火焰烟黑三维温度场和浓度场同时重建实验研究

利用电荷耦合器件摄像机采用烟黑温度场和浓度场同时重建模型对自由火焰烟黑的三维温度场和浓度场进行了同时重建实验研究,所利用的重建模型是基于区域重建的方法.将重建的烟黑温度场和浓度场与文献结果进行了对比,而且还将重建温度场与热电偶所测量的温度场进行了对比.结果表明,重建的烟黑温度场和浓度场与文献结果趋势相一致,重建温度值与热电偶测量值符合较好.因此,同时重建模型可以较好地重建出火焰烟黑的三维温度场和浓度场. 关键词： 火焰烟黑 温度场 浓度场 三维同时重建     

多光谱辐射层析重建三维火焰温度场

提出一种基于多光谱辐射测温理论及光学层析技术的三维温度场重建方法。建立了基于参考温度的多光谱测温法数学模型，提出了一种基于模拟退火理论的变松弛因子的光学层析技术新算法，通过计算机数值模拟，详细考察了该算法对非对称温度场分布的重建效果并与传统的代数迭代重建算法及滤波反投影算法进行比较。计算结果表明，变弛豫因子重建算法重建精度最高。作为一个应用实例，用多光谱辐射变弛豫因子重建层析方法重建了四峰蜡烛火焰某一截面的温度分布。     

基于阻尼LSQR-LMBC的火焰三维温度场重建

光场相机可以解决辐射测温多相机系统光路复杂、同步触发难等问题,在辐射成像三维温度重建时有其独特优势. LSQR是求解基于大型稀疏矩阵最小二乘问题的经典算法,该算法用于重建三维温度场时对温度初值依赖较大,在信噪比较低的情况下重建精度不理想.本文提出阻尼LSQR-LMBC重建算法,通过在LSQR方法中添加阻尼正则化项,提高火焰三维温度场重建的抗噪性能,并结合LMBC算法,实现吸收系数和三维温度场同时求解.在数值模拟部分,随着信噪比逐渐降低,阻尼LSQR的重建效果比LSQR更加稳定,在信噪比达到13.86 d B时,重建精度大约提高30%.阻尼LSQR-LMBC的平均重建误差为6.63%.用丁烷火焰进行了实验,重建的丁烷火焰三维温度场分布符合辐射火焰燃烧的特征,和热电偶的测温数据结果进行对比,相对误差在6.8%左右.     

大型电站锅炉炉内三维燃烧温度场可视化实验研究

本文利用 8只火焰图像探测器和相应的计算机图像采集处理系统,在一台 200 MW 四角切圆燃煤锅炉上进行了炉膛三维温度场可视化实验研究。现场实验结果表明,炉膛上部温度分布较低,并且呈典型的单峰形状;燃烧器区域的温度分布较高,能够反应四角切圆燃烧特性。用水冷枪抽气热电偶对温度场可视化结果进行了检验,相对误差在5％之内。三维温度场可视化结果刷新一次的时间不超过5秒,满足在线监测的要求。     

多焦距微透镜阵列光场成像火焰三维温度场测量

多焦距微透镜阵列可提高聚焦光场相机的深度分辨率。为了研究多焦距微透镜阵列对光场成像火焰三维温度场测量的影响,本文在火焰辐射光场成像模型的基础上,分析了单焦距微透镜阵列和多焦距微透镜阵列的火焰辐射光场成像特征,计算了两种不同微透镜阵列下的火焰辐射图像,根据火焰光场图像重建了火焰的三维温度场。开展了多焦距微透镜阵列聚焦光场相机火焰三维温度场重建的实验研究,并对数值计算和实验结果进行了分析。     

基于聚焦型光场相机的火焰温度场重建

光场成像技术可以在一次曝光中,同时记录下入射光线的空间分布信息和传播方向信息,能够得到更丰富的热辐射信号。本文利用聚焦型光场相机对三维火焰进行了光场采集,并利用这些光场信息通过截断奇异值分解(TSVD)重建了不同火焰的三维温度场分布,在重建过程中考虑了光场相机白图像的特点,剔除了对重建不利的无效像素,并且分别对均匀分布、轴对称分布和非轴对称分布的火焰进行了温度场重建,重建结果表明均匀温度分布的重建结果最佳,轴对称分布的重建结果次之,非轴对称分布的重建结果最差。最后考察了不同测量误差下重建结果,重建结果表明在一定的测量误差范围内,TSVD方法的重建效果对测量误差不敏感。     

利用迈克耳孙干涉仪重建蜡烛火焰温度场

利用教学实验中的迈克耳孙干涉仪,进行蜡烛火焰温度场的测量.对干涉条纹进行了处理和细化,并分别用阿贝尔变换法和环带法对蜡烛火焰的温度场进行了计算,得到蜡烛火焰横截面上温度场的定量结果.     

