Heat Transfer Coefficients in a Three-Passage Ribbed Channel Using a Transient Liquid Crystal Technique

One-dimensional (1D) transient heat conduction in a semi-infinite solid material with a convection boundary condition has been widely used for determining the surface convection heat transfer coefficient distributions. In this work, the full heat transfer characteristic maps of a turbine blade with a realistic, three-passage, ribbed channel are examined using the 1D transient heat conduction model with narrow-band liquid crystals. The tests were conducted at two different engine representative flow conditions. The time map for the blade’s internal surfaces to reach a target temperature was obtained from the liquid crystal using the maximum green intensity approach. The conventional hue value approach was also applied to obtain the surface time map for data comparison. Since the test channel is of high blockage, delayed flow history was observed and a time correction was needed to address the asynchronous behavior between the flow and heat transfer. In addition, the difficulty of accurately capturing the bulk mean flow temperature within the three-passage channel leads to additional uncertainty for heat transfer coefficient calculations. The effects of delayed flow, time correction, and using different reference fluid temperatures on the Nusselt number calculations are demonstrated and analyzed. Using the current blade as an example, this study compares two different temperature interpretation approaches (maximum green intensity and hue value). In addition, other factors that affect the measurement of detailed heat transfer coefficient distributions using 1D transient conduction model are presented and discussed.