Five asymmetrical shaped microchannels were used to investigate the effect of channel confluence angle, flow rate and flow rate ratio on the mixing performance in a passive mixing test. The flow characteristics for all geometries were studied experimentally and numerically using CFD technique. The results reveal that the mixing performance depends on the channel geometry, total flow rate and inlet flow rate ratios. The classical T-shape microchannel had the worst performance in the lower flow rate and in higher Re numbers its performance was placed between the other ones. Furthermore, the mixing effectiveness for all microchannels was defined and measured at various feed flow rates. The results indicate that the mixing effectiveness increases with increasing flow rate ratio and decrease of confluence angle. The reasons for the observed experimental results were analyzed by the predicted CFD flow patterns. (C) 2014 Elsevier Ltd. All rights reserved.