Determination of Interior Surface Temperature Using Luminance Measurement of Thermochromic Liquid Crystals

Abstract

This paper presents a new method to measure interior surface temperature distributions. An image-resolved luminance measurement camera is used to capture light transmitted through thermochromic liquid crystals (TLC). These crystals change their optical properties with temperature. The experiments clearly show a unique relationship between temperature and the luminance value of the TLC. A calibration function is detected to transform the measured luminance distribution into corresponding temperatures. The developed method is applied to a model of an automotive headlamp. The data are compared with results obtained by using standard techniques such as infrared camera and thermocouple measurement. By that, a reasonable accuracy of the developed method of about ± 0.7°C can be determined. Knowing the temperature on both inner and outer surfaces, the heat transfer can be evaluated.

Keywords:

• thermochromic liquid crystals
• luminance measurement
• temperature measurement
• heat transfer

ACKNOWLEDGMENTS

The authors of the article would like to thank Professor Dietrich Gall (TU Ilmenau) and Mr. Rainer Nolte (TU Ilmenau) for their support and interesting discussions. This work was supported by AUDI AG Ingolstadt and Automotive Lighting Reutlingen GmbH.