Process rheokinetics and microstructure of recycled EVA/LDPE-modified bitumen

Knowledge of the kinetics of the manufacturing process of polymer–bitumen blends is of great interest because it provides information on the behaviour of the binder at different stages of the mixing operation, which is useful for the establishment of the optimum processing conditions, involving temperature and operation time. The purpose of this research was to study the evolution of the rheological properties and microstructure of a polymer-modified bitumen during its processing. A 60/70-penetration grade bitumen and recycled EVA/LDPE were mixed under different processing conditions. Measurements of the evolution of viscosity with time, at different temperatures and agitation speeds, were carried out with an experimental device known as ‘rheomixer’, that is, a helical ribbon impeller inside a mixing vessel coupled with the transducer and motor of a conventional rheometer. Under the experimental conditions selected (within the laminar region, Re<10), temperature is the most important processing variable. Hence, low agitation speeds and a processing temperature of around 180°C should be chosen for bitumen modification with the polymer used.     

The Application of Intelligent Technology on a Multi-Variable Dynamical System

Conventional control systems express control solutions by means of control expressions, usually mathematically based. To completely express the control solution, a vast amount of data is required. This is either difficult or virtually impossible to obtain. In contrast, knowledge-based solutions require far less plant data and mathematical expression. This reduces development time proportionately. A dynamical temperature control system is used in this project, within which a Fuzzy Logic Controller is used to maintain the system temperature. A Fuzzy Logic Control algorithm is implemented to test its performance in temperature control. An experimental analysis indicated that for approximately 50% decrease in flow rate, considering that the flow rate could not be increased to the desired value, owing to process problems, neither of the two temperature valves was subjected to oscillations. After approximately 30 s, the process temperature began to steady out. Mathematical reasoning would have increased the settling time tremendously.     

Towards a Thermal Optimization of a Methane/Steam Reforming Reactor

Plug-flow reactors are very common in methane/steam reforming applications. Their operation presents many challenges, such as a strong dependence on temperature and inlet composition distribution. The strong endothermic steam reforming reaction might result in a temperature drop at the inlet of the reactor. The strong non-uniform temperature distribution due to an endothermic chemical reaction can have tremendous consequences on the operation of the reactor, such as catalyst degradation, undesired side reactions and thermal stresses. One of the possibilities to avoid such unfavorable conditions and control thermal circumstances inside the reforming reactor is to use it as a fuel processor in the solid oxide fuel cell (SOFC) system. The heat generated by exothermic electrochemical SOFC reactions can support the endothermic reforming reaction. Furthermore, the thermal effects of electrochemical reactions help to shape the uniform temperature distribution. To examine thermal management issues, a detailed modeling and corresponding numerical analyses of the phenomena occurring inside the internal reforming system is required. This paper presents experimental and numerical studies on the methane/steam reforming process inside a plug-flow reactor. Measurements including different thermal boundary conditions, the fuel flow rate and the steam-to-methane ratios were performed. The reforming rate equation derived from experimental data was used in the numerical model to predict gas composition and temperature distribution along the steam reforming reactor. Finally, an attempt was made to control the temperature distribution by adopting locally controlled heating zones and non-uniform catalyst density distributions.     

三河口碾压混凝土拱坝温控仿真研究

针对三河口碾压混凝土拱坝温度控制问题,综合考虑外界气温和混凝土热、力学性质随时间变化的影响,采用施工全过程仿真分析方法,动态模拟大坝碾压混凝土入仓温度、分层铺筑方式、通水冷却、后期养护等施工参数;分析了坝体温度场和温度应力场,提出了大坝温度、应力控制标准;根据计算结果及时进行温控方案的动态比较和调整,制定了具体的温控防裂要求和措施;在施工中对比实测监测数据。结果表明:坝体温度、应变的数值基本符合坝体温度控制的设计要求,证明温控措施有效。     

Temperature field analysis of IC molding process based on three dimensional finite element model

In the case presented in this paper, the distribution of temperature fields of the molding model during each time interval was obtained as the simulation proceeded along the molding time by using the 3D FEM with a simple division mesh. The simulation results indicate that the most temperature rise is located at the upper right hand corner of the die pad, while the least temperature rise during the molding process is located at the upper right hand corner of the lead frame. Based on the simulation results of the temperature field distribution in the molding model, we obtained the temperature variation trend as a result of changes in the geometric shapes of the molding model. Therefore, the information on the molding model and the analysis of temperature distribution during the integrated circuit molding process presented in this paper can be considered as references for the molding design for integrated circuit packaging process.     

