<p>Transpiration cooling is an active technique to effectively protect the component surface from contacting the hot gas. Compared to conventional film cooling, transpiration cooling is able to provide more uniform coolant coverage and reduce lift-off of the coolant film. Thus, transpiration cooling has shown higher potential to be applied to turbine blade cooling as the manufacturing technologies of porous media advances. However, heat transfer coefficient measurement remains as a significant challenge for understanding the heat transfer effect of the thin film on the target surfaces. The conventional transient TLC or IR method for film cooling heat transfer measurement requires semi-infinite wall assumption, which does not hold for porous media in transpiration cooling. Therefore, a surface heater without blocking outlets at the surface of cooling channels is needed for steady state heat transfer measurement. This study proposed a micro-lithography method to fabricate a silver coil pattern on top of the additively manufactured polymer porous media as the surface heater for heat transfer coefficient measurement. The circuit was designed in a combination of series connection and parallel connection to make sure the power in each unit cell area at the target surface was identical. The steady-state tests showed that the adiabatic cooling effectiveness could reach 0.7 with a blowing ration lower than 0.5, meanwhile,&nbsp;the heat transfer coefficient ratio (hf/h0) of transpiration cooling was close to 1, smaller than those of the multi-row film cooling studies, which meant the coolant coverage was more effective.</p>

Surface Heater Fabrication Using Micro-Lithography for Transpiration Cooling Heat Transfer Coefficient Measurements

Paper Proceedings: https://asmedigitalcollection.asme.org/GT/GT2021/volume/84898

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