Channel Height and Jet Spacing Effect on Heat Transfer and Uniformity Coefficient on an Inline Row Impingement Channel

Future high performance turbine airfoils will likely be cooled in a near wall configuration, potentially employing a combination of narrow, distributed internal cooling channels and impingement. In such applications, the jets impinge against a target surface, and then exit along the channel formed by the jet plate, target plate, and side walls. Local convection coefficients are the result of both the jet impact, as well as the channel flow produced from the exiting jets and the complex interaction between the jet and the cross flow. Numerous studies have explored the effects of jet array and channel configurations on both target and jet plate heat transfer coefficients, yet with little consideration of thermal stress related effects. A detailed study on the uniformity coefficient that these jets and cross flow generate on the surface is carried out. It is important to maintain a high uniformity coefficient while still having a high heat transfer coefficients to reduce thermal stresses. It is also important to use as little flow as possible while maintaining a high heat transfer coefficient. The study presented experimentally investigates the effects of wall height, jet Reynolds number, and jet spacing on the Nusselt number and uniformity of a narrow inline row impingement channel. The channel height was set at 1, 3, and 5 diameters, jet spacing was 5 and 15 diameters, and the channel width was kept constant at 4 diameters. Although heat transfer coefficients are highly sensitive to the jet Reynolds number and channel height, the uniformity of the distribution is mainly governed by the channel height and jet spacing. A channel height of 3 jet diameters tended to produce the best uniformity coefficients, regardless of the jet to jet spacing; with side walls out performing target surfaces.