Solution In Microchannel Research Articles

Numerical investigation on the enhanced heat transfer characteristics of non-Newtonian viscoelastic fluids in microchannel with chip arrays

Elastic turbulence is an efficient heat transfer method at microscale. In this work, we conduct a systematic investigation on the flow and heat transfer performances of viscoelastic polymer solutions in microchannels with chip arrays by means of high-fidelity numerical simulations. Focusing on the effects of fluid elasticity [i.e. polymer relaxation time (λ)] and flow Reynolds number (Re), we find that the synergistic interplay between inertial and elastic forces is strategically exploited to amplify convection, thereby facilitating an enhanced heat transfer performance. For highly elastic fluid, the Nusselt number (Nu) can be improved by 76.13 % compared to that of less elastic fluid, while the pressure drop is reduced appropriately. In addition, as the fluid elasticity increases, the pressure drop decreases and eventually converges to a constant. In the zone of elastic turbulence, the fluid reinforces the convective heat transfer, which can be ascribe to the deformation of long-chain polymer molecules. Particularly, we consider the effect of temperature-dependent λ on the heat transfer performance. Our results demonstrate that the increased temperature-dependent λ decreases the value of Nu, and the variation between values of variable and constant λ is reduced with increasing Re or λ. Hence, in some cases of large fluid elasticity or high Re, it is possible to safely ignore the impact of temperature-dependent λ with an acceptable accuracy. The present work provides important insights into the enhanced heat transfer via elastic turbulence, which could guide the applications in the field of chip cooling.

Mass transfer enhancement for CO2 chemical absorption in a spiral baffle embedded microchannel

This paper presents an experimental study on CO2 chemical absorption by Monoethanolamine (MEA) solution in microchannel. In particular, a novel spirally distributed baffle structure is proposed to be embedded into the microchannel so as to generate the swirling flow pattern and to enhance the mass transfer. The effect of spiral baffle structure on the two phase flow pattern transition, the CO2 gas void fraction, the pressure drop, and the mass transfer performance are characterized and discussed, under varied gas and liquid flow rates, and MEA concentrations. Results demonstrate that the spiral baffle structure could significantly enhance the gas–liquid mass transfer, with overall liquid side volumetric mass transfer rate (kLa) up to 2.35 s−1 and enhancement number E up to 1.387 at small gas and liquid Reynolds numbers (ReG < 5.5; ReL < 14). New predictive correlations have also been proposed by considering both the structure enhancement factor and the chemical reaction factor.

A pump-free and high-throughput microfluidic chip for highly sensitive SERS assay of gastric cancer-related circulating tumor DNA via a cascade signal amplification strategy

Circulating tumour DNA (ctDNA) has emerged as an ideal biomarker for the early diagnosis and prognosis of gastric cancer (GC). In this work, a pump-free, high-throughput microfluidic chip coupled with catalytic hairpin assembly (CHA) and hybridization chain reaction (HCR) as the signal cascade amplification strategy (CHA–HCR) was developed for surface-enhanced Raman scattering (SERS) assays of PIK3CA E542K and TP53 (two GC-related ctDNAs). The chip consisted of six parallel functional units, enabling the simultaneous analysis of multiple samples. The pump-free design and hydrophilic treatment with polyethylene glycol (PEG) realized the automatic flow of reaction solutions in microchannels, eliminating the dependence on external heavy-duty pumps and significantly improving portability. In the reaction region of the chip, products generated by target-triggered CHA initiated the HCR, forming long nicked double-stranded DNA (dsDNA) on the Au nanobowl (AuNB) array surface, to which numerous SERS probes (Raman reporters and hairpin DNA-modified Cu2O octahedra) were attached. This CHA–HCR strategy generated numerous active “hot spots” around the Cu2O octahedra and AuNB surface, significantly enhancing the SERS signal intensity. Using this chip, an ultralow limit of detection (LOD) for PIK3CA E542K (1.26 aM) and TP53 (2.04 aM) was achieved, and the whole process was completed within 13 min. Finally, a tumour-bearing mouse model was established, and ctDNA levels in mouse serum at different stages were determined. To verify the experimental accuracy, the gold-standard qRT–PCR assay was utilized, and the results showed a high degree of consistency. Thus, this rapid, sensitive and cost-effective SERS microfluidic chip has potential as an ideal detection platform for ctDNA monitoring.

