碳纤维复合材料薄壁圆筒的轴向导热系数测试

碳纤维复合材料薄壁圆筒为各向异性导热,其轴向导热系数是筒体温度场理论计算、成型工艺优化的重要参数。碳纤维复合材料圆筒由于较小的截面面积给筒体加热、热量有效传递带来了较大困难。本文以平板材料导热系数的稳态法测试国家标准为基础,基于傅里叶一维稳态导热原理,设计了一套用于薄壁圆筒轴向导热系数测试的装置,采用双试件对称加热、辐射换热防护及热对流环境控制等实现了热量沿筒体轴向的有效传导,利用该装置对导热系数已知的铝筒进行测试,验证了该装置设计的可行性,得到了碳纤维复合材料薄壁圆筒的轴向导热系数为（4.60±0.13） W/(m•K)。     

Transient thermal stresses in a composite hollow cylinder subjected to γ-ray heating

Transient temperature and thermal-stress distributions arising in an infinite long composite hollow circular cylinder subjected to internal heat generation decaying exponentially along the wall thickness resulting from γ-ray radiation are analyzed, under the thermal conditions of cooling by convection on the inner surface and insulation on the outer surface. Numerical calculations of the transient temperature and thermal-stress distributions are carried out for the case of a composite cylinder of stainless steel and carbon steel. The influence of the absorption coefficient, the Biot number and the splicing radius on the results are considered.     

Transient thermal stresses in a bonded composite hollow circular cylinder under symmetrical temperature distribution

A general treatise for the transient thermal stress problem of a composite circular cylinder made by bonding is described under a symmetrical temperature distribution. Analysis is developed by stress function method by the aid of Laplace transforms. Numerical examples are illustrated for the hollow composite cylinder with several radius-ratios made by the different materials due to transient heating at the internal surface by liquid.     

Thermal stress in a bimodulus thick cylinder

Certain materials are known to behave differently under tension and compression. This reports an investigation of a simple thermal stress problem based on the bimodulus elasticity in the framework of the classical-type uncoupled thermoelasticity. Because of an unavoidable complexity of three-dimensional analysis in bimodulus elasticity, as a fundamental illustration we consider herein an axisymmetric plane strain state of a thick orthotropic circular cylinder under axisymmetric heat conditions. A system of transcendental simultaneous algebraic equations with respect to eight unknowns are derived. Numerical analyses are carried out for a steady-state temperature field and for a quasi-stationary state with internal heat generation. Results of calculations show that the states of a cylinder are affected significantly by the difference between tensile and compressive moduli of elasticity.     

Length effects of unsteady thermal stresses in a finite short circular cylinder with an arbitrary heat supply

An unsteady thermoelastic study, taking consideration of the length effects, was made of a finite short circular cylinder under an arbitrary heat supply along its cylindrical surface in the longitudinal direction. The analysis was treated by the thermoelastic potential method using a general form of the Love's displacement function which has not so far been used. The results obtained were compared with those of an approximate solution for the finite cylinder using Saint-Venant's principle. From the results the effects of the length-to-diameter ratio evidently appear in the transient thermal stress distributions for the finite short cylinder.     

微细化沸腾传热实验研究

气泡微细化沸腾是沸腾到达某个临界热负荷后,加热面温度升高不大,与该临界热负荷相比,热流密度大幅提高的沸腾现象。本文在设计完成一可视化实验装置的基础上,通过高速摄影仪观察并结合采集的壁温数据,对常压下直径为10 mm铜加热面上的池式气泡微细化沸腾现象进行了研究,并讨论了液体过冷度对其的影响。实验发现,气泡微细化沸腾状态下,加热面上生成1层极其不稳定的气膜,气液交界面上不停地有大量微小气泡生成并以极高速度射入过冷液体中。随加热面热流密度的增大,气膜厚度波动周期缩短,气膜最大厚度减小,所生成微小气泡的直径也明显减小。实验中获得的最高热流密度达9 MW/m²。     

Analytical Modelling of Overpack of Enriched Uranium Hexafluoride Package in a Fire Event

