Hybrid lattice-Boltzmann-finite-difference approach for the simulation of micro-phase-change-material slurry in convective flow.

In this paper, we present a hybrid numerical scheme that couples the lattice Boltzmann method (LBM) with the finite difference method (FDM) to model micro-phase-change-material (MPCM) suspensions in a minichannel. Within this framework, the LBM was employed to solve the continuity, momentum, and energy equations for the fluid domain, while a Lagrangian scheme replicates the motion of MPCM particles. The LBM is coupled with an FDM solver which operates under the lumped capacitance assumption to address the phase-change phenomena within the microparticles. This hybrid coupling eliminates the necessity for any specific treatment in handling phase transitions and tracking phase interfaces. The proposed method is first evaluated on classic particle cases, demonstrating its ability to achieve four-way coupling. Furthermore, the current model effectively adapted viscosity changes when integrating the microparticles, obviating the need for homogenous viscosity models. Subsequently, the potential of this approach is demonstrated by examining the influence of the near-wall thermal interaction of MPCM particles considering three scenarios based on particle density: light (ρ_{p}<ρ_{f}), neutrally buoyant (ρ_{p}≈ρ_{f}), and dense (ρ_{p}>ρ_{f}) microparticles. The hybrid approach further revealed insights into the impact of the volume fraction on the heat transfer coefficient as well as on the overall heat transfer coefficient and performance index from a Lagrangian perspective.

A review on microfluidic-assisted nanoparticle synthesis, and their applications using multiscale simulation methods.

Recent years have witnessed an increased interest in the development of nanoparticles (NPs) owing to their potential use in a wide variety of biomedical applications, including drug delivery, imaging agents, gene therapy, and vaccines, where recently, lipid nanoparticle mRNA-based vaccines were developed to prevent SARS-CoV-2 causing COVID-19. NPs typically fall into two broad categories: organic and inorganic. Organic NPs mainly include lipid-based and polymer-based nanoparticles, such as liposomes, solid lipid nanoparticles, polymersomes, dendrimers, and polymer micelles. Gold and silver NPs, iron oxide NPs, quantum dots, and carbon and silica-based nanomaterials make up the bulk of the inorganic NPs. These NPs are prepared using a variety of top-down and bottom-up approaches. Microfluidics provide an attractive synthesis alternative and is advantageous compared to the conventional bulk methods. The microfluidic mixing-based production methods offer better control in achieving the desired size, morphology, shape, size distribution, and surface properties of the synthesized NPs. The technology also exhibits excellent process repeatability, fast handling, less sample usage, and yields greater encapsulation efficiencies. In this article, we provide a comprehensive review of the microfluidic-based passive and active mixing techniques for NP synthesis, and their latest developments. Additionally, a summary of microfluidic devices used for NP production is presented. Nonetheless, despite significant advancements in the experimental procedures, complete details of a nanoparticle-based system cannot be deduced from the experiments alone, and thus, multiscale computer simulations are utilized to perform systematic investigations. The work also details the most common multiscale simulation methods and their advancements in unveiling critical mechanisms involved in nanoparticle synthesis and the interaction of nanoparticles with other entities, especially in biomedical and therapeutic systems. Finally, an analysis is provided on the challenges in microfluidics related to nanoparticle synthesis and applications, and the future perspectives, such as large-scale NP synthesis, and hybrid formulations and devices.

Numerical Modeling Using Immersed Boundary-Lattice Boltzmann Method and Experiments for Particle Manipulation under Standing Surface Acoustic Waves.

