Detached Eddy Simulations were conducted for pressurized helium-gas flow in cooling channels with rib-arrays detached from one wall at a Reynolds number of Re = 1.05 × 10⁵. Turbulent flow fields and conjugated heat transfer were predicted. The rib-arrays consisted of 60° (with respect to the centerline) V-shape or 90° transverse ribs with a rib-height of e and a square cross section. The clearance to the channel wall was c/e = 0.0, 0.1, 0.3 and 0.5, the cooling channel cross section was 15 e × 15 e, the rib-pitch-to-rib-height-ratio was p/e = 10 and the rib-height-to-hydraulic-diameter-ratio was e/D_h = 0.06532. Friction factors, Nusselt numbers and thermal performance were analyzed. An efficiency criterion and a thermal performance number were evolved for evaluating the thermal performance of rib-roughened cooling channels. It was shown, that for both types of detached rib-array configurations, the averaged heat transfer and the thermal performance deceased with increasing clearance. Maximum heat transfer and best thermal performance were provided by the 60° V-shape rib-configuration with c/e = 0.1.