多孔介质通道中单相流动压降预测模型

与常规管通道相比较,流体在多孔介质通道中的流动过程更复杂,流动阻力也大幅增加,这就使得难以准确预测流体流过多孔介质通道时的压降。通过构建多孔介质通道的几何模型,并求解N-S方程,虽然可以准确预测阻力压降,但计算时需要划分大量的网格,很难广泛应用。本文在相似理论基础上,以Fluent 6.3为平台,建立了颗粒填充多孔介质通道的压降预测模型,通过求解3维N-S方程,对模型中单相水的绝热流动进行了数值模拟。通过与实验结果进行比较,证明该预测模型对于不同工况下单相流体的压降计算具有较高的计算精度,误差范围小于5%。     

多孔介质通道内单相流阻力特性数值研究

采用Brinkman-Darcy-Forchheimer模型对各向同性、饱和均匀多孔介质通道内单相流体的绝热流动阻力进行了数值模拟.结果表明:在多孔介质中,对于单相流体压降,现有模型可以较好地进行预测.其中损失系数Kloss对流动阻力影响很大;高雷诺数(Pe)下需考虑Re对Kloss的影响;随着无量纲直径D的增大,流动阻力减小.     

变粘性效应对含内热源多孔介质通道内流动阻力特性的影响

在整体加热多孔介质热工水力实验回路上,以纯净水为冷却工质,研究变粘性效应对含内热源多孔介质流动阻力特性的影响。结果表明,流体流过加热多孔介质通道时,由于温度变化引起粘度的改变对多孔介质流动阻力特性产生影响。低雷诺数时变粘性效应对阻力压降的影响显著,随着雷诺数的增加其影响逐渐减弱。入口温度较低时,加热与绝热情况下的无量纲阻力压降曲线有明显差别;随着入口温度的升高,两者之间的差别逐渐减小,曲线最终趋于一致。提出了新的Hazen-Dupuit-Darcy(HDD)模型的修正因子ξμ和ξC,由此得到的阻力压降系数的计算值与实验值的相对误差在±11.8%的范围内。     

骨架发热多孔介质内单相水流动传热实验研究

针对骨架发热多孔介质内单相水流动阻力和传热特性开展了实验研究,拟合获得骨架发热多孔介质内热态流动阻力和对流换热关系式。实验参数范围是:雷诺数Re取127～394,表面热流密度12～62 kW/m2。实验结果表明:在本文研究的孔隙有效雷诺数范围内,惯性项阻力系数Rf受流动参数影响;基于骨架发热条件下获得的阻力关系式具有较好的扩展性,可以较好地预测骨架不发热条件下多种几何结构的多孔介质通道内单相水、单相蒸汽流动阻力;随着表面热流密度增大,对流换热系数不断降低;在相同热流密度条件下,随着质量流速的增大,对流换热系数也会随之增大。     

熔盐冷却球床堆热通道热工水力特性数值分析

基于计算流体力学(Computational Fluid Dynamics,CFD)通用计算程序Fluent,研究了模块化熔盐冷却球床堆(Pebble Bed Advanced High Temperature Reactor,PB-AHTR)中心热通道稳态热工水力行为。利用已开发的多孔介质流固两相局域非热平衡模型计算了球床堆中的压降、冷却剂的温场分布以及固相球床的温场分布,计算并比较了不同的多孔介质阻力因子(Ergun与KTA)对通道内的冷却剂流动以及温场分布的影响,并对丧失部分冷却剂情况下通道内的冷却剂及燃料温度进行了计算分析。结果表明使用不同的阻力因子对堆芯压降计算结果和流场的分布影响较大;而冷却剂温场及固相球床温场和球心的温度分布在不同的阻力因子下的差别较小,在PB-AHTR的设计参数下堆芯产生的热量能够被有效的输出,设计具有较大的安全裕度。计算结果对于球床堆的优化设计提供了一定的参考价值。     