In this work, we employed the Immersed Boundary-Lattice Boltzmann Method (IB-LBM) to simulate the motion of a microparticle in a microchannel under the influence of a standing surface acoustic wave (SSAW). To capture the response of the target microparticle in a straight channel under the effect of the SSAW, in-house code was built in C language. The SSAW creates pressure nodes and anti-nodes inside the microchannel. Here, the target particle was forced to traverse toward the pressure node. A mapping mechanism was developed to accurately apply the physical acoustic force field in the numerical simulation. First, benchmarking studies were conducted to compare the numerical results in the IB-LBM with the available analytical, numerical, and experimental results. Next, several parametric studies were carried out in which the particle types, sizes, compressibility coefficients, and densities were varied. When the SSAW is applied, the microparticles (with a positive acoustic contrast factor) move toward the pressure node locations during their motion in the microchannel. Hence, their steady-state locations are controlled by adjusting the pressure nodes to the desired locations, such as the centerline or near the microchannel sidewalls. Moreover, the geometric parameters, such as radius, density, and compressibility of the particles affect their transient response, and the particles ultimately settle at the pressure nodes. To validate the numerical work, a microfluidic device was fabricated in-house in the cleanroom using lithographic techniques. Experiments were performed, and the target particle was moved either to the centerline or sidewalls of the channel, depending on the location of the pressure node. The steady-state placements obtained in the computational model and experiments exhibit excellent agreement and are reported.

A review of active and passive hybrid systems based on Dielectrophoresis for the manipulation of microparticles.

Particle separation is essential in a broad range of systems and has several biological applications. Microfluidics has emerged as a potentially transformational method for particle separation. The approach manipulates and separates particles at the micrometer scale by using well-defined microstructures and precisely managed force fields. Depending on the source of the principal manipulating forces, particle manipulation and separation in microfluidics may be classified as active or passive. Passive microfluidic devices depend on drag and inertial forces and microchannel structure, while active microfluidic systems rely on external force fields. Active microfluidics, in general, can properly control and place particles of interest in real time. Due to the low flow rate, the residual time required to apply an appropriate external manipulating force to the target particles is reduced, thereby limiting overall throughput. Passive microfluidics, on the other hand, has a simple architecture, robustness, and high throughput. Hybrid techniques, which combine active and passive processes, have been created to address the shortcomings of each while maximizing the benefits of each. Numerous hybrid techniques for particle separation have been developed. This study reviews the most recent developments in the field of hybrid devices based on dielectrophoresis. Dielectrophoresis-passive and dielectrophoresis-active hybrid approaches are described and evaluated. Dielectrophoresis-inertial, dielectrophoresis-hydrophoresis, dielectrophoresis- deterministic lateral displacement, and insulator-based dielectrophoresis are examples of dielectrophoresis-passive hybrid devices. Dielectrophoresis with acoustophoresis, magnetophoresis, and optophoresis are examples of dielectrophoresis-active devices. Each hybrid system will be assessed based on its operating principles, advantages, and disadvantages. Following that, a comprehensive explanation of dielectrophoresis physical concepts and operating procedures will be offered. As part of this review, the advantages and disadvantages of DEP-based separation devices will be examined. All these hybrid devices will be thoroughly examined and evaluated. Finally, a summary of present difficulties in the hybrid separation sector will be offered, as well as future suggestions and aspirations.

Numerical investigation of nanoparticles slip mechanisms impact on the natural convection heat transfer characteristics of nanofluids in an enclosure.

This study intends to give qualitative results toward the understanding of different slip mechanisms impact on the natural heat transfer performance of nanofluids. The slip mechanisms considered in this study are Brownian diffusion, thermophoretic diffusion, and sedimentation. This study compares three different Eulerian nanofluid models; Single-phase, two-phase, and a third model that consists of incorporating the three slip mechanisms in a two-phase drift-flux. These slip mechanisms are found to have different impacts depending on the nanoparticle concentration, where this effect ranges from negligible to dominant. It has been reported experimentally in the literature that, with high nanoparticle volume fraction the heat transfer deteriorates. Admittingly, classical nanofluid models are known to underpredict this impairment. To address this discrepancy, this study focuses on the effect of thermophoretic diffusion and sedimentation outcome as these two mechanisms turn out to be influencing players in the resulting heat transfer rate using the two-phase model. In particular, the necessity to account for the sedimentation contribution toward qualitative modeling of the heat transfer is highlighted. To this end, correlations relating the thermophoretic and sedimentation coefficients to the nanofluid concentration and Rayleigh number are proposed in this study. Numerical experiments are presented to show the effectiveness of the proposed two-phase model in approaching the experimental data, for the full range of Rayleigh number in the laminar flow regime and for nanoparticles concentration of (0% to 3%), with great satisfaction.

Dielectrophoresis-field flow fractionation for separation of particles: A critical review.