Mass transfer and capture of carbon dioxide using amino acids sodium aqueous solution in microchannel

Capture and storage of CO2 are important to restrain the greenhouse effect. The amino acid salt solution as a new type of CO2 absorbent shows good application potential. Besides, microchannel has a unique enhancement to mass transfer, which is conducive to promote CO2 capture. The absorption performance of CO2 into aqueous solutions of sodium salts of l-threonine, l-valine, l-alanine and glycine in the microchannel was investigated. It was found that the CO2 absorption rate of four sodium amino acid aqueous solutions under the same condition follows in the order: ñ (sodium glycinate) > ñ (sodium l-alaninate) > ñ (sodium l-valinate) > ñ (sodium l-threoninate). The sodium glycinate aqueous solution has maximum CO2 absorption ability, thus the mass transfer and capture of CO2 absorbed into the sodium glycinate aqueous solution were studied systematically. The effects of operating conditions including gas flow rate, liquid flow rate, and sodium glycinate concentration on the specific surface area, overall volumetric mass transfer coefficient, overall mass transfer coefficient and absorption fraction of CO2 were explored. Furthermore, a new correlation was proposed to predict the volumetric mass transfer coefficient.

Mass transfer enhancement of CO2 absorption into [Bmim][BF4] aqueous solution in microchannels by heart-shaped grooves

CO2 absorption into [Bmim][BF4] aqueous solution was investigated experimentally. To enhance gas-liquid mass transfer, the heart-shaped grooves were engraved in the microchannel. It was found that the grooves could cause eddy flow of liquid phase and accordingly promote turbulent and convective mass transfer. Liquid side volumetric mass transfer coefficient and mass transfer enhancement factor could be remarkably increased, and the enhancement factor could reach up to 2.2. Moreover, the effective mass transfer enhancement efficiency was analyzed considering the energy consumption, and its value could reach 2.1. A correlation was proposed to predict the liquid side volumetric mass transfer coefficient for the grooved microchannel.

Isolated Taylor Bubbles in Co-Current with Shear Thinning CMC Solutions in Microchannels—A Numerical Study

Slug flow is a multiphase flow pattern characterized by the occurrence of long gas bubbles (Taylor bubbles) separated by liquid slugs. This multiphase flow regime is present in many and diversified natural and industrial processes, at macro and microscales, such as in eruption of volcanic magmas, oil recovery from pre-salt regions, micro heat exchangers, and small-sized refrigerating systems. Previous studies in the literature have been mostly focused on tubular gas bubbles flowing in Newtonian liquids. In this work, results from several numerical simulations of tubular gas bubbles flowing in a shear thinning liquid in microchannels are reported. To simulate the shear thinning behavior, carboxymethylcellulose (CMC) solutions with different concentrations were considered. The results are compared with data from bubbles flowing in Newtonian liquids in identical geometric and dynamic conditions. The numerical work was carried out in computational fluid dynamics (CFD) package Ansys Fluent (release 16.2.0) employing the volume of fluid (VOF) methodology to track the volume fraction of each phase and the continuum surface force (CSF) model to insert the surface tension effects. The flow patterns, the viscosity distribution in the liquid, the liquid film thickness between the bubble and the wall, and the bubbles shape are analyzed for a wide range of shear rates. In general, the flow patterns are similar to those in Newtonian liquids, but in the film, where a high viscosity region is observed, the thickness is smaller. Bubble velocities are smaller for the non-Newtonian cases.

