Abstract
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.Graphic abstract
Highlights
For the detailed analysis of many natural and technical systems, the simultaneous determination of several physi‐ cal quantities is necessary
In order to perform the temperature calibration, the color signal of the thermochromic liquid crystals (TLCs) in dependency of the temperature was investigated in detail
It should be noted that those results concerning the mean absolute deviation and the standard deviation originate from the specific appli‐ cation presented in this study and, cannot be
Summary
For the detailed analysis of many natural and technical systems, the simultaneous determination of several physi‐ cal quantities is necessary. Simultaneous measurements of the velocity and temperature are of inter‐ est, as these quantities allow for investigations of the trans‐ port of momentum and heat, e.g., in natural convection (Schmeling et al 2014; Tummers and Steunebrink 2019), process engineering (Massing et al 2018) and general heat transfer problems (Cafiero et al 2014; Irwansyah et al 2016) For this purpose, many different measurement tech‐ niques with each having its own specific advantages and disadvantages have proven to be successful, enabling the choice of an appropriate measurement technique based on the application. The well-established temperature measurement technique laser-induced fluorescence (LIF) is frequently used to determine temperature fields covering a larger tem‐ perature range (Sakakibara and Adrian 1999; Banks et al 2019), at the expense of an increased uncertainty of temperature measurement
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