Microfluidic flows in metallic microchannels fabricated by the spacer method

Straight and bent copper microchannels are fabricated by the spacer method and their microfluidic flow characteristics are investigated. The effect of the surface roughness of the microchannel walls, which can be controlled by selecting the starting copper powder size, is focused on. The rough surface of a thin straight microchannel (with an arithmetic surface roughness of 4.3 µm and a diameter of 180 µm) caused a higher pressure gradient than other straight microchannels. The pressure gradient for the rough and thin microchannel exceeded the theoretical value for laminar flow at a lower Reynolds number than that reported for a cylindrical pipe with larger dimensions. It is concluded that the large surface roughness relative to the microchannel diameter leads to the early transition from laminar to turbulent flow. Experimental results for bent microchannels also indicate that the large surface roughness at a sharp bend causes significant flow separation.

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