高温堆热气联箱内部流场分析

以高温堆热气联箱为研究对象,在实验研究的基础上,采用流体力学计算程序CFX5对热气联箱和热气导管内部流场进行了数值模拟,以获得热气联箱和热气导管内的速度场、压力场和温度场,为高温堆热气联箱的设计和实验研究提供参考.数值计算结果表明:热气联箱内气流发生剧烈搅混,加速了不同温度气流间的热传递,有利于高温和低温气流间的温度混合.但存在肋片的区域没有发生剧烈的气流搅混,不利于气流间的热传递.热气导管内温度混合率随其长度的增加逐渐增大,热气导管长度2.5m以上时,温度混合率达到99%以上.     

高温气冷堆热气联箱内部流场数值模拟

以高温气冷堆热气联箱为研究对象，在实验研究基础上，采用流体力学计算程序CFX5对热气联箱和热气导管内部流场进行数值模拟，以获得热气联箱和热气导管内的速度场、压力场和温度场，为高温气冷堆热气联箱的设计和实验研究提供参考。数值计算结果表明：热气联箱内气流发生剧烈搅混，加速了不同温度气流间的热传递，有利于高温和低温气流间的温度混合，存在肋片的区域未发生剧烈的气流搅混，不利于气流间的热传递；热气导管内温度混合率随其长度的增加逐渐增大，当热气导管长度为2.5m以上时，温度混合率达到99％以上。     

Numerical investigations of thermal mixing performance of a hot gas mixing structure in high-temperature gas-cooled reactor

A numerical simulation study was performed to clarify the thermal mixing characteristics of coolant in the core bottom structure of the high-temperature gas-cooled reactor(HTR). The flow field and temperature field in the hot gas chamber and the hot gas duct of the HTR were obtained based on the commercial computational fluid dynamics(CFD) program. The numerical simulation results showed that the helium flow with different temperatures in the hot gas mixing chamber and the hot gas duct mixed intensively, and the mixing rate of the temperature in the outlet of the hot gas duct reached 98 %. The results indicated many large-scale swirling flow structures and strong turbulence in the hot gas mixing chamber and the entrance of the hot gas duct, which were responsible for the excellent thermal mixing of the hot gas chamber and the hot gas duct. The calculated results showed that the temperature mixing rate of the hot gas chamber decreased only marginally with increasing Reynolds number.     

Numerical Investigation of Channel for Helium Cooled China HCCB-TBM First Wall by Application Enhance Heat Transfer Method

To enhance heat transfer efficiency on first wall (FW) of ITER China Helium-Cooled Ceramic Breeder-Test Blanket Module (HCCB-TBM), CFD numerical simulation method is adopted. On the basis of calculating helium gas cooling scheme of FW smooth channel, FW structural temperature gradient, maximum wall temperature, average heat transfer coefficient, and pressure drop of channel are selected as evaluation indexes. Numerical simulation comparison are performed on heat transfer schemes like placing transversal ribs and V-shaped ribs in the flow channel of front wall and the helium gas turbulence intensity and the heat transfer area are improved through optimizing the distance and angle between V-shaped ribs and other parameters to enhance heat transfer. The optimization scheme of helium-cooled FW for HCCB-TBM through the three dimensional numerical simulation is: V-shaped ribs are placed on the inner surface of front wall, the rib cross section is 1 mm × 1 mm, the distance between rib pitches is 10 mm and the rib angle is 60°. Under the same helium cooling condition, compared with the FW smooth channel, the optimized V-shaped rib scheme enhances the average heat transfer efficiency by about 70 % and the FW maximum temperature drops by 349.3 K. The result provides support for further research on FW helium cooling heat transfer enhancement experiment and engineering design optimization for China HCCB-TBM.     

CFD analysis on subcooled boiling phenomena in PWR coolant channel

Eulerian two-fluid model coupled with wall boiling model was employed to calculate the three dimensional flow field and heat transfer characteristics in a hot channel with vaned spacer grid in PWR. The heat transfer from pellet-gap-cladding to coolant was also taken into account by a system coupled code MpCCI. The wall boiling model utilized in this study was validated by Bartolomei experiment data, and a good agreement can be observed. By solving the governing equation in a two-way coupled method, the distribution of temperature in the pellet-gap-cladding region and the distribution of temperature, void fraction and velocity of two-phase flow in coolant channel can be obtained. The influences of spacer grid and mixing vane on the thermal-hydraulic characteristics were analyzed. The heat transfer capacity was strongly improved by the spacer grid and mixing vane, while the flow resistance was also enlarged. Localized volume fraction of vapor phase decreased due to mixing vane, which will decrease the possibility of the departure from nucleate boiling (DNB) and increase the critical heat flux (CHF). By analyzing the temperature and void fraction at cladding outer surface, the critical regions where hot spot may occur were determined.     