基于截断奇异值分解的三维火焰温度场重建研究

利用CCD摄像机得到的火焰辐射能图像进行炉膛三维火焰温度场重建，但温度重建矩阵方程是一个不适定方程组，从而重建问题是一个不适定问题.应用截断奇异值分解(truncated singular value decomposition，TSVD)的正则化方法对该不适定方程组进行求解，并且采用了L曲线法对正则化参数进行选取.结合重建算例，采用奇异值分解(singular value decomposition，SVD)与离散Picard条件对这个不适定问题进行了分析.重建结果表明，在不同的模拟测量误差下，TSVD能够成功得到合理的解，重建温度场较好的再现了原始假设温度场的特征.     

炉膛三维温度场重建中Tikhonov正则化和截断奇异值分解算法比较

在煤粉锅炉诊断中火焰辐射能图像扮演着越来越重要的角色, 通过电荷耦合器件(CCD)获得的辐射能图像可以重建出炉内火焰三维温度场, CCD 用于获取视场角内的辐射能图像. 温度场重建的矩阵方程是一个严重病态的方程, 本文使用两种算法(Tikhonov正则化算法和截断奇异值分解(TSVD)算法)来重建温度场. 应用广义交叉检验算法来选取正确的正则化参数. 数值模拟的环境为一个10 m×10 m×10 m的三维炉膛, 系统被划分为10×10×10的1000个网格, 每个网格单元都是边长为1 m的立方体. 在正问题求解所得到的CCD接受信号基础上加上不同随机误差以模拟测量时的CCD接受信号. 研究两种算法重建后的温度重建误差、两者的重建时间, 以及最高温度的重建效果. 初步的研究结果显示, 一般情况下基于Tikhonov算法重建的温度场比基于TSVD算法重建的温度场误差要小, 计算所需时间短, 最高温度重建更准确.     

三维复杂温度场高精度声学测量方法

声学温度场检测技术通过多路径声波传播时间数据,反演被测区域的温度分布。提供了一种高精度的三维复杂温度场的声学测量方法。首先从射线声学角度给出了三维非均匀温度场中声波传播路径的数学模型。在此基础上,将三维温度场的重建问题转化为声波传播路径的求解和温度场的反演问题,建立了基于多项式修正径向基函数(RBF-PR)和改进的Tikhonov正则化三维温度场重建算法。采用两种典型的炉膛三维温度场模型,在信噪比SNR=35 dB下进行了数值模拟,分析了声波传播路径在非均匀温度场中的弯曲特性、算法的重建质量和抗噪性,同时进行了实际炉膛内二维温度场的重建。结果表明了提出的考虑声线弯曲的温度场重建算法具有精度高,抗噪性强、适用性好的特点,为实现高精度的复杂温度场的声学测量提供了有效方法。      

3-D flame temperature field reconstruction with multiobjective neural network

A novel 3-D temperature field reconstruction method is proposed in this paper, which is based on multi-wavelength thermometry and Hopfield neural network computed tomography. A mathematical model of multi-wavelength thermometry is founded, and a neural network algorithm based on multiobjective optimization is developed. Through computer simulation and comparison with the algebraic reconstruction technique (ART) and the filter back-projection algorithm (FBP), the reconstruction result of the new method is discussed in detail. The study shows that the new method always gives the best reconstruction results. At last, temperature distribution of a section of four peaks candle flame is reconstructed with this novel method.     

The measurement of 3-D asymmetric temperature field by using real time laser interferometric tomography

A real time nondestructive temperature measurement technique based on laser holographic interference tomography technique is presented. An He–Ne laser is used as light source, and a CCD video camera is used to grab the interferogram. This laser holographic tomography technique is applied to the measurement of the temperature fields generated by two heated rods. Since data error is inevitable in engineering measurement, it is necessary to study the reconstruction techniques for reconstructing the temperature field. Three techniques including convolution back projection (CBP), algebra reconstruction technique (ART) and simultaneous iterative reconstruction technique (SIRT) are studied. Based on the reconstruction techniques and experimental situation, ART is used to reconstruct the asymmetric temperature fields. The thermocouples are used to measure the temperatures of the two heated rods. Comparing the reconstructed result with the measured temperature value, a satisfactory result is obtained.     