Effect of solvent quality on Poiseuille flow of polymer solutions in microchannels: A dissipative particle dynamics study

ABSTRACTThe Poiseuille flows of polymer solutions for varying quality solvents in microchannels have been simulated using dissipative particle dynamics. In particular, the velocity distributions and the polymer migration across the channel have been investigated for good, athermal, and poor solvents. The velocity profiles for all three kinds of solvent deviate from the parabolic profile, and the velocity profile of the athermal solvent falls in between the good solvent and the poor solvent. For the athermal solvent, a migration away from the wall due to the hydrodynamic interactions between the chains and the wall is observed, and a migration away from the channel center due to the different chain Brownian diffusivities is also observed. For the good solvent, because of the more stretched polymer chains, the migration away from the wall is stronger than that for the athermal solvent. However, the migration away from the channel center is not observed for good solvents. For the poor solvent, the hydrodynamic interaction within the chains is screened, and the polymer chains migrate toward the wall and appear to be absorbed by the wall. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47345.

Mass transfer characteristics of CO2 absorption into 1-butyl-3-methylimidazolium tetrafluoroborate aqueous solution in microchannel

The mass transfer characteristics of CO2 absorption into aqueous solution of ionic liquid in microchannel was investigated experimentally by a high speed camera. The influences of the ratio of gas and liquid flow rates (QG/QL) and the concentration of ionic liquid on the liquid side volumetric mass transfer coefficient (kLa), liquid side mass transfer coefficient (kL) and length of mass transfer zone (LM) were studied systematically. The results show that both kLa and kL increase but LM decreases with the increasing QG/QL and the concentration of ionic liquid. Taking the enhancement of 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF4]) on the mass transfer into account, a dimensionless correlation for predicting kLa was proposed. This work is conducive to the design, optimization and the application of the microchannel reactor for CO2 capture and removal.

Numerical Simulation of Residual Oil Flooded by Polymer Solution in Microchannels

This paper establishes a flow equation using non-Newtonian fluid mechanics and defines the deformation of residual oil using numerical computation in order to conduct a study on the flow law of residual oil in microchannels of rock during polymer flooding, the influence of flooding fluid elasticity on the deformation of residual oil, and flooding mechanism of viscoelastic displacing fluid. Computation shows that advancing contact angle increases and receding contact angle decreases as the viscosity ratio decreases. The higher elasticity of polymer solution with higher concentration or molecular weight leads to significantly more obvious deformation of residual oil and benefits migration and stripping of residual oil. The impact of the initial wetting angle of residual oil film on deformation is analyzed. A smaller initial wetting angle corresponds to a bigger change of advancing contact angle and smaller change of receding contact angle. A better understanding of the flooding process is gained via a study on residual oil deformation in polymer flooding. Consequently, oil flooding efficiency and oil recovery can be enhanced. This is the hydrodynamic mechanism of enhanced oil recovery (EOR) by polymer flooding.

Ethylene/ethane separation and mass transfer characteristics through absorption by AgNO3 solutions in microchannels

Chemical absorption using silver ion is a potential way for ethylene recovery, which can be significantly enhanced by the use of microreactors. This work presents an experimental study on the characteristics of absorption of ethylene into aqueous AgNO3 solutions. The effects of several parameters including channel length, channel diameter, flow rates, temperature and AgNO3 concentration are investigated in terms of absorption fraction, molar absorptivity and mass transfer coefficients. It is demonstrated that very high liquid side mass transfer coefficients in the range of 3–85 s−1 can be obtained in microchannels, indicating significant process intensification. Based on the results, an empirical correlation was proposed for the prediction of mass transfer coefficients.

Hydrodynamics of residual oil droplet displaced by polymer solution in micro-channels of lipophilic rocks

Hydrodynamics of residual oil droplet displaced by polymer solution in micro-channels of lipophilic rocks

A novel heating area design of temperature-jump microfluidic chip for synchrotron radiation solution X-ray scattering

In this paper, we present a novel design scheme of temperature-jump (T-jump) area for microfluidic device. Numerical simulation and experimental research of thermal characteristics of the solution in microchannels is completed. Numerical simulation of the temperature-jump microchannel is analyzed to study the heat transfer characteristics by comparing performance of three proposed configurations. Calculation of the power requirement is discussed in the dimensional design of microheater. Temperature-sensitive fluorescent dye is applied to investigate the temperature field of microchannel heated by a designed microheater. It is found that the T-jump microfluidic device can provide rapid heating for solutions with strong convection heat transfer ability.