含内热源多孔介质通道内流动沸腾两相压降的预测

为预测含内热源多孔介质通道内流动沸腾的两相阻力压降,以Ergun方程为基础,定义了多孔介质通道的Chisholm参数Y和全液相折算因子Φ_l0。通过理论分析和实验数据测量,明确了出口质量含气率x_e、质量流速G和小球直径d等对参数Y和Φ_l0的影响,并提出1个Lockhart-Martinelli（L-M）类型的两相阻力压降关系式。与文献中的其他公式相比,本工作提出的公式对实验结果能做出更好的预测。     

多孔介质通道内气-液两相流动阻力特性实验

基于新型水冷球床反应堆,以水和空气为工质,分别在直径为2、5、8 mm的玻璃球填充圆管形成多孔介质通道中,对竖直向上气-液两相流动阻力特性进行了实验研究.结果表明,阻力压降随着气液流量的增加而增大,并且与流型存在一定的对应关系;在相同流动条件下,颗粒直径和孔隙率对压降有明显影响.结合实验所得的234组实验点,对两类阻力...     

起伏振动下倾斜管内单相流流动阻力特性分析

起伏振动状态下单相流流动阻力的正确计算对漂浮核电站的安全性有显著影响。实验研究了不同起伏振动工况和流动工况对倾斜圆管通道内单相水摩擦压降的影响,提出了方便计算的振动摩擦阻力系数。结果表明,振动摩擦压降大于稳定状态的,并呈周期性波动,波动周期与振动频率一致。振动摩擦阻力系数平均值随雷诺数和倾角的增大而减小,随管径和振动频率的增大先增大后减小,随振幅的增大而增大。通过实验数据拟合得到起伏振动下倾斜管内单相水振动摩擦阻力系数计算经验关系式,计算结果与实验结果吻合较好,为起伏振动单相水流动阻力的计算提供了新思路。     

起伏振动下倾斜管内单相流流动阻力特性分析

起伏振动状态下单相流流动阻力的正确计算对漂浮核电站的安全性有显著影响。实验研究了不同起伏振动工况和流动工况对倾斜圆管通道内单相水摩擦压降的影响,提出了方便计算的振动摩擦阻力系数。结果表明,振动摩擦压降大于稳定状态的,并呈周期性波动,波动周期与振动频率一致。振动摩擦阻力系数平均值随雷诺数和倾角的增大而减小,随管径和振动频率的增大先增大后减小,随振幅的增大而增大。通过实验数据拟合得到起伏振动下倾斜管内单相水振动摩擦阻力系数计算经验关系式,计算结果与实验结果吻合较好,为起伏振动单相水流动阻力的计算提供了新思路。     

摇摆运动下矩形窄通道内流动沸腾阻力特性

本工作对摇摆运动下水在矩形窄通道内流动沸腾阻力特性进行实验研究分析。一方面利用竖直静止实验数据对已有两相压降的计算方法进行评价,结果表明,应用于常规通道的关系式已不适用于窄通道中流动沸腾压降的计算,基于窄通道的Zhang-Mishima及Sun-Mishima关系式预测结果与实验值符合较好;另一方面得出了摇摆运动下流动沸腾阻力特性,摇摆运动使两相压降周期性波动,但摇摆角度和摇摆周期对压降的波动幅度、两相平均摩擦压降几乎无影响。     

棒束通道内定位格架的两相流动局部阻力实验研究

在常温、常压条件下,对竖直3×3棒束通道内定位格架的单相及两相局部阻力特性进行了实验研究。单相流动实验时,水雷诺数的变化范围为290~18 007;两相实验时,气相、液相表观速度变化范围分别为0.013~3.763m/s和0.076~1.792m/s。利用单相实验数据得到的定位格架局部阻力系数计算关系式,用两相实验数据对均相流模型中8种不同的两相等效黏度计算方法进行了评价。Rel9 000时,Dukler模型的预测效果最好;Rel≥9 000时,McAdams计算方法预测效果最好;基于所有数据,Dukler模型的计算值与实验值吻合最好,平均相对误差为29.03%。考虑了质量含气率、两相雷诺数及气液相密度的影响,对Rel9 000时的实验数据进行了拟合,得到的经验关系式的计算值与实验值符合较好。     