Thermal and hydraulic tests of test sections in the helium engineering demonstration loop

The helium engineering demonstration loop (HENDEL) has been constructed and operated to test the large-scale components of the high temperature engineering test reactor (HTTR) under simulated reactor operating conditions. The fuel stack test section (T₁) of HENDEL simulates the fuel stack of the HTTR core and is used to investigate thermal and hydraulic performance. Hot tests with 1000°C helium gas have been conducted using simulated fuel rods having uniform, exponential and cosine axial heat flux distributions. The test results agreed with previously proposed correlations, although the simulated fuel rods had various heat flux distributions and high heat flux rates.

The in-core structure test section (T₂) also was installed in the HENDEL to verify the performance of the core bottom structure of the HTTR. The tests show that good performance was obtained. Examination of the thermal mixing characteristics indicated that mixing started at the location where the hot helium gas flowed into the hot plenum and that complete mixing was achieved during the downward flow in the outlet hot gas duct. The seal performance testing indicated no change of the leakage flow rate after 4000 hours of operation. The temperature of the metal portion of the structure was below 500°C and uniform around circumferential cross-sections due to the good performance of the thermal insulation blocks.     

Simulating test for thermal mixing in the hot gas chamber of the HTR-10

The helium coolant at the outlet of the pebble bed core of the 10 MW High Temperature Gas-cooled Reactor-Test Module exhibits a severe radial temperature deviation. In order to avoid damages at the downstream components due to alternating thermal loads such as the steam generator, a hot gas chamber is especially designed to solve the problem. Thermal mixing performance of the coolant in the hot gas chamber is experimentally investigated on a 1:1.5 scale model by air. The experimental result shows that within the Reynolds number range of 1.4×10⁵–5.8×10⁵, the hot gas chamber with a radial mixer reaches excellent thermal mixing of the coolant of about 94%. The flow resistance coefficient for the hot gas chamber is also presented.     

HTR-PM堆芯出口热气混合实验相似性分析

球床模块式高温气冷堆核电站（HTR-PM）堆底设有热气混合结构，使堆芯流出的氦气混合均匀。堆芯出口热气混合实验用于测量和分析该混流结构的混合性能及其阻力特性。为使设计的热气混合实验系统及实验工况能反映HTR-PM的混流结构的实际混合性能和阻力特性，在确保实验经济成本的前提下，根据相似性准则，分析确定了堆芯出口热气混合实验系统的设计准则和具体参数，并利用Fluent软件对所设计的实验装置内的流场和温度分布进行了数值模拟。该混合实验系统及其工况与HTR-PM实际堆底混流结构具有相似性，在此实验的基础上，可通过理论分析和数值模拟得到HTR-PM实际堆底混流结构的混合性能和阻力特性。     

基于CFD方法的高温热管特性研究

高温热管运行特性的分析与预测,对热管设计和应用具有重要意义。为分析高温热管内两相流动传热特性,首先建立钠热管的计算流体力学（CFD）分析模型,并对模型计算值与钠热管稳态实验数据进行对比校核,模拟结果与实验测点温度的绝对误差小于40℃,相对误差在5%以内;其次,利用本文模型与方法对不同传热功率和倾角下的热管内部流场特性进行分析研究。研究表明,均匀加热条件下,蒸气腔内的速度在蒸发段接近线性变化,而在冷凝段,气体流速减小致使压强回升,同时,蒸气的流动压降和速度随加热功率增加呈下降趋势;在热管水平和倾角运行工况,热管内两相流动压降中液相压降均占主导;而气液间剪切效应中,气体流动速度为主导效应。本文模型可为热管堆等高温热管应用领域提供热管设计与分析方法。      

高温气冷实验堆堆芯出口热气联箱混合性能对比试验

１０ＭＷ高温气冷实验堆堆芯出口冷却剂温度径向分布很不均匀，若不使之均匀化，将造成蒸汽发生器件部上过大的热应力，设置在堆底反射层中的堆芯出口热气联箱的作用之一是使冷却剂氦气在其中得到充分的热混合。     

HL-2M偏滤器热氮气烘烤仿真及优化

为提供高质量的等离子体真空运行环境,需对偏滤器进行高温烘烤。根据热传导与对流换热方程对偏滤器的烘烤过程进行了数值模拟及优化。结果表明:当热氮气等质量流量控制时,偏滤器回路压力损失逐渐增大,各部件烘烤温度爬升速率呈线性增加;当热氮气等体积流量控制时,偏滤器回路压力损失逐渐降低,各部件烘烤温度爬升呈线性增加。当初始条件近似相等(等质量流量为3×10~(-3)kg/s和等体积流量为4.8×10~(-4)m~3/s)时,前者的部件温升速率略低于后者,但各部件烘烤过程中最大温差均未超过90℃。     

