Angular effects on thermochromic liquid crystal thermography

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.

[1]  T. J. Praisner,et al.  A high-accuracy calibration technique for thermochromic liquid crystal temperature measurements , 2000 .

[2]  James W. Baughn,et al.  Liquid-Crystal Thermography: Illumination Spectral Effects. Part 1—Experiments , 2005 .

[3]  J. Eaton,et al.  Discrete Green’s Function Measurements in a Single Passage Turbine Model , 2005 .

[4]  D. K. Hollingsworth,et al.  A comparison of trichromic systems for use in the calibration of polymer-dispersed thermochromic liquid crystals , 1996 .

[5]  Influence of the optical configuration on temperature measurements with fluid-dispersed TLCs , 2002 .

[6]  J. L. Fergason,et al.  Liquid crystals in nondestructive testing. , 1968, Applied optics.

[7]  Z. Yao.  A review of: “Fundamentals of Interfacial Engineering” by R. J. Stokes and D. F. Evans Wiley-VCH 605 Third Avenue New York, NY 10158-0012 , 1998 .

[8]  James W. Baughn,et al.  Liquid crystal methods for studying turbulent heat transfer , 1995 .

[9]  S. J. Kline,et al.  Describing Uncertainties in Single-Sample Experiments , 1953 .

[10]  G. T. Roberts,et al.  Liquid Crystal Thermography for Heat Transfer Measurement in Hypersonic Flows: A Review , 1996 .

[11]  R. J. Moffat,et al.  Measurement of temperature and heat transfer coefficient distributions in a complex flow using liquid crystal thermography and true-color image processing , 1989 .

[12]  T. J. Praisner,et al.  Temperature sensing with thermochromic liquid crystals , 2001 .

[13]  A. Bölcs,et al.  Investigation of Detailed Film Cooling Effectiveness and Heat Transfer Distributions on a Gas Turbine Airfoil , 1999 .

[14]  S. Maynard.  Part 2. Theory , 2002 .

[15]  D. K. Hollingsworth,et al.  Calibration of micro-encapsulated liquid crystals using hue angle and a dimensionless temperature , 1998 .

[16]  M. Parsley,et al.  The use of thermochromic liquid crystals in research applications, thermal mapping and non-destructive testing , 1991, 1991 Proceedings, Seventh IEEE Semiconductor Thermal Measurement and Management Symposium.

[17]  C. Elkins,et al.  Thermochromic liquid crystal temperature measurements through a borescope imaging system , 2007 .

[18]  James W. Baughn,et al.  Thermochromic Liquid Crystal Thermography: Illumination Spectral Effects. Part 2: Theory , 2005 .

[19]  P. Sheng,et al.  Introduction to Liquid Crystals , 1976 .

[20]  S. A. Hippensteele,et al.  Evaluation of a Hue Capturing Based Transient Liquid Crystal Method for High-Resolution Mapping of Convective Heat Transfer on Curved Surfaces , 1993 .