Determining mainstream reference temperature using the non-dimensional temperature analysis in the transient liquid crystal technique

Transient thermochromic liquid crystal technique (TLC) has been widely used for measuring surface temperature distribution and local heat transfer coefficient (h). For flow inside ducts, the mass-flow-averaged temperature (Tm) and the adiabatic wall temperature (Taw) are often used as mainstream reference temperature. They are difficult to measure and a systematic error is often introduced into the results. In the present study, a novel method is developed to resolve the mainstream reference temperature from the measured temperatures at several locations using non-dimensional temperature analysis. TLC experiments of a square channel with vertical ribs, 45° ribs or V-shaped ribs are carried on, with relative CFD simulations. It is showed in the results that using the non-dimensional temperature analysis method, Nusselt number based on Tm can be adjusted by 4-15%, especially when there is large spanwise temperature variations. The systematic error of transient experiments is reduced. Taw and h can be solved in the experiments using mixed liquid crystals whether mainstream temperature history is an ideal step or not.