T-shaped Microchannel Research Articles

Effects of Channel Wall Twisting on the Mixing in a T-Shaped Micro-Channel.

A new design scheme is proposed for twisting the walls of a microchannel, and its performance is demonstrated numerically. The numerical study was carried out for a T-shaped microchannel with twist angles in the range of 0 to 34π. The Reynolds number range was 0.15 to 6. The T-shaped microchannel consists of two inlet branches and an outlet branch. The mixing performance was analyzed in terms of the degree of mixing and relative mixing cost. All numerical results show that the twisting scheme is an effective way to enhance the mixing in a T-shaped microchannel. The mixing enhancement is realized by the swirling of two fluids in the cross section and is more prominent as the Reynolds number decreases. The twist angle was optimized to maximize the degree of mixing (DOM), which increases with the length of the outlet branch. The twist angle was also optimized in terms of the relative mixing cost (MC). The two optimum twisting angles are generally not coincident. The optimum twist angle shows a dependence on the length of the outlet branch but it is not affected much by the Reynolds number.

Elastic instabilities in the electroosmotic flow of non-Newtonian fluids through T-shaped microchannels.

Electroosmotic flow (EOF) has been widely used to transport fluids and samples in micro- and nanofluidic channels for lab-on-a-chip applications. This essentially surface-driven plug-like flow is, however, sensitive to both the fluid and wall properties, of which any inhomogeneity may draw disturbances to the flow and even instabilities. Existing studies on EOF instabilities have been focused primarily upon Newtonian fluids though many of the chemical and biological solutions are actually non-Newtonian. We carry out a systematic experimental investigation of the fluid rheological effects on the elastic instability in the EOF of phosphate buffer-based polymer solutions through T-shaped microchannels. We find that electro-elastic instabilities can be induced in shear thinning polyacrylamide (PAA) and xanthan gum (XG) solutions if the applied direct current voltage is above a threshold value. However, no instabilities are observed in Newtonian or weakly shear thinning viscoelastic fluids including polyethylene oxide (PEO), polyvinylpyrrolidone (PVP), and hyaluronic acid (HA) solutions. We also perform a quantitative analysis of the wave parameters for the observed elasto-elastic instabilities.

Ionic liquid-water flow in T-shaped microchannels with different aspect ratios

In this article we investigate the influence of a rectangular microchannel aspect ratio on the liquid–liquid flow. An ionic liquid was chosen as one of the working fluids due to a vast scope of applications. Immiscible ionic liquid-water flow in T-shaped microchannels with 160μm hydraulic diameter and aspect ratios equal to 2 and 4 was studied experimentally. Flow pattern maps were drawn and compared for two channels in terms of We*Oh dimensionless number. Parallel flow was shown to prevail for the channel with higher aspect ratio. The influence of channel aspect ratio on plug flow peculiarities was studied in detail. Plug length and velocity were measured at different bulk flow rates. Velocity fields in aqueous plugs were measured using the micro-PTV technique. Velocity circulations were calculated for different flow rates. Total circulation value inside plugs was found to be higher in the channel with the lower aspect ratio.

Estimation of the flows mixing efficiency inside T-micromixer with an external perturbation for low Reynolds numbers

The flow pattern regimes and mixing quantities in case of an external perturbation for low Reynolds numbers in a T-shape microchannel were studied experimentally using the LIF technique. Formation of a hydrodynamic wave travelling along the outlet channel for the stratified regime was discovered. The wave amplitude is 0.057Wout. The wavelength corresponding to distance between two nearest pits is 3.86Dh. The change of mixing efficiency between undisturbed and perturbated flows in each of the considered sections is less than 6%. However, the arising of wave causes a decrease in the distance at which the flows are completely mixed.

Electrokinetic instability in microchannel viscoelastic fluid flows with conductivity gradients

Electrokinetic instability (EKI) is a flow instability that occurs in electric field-mediated microfluidic applications. It can be harnessed to enhance sample mixing or particle trapping but has to be avoided in particle separation. Current studies on EKI have been focused primarily on the flow of Newtonian fluids. However, many of the chemical and biological solutions exhibit non-Newtonian characteristics. This work presents the first experimental study of the EKI in viscoelastic fluid flows with conductivity gradients through a T-shaped microchannel. We find that the addition of polyethylene oxide (PEO) polymer into Newtonian buffer solutions alters the threshold electric field for the onset of EKI. Moreover, the speed and temporal frequency of the instability waves are significantly different from those in the pure buffer solutions. We develop a three-dimensional preliminary numerical model in COMSOL, which considers the increased viscosity and conductivity as well as the suppressed electroosmotic flow of the buffer-based PEO solutions. The numerically predicted threshold electric field and wave parameters compare favorably with the experimental data except at the highest PEO concentration. We attribute this deviation to the neglect of fluid elasticity effect in the current model that increases with the PEO concentration.