Studies on diversion cross-flow between two parallel channels communicating by a lateral slot. I: Transverse flow resistance coefficient

In this investigation, pressure-induced cross-flow between two parallel single-phase flows communicating by a long lateral slot has been studied. The analysis of experimental data on the transverse resistance coefficient, K, defined by , has shown that this coefficient is mainly a function of the ratio of the lateral flow velocity to the donor channel axial velocity, of the recipient channel axial velocity and of the gap clearance and thickness of the slot. Its variation with different parameters is given graphically.     

Experimental investigations on single-phase heat transfer enhancement with longitudinal vortices in narrow rectangular channel

Four pairs of rectangular block as longitudinal vortex generators (LVG) were mounted periodically in a narrow rectangular channel to investigate fluid flow and convective heat transfer respectively in the narrow rectangular channel with LVG and without LVG. Both the channels have the same narrow gap (d) = 3 mm, the same hydraulic diameter (D_h) = 5.58 mm and the same length to diameter ratio (L/D_h) = 80.65. The experiments were performed with the channels oriented uprightly and uniform heat fluxes applied at the one side of the heating plate and single-phase water was used as test fluid. The parameters that were varied during the experiments included the mass flow rate, inlet liquid temperature, system pressure, and heat flux.In each of the experiments conducted, the temperature of both the liquid and the wall was measured at various locations along the flow direction. Based on the measured temperatures and the overall energy balance across the test section, the heat transfer coefficients for single-phase forced convection have been calculated. At the same time, in these experiments, the single-phase pressure drop across the channels was also measured. The correlations have been developed for mean Nusselt numbers and friction factors. Additionally, the visual experiments of infrared thermo-image recording the temperature on the outer wall of the heating plate have been conducted for validating the effects of LV.In these experimental investigations, both laminar regime and turbulent regime were under the thermo-hydraulic developing conditions, laminar-to-turbulent transition occurred in advance with the help of LV when Reynolds numbers vary between 310 and 4220. In laminar regime, LV causes heat transfer enhancement of about 100.9% and flow resistance increase of only 11.4%. And in turbulent regime, LV causes heat transfer enhancement of above 87.1% and flow resistance increase of 100.3%. As a result, LV can obviously enhance heat transfer of single-phase water, and increase flow resistance mildly.     

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％。     

Steady-state performances and scaling analyses for an open flashing-driven natural circulation system

Simulating investigations are carried out to study the steady-state performances, the pressure resistance distributions and the scaling methods of the single-phase and flashing-induced two-phase flow in the open natural circulation system, which is designed for the passive containment cooling system. The results show that the steady-state mass flow rate changes with the heat transfer regularly both in the single-phase and flashing-induced two-phase flow under a certain inlet subcooling. From the sensitivity analysis, it can be found that the riser height only has impact on the single-phase flow but has little influence on the flashing-driven two-phase flow. Both increasing the diameters of the riser and downcomer can enhance the flow and heat transfer in sing-phase and two-phase flow when keeping the structure of the heat exchanger unchanged, but the influence degree for each flow type is different. The flow resistance distributions of the loops under different flow modes have been studied to provide the foundation for improving the heat transfer capacity by choosing the structural parameters reasonably. The pressure resistance distribution of the steady single-phase flow only relates to the geometrical, but the pressure resistance distribution of the two-phase flow relates both to the pipe diameters and to the external conditions. The acceleration pressure resistance in the riser section is the main resistance under the higher-quality two-phase conditions. Therefore, the influence of the riser diameter on the flashing-induced two-phase flow is far greater than that of downcomer diameter and the most effective method to improve the two-phase flow and heat transfer is to increase the diameter of the riser. Finally, the scaling analysis is performed for the penetration and economy considerations after selecting the optimal dimensions. The scaling of the cold and hot sections is considered separately to insure the driven force of the system unchanged, and different scaling criterions are given for the single-phase and flashing-induced two-phase flow according to the analyses of the pressure resistance distributions. The results show that the scaling criterion of the two-phase flow can deal with the scaling problem accurately both in the single-phase and two-phase flow. However, the scaling criterion of the single-phase flow only can solve the single-phase scaling problem, but it will overestimate the operating results in the scaling model.     

