Search Results (3)

This study presents an innovative wedge-shaped inlet weir-type microfluidic chip designed to address common issues of clogging and inefficiency in microfiltration processes. Driven solely by centrifugal force, the chip integrates a crossflow separation mechanism and enables selective droplet sorting based on size, without the need for external pumps. Fabricated from PMMA, the device features a central elliptical chamber, a wedge-shaped inlet, and spiral microchannels. These structures leverage shear stress and Dean vortices under centrifugal fields to achieve high-throughput separation of droplets with different diameters. Using water-in-oil emulsions as a model system, we systematically investigated the effects of geometric parameters and rotational speed on separation performance. A theoretical model was developed to derive the critical droplet size based on force balance, accounting for centrifugal force, viscous drag, pressure differentials, and surface tension. Experimental results demonstrate that the chip can effectively separate droplets ranging from 0 to 400 μm in diameter at 200 rpm, achieving a sorting efficiency of up to 72% and a separation threshold (cutoff accuracy) of 98.2%. Fluorescence analysis confirmed the absence of cross-contamination during single-chip operation. This work offers a structure-guided, efficient, and contamination-free droplet sorting strategy with broad potential applications in biomedical diagnostics and drug screening. Full article

In this work, the effects of the deteriorating affinity-related properties of membranes due to leaching and erosion on their rejection capacity were studied via computational fluid dynamics (CFD). The function of affinity-enhancing agents is to modify the wettability state of the surface of a membrane for dispersed droplets. The wettability conditions can be identified by the contact angle a droplet makes with the surface of the membrane upon pinning. For the filtration of fluid emulsions, it is generally required that the surface of the membrane is nonwetting for the dispersed droplets such that the interfaces that are formed at the pore openings provide the membrane with a criterion for the rejection of dispersals. Since materials that make up the membrane do not necessarily possess the required affinity, it is customary to change it by adding affinity-enhancing agents to the base material forming the membrane. The bonding and stability of these materials can be compromised during the lifespan of a membrane due to leaching and erosion (in crossflow filtration), leading to a deterioration of the rejection capacity of the membrane. In order to investigate how a decrease in the contact angle can lead to the permeation of droplets that would otherwise get rejected, a CFD study was conducted. In the CFD study, a droplet was released in a crossflow field that involved a pore opening and the contact angle was considered to decrease with time as a consequence of the leaching of affinity-enhancing agents. The CFD analysis revealed that the decrease in the contact angle resulted in the droplet spreading over the surface more. Furthermore, the interface that was formed at the entrance of the pore opening flattened as the contact angle decreased, leading the interface to advance more inside the pore. The droplet continued to pass over the pore opening until the contact angle reached a certain value, at which point, the droplet became pinned at the pore opening. Full article

Spacer design in spiral-wound membranes (SWMs) significantly affects the axial pressure drop in the flow channel but also the deposit layer removal. However, the effects of the spacer design and feed flow distribution in the module on the filtration performance have not yet been investigated during the highly fouling-susceptible fractionation of proteins from skim milk by SWMs. Therefore, a parallel spacer with no turbulence promotion and a less homogeneous feed flow distribution in the SWM was compared to a diamond spacer with regard to its impact on deposit formation and filtration performance. The experiments were conducted in a flat sheet test cell and in SWMs. The parallel spacer induced a more homogeneous deposit layer formation. However, no difference in filtration performance could be observed in the experiments with the test cell. Even though deposit layer formation dominates the microfiltration, its amount and spatial distribution could not be directly linked to the filtration performance. Furthermore, both spacers were assessed in SWM. Despite the higher crossflow velocity applicable in the more open channels of the parallel spacer, the performance of the parallel spacer was inferior to the diamond spacer. This was independent of the viscosity of the feed. Due to the high curvature of the membrane sheets close to the permeate collection tube, the cross-section of the flow channels in the SWM equipped with the parallel spacer was reduced. This resulted in a distinctly lower deposit layer control and performance, which could not be compensated by the resulting higher crossflow velocity far from the permeate collection tube. Full article