The use of an inner pipe within internal passages of gas turbine vanes has been proposed as a solution to address the issue of secondary air supply to the vane hub. This study investigates the effect of the inner pipe on heat transfer of the internal passage. An experiment using the naphthalene sublimation method is performed to acquire local heat/mass transfer coefficients for Reynolds numbers of 20,000, 40,000, and 60,000. Two configurations of square channels are analyzed: base case and inner pipe case. The flow structure of the channel was also analyzed through a numerical simulation method. The presence of the pipe changes flow patterns by the regeneration of swirling flow motion and the expansion of vortices, increasing heat transfer. In the upstream region (x/Dh < 7.8), the heat transfer patterns are similar between the cases, despite a slight increase in values. However, in the downstream region (x/Dh>8), which includes the fully developed region of the channel flow, a tremendous increase in the heat transfer between the two cases is observed. Overall, the study concludes that the use of an inner pipe in internal passage of gas turbine vanes can enhance heat transfer on the surface.

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