棒束通道单相和两相交混模型评估

本研究利用子通道程序,基于已有的实验数据,对棒束通道的单相和两相交混模型进行了评估。单相交混主要考虑横流和湍流交混,横流由守恒方程决定并在流量分布中占主导作用,湍流交混取决于交混系数,对湍流交混研究发现Sadatomi模型预测结果与实验结果吻合较好。两相交混由横流、湍流交混和空泡漂移共同作用,通过已有模型预测结果与实验数据对比分析,推荐两相交混中空泡漂移采用Hotta模型、湍流交混系数采用Sadatomi模型和两相乘子采用Beus模型,这是一个预测结果较为保守的组合模型,有利于反应堆安全的保守性评估。      

矩形窄缝通道内水稳态和瞬态流动换热特性实验

以去离子水为工质,在压力0.5～5.0 MPa的范围内,对矩形窄缝通道内水稳态及瞬态流动换热特性进行了实验研究。结果表明:矩形窄缝通道在水平和竖直放置以及稳态和瞬态条件下,水的流动换热特性呈现出基本相同的规律。层流向紊流过渡区域的雷诺数(Re)为900Re1300,比常规通道提前,单相摩擦阻力系数比常规通道大;采用Dittus-Boelter公式的形式拟合得到了新的换热实验关联式,其系数较Dittus-Boelter公式的系数约小11.3%。在稳态条件下,紊流区换热系数随质量流速的增加而增大,增大趋势比较明显;换热系数随热流密度的变化不明显;压力对单相强迫对流换热特性基本没有影响。     

中国先进研究堆矩形通道流场数值计算分析

通过SIMPLE数值方法,编制程序,对中国先进研究堆(CARR)全流道进行流场数值模拟.采用对CARR的单个冷却剂通道进行单相水的数值传热计算,并递增地改变流道入口流速,计算获得与入口流速对应的流道速度场与温度场分布,展现其变化规律,分析入口流速对流道热工水力参数分布的影响.采用所编制的程序,对板式燃料组件构成的窄矩形通道进行数值模拟,由此来确定热工水力设计需要的一些反应堆安全参数.这些安全参数为反应堆事故监测系统提供必要的热工过程状态信息,也为CARR提供必要的数据参考.     

Flow Transition Characteristics in 5×5 Rod Bundle Channel

The special geometric structure of the rod bundle channel can induce complicated flow transition of the coolant, and investigation on the flow transition rules is sufficiently important. In the current study, experimental and numerical study on the flow transition characteristics in the 5×5 rod bundle channel was carried out. Experiments were performed to obtain the variation characteristics of the resistance coefficient and CFD simulation was performed using different turbulence models in ANSYS Fluent. The results show that the simulation with SST k-ω turbulence model agrees well with the experimental data. The simulated turbulence intensity and resistance coefficient at different measurement locations and in different flow conditions were compared. For different subchannels, the turbulence intensity and the resistance coefficient are higher in the center subchannel than those in the edge subchannel. For the same subchannel, the turbulence intensity and the shear stress in the subchannel center are higher than those in the subchannel edge. This result indicates that the turbulence intensity, shear stress and resistance coefficient in the rod bundle are not uniform due to the influence of the wall surface. This non-uniform spatial interaction makes the transition point obscure.