On the Applicability of a Triple Thermochromic Liquid Crystal Layer for Transient Heat Transfer Experiments

This paper examines the applicability of a triple layer of thermochromic liquid crystals on the evaluation of local heat transfer coefficients using the transient liquid crystal measurement technique. The experiments were carried out in a narrow impingement cooling channel typically found in turbine airfoils. Narrow-band liquid crystals of 35°C, 38°C and 41°C were individually painted on the target plate of the cooling cavity and the overall paint thickness was accurately measured. Therefore, the 1D transient heat conduction equation was implicitly solved for each individual liquid crystal layer on its realistic depth on the painted surface. As a result, local heat transfer coefficients were calculated three times for the same location improving the measurement accuracy, especially at regions where liquid crystal detection times are too short or wide. The results indicate that if multiple liquid crystals layers are used and the paint thickness is not considered, heat transfer coefficients can be underestimated.