The micro-channels and micro-devices have been widely used in mechanical engineering applications. A number of investigations have been conducted to better design the fluid flow and heat transfer in micro-channel, particularly as it pertains to applications involving the thermal control of electronic devices. The analysis of entropy generation mechanism is very important to optimize the second-law performance of these energy conversion devices in micro-scale. The main concern of this paper is to investigate the channel geometry effect on the mixing performances in the X-shaped micro-channels. Seven different tested channels consisting of shrunk-channel, normal-channel and magnified-channel, made of acrylic fabric with the width ranging from 0.7 to 1.3 mm, are considered. As the working fluid, water, is injected to microchannel at different mass flow rate, over a wide range of flow condition, 0.52 < Re < 718, have been discussed. Numerical simulation of the entropy generation, temperature gradient, velocity vector, and pressure drop has deliberated with experiment. Through the evaluations of the overall entropy generation in the whole flow domain, the results show that; as the Reynolds number below 136.68, magnified-channels have the lower entropy generation and best mixture of performance; above 136.68, in the smallest the channel geometry, the transition form early from laminar flow, the unsteady flow is an advantage for mixing in the limited mixing area, therefore, they generated the best mixing performance. It is clear that the channel geometry plays an important role on the mixing performances in the X-shaped micro-channels.

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