1,720,991 research outputs found
Numbering-up strategies for microfluidics-assisted water treatment processes. Deterministic lateral displacement for the removal of bacteria and parasites as a case study
Full text linkMicrofluidic channels filled with spatially periodic arrays of impermeable obstacles have been proved successful for the size-based continuous separation of mesoscopic objects suspended in a buffer solution with unprecedented resolution. To date however, this technique - referred to as Deterministic Lateral Displacement (DLD) - has been implemented only for small volume samples, mainly for analytical purposes. In this article, we investigate the feasibility of the DLD separation technique for water purification from bacteria. The accurate numerical solution of the three-dimensional Stokes flow problem is used to establish the hydraulic resistance of several different geometries of the unit periodic cell. Results suggest that DLD-based microfilters resulting from numbering-up DLD microseparation units could provide sizeable flowrates and could prove competitive when compared to membrane-based modules
Combining electrostatic, hindrance and diffusive effects for predicting particle transport and separation efficiency in deterministic lateral displacement microfluidic devices
Full text linkMicrofluidic separators based on Deterministic Lateral Displacement (DLD) constitute a promising technique for the label-free detection and separation of mesoscopic objects of biological interest, ranging from cells to exosomes. Owing to the simultaneous presence of different forces contributing to particle motion, a feasible theoretical approach for interpreting and anticipating the performance of DLD devices is yet to be developed. By combining the results of a recent study on electrostatic effects in DLD devices with an advection-diffusion model previously developed by our group, we here propose a fully predictive approach (i.e., ideally devoid of adjustable parameters) that includes the main physically relevant effects governing particle transport on the one hand, and that is amenable to numerical treatment at affordable computational expenses on the other. The approach proposed, based on ensemble statistics of stochastic particle trajectories, is validated by comparing/contrasting model predictions to available experimental data encompassing different particle dimensions. The comparison suggests that at low/moderate values of the flowrate the approach can yield an accurate prediction of the separation performance, thus making it a promising tool for designing device geometries and operating conditions in nanoscale applications of the DLD technique
Brownian sieving effect for boosting the performance of microcapillary hydrodynamic chromatography. Proof of concept
Full text linkMicrocapillary hydrodynamic chromatography (MHDC) is a well-established technique for the size-based separation of suspensions and colloids, where the characteristic size of the dispersed phase ranges from tens of nanometers to micrometers. It is based on hindrance effects which prevent relatively large particles from experiencing the low velocity region near the walls of a pressure-driven laminar flow through an empty microchannel. An improved device design is here proposed, where the relative extent of the low velocity region is made tunable by exploiting a two-channel annular geometry. The geometry is designed so that the core and the annular channel are characterized by different average flow velocities when subject to one and the same pressure drop. The channels communicate through openings of assigned cut-off length, say A. As they move downstream the channel, particles of size bigger than A are confined to the core region, whereas smaller particles can diffuse through the openings and spread throughout the entire cross section, therein attaining a spatially uniform distribution. By using a classical excluded-volume approach for modeling particle transport, we perform Lagrangian-stochastic simulations of particle dynamics and compare the separation performance of the two-channel and the standard (single-channel) MHDC. Results suggest that a quantitative (up to thirtyfold) performance enhancement can be obtained at operating conditions and values of the transport parameters commonly encountered in practical implementations of MHDC. The separation principle can readily be extended to a multistage geometry when the efficient fractionation of an arbitrary size distribution of the suspension is sought
Fractionation of a three-particle mixture by Brownian sieving hydrodynamic chromatography
Full text linkParticles ranging in size from a few nanometers (exosomes or viruses) to a few micrometers (bacteria or red blood cells) can be sorted using a size-based separation process. One of the simplest techniques is provided by hydrodynamic chromatography (HDC) which typically requires long channels to achieve adequate resolution. A new separation mechanism based on a Brownian sieving effect coupled with HDC has recently been proposed to overcome these limitations. An efficiency improvement of up to 2000 % has been predicted for a two-size mixture. The aim of this work is to study and optimize a modified geometry useful for obtaining the simultaneous separation of a three-size diluted suspension. The results suggest a significant performance improvement, up to 3000 %, over the standard HDC
Toward minimal complexity models of membrane reactors for hydrogen production
Full text linkMembrane reactors are inherently two-dimensional systems that require complex models for an accurate description of the different transport phenomena involved. However, when their performance is limited by mass transport within the reactor rather than by the selective product permeation across the membrane, the 2D model may be significantly simplified. Here we extend results previously found for methane steam reforming membrane reactors to show that such simplified two-dimensional model admits either a straightforward analytical solution for the cross-section averaged concentration profile, or can be reduced to a 1D model with an enhanced Sherwood number, depending on the stoichiometry of the reaction considered. Interestingly, the stoichiometry does not affect the expression of the enhanced Sherwood number, indicating that a versatile tool has been developed for the determination of membrane reactor performance at an extremely low computational cost and good degree of accuracy
Tracer dispersion in stirred tank reactors: Asymptotic properties and mixing characterization
No full textThis article addresses the characterization of dispersion and homogenization phenomena in stirred vessels through the analysis of dispersion curves that can be obtained experimentally by means of conductivity measurements. New insights on mixing conditions can be achieved from the analysis of the qualitative and asymptotic properties of tracer dispersion curves. The results obtained are interpreted in the context of the spectral approach to the advection-diffusion equation. It is shown that any flow model aimed at reproducing the experimentally determined dispersion curves must be at least two-dimensional. Convection-enhanced dispersion associated with the spectral structure of the advection-diffusion equation is addressed
Space-time resolution of size-dispersed suspensions in Deterministic Lateral Displacement microfluidic devices. Running Deterministic Lateral Displacement under transient conditions to improve separation resolution: a proof of concept
No full textDeterministic Lateral Displacement (DLD) is a relatively recent microfluidics-assisted technique which allows the size-based separation of a population of micrometric particles suspended in a buffer solution. The core of the device is a shallow channel with rectangular cross-section filled with an array of solid obstacles arranged in a spatially periodic lattice, whose directions are slanted with respect to the channel walls. In practical implementations of DLD, particles are continuously introduced at a localized position of the channel entrance and migrate along different average directions downstream the device according to their size. Thus, at steady state, size-sorted subpopulations can be collected at different positions of the channel outlet. Besides, theoretical predictions of recent models of particle transport in these devices suggest that not only the direction of the average particle velocity, but also its magnitude (i.e. the mobility) depends sensitively on particle size. By exploiting this dependence, a novel use of DLD devices is here proposed, where the size-driven separation is realized over time and space by running the process under transient conditions, thus mimicking a classical chromatographic separation. We show how this approach is particularly effective for particles of specific (critical) dimensions, which are known to impair the efficiency of the steady-state separation process. Numerical predictions based on a hard-wall repulsive potential for the particle-obstacle interaction suggest that unprecedented separation performance for near-critical particle size could be obtained in transient conditions within the same channel length used for the time-continuous separation. The case of cylindrical obstacles and spherically shaped particles is considered in detail as an illustrative example
- …
