Abstract
The necessity of microscale mixing processes has been tremendously increasing in most of the microsize chemical and biochemical devices during recent years, particularly in the design of lab-on-a-chip and micrototal analysis systems. Different approaches were implemented in the available micromixers in the literature for improving the mixing performance. Due to the absence of any external source, mixing by utilizing passive mixing techniques is more economical. In curvilinear microchannels, which offer effective passive mixing, chaotic advection results in continuous radial perforation of inter-diffusion layer between the fluid streams due to the transverse secondary flows. In this study, the effects of Dean vortices and secondary flows were investigated in asymmetrical polydimethylsiloxane curvilinear rectangular microchannels, which were fabricated by one-step lithography process and had repeated S-shape patterns with a curvature of 280° along the channel. Moreover, the effect of asymmetry was assessed by comparing the mixing results with symmetrical microchannels. Mixing performance was analyzed by using NaOH and phenolphthalein solutions as mixing fluids, which entered from the channel inlets. According to the results, the significant effects of stretching and contracting motion of Dean vortices revealed themselves above a certain Dean number value, thereby making the asymmetrical microchannel outperform the symmetrical channel in the mixing performance. Below this threshold, the symmetrical microchannel was observed to be superior to the asymmetrical microchannel.
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Abbreviations
- \(D_{\text{h}}\) :
-
Hydraulic diameter (m)
- \(I\) :
-
Pixel intensity (–)
- \(K\) :
-
Dean number (–)
- \({\text{MI}}\) :
-
Mixing index (–)
- \(R\) :
-
Flow path radius (m)
- \(Re\) :
-
Reynolds number (–)
- \(u\) :
-
Characteristic velocity (m/s)
- \(U_{\text{f}}\) :
-
Mean fluid velocity (m/s)
- \(\delta\) :
-
Curvature ratio (–)
- \(\rho\) :
-
Density (kg/m3)
- \(\mu\) :
-
Dynamic viscosity (kg/ms)
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Acknowledgements
The authors are thankful to Dr. Devrim Gözüaçık’s group members from Sabanci University Molecular Biology, Genetics and Bioengineering Program. The equipment and characterization support provided by the Sabanci University Nanotechnology Research and Applications Center (SUNUM) is appreciated. This work was supported by the Sabanci University Internal Research Grant, No: IACF15-1444, Science Academy Outstanding Young Investigator Support Program (BAGEP), Turkish Academy of Science (TUBA) and Outstanding Young Investigator Support Program (GEBIP). The authors thank Ms. Eda Şener for her greatly appreciated contributions.
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Akgönül, S., Özbey, A., Karimzadehkhouei, M. et al. The effect of asymmetry on micromixing in curvilinear microchannels. Microfluid Nanofluid 21, 118 (2017). https://doi.org/10.1007/s10404-017-1952-1
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DOI: https://doi.org/10.1007/s10404-017-1952-1