Abstract

A fissile package must be subjected to a fire test at 800°C for 30 min. For a package that contains enriched uranium hexafluoride (UF₆), the temperature of the contents has to be kept below 121°C in order to avoid rupture of the 30B cylinder. A previous study on heat transfer mechanisms in an enriched UF₆ package type ‘DOT-21PF-1’ found that decomposed gas with a temperature of around 100°C generated from heated penolic foam thermal insulator was a major heat source heating the cylinder in the initial period of the fire test, in addition to the heat conducted from the outer surface through the thermal insulator into the interior of the package. Mitsubishi Materiass Corporation has developed a new packaging for enriched UF₆ ‘MST-30’ that also uses phenolic foam as the thermal insulator, and has pelformdd a fire test at 800°C for 30 min, which also indicated the temperature history of the package interior affected by heating from the decomposed gas. In this study, a laboratory test was carried out to identify the kind of gas generated from the heated phenoiic foam. The test found that the decomposed gas was water vapour. Since water vapour has a large latent heat, it has a large heat transfer coefficient when it condenses on a cool surface. By taking the water vapour heating mechanssm into account, an analytical model was developed for MST-30 to simulate the measured cylinder temperature history. Analytical models for evaluaiing the cylinder temperature under the 800°C/30 min fire test considering conservativeness are also presented.     

核废物自热升温过程数学模型研究

获得了核衰变热源圆柱体传热方程第三类边值问题的解释式解。进行了各种工艺条件对升温过程影响的理论计算研究,得到了一些有价值的结果。为现场工艺设计和预测提供了必要的理论根据。     

氢气-空气混合气体燃烧特性试验分析

为了保证严重事故下安全壳的完整性,氢气点火器燃烧缓解措施被广泛应用于核电站内。本文在1个20m3立式圆柱罐体内进行9.28%浓度下的氢气燃烧试验,结合GASFLOW数值模拟和其他试验数据,对本次试验结果进行了综合分析。试验和模拟结果均表明:9.28%浓度下氢气完全燃烧,罐体内温度和压力快速增加;燃烧过程中罐体内高温气体通过辐射传热、对流换热和相变传热3种方式向罐体结构散热,使得罐体内温度和压力随时间逐渐降低,达到泄压和冷却的作用;燃烧过程有明显的方向性,即点燃后火焰在浮力作用下沿罐体中心线向上传播,到达顶部后转而沿罐体四周向下燃烧,燃烧初期火焰速度为11.15m/s;试验中由于内部构件的影响,火焰传播更为复杂。     

Transient thermal stresses in a finite solid circular cylinder due to a cylindrical surface heat source over the lateral surface

An exact solution is given for the determination of transient thermal stresses in a traction-free, finite solid, circular cylinder subjected to a cylindrical surface heat source over the lateral surface and having a heat loss to a surrounding medium over the entire boundary surface. The problem is formulated in terms of thermo-elastic displacement potential and Love's function, and the solution rigorously satisfies traction-free boundary conditions on both the lateral and end surfaces of the cylinder.

The problem is of considerable technological importance, particularly to certain nuclear reactor analyses related to the behavior of fuel elements and control rods during power transients.

Numerical calculations are carried out for various combinations of Biot's number and the ratio of length to diameter of the cylinder. The results obtained are compared with those of an infinite, solid, circular cylinder and of a solid circular disc.     

Natural convection heat transfer from a horizontal cylinder in liquid sodium: Part 2: generalized correlation for laminar natural convection heat transfer

Rigorous numerical solution of natural convection heat transfer, from a horizontal cylinder with uniform surface heat flux or with uniform surface temperature, to liquid sodium was derived by solving the fundamental equations for laminar natural convection heat transfer without the boundary layer approximation. It was made clear that the local and average Nusselt numbers experimentally obtained and reported in part 1 of this paper were described well by the numerical solutions for uniform surface heat fluxes, but that those for uniform surface temperatures could not describe the angular distribution of the local Nusselt numbers and about 10% underpredicted the average Nusselt numbers. Generalized correlation for natural convection heat transfer from a horizontal cylinder with a uniform surface heat flux in liquid metals was presented based on the rigorous theoretical values for a wide range of Rayleigh numbers. It was confirmed that the correlation can describe the authors’ and other workers’ experimental data on horizontal cylinders in various kinds of liquid metals for a wide range of Rayleigh numbers. Another correlation for a horizontal cylinder with a uniform surface temperature in liquid metals, which may be applicable for special cases such as natural convection heat transfer in a sodium-to-sodium heat exchanger etc. was also presented based on the rigorous theoretical values for a wide range of Rayleigh numbers. These correlations can also describe the rigorous numerical solutions for non-metallic liquids and gases for the Prandtl numbers up to 10.     

