垂直向上流动通道内环状流干涸点的理论研究

本文基于分离流模型,建立了垂直向上流动环形通道内环状流的三流体模型,并对干涸点进行了数值模拟.比较计算结果和实验结果,发现两者符合较好.结果显示:当干涸点发生在内管并且外管热流密度不变时,临界含汽率随曲率和间隙的减小而增大,当干涸点发生在外管且内管热流密度不变时,情况相反;对于固定的间隙,当外管内径大于20 mm时,或间隙小于0.5 mm时,压力和质量流速对临界含汽率的影响非常微弱.     

Study on dryout point in vertical narrow annuli

Prediction of dryout point is experimentally investigated with deionized water upflowing through narrow annular channel with 1.0 mm and 1.5 mm gap respectively. The annulus with narrow gap is bilaterally heated by AC current power supply. The experimental conditions covered a range of pressure from 0.8 to 3.5 MPa, mass flux of 26.6 to 68.8 kg?m-2?s-1 and wall heat flux of 5 to 50 kW?m-2. The location of dryout is obtained by observing a sudden rise in surface temperature. Kutateladze cor…     

Experimental research on dryout point of flow boiling in narrow annular channels

1 Introduction There are basically two classes of critical heat flux (CHF) situations: departure from nucleate boiling (DNB) and dryout (DO) [1]. DO is also sometimes known as burnout or departure from forced convective boiling in vapor-continuous flow. From the point of view of engineering, the CHF caused by the DO mechanism is of particular importance since boiling annular flow is one of the most common flow patterns in gas–liquid two-phase flow and occurs in a wide range of vapor qua…     

Prediction of Liquid Film Dryout in Two-Phase Annular-Mist Flow in a Uniformly Heated Narrow Tube Development of Analytical Method under BWR Conditions

A method was developed based on the conservation lows to predict critical heat flux (CHF) causing liquid film dryout in two-phase annular-mist flow in a uniformly heated narrow tube under BWR conditions. The applicable range of the method is within the pressure of 3–9 MPa, mass flux of 500–2,000 kg/m²·s, heat flux of 0.33–2.0 MW/m² and boiling length-to-tube diameter ratio of 200–800.

The two-phase annular-mist flow was modeled with the three-fluid streams with liquid film, entrained droplets and gas flow. Governing equations of the method are mass continuity and energy conservation on the three-fluid streams. Constitutive equations on the mass transfer which consist of the entrainment fraction at equilibrium and the mass transfer coefficient were newly proposed in this study.

Confirmation of the present method were performed in comparison with the available film flow measurements and various CHF data from experiments in uniformly heated narrow tubes under high pressure steam- water conditions. In the heat flux range (q“<2MW/m²) practical for a BWR, agreement of the present method with CHF data was obtained as, (Averaged ratio)±(Standard deviation)=0.984±0.077, which was shown to be the same or better agreement than the widely-used CHF correlations.     

An analytical model for predicting dryout point in bilaterally heated vertical narrow annuli

Based on the droplet-diffusion model by Kirillov and Smogalev (1969, 1972), a new analytical model of dryout point prediction in the steam-water flow for bilaterally and uniformly heated narrow annular gap was devel- oped. Comparisons of the present model predictions with experimental results indicated that a good agreement in ac- curacy for the experimental parametric range (pressure from 0.8 to 3.5 MPa, mass flux of 60.39 to 135.6 kg?m-2?s-1 and heat flux of 5 to 50 …     

曲率对竖直向上环形狭窄通道内环状流特性的影响

基于三流体分离流模型，以液膜质量、动量和能量守恒方程为基础，结合汽芯动量方程，对双面加热垂直向上流动环形狭窄通道内环状流特性进行数值模拟。将计算结果与实验结果相比较，两者符合较好。通过数值模拟，分析了曲率对环状流特性的影响，得到了曲率对液膜厚度、液膜内温度、液膜内速度、临界热流密度等的影响曲线。曲率越大，内液膜越薄，而外液膜越厚。内管干涸时，临界热流密度随曲率的减小而增大；外管干涸时，则反之。     

