What can be learned from optical two-color diffusion and thermodiffusion experiments on ternary fluid mixtures?
What can be learned from optical two-color diffusion and thermodiffusion experiments on ternary fluid mixtures?
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DOI：
10.1063/1.4908538
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发表时间：
2015-02-28
影响因子：
4.4
通讯作者：
Koehler, W.
中科院分区：
文献类型：
--
作者：
Gebhardt, M.;Koehler, W.
近年来，为研究地面和国际空间站上三元流体混合物中的扩散和热扩散，开发了一些光学技术。所有这些方法都是基于同时测量两个不同波长下的折射率变化。在这里，我们讨论和比较不同的技术，重点是光束偏转（OBD），光学数字干涉，和热扩散强迫瑞利散射（TDFRS）。我们建议正式分裂成一个现象学参数化的测量瞬态和随后的转换从折射率到浓度空间的数据评估。在所有实验中，在两个不同的检测波长下测量的瞬态可以由扩散系数矩阵的四个振幅和两个特征值来描述。事实证明，这六个参数受到很大的误差，不能可靠地确定。五个好的数量，这可以被确定为具有高精度，是固定的振幅，初始斜率定义在TDFRS实验和应用的启发式标准相似的曲线，一定的平均扩散系数。这些振幅和斜率直接与Soret和热扩散系数变换后的逆对比因子矩阵，这是经常病态。由于六个自由参数中只有五个被可靠地确定，包括单个平均扩散系数，因此不可能确定扩散矩阵的四个条目。我们将我们的结果应用到对称（质量分数0.33/0.33/0.33）三元基准混合物正十二烷/异丁基苯/1，2，3，4-四氢萘和现有文献数据相同的系统的新OBD测量。(C)2015 AIP Publishing LLC.
A number of optical techniques have been developed during the recent years for the investigation of diffusion and thermodiffusion in ternary fluid mixtures, both on ground and on-board the International Space Station. All these methods are based on the simultaneous measurement of refractive index changes at two different wavelengths. Here, we discuss and compare different techniques with the emphasis on optical beam deflection (OBD), optical digital interferometry, and thermal diffusion forced Rayleigh scattering (TDFRS). We suggest to formally split the data evaluation into a phenomenological parameterization of the measured transients and a subsequent transformation from the refractive index into the concentration space. In all experiments, the transients measured at two different detection wavelengths can be described by four amplitudes and two eigenvalues of the diffusion coefficient matrix. It turns out that these six parameters are subjected to large errors and cannot be determined reliably. Five good quantities, which can be determined with a high accuracy, are the stationary amplitudes, the initial slopes as defined in TDFRS experiments and by application of a heuristic criterion for similar curves, a certain mean diffusion coefficient. These amplitudes and slopes are directly linked to the Soret and thermodiffusion coefficients after transformation with the inverse contrast factor matrix, which is frequently ill-conditioned. Since only five out of six free parameters are reliably determined, including the single mean diffusion coefficient, the determination of the four entries of the diffusion matrix is not possible. We apply our results to new OBD measurements of the symmetric (mass fractions 0.33/0.33/0.33) ternary benchmark mixture n-dodecane/isobutylbenzene/1,2,3,4-tetrahydronaphthalene and existing literature data for the same system. (C) 2015 AIP Publishing LLC.