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Angular effects on thermochromic liquid crystal thermography

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Abstract

This paper directly discusses the effects of lighting and viewing angles on liquid crystal thermography. This is because although thermochromic liquid crystals (TLCs) are a widely-used and accepted tool in heat transfer research, little effort has been directed to analytically describing these effects. Such insight is invaluable for the development of effective mitigation strategies. Using analytical relationships that describe the perceived color shift, a systematic manner of improving the performance of a TLC system is presented. This is particularly relevant for applications where significant variations in lighting and/or viewing angles are expected (such as a highly curved surface). This discussion includes an examination of the importance of the definition of the hue angle used to calibrate the color of a TLC-painted surface. The theoretical basis of the validated high-accuracy calibration approach reported by Kodzwa et al. (Exp Fluids s00348-007-0310-6, 2007) is presented.

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Abbreviations

CCD:

charge coupled device

B :

blue component value

BL:

referring to black reference

c :

arbitrary constant

G :

green component value

i :

integer value

max:

maximum value

min:

minimum value

MV:

measured voltage

N :

number of calibration curves

n air :

index of refraction for air

\(\overline{n}_{\rm TLC}\) :

average index of refraction for TLC

0:

initial conditions

Q :

hue angle

R :

red component value

REF:

reference

ROI:

region of interest

S :

saturation

S′:

partial saturation

\({{\mathcal{T}}}\) :

time required to collect calibration curves (h)

TLC:

Thermochromic Liquid Crystal

V :

voltage or color parameter (Hay and Hollingsworth 1996)

V′:

color parameter (Hacker and Eaton 1995)

WH:

referring to white reference

x :

spatial coordinate

y :

spatial coordinate

\({{\mathcal{Z}}}\) :

channel value

Δ :

spacing

Δ x|min :

minimum cell size in x-direction

Δ y|min :

minimum cell size in y-direction

δ:

change

δ u :

uncertainty

ɛ:

difference between mean component values

ϕTLC,i :

angle of illumination

ϕTLC,s :

angle of scattering or viewing

λ:

wavelength (nm)

λ n :

wavelength of maximum scattering for normal incidence and observation (nm)

τ1 :

time necessary to convert \({{\mathcal{Z}}}\) for each pixel (s)

τ2 :

time necessary to set temperature of calibration surface (s)

\(\vartheta\) :

number of pixels in a given ROI

References

  • Anderson M, Baughn J (2005a) Thermochromic liquid crystal thermography: illumination spectral effects. Part 1—experiments. J Heat Transf 126(3):581–587

    Article  Google Scholar 

  • Anderson M, Baughn J (2005b) Thermochromic liquid crystal thermography: illumination spectral effects. Part 2—theory. J Heat Transf 127(6):588–597

    Article  Google Scholar 

  • Baughn J (1995) Liquid crystal methods for studying turbulent heat transfer. Int J Heat Fluid Flow 16(5):365–375

    Article  Google Scholar 

  • Camci C, Kim K, Hippensteele S, Poinsatte P (1993) Evaluation of a hue capturing based transient liquid crystal method for high-resolution mapping of convective heat transfer on curved surfaces. J Heat Transf 115(2):311–318

    Article  Google Scholar 

  • Collings P, Hird M (1997) Introduction to liquid crystals. Taylor & Francis Inc., 325 Chestnut St., 8th Floor, Philadelphia, PA 19106

  • Drost U, Bölcs A (1999) Investigation of detailed film cooling effectiveness and heat transfer distribution on a gas turbine airfoil. J Turbomach 121(2):233–242

    Google Scholar 

  • Fergason J (1968) Liquid crystals in nondestructive testing. Appl Opt 7(9):1729–1737

    Google Scholar 

  • Ferziger J (ed) (1998) Numerical methods for engineering application, 2nd edn. Wiley, 605 Third Avenue, New York, NY 10158-0012

  • Günther A, von Rohr P (2002) Influence of the optical configuration on temperature measurements with fluid-dispersed TLCs. Exp Fluids 32(5):533–541

    Article  Google Scholar 

  • Hacker J, Eaton J (1995) Heat transfer measurements in a backward facing step flow with arbitrary wall temperature variations. Technical report MD-71, Stanford, California 94305

  • Hay J, Hollingsworth D (1996) A comparison of trichromic systems for use in the calibration of polymer-dispersed thermochromic liquid crystals. Exp Therm Fluid Sci 12(1):1–12

    Article  Google Scholar 

  • Hay J, Hollingsworth D (1998) Calibration of micro-encapsulated liquid crystals using hue angle and a dimensionless temperature. Exp Therm Fluid Sci 18(3):251–257

    Article  Google Scholar 

  • Hollingsworth D, Boehman A, Smith E, Moffat R (1989) Measurement of temperature and heat transfer coefficient distributions in complex flow using liquid crystal thermography and true-color image processing. Collected papers in heat transfer. The American Society of Mechanical Engineers, New York, pp 35–42

    Google Scholar 

  • Kline S, McClintock F (1953) Describing uncertainties in single sample experiments. Mech Eng 75:3–8

    Google Scholar 

  • Kodzwa P, Elkins C, Mukerji D, Eaton J (2007) Thermochromic liquid crystal temperature measurements through a borescope imaging system. Exp Fluids s00348-007-0310-6

  • Mukerji D, Eaton J (2005) Discrete Green’s function measurements in a single passage turbine model. J Heat Transf 127(4):366–376

    Article  Google Scholar 

  • Parsley M (1991a) An introduction to thermochromic liquid crystals. Technical report, 1820 Pickwick Ln., Glenview, Illinois, 60025, USA

  • Parsley M (1991b) The use of thermochromic liquid crystals in research applications, thermal mapping and non-destructive testing. In: Proceedings of the 7th IEEE SEMI-THERM symposium, pp 53–58

  • Roberts G, East R (1996) Liquid crystal thermography for heat transfer measurement in hypersonic flows: a review. J Spacecraft Rockets 33(6):761–768

    Article  Google Scholar 

  • Sabatino D, Praisner T, Smith C (2000) A high-accuracy calibration technique for thermochromic liquid crystal measurements. Exp Fluids 28(1):497–505

    Article  Google Scholar 

  • Smith C, Praisner T, Sabatino D (2001) Temperature sensing with thermochromic liquid crystals 30(2):190–201

    Google Scholar 

Download references

Acknowledgments

This research was sponsored by General Electric Aircraft Engines, through their University Strategic Alliance Program. The first author received support from the National Science Foundation via a 3-year Graduate Fellowship. The authors would like to express their sincere gratitude to F. Buck, B. Bergholz and D. Wisler (at GEAE) and D. Dods (at Instrument Technology Incorporated) and V. Davison at (QC/NDT) for their assistance and advice in the course of this experimental program. S. Carver, J. Hammer, J. Glassman, T. Hasler and L. Johal are gratefully acknowledged for their high level of expertise in manufacturing various parts in this experimental program.

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Authors and Affiliations

  1. Department of Mechanical Engineering, Flow Physics and Computation, Stanford University, Stanford, CA, 94305, USA

    Paul M. Kodzwa Jr & John K. Eaton

Authors
  1. Paul M. Kodzwa Jr
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  2. John K. Eaton
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Correspondence to John K. Eaton.

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This work was funded by the General Electric Aircraft Engines University Strategic Alliance Program.

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Kodzwa, P.M., Eaton, J.K. Angular effects on thermochromic liquid crystal thermography. Exp Fluids 43, 929–937 (2007). https://doi.org/10.1007/s00348-007-0363-6

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  • DOI: https://doi.org/10.1007/s00348-007-0363-6

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