Dielectrophoresis-field flow fractionation (DEP-FFF) has emerged as an efficient in-vitro, non-invasive, and label-free mechanism to manipulate a variety of nano- and micro-scaled particles in a continuous-flow manner. The technique is mainly used to fractionate particles/cells based on differences in their sizes and/or dielectric properties by employing dielectrophoretic force as an external force field applied perpendicular to the flow direction. The dielectrophoretic force is the result of a spatially non-uniform electric field in the microchannel that can be generated either by exploiting microchannel geometry or using special arrangements of microelectrode arrays. Several two-dimensional (e.g., coplanar interdigitated, castellated) and three-dimensional (e.g., top-bottom, side-wall) microelectrode designs have been successfully utilized to perform fractionation of heterogeneous samples. Although originally introduced as a separation technique, DEP-FFF has attracted increasing interest in performing other important operations such as switching, focusing, dipping, and surface functionalization of target particles. Nonetheless, the technique still suffers from limitations such as low throughput and joule heating. By comparatively analyzing recent developments that address these shortcomings, this work is a step forward towards realizing the full potential of DEP-FFF as an ideal candidate for point-of-care (POC) devices with diverse applications in the fields of biomedical, chemical, and environmental engineering.

Investigation of the novelty of latent functionally thermal fluids as alternative to nanofluids in natural convective flows.

This paper presents a detailed comparison between the latent functionally thermal fluids (LFTFs) and nanofluids in terms of heat transfer enhancement. The problem used to carry the comparison is natural convection in a differentially heated cavity where LFTFs and nanofluids are considered the working fluids. The nanofluid mixture consists of Al2O3 nanoparticles and water, whereas the LFTF mixture consists of a suspension of nanoencapsulated phase change material (NEPCMs) in water. The thermophysical properties of the LFTFs are derived from available experimental data in literature. The NEPCMs consist of n-nonadecane as PCM and poly(styrene-co-methacrylic acid) as shell material for the encapsulation. Finite volume method is used to solve the governing equations of the LFTFs and the nanofluid. The computations covered a wide range of Rayleigh number, 104 ≤ Ra ≤ 107, and nanoparticle volume fraction ranging between 0 and 1.69%. It was found that the LFTFs give substantial heat transfer enhancement compared to nanofluids, where the maximum heat transfer enhancement of 13% was observed over nanofluids. Though the thermal conductivity of LFTFs was 15 times smaller than that of the base fluid, a significant enhancement in thermal conductivity was observed. This enhancement was attributed to the high latent heat of fusion of the LFTFs which increased the energy transport within the cavity and accordingly the thermal conductivity of the LFTFs.

Multiple Particle Manipulation under Dielectrophoresis Effect: Modeling and Experiments.

The dissipative particle dynamics (DPD) technique was employed to design multiple microfluidic devices for investigating the motion of bioparticles at low Reynolds numbers. A DPD in-house FORTRAN code was developed to simulate the trajectories of two microparticles in the presence of hydrodynamic and transverse deflecting force fields via considering interparticle interaction forces. The particle-particle interactions were described by using a simplified version of the Morse potential. The transverse deflecting force considered in this microfluidic application was the dielectrophoresis (DEP) force. Multiple microfluidic devices with different configurations of microelectrodes were numerically designed to investigate the dielectrophoretic behavior of bioparticles for their trajectories and the focusing of bioparticles into a single stream in the middle of the microchannel. The DPD simulation results were verified and validated against previously reported numerical and experimental works in the literature. The computationally designed microdevices were fabricated by employing standard lithographic techniques, and experiments were conducted via taking red blood cells as the representative bioparticles. The experimental results for the trajectories and focusing showed good agreement with the numerical results.

Dissipative particle dynamics for modeling micro-objects in microfluidics: application to dielectrophoresis.

