Numerical Simulation of Casting Explosives in Shell

Predicting interface position of solid-liquid phase change is important for the filling of explosives in the shell. The cooling process of casting charge is discussed analytically and experimentally. The basic equations describing this process are derived from a modified and extended equivalent heat capacity model. Numerical calculations are then performed to determine the solidification front distributions and temperature distributions. The experiments are performed using TNT as the phase change material. Comparison between practical experiments and computer simulation has shown that there is a good agreement. By using computer calculations, a better knowledge of important parameters for the casting process can be easily obtained.     

一种高等温两相闭式热虹吸管的瞬态特性

介绍了一种具有工作阱的两相闭式热虹吸管的结构和特点。通过观察实验,将热虹吸管的启动模型简化为蒸汽温度只随时间变化的非稳态模型,通过数值计算求解热虹吸管内蒸汽随时间的变化关系。将热虹吸管的工作阱作为研究对象,数值计算得到的温度响应作为工作阱的温度边界条件,利用FLUENT求解工作阱内温度及压力分布。结果显示计量阱内除管口位置外具有良好的等温特性。将模拟值与实验值进行比较,计算值和测量值吻合较好,最大偏差出现在响应时间为100 s左右,温度偏差为3.7 K。模拟和实验均证明工质充灌量对具有工作阱的两相闭式热虹吸管的启动性能影响不大。     

Cracking on the Compaction of a Model Composition Based on Natural Flake Graphite and Binder Pitch

The experimental temperature dependence of the electrical resistivity of a model composition based on natural flake graphite was compared with the results of a mathematical simulation performed with the use of a flake graphite polycrystal model. For increasing the section of contacts between flakes, the density of the material was increased as a result of impregnation with pitch and the subsequent calcination. The average values of the sizes of flakes in the composition and the tabular values of the conductivity tensor of a graphite quasi-single crystal served as the parameters of calculations. Based on the results of the mathematical simulation, it was found that temperature cracking due to the shrinkage of flakes on cooling should be taken into account for the correspondence of computed values to the experimental results. This cracking almost ceased at temperatures lower than 200°C regardless of the compaction of the material.     

Strongly Nonequilibrium Model of Thermal Ignition with Account for Space–Time Nonlocality

A modified Fourier law with account for heat flux relaxation and scalar value of the temperature gradient serves as a basis for the mathematical model of the locally nonequilibrium process of thermal ignition of systems with a hear source exponentially changing due to temperature. It is shown by the studies performed under the boundary conditions of the first kind that accounting for the space–time nonlocality increases the time delay of thermal ignition. Moreover, it is shown that, when the relaxation properties of the material are considered, the boundary conditions can only be accepted after a certain time rather than instantaneously. Consequently, the amount of heat fed to the system has a limit that depends on the physical properties (including relaxation properties) of the medium.     

核态池沸腾换热的数值模拟

以沸腾壁为研究对象 ,以气泡或核心为边界建立了沸腾换热的数学模型 ,进行了核态池沸腾换热的直接数值模拟 ,模拟结果与现有的实验数据具有很好的一致性 ,从而验证了数值模拟的可靠性 .通过数值模拟得到了气泡影响面积系数和气泡扰动强度系数的计算方法 ,揭示了气泡等待时间和沸腾表面温度波动的非线性特征 .     

烧结床层的热质分析

基于烧结生产的复杂物理化学过程,建立了烧结床层传热、传质和流动的二维非稳态数学模型,考虑了孔隙率、物料颗粒当量直径等床层结构影响参数的变化,并对气固传热系数进行了修正。通过数值计算,获得了烧结床层的温度场、结构变化和烟气的流场、温度场、浓度场等。烟气出口温度、床层总压降与生产实测值吻合较好,验证了数学模型的正确性。进一步分析了燃料配比、风量和给料温度等操作参数对烧结过程的影响。研究结果表明：燃烧带的厚度、最高温度随着烧结过程的进行而逐渐增加。床层孔隙率、颗粒当量直径的变化主要发生在燃烧带的熔融、冷凝阶段。料层压损最大的是燃烧熔融层,其次是混合料带,最小的是烧结矿层。增加焦粉含量、提高烧结混合料的初温,有利于提高成矿质量;风量过大时,会造成成矿质量下降、生产成本提高。     

Mathematical Model of Ignition of Condensed Systems by a High-Temperature Supersonic Underexpanded Jet

An approximate mathematical model is constructed and characteristics are calculated of ignition of a reactive plane infinite obstacle by a high-temperature nonstationary axisymmetric supersonic jet of combustion products escaping from the igniter. The approximate model data are compared with the results of numerical calculations using the system of equations of motion of an ideal gas, nonstationary equations of heat conduction and chemical kinetics, and conditions of conjugate heat exchange at the gas–condensed medium interface. The suggested approximate model adequately describes the ignition process and can be used for proximate evaluation of ignition time and temperature. Key words: ignition, jet, gas dynamics, supersonic flow, mathematical simulation.     

