Paper presented to the 10th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Florida, 14-16 July 2014.
Hypersonic vehicles operate at high flight Mach numbers
exposing the airframe and engine structures to high heat loads
which are quite severe in the combustor part of the high-speed
air breathing engine. In order to withstand high heat loads
experienced in the combustor region of the engine during
hypersonic flight, actively cooled panels are employed. Herein,
a fuel before being injected into the combustor serves as a
coolant and is made to flow through the combustor heat
exchanger panels such that the material and coolant
temperatures are maintained below their critical limits. A few
of the candidate materials considered for the active panels of
the engine are Nb alloy Cb 752, Ni alloy Inconel X-750, and CSiC.
To enhance the heat withstanding capacity of these
materials, low thermal conductivity thermal barrier coatings
(TBC) are employed. Currently Yttria-Stabilized Zirconia
(YSZ) material and ceramic materials are being used as popular
TBC materials because of their very low thermal conductivity
and high phase stability. In this analytical study, thermal
properties of air-plasma-sprayed zirconia based lanthanum
zirconate (La2Zr2O7) – LZ- coatings were employed in the
investigations. Lanthanum-cerium oxide (La2Ce2O7) –LC- is
considered as a new candidate material for TBCs because of its
low thermal conductivity and high phase stability. With the use
of La2Ce2O7 and La2Zr2O7 as TBC materials, the difference in
the weight of the active panel material and the heat gained by
the fuel are nearly identical as compared to active panel
material coated with YSZ TBC. Results showed that the effect
of TBC thickness on the weight of the optimised actively
cooled panel is negligible, because of very small TBC layer
thickness ranging from 0.5 to 3.0 mm and nearly identical
thermal properties of the TBC’s. Results showed that Inconel
X-750 is capable of sustaining high heat transfer coefficients
with fuel/coolant heat gain well below fuel coking temperature
with moderate weight to area ratio.