Effect of surface tension on filling flow of carboxymethyl cellulose solution in microchannel

The effect of surface tension on filling flow is neglected generally in macroscale flow. However, it may become a significant factor to impact the filling flow in microchannel. In this paper, the effect of surface tension on filling flow was investigated by a visualisation device to facilitate the observation of flow behaviour. Capillaries in the diameter range of 0·1–0·5 mm were chosen as microchannels and 3% solutions of carboxymethyl cellulose polymer were studied. The results indicate that additional pressure accounting for surface tension influences the filling flow in microchannel slightly. The error of theoretical velocity considering the surface tension reaches 8% in capillary of 0·1 mm in diameter. The surface tension can be neglected when feature size of flow channel is >0·1 mm. Meanwhile, wall slip exists during the filling flow into capillaries and slip velocity increases as decreasing feature size. Therefore, some other factors such as wall slip and size effect could impact filling flow together in microchannel if the feature size of channel is <0·1 mm.

Immiscible liquid–liquid slug flow characteristics in the generation of aqueous drops within a rectangular microchannel for preparation of poly(2-hydroxyethylmethacrylate) cryogel beads

The microchannel liquid-flow focusing and cryo-polymerization is an efficient method for the preparation of cryogel beads with a narrow diameter distribution. In order to prepare cryogel beads with expected diameters, it is necessary to get insights in the liquid–liquid immiscible flow characteristics of the flow-focusing fluid and the monomer solution in microchannels. In this work, the slug flow behaviors of two immiscible liquids regarding the preparation of poly(2-hydroxyethylmethacrylate) (pHEMA) cryogel beads in a rectangular cross-junction microchannel were investigated experimentally by the high-speed imaging method. Correlations of the immiscible liquid–liquid slug flow parameters like the aqueous slug velocity and length, the aqueous slug nose and tail lengths, the water-immiscible slug length as well as the aqueous droplet size were obtained. The pHEMA cryogel beads were prepared under certain flow conditions and the bead sizes were measured by laser particle size analyzer. The obtained correlations were then employed to estimate the bead sizes and compared with those obtained experimentally. The results showed that the present correlations gave reasonable estimations of the mean bead diameters at various conditions and thus, could be useful and helpful in the preparation of cryogel beads with expected size distributions in rectangular microchannels.

Polymer microchip impedance spectroscopy through two parallel planar embedded microelectrodes: Understanding the impedance contribution of the surrounding polymer on the measurement accuracy

The present work describes a new methodology for contact free impedance of a solution in a polymer microchip taking into account the role played by the surrounding polymer on the impedance accuracy. Measurements were carried out using a photoablated polyethylene terephthalate (PET) microchannel above two embedded microband electrodes. The impedance diagrams exhibit a loop from high frequencies to medium frequencies (1MHz–100Hz) and a capacitive behavior at low frequencies (100–1Hz). The impedance diagrams were corrected by eliminating from the global microchip response the contribution of the impedance of the PET layer between the two microband electrodes. This operation enables a clear observation of the impedance in the microchannel solution, including the bulk solution contribution and the interfacial capacitance related to the surface roughness of the photoablated microchannel. Models for the impedance of solutions of varying conductivity showed that the capacitance of the polymer–solution interface can be modeled by a constant phase element (CPE) with an exponent of 0.5. The loop diameter was found to be proportional to the microchannel resistivity, allowing a cell constant around 4.93×105m−1 in contactless microelectrodes configuration.

