Using hydrophobic surfaces is one of the efficient methods to preserve energy in fluid transfer systems. However, the studies have been concentrated on Newtonian fluids despite the wide applications of non-Newtonian fluids in daily life and many industries such as the biological, foodstuff, chemical, petroleum, cosmetic, and lab on a chip fields. In this study, we consider power-law fluids as a typical example of non-Newtonian fluids and investigate the effect of hydrophobic microgrooves on the pressure drop in channels by utilizing the phase field method. We demonstrate that the optimum size of the rectangular microgrooves in which the maximum pressure drop reduction (PDR) happens for both the considered Newtonian and non-Newtonian fluids is identical, but the PDR is different for the Newtonian and non-Newtonian fluids. For shear-thickening fluids, the PDR is more than shear-thinning fluids, which means that using the hydrophobic surfaces in dilatant fluids provides the best performance. It is seen that pressure drop reduces more at lower Reynolds numbers. We also investigate the efficiency of the microgrooved surfaces in convergent and divergent channels for both the Newtonian and non-Newtonian fluids and find the critical slope angles for a specific length of the channels in which the hydrophobic microgrooves have a sufficient performance in the PDR and stability.
The microfluidics separation has absorbed wide-ranging attention in recent years due to its outstanding advantages in biological, medical, clinical, and diagnostical cell studies. While conventional separation methods failed to render the acceptable performance, microfluidics sorting methods offer many privileges such as high throughput, user-friendliness, minimizing sample volumes, cost-efficiency, non-invasive procedures, high precision, improved portability, quick processing, etc. Among the inertial microfluidics approaches such as the straight and curved microchannels, although the spiral microchannels, which are the sorts of passive separations, are complicated in concepts and geometries, they have demonstrated auspicious benefits for this purpose. Thus, numerous studies have strived to explain the principle of particle migrating and forces in these complex microchannels. However, a comprehensive understanding is still necessary. On the other side, it is manifest that the diagnosis and separation of circulating tumor cells (CTCs) from the blood are significant for targeted treatments of this detrimental disease. Therefore, this study aims to review the previous investigations and developments for understanding the CTC separation using the spiral microchannels straightforwardly and profoundly. After elucidating the inertial microfluidics and their governing physics in simple terms, we provide insights about spiral microchannels’ mechanism and concepts, the secondary flow, the cross-section effects on the separation processes, the investigation about CTCs in the spiral microchannels specifically, and finally, the future applications and challenges of this kind of inertial microfluidics. The analyses reveal that new approaches should be conducted to use spiral microchannels with combined cross-sections. These kinds of microchannels with optimum size and shape of cross-sections can improve performance efficiently.
The lab on a chip is utilized as a background and a substrate for creating a proper flow for cellular processes in medicine. In this study, the concepts of cell isolation and cell transfer methods have been discussed. After that, the device of separation and transfer systems has been designed, simulated, and verified by placing the frequency of particle separation and droplet formation, which is tried to introduce a new device that can be used in cellular studies. The optimal operation conditions for the problem have also been investigated. High separation efficiency (99%) could be achieved when the velocity of the sample inlet in the microchannel separator is 180 μm/s. Also, a microfluidic device for droplet generation has been designed to transfer the isolated cells to the culture medium. For this purpose, the frequency of droplet production must be synchronized with particle ejection frequency and equals 9.09 Hz.
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