Evaporative Turbine Blade Cooling Using a Return Flow Cascade

High intensity cooling of expansion turbine blades is proposed, using a self-stabilized evaporation/condensation process within each blade. The result is low blade structural temperature, with waste heat delivered to a low pressure air flow. This is a key technology requirement for development of a fully cooled gas turbine, with potential for operation at radically increased turbine inlet temperature, while avoiding high cost superalloys. The approach provides uniform and stable cooling of the entire blade, with the evaporated coolant flowing as vapor to the blade root, where it condenses while transferring heat to low pressure air flow. The key to achieving uniform evaporative cooling is establishment of a liquid flow, driven by the centrifugal acceleration field of the turbine, filling numerous transverse capture shelves on the inside blade wall surfaces. It cascades from the inner shelf outward, with vapor from each returning to the root region for condensation and recycle. The high acceleration field forces highly efficient nucleate pool boiling at each shelf, resulting in metal temperature close to the liquid boiling point. Thus a fully enclosed Return Flow Cascade of alkali metal coolant is established. The Phase I program will experimentally validate this approach under high acceleration conditions.