The dissipative particle dynamics (DPD) technique is employed to model the trajectories of micro-objects in a practical microfluidic device. The simulation approach is first developed using an in-house Fortran code to model Stokes flow at Reynolds number of 0.01. The extremely low Reynolds number is achieved by adjusting the DPD parameters, such as force coefficients, thermal energies of the particles, and time steps. After matching the numerical flow profile with the analytical results, the technique is developed further to simulate the deflection of micro-objects under the effect of a deflecting external force in a rectangular microchannel. A mapping algorithm is introduced to establish the scaling relationship for the deflecting force between the physical device and the DPD domain. Dielectrophoresis is studied as a case study for the deflecting force, and the trajectory of a single red blood cell under the influence of the dielectrophoretic force is simulated. The device is fabricated using standard microfabrication techniques, and the experiments involving a dilute sample of red blood cells are performed at two different cases of the actuation voltage. Good agreement between the numerical and experimental results is achieved.

Investigation of DPD transport properties in modeling bioparticle motion under the effect of external forces: Low Reynolds number and high Schmidt scenarios.

We have used a dissipative particle dynamics (DPD) model to study the movement of microparticles in a microfluidic device at extremely low Reynolds number (Re). The particles, immersed in a medium, are transported in the microchannel by a flow force and deflected transversely by an external force along the way. An in-house Fortran code is developed to simulate a two-dimensional fluid flow using DPD at Re ≥ 0.0005, which is two orders of magnitude less than the minimum Re value previously reported in the DPD literature. The DPD flow profile is verified by comparing it with the exact solution of Hagen-Poiseuille flow. A bioparticle based on a rigid spring-bead model is introduced in the DPD fluid, and the employed model is verified via comparing the velocity profile past a stationary infinite cylinder against the profile obtained via the finite element method. Moreover, the drag force and drag coefficient on the stationary cylinder are also computed and compared with the reported literature results. Dielectrophoresis (DEP) is investigated as a case study for the proposed DPD model to compute the trajectories of red blood cells in a microfluidic device. A mapping mechanism to scale the external deflecting force from the physical to DPD domain is performed. We designed and built our own experimental setup with the aim to compare the experimental trajectories of cells in a microfluidic device to validate our DPD model. These experimental results are used to investigate the dependence of the trajectory results on the Reynolds number and the Schmidt number. The numerical results agree well with the experiment results, and it is found that the Schmidt number is not a significant parameter for the current application; Reynolds numbers combined with the DEP-to-drag force ratio are the only important parameters influencing the behavior of particles inside the microchannel.

Lateral fluid flow fractionation using dielectrophoresis (LFFF-DEP) for size-independent, label-free isolation of circulating tumor cells.

This short communication introduces a continuous-flow, dielectrophoresis-based lateral fluid flow fractionation microdevice for detection/isolation of circulating tumor cells in the presence of other haematological cells. The device utilizes two sets of planar interdigitated transducer electrodes micropatterned on top of a glass wafer using standard microfabrication techniques. A microchannel with a single inlet and two outlets, realized in polydimethylsiloxane, is bonded on the glass substrate. The two sets of electrodes slightly protrude into the microchannel. Both of the electrode sets are energized with signals at different frequencies and different operating voltages ensuring that the cancer cells experience positive dielectrophoretic force from one set of the electrodes and negative dielectrophoretic force from the other array. Normal cells experience unequal negative dielectrophoretic forces from opposing sets of electrodes. The resultant dielectrophoretic forces on cancer and normal cells push them to flow towards their designed outlets. Successful isolation of green fluorescent protein-labelled MDA-MB-231 breast cancer cells from regular blood cells, both suspended in a sucrose/dextrose medium, is reported in this work.

Natural convection heat transfer simulation using energy conservative dissipative particle dynamics.

Dissipative particle dynamics with energy conservation (eDPD) was used to study natural convection via Rayleigh-Bénard (RB) problem and a differentially heated enclosure problem (DHE). The current eDPD model implemented the Boussinesq approximation to model the buoyancy forces. The eDPD results were compared to the finite volume solutions and it was found that the eDPD method predict the temperature and flow fields throughout the natural convection domains properly. The eDPD model recovered the basic features of natural convection, such as development of plumes, development of thermal boundary layers, and development of natural convection circulation cells (rolls). The eDPD results were presented via temperature isotherms, streamlines, velocity contours, velocity vector plots, and temperature and velocity profiles. Further useful quantities, such as Nusselt number was calculated from the eDPD results and found to be in good agreement with the finite volume calculations.