Examination of flame length for burning pulverized coal in laminar flow reactor

Because there has been a recent increase in the use of low calorific coal compared to standard coal, it is crucial to control the char flame length governing the burning life-time of coal in a coal-fired utility boiler. The main objective of this study is to develop a simplified model that can theoretically predict the flame length for burning coal in a laboratory-scale entrained laminar flow reactor (LFR) system. The char burning behavior was experimentally observed when sub-bituminous pulverized coal was fed into the LFR under burning conditions similar to those in a real boiler: a heating rate of 1000 K/s, an oxygen molar fraction of 7.7 %, and reacting flue gas temperatures ranging from 1500 to 2000 K. By using the theoretical model developed in this study, the effect of particle size on the coal flame length was exclusively addressed. In this model, the effect of particle mass was eliminated to compare with the experimental result performed under a constant mass feeding of coal. Overall, the computed results for the coal flame length were in good agreement with the experimental data, particularly when the external oxygen diffusion effect was considered in the model.     

Selective diagnostics of multiflame burning using simulation

A problem of tongue-selective diagnostics of the burning process in multiburner research and industrial installations is considered. The main factors that govern the response of optical sensors and gas analyzers to changing processes in the chamber as a result of fuel redistribution are determined. A simulation model of the object investigated is created. The model takes into account the determined dependences. A tongue-selective combustion diagnostics algorithm based on the developed model is proposed and demonstrated.     

Non-adiabatic flamelet modeling for combustion processes of oxy-natural gas flame

In order to realistically predict the combustion characteristics of the oxy-fuel flame, the present study employs the non-adiabatic flamelet approach. In this combustion model, the detailed equilibrium chemistry is utilized to accurately account for the thermal dissociation as well as to properly include the radiative cooling effects on the detailed chemistry. Numerical results indicate that the present approach has the capability to correctly capture the essential features and precise structure of the oxy-fuel flames. In this work, the detailed discussion has been made for the characteristics of oxy-fuel flames, the capability and defect of the present approach and also uncertainties of experimental data.     

用户期望意象驱动的产品造型融合创新设计

根据用户期望意象,采用语义差异法提取目标产品和参考产品的产品造型特征曲线;采用二叉树结构建立造型特征曲线对应的曲线树,对曲线树实施交叉、变异、选择及融合等操作,产生新的造型特征线;建立用户期望意象驱动下的适应度评估机制,对设计方案进行筛选,从而得到了基于用户期望意象驱动的造型设计方案。最后,用台灯设计案例证明,该方法在设计创新过程中是可行的。     

高速凸轮-从动件系统动力学模型的建立与动态分析

阐述了高速凸轮-从动件系统动力学模型建立与动态分析的一般方法。以内燃机配气凸轮机构为例,建立了单自由度动学分析模型,探讨了用谐波分析的数值计算法对系统动态响应进行求解的过程。     

一种电气化铁路牵引网电磁暂态建模方法

针对电气化铁路牵引网电能质量分析问题,对电气化铁路牵引网电磁暂态过程进行了仿真建模研究,推导了包括基于贝杰龙模型的牵引网导线模型、基于受控源原理的牵引变压器和自耦变压器模型在内的牵引网主要电气元件的独立电磁暂态模型,提出了"以牵引网导线为系统主体,其他电气元件描述为网络上的串联元件和并联元件"的牵引网全网电磁暂态模型建立方法。编写了电气化铁路电磁暂态仿真计算软件,通过实例比对测试了该软件计算结果和PSCAD仿真结果。研究结果表明,该建模方法多种工况计算结果与PSCAD仿真结果吻合,具有建立整网模型便捷、调节仿真参数方便及支持二次开发等特点,对电气化铁路牵引网建模仿真和电能质量问题研究具有重要价值。     

Methods of modeling interaction of atoms with polarized radiation

Methods of the numerical solution of equations that describe the resonant interaction of polarized radiation with alkali atoms are presented. Some procedures of converting these equations to a form reducing the calculation time are given. Typical simplifying assumptions used in solving these equations are discussed. Based on comparisons of magnetic-optical resonances for Rb⁸⁷ with various simplifying assumptions, a conclusion is made on applicability of these approximations and possible inherent errors.     

