Micro-sized Channels Research Articles

Transformer oil-dissolved acetylene detection with photonic crystal fiber loop ringdown spectroscopy

When faults happen in a power transformer, a variety of small-molecular gases will generate and dissolve in transformer oil. Therefore, dissolved gas analysis is one of the important methods to monitor the operating status of transformers. This paper proposes an optical acetylene sensing method based on hollow core photonic crystal fiber (HC-PCF) and fiber loop ringdown spectroscopy (FLRDS). Focused ion beam technique is used to complete the processing of micro-sized channels along a HC-PCF. It takes about 11 min to fully fill the entire length of a 0.83 m HC-PCF with acetylene. Furthermore, the FLRDS system based on the dual-wavelength method achieves a minimum detection limit of 0.71 ppm. This detection system improves detection stability and provides a new idea for online monitoring of dissolved gases in transformer oil.

Gold nanoparticles supported onto amine-functionalized in-capillary monoliths meant for flow-through catalysis: A comparative study

Monoliths functionalized with ethylene diamine-derived ligands were synthetized within micro-sized channels as highly permeable catalytic supports for the immobilization of in-situ generated gold nanoparticles. The as-obtained hybrids, essentially differing on the grafted amine-containing ligands were compared, notably regarding the immobilized nanoparticles morphology and their dispersion at the monolith pore surface. Further, such in-capillary hybrid monoliths were successfully applied as flow-through microreactors for the catalytic reduction of nitroaromatic compounds. The general synthetic route for preparing these composite materials consisted in a three-step procedure involving (i) UV-induced polymerization of N-acryloxysuccinimide and ethylene glycol dimethacrylate in toluene, (ii) surface grafting of a series of ethylene diamine derivatives through nucleophilic substitution of N-hydroxysuccinimide leaving groups, and (iii) successive in situ reduction of tetrachloroauric acid to generate monolith-adsorbed gold nanoparticles. The successful synthesis of such hybrid monoliths was ascertained by in-situ Raman spectroscopy, EDX analysis and SEM observations. Microscopy demonstrated the key role of the grafted amine-bearing ligand regarding the morphology, size and surface coverage of the immobilized gold nanoparticles at the monolith pore surface. Monolith-adsorbed gold nanoparticles exhibited good catalytic activities towards the conversion of nitroaromatic compounds into the corresponding amino derivatives in a flow-through process. This study clearly demonstrates the key role of the nature, primary vs. secondary, of the chelating amine in the morphology (shape, size, dispersion) of the supported gold nanoparticles.

Simulation of the calcium salts formation in micro-sized channels (capillaries) in continuous flow mode

The conception “organ-on-a-chip” is a simulation of a living organism functional unit using a microfluidic device and additional technologies. Such technology can clarify some process in human body, reactions on drugs and help to create the new way of treatment without animal models. Calcific aortic stenosis is characterized as long developing disease that is more often observed among the elderly people. “Organ-on-a-chip” via microfluidic technology can simulate some process of this disease such as the calcium salts deposition in shorter time than it happens in living human body. Moreover it can explain the nature of disease. In this work we investigated the deposition of calcium salts in vessels by imitating the processes in the microfluidic chip and mathematical modelling.

Polymer-derived SiOC ceramic lattice with thick struts prepared by digital light processing

Compared with the photosensitive ceramic slurry containing ceramic particles, the photosensitive preceramic polymer was more suitable for the digital light processing (DLP) printing of ceramics. However, the strut thickness of the DLP 3D printed polymer-derived ceramics is always limited due to the serious deformation caused by the aggregation of the enormous by-product gases during the pyrolysis process. Herein, a novel photosensitive epoxy-acrylic siloxane was employed as the matrix for the digital light processing and a non-photosensitive liquid siloxane was introduced as an additive to generate micro-sized channels during pyrolysis, consequently ensuring that the by-product gases can be smoothly released through these channels. With the increase of the pyrolysis temperature, those micro-sized channels would shrink, leaving some nano-pores (or uneven surface) in the pyrolyzed SiOC components. Results show that the DLP 3D printed SiOC lattices with the addition of liquid siloxane show a better macro-appearance and macro-mechanical property with scarifying its micro-hardness. We believed that the method of promoting the release of by-product gases by introducing a non-photosensitive siloxane can be further applied to other DLP 3D printed polymer-derived ceramics.