流化床氛围下多孔物料干燥传热传质的数值模拟

用有限差分法数值求解一个热、质传递耦合模型,理论研究多孔物料流化床干燥过程。方程离散采用全隐格式的控制容积方法,三对角矩阵法（TDMA）用来求解线性方程组。选用球形的苹果丁作为多孔物料。在典型操作条件下,通过分析温度、饱和度和压力的分布侧形,讨论了物料内部的热、质传递机理。在对比条件下,考察了气体入口温度、气速和床面积因子对干燥过程的影响。结果表明：干燥过程受气、固相间的耦合传热传质的影响十分明显,干燥时间随气体入口温度和气速的提高而减少;随床面积因子的增大而增加。     

机载综合环控系统的热管理

利用燃油作为主要热沉,同时引入液体PAO与R134a作为辅助热沉,提出了一种环控系统热管理的新方案。空气压缩制冷子系统与高温PAO子系统以空气-PAO换热器为连接点,耦合为座舱与电子舱室1的热管理子系统;低温PAO子系统与蒸发压缩制冷循环以蒸发器为连接点,耦合为电子舱室2的热管理子系统。采用数学理论计算与计算机建模仿真研究相结合的方法,建立了空气-液体换热器、液-液蒸发器/冷凝器等主要元件的仿真模型,对环控系统进行性能分析。结果表明,在一定的引气温度和压力条件下,燃油作为主要热沉可以吸收大量的热量,同时各子系统的热量互补能够满足驾驶舱与电子舱的温度控制,保证其稳定、高效的运行。     

High temperature ablation of highly filled polymer‐layered silicate nanocomposites

At instantaneous thermal shocks and high temperature conditions, using the charring ablative heat shields is more effective than the other heat protection methods. In recent years, low‐filled layered silicate polymeric nanocomposites were introduced as new class of ablative materials. In this work, highly filled ablative polymeric nanocomposite is prepared and its thermal stability and ablation mechanism is studied under high external heat flux. The thermal degradation kinetics during pyrolysis, the variation of thermophysical properties as a result of ablation process and mathematical modeling of ablation process are performed for highly filled ablative polymeric nanocomposite samples compared with those of their composite counterparts under oxyacetylene flame test. The results show that the ablation performance of highly filled polymeric nanocomposite is higher than that of the composite, and the mathematical model is adequately confirmed by the experimental data of the thermophysical and ablation properties of highly filled nanocomposites. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

High-temperature mechanical characterisation of an alumina refractory concrete for Blast Furnace main trough: PART II. Material behaviour

This paper deals with the experimental mechanical characterisation of a high alumina carbon containing refractory concrete at temperatures ranging from room to high temperature (1500 °C). Uniaxial compression, indirect tensile, creep and cyclic loading–unloading tests have been performed. Scale factor effect, influence of interfaces lubrication, material initial heat treatment as well as oxidising or reducing atmosphere test conditions have been investigated. Some of the material mechanical properties have been found to depend not only on the level of applied temperature but also on its duration revealing then the sensible influence of chemical transformation kinetics within the material. An analysis of the global macroscopic mechanical behaviour of the material through the range of temperature is lastly exposed. The data collected are aimed at identifying damage behaviour constitutive equations for numerical simulation of structures built within this material.     