DLZ2.0车载液压打桩机及导向模板的设计与建模

阐述DLZ2.0新型车载液压打桩机的基本结构、工作原理、主要技术参数,研究该机采用的创新性结构———曲线导向模板机构的设计与建模,此机构从根本上解决了打桩过程中桩体的水平偏移问题。     

基于恒流源的矿用隔爆兼本安型瞬变电磁发射机研制

由于瞬变电磁技术对水体反应灵敏,已被应用于煤矿井下水害探测。为提高探测精度,研究了恒流发射技术,采用脉冲宽度调制与功率场效应管结合,保证发射电流在探测过程中保持恒定;为提高二次场强度,采用了电感反向截断技术,利用电感中电流突然关断产生反向高压原理,缩短电流关断时间;通过外部中断与微控制器内部定时器配合,记录发射电流关断时间;采用隔爆兼本安型结构设计,保证仪器在井下安全使用。最后通过实验室测试和充水巷道探测,验证了仪器的准确性和有效性。     

ECT在多孔介质内火焰分布可视化测量中的应用研究

本文利用电容层析成像（ECT）的方法,对通道型多孔介质内单/双火焰分布情况以及泡沫型多孔介质内火焰分布进行可视化测量。在介绍和分析多种成像方法的适应性和局限性的基础上,针对被测对象的性质和特点采用了适当的成像方法及其合适的满标定物质,得到了清晰的火焰图像。测量结果显示了ECT可以较为准确地判断多孔介质内火焰的位置、大小以及脉动情况。其成果为多孔介质燃烧领域提供了新的研究方法和测量手段。本文最后指明了测量过程中存在的问题以及今后的发展方向。     

Neutral representation of tolerance information for process planning using STEP AP 224

The focus of CIM is on information as it is the crucial element for integrating all the manufacturing activities. CAPP, as one of the key elements in CIM, needs to extract the manufacturing information such as machining features and precision specifications like surface roughness and tolerances from a geometric model in order to link CAD and CAM. However, these data are not real attributes of the geometric model in most of the current CAD systems. Therefore, human interpretation is inevitable for further processing of CAD model for downstream application like process planning or inspection. This paper proposes a scheme to represent the manufacturing information in a neutral format using STEP technology in order to enable downstream users such as process planner and inspection planner to make correct decisions on process selection, processing conditions, etc. It is shown that by using STEP AP224 manufacturing information encompassing machining features, surface roughness, dimensional and geometric tolerances can be completely represented together with part geometry, which certainly contributes to successful implementation of CIM.     

Centrifugal pump transient characteristics and analysis using the method of characteristics

A theoretical and experimental study has been carried out on the transient characteristics of a centrifugal pump during starting and stopping periods. Experiments have been conducted on a volute pump with different valve openings to study the dynamic behaviour of the pump during normal start up and stopping, when a small length of discharge pipe line is connected to discharge flange of the pump. Similar experiments have also been conducted when the test pump was part of a hydraulic system to study the system effect on the transient characteristics. Instantaneous rotational speed, flowrate, and delivery and suction pressures of the pump are recorded and it is observed in all the tested cases that the change of pump behaviour during the transient period is quasi-steady. The dynamic characteristics of the pump have been analysed by a numerical model using the method of characteristics. The model is presented and the results are compared with the experimental data. As the model contains speed acceleration and unsteady discharge terms, the model can be applied for analyses of purely unsteady cases where the pump dynamic characteristics show considerable departure from their steady-state characteristics.     