液钠沸腾两相流流型与临界热流密度(CHF)机理实验研究

通过大量的液态金属钠临界热流密度 (CHF)的实验研究 ,结合液钠两相传热流动特性及液钠的物性特点 ,分析了起始沸腾流型 ,泡状流 ,块状流 ,环状流和双向环状流的热工水力特性 ;并从实验结果出发 ,深入分析了液钠发生临界热流密度时的气泡爆炸和液膜撕裂或局部蒸干的两种传热恶化机理     

Numerical study on effect of gap width of narrow rectangular channel on critical heat flux enhancement

According to the flow passage characteristic of narrow rectangular channel and liquid film dry-out mechanics of annular flow critical heat flux (CHF), an annular flow CHF analytical model for narrow rectangular channel has been achieved. This model may be used to predict the CHF behavior of boiling two-phase flow in narrow rectangular channel with gap width of not being less than 0.0005 m (the equivalent diameter of this channel is 0.001 m). Through analyzing and calculating, when the inlet dimensionless gap width of narrow rectangular channel is within 30-85, the enhancement of CHF in channel is obvious. At the same time, according to the characteristic of two-phase flow, the new determinant laws of CHF in boiling two-phase flow system have been derived. Through analyzing and calculating, it is substantial that this determinant laws is appropriate. The best dimensionless gap width of heat flux enhancement has been achieved to be 45-75.     

环形流道两相流特性实验研究

在日本原子力研究所的一个两以试验台架上，进行了环形流道空气－水丙相流窟泡份额和逆向流试验，观察了其流型。通过试验和分析，提出了漂移流模型中分布系数Co和气相漂移速度Vgi的经验关系式；得到了逆向流Wallis表达式的拟合参数。对试验结果的分析表明，当流道间隙很小（Bond数小于1）时，流型和两相流动与间隙较大时有所不同。     

Type of flow, pressure drop, and critical heat flux of a two-phase sodium flow

Little is known about the two-phase pressure loss, the flow pattern, and the critical heat flux conditions for boiling sodium under forced convection. The specific thermohydraulic properties of sodium prohibit extrapolation to sodium of experimental data obtained for other liquids. Therefore, some new test series were carried out in a sodium loop with an induction heated test section of 9 mm inner diameter and 200 mm heated length. The two-phase pressure loss and the film thickness were measured up to the critical cooling conditions. The experimental results are compared with values predicted by known models on annular flow and annular mist flow, respectively. Satisfactory predictions of the flow pattern and the critical heat flux conditions could only be obtained using the measured two-phase pressure losses.     

不对称加热矩形窄缝通道临界热流密度研究

以氟利昂12为冷却介质,对4种加热比条件下的矩形窄缝通道双面不对称加热工况下的临界热流密度(CHF)进行实验分析,获得各种工况下CHF与冷却剂质量流速、入口过冷度、出口含汽率的关系。实验结果表明:低含汽率下,CHF随加热比的增加而增加,随着含汽率的增加,不同加热比的实验通道内CHF差异减小;高含汽率下,CHF随加热比变化趋势与低含汽率的相反。     

Pressure drops for steam and water flow in heated tubes

Measurements of pressure drop for a steam and water flow inside several heated tubes were obtained at two different laboratories (Chalk River Laboratories and École Polytechnique). The test sections used to carry out the experiments were constructed with Inconel-600 tubes, and were cooled internally with an upward flow of water. A reduction in frictional pressure gradient with an increase in heat flux was observed for single-phase flows at the same cross-sectional-average conditions. After boiling was initiated, the two-phase friction multiplier increased with increasing heat flux in the bubbly-flow region, but decreased in the annular-flow region. As the heated surface approached dryout, the two-phase friction multiplier exhibited a maximum value and decreased with increasing thermodynamic quality, until dryout occurred. The decreasing trend was attributed to a reduction in the liquid-film thickness and the termination of liquid entrainment. Following the occurrence of critical heat flux, a significant drop in frictional pressure gradient was noted, caused by the change in the near-wall sublayer to a low-viscosity vapor blanket.     

