SA508钢表面临界热流密度强化试验研究

利用“冷喷涂”多孔涂层制备技术,在反应堆压力容器真实材料SA508Gr3碳钢试验件表面制备了微米尺度多孔涂层。通过可旋转实验装置,在常压下开展了下朝向不同角度条件下池沸腾SA508钢试验件光表面、冷喷涂涂层表面的临界热流密度（CHF）试验研究,获得了2种表面在不同倾角下的沸腾冷却曲线。试验结果表明,随着倾角的增加,CHF增加;采用涂层表面的CHF始终高于光表面的CHF,CHF强化至少在25%以上;在多次加热和冷却循环后,多孔涂层表面保持足够的强度和稳定性。      

老化效应对涂层表面池沸腾传热性能的影响

压力容器外部冷却(ERVC)是第三代压水堆核电站严重事故缓解策略的关键技术,其表面临界热流密度(CHF)决定了压力容器的完整性。为探究压力容器真实材料SA508钢表面老化对涂层表面CHF特性的影响,开展了SA508钢光表面和基于SA508钢的TC4钛合金多孔涂层表面在不同老化状态下的沸腾换热特性实验研究。结果表明：SA508钢光表面在水中会快速氧化,随着老化的加深,其CHF呈上升趋势,上升幅度在20%以内;CHF增强的原因在于SA508钢氧化生成了能改善表面润湿性的Fe₃O₄磁性微纳米颗粒层。随着氧化的加深,TC4涂层表面由超亲水特性变为疏水特性,基体SA508钢生成的氧化物易堵塞涂层孔隙,CHF呈恶化趋势。     

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.     

倾斜限制空间内池式沸腾临界热流密度试验研究

在大气压下近饱和去离子水中,表面倾角(θ)从0°变化到30°、窄缝尺寸(e)从3mm变化到8mm,开展限制空间内池式沸腾临界热流密度(CHF)试验.研究表明:CHF值(qCHF)随θ的降低而减小;随e的增加而增大.qCHF变化存在明显的过渡角,当表面倾角大于过渡角时,CHF随窄缝尺寸的变化速率趋缓;当表面倾角小于过渡角...     

超亲水特性传热面上水喷流冷却时的沸腾换热特性实验研究

研究了在纳米材料涂层形成的超亲水材料传热表面上水喷流冷却时的沸腾换热特性,并与普通金属面上的喷流沸腾特性进行了比较.介绍了流动条件、加热方式、加热条件、超亲水材料涂层等条件对高温沸腾换热、临界热流密度的定量影响和一些基本换热规律.实验发现,超亲水传热表面对沸腾换热特性有十分显著的影响,超亲水传热面强化了喷流沸腾临界热流密度.     

池沸腾下朝向SA508钢表面临界热流密度特性试验研究

反应堆压力容器外部冷却（ERVC）是实现熔融物堆内滞留（IVR）的重要方案之一,而反应堆压力容器（RPV）外壁面的临界热流密度（CHF）决定了ERVC冷却能力的限值。为此建立小型CHF试验装置,并采用RPV用SA508钢制作试验块加热表面。以去离子水为试验工质,开展池沸腾下朝向CHF试验,研究真实RPV表面材料在不同倾角和过冷度条件下的CHF特性,及其老化效应对CHF的影响。结果表明：SA508钢表面极易氧化生锈,其CHF较不易生锈的铜和不锈钢表面要高;SA508钢表面CHF随倾角的增大而增加,但在30°附近存在转折,转折角以下范围内的CHF随倾角增加趋势不明显;CHF随过冷度的增加而增加,且基本呈线性变化。本试验有助于进一步认识RPV外壁面的CHF行为,为后续开展CHF增强方法研究奠定基础。     

池式沸腾和流动沸腾的人工神经网络研究

成功构建了2个分别用于预测同心圆管开式热虹吸器内自然循环临界热流密度(CHF)和池式核态沸腾换热系数的人工神经网络。其预测均方误差分别为16.43%和19.57%。用训练成功的人工神经网络分析了2种沸腾换热的影响因素,分析结果表明:热虹吸器内同心内管的出现使CHF增加,热虹吸器内的CHF随内管外径的增加先增加后减小。池式核态沸腾表面传热系数随压力的增加先呈线性增加,当压力接近临界压力时,增加速度增大。     

