Temperature Distributions in Channel Walls with Translucent Thermal Barrier Coatings

Abstract

Thermal barrier coatings are important for reducing metal temperatures and thermal gradients in high-temperature applications. At elevated temperatures radiative transfer becomes important, and if several hot surfaces view each other, the coated surfaces exchange radiation. Usually in radiative exchange computations, the surfaces are opaque and each has a unique radiating temperature. Some thermal barrier coating materials such as zirconia are partially transparent to thermal radiation. Hence, an exchange involving coated walls is complicated by radiation penetrating into and coming out of each coating. Radiation leaving an area depends on the temperature distribution inside its coating that is unknown and is affected by the exchange process; each area does not have a unique temperature. The analysis here is for a hot transparent gas flowing in a symmetric parallel-plate channel with translucent coatings on the inside. The coatings view each other and exchange radiation. From symmetry the flux leaving each coating equals its incident value. Relations are developed for the temperature distribution within each coating that satisfies zero-net radiation at the coating surface. This differs from having cold surroundings