近临界压力区垂直内螺纹管临界热流密度实验研究

在近临界压力区,对垂直上升内螺纹管流动沸腾的偏离泡核沸腾(DNB)型临界热流密度(CHF)现象进行了实验研究。试验段采用ф35 mm×5.67 mm六头内螺纹管。实验参数范围为:压力18~21 MPa,质量流速500~1 000kg/(m~2·s),进口过冷度3~5℃,内壁热负荷40~960kW/m~2。实验得到了不同工况下的内壁温度和传热系数分布特性,分析了流动参数对内螺纹管中DNB型CHF的影响,并根据实验数据拟合出两相区的传热关联式与临界热流密度(qCHF)预测关联式。内螺纹管的qCHF实验数据被用于与光管的qCHF预测值进行对比,发现内螺纹管具有一定的CHF强化作用,但当压力越靠近临界压力时这种作用会被抑制甚至消失。实验结果表明:在近临界压力下,内螺纹管会在低干度区甚至过冷区发生DNB现象,压力的增大和质量流速的减小均会使DNB提前发生。qCHF随压力的减小和质量流速的增大而增大。在特定工况下,试验段不同截面会分别发生偏离泡核沸腾与蒸干。     

液膜蒸干模型在液态金属CHF预测中的应用

为对圆管中环状流烧干型沸腾临界进行预测,建立了考虑液滴沉积夹带作用的液膜蒸干模型。沉积率、夹带率等相关关系式采用水等常规流体的已有关系式。在一定参数范围内,将模型预测结果与实验数据和经验关系式进行了比较。结果表明：基于常规流体的液膜蒸干模型大体可应用于液态金属,但在临界热流密度（CHF）较大时可能造成较大偏差;钠、钾两种液态金属在CHF较低时预测准确度区别不大,但在CHF较高时区别较为明显。为更加准确预测液态金属CHF,应开发专门的沉积率、夹带率等相关关系式。     

窄矩形通道两相流动实验回路设计研究

为了更好地研究某燃料堆内窄矩形冷却剂通道的流动传热特性，调研了窄矩形通道传热的研究现状和发展趋势，结合NP工程反应堆相关参数和实验需求，搭建了一套热工水力两相流实验回路用来研究分析某燃料冷却剂通道传热特性。该实验回路根据实际的反应堆运行操作要求，设计了与实际冷却剂通道一致的实验段，流动方向设定为竖直向下流动，采用双面加热，流道间隙尺寸设定为2.3 mm，通道宽度为67 mm（加热宽度为62 mm），流道长度为1000 mm（加热长度为750 mm），并通过实验对其进行了验证。结果表明，本文装置正确可行。      

A numerical assessment of copper oxide and alumina nanoparticles during CHF occurrence

Subcooled nucleate boiling in forced convection has been drawing significant attention in many fields due to its good heat transfer efficiency and high heat removal capacity. Such advancement in sub-cooled nucleate boiling is the result of continuing efforts from experimental, theoretical and numerical researchers, particularly focusing on critical heat flux (CHF). CHF heat transfer regimes are inefficient and the occurrence of CHF can cause a large temperature gradient in the heated wall leading to physical burnout. One way to increase the level of the CHF is to add certain nanoparticles to the base fluid. The present paper compares the effects of the addition of copper oxide and alumina nanoparticles on CHF phenomenon within the general-purpose computational fluid dynamics (CFD). The governing equations solved are generalized phase continuity, momentum and energy equations. Wall boiling phenomena are modeled using the baseline mechanistic nucleate boiling model developed in Rensselaer Polytechnic Institute (RPI). To simulate the critical heat flux phenomenon, the RPI model is extended to the dry-out phenomenon by partitioning wall heat flux to both liquid and vapor phases considering the existence of thin liquid wall film. It was shown that the presence of copper oxide in comparison with alumina nanoparticles in the base fluid, delays the dryout phenomenon more dramatically and in specific concentration, CHF threshold would be enhanced and consequently the safety margins of the operation would be improved.     

