Comparison of the cooling effectiveness of superheated steam and hot air in internal turbine blade cooling

Turbine inlet temperatures continue to increase, and this increase in temperature has led to an unfavorable combination of thermal stresses, oxidation and creep in the hot sections of the turbine engine components, particularly in the turbine blades section. The reduction of the blade temperature to an appropriate level in order to maintain the material integrity and decomposition of temperature gradients in the blade profile sections becomes a principal concern. Combination of various cooling methods and cooling agents are used to address this problem and the current discussion concentrates on comparing the heat transfer characteristics of compressed air and super heated steam in a single pass internal cooling configuration, both experimentally and numerically. The experiments establish a base line data for the internal coolant capabilities of steam and air on the basis of heating tests on a simple flat blade geometry. Once the base line data have been established, the coolant properties of air and steam are compared and an evaluation of the experimental technique for conduction and convective heat transfer for this geometry is performed using analytical tools to compare the experimental results with the analytical predictions. The experimental surface temperatures are measured using precisely calibrated liquid crystals, and the temperature gradients above the blade are determined using specially designed thermocouple probe and the numerical validation is done using ANSYS53 package.