Three-Dimensional Reconstruction of Temperature and Velocity Fields in a Furnace

In this paper a reconstruction method is presented, which allows the calculation of three-dimensional temperature and velocity fields in an industrial furnace by measuring the propagation times of sound waves. Transceiver systems working in a coal fired power station and reconstructing two-dimensional fields are well known. Referring to these real conditions, the idea was to use two measurement planes situated over each other and projecting the fields in the volume between them. Some simulations show that weak inhomogeneous fields can be well reconstructed, whereas in the presence of turbulent flow and noise a reconstruction is critical.     

Fourier Transform Moire Deflectometry for Measuring the 3-D Temperature Field

Fourier transform evaluation of fringe phase is applied to Moire deflectometry. 3-D gas temperature distribution for a given layer is reconstructed by optical tomography. The results show that the high-precise and automatic measurement for the 3-D gas temperature field can be realized by this technique.     

Digital speckle photography and speckle tomography in heat transfer studies

The line-of-sight speckle photography of transparent media is used for quantitative measurements of the instantaneous temperature fields in 3D unsteady flows. Both electronic and photographic methods are employed for specklegram recording. The subsequent specklegram treatment uses the Young's fringes method as well as cross-correlation analysis of small interrogation areas of the recordings. Experimental data for three different heat transfer configurations are obtained and discussed. The first one is natural convection over extended vertical heated plates with forward facing steps, the second is unsteady 3D convective flow around a suddenly heated vertical thin wire, and the third one is a convective plume above a multi-jet flame. Both local and global Nusselt numbers are determined via measuring local surface temperature gradients for these convective flows. The results are compared with Ostrach's theory for a single vertical plate and with the data obtained by Mach–Zehnder interferometry. The 3D temperature fields are reconstructed for axisymmetric convective flows around a suddenly heated vertical wire using quasi-double projection measurement and the Radon inversion. 3D temperature distributions above the combustion zone are reconstructed using multi-projection speckle photography measurements and computerised tomography.     

Burning characteristics of candle flames in sub-atmospheric pressures: An experimental study and scaling analysis

Burning characteristics (mass burning rate, natural convection boundary layer thickness, flame height and dark zone height) of laminar diffusion flames produced by a candle at sub-atmospheric pressures in the range of P_∞?=?50–100?kPa were experimentally studied in a reduced-pressure chamber; such data are not reported to date. Scaling analysis was performed to interpret the pressure dependence. The new experimental findings for candle flames in the sub-atmospheric pressures were well interpreted by the proposed scaling laws: (1) the mass burning rate was higher for a candle with larger wick length, and it increased with increasing ambient pressure, a stagnant layer B-number model based on natural convection boundary (flame boundary layer thickness) was developed to scale the mass burning rate of candle flames at various pressures; (2) the flame boundary layer thickness was wider in lower pressure and can be well represented by a natural convection boundary layer solution; (3) flame height was higher for a candle with larger wick length, meanwhile the ratio of flame height to burning rate was independent of pressure; (4) the flame dark zone height representing a soot formation length scale changes little with pressure, meanwhile its ratio to the total flame height is scaled with pressure by $P_{\infty }^{?1/2}/L_{w,e}^{3/4}$ (L_w,e is effective wick length inside flame). This work provided new experimental data and scaling laws of candle flame behaviors in sub-atmospheric pressures, which provided information for future characterization and soot modeling for diffusion flames associated with melting and evaporation processes of solid fuels.     

用于三维傅氏轮廓术的一种自适应基频带通滤波器

介绍了傅氏轮廓术的基本原理,通过仿真与调相频谱分析,提出了一种新的自适应基频带通滤波器算法。利用此算法设计出了基频带通滤波器并用于傅氏轮廓术的位相提取。结果表明,相对于非自适应性的滤波器,使用本文设计的滤波器其三维面型测量精度可以提高5％,并且具有稳定的重复测量精度,在不受主观因素的影响下实现了实时三维面形重建。以螺纹钢面型为例进行了位相提取实验,实验中计算了面型测量精度,并与理论仿真精度进行比对与分析,得出的实验结果与理论仿真结果相一致,验证了该算法的有效性。     

Integral three-dimensional imaging with digital reconstruction

A computed three-dimensional (3-D) display system based on integral imaging is presented. The 3-D image is reconstructed by numerical processing of an optically observed image array formed by a microlens array. The algorithm for reconstructing 3-D images is robust, and it enables us to obtain the images viewed from arbitrary directions. This computer-based image retrieval makes it possible to improve qualities of the image such as contrast, brightness, and resolution by numerical techniques. Also, this method eliminates the need for special purpose optical equipment such as high-quality liquid-crystal display and micro-optics components to display the 3-D images. We present experimental results of 3-D image reconstruction to test and verify the performance of the algorithms and the imaging system.