Spiral Microreactor Research Articles

A continuous polymerase chain reaction 3D spiral microreactor capable of facile and on-demand fabrication

A continuous polymerase chain reaction 3D spiral microreactor capable of facile and on-demand fabrication

Microfluidic production of silica nanofluids for highly efficient two-phase cooling with micro pin-fins structure

Flow boiling heat transfer in microchannels is fundamentally important for the thermal management of high-power electronics. The combination of silica nanofluids and micro pin-fins structure is expected to solve the limitations of the internal trade-off between the heat transfer coefficient (HTC) and critical heat flux (CHF). However, the high cost, preparation complexity, poor stability, and particle agglomeration limit the further development of silica nanofluids. Herein, we present a simple and straightforward microfluidic strategy for continuous, ultrafast, and high-throughput synthesis of functional silica nanofluids with excellent stability. Numerical simulation and experimental validation are conducted to investigate the excellent mixing performance of spiral microreactor. The morphology and size of SiO2 can be precisely controlled by simple flow rate. The excellent stability of time (∼30 d) and temperature (∼80 ℃) significantly improved the problem of easy aggregation of nanofluid particles previously used for heat transfer. The flow boiling heat transfer in microchannels on micro pin-fins silicon chip demonstrates the simultaneous enhancement of CHF (124%) and HTC (153%) at extremely low power consumption (pressure drop less than 1.5 kPa) compared to the base fluid. These findings provide important guidelines for the embedded cooling and shed new light on significant energy savings on electronics.

A compact heat recirculating spiral geometry for thermal integration for Sabatier reaction in microreactor

Sabatier reaction, the catalytic reduction of CO2 to methane, is a reversible and exothermic reaction that produces CO as a by-product. We use two-dimensional computational fluid dynamics (CFD) simulations to analyze the performance of a three-turn spiral microreactor, useful for portable or modular applications. Spiral reactor has inlet at the center followed by three turns that spirals outwards. It allows thermal integration via co-current self-coupling of Sabatier reaction, which enables utilizing the exothermic heat of methanation for preheating of the cold reactants by hot products. Due to compact nature of the geometry, heat released spreads out in the reactor causing an overall moderation of temperature. A favorable cooling effect is achieved in spiral geometry without using external cooling or feed dilution, merely by the property of reactor configuration. For the base case, 71% conversion with 92.6% selectivity to CH4 is attained. Comparison with counter-current operating strategy in U-bend reactor is presented.

Performance of continuous-flow micro-reactors with curved geometries. Experimental and numerical analysis

One of the major challenges in the design of micro-devices, when very fast reactions are carried out, is to overcome the limited performance due to the poor mixing efficiency of the reactants. Here, we report a holistic analysis of reactants mixing and reaction rate in liquid phase flow micro-reactors with curved geometries. In this sense, a mathematical model that accounts for momentum and mass conservation equations, together with species transport and chemical reaction rate under isothermal conditions, has been developed using computational fluid dynamics techniques (CFD). To validate the predictive model, four micro-reactor geometries with different radius and curved length (straight reactor, two types of serpentines and an Archimedean spiral) have been evaluated. Simulated results proved that mixing is promoted through the formation of Dean vortices as a consequence of the reduction of the radius of curvature and at the same time of the extension of the curve. Thus, the overall performance of the micro-reactor is improved because mass transport limitations are minimized and the process kinetics are greatly enhanced. Accordingly, the spiral micro-reactor reported the best performance by reducing by half the time required to obtain 95 % conversion when compared with the straight reactor. Simulated findings have been confirmed with the experimental analysis of the reaction between aqueous ammonium and hypochlorite ions. Very good agreement between simulated and experimental results has been achieved with an error lower than 10 %. Therefore, the robust model herein reported is a novel and valuable tool to assist in the optimum design of micro-reactors for fluid-phase isothermal applications.

A New Self-Activated Micropumping Mechanism Capable of Continuous-Flow and Real-Time PCR Amplification Inside 3D Spiral Microreactor.

A self-activated micropump which is capable of stable velocity transport for a liquid to flow a given distance inside a 3D microchannel has been a dream of microfluidic scientists for a long time. A new self-activated pumping mechanism has been proposed in this paper. It is different from the authors’ previous research which relied on the fluid resistance of a quartz capillary tube or end-blocked gas-permeable silicone or a polydimethylsiloxane (PDMS) wall to automate the flow. In this research, an end-open stretched Teflon tube was utilized for passive transport for the first time. A new fluid transmission mode was adopted with the assistance of a cheaper easily accessible oil mixture to achieve stable continuous flow. Finally, this novel micropump has been applied to real-time continuous-flow polymerase chain reactions (PCRs), with an amplification efficiency similar to that of a commercial PCR cycler instrument.