不凝性气体对高温锂热管传热特性的影响研究

热管作为一种具有高热导率的传热装置,工作核心在于其内部工作流体的蒸发和冷凝。若热管工作过程中气腔内存在不凝性气体,主流区中蒸气和不凝性气体在对流运动的作用下将一起移动到气-液分界面,不凝性气体的存在阻碍了工作流体在气-液交界面处的正常冷凝。本文基于热阻网络法添加了不凝性气体区域传热模型,研究了不凝性气体对高温锂热管稳态传热特性的影响。结果表明,热管达到稳态时不凝性气体的存在缩短了热管的有效传热长度,破坏了热管的等温性和良好的传热效率。此外随着不凝性气体体积份额的增大,不凝性气体区域温度降低幅度越大;随着热管蒸发段输入功率的增大,热管正常工作区域整体温度越高,相同质量的不凝性气体占据的体积份额越小,热管壁面温度出现明显温度梯度降低的位置随着功率升高而向下游移动。     

Simulation tests for temperature mixing in a core bottom model of the HTR-Module

Interatom and Siemens are developing a helium-cooled Modular High Temperature Reactor. Under nominal operating conditions temperature differences of up to 120°C will occur in the 700°C hot helium flow leaving the core. In addition, cold gas leakages into the hot gas header can produce even higher temperature differences in the coolant flow. At the outlet of the reactor only a very low temperature difference of maximum ±15°C is allowed in order to avoid damages at the heat exchanging components due to alternating thermal loads. Since it is not possible to calculate the complex flow behaviour, experimental investigations of the temperature mixing in the core bottom had to be carried out in order to guarantee the necessary reduction of temperature differences in the helium. The presented air simulation tests in a 1:2.9 scaled plexiglass model of the core bottom showed an extremely high mixing rate of the hot gas header and the hot gas duct of the reactor. The temperature mixing of the simulated coolant flow as well as the leakage flows was larger than 95%. Transfered to reactor conditions this means a temperature difference of only ±3°C for the main flow at a quite reasonable pressure drop. For the cold gas leakages temperature differences in the hot gas up to 400°C proved to be permissible. The results of the simulation experiments in the Aerodynamic Test Facility of Interatom permitted to design a shorter bottom reflector of the core.     

高温氦氙气体微通道回热器的传热流动特性分析

以氦氙气体作为工质的闭式布雷顿循环系统是大功率空间热电转换目前最可行的技术方案。高温氦氙气体回热器是闭式布雷顿循环系统的关键部件,其性能明显影响系统发电效率、系统发射质量以及系统布置的紧凑性。本文采用计算流体力学和传统理论分析方法,针对高温氦氙气体微通道的结构及成型工艺选择、工作温度与回热器回热度的关系、流量与性能参数的关系等进行了研究。研究结果表明,采用精雕工艺作为微通道的成型工艺可在不降低回热器换热性能的前提下降低压降40%,减少质量17%。在设计参数条件下,微通道之间设置联通通道不会增加换热能力。回热器回热度随流量的增加而减小,且存在拐点,对于拟研制回热器的设计参数,设计流量应不高于0.24 g/s。回热器结构合理性用单位压降和温降条件下换热面积与功率的比值来判断,降低雷诺数能有效提高回热器的结构合理性。     

高温气冷堆下联箱热气混合的数值模拟和几何优化

高温气冷堆下联箱用于混合温度不均的堆芯出口气体。已有研究显示,当前下联箱设计方案的气体混合能力尚待提高,由其导致的压力损失则需进一步降低。本文采用数值模拟方法,并对比实验数据,讨论了适用于下联箱几何优化的网格类型和网格规模,通过合并原有的肋片状流道以及扩展热气导管起始端,对下联箱的几何形状进行了优化,并通过对比不同优化方案选出了兼具提升气体混合率和减小压力损失的改进方案。本文的研究结果可为高温气冷堆下联箱的改进设计提供参考依据。     

Evaluation of high temperature gas reactor for demanding cogeneration load follow

Modular nuclear reactor systems are being developed around the world for new missions among which is cogeneration for industries and remote areas. Like existing fossil energy counterpart in these markets, a nuclear plant would need to demonstrate the feasibility of load follow including (1) the reliability to generate power and heat simultaneously and alone and (2) the flexibility to vary cogeneration rates concurrent to demand changes. This article reports the results of JAEA's evaluation on the high temperature gas reactor (HTGR) to perform these duties. The evaluation results in a plant design based on the materials and design codes developed with JAEA's operating test reactor and from additional equipment validation programs. The 600 MWt-HTGR plant generates electricity efficiently by gas turbine and 900°C heat by a topping heater. The heater couples via a heat transport loop to industrial facility that consumes the high temperature heat to yield heat product such as hydrogen fuel, steel, or chemical. Original control methods are proposed to automate transition between the load duties. Equipment challenges are addressed for severe operation conditions. Performance limits of cogeneration load following are quantified from the plant system simulation to a range of bounding events including a loss of either load and a rapid peaking of electricity.     