Film boiling heat transfer from a vertical cylinder in forced flow of liquids under saturated and subcooled conditions at pressures

Forced convection film boiling heat transfer on a vertical 3-mm diameter and 180-mm length platinum test cylinder located in the center of the 40-mm inner diameter test channel was measured. Saturated water, and saturated and subcooled R113 were used as the test liquids that flowed upward along the cylinder in the test channel. Flow velocities ranged from 0 to 3 m s⁻¹, pressures from 102 to 490 kPa, and liquid subcoolings for R113 from 0 to 60 K. The heat transfer coefficients for a certain pressure and liquid subcooling are almost independent of flow velocity and of a vertical position on the cylinder for the flow velocities lower than ≈1 m s⁻¹ (the first range), and they become higher for the velocities higher than ≈1 m s⁻¹ (the second range). Slight dependence on a vertical position being nearly proportional to z^−1/4, where z is the height from the leading edge of the test cylinder, exists for the flow velocities in the second range. The heat transfer coefficients at each velocity in the first and second ranges are higher for higher pressure and liquid subcooling. Correlation for the forced convection film boiling heat transfer with radiation contribution on a vertical cylinder was derived by modifying an approximate analytical solution for a two-phase laminar boundary layer model to agree better with the experimental data. It was confirmed that the experimental data of film boiling heat transfer coefficients in water and R113 were described by the correlation within ±20% difference.     

Evaluation of heat transfer by sublimation for the application to the divertor heat sink for high fusion energy conversion

Thermal and structural responses of divertor target were evaluated by using finite element method. High heat flux simulating ELMs at the level of 100 MW/m² was assumed onto the tungsten armor, and surface temperature profile was obtained. When dynamic heat load over 100 MW/m² was applied, the maximum surface temperature exceeded 1300 °C, and it caused recrystallization of tungsten regardless of the heat transfer below it. The result was used to conduct dynamic heat load experiment on tungsten, and material behavior of tungsten was evaluated under dynamic heat load. This study also proposed new concept of divertor heat sink which can distribute high heat flux and transfers the heat to high temperature medium. It consists of tungsten armor, composite enhanced with high thermal conductivity fiber, and heat transport system applying phase transition. High heat flux simulating ELMs was also applied to target surface of the divertor, temperature gradient, thermal stress of tungsten and composite were evaluated. Based on the results of analysis, thermal structural requirement was considered.     

Induced Activity and Dose Rate in a Fusion Reactor with Molybdenum Blanket Structure

Flow around a circular, square and trapezoid-type turbulence promoter was studied putting it in a center of channels or on a wall for low Reynolds number. Frequencies and power spectrum intensities of shedding vortices behind a promoter were measured.

Results show that vortices behind the trapezoid cylinder were the strongest and the widest. Flow characteristics behind the trapezoid cylinder were similar to that behind the circular cylinder. Vortices behind the square cylinder were the weakest and the narrowest. Adequate shape of turbulence promoter for augmentation of heat transfer was discussed.     

Simplified method to evaluate upper limit stress intensity factor range of an inner-surface circumferential crack under steady state thermal striping

Simplified method to evaluate the upper limit stress intensity factor (SIF) range of an inner-surface circumferential crack in a thin- to thick-walled cylinder under steady state thermal striping was considered in this paper. The edges of the cylinder were rotation-restrained and the outer surface was adiabatically insulated. The inner surface of the cylinder was heated by a fluid with constant heat transfer coefficient whose temperature fluctuated sinusoidally at constant amplitude ΔT. By combining our analytical temperature solution for the problem and our semi-analytical-numerical SIF evaluation method for the crack, we showed that the desired maximum steady state SIF range can be evaluated with an engineering accuracy after ΔT, the mean radius to wall thickness ratio r_m/W of the cylinder, the thermal expansion coefficient and Poisson's ratio are specified. By applying our method, no transient SIF analysis nor sensitivity analysis of the striping frequency on the SIF range is necessary. Numerical results showed that our method is valid for cylinders in a range of r_m/W = 10–1.     