A rotating permanent magnetic actuator for micropumping devices with magnetic nanofluids

In this study, a novel rotating permanent magnetic actuator (PMA) system is proposed to manipulate magnetic nanofluids to pump chemicals inside micro-sized channels with circular paths. The PMA consists of two permanent magnet pairs and a rotor-like structure. A semicircular-shaped microchannel with a square cross-section area is located at the top of the actuator in order to investigate the performance of the PMA. Fe3O4-water magnetic nanofluid is employed as a working fluid for the manipulation inside the microchannel. In the first stage of this work, a numerical survey is conducted to determine the most suitable angular distance between permanent magnets of a pair in terms of generated magnetic field form in the microchannel region and velocity distribution of magnetic nanofluid within the semicircular microchannel when the permanent magnets are stationary. Preliminary experiments are then carried out for the stationary permanent magnets to validate the predicted flow-field results. Performance tests for different PMA speeds (7.5–30 rpm) and particle concentrations (1%–3% by vol.) indicate that it is possible to manipulate the magnetic nanofluid inside the semicircular channel within a velocity range of 58.7–940 µm s−1, which corresponds to a flow rate range of 0.56–9.02 µL min−1. The results confirm that the proposed PMA system provides flow rate requirements in analytical microfluidic applications such as low flow drug delivery (1–10 µL min−1), cell sorting (6.1 µL min−1), and pathogen detection (3–5.83 µL min−1).

Microfluidics for pharmaceutical nanoparticle fabrication: The truth and the myth.

Using micro-sized channels to manipulate fluids is the essence of microfluidics which has wide applications from analytical chemistry to material science and cell biology research. Recently, using microfluidic-based devices for pharmaceutical research, in particular for the fabrication of micro- and nano-particles, has emerged as a new area of interest. The particles that can be prepared by microfluidic devices can range from micron size droplet-based emulsions to nano-sized drug loaded polymeric particles. Microfluidic technology poses unique advantages in terms of the high precision of the mixing regimes and control of fluids involved in formulation preparation. As a result of this, monodispersity of the particles prepared by microfluidics is often recognised as being a particularly advantageous feature in comparison to those prepared by conventional large-scale mixing methods. However, there is a range of practical drawbacks and challenges of using microfluidics as a direct micron- and nano-particle manufacturing method. Technological advances are still required before this type of processing can be translated for application by the pharmaceutical industry. This review focuses specifically on the application of microfluidics for pharmaceutical solid nanoparticle preparation and discusses the theoretical foundation of using the nanoprecipitation principle to generate particles and how this is translated into microfluidic design and operation.

Graphene Nanoparticles (GNP) nanofluids as key cooling media on a flat solar panel through micro-sized channels

Typically, in a solar-to-electricity energy conversion process from a PV solar panel, this mechanism often accompanied with a creation of by-products which refers to unproductive heat on the surface of PV solar panel. This unwanted heat energy produced will lead to reduction of total effective output of electrical parameters due to the negative inversely proportional relationship between PV temperature and output efficiency. Therefore, it is important to cool the temperature of PV panel relatively in optimizing the output efficiency. This paper is focusing on using state-of-arts nano-sized materials (graphene particles (GNP) in a liquid solution) to achieve the cooling desired. In the previous simulation research carried out on the similar subject, it was found that by having multiple channels with equal volume, the cooling effects will be peaked using graphene nanofluids. This paper presents the experimental setup and fabrication methods using GNP nanofluids as key media in studying the effectiveness of GNP in cooling of a flat solar panel through continuous flowing of GNP nanofluids inside multiple micro-sized channels which were made in direct contact with the exposed backside of the PV solar panel. It is expected that GNP with its enhanced thermo-physical properties compared to water, the cooling efficiency will increase subsequently. Cooling effects due to different pumping flowrates were also being studied respectively.

A Flexible Two-Fold Interpenetrated Indium MOF Exhibiting Dynamic Response to Gas Adsorption and High-Sensitivity Detection of Nitroaromatic Explosives.

