Extended surface convective cooling studies of engine components using the transient liquid crystal technique

Abstract

A heat transfer tunnel used for local convective heat transfer coefficient measurements on liquid crystal instrumented models is described. The tunnel uses the new mesh heater device to produce a good approximation to a step change in the test section flow temperature. A simple analytical model of the cooling performance of cylindrical extended surfaces is derived from empirical relations obtained from the literature. Experiments conducted on a smooth cylinder and selected cylindrical finned geometries are discussed. In the configurations investigated, the relative sizes of the fin diameter to the fin array greatly exceed any geometries previously reported. The use of liquid crystal mapping techniques is shown to provide the full distribution of local heat transfer coefficients across the fin surface. This enables a greater understanding of the convective cooling process than could be obtained from the simple average measurements of h previously reported in the literature. Existing finned tube correlations are shown to be unable to predict the measured heat transfer levels. The investigation shows that correct selection of fin geometry can result in a significant increase in overall convective cooling performance.