Simultaneous three-dimensional temperature and velocity field measurements using astigmatic imaging of non-encapsulated thermo-liquid crystal (TLC) particles

Segura, Rodrigo; Rossi, Massimiliano; Cierpka, Christian; Kähler, Christian J.

doi:10.1039/c4lc01268b

Cited by 25 publications

(25 citation statements)

References 18 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Recently, APTV is combined with special particles to measure properties other than velocity. Segura et al (2015) utilized non-encapsulated thermochromic liquid crystals (TLC) particles, to measure the volumetric 3D velocity-and temperature field in an evaporating droplet with a measurement volume depth of 20 μm . Also, Massing et al (2016Massing et al ( , 2018 used luminescent polymer particles to measure the three-dimensional temperature and velocity field of a heated flow in a channel with a cross section of 2 × 2 mm 2 .…”

Section: Introductionmentioning

confidence: 99%

“…However, compared to the particle diameter, the error was relatively large ( z ∕d p = 127% ). Segura et al (2015) used a white light source with a circular polarization filter to excite their TLC particles and reported a relative high uncertainty of z ∕ z = 8.5% in reconstructing the z-position compared to laser-based APTV. They concluded it was due to the less bright particle images obtained with a white light source.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Utilizing the ball lens effect for astigmatism particle tracking velocimetry

et al. 2020

View full text Add to dashboard Cite

In the present study, a simple method is developed to apply astigmatism particle tracking velocimetry (APTV) to transparent particles utilizing backlight illumination. Here, a particle acts as ball lens and bundles the light to a focal point, which is used to determine the particle's out-of-plane position. Due to the distance between focal point and particle, additional features have to be considered in ball lens astigmatism particle tracking velocimetry (BLAPTV) compared to conventional APTV. We describe required calibration steps and perform parameter studies to show how the autocorrelation coefficient and the light exposure affect the accuracy of the method. It is found that the accuracy and robustness of the Euclidean calibration approach as also used in conventional APTV (Cierpka et al. in Meas Sci Technol 22(1):015401, 2010a) can be increased if an additional calibration curve for the light intensity of the particle's focal point is considered. In addition, we study the influence of the particle diameter and the refractive index jump between liquid and particles on the calibration curves and the accuracy. In this way, particles of the same size, but different material, can be distinguished by their calibration curve. Furthermore, an approach is presented to account for shape changes of the calibration curve along the depth of the measurement volume. Overall, BLAPTV provides high out-of-plane particle reconstruction accuracies with respect to the particle diameter. In test cases, position uncertainties down to 1.8% of the particle diameter are achieved for particles of d p = 124 μm. The measurement technique is validated for a laminar flow in a straight rectangular channel with a cross-sectional area of 2.3 × 30 mm 2. Uncertainties of 0.75% for the in-plane and 2.29% for out-of-plane velocity with respect to the maximum streamwise velocity are achieved.

show abstract

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Utilizing the ball lens effect for astigmatism particle tracking velocimetry

et al. 2020

View full text Add to dashboard Cite

show abstract

“…However, in general a compromise must be found to prevent overfitting caused by too high polynomial orders, while the order must still be high enough to represent complex functions. A big advantage of using the system matrix is that also other functional approaches could be checked as well as additional variables like for example the saturation S and the value V could be implemented easily, which might improve the results considerably (Segura et al 2015). For the current application hue was chosen to be the only temperature-dependent variable in the system matrix to circumvent problems caused by a varying particle image density during the measurements.…”

Section: Discussion Of the Calibration Methodsmentioning

confidence: 99%

On the application of neural networks for temperature field measurements using thermochromic liquid crystals

2020

Self Cite

View full text Add to dashboard Cite

This study presents an investigation regarding the applicability of neural networks for temperature measurements using thermochromic liquid crystals (TLCs) and discusses advantages as well as disadvantages of common calibration approaches. For the characterization of the measurement technique, the dependency of the color of the TLCs on the temperature as well as on the observation angle and, therefore, on the position within the field of view of a color camera is analyzed in detail. In order to consider the influence of the position within the field of view on the color, neural networks are applied for the calibration of the temperature measurements. In particular, the focus of this study is on analysis of the error of temperature measurement for different network configurations as well as training methods, yielding a mean absolute deviation and a mean standard deviation in the range of 0.1 K for instantaneous measurements. On the basis of a comparison of this standard deviation to that of two further calibration approaches, it is shown that neural networks are suited for temperature measurements via the color of TLCs. Finally, the applicability of this measurement technique is illustrated at an exemplary temperature measurement in a horizontal plane of a Rayleigh-Bénard cell with large aspect ratio, which clearly shows the emergence of convective flow patterns by means of the temperature field.

show abstract

“…Thermochromic liquid crystals (TLCs) are increasingly being used as an accurate and convenient means of measuring surface temperature and heat-transfer coefficient because their optical properties are dependent on temperature in a predictable and repeatable manner [1][2][3][4][5][6]. TLCs, whose molecular structure changes with temperature, selectively reflect light at a wavelength characteristic of the local surface temperature.…”

Section: Introductionmentioning

confidence: 99%