Prediction of Film Cooling Effectiveness of Steam

Abstract

The intent of this work is to show, analytically, that superheated steam can provide better film cooling than conventional air for gas turbine blades and vanes. Goldstein’s two-dimensional and Eckert’s three-dimensional models have been reexamined and modified in order to include the effects of thermal-fluid properties of foreign gas injection on the film cooling effectiveness. Based on the modified models, the computed results for steam film cooling effectiveness, showing an increase of 80 to 100 percent when compared with air cooling at the same operating conditions, are presented.

Film Cooling With Steam Injection Through Three Staggered Rows of Inclined Holes Over a Straight Airfoil

“…The explanation of this phenomena is that steam has a larger specific heat and a larger Prandtl number than those of air. The results generally support the previous analytical prediction [18]. Upon examination of Figures 7 through 9 from the first position to the trailing edge, the effectiveness for steam is seen to decrease at a more rapid rate than air, although still maintaining the much higher effectiveness for each point.…”

“…Recently, Rice [17] proposed to use superheated steam from a conventional steam cycle for the gas trubine blade and vane cooling in a combined cycle for power generation. Han and Jenkins [18] predicted that the film cooling effectiveness of steam, due to its favorable thermal properties (such as specific heat and Prandtl number), was about twice that of air under the same operating conditions. However, the prediction has not been verified experimentally.…”

Gas Turbine Heat Transfer With Alternate Cooling Fluids

“…For the film cooling effectiveness studies with various secondary cooling gases, the two-dimensional slit geometry was chosen because a number of theoretical correlations and predictions exist for the specific geometry. The five widely accepted theoretical correlations predicting the two-dimensional film cooling effectiveness -rt = Tm, -T,,,/(T2 -T00) -were extensively reviewed by Goldstein (1971) and rearranged by Han and Jenkins (1982) to account for the cooling gas physical properties. The models include those of Tribus and Klein (1953),…”

“…Injection of steam into gas turbines offers the potential of improving the efficiencies and the specific output for utility and industrial applications. The steam or steam-air mixtures, which are used as an additional expansion fluid, could also be used directly as an effective cooling gas for turbine parts situated in the hot gas path (Han and Jenkins, 1982;El-Masri and Pourkey, 1986;Han and Mehendale, 1986).…”

A Computer Model for Gas Turbine Blade Cooling Analysis

“…Zirconium alloy base, ceramic-coated blades, capable of withstanding much higher firing temperatures than any cooled blade, have been studied by NASA [1] for several years, but have not been scheduled for production. On the other hand, several physical approaches to blade cooling such as transpiration cooling [2], internal water cooling [3], steam film cooling [4,5] have been suggested. However, all those new cooling techniques are still in the experimental stages.…”