A model for the time response of solid-embedded thermocouples

Unlike the transient response of a fluidimmersed thermocouple, and in contrast to common belief, the time response of a solid-embedded thermocouple is far from being similar to that of a first-order process. The current study arises from efforts to characterize the transient response of a solid-embedded thermocouple as a result of a step-like temperature change of the measured domain. Results of this study suggest that the response function of the thermocouple is nearly exponentially dependent on the square root of Fourier number (dimensionless time). It follows that, with respect to fluid temperature measurements, significantly faster time response is expected at the initiation of the process on one hand, and much longer time is required for reaching a steady-state temperature on the other hand. It is shown that the thermal diffusivity of the thermocouple is required to be at least one order of magnitude higher than that of the measured domain in order to obtain meaningful results in transient measurements.     

微型热驱动回路的脉动及位差对热性能的影响

以甲醇为工质，采用高速数据采集系统测定了微型热驱动回路在不同运行参数下的压力 及温度脉动，其脉动周期及脉动幅度随蒸发段热流密度的增加而减小. 实验发现，在蒸发段 热流密度较低的情况下，蒸气管中是泡状流或弹状流交替存在，而在蒸发段热流密度较高时， 蒸气管中为环状流. 就位差对热性能的影响进行了详细的实验研究，并在冷凝器空气自 然对流和强迫对流情况下，以加热块温度90${^\circ}$C为上限，得出微通道蒸发器和冷凝 器在不同位差下的最大蒸发段热流密度. 通过对实验现象的观察及分析，以期开发出适用于 未来电子产品高功率需求的微型化电子冷却器.     

Flow characteristics of primary and digested sewage sludge

Summary Rheological study of sewage sludge is useful for the design, operation and control of sewage treatment plants. The rheology is highly dependent on physical, chemical and biological characteristics of the sludge. A pipeline rheometer is described in this paper for measurement of rheological properties of the sludge. Primary sewage sludge is a complex flocculated suspension having no fixed particle dimension, shape, size distribution or surface characteristics. The information available so far on rheology of sewage sludge is not suitable for application in design because of the lack of data on physico-chemical characteristics of this sludge.Primary and digested sewage sludge are non-Newtonian in character. Both exhibit yield stress and while primary sludge is shear-thinning in nature, digested sludge has been found to be shear-thickening. Parabolic and yield-power law models have been used to express the experimental data obtained for sludges at various concentrations and temperatures. Yield stress of primary sludge varies exponentially with concentration and linearly with temperature within the short temperature range studied. Primary sludge is found to be antithixotropic at low shear stress. Digested sludge does not exhibit time dependency.With 9 figures and 5 tables     

Development of a hybrid-fuzzy air temperature controller for a supersonic combustion test facility

 Hydrogen gas is burned in air to raise and maintain the stagnation temperature of a supersonic combustion test facility to a desired setpoint. In order to reach the desired operating conditions for stagnation temperature, there are three phases to the hydrogen control; H₂ ignition at facility start-up, H₂ ramp-up while the facility is ramped-up, and H₂ iteration to achieve the desired temperature setpoint. Each phase incorporates a different type of control. Fuzzy logic is used to design a computer based supervisory controller that recognizes the different phases of operation and chooses the appropriate control method. Received: 28 November 1999/Accepted: 2 November 2000     

等压比热在基于壁面放电的激波控制中的影响

放电等离子体对流动的控制机理可按热效应和非热效应分为两大类,其中放电等离子体的热效应对流场中激波结构有着明显的控制作用. 目前在放电等离子体热激励对激波控制的数值模拟过程中,通常采用等效热源的方式来实现放电的热效应,数值模拟和实验的结果显示放电产生的局部温度可达到上万度. 如果数值模拟的过程中没有考虑到气体等压比热随温度的非线性变化,计算得到的结果是有失真实性的. 本文以5 马赫的超音速进气道为平台,对基于壁面放电的激波控制过程进行了数值模拟. 选取了随温度非线性变化的等压比热,并且将其结果与定等压比热的计算结果进行了对比. 结果发现:(1) 两种等压比热下,计算结果显示放电热激励在激波控制上都有着显著的效果;(2) 两种计算结果在模拟与温度相关的参数(温度、马赫数和总压恢复系数)上的差别非常明显. 因此,为了获得壁面放电对激波控制更真实的计算结果,必须考虑到等压比热随温度发生非线性变化效应的影响.      