Microfluidic study of effects of flow velocity and nutrient concentration on biofilm accumulation and adhesive strength in the flowing and no-flowing microchannels.

Biofilm accumulation in porous media can cause pore plugging and change many of the physical properties of porous media. Engineering bioplugging may have significant applications for many industrial processes, while improved knowledge on biofilm accumulation in porous media at porescale in general has broad relevance for a range of industries as well as environmental and water research. The experimental results by means of microscopic imaging over a T-shape microchannel clearly show that increase in fluid velocity could facilitate biofilm growth, but that above a velocity threshold, biofilm detachment and inhibition of biofilm formation due to high shear stress were observed. High nutrient concentration prompts the biofilm growth; however, the generated biofilm displays a weak adhesive strength. This paper provides an overview of biofilm development in a hydrodynamic environment for better prediction and modelling of bioplugging processes associated with porous systems in petroleum industry, hydrogeology and water purification.

Highly mono-dispersed liquid crystal capsules with core–shell structure

Microfluidics have driven innovations in various fields including biology, soft-matter, and micro-chemical processes. Microfluidic systems provide a unique research environment for micro-scale liquid droplets. Especially encapsulated liquid crystal (LC) droplet fabrication, which can provide a considerable advancement for the relevant fundamental study and applications. We demonstrate the fabrication of uniform sized LC droplets using a microfluidic device system with a T-shaped junction micro-channel. The droplet size can be controlled by changing the flow rate of two immiscible fluids. Also, by adjusting the device’s geometrical structure, a desired droplet size can be obtained. The principle of generation of the droplet and the factors that determine the size of the droplet are theoretically briefly explained. These produced LC droplets were encapsulated by the complex coacervation method. The thickness of the fabricated capsule shell was about 1 μm. The texture transition of the encapsulated mono-dispersed droplets driven by in-plane field shows their potential for various applications, such as various fields of display and biotechnology.

3D simulation of droplet coalescence in T-shaped microchannel

Three Droplet coalescence behaviour in T-shaped microchannel under different conditions is investigated numerically using coupled volume of fluid and level set (CLSVOF) method. The effects of continuous phase (water) flow rate and physical properties of dispersed phase are examined respectively. The results show that with the increase of water flow rate, the volume of coalesced droplet decreases, its deformation increases but coalesced time hasn’t changed significantly. Droplet coalescence time go down, however the aspect ratio of the coalesced droplet increase first and then decrease in the order of pentanol, octanol and decanol, with no obvious impact on coalesced droplet volume.

Mass-Transfer Characteristics of CO2 Absorption into Aqueous Solutions of N-Methyldiethanolamine + Diethanolamine in a T-Junction Microchannel

The mass-transfer process of CO2 absorption into aqueous solution of N-methyldiethanolamine (MDEA) + diethanolamine (DEA) in a T-shaped microchannel was studied using a high-speed camera. The effec...

Experimental investigation of pressure disturbances influence on a parallel flow of viscous immiscible liquids in a T-shaped microchannel

In the present paper pressure disturbances influence on parallel flow of immiscible liquids, viz. castor oil and paraffin oil, in a T-shaped microchannel with 320 um hydraulic diameter is studied experimentally. Pressure disturbances with sinusoidal and meander wave shape were applied at different frequencies and pulse ratio to the flow of carrying phase, dispersed phase or both of them simultaneously. It was shown that pressure disturbances can lead to the transition to the slug flow. A parameter taking into account signal amplitude and frequency was introduced for flow map construction. Slug length and velocity was measured for all regimes studied.

Continuous production of lignin nanoparticles using a microchannel reactor and its application in UV-shielding films.

