Problems of the photographic documentation of liquid crystalline thermographs

Herold, W.; Wiegel, D

doi:10.1016/b978-0-08-026191-1.50050-5

Cited by 10 publications

(4 citation statements)

References 1 publication

Supporting

Mentioning

Contrasting

Order By: Relevance

“…If the illumination and viewing are on the same line (on-axis), the angle effect was minimized, amounting to a measurement error of only a few percent of the effective hue range for angles 0 to 70°, while off-axis light and viewing can result in much higher errors. 24,14,23,25,26…”

Section: Illumination and Viewing Incidence Anglesmentioning

confidence: 99%

Errors in thermochromic liquid crystal thermometry

Wiberg¹,

Lior

2004

Review of Scientific Instruments

View full text Add to dashboard Cite

This article experimentally investigates and assesses the errors that may be incurred in the hue-based thermochromic liquid crystal thermochromic liquid crystal (TLC) method, and their causes. The errors include response time, hysteresis, aging, surrounding illumination disturbance, direct illumination and viewing angle, amount of light into the camera, TLC thickness, digital resolution of the image conversion system, and measurement noise. Some of the main conclusions are that: (1) The 3 ϫ 8 bits digital representation of the red green and blue TLC color values produces a temperature measurement error of typically 1% of the TLC effective temperature range, (2) an eight-fold variation of the light intensity into the camera produced variations, which were not discernable from the digital resolution error, (3) this temperature depends on the TLC film thickness, and (4) thicker films are less susceptible to aging and thickness nonuniformities.

show abstract

Section: Illumination and Viewing Incidence Anglesmentioning

confidence: 99%

Errors in thermochromic liquid crystal thermometry

Wiberg¹,

Lior

2004

Review of Scientific Instruments

View full text Add to dashboard Cite

show abstract

“…Cahbration of the TLC was performed using the spectral peaks of light intensity for each of the three observed colon. A diffuse-light source was mounted on the camera to eliminate the view-angle dependency of the TLC color transition discussed by Herold and Wiegel (1980). TLC was calibrated with a coupon at the representative view angle at the beginning of each test.…”

Section: Fig 10 Schematic View Of Test Apparatusmentioning

confidence: 99%

A Novel Technique for the Internal Blade Cooling

Glezer¹,

Moon²,

O’Connell³

1996

Volume 4: Heat Transfer; Electric Power; Industrial and Cogeneration

View full text Add to dashboard Cite

Development of an adequate air cooling system for the thermally highly loaded leading edge and tip of the blade, that is cost effective and also relatively insensitive to manufacturing tolerances and operating environment continues to be one of the major challenges in advanced gas turbine design. Extensive studies on the convective (including impingement) and film cooling techniques produced remarkable progress in achieving a high cooling effectiveness level for turbine airfoils. However, in the case of turbine blades, application of these techniques has severe limitations. Highly effective impingement cooling needs to be combined with film discharge of the spent air to avoid a negative impact of crossflow on internal heat transfer and also provide additional thermal protection of the surface downstream of the discharge holes. Noticeable aerodynamic penalties, stress concentration and significant increase in manufacturing cost limit application of blade film cooling, particularly for moderately high operating temperatures. Search for a highly effective robust design of internal airfoil cooling which can delay the use of film cooling resulted in the creation of a new technique which is described in this paper. This technique is based on generation of a swirling flow structure in the blade internal leading edge passage. Significant heat transfer augmentation can be achieved when the cooling air is delivered into the leading edge plenum tangentially to the inner concave surface. The best results can be obtained when the swirling flow is allowed to move radially, creating a three-dimensional screw-shaped flow in the plenum. The presented results of the flow and heat transfer studies performed for the practical range of Reynolds numbers for the internal flow show that the leading edge screw-shaped cooling technique provides internal heat transfer rate comparable with impingement coupled with film discharge of the spent air, is more effective than impingement with cross flow and is almost five times higher than heat transfer in the smooth channel.

show abstract

“…They used (1) a fibre optic ring light which was coaxially mounted to the camera lens (on-axis) and calibrated the TLCs for angles (measured from the surface normal) between 10 and 25 ° and (2) positioned the camera normal to the TLC-coated surface and varied the illumination angle (off-axis) between 15 and 35 ° . The authors showed that the change of the hue values is negligible for the on-axis arrangement if the illumination and viewing angle are changed in the same way (see also Herold and Wiegel [16]). Further they showed that the hue values change to higher values for on-axis off-axis the off-axis arrangement with increasing illumination angle (the camera was fixed with its optical axis normal to the TLC-coated surface) which corresponds to a change to shorter dominant wavelengths (over 10% for a change of the illumination angle between 15 and 35°).…”

Section: Comparison Of Tlc Sheet Versus Tlc Inkmentioning

confidence: 97%

“…This effect is confirmed by Farina et al [15] who showed that an angle between camera and light source of 35 ° (light source fixed normal to the surface) can cause a change of hue of about 14% (to shorter wavelengths) as compared to a 0°-configuration. Based on a study of Herold and Wiegel [16], Farina et al show that a position of a light source fixed coaxially to the camera axis avoids any angle dependence. They attached a fibre optic ring light coaxially to the camera lens and changed the angle of both camera and light source measured from the normal of the TLC-coated surface between 0 and 25 ° without any significant effect on the hue values.…”

Section: Introductionmentioning

confidence: 99%

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

et al. 1996

View full text Add to dashboard Cite

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 hue versus 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.

show abstract

Problems of the photographic documentation of liquid crystalline thermographs

Cited by 10 publications

References 1 publication

Errors in thermochromic liquid crystal thermometry

Errors in thermochromic liquid crystal thermometry

A Novel Technique for the Internal Blade Cooling

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

Contact Info

Product

Resources

About