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 degrees turn. One wall of the channel has periodically placed rib turbulators and bleed holes. Four different configurations of 90 degrees parallel, 60 degrees parallel, 60 degrees V ribs, and 60 degrees 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 degrees parallel, 60 degrees V, and 60 degrees inverted V ribbed channels produce similar levels of heat transfer enhancement in the first pass. However, the 60 degrees 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. (C) 1998 Elsevier Science Ltd. All rights reserved.