With the severe energy and environmental issues, lignin has received increasing attention as a renewable biomass feedstock. The development of lignin-based nanoparticles provides a new route to the valorization of lignin. In this work, we propose a simple continuous method to prepare lignin nanoparticles (LNS) using a microchannel reactor. Polyvinylpyrrolidone (PVP)/sodium dodecyl sulfate (SDS) were selected as stabilizers. Spherical-like lignin nanoparticles with an average size of 13 nm were obtained in a T-shaped microchannel reactor. The effects of solvent species, PVP/SDS mass ratio, and lignin solution flow rate on the size of LNS were investigated. The as-prepared LNS had a good stability during 60 days-storage and were used as an additive to form UV-shielding composite films with poly(vinyl alcohol) (PVA). Compared with raw lignin, the addition of LNS could enhance the UV-shielding efficacy by 13.3% in the ultraviolet spectrum (250 nm). The present work suggests that the microchannel reactor is a promising continuous approach to prepare LNS with versatile applications.

Non-Newtonian effects of a lubricant flow through a T-shaped microchannel

In this paper, the importance of non-Newtonian effects of a lubricant flow through a T-shaped microchannel with a moving lead are investigated. The lubricant flow isrepresented by Navier-Stokes equation for viscous, incompressible and steady fluid flows.Non-Newtonian characteristics are simulated by FENE-P constitutive equation. Finite Volume method was used to solve the case numerically. PSD distribution for Reynolds number Re=0.01 and Weissenberg number We =1 were compared with Newtonian case. Clear numerical evidence of a higher stresses for non-Newtonian case is discussed.

Investigation of mixing efficiency and pressure drop in T-shaped micromixers

The numerical investigation of the flow regimes in the T-shaped microchannels with different width-to-height aspect ratios of mixing channel was carried out. In the first case, the mixing channel width was varied from 200 μm to 1000 μm while its height was constant; in the second case, the mixing channel height was varied from 100 μm to 2000 μm, while its width was constant. The Reynolds number was varied from 5 to 700. The dependences of fluids mixing efficiency and the pressure drop on the Reynolds number at different width-to-height aspect ratios of mixing channel were numerically established. The correlations to determine the critical Reynolds number, as well as the friction factor at different widths and heights of the mixing channel, were proposed. The mixing efficiency, reduced to the pressure drop and the volume unit was analyzed for the first time. The optimal range of parameters in terms of the working efficiency of the micromixer was determined.

Microfluidics to determine the diffusive mass transfer of a low viscosity solvent into a high viscosity hydrocarbon

In this work, a microfluidic platform along with X-ray computerized tomography were employed to analyze diffusive mass transfer of a low viscosity solvent (hexane) into a high viscosity hydrocarbon (bitumen). T-shaped microfluidic channels were fabricated to measure the diffusion coefficient in significantly shorter times and lower sample volume compared with traditional methods. Semitransparent nature of bitumen facilitates the application of light transmission imaging during the time and relating intensities to solvent concentration. Diffusion mass transfer was studied with respect to Fickian and Single-File mass transfer mechanisms and corresponding equation was applied to calculate both constant and concentration dependent diffusion coefficients. The accuracy of Fickian mass transfer mechanism was confirmed with calculating values of fitting parameter (i.e. nw) in addition to superimposition of data for both techniques. The optimum values of constant diffusion coefficient for T-shaped microchannel and X-ray technique were 2 × 10−10 and 1.8 × 10−10 m2·s−1, respectively. Concentration dependent diffusion coefficients ranged from 1 × 10−12 to 3.6 × 10−10 m2·s−1 for the experiments that reveal constant mutual diffusion coefficient assumption can result in significantly high errors particularly at low and high solvent mass fractions.

Reexamination of Murray’s law for tree-like rectangular microchannel network with constant channel height

The present work theoretically and numerically reexamines the Murray’s law to design a tree-like rectangular microchannel network with constant microchannel height under the constraint of constant total channel volume, and investigates effects of the dimensional and structural parameters of the tree-like network on the optimal width ratio and optimal hydraulic diameter ratio of rectangular microchannels at two successive branching levels to achieve a minimum hydraulic resistance. The results show that the optimal hydraulic diameter ratio of the tree-like rectangular microchannel network does not follow the conventional Murray’s law. Both the optimal width ratio and the optimal hydraulic diameter ratio to achieve a minimum hydraulic resistance strongly depend on the dimensional and structural parameters including rectangular channel height H, total channel volume V, channel length ratio γ, channel length at the initial branching level L0, branching number N and branching level m of the tree-like network. Additionally, the present work finds that the average convective heat transfer coefficient of a heat sink with an elementary T-shaped tree-like rectangular liquid-cooling microchannel network with the constant channel height increases with both the increasing width ratio of microchannels at two successive branching levels and the increasing channel height.

