半透明平板边界放射辐射热流密度的反问题

对一维半透明平板内辐射、导热及边界对流耦合换热过程进行了研究。提出了一种由一侧边界出射辐射强度反演另一侧边界入射辐射热流密度的方法。通过对各种向异性散射、吸收系数、散射系数、边界外侧来流温度、对流换热系数、半透明平板的导热系数和平板厚度等参数对反学演精度影响的分析表明,方法是可行的。     

半透明介质表面红外测温的辐射传输模拟

考虑不透明漫射基底的反射/发射和半透明介质层的吸收/发射,建立半透明介质层表面红外测温过程的辐射传输模型,采用反向蒙特卡罗法进行模拟,获得探测表面在热像仪的指示辐射温度。与不透明表面红外测温进行比较,分析表面形状、基底发射率ε_s及介质层光学厚度τ的影响。结果表明,半透明介质层表面的指示辐射温度在ε_s1.0时,随τ的增大而增大,τ≥2时数值趋于ε_s=1.0时的结果,与不透明表面存在较大差异;针对复杂形状或内凹曲面红外测温,不透明表面和半透明介质层表面均受到反射其他部位辐射现象的影响。     

计算半透明介质层光谱发射特性的一种新方法——伪光源迭加法

从介质的内部辐射传递出发，提出一种计算半透明介质层表观光谱发射特性的新方法－－伪光源迭加法。文中以两种情况（１）基底面漫射不透明、出射面镜反半透明；（２）基底面漫射不透明、出射面漫反射半透明）下半行平板状介质层的表观发射为例，介绍了这种方法的基本思想，推导出了表观光谱发射率计算式，具体计算了等温半透明灰介质层在不同条件下的表观半球发射率和方向发射率分布。     

表面不透明三层漫反射散射性介质耦合换热

本文采用射线踪迹、节点分析法研究了三层吸收、各向同性散射性介质层内的一维辐射和导热瞬态耦合换热,复合层表面不透明漫反射,介质层交界面半透明漫反射,且半透明漫反射交界面的反射率采用Fresnel反射定律确定。采用一层和二层辐射能量传递模型跟踪辐射能量在三层介质内的传递,从而推导出辐射传递系数。运用辐射传递系数求解辐射源项,在辐射对流边界条件下、采用全隐格式求解瞬态能量方程,并从机理上研究了辐射和导热耦合换热过程。     

半透明介质场参数的非接触测量算法研究

本文在考虑半透明介质吸收、发射以及散射衰减作用的情况下采用视在光线法计算某探测方向上介质边界出射辐射强度分布作为逆问题的输入数据,采用LSQR方法在介质辐射特性参数已知情况下重建介质三维温度分布,重建结果显示,无论有无测量误差存在,利用LSQR方法都可以在已知辐射特性参数的条件下很好地重建出介质的三维温度场。在此基础上提出LSQR-SPSO混合算法,并应用于同时重建三维温度场及辐射特性参数(吸收系数、散射系数)。计算结果显示,无论有无测量误差存在,利用LSQR-SPSO混合算法都可以很好地同时重建出介质的吸收系数、散射系数及三维温度场,相比较而言,介质的温度场更容易被重建出来。     

瞬态激光脉冲在吸收、发射性介质内引起的温度响应

本文导出了平行光入射辐射穿过半透明界面,在吸收、发射性介质内产生的辐射热源的表达式。数值模拟了瞬间激光脉冲入射下：（1）半透明介质与不透明介质在非人射面上的过余温度响应;（2）入的激光的波长对温度响应的影响;（3）界面光学特性（两侧均为不透明界面,两侧均为半透明界面,一侧为半透明、另一侧为不透明界面）对温度响应的影响;（4）采用Planck、Rosseland平均吸收系数处理非灰介质时,对辐射与导热瞬态耦合换热的影响。     

漫反射各向异性散射介质内的温度热流场

本文采用射线踪迹结合节点分析法和谱带模型,研究了漫反射不透明边界下吸收、发射、各向异性散射介质内的热辐射传递过程。考虑介质辐射能的入射和散射方向,导出漫反射、不透明边界、各向异性散射介质的辐射传递系数。在辐射平衡的情况下,考察了表面发射率和散射反照率对介质内辐射热流和温度场的影响。研究表明,介质不透明边界处存在温度跃迁现象,而且,内界面发射率越大,相应界面温度跃迁越小。     

