EFFECT OF RIB ANGLE ORIENTATION ON LOCAL MASS-TRANSFER DISTRIBUTION AROUND SHARP 180-DEG TURN WITH RIB-TURBULATORS MOUNTED IN ENTIRE 2-PASSCHANNELS

The local mass transfer distributions around sharp 180 deg turn with r ib-turbulators in a relatively short (L/D = 4) two-pass, square channe l were determined via the naphthalene sublimation technique. The rib h eight-to-hydraulic diameter ratio (e/D) was 0.05 and the rib pitch-to- height ratio (p/e) was 10. Experiments were conducted for five attack angles (alpha = 90, 45, 60, -45, and -60 deg), and for three Reynolds numbers (3.0 x 10(4), 6.0 x 10(4) and 9.0 x 10(4)). Results show that the rib-roughened wall Sherwood numbers after the turn are higher than those in the turn region, which, in turn, are higher than those befor e the turn due to the ribs installed in the turn region. While in the previous studies, the ratio Sh/Sh(0) in the turn region was found to b e lower than that in the before turn region, because of the absence of rib in the turn region. The rib angle and rib orientation have signif icant effect on both the local and average Sherwood number ratios. The average Sherwood number ratios (Sh(m)/Sh(0)) for alpha = 60 deg have the highest values, then comes the case of alpha = 45 deg, and the She rwood number Re ratios (Sh(m)/Sh(0)) for alpha = 90 and -45 deg are th e lowest. Correlations for the average rib-roughened wall Sherwood num ber ratios for the before-turn, in-turn and after-turn segments are pr ovided.