Leak detection in pipe using transient flow and genetic algorithm

An inverse transient method with genetic algorithm (GA) was applied to leak detection in pipeline. Transient flow caused by valve operation was calculated using the characteristics method. The location and discharge of leak were determined so that the difference of the calculated pressure may be minimized from the reference pressure calculated under a given leak condition. Calculations were done for the leak at one and two locations in pipeline. Furthermore, the effect of noise in pressure data was discussed, and the leak locations and leak discharges can be predicted precisely even in the case of noisy data. This paper was presented at the 9^th Asian International Conference on Fluid Machinery (AICFM9), Jeju Korea, October 16–19, 2007.     

Analog analysis of exponential decays using a transient recorder

An analog computation technique is described for the determination of amplitudes and time constants of one or two exponentials captured with a transient recorder. The method is based on operator-controlled processing of the periodic analog output of the recorder with log-antilog circuitry. In many cases the accuracy of the analysis approaches that obtained with numerical curve fitting procedures.     

Analysis of transient multiexponential signals using exponential compensation deconvolution

A three-step procedure for the parameter estimation of transient multiexponential signals is proposed. The first step involves the use of the classical Gardner transform to convert the data signal into a convolution model which is deconvolved using exponential compensation deconvolution technique in the second step. In the third step, eigenvector algorithms are used to process the resulting complex exponentials to obtain better estimates of decay rates and number of components. Simulation and experimental results show that this method outperforms previous approaches if a number of preprocessing parameters are correctly selected.     

Development of measurement technique of explosive flame using an optical measurement method

Journal of Mechanical Science and Technology - It is essential in weapons systems to understand how much explosive power is applied according to various chemicals and methods of the explosion. In...     

Numerical studies of transient opposed-flow flames using adaptive time integration

Numerical simulations of unsteady opposed-flow flames are performed using an adaptive time integration method designed for differential-algebraic systems. The compressibility effect is considered in deriving the system of equations, such that the numerical difficulties associated with a high-index system are alleviated. The numerical method is implemented for systems with detailed chemical mechanisms and transport properties by utilizing the Chemkin software. Two test simulations are performeds hydrogen/air diffusion flames with an oscillatory strain rate and transient ignition of methane against heated air. Both results show that the rapid transient behavior is successfully captured by the numerical method.     

Measurement of the properties of liquids and gases using a transient hot-wire technique

A transient method of making simultaneous, in situ measurements of the thermal conductivity, volumetric specific heat, and kinematic viscosity of liquids and gases is presented. The technique utilizes the temperature response record of a fine horizontal wire, functioning as a resistance thermometer, when subjected to a sudden and constant electrical heating. It is shown that a formulation of the transient mechanisms governing the transition from pure conductive to free convective heat transfer from the wire can be used to produce simultaneous determinations of fluid properties from a single wire temperature versus time record. A simple apparatus is presented, along with the results of its use in determining the properties of air.     

Measurement of thermal conductivity of fluid using single and dual wire transient techniques

A modified measurement device to measure thermal conductivity of fluids using transient hot-wire technique has been designed, developed, tested and presented in this paper. The equipment is designed such that the thermal conductivity could be measured using both single wire sensor of different length and dual wire sensor. The sensor, which is also a heater, is a platinum micro-wire of 50 μm diameter. The influence of wire length on the measurement of thermal conductivity of fluids is tested using two single wires of length 50 mm and 100 mm. The thermal conductivity is also measured using a dual hot wire arrangement; which is achieved by placing the 100 mm and 50 mm wires in a Wheatstone bridge with the 100 mm wire as the sensor and 50 mm wire as a compensation wire. The apparatus requires a 100 ml of test fluid to perform the experiment. The testing temperature of the test fluid during the experimentation can be suitably varied by the choice of heat exchange fluid used in the apparatus. Water is chosen as testing fluids for primary standards. When compared to single wires, the thermal conductivity of the fluids measured is consistent with dual-wire method with an uncertainty of ±0.25%.