整体针翅管强化传热实验研究

在润滑油竖直纵向冲刷的条件下,对整体针翅管进行了换热特性的实验研究,分析了针翅管的节距(T)、翅高(b)、加工方向、润滑油进口温度(t)和冷却水流速(v)对针翅管传热性能的影响。在本实验范围内,整体针翅管的总换热系数k可达200~1470W/m2ˇK,比相同条件下的光管可增加1~4倍。实验结果表明,整体针翅管是一种比较适合于以高粘度流体作为工质的换热器的新型强化换热管。     

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。     

针翅管传热与压降特性研究

以润滑油为换热介质,对整体针翅管传热与阻力特性进行了理论分析与试验研究,研究结果可为针翅管的优化设计提供参考。在换热介质纵向冲刷换热管的条件下,对不同针翅长度的3种整体针翅管与光管进行了传热与阻力试验。结果表明：整体针翅管对润滑油换热具有很好的强化能力,在本试验范围内,整体针翅管对油流体扰动强烈,换热强度是同条件下光管的2~6倍;针翅长度是影响针翅管压降的主要因素,在雷诺数达300时,压降曲线出现转折。     

Steady-state Experimental Study of Critical Boiling Heat Transfer on Downward Facing Surface with Pin-fin Coating Structure

Enhancing the critical heat flux (CHF) of boiling heat transfer to achieve in-vessel retention (IVR) strategy has become an urgent requirement of commercial PWR nuclear power plants’ security. A new kind of millimeter-micro multi-scale structure surface was fabricated on the surface of copper substrates by cold spraying technology, which combined pin-fin structures with porous coating structures. Steady-state pool boiling experiment was conducted on a plain copper surface and the pin-fin coating structure surface under different inclination angles. The experimental results show that the CHF increases with the inclination angles on downward facing surface, compared with the plain surface, the pin-fin coating structure enhances the CHF more than 63%, which testifies its superior engineering application prospects.     

Experimental Research on Critical Heat Flux for Downward-facing Pool Boiling with SA508 Steel Plate

The external reactor vessel cooling (ERVC) is one of the important methods to achieve the in-vessel retention (IVR), while the critical heat flux (CHF) on the outside wall of the reactor pressure vessel (RPV) decides the maximum heat removal capacity of ERVC. In present work, a small CHF test facility was established. The test surface was made of SA508 steel which was the same surface material of prototype RPV. The deionized water was used as coolant in downward-facing CHF test under pool boiling condition. The influence of the real RPV material surface at different inclination angles and sub-cooling conditions on the CHF characteristics was studied. The influence of aging on CHF was also studied. The results show that the SA508 steel surface is easily oxidized, so its CHF is higher than that of copper and stainless steel surfaces. The CHF of SA508 steel surface increases with inclination angle, but there is a turning point near 30° and the CHF below the turning angle has no obvious trend with the increase of inclination angle. The CHF increases with the sub-cooling, and it shows linear growth characteristics. The test results provide a further understanding of the CHF behavior on the RPV outside wall and lay the foundation for future research work on CHF enhancement methods.     

液态铅铋合金在绕丝燃料棒组件子通道间湍流交混数值模拟

液态铅铋合金（LBE）是第四代液态金属核反应堆候选冷却剂,由于LBE热物性具有一定的特殊性,亟待对LBE在燃料组件子通道中的流动与传热过程开展研究。本文对LBE在带绕丝燃料棒组件中湍流流动进行数值模拟与分析,将燃料棒壁面温度的数值模拟结果与响应的实验数据相比较,2者具有较高的吻合度,说明数学模型及数值结果具有较高的可靠性与准确性;使用湍流交混系数β表征LBE在不同子通道间、不同燃料棒间隙宽度与燃料棒直径比（S/D）结构下的湍流交混情况,结果表明,不同子通道间β波动程度具有差异性,β的大小与S/D呈负相关。基于不同S/D与雷诺数的计算结果,拟合出不同子通道间β关联式,为绕丝燃料棒三角形排列方式的燃料组件子通道分析程序开发提供交混模型。      

