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Not Available In high heat flux applications, typical regeneratively-cooled combustion chambers have very high pressure drops which significantly increase the demands on turbomachinery. These high pressure drops are largely due to high coolant velocities in the regen circuits caused by the use of low-aspect ratio coolant channels (4:1). In addition, low aspect ratio coolant lines cannot be tailored to optimize heat transfer throughout the regen circuit, this results in overcooling near the injector and nozzle exit. Adopting coolant channels with higher aspect ratios (15:1 instead of 4:1) would significantly reduce the pressure drop of the combustion chamber. However, in high aspect ratio channels, flow stratification causes heated coolant to stay near the hot gas wall, resulting in higher wall temperatures, reduced cycle life, and potential chamber failure. Flow stratification must be understood and eliminated if higher aspect ratio cooling channels are to become a practical technology. This effort will develop a theoretical model of flow stratification and a methodology for its mitigation in coolant channels by: 1) performing combined CFD/Heat Transfer analyses of channels with various aspect ratios to obtain an initial assessment of flow stratification, 2) anchoring the numerical results with experimental testing, and 3) developing technologies to mitigate the stratification of the coolant in the channels.