Abstract
This article attempts to provide a cooling performance comparison of various mass transfer cooling methods and different cooling media through two experiments. In the first experiment, pressurized air was used as a cooling medium and two different circular tubes were used as specimens. One is made of impermeable solid material with four rows of discrete holes to simulate film cooling, and the other consists of sintered porous material to create a porous transpiration cooling effect. The natures of transpiration cooling and film cooling including leading and trailing edge injection cooling were compared. This experiment found that by using a gaseous cooling medium, transpiration cooling could provide a higher cooling effect and a larger coolant coverage than film cooling in the leading stagnation region, and on the side of the specimen at the same coolant injection flow rates; but in the trailing stagnation region, the traditional coolant injection method through discrete film holes might be better than transpiration cooling, especially for turbine blades with thin trailing edges. In the second experiment, the cooling effects of gaseous and liquid media on the same porous tube's surface were compared. This experiment showed that the porous areas cooled using gaseous and liquid cooling media were almost identical, but the cooling effect of liquid evaporation was much higher than that of gaseous cooling, especially in the leading and trailing stagnation regions of turbine blades. This important discovery makes it possible to solve the stagnation region problems in turbine blade cooling.
Highlights
This article attempts to provide a cooling performance comparison of various mass transfer cooling methods and different cooling media through two experiments
The natures of transpiration cooling and film cooling including leading and trailing edge injection cooling were compared. This experiment found that by using a gaseous cooling medium, transpiration cooling could provide a higher cooling effect and a larger coolant coverage than film cooling in the leading stagnation region, and on the side of the specimen at the same coolant injection flow rates; but in the trailing stagnation region, the traditional coolant injection method through discrete film holes might be better than transpiration cooling, especially for turbine blades with thin trailing edges
In the trailing stagnation region, traditional injection cooling through discrete film holes may be better, especially for the turbine blades with thin trailing edges
Summary
This article attempts to provide a cooling performance comparison of various mass transfer cooling methods and different cooling media through two experiments. The thermal conductivity and diffusivity of these impermeable materials are relatively low, water evaporation could lead to thermal failure of the turbine components due to the large temperature gradients brought by water droplets created during the water evaporation process In comparison with these materials, sintered porous materials have much higher thermal conductivity and diffusivity, and the water droplet sizes can be homogenized through the pores of the materials. In the first part of this article, an application of the infrared thermal imaging technique was presented In this part, the performances of film cooling and transpiration cooling were quantitatively compared, and the difference between gaseous and liquid cooling media in porous transpiration cooling was experimentally analyzed using this measurement technique. The goal of this work is to provide a quantitative comparison for the researchers and designers of the turbine components with mass transfer cooling function to choose a cooling method and medium, to improve coolant chamber configuration design, and to control coolant consumption level
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