Spatially resolved measurement of transient concentration and temperature fields using Schlieren and LIF technique

提出的项目涉及界面附近局部和瞬态浓度和温度场的定量确定。这些场决定了发生的质量或能量输运，并将使用纹影技术进行光学量化。这种测量技术允许对测量体积进行几乎瞬时的二维检查。从获得的图像中，可以无创地确定传递系数，并且可以分辨空间和时间。因此，有可能阐明传质过程中的瞬态行为。接触装置的设计还没有充分考虑到这种行为，目前依赖于积分经验方程。瞬态界面现象的一个例子是马兰戈尼对流，它影响静滴处的传质。对这些影响的考虑为优化准稳态设计开辟了巨大的潜力，并有助于对传质过程的基础有更深入的了解。此外，测量提供了准确的实验数据，以验证数值方法和改进预测。作为测量的一部分，将确定不同几何形状下的输运系数。首先，测量自构建测试样品上的能量输运，因为使用温度场可以更好地再现并能够可靠地验证测量程序。在此验证过程的背景下，实现了球面场自动分析的算法。在此基础上，研究了近平面和单液滴的浓度场。对于单个液滴，首先研究了无界面不稳定性的液/液系统，然后是具有界面不稳定性的系统。该项目的一个重要部分是开发测量装置，以提高测量精度和可靠性。在这里，实现了硬件和软件的改进，例如，集成线性导轨以实现更精确的滤波器定位或使用先进的图像处理方法。由于纹影技术首次用于液/液质量输运的定量测定，因此需要进行几个验证步骤。采用激光诱导荧光（LIF）对纹影数据进行了实验验证。此外，测量数据将使用计算流体动力学（CFD）和光线追踪计算进行数值验证。此外，射线跟踪计算提供了检查纹影测量的准确性和灵敏度的可能性。最后，第二光轴的构造使关于折射率场的假设得以验证。此外，使用第二光轴作为分析界面不稳定期间出现的不规则形状浓度场的起点。

The proposed project deals with the quantitative determination of local and transient concentration and temperature fields near interfaces. Those fields determine the occurring mass or energy transport and will be quantified optically using Schlieren technique. This measurement technique allows a nearly instantaneous, two-dimensional examination of the measurement volume. From the obtained images, the transfer coefficients can be determined non-invasively as well as space- and time-resolved. As a result, it is possible to elucidate transient behavior during mass transfer pro-cesses. This behavior has not yet been sufficiently taken into account for the design of contact apparatuses, which currently depends on integral empirical equations. An example of transient interfacial phenomena is Marangoni convection, which influences the mass transfer at quiescent single droplets. The consideration of these influences opens up great potential for optimizing appa-ratus design and helps to gain a deeper understanding of the basics of mass transfer processes. In addition, the measurements provide accurate experimental data to validate numerical approaches and improve predictions.As part of the measurements, transport coefficients at different geometries will be determined. At first, energy transport on self-constructed test specimen is measured since the use of temperature fields allow better reproducibility and enable a reliable validation of the measuring procedure. In the context of this validation process, an algorithm for automated analysis of spherical fields is imple-mented. Based on this, concentration fields near planar surfaces and single droplets are examined. For single droplets, liquid/liquid systems without interfacial instabilities are investigated followed by systems with interfacial instabilities.An important part of the project is the development of the measurement setup with regard to measurement accuracy and reliability. Here, improvements of hardware and software, for example, the integration of a linear guide for a more precise filter positioning or the use of advanced image processing methods are implemented.Due to the first-time use of Schlieren technique for quantitative determination of liquid/liquid mass transport, several validation steps are carried out. Laser Induced Fluorescence (LIF) is used to validate the Schlieren data experimentally. In addition, measurement data will be validated numerically using computational fluid dynamics (CFD) and ray tracing calculations. Additionally, ray trac-ing calculations offer the possibility to check accuracy as well as sensitivity of the Schlieren meas-urements. Finally, the construction of a second optical axis enables the validation of assumptions made about the refractive index field. Furthermore, the use of a second optical axis acts as starting point for the analysis of irregularly shaped concentration fields as they occur during interfacial instabilities.