倾斜窄长套管内自然对流沸腾临界热流密度的实验研究

用实验方法对浸没在饱和液体中的倾斜窄长加热套管内的自然对流沸腾临界热流密度进行了实验研究,考察了套管间隙、管长、倾斜角和工质对临界热流密度的影响,并考虑了倾斜角对重力的影响,对用于预测垂直套管内自然对流沸腾临界热流密度的半理论半经验公式进行了修正。修正后的公式能较好地预测本实验和他人实验的结果。     

One-dimensional critical heat flux concerning surface orientation and gap size effects

Tests were conducted to examine the critical heat flux (CHF) on a one-dimensional downward heating rectangular channel having a narrow gap by changing the orientation of the copper test heater assembly in a pool of saturated water under atmospheric pressure. The test parameters include both the gap sizes of 1, 2, 5 and 10 mm, and the surface orientation angles from the downward-facing position (180°) to the vertical position (90°), respectively. Also, the CHF experiments were performed for pool boiling with varying heater surface orientations in the unconfined space at atmospheric pressure using the rectangular test section. It was observed that the CHF generally decreases as the surface inclination angle increases and as the gap size decreases. In consistency with several studies reported in the literature, it was found that there exists a transition angle at which the CHF changes with a rapid slope. An engineering correlation is developed for the CHF during natural convective boiling in the inclined, confined rectangular channels with the aid of dimensional analysis. This correlation agrees with the experimental data of this study within ±20%.     

Critical Heat Flux and Near-Wall Boiling Behaviors in Saturated and Subcooled Pool Boiling on Vertical and Inclined Surfaces

The mechanism of the critical heat flux (CHF) where the departure from nucleate boiling (DNB)-type boiling transition takes place has not been fully elucidated. In this paper, we examine the trigger mechanism of the CHF for saturated and subcooled pool boiling on vertical and inclined surfaces based on measurements of the liquid-vapor behaviors near heating surfaces by using a conductance probe. The angle of inclination was varied from 90° (vertical) to 170° (facing almost horizontally downwards). The probe signals and the void fraction distributions showed that a liquid layer remains beneath the vapor masses moving upward along the heating surface at high heat fluxes near the CHF. The thickness of the liquid layer was determined from the location where the probe signals corresponding to the vapor masses disappeared. The thickness of the liquid layer formed on the vertical surface increased with increasing degree of subcooling, which may be the cause of the increases in CHF with increasing degree of subcooling. The measurements of saturated boiling on the inclined surface confirmed that the orientation of the heating surface greatly affects the period it takes for vapor masses to pass, but it negligibly affects the liquid layer thickness. This suggests that the decrease in CHF with increasing angle of inclination is primarily caused by the lengthening of the duration of vapor mass passage.     

HFE-7100工质稳态临界沸腾传热实验研究

池沸腾临界热通量是沸腾相变传热的重要参数,决定了相变换热器件的推广应用。表面粗糙度和饱和压力对沸腾传热边界层分布、表面铺展润湿及工质动力学特性具有重要影响,进而对临界热通量作用显著。本文对HFE-7100工质在4种不同粗糙度的铜基表面（0.019、0.205、0.311和0.587 μm）条件及在不同饱和压力（0.07、0.10、0.15及0.20 MPa）工况下的池沸腾稳态临界状态下的传热及可视化实验进行了研究。对表面粗糙度及饱和压力对稳态临界沸腾的影响机制进行了分析,并考察了临界热通量预测模型对临界热通量的预测准确性。可视化研究表明,临界状态下的沸腾气液两相工质由小气泡、大气泡、气柱及蘑菇状气团组成,而在过渡状态下,沸腾表面会形成非平滑气膜,并不断分离出气泡。同时传热数据表明,表面粗糙度及饱和压力的增加能使表面临界热通量得到提升。相比而言,Bailey等建立的临界热通量预测模型能相对准确地预测HFE-7100工质沸腾临界热通量数据。为进一步提升预测准确度,建立了临界热通量无因次参数K预测经验关联式,其预测值与本实验及文献实验数据吻合较好。