Hydrodynamic, Mass Transfer and RTD Studies of Fluid Flow in a Spiral Microreactor

In this article, the spiral microreactor made of copper tube with U-junction, mixing region, was used to study the reactor performance on sodium hydroxide-n-butyl acetate system. The internal diameter of microreactor is 1.5 mm and length is 2 m. The performance of spiral microreactor was studied considering hydrodynamic flow, mass transfer characteristics, RTD and computational analysis of fluid flow using n-butyl acetate and sodium hydroxide system. Pressure drop was estimated in spiral geometry using dean number and compared with simulation results for laminar flow. The volumetric mass transfer coefficient obtained was in the range of 0.02–0.37 s−1. The dispersion number calculated from the RTD study was equal to 0.0526 indicating the plug flow conditions.

A 3D CFD study of homogeneous-catalytic combustion of hydrogen in a spiral microreactor

A spiral microreactor is analyzed for combustion of hydrogen on Pt catalyst using 3D computational fluid dynamics (CFD) simulations with detailed mechanisms for both catalytic and gas phase reactions. A spiral microreactor comprises of a single channel that is curled-up in a spiral, starting at the center and spiraling outwards. A comparison of the spiral with a conventional straight-channel reactor is presented. Maximum temperature attained in the spiral microreactor, investigated for equivalence ratios within the range of 0.3 to 0.65 under non-adiabatic conditions (with heat losses by convection and radiation), is found to be greater than the adiabatic flame temperatures. Comparison with a straight-channel reactor of equivalent dimensions shows higher temperature and higher contribution of homogeneous chemistry in the spiral microreactor. The nature of homogeneous reactions in the presence of catalytic micro reactor is presented. Combustion characteristics presented herein indicate that the preheating of reactants and protection of reaction zone in the spiral reactor make it superior to the straight channel reactor. The effect of inlet velocity is presented and the effect of heat recirculation on homo-catalytic interactions is analyzed.

A PCR microreactor machinery with passive micropump and battery-powered heater for thermo-cycled amplifications of clinical-level and multiplexed DNA targets.

A self-contained polymerase chain reaction (PCR) platform with miniaturized power-system is introduced. Itis powered by portable lithium batteries and integrated continuous-flow PCR amplification platform. Generally speaking, traditional commercial thermal cyclers rely on external electric supply and thus they are too big in instrument size. This prevents real-timely and field testing during PCR diagnosis. The authors are introducing a continuous-flow 3D spiral microreactor for DNA amplifications and high-resolution multiplexed targets' detection by utilizing the polyvinyl chloride (PVC) tubing-polymer to fabricate the microreactor for the first time. The whole setup (that can all be placed in one hand) includes (a) the thermo-cycled control (5.5cm width, 10cm length and 11cm height), (b) the passive continuous-flow control, and (c) the trapezoidal PCR microreactor. The PCR platform can work for 4.5h continuously. With minimal accessories and operations, the total cost of the self-contained PCR machinery is <20 $, much lower than the mainstream of commercial PCR machinery. By waiving external electric supply, this miniaturized PCR platform is applied to amplify the typical DNA fragments of plasma isolated hepatitis B virus (HBV), influenza virus (H7N9avian influenza) bacterium (Escherichia coli) plasmid and multiplexed targets. The efficiency of the method is 70% of that of commercial thermal cycler (CFX Connect, Bio Rad). The DNA of H7N9avian influenza can be detected in concentrations as low as 103 copies per μL. Graphical abstract By utilizing the polyvinyl chloride (PVC) tubing-polymer to fabricate the microchip for the first time, this paper introduces a 3D spiral microreactor with a miniaturized power-system supplied by portable AA-batteries, applied in DNA amplifications and high-resolution multiplexed targets' detection. In this microdevice, we made the machinery portable by waiving the external plugs, which solved the problem of traditional commercial thermal cyclers about large volume and expensive price.

Synthesis of anatase nanoparticles in a spiral microreactor

Herein, we report on an efficient strategy to synthesize anatase nanoparticles in a spiral microreactor. The synthesized nanopowders were characterized by X-ray diffraction and high