双侧加热环形窄缝通道内单相水的流动传热特性研究

对环形窄缝通道内单相水在双面处于不同的加热热流密度情况下的对流换热特性进行了数值计算.计算结果表明,环形通道内、外壁加热热流密度比值的不同,对环形通道内、外壁与单相水的对流换热特性有着显著的影响.内、外壁面加热热流密度比值较小时,内壁的换热强于外壁的换热,随着内壁加热热流密度的增大,外壁的换热得到增强.但是,当内、外壁加热热流密度比值增加到一定程度时,外壁的对流换热特性将超过内壁的对流换热特性,与文献报道的实验结果一致.此外,环缝间隙的减小将导致环形通道的换热性能下降.     

An experimental study on pressure drop and dryout heat flux of two-phase flow in packed beds of multi-sized and irregular particles

This paper is concerned with debris bed coolability in a postulated severe accident of light water reactors, where the debris particles are irregular and multi-sized. To obtain and verify the friction laws predicting the hydrodynamics of the debris beds, the drag characteristics of air/water single- and two-phase flow in a particulate bed packed with multi-sized spheres or irregular sand particles were investigated on the POMECO-FL test facility. The same types of particles were then loaded in the test section of the POMECO-HT facility to obtain the dryout heat fluxes of the particulate beds heated volumetrically. The effective (mean) particle diameter is 2.25 mm for the multi-sized spheres and 1.75 mm for the sand particles, determined from the Ergun equation and the measured pressure drop of single-phase flow through the packed bed. Given the effective particle diameter, both the pressure drop and the dryout heat flux of two-phase flow through the bed can be predicted by the Reed model. The experiment also shows that the bottom injection of coolant improves the dryout heat flux significantly and the first dryout position is moving upward with increasing bottom injection flowrate. Compared with top-flooding case, the dryout heat flux of the bed can be doubled if the superficial velocity of coolant injection is 0.21–0.27 mm/s. The experimental data provides insights for interpretation of debris bed coolability (how to deal with the multi-sized irregular particles), as well as high-quality data for validation of the coolability analysis models and codes.     

基于液膜蒸干模型的低压低流量环状流CHF理论研究

为对低压低流量下的环状流临界热流密度（CHF）进行预测，建立了考虑液膜蒸发、液滴沉积和夹带的液膜蒸干模型，并用已有的实验数据对其进行验证。计算结果表明：在实验参数范围内，CHF计算值与实验值相对偏差在25%以内，两者符合较好。以建立的环状流CHF模型为基础，研究了进口焓差、质量流速、管径和加热长度对CHF的影响。该模型能够有效地计算低压低流量环状流CHF和分析CHF随不同参数的变化趋势。     

基于CFD方法的矩形窄缝通道内过冷流动沸腾模型研究

板状燃料元件中的矩形窄缝通道具有宽高比大的几何特征,高度方向速度梯度大、分布陡峭,发生过冷沸腾时,近壁面汽泡运动行为将受其影响而改变,其中汽泡滑移现象对沸腾换热影响较大。本文针对矩形窄缝通道中的汽泡滑移行为,构建了包含滑移热流的壁面热流分配模型,并建立机理性的汽泡受力模型和滑移模型计算汽泡脱离直径、浮升直径和滑移距离等辅助参数,开发了一套适用于矩形窄缝通道内向上流动沸腾的壁面沸腾模型。选用Nuthel窄缝通道沸腾实验进行数值模拟验证,结果表明：本文模型可以较好地预测1～4 MPa中低压工况窄缝通道向上流动沸腾的壁面过热度,最大误差相比RPI模型由80%降低至17%;蒸发热流份额和近壁面空泡份额相比RPI模型更低。