半透明平板边界入射辐射热流密度的反问题

对一维半透明平板内辐射、导热及边界对流耦合换热过程进行了研究。提出了一种由一侧边界出射辐射强度反演另一侧边界入射辐射热流密度的方法。通过对各向异性散射、吸收系数、散射系数、边界外侧来流温度、对流换热系数、半透明平板的导热系数和平板厚度等参数对反演精度影响的分析表明,方法是可行的。     

有限体积法求解圆柱形散射介质内辐射与导热耦合换热

将谱带模型与有限体积解法相结合;求吸收、发射、散射性非灰介质圆柱体内辐射传递方程。考虑辐射强度场与热扩散温度场的耦合,将控制容积法与有限体积法结合,求解辐射与导热耦合换热。经与光线踪迹法、离散传递法的计算结果比较表明,谱带模型与有限体积解法相结合能处理多场耦合下非灰介质内的辐射换热。     

煤粉炉内弥散介质辐射传热的综合模拟

本文基于辐射传热计算的DT法和颗粒运动计算的随机轨道法,并结合单颗粒的辐射特性模型,构造了能够详细考虑颗粒燃尽、湍流弥散诸因素对炉内空间局部辐射特性及总体辐射传热影响的弥散介质辐射传热计算模型,并将其耦合到炉内过程的总体数值模型中。采用该程序,比较计算了几种颗粒辐射特性模型对某300MW锅炉炉内温度场的预报结果,结果表明：通常采用的均匀颗粒辐射特性模型会导致温度场的极大误差;由于炉内颗粒浓度的不均匀分布,炉内的温度分布呈现高度非均匀状态,在炉膛轴线上有大面积的高温烟气区存在;考虑残炭存在时,温度分布的不均匀性更显著．     

Temperature measurements of high-temperature semi-transparent infrared material using multi-wavelength pyrometry

Temperature measurements inside semi-transparent materials are important in many fields. This study investigates the measurements of interior temperature distributions in a one-dimensional semi-transparent material using multi-wavelength pyrometry based on the Levenberg–Marquardt method (LMM). The investigated material is semi-transparent Zinc Sulfide (ZnS), an infrared-transmitting optical material operating at long wavelengths. The radiation properties of the one-dimensional semi-transparent ZnS plate, including the effective spectral–directional radiation intensity and the proportion of emitted radiation, are numerically discussed at different wavelengths (8.0–14.0 μm) and temperature distributions (400–800 K) to provide the basic data for the temperature inversion problem. Multi-wavelength pyrometry was combined with the Levenberg–Marquardt method to resolve the temperature distribution along the radiative transfer direction based on the line-of-sight spectral radiation intensities at multiple wavelengths in the optimized spectral range of (11.0–14.0 μm) for the semi-transparent ZnS plate. The analyses of the non-linear inverse problem show that with less than 5.0% noise, the inversion temperature results using the Levenberg–Marquardt method are satisfactory for linear or Gaussian temperature distributions in actual applications. The analysis provides valuable guidelines for applications using multi-wavelength pyrometry for temperature measurements of semi-transparent materials.     

吸收散射性三维矩形介质内辐射源项的反问题

提出了一种由边界出射辐射强度反演吸收散射性三维矩形介质内辐射源项分布的方法。该方法是在辐射传递方程离散坐标近似的基础上,用求目标函数极小值的共轭梯度法进行反演计算。通过对介质辐射特性、光学厚度等参数对反演精度影响的分析,结果表明,即使存在测量误差,本文所提出的方法可较精确地反演辐射源项。     

Inverse radiation problem of temperature distribution in one-dimensional isotropically scattering participating slab with variable refractive index

In this paper, an inverse analysis is performed for estimation of source term distribution from the measured exit radiation intensities at the boundary surfaces in a one-dimensional absorbing, emitting and isotropically scattering medium between two parallel plates with variable refractive index. The variation of refractive index is assumed to be linear. The radiative transfer equation is solved by the constant quadrature discrete ordinate method. The inverse problem is formulated as an optimization problem for minimizing an objective function which is expressed as the sum of square deviations between measured and estimated exit radiation intensities at boundary surfaces. The conjugate gradient method is used to solve the inverse problem through an iterative procedure. The effects of various variables on source estimation are investigated such as type of source function, errors in the measured data and system parameters, gradient of refractive index across the medium, optical thickness, single scattering albedo and boundary emissivities. The results show that in the case of noisy input data, variation of system parameters may affect the inverse solution, especially at high error values in the measured data. The error in measured data plays more important role than the error in radiative system parameters except the refractive index distribution; however the accuracy of source estimation is very sensitive toward error in refractive index distribution. Therefore, refractive index distribution and measured exit intensities should be measured accurately with a limited error bound, in order to have an accurate estimation of source term in a graded index medium.     

