Numerical investigation was conducted with ANSYS CFX to investigate the flow characteristics in a rectangular microchannel. The performance of laminar model

γ-Reθt transition model and shear stress transport model in microchannel transition simulation was examined by comparing the predicted results with the experimental data. Furthermore

the effects of length-to-diameter ratio and aspect ratio were also investigated. Results indicated that only the γ-Reθt model predicted the trend of transition and forecasted a critical Reynolds number close to the experimental result. Length-to-diameter ratio over 200 was suggested to eliminate the influence of the entrance effect. The critical Reynolds number increased when the aspect ratio varied from 1 to 5.