数据进行整理 ,得到的公式中的系数明显增大 ,而以Chen公式对实验数据进行整理 ,得到的公式中的系数则有所减小 ,说明此时环形狭缝间隙内的流动沸腾换热很可能是泡核沸腾和两相强制对流共同起作用的结果。 2 在实验所做的参数范围之内 ,内管的传热系数比外管的高。     

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.     

针翅管滑油冷却器壳侧传热与阻力性能实验研究

以润滑油为换热介质,对1个光管滑油冷却器和3个采用了针翅管的滑油冷却器实验体进行了对比实验研究。结果表明：在本实验范围内,针翅管滑油冷却器的总传热系数较高,是相同条件下光管滑油冷却器总传热系数的1.4～2倍;不同结构针翅管滑油冷却器的传热与阻力性能差别较大,针翅管结构参数和壳侧流程数目是影响滑油冷却器壳程传热与阻力性能的主要因素。实验范围内,较大的针翅高度有利于油流体的扰动,但不利于针翅管一次传热面处的换热;单流程结构的针翅管滑油冷却器具有较高的传热系数和单位体积换热量,其总体换热性能与阻力性能优于双流程结构的针翅管滑油冷却器。     

冷凝器强化传热特性分析

分析了影响冷凝器总传热系数的主要因素 ,阐述了管壁污垢系数对冷凝器传热性能的影响。提出了冷凝器强化传热的关键问题在于管外 ,增加管外侧传热系数会使冷凝器的效率大幅度提高。对冷凝器中采用螺纹槽管强化传热的方法进行了分析 ,提出了采用低翅片管或在螺纹槽管外侧采用适当的强化传热手段可以使冷凝器的传热效率得到提高。     

几何参数对含空气蒸汽冷凝影响的数值分析

含空气蒸汽冷凝是反应堆失水事故时安全壳内重要的热工水力现象。已有研究多关注气体压力、温度等热工参数对传热特性的影响,而对几何参数的影响及其作用原理分析较少。采用三维CFD数值模拟方法,基于扩散边界层冷凝机理模型研究了管径(4~60 mm)、管长(0.1~7 m)及倾角(0°~90°)对含空气蒸汽冷凝传热特性的影响。结果表明,管径、管长及倾角均对含空气蒸汽冷凝传热特性有显著影响。平均冷凝传热系数随管径的增大而减小;随管长的增长先减小后增大,3 m左右达到最小值;随倾角的增大而增大。局部冷凝传热系数沿管长方向先迅速减小后缓慢增大。倾斜布置时,迎流面产生明显传热强化,向两侧逐渐减弱,背流面存在一定的传热抑制。     

Recovery of Electrical Resistivity in Neutron Irradiated Uranium Monocarbides

An experimental study was performed on the heat transfer to a turbulent water film which is falling down the outside surface of a heated vertical tube. The test section was made of stainless steel tube 13 mm in outside diameter and 1,500 mm long. It was found that a nearly constant heat transfer coefficient was obtained for the lower half of the test section covering a length of about 1 m, which was direct-heated by electric current. The resulting values of the Nusselt number in this region were correlated to the Reynolds number, and the plots fell in a region intermediate between those given by Wilke and by McAdams. An analytical model taking account of the undulation on the film surface is proposed. The predictions from the model give fairly good agreement with the experimental data.     

Effects of tube inclination on pool boiling heat transfer

Effects of tube inclination angles on nucleate pool boiling heat transfer of water at atmospheric pressure have been investigated experimentally. Experiments were performed for seven angles (0, 15, 30, 45, 60, 75, and 90°) with two tubes (12.7 and 19.1 mm in diameter) of 540 mm in length. Through the study, it can be concluded that tube inclination gives much change on nucleate pool boiling heat transfer. When the tube is near the horizontal and the vertical positions, the maximum and minimum of heat transfer coefficients are expected, respectively. The decrease in bubble slug formation on the tube surface and easy liquid access to the surface are thought to be the causes for the enhanced heat transfer.     

套管式直流蒸汽发生器的换热特性优化

介绍了一种双面换热的套管式直流蒸汽发生器,其元件由直管外管和螺旋内管组成。这种结构的蒸汽发生器虽强化了换热,却增加了流动阻力,因而存在沿轴向的螺距变化使阻力增加最小而使总体换热量达到最大的最优化问题。通过分析内管螺距对强化换热和流动阻力的影响,采用有约束非线性优化方法对螺距进行了优化。在不同的换热区得出了不同的优化结果,可为直流蒸汽发生器的工程设计提供理论依据。     

Liquid metal heat transfer in heat exchangers under low flow rate conditions

The present paper describes the liquid metal heat transfer in heat exchangers under low flow rate conditions. Measured data from some experiments indicate that heat transfer coefficients of liquid metals at very low Péclet number are much lower than what are predicted by the well-known empirical relations. The cause of this phenomenon was not fully understood for many years. In the present study, one countercurrent-type heat exchanger is analyzed using three, separated countercurrent heat exchanger models: one is a heat exchanger model in the tube bank region, while the upper and lower plena are modeled as two heat exchangers with a single heat transfer tube. In all three heat exchangers, the same empirical correlation is used in the heat transfer calculation on the tube and the shell sides. The Nusselt number, as a function of the Péclet number, calculated from measured temperature and flow rate data in a 50 MW experimental facility was correctly reproduced by the calculation result, when the calculated result is processed in the same way as the experiment. Finally, it is clarified that the deviation is a superficial phenomenon which is caused by the heat transfer in the plena of the heat exchanger.     

管内覆丝网强化对流换热及阻力特性的实验研究

通过实验对管内覆丝网管进行了强迫对流换热和阻力特性研究。结果表明：管内覆丝网使换热明显增强，阻力也相应增长。菱形丝网对角线距离与平行边距离之比对换热效果有决定作用，丝网厚度对换热的影响比较小，而丝网网格的大小对换热几乎没有影响，在相同的泵功率和几何条件下，换热系数最大增加２１％。