A flexible two-fold interpenetrated indium metal-organic framework InOF-23, featuring one-dimensional micro-sized channels decorated by exposed N groups, was successfully synthesized. Interestingly, InOF-23 displays unique dynamic responses to different gases (N2 , Ar, and CO2 ) at low and room temperatures, which indicates that it can be a good candidate for gas adsorption and separation. Furthermore, the high efficiency detection for p-nitroaniline (pNA) makes InOF-23 a potential chemosensor for nitroaromatic explosives.

Compressible liquid flow in nano- or micro-sized circular tubes considering wall–liquid Lifshitz–van der Waals interaction

Although nano- and micro-scale phenomena for fluid flows are ubiquitous in tight oil reservoirs or in nano- or micro-sized channels, the mechanisms behind them remain unclear. In this study, we consider the wall–liquid interaction to investigate the flow mechanisms behind a compressible liquid flow in nano- or micro-sized circular tubes. We assume that the liquid is attracted by the wall surface primarily by the Lifshitz–van der Waals (LW) force, whereas electrostatic forces are negligible. The long-range LW force is thus introduced into the Navier–Stokes equations. The nonlinear equations of motion are decoupled by using the hydrodynamic vorticity-stream functions, from which an approximate analytical perturbation solution is obtained. The proposed model considers the LW force and liquid compressibility to obtain the velocity and pressure fields, which are consistent with experimentally observed micro-size effects. A smaller tube radius implies smaller dimensionless velocity, and when the tube radius decreases to a certain radius Rm, a fluid no longer flows, where Rm is the lower limit of the movable-fluid radius. The radius Rm is calculated, and the results are consistent with previous experimental results. These results reveal that micro-size effects are caused by liquid compressibility and wall–liquid interactions, such as the LW force, for a liquid flowing in nano- or micro-sized channels or pores. The attractive LW force enhances the flow’s radial resistance, and the liquid compressibility transmits the radial resistance to the streaming direction via volume deformation, thereby decreasing the streaming velocity.

Bioinspired Diatomite Membrane with Selective Superwettability for Oil/Water Separation

Membranes with selective superwettability for oil/water separation have received significant attention during the past decades. Hierarchical structures and surface roughness are believed to improve the oil repellency and the stability of Cassie-Baxter state. Diatoms, unicellular photosynthetic algae, possess sophisticated skeletal shells (called frustules) which are made of hydrated silica. Motivated by the hierarchical micro- and nanoscale features of diatom, we fabricate a hierarchical diatomite membrane which consists of aligned micro-sized channels by the freeze casting process. The fine nano-porous structures of frustules are well preserved after the post sintering process. The bioinspired diatomite membrane performs both underwater superoleophobicity and superhydrophobicity under various oils. Additionally, we demonstrate the highly efficient oil/water separation capabililty of the membranes in various harsh environments. The water flux can be further adjusted by tuning the cooling rates. The eco-friendly and robust bioinspired membranes produced by the simple, cost-effective freeze casting method can be potentially applied for large scale and efficient oil/water separation.

Abstract IA06: Mechanism of metastatic migration and invasion in confined matrices

Abstract IA06: Mechanism of metastatic migration and invasion in confined matrices

Development of Microfluidic Channel Devices Integrated on Microelectrode Arrays for Drug Screening with In Vitro Neuronal Culture

Development of Microfluidic Channel Devices Integrated on Microelectrode Arrays for Drug Screening with In Vitro Neuronal Culture

Cholesteric liquid crystals in rectangular microchannels: skyrmions and stripes.

In this paper, we present experimental and numerical studies on the microstructures of a cholesteric liquid crystal (CLC) confined in rectangular micron-channels. By using a sequence of microfabrication techniques we fabricated the micro-sized channels with accurately controlled size, aspect ratio and homeotropic surface anchoring. Through optical microscopic studies we established a phase diagram for the liquid crystal defect textures as a function of the channel depth and width. For the channel width larger than ∼2 times the cholesteric pitch p, the LC molecules are oriented primarily vertical to the channel when the channel depth is below 0.75p, form bubble domain defects when the channel depth is around 0.75p, and form stripe textures when the cell depth is above the cholesteric pitch p. In addition, the bubble domain size and the stripe texture periodicity are found to grow with the increase of the channel width. For the channel width smaller than ∼2p and the channel depth between 0.6p to 1.1p, no textures can be observed in the channels. Numerical simulations based on a director tensor relaxation approach yield detailed molecular director fields, and show that the bubble domain defects are baby-skyrmions and that the stripes are the first type of cholesteric fingerprints. A comparison with previous experiments and numerical simulations indicates that the size of the microchannels also influences what type of soliton-like topological textures form in the CLCs confined in the channels.

Liquid slip and heat transfer in rotating rectangular microchannels

Although the no-slip boundary condition has been extensively used in conventional fluid flow problems, the recent experimental results show that liquid slip can occur in micro-sized channels with hydrophobic or superhydrophobic surfaces. By exploring the liquid slip phenomena, it is possible to reduce the hydrodynamic resistance inside a microchannel. In this article, we will study the water slip phenomena in rotating microchannels. The rotating microchannel is an essential part of centrifugal microfluidic platform, which has emerged as an advanced technique in biomedical applications and chemical separations. We have numerically investigated the flow and heat transfer inside a straight rectangular microchannel subjected to orthogonal rotation and slip boundary conditions at the channel walls. A pressure based finite volume technique in a staggered grid was applied to solve the steady incompressible Navier–Stokes and energy equations. A grid independence study was performed and the code was validated against benchmark problems. The numerical results showed that, for an orthogonally rotating microchannel, different slip velocities were induced at the left and right walls whereas identical slip velocities were produced in the bottom and top walls. In the fully developed region, the effect of secondary flow increased with the rotation but decreased with the slip length. A reduction of about 28.5–36% in hydrodynamic resistance was observed using a slip length of 10μm for channel aspect ratio α (=width/height)=1.0−20.0. Correlations for friction relation (fRe) as a function of slip length (λ) and rotational Reynolds number (Reω) was proposed. The combined effect of slip length and rotation on convective heat transfer parameters was also studied. It was found that, the liquid slip can increase or decrease the Nusselt number depending on the secondary flow effect and the aspect ratio of the microchannel.

A combined additive manufacturing and micro-syringe deposition technique for realization of bio-ceramic structures with micro-scale channels

This article presents a novel rapid layered manufacturing approach based on a combined additive manufacturing (AM) process and a UV-based micro-syringe deposition (μSD) technique to be used in the fabrication of bio-ceramic structures with controlled micro-sized channels for bone and osteochondral tissue regeneration. In the proposed rapid manufacturing method, micro-scale sacrificial photopolymer networks are integrated within the manufactured part by depositing the photopolymer on selected bio-ceramic powder layers using an injection system. This AM–μSD method along with a post-processing protocol can potentially overcome current limitations of traditional powder-based AM approaches that are restricted in terms of complexity of internal architecture and feature size. For bone or osteochondral repair applications, the material system composed of the bio-ceramic and sacrificial photopolymer, along with the post-processing protocol, must ensure that the final implants are free from manufacturing residuals that could trigger an immune response post-implantation. In this study, calcium polyphosphate bio-ceramic was used as the substrate material based on prior art, polyvinyl alcohol solution was used as the powder binding agent, and ethoxylated (10 bisphenol A diacrylate) photopolymer solution was used as the sacrificial photopolymer element. Material characterization suggests that the proposed material system along with heat treatment protocol is suitable for the targeted applications where micro-scale channels within the implant are produced by AM–μSD.

Microchannel Roughness Effects: A Close-Up View

The effect of wall roughness on laminar flows may be important in micro-sized channels though it is often neglected in macro-sized flow geometries. Based on entropy production considerations, we show how its influence can be determined theoretically. The appropriate definition of the wall location when there is no obvious choice (like for smooth walls) is also discussed. This definition has an immediate impact on the actual values of the Poiseuille number.

Variable property effects in single-phase incompressible flows through microchannels

In a systematic approach we address the question of how important variable property effects are for flows in micro-sized channels. Due to heat transfer, the temperature dependence of fluid properties like viscosity and thermal conductivity results in deviations in a solution which accounts for that dependence compared to a solution only considering constant fluid properties. Compared to flows through macro-sized geometries, it turns out that two distinct scaling effects lead to a strong influence of variable fluid properties in micro-sized channels; Reynolds numbers are Re = O ( 1 ) and not large, and axial temperature gradients are no longer small. These scaling effects can be identified after the basic equations are nondimensionalized properly. Examples are given in which Nusselt numbers differ by up to 30% depending on how the property behaviour is accounted for.