余热利用集热器性能的实验研究与数值计算

以回转窑表面余热回收用集热器为研究对象,采用实验研究和数值计算方法,分析了集热器的流动和传热特性及其在线运行规律。实验中选取了一种辐射型和两种耦合型结构的集热器进行研究,分析了出口水温、出口压力和工质流量的变化对集热器性能的影响,总结了三种结构类型的集热器在换热量上的变化规律。采用Matlab软件编程进行数值求解,将数值计算结果与实验结果对比,验证了数值计算的准确性。数值分析了入口空气温度、入口空气流速和窑体温度变化时对应的集热器内熵增、火积耗散以及有效度的变化规律。相关计算结果为集热器的优化设计和在线运行参数的选择提供了数据支持。     

低温输运管道预冷过程的气液两相数值分析

低温流体在输运管道中预冷时会出现复杂的气液两相流现象。本研究的数值仿真主要针对液氮在管道内沸腾过程中的传热特性、气泡的生成规律、临界热通量等进行分析。通过改变管道直径、入口液氮流量,讨论了不同时刻计算域内部的温度、热通量以及两相分布规律,最终得到研究范围内的临界热通量（CHF）特性。研究发现,流体温度突变时间随着管径的减小而提前,随着流量的增大而后延;壁面温度变化幅度随着管径的增大而增大;CHF值随着管径的减小而增加,随着入口流量的增加而减小。     

离心流化床干燥过程中传热传质的数值模拟

通过对典型的多孔湿物料在离心流化床中干燥过程的理论分析和实验研究 ,首次将含湿多孔介质传热传质过程和物料与气流之间的外部传递过程相耦合 ,导出了离心流化床的理论模型和控制方程组 ,对于离心流化床中湿物料的干燥过程引进了数值模拟 ,结果表明增加气体表观流速、控制入口气体的温度和相对湿度以及加大床体转速均对干燥有不同的影响     

基于努赛尔方程的逆流管式换热器的性能研究

以努赛尔方程为基础建立数学模型,计算逆流管式换热器的总换热系数U、局部换热系数h,以及换热温差ΔT,并将理论计算结果与实验结果进行比较分析,表明该数学模型是合适的,为数学模拟逆流管式换热器提供了可行的方案。     

超音速喷管内准一维气相流动建模与数值模拟

通过理论分析建立考虑壁面摩擦和换热影响的喷管内气相准一维流动数理模型，在气动方程组矢通量分裂基础上，采用有限差分方法对其变体形式进行离散，空间导数采用五阶精度WENO格式，时间导数采用三阶精度三步TVD龙格库塔方法，在Fortran平台上进行编程和计算，进行模型方法验证和参数研究。结果表明，在适当选取摩擦修正因子时，数值模拟与实验数据吻合较好，验证了数理模型、数值计算与求解方法的有效性。喷管半扩张角增大时，出口气流速度和马赫数增大，而静压减小；进口总温提高时，出口速度显著升高，但由于壁面摩擦和换热加剧，相应的出口马赫数会减小；进口总压提高时，出口气流速度并不显著增大；壁面温度升高时，出口气流速度和马赫数均减小。     

Heat transfer to molten polymers flowing through tubes

A theoretical and experimental study of heat transfer to polymer melts flowing through circular tubes is presented. The mathematical model provides for shear heating and expansion cooling effects, and also heat of reaction during flow for various wall boundary conditions. Experimental results, obtained using low density polyethylene, show reproducible temperature and velocity profiles. The measured inlet melt temperature profile and the axial wall temperature profile provide the boundary conditions for the calculations. The experimental data confirm the predictions of the magnitude of the shear heating and expansion cooling effects during tube flow.     

The measurement of PVC primary particle breakdown

The breakdown of primary particle structure in PVC is intimately related to the mechanical properties of the material. This article addresses the measurement of primary particle breakdown through microscopic observation, torque bowl rheometry, penetration impact, yield stress determinations, and zero length capillary rheometry. It is found that each method gives information which identifies certain stages in the breakdown process and complements information obtained from the other methods. Characterization via penetration impact identifies the melt conditions at which both the onset of a continuous network on the microscopic scale and primary particle breakdown occurs. Yield stress determined as a function of melt temperature identifies the completion of primary particle breakdown. The onset of primary particle breakdown, as well as the breakdown of other structural units, such as grains, are readily determined by torque bowl rheometry. However, the results from zero-length capillary rheometry cannot, as yet, be readily generalized in terms of the particulate breakdown process.     

Cristallisation du trihydrate d'alumine: Un modèle pour l'attrition

The breakdown of alumina trihydrate particles was studied in a batch isothermal stirred reactor. Experiments were performed using mono-dispersed particles. Crystal size distribution of precipitate was evaluated to study the variation of the number of particles as a function of time. Experimental results were used to develop a mathematical model for the breakdown phenomena. The new data obtained are applicable for simulation of industrial crystallizers in the aluminum industry.