Experimental investigation of pebble beds thermal hydraulic characteristics

The purpose of this paper is to present the results of the experimental investigation of the thermal hydraulic characteristics for two types of test sections—thin annular pebble beds (i.e. spheres dumped in thin annular slots) and pebble beds placed between cylinders. The experimental results of heat transfer from the spheres and from a cylinder, as well as hydraulic drag for both types of test sections are presented in this paper. The results of performed experiments in the case of thin annular pebble beds demonstrated that maximum heat transfer and hydraulic drag is at the relative width of the annular slot K equal to 1.07 and 1.75 of spheres diameter. The heat transfer in internal layers at these values of K is equal to the heat transfer in the internal layers of large (unlimited) rhombic packing. The results of the experimental investigation of pebble beds between cylinders demonstrated that the randomly arranged pebble bed is preferable to the regular rhombic structure from the point of view of design simplicity, heat transfer from the cylinder and drag coefficient.     

A turbogenerator designed for atomic electro-stations

The basic type of atomic electrogenerating station should be the heat and power central station, since it allows good fuel economy, utilizing the fuel not only for generation of electricity but for heating of buildings and supply of hot water. This is very important in areas that are short of fuels. The existing type of heat extraction turbogenerator with adjustable steam extraction and condensation, does not provide constant loading of the reactor, and therefore its use in an atomic central station is not justifiable. In view of this, a new type of heat extraction turbogenerator for these stations is proposed, incorporating constant steam flow through the high pressure cylinder. The quantity of steam flowing to the low pressure cylinder of the turbine varies with the demand for steam. When there is no demand for heat the steam flow through the two cylinders is equal. The proposed turbogenerator has variable power output, which with no steam extracted, increases 38 to 69% over the output of existing types, depending on the initial steam conditions. This turbogenerator insures a constant load on the reactors.     

余热排出系统中的热管设计及传热性能研究

本文建立了单根热管的优化设计流程及其传热传质数学物理模型,考虑热管的工作环境,对用于核反应堆非能动余热排出系统中热管换热器的热管进行了完整的优化设计和传热特性分析。分析表明：复合型吸液芯热管满足余热排出系统的传热需求,其传热功率主要受热管毛细极限、沸腾极限及总热阻的影响。相同吸液芯厚度下,复合型吸液芯热管的毛细极限较单一丝网吸液芯热管的毛细极限提高100%～700%。改变热管的外径或吸液芯厚度,即蒸气腔直径减小,沸腾极限明显减小。当单根热管传热功率大于1 kW时,热管各段长度分别为0.4、0.2、0.4 m,外径为30 mm,吸液芯是厚度为2 mm的400目+50目复合型丝网结构。本文为高性能的热管换热器设计及传热特性分析提供了理论支撑。     

Numerical simulation of cylinder oscillation by using a direct forcing technique

Fluid-structure interaction (FSI) is an important safety issue of nuclear components such as reactor vessel internals, heat exchangers, steam generators and piping, etc. For instance, when continuous repetitive flow is rapidly exerted on cylinders, resulting oscillation induces high vibration that may lead to fretting wear on the contact surface of cylinder. In the present research, to assess vibration characteristics of cylinders in fluidic channels, a modified immersed finite element method (IFEM) is developed by using a direct forcing technique coupled with cylinder oscillation. Then, this method is tested for an elastically mounted cylinder in still fluid or subjected to uniform inlet fluid flow and further a simple tube bundle to examine effects of vibration-related parameters.     

Transient thermal stresses and displacements in a transversely isotropic semi-infinite circular cylinder subjected to an arbitrary surface heat generation and a convective heat loss

The transient thermal stresses and displacements in a traction-free, transversely isotropic, semi-infinite circular cylinder subjected to a convective heat loss on the end surface is analyzed by means of a set of stress functions and a generalized Fourier-integral representation for exponential function.The purpose of this paper is to present the results of theoretical analysis which considers the effects of the thermal and elastic anisotropes of the material properties on the thermal stresses and displacements in the transversely isotropic, semi-infinite circular cylinder due to an arbitrary cylindrical surface heat generation.A detailed numerical result of the thermal stresses and displacements is given for various values of the ratios of the thermal conductivity coefficients, Young's moduli and linear thermal expansion coefficients in the axial and radial directions and it is demonstrated that the sensivity of the maximum stress and displacement to the anisotropy of the thermal conductivity coefficient is significant.