Experimental investigation on heat transfer characteristics in a safety injection nozzle component in PWR

Thermal fatigue is a potentially significant degradation mechanism in Nuclear Power Plants (NPP). For the fatigue analysis, the thermal load information about components must be determined firstly. In this paper, an experimental study was carried out to obtain local fluid temperatures and local heat transfer coefficients for the safety injection nozzle component in reactor coolant system (RCS). In this mixing tee component a hot jet issues into a cold cross-flow stream from an oblique pipe and the turbulent mixing of two fluids induces local cycling stresses on the adjacent piping wall. Experiments were performed using a special-made heat fluxmeter, which can measure the mixed fluid temperature close to the wall and the heat transfer coefficient between the fluid and the wall. Plexiglass and metallic 1/9-scale mockups were manufactured for flow visualization and heat transfer tests, respectively. All tests were conducted at range of 0–40 for the jet-to-cross-flow velocity ratio. The flow visualization test has obtained general pattern of the flow and identified sensitive zones in the component where the jet and cross-flow interact intensively to cause thermal fatigue more possibly. In the heat transfer test, heat fluxmeters were positioned in the wall at these sensitive zones. The measurement results of temperatures and heat transfer coefficients have been discussed in detail in the paper. These experimental results allow us improving the state of knowledge of the thermal load to be used in the industrial mixing tees in operating for long lifetime assessment and for the design in the basic Nuclear Power Plants.     

Numerical study by large-eddy simulation on effects and mechanism of air-cooling enhancing technologies

ABSTRACT

Learning from the lessons of the Fukushima Daiichi Nuclear Power Station incident in which a long-term station blackout occurred, we have been developing an air-cooling system that can operate without electricity for a virtually indefinite time. We developed air-cooling enhancing technologies by using heat transfer fins, turbulence-enhancing ribs and a micro-fabrication surface. To achieve further improvement of the heat transfer performance, it is important to understand the mechanism of the air-cooling enhancing technologies. In this study, we used numerical analysis to investigate the effects and the mechanism of the developed air-cooling enhancing technologies. We confirmed that the Nusselt number was increased 75% by the heat transfer fins. In the heat transfer enhancement by the turbulence- enhancing ribs, the Nusselt number was increased 43% by the turbulence-enhancing ribs. The enhancement ratio of the Nusselt number by the micro-fabrication surface can be explained by the apparent thermal conductivity. The Nusselt number was increased 4%–8% by adding the micro-fabrication to the surface of the pipe with the turbulence-enhancing ribs. For the combination of the micro-fabrication surface and the turbulence-enhancing ribs, the interaction between the better heat transport in the thermally conductive layer and the mixing effect by the large-scale vortex is the heat transfer enhancement mechanism.     

Research of Arc Chamber Optimization Techniques Based on Flow Field and Arc Joint Simulation

The preliminary design of an arc chamber in the 550 kV SF_6 circuit breaker was proposed in accordance with the technical requirements and design experience.The structural optimization was carried out according to the no-load flow field simulation results and verified by no-load pressure measurement.Based on load simulation results such as temperature field variation at the arc area and the tendency of post arc current under different recovery voltage,the second optimal design was completed and its correctness was certificated by a breaking test.Results demonstrate that the interrupting capacity of an arc chamber can be evaluated by the comparison of the gas medium recovery speed and post arc current growth rate.     

COSINE多相场子通道分析程序的开发与评估

COSINE多相场子通道分析程序基于两流体三相子通道守恒方程,在气液两相的基础上,单独考虑了液滴相的行为,并通过考虑通道间的交混,提高了对压水堆压力容器内的热工水力学现象分析能力及大破口事故的计算能力。本研究介绍了程序的基本模型及求解方法,选取代表性算例及实验工况进行建模计算,验证多相场子通道程序的计算能力。计算结果表明：程序可以对多通道热工水力现象进行模拟计算,计算结果与理论分析相符,程序可以精确模拟堆芯交混及再淹没工况,计算结果与实验数据具有良好的一致性,COSINE多相场子通道程序具备对压力容器内热工水力工况的计算能力。