高精度单晶硅挠性摆式加速度计组件的工程化实现

针对单晶硅挠性摆式加速度计的高精度工程化应用需求,设计了加速度计组件及温控系统。针对大多数温控系统工作时的瞬时电流较大问题,设计了一种带抽头的加热片,将温控分为粗温控和精温控两个阶段,不同阶段采用不同的加热电阻。测试结果表明,设定目标温度为60℃,当外界环境温度从5℃到55℃变化时,温控系统到温时间小于15 min,控温精度小于±0.1℃,精温控时的最大电流为粗温控时的33.4%。连续15天通电实验表明,该组件的加速度计刻度系数K1稳定性小于10×10~(-6),偏值K0稳定性小于10μg,满足各类高精度、工程化的应用需求。     

运行过程中载荷突变时可倾瓦推力轴承瞬态热效应的实验研究

研究了可倾瓦推力轴承在名义转速分别为2000r/min和4000r/min下,当载荷突然变化时推力轴在油膜温度和油膜厚度的瞬态变化规律。实验结果表明：当载荷突然增大时,油膜温度以及进油边温度上升,油膜厚度减小;随着载荷变化幅度的增大,温度上升幅度也增大,油膜厚度进一步减小;在载荷变化相同的情况下,相同时间间隔内转速高时油膜温度增大幅度比转速低时要大,而油膜厚度减小幅度比低转速下小。     

A study of frost growth and densification on flat surfaces

The present study advances a theoretical and experimental investigation of the frost growth and densification on flat surfaces. This study focuses on the most important factors affecting the frost formation process, i.e. the surrounding air temperature, humidity and velocity, and the surface temperature. The processes of frost growth and densification were investigated experimentally in order to provide a physical basis for the development of a theoretical model to predict the variation of the frost layer thickness and mass with time. The mathematical model was based on mass and energy balances within the frost layer, assuming the frost as a porous medium and accounting for the supersaturation of the moist air on the frost surface. The governing equations for mass and heat diffusion were integrated analytically, giving rise to a semi-algebraic formulation which requires numerical integration of only one time dependent ordinary differential equation. When compared with experimental data, the model predictions of the frost thickness as a function of time agreed to within ±10% error bands. The experimentally-validated model was then used to predict the frost layer growth and densification with respect to the operation conditions such as plate surface temperature, air stream temperature, humidity and velocity.     

Cryosurgery of a biological tissue with multiprobe: effect of central cryoprobe

In this paper a three-dimensional numerical model for cryosurgery is developed to study the effect of central probe on the cryosurgery process. The irregular boundary resulting due to the presence of cryoprobes is taken care by body-fitted multi-block non-orthogonal grids. The thermo-physical properties of biological tissue are considered as a function of temperature as phase change takes place over a wide temperature range for the biological tissue. It has been found that the cooling power requirement by the single offset cryoprobe is greater than that of the central cryoprobe. However, the presence of central cryoprobe markedly influenced the cryosurgery process, resulting in an increase in the ablation ratio by 57 % with an insignificant increase in cooling power by 4.5 %. This information can be utilised effectively in computerised planning of a cryosurgery protocol.     

The effect of shrinkage on the cooking of meat

In this paper the cooking of meat is modeled as a process of time-dependent conduction through a constant-property medium that shrinks as its temperature increases. The overall shrinkage is the integrated result of shrinking that is distributed volumetrically through the piece of meat and depends on the temperature history at every point. The meat temperature history and associated shrinkage are determined numerically. The geometric configuration is the one-dimensional conducting slab with convective heating on both sides. Means for calculating the required cooking time are reported in the form of dimensionless charts for the temperature in the midplane of the meat slab. A numerical example shows that the cooking time calculated by accounting for meat shrinkage is appreciably shorter than the time estimate based on the classical Heisler chart for conduction in a constant-volume slab.     

