Conjugate Heat Transfer Scaling for Inconel 718

Abstract

Over the last decade, conjugate heat transfer testing has been shown to be important because it replicates the sum of the hot gas path heat transfer coefficient, film cooling, film cooling heat transfer augmentation, bore cooling, conduction through the wall, internal cooling heat transfer coefficients, and the relative amounts of heat pick up in the cooling flow. Instead of measuring these boundary conditions in individual experiments, conjugate heat transfer testing measures the cumulative effect as well as each boundary condition’s effect on the others. Typically, matched Biot number heat transfer experiments are performed at near room temperature with a surrogate material; however, this study examines how the thermal conductivity of a nickel alloy sufficiently changes between room temperature and temperatures representative of turbine engines to allow matched Bi heat transfer tests using nickel at laboratory conditions. The ratio of the thermal conductivity of air to the thermal conductivity of Inconel 718 stays mostly constant between engine representative temperatures and room temperature. Over this range, the thermal conductivity of both air and Inconel 718 change ∼2.5X, and the change in thermal conductivity allows for conjugate heat transfer tests to match Reynolds number, Nusselt number, film effectiveness, Biot number, and Stanton number. Experimental results at two temperature conditions are shown confirming the theory. Finally, a method for scaling the thermal impact of dust accumulation at laboratory conditions to turbine conditions is proposed.