EXPERIMENTAL ANALYSIS ON MICRO-CHANNELS WITH DIFFERENT CROSS-SECTIONAL SHAPES FOR INTERNAL COOLING APPLICATIONS

The use of additive manufactured micro-channels for gas turbine cooled components is widely considered as a promising approach to enhance the internal cooling efficiency. On the other hand, the evaluation of heat transfer and pressure loss characteristics is complicated by the fact that several manufacturing choices can affect the as-built geometry and surface roughness, thus making it difficult to predict their performance with simple relations. Moreover, the evaluation of the channels characteristic dimension, expressed in the form of a hydraulic diameter, must be carried out through complex processes - mostly CT scan - and the distinction between channel shape, and thus dimensions, and its intrinsic roughness is in general a non-ambiguous aspect. In this regards, the possibility to adopt micro-channels with cross-sectional shapes different from the standard cylindrical one introduces an additional degree of freedom. The present paper builds on a previous one, where a procedure to retrieve the micro-channels characteristic dimension was developed and tested on cylindrical micro-channels; such a method was based on a differential flow check of the channels, allowing to by-pass the direct geometrical investigation that is generally adopted. In the present paper, the methodology is applied to micro-channels with various cross-sectional shapes, in order to assess its capabilities. The results are discussed, especially in terms of performance scaling capabilities, and compared to the ones achieved from the conventional approach based on geometrical inspection. The results showed that the approaches returned slightly different values of the characteristic dimension and, in turn, of the quantitative values of the parameters of interest. Nevertheless, the same conclusions and performance were achieved, as far as the comparative analysis of different coupons and the scaling capability are concerned.