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Color-based image processing to measure local temperature distributions by wide-band liquid crystal thermography

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Abstract

This study presents a color-image-processing procedure for non-intrusive local temperature measurements by thermochromic liquid crystals (TLCs). The image evaluation software is completely independent of the color detection and acquisition hardware. This allows to use a wide variety of hardware solutions. An easy reproducible calibration of camera and light source is presented. The dependence of the detected hue values on intensity is investigated and further the hueversus temperature relation is studied.

Sprayable TLC formulations and TLC-coated polyester sheets are studied and compared with regard to their signal-to-noise ratio and the dependence of their hue values on illumination and viewing angle. Furthermore, a method to investigate the hue resolution is presented. The relation between the resolution of hue values and the illumination intensity and its influence on signal noise is discussed for the first time for TLC applications. Different techniques of signal noise reduction are implemented in the image processing system. Their effects on the signal noise level are discussed. As an example the two dimensional temperature distribution caused by wing-type vortex generators in a channel flow is given.

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Abbreviations

Δ (H,S,I):

smallest change ofH,S orI for variation of R, G or B by one amplitude step

Δ(T rep):

reproducibility error of temperature

ΔT :

usable calibrated temperature range, K

H,S,I:

hue, saturation, intensity

k :

index

N :

number of averaged images

n′ :

index of refraction of TLCs, ≅ 1.5

R, G, B:

red, green, blue intensities

res(H,S,I):

resolution ofH,S orI, bit

t :

time, s

T :

temperature, °C

x,y :

spatial coordinates

x :

coefficient

Y/C :

luminance and chrominance signal

φ i :

angle, degree

λ:

heat conductance, W/(mK)

λ:

dominant wavelength, 10−6·m

i :

index

i :

calibration no.i

i :

illumination

j :

calibration no.j

M :

object (model)

n :

viewing- and illumination angle =0°C (perpendicular to the surface)

s :

viewing

TLC:

thermochromic liquid crystals

References

  1. 1.

    Moffat, R.J., Experimental heat transfer. In:IHTCC 9th International Heat Transfer Conference Vol. 1 (1990) pp. 187–205.

  2. 2.

    Cooper, T.E., Field, R.J. and Meyer, J.F., Liquid crystal thermography and its application to the study of convective heat transfer.Transactions of the ASME (1975) 442–450.

  3. 3.

    Hippensteele, S.A., Russell, L.M. and Stepka, F.S., Evaluation of a method for heat transfer measurements and thermal visualization using a composite of a heater element and liquid crystals.Transactions of the ASME 105 (1983) 184–189.

  4. 4.

    Bütefisch, K.-A. and Ahlbrecht, H., Quantitative Wärmeübergangsmessungen mit geheizten Flüssigkristallen. DGLR Bericht, 2D Meßtechnik, DGLR Workshop 88-04 (1988) 233–244.

  5. 5.

    Tiggelbeck, S., Experimentelle Untersuchungen and Kanalströmungen mit Einzel- und Doppelwirbelerzeuger-Reihen in kompakten Wärmetauschern. Dissertation, Ruhr-Universität Bochum (1990).

  6. 6.

    Kallweit, P.: Längswirbelerzeuger fur den Einsatz in Lamellenwärmetauschem. Dissertation, Ruhr-Universität Bochum (1986).

  7. 7.

    Valencia, A., Wärmeübergang und Druckverlust in Lamellen-Rohr-Wärmeübertragern mit Längswirbelerzeugern. Dissertation, Ruhr-Universität Bochum (1993).

  8. 8.

    Wang, Z., Ireland, P.T. and Jones, T.V., An advanced method of processing liquid crystal video signals from transient heat transfer experiments. ASME Paper No. 93-GT-282 (1993).

  9. 9.

    Behle, M., Entwicklung eines Verfahrens zur Auswertung instationärer Flüssigkristallthermographie-Aufnahmen mittels digitaler Bildverarbeitung. Diplomarbeit, Ruhr-Universität Bochum No. 93-16 (1993).

  10. 10.

    Akino, N., Kunugi, T., Ichimiya, K., Mitsushiro, K. and Ueda, M., Improved liquid-crystal thermometry excluding human color sensation.Transactions of the ASME 111 (1989).

  11. 11.

    Dabiri, D. and Gharib, M., Digital particle image thermometry: The method and implementation.Experiments in Fluids 11 (1991) 77–86.

  12. 12.

    Camci, C., Kim, K. and Hippensteele, S.A., A new hue capturing technique for the quantitative interpretation of liquid crystal images used in convective heat transfer studies.ASME Transactions, Journal of Turbomachinery 114 (1992) 765–775.

  13. 13.

    Frey, H., Digitale Bildverarbeitung in Farbräumen. Dissertation, TU München (1988).

  14. 14.

    Fergason, J.L., Liquid crystals in nondestructive testing.Applied Optics 7 (1968) 1729–1737.

  15. 15.

    Farina, D.J., Hacker, J.M., Moffat, R.J. and Eaton, J.K., Illuminant invariant calibration of thermochromic liquid crystals.Experimental Thermal and Fluid Science 9 (1994) 1–12.

  16. 16.

    Herold, W. and Wiegel, D., Problems of the photographic documentation of liquid crystalline thermographs.Advances in Liquid Crystal Research and Applications (1980) 1255–1259.

  17. 17.

    Pratt, W.K.,Digital Image Processing. John Wiley & Sons Inc. (1991).

  18. 18.

    Goeser, M.O., Entwicklung eines Software-Programms zur Auswertung instationärer Farb-Flüssigkristallthermografie-Aufnahmen mittels digitaler Bildverarbeitung. Konstraktiver Entwurf, Ruhr-Universität Bochum No. 94–08 (in preparation).

  19. 19.

    Lohmberg, A., Entwicklung eines Aufbaus zur winkelabhängigen Kalibrierung von Oberflächentemperaturmessungen mittels Breitband-Flüssigkristallthermografie und IR-Thermografie. Konstraktiver Entwurf, Ruhr-Universität Bochum No. 94–03 (1994).

  20. 20.

    Wundes, K., Verbesserte Farbton-Temperatur-Kalibrierung von thermochromen Breitbandflüssigkristallen zur Erzielung einer hoheren Informationsdichte. Studienarbeit, Ruhr-Universität Bochum No. 94–08 (1994).

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Behle, M., Schulz, K., Leiner, W. et al. Color-based image processing to measure local temperature distributions by wide-band liquid crystal thermography. Appl. Sci. Res. 56, 113–143 (1996). https://doi.org/10.1007/BF02249377

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Key words

  • liquid crystal thermography
  • color image processing
  • hue-to-temperature—calibration