Calculation of radiation field in semi-transparent medium with consideration of incident collimated radiation

The mathematical model of radiation field in a semi-transparent medium formed under the action of incident collimated and diffusion radiation was developed and implemented numerically. To solve the problem, the approach on the basis of modified average flux method was developed. Method testing via comparison with results of other authors has proved its high reliability and accuracy. As an example, the effect of different factors on radiation field was analyzed: self-radiation of medium, scattering anisotropy, and bottom reflectance.     

Inverse radiation problem in one-dimensional slab by time-resolved reflected and transmitted signals

A time-domain inverse approach is proposed for estimating the distribution of absorbing and scattering coefficients in one-dimensional inhomogeneous media. The temporal reflected and transmitted signals are detected when an ultra-short pulse irradiates on the boundary of semi-transparent scattering media. Forward computation and inverse algorithm employ the least-squares finite element method and conjugate gradient method, respectively. As the prevalent diffusion approximation is not employed in our model, the present approach can be extended to more comprehensive application. The investigation about detected signals indicates that the reflected signals play a significant role in reconstructing optical properties; the signals in early sampling time are more important than those at long-time logarithm slope, and so, more attention should be paid to the early signals in the solution of inverse radiation problem. Three different inverse radiation problems are investigated to show the ability of the present approach to deal with the two-layer, three-layer and continuous inhomogeneous media. The effect of measured errors on the accuracy of reconstruction is investigated by adding artificial random errors. The results indicate that accurate reconstruction depends on not only precise numerical simulation but also quality of detected data.     

Efficient inverse radiation analysis of temperature distribution in participating medium based on backward Monte Carlo method

An efficient numerical inverse radiation analysis based on the backward Monte Carlo (BMC) method is presented to determine the three-dimensional (3-D) temperature distribution in a large rectangular enclosure containing the participating medium, using radiative intensities in the visible range received by charge-coupled device (CCD) cameras. For large radiative sources and small detectors, when the radiation onto a small spot and onto a small direction cone is desired, the BMC method is more efficient than the forward Monte Carlo (FMC) method. Because the temperature reconstruction from the measured radiative intensities is an ill-posed inverse problem, least-square QR decomposition (LSQR) method is introduced to determine the meaningful temperature distribution. In order to gain insight into the effects on the accuracy of temperature distribution reconstruction, the detailed analyses are made using numerical simulations. The results show that the temperature distribution can be reconstructed accurately for the exact and noisy data.     

Inverse analysis of non-uniform temperature distributions using multispectral pyrometry

Optical diagnostics can be used to obtain sub-pixel temperature information in remote sensing. A multispectral pyrometry method was developed using multiple spectral radiation intensities to deduce the temperature area distribution in the measurement region. The method transforms a spot multispectral pyrometer with a fixed field of view into a pyrometer with enhanced spatial resolution that can give sub-pixel temperature information from a “one pixel” measurement region. A temperature area fraction function was defined to represent the spatial temperature distribution in the measurement region. The method is illustrated by simulations of a multispectral pyrometer with a spectral range of 8.0–13.0 μm measuring a non-isothermal region with a temperature range of 500–800 K in the spot pyrometer field of view. The inverse algorithm for the sub-pixel temperature distribution (temperature area fractions) in the “one pixel” verifies this multispectral pyrometry method. The results show that an improved Levenberg–Marquardt algorithm is effective for this ill-posed inverse problem with relative errors in the temperature area fractions of (–3%, 3%) for most of the temperatures. The analysis provides a valuable reference for the use of spot multispectral pyrometers for sub-pixel temperature distributions in remote sensing measurements.     

Simultaneous estimation of the temperature and heat rate distributions within the combustion region by a new inverse radiation analysis

A new inverse radiation analysis is presented for estimating the heat rate and temperature distributions in the combustion region from the information of the temperature and heat flux profiles of wall elements in the system. The Monte Carlo method is employed to solve the radiative heat transfer equation. The inverse radiation problem is posed as a minimization problem of the least squares criterion, which is solved by the conjugate gradient method. The performance of the present technique of inverse analysis is evaluated and the effects of the errors of the absorption coefficient, emissivity and convective heat transfer coefficient on the inverse analysis are investigated. The results show that the present technique is robust and yields accurate estimation even with noisy measurement.