Local heat transfer measurements in narrow impingement channel by transient liquid crystal technique

A transient liquid crystal technique is used to measure the local heat transfer coefficients on the inner surfaces of an impingement channel that models the cooling passages in gas turbine blades. The effects on the heat transfer of jet Reynolds number Re and the ratio of the jet-to-jet spacing to the diameter of the jet hole S/d are investigated. The effect of the film holes is also studied. Results show that the heat transfer coefficients on all surfaces increase with an increase in jet Reynolds number, and that the average heat transfer coefficient on an impingement target surface is the highest. When the jet Reynolds number is sufficiently high, the average heat transfer coefficient on an impingement surface is higher than that on the channel side. The bleeding of film holes and increase in S/d both tend to significantly decrease the average heat transfer coefficients on the channel side and impingement surface, but its effect on the target surface is comparatively small. Heat transfer coefficient in the region which is directly subjected to the impingement flow is the highest for every inner surface, while in regions around jet holes and film holes it also remains fairly high.