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In this paper, periodic vortices are generated by a fluid passing a cylindrical obstacle near the microchannel inlet. Two elastic pillars are arranged on the walls, and the effect of the pillar spacing on heat transfer performance is studied using the Arbitrary Lagrangian-Euler method. With the spacing of 10d, the small pillar amplitude of 2 ?m is not conducive to the generation of vortices. The flexible vortex generator has higher heat transfer efficiency and lower pressure loss than the rigid vortex generator. The two pillars with no spacing generate isolated vortices, and the mixing of these vortices is insufficient downstream the pillars. It is found that with the pillar spacing of 5d, the overall performance factor is significantly higher than that with the pillar spacing of 0 and 10d in the Reynolds number range of 800 to 1,100. The average Nusselt number with the spacing of 5d increases by 19.2% compared to that with the spacing of 0 at the Reynolds number of 1,000. When the Reynolds number is 1,100, the overall performance factor is 43% higher than that with a single rigid pillar. The vortices are periodically generated by the two pillars with the 5d spacing, and the disturbance to the boundary layer enhances the heat transfer downstream the region in the microchannel.

This research investigated heat transfer performance and flow characteristics of three polydimethylsiloxane microchannels full of deionised water as a working fluid. A single micropillar, horizontal micropillars, and vertical micropillars along the flow direction were prepared on the microchannels experimentally. Results show that the Nusselt number of microchannels with two horizontal micropillars is 19% higher than that with a single micropillar. The microchannel with two vertical micropillars has the Nusselt number is 29% higher than that with a single micropillar, which shows the best performance on the heat transfer enhancement. Visualization experiments of the flow field were carried out to explore the enhanced mechanism of the heat transfer for microchannels with various micropillar arrangements. When the flow rate is 7 mLpm, the maximum velocities near the single cylinder and the horizontal micro-column are 0.5 m/s and 0.52 m/s. Fluid velocity in a region between two vertical micropillars reaches 0.72 m/s when the flow rate is 7 mLpm. The fluid in the high-speed region is fully mixed around the micropillar, which reduces the stagnation region area down-stream of the vertical micropillar and enhances heat transfer.