Pressure loss through sharp 180 deg turn in a relatively short two-pass smooth and rib-roughened channel

The local pressure distributions and resistance coefficients (f ₁ and f ₂) through the sharp 180 deg turn in a relatively short (L/D _e=4) two-pass smooth and rib-roughened channel were investigated for a Reynolds number range of 1.0×10³-9.0×10³. The rib pitch-to-height ratios (p/e) were 5,10, and 20. The rib height-to-hydraulic diameter ratios (e/D _e) were 0.025, 0.050 and 0.10, and the rib angles of attack (α) were 90, 45, 60, -45, and -60 deg. Ribs were installed not only in before and after turn regions but also in turn region. The results show that the resistance coefficients remain approximately constant when Reynolds number is more than 3.0×10⁴. The effects of the rib configuration (rib spacing, rib height, and rib orientation) on the inlet straight duct resistance coefficient (f ₂) were significant, however, their effects on the overall resistance coefficient (f ₁) were diluted by the sharp-180 turn. For this relatively short channel (L/D _e=4), the overall resistance coefficient (f ₁) was greatly affected by the sharp turn. Correlations for the overall resistance (f ₁) and inlet straight duct resistance coefficient (f ₂) are presented.