An icing physics study by using lifetime-based molecular tagging thermometry technique

An experimental investigation was conducted to quantify the unsteady heat transfer and phase changing process within small icing water droplets in order to elucidate underlying physics to improve our understanding of the important micro-physical process of icing phenomena. A novel, lifetime-based molecular tagging thermometry (MTT) technique was developed and implemented to achieve temporally-and-spatially resolved temperature distribution measurements to reveal the time evolution of the unsteady heat transfer and dynamic phase changing process within micro-sized water droplets in the course of icing process. It was found that, after a water droplet impinged onto a frozen cold surface, the liquid water at the bottom of the droplet would be frozen and turned to solid ice rapidly, while the upper portion of the droplet was still in liquid state. As the time goes by, the interface between the liquid phase water and solid phase ice was found to move upward continuously with more and more liquid water within the droplet turned to solid ice. Interestingly, the averaged temperature of the remaining liquid water within the small icing droplet was found to increase, rather than decrease, continuously in the course of icing process. The temperature increase of the remaining liquid water is believed to be due to the heat release of the latent heat during solidification process. The volume expansion of the water droplet during the icing process was found to be mainly upward to cause droplet height growth rather than radial to enlarge the contact area of the droplet on the test plate. As a result, the spherical-cap-shaped water droplet was found to turn to a prolate-spheroid-shaped ice crystal with cusp-like top at the end of the icing process. The required freezing time for the water droplets to turn to ice crystals completely was found to depend on the surface temperature of the test plate strongly, which would decrease exponentially as the surface temperature of the frozen cold test plate decreases.     

Noise measurements on germanium avalanche photodetectors

In this paper the overall-noise in a photodetection system, consisting of a Germanium avalanche-photodiode and a low-noise amplifier is determined. It turns out, that the main contributions to the overall-noise stem from the bulk- and guardring leakage currents and from the amplifier. The main parameter of interest for laser rangefinder applications is the noise-equivalent signal current, being equal to the peakvalue of the equivalent noise current at the amplifier input, divided by the avalanche multiplication factor. It turns out, that the optimum bias conditions for low-noise operation are rather temperature dependent. It is argued that current control is preferable to voltage control in order to stabilize against temperature variations. The optimum bias conditions and the corresponding minimum noise-equivalent signal currents are measured as functions of the ambient temperature. Besides the noise measurements the dynamic responses of some types of photodetectors are compared. It turns out, that various types of photo-responses are possible, dependent on the construction details of the device.     

含肿瘤皮肤组织传热分析的广义有限差分法

生物传热分析在低温外科手术、肿瘤热疗、病热诊断等临床医学治疗和诊断中有着广泛的应用. 由于健康皮肤组织内肿瘤的存在使得肿瘤附近区域的温度会明显升高, 这一特性常被用于检测皮肤组织内的肿瘤生长, 因此有必要开展生物传热数值分析的研究. 本文以含肿瘤的皮肤组织为研究对象, 将一种新型区域型无网格配点法——广义有限差分法应用于能描述含肿瘤皮肤组织传热过程的Pennes方程求解. 广义有限差分法利用泰勒展开式与移动最小二乘法将计算区域内的每个离散点上的物理量导数表示成其与邻近点物理量及权重系数的线性组合, 进而构建得到仅含各离散点未知物理量的线性方程组. 该方法不仅具有无需划分网格、避免数值积分等无网格配点法的优点, 同时还克服了大多数无网格配点法中插值矩阵高度病态的问题, 为此类方法在大规模工程数值计算中的应用提供了可能性. 本文首先介绍了模拟含肿瘤皮肤组织传热过程的广义有限差分法离散模型, 随后通过不含肿瘤与含规则形状肿瘤的基准算例, 检验广义有限差分法的计算精度与收敛性; 在此基础上, 通过数值模拟研究不同肿瘤形状及肿瘤位置分布对皮肤组织内温度分布的影响.      

基于时域间断有限元方法的生物组织非傅立叶热行为数值分析

在热传导分析中,当热流与温度梯度存在时间延迟时,需采用非傅立叶热传导模型进行分析。生物组织具有较强的热松弛时间系数,承受激光、微波及烧烫等作用时,其呈现出较强的非傅立叶行为。本文对脉冲热源作用下生物组织的非傅立叶热传导进行研究,针对强脉冲引起的温度场在空间域的高梯度变化、波阵面的间断行为以及通用传统时域数值方法会带来虚假数值振荡的特点,提出采用所发展的时域间断Galerkin有限元法（DG-FEM ）进行求解计算。对多种脉冲热源作用下的非傅立叶热传导过程进行数值模拟,通过考量强脉冲作用下温度场分布和热致生物组织损伤行为的影响,表明了本文所发展的DGFEM 能够有效、准确地描述温度场空间分布和热传导过程以及非傅立叶行为下的生物热损伤更为明显,在生物组织热行为分析中应该受到重视。