Effects of aspect ratio on heat/mass transfer were investigated in rectangular channels with two different V-shaped rib configurations, which are continuous V-shaped rib configuration with a 60 degrees attack angle, and multiple (staggered) V-shaped rib configuration with a 45 degrees attack angle. The square ribs were attached on the test section in a parallel manner. A naphthalene sublimation method was used to measure the local heat/mass transfer coefficients. For the continuous V-shaped rib configuration, two pairs of counter-rotating vortices were generated in the channel, and high transfer region was formed at the center of the ribbed walls. However, for the multiple V-shaped rib configuration with 45 degrees attack angle, asymmetric secondary flow patterns were generated due to its geometric features, resulting in uniform heat/mass transfer distributions. The effect of channel aspect ratio was more significant for the continuous 60 degrees V-shaped rib than for the multiple 45 degrees V-shaped rib configuration. (C) 2009 Elsevier Ltd. All rights reserved.