The apparent hydrodynamic slip of polymer solutions and its implications in electrokinetics

The apparent hydrodynamic slip of polymer solutions is a result of polymer depletion at channel walls, and its fluid dynamic effects are well known. This work reviews the evidences of apparent slip in electrokinetics, and discusses practical consequences in the following fields: (i) electrokinetic transport of polymer solutions in microchannels, which is of interest for the design and operation of microfluidic chips, particularly for electrophoresis; (ii) electroosmotic pumping, where it has been observed that the employment of polymer solutions greatly enhances the output pressure; and (iii) electrokinetic energy conversion, where the apparent slip also contributes to improve the conversion efficiency. In all cases, critical discussions are taken from basic physical concepts.

Modeling of capacitively coupled contactless conductivity detection on microfluidic chips

A novel equivalent circuit model of capacitively coupled contactless conductivity detection (C4D) on microfluidic chips is presented. The impedance of the solution in microchannels facing the two electrodes for C4D was first introduced in the model of C4D on microfluidic chips. The electrodes and the solution facing electrodes were divided into individual segments in the model, and the effect of the length of divided segments on the model was studied. A back-calculating method was put forward to calculate the stray capacitance between the electrodes, and the variation between the calculated value and the simulated value was only 6 %. To evaluate the accuracy of the model, a hybrid poly (methyl methacrylate) (PMMA)/polydimethylsiloxane (PDMS) microchip was fabricated and a simple model was built. Compared with the outputs of the simple model, the data predicted by the novel model show a much closer fit to experimental results, and the variations were within 8 % over a wide concentration range of 1–500 μm for potassium chloride.

F112 近赤外域の2波長同時イメージング法を利用したマイクロ流路内の発熱反応の可視化 : HClとNaOH水溶液の吸収スペクトルと2波長画像の考察(一般講演(7))

This paper presents the visualization of heat and mass transfer of aqueous solutions in microchannels by using the simultaneous imaging method of the temperature and solute concentration. This method is based on the absorption characteristics of water in a near-infrared region: absorbance at a wavelength of 1412 nm is dependent on the temperature whereas that at 1442 nm is independent. This visualization method is applied to experimental researches on chemical reactions between hydrochloric acid and sodium hydroxide aqueous solutions. These two reagents are supplied into two inlets of a Y-shaped rectangular microchannel at several different flow rates. Absorbance difference images in the merging region of the two flows are obtained at the two wavelengths simultaneously, which demonstrate that the magnitude and distribution of the absorbance difference vary with the concentrations and flow rates.

Electrokinetic Flow and Measure Method in Microfluidic

An analytical solution for pressure-driven electrokinetic flows in a narrow capillary is presented based on the Poisson–Boltzmann equation for electrical double layer and the Navier–Stokes equations for incompressible viscous fluid. The analytical solutions indicate that pressure-driven flow of an electrolyte solution in microchannel with charged solid wall induces a streaming potential, which is proportional to the flowrate and induces an electroviscous effect on flow. A device for measuring the electrokinetic flow rate and streaming potential is proposed.

The impact of crystallization fouling on a microscale heat exchanger

Due to their very high surface-to-volume ratios micro heat exchangers provide possible advantages in heat and mass transfer operations. Besides the potential of process intensification and low investment the process stability of these micro structured devices is a required criterion for industrial applications. Micro structured devices are very sensitive to unwanted deposition such as crystallization of inverse soluble salts on the surface (fouling). In general, fouling results in (i) an increase of the pressure drop, (ii) a decrease of the heat exchanger performance, (iii) a maldistribution of the flow in the micro structures and (iv) a change of the residence time behavior. This paper presents investigations about the impact of crystallization fouling on the heat transfer performance of a micro heat exchanger. Fouling experiments with calcium carbonate (CaCO3) were analyzed regarding thermal and fluid dynamic behavior. The observed fouling developed heterogeneously from a supersaturated solution in micro channels and caused a decrease of the heat transfer performance and a strong increase of the pressure drop. The extracted fouling resistances Rf were in the range of 10−5–10−3m2KW−1. In general, the fouling behavior in microscale is comparable to that in macroscale.