Detailed heat transfer distributions in two-pass square channels with rib turbulators and bleed holes

Detailed heat transfer coefficient distributions are presented for a two-pass square channel with a 180° turn. One wall of the channel has periodically placed rib turbulators and bleed holes. Four different configurations of 90° parallel, 60° parallel, 60° V ribs, and 60° inverted V ribs are studied in conjunction with the effect of bleed holes on the same wall. The surface is coated with a thin layer of thermochromic liquid crystals and a transient test is run to obtain the detailed heat transfer distributions. Detailed distributions show distinctive peaks in heat transfer levels around bleed holes and on rib turbulator tips. The 60° parallel, 60° V, and 60° inverted V ribbed channels produce similar levels of heat transfer enhancement in the first pass. However, the 60° inverted V ribbed channel produces higher enhancement in the second pass. Regional-averaged heat transfer results indicate that a surface with bleed holes provides similar heat transfer enhancement as that for a surface without bleed holes although 20–25% of the inlet mass flow exits through the bleed holes.