Investigation of temperature-induced flow stratification and spiral flow in T-shaped microchannel

In this study, the heat and fluid flows were investigated when fluids at varying temperatures are mixed in a T-shaped microchannel. A temperature gradient was formed using two Peltier modules in the junction of a T-shaped microchannel, and the velocity fields were measured using microparticle image velocimetry (µ-PIV). Measurements were obtained at five planes in the direction of the depth by changing the focal position of the objective lens. Under the operation of the Peltier modules, the flow velocity on the heated side was increased and the velocity on the cooled side was decreased in the upper area in the vertical direction. Furthermore, in the lower area, the flow velocity on the cooled side was increased and the velocity on the heated side was decreased. The velocity difference between the two inlets depends on the applied power of the Peltier modules. We also investigated the mixing behavior downstream of the channel, and a strong spiral flow was clearly observed. The spiral flow should enlarge the contact interface area, and it should be useful for application to a micromixer. We first observed the fluid stratification induced by the temperature in the microchannel. This phenomenon is useful for application in microfluidic devices as a contactless micromixer.

Flow hydrodynamics of immiscible liquids with low viscosity ratio in a rectangular microchannel with T-junction

We present an experimental study of the liquid-liquid system with extremely low viscosity ratio (10−3) in a T-shaped microchannel with 120 × 120 μm inlets and a 240 × 120 μm outlet channel. Six different flow patterns have been observed: plug, droplet, slug, throat-annular and parallel flow. A specific plug flow pattern was found where micron-sized droplets or even a jet breaks off from the rear meniscus of a plug. In addition to typical Taylor-shaped plugs the dumbbell-like plugs were observed. Flow visualization data were summarized in the flow pattern maps. Plug length and velocity were measured based on flow visualization results. It was found that the plug velocity can be fitted by power function rather than the linear function, which disagrees with experimental data at a low plug velocity. Front and tail plug surface curvature was scaled using dimensionless parameter, the flow rate ratio multiplied by Capillary number based on bulk velocity (Qd/Qc * Cabulk). Instantaneous velocity vector fields inside water plugs were measured by means of PTV technique. Different flow structures were found and discussed. As a result, it is proposed to use the values of Qd/Qc * Cabulk for distinguishing different plug shapes and circulation patterns inside the plugs.

Study of droplet flow in a T-shape microchannel with bottom wall fluctuation

Droplet generation in a T-shape microchannel, with a main channel width of 50 $$\upmu \hbox {m}$$ , side channel width of 25 $$\upmu \hbox {m}$$ , and height of 50 $$\upmu \hbox {m}$$ , is simulated to study the effects of the forced fluctuation of the bottom wall. The periodic fluctuations of the bottom wall are applied on the near junction part of the main channel in the T-shape microchannel. Effects of bottom wall’s shape, fluctuation periods, and amplitudes on the droplet generation are covered in the research of this protocol. In the simulation, the average size is affected a little by the fluctuations, but significantly by the fixed shape of the deformed bottom wall, while the droplet size range is expanded by the fluctuations under most of the conditions. Droplet sizes are distributed in a periodic pattern with small amplitude along the relative time when the fluctuation is forced on the bottom wall near the T-junction, while the droplet emerging frequency is not varied by the fluctuation. The droplet velocity is varied by the bottom wall motion, especially under the shorter period and the larger amplitude. When the fluctuation period is similar to the droplet emerging period, the droplet size is as stable as the non-fluctuation case after a development stage at the beginning of flow, while the droplet velocity is varied by the moving wall with the scope up to 80% of the average velocity under the conditions of this investigation.

Blood cells separation in a T-shaped microchannel fabricated by a micromilling technique

Blood cells separation in a T-shaped microchannel fabricated by a micromilling technique

A counter-flow-based dual-electrolyte protocol for multiple electrochemical applications

This paper reports a computational demonstration and analysis of an innovative counter-flow-based microfluidic unit and its upscaling network, which is compatible with previously developed dual-electrolyte protocols and numerous other electrochemical applications. This design consists of multidimensional T-shaped microchannels that allow the effective formation of primary and secondary counter-flow patterns, which are beneficial for both high-performance regenerative H2/O2 redox cells and flow batteries at a low electrolyte flow-rate operation. This novel design demonstrates the potential to achieve high overall energy throughput and reactivity because of the full utilization of all available reaction sites. A computational study on energy and pressure loss mechanism during scale-out is also examined, thereby advancing the realization of an economical electrolyte-recycling scheme.