Vaporization Cooling for Gas Turbines, the Return-Flow Cascade

A new paradigm for gas turbine design is treated, in which major elements of the hot section flow path are cooled by vaporization of a suitable two-phase coolant. This enables the blades to be maintained at nearly uniform temperature without detailed knowledge of the heat flux to the blades, and makes operation feasible at higher combustion temperatures using a wider range of materials than is possible in conventional gas turbines with air cooling. The new enabling technology for such cooling is the return-flow cascade, which extends to the rotating blades the heat flux capability and self-regulation usually associated with heat-pipe technology. In this paper the potential characteristics of gas turbines that use vaporization cooling are outlined briefly, but the principal emphasis is on the concept of the return-flow cascade. The concept is described and its characteristics are outlined. Experimental results are presented that confirm its conceptual validity and demonstrate its capability for blade cooling at heat fluxes representative of those required for high pressure ratio high temperature gas turbines.