On liquid crystal thermography for determination of heat transfer coefficient in rectangular ducts

Liquid crystal thermography (LCT) has been employed by researchers in heat transfer and fluid flow communities as a reliable and non-intrusive temperature measurement technique. This technique correlates the colour response to temperature for a heated surface which has been treated with thermochromic liquid crystals (TLCs). The LCT has been used extensively in convective heat transfer research in duct flows. In this paper, some experiences by LCT in thermal measurements for rectangular duct flows are provided. A few TLCs examples associated with continuous ribs for two different values of rib pitch-to-height ratio of 4 and 8 at Re=8900 and 28500 are illustrated. Important issues such as heating principles, calibration of TLCs, image acquiring and analysis, problems of treating the surface by TLCs, and expected measurement accuracy are summarized. The main purpose is to assist newcomers in the field and provide some guidelines for proper use of the LCT in heat transfer research.