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-toheight 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.
This paper investigates the effect of the presence of a rib on the local heat transfer around an obstacle using liquid crystal technique. An obstacle with a rectangular cross section is placed in a channel and attached to the end-wall. A rib is positioned in the downstream region of the obstacle. The spacing S between the rib and the obstacle is normalized by the spanwise width of the obstacle and the value is 1.25d. The effects of the rib height e/Dh and Reynolds number are investigated. The e/Dh has the values 0.039 and 0.078. The Reynolds number varies between 35,600 and 55,600. It is shown that the local heat transfer in the upstream region of the obstacle remained unaffected by the presence of the rib. The feature of local heat transfer in the downstream area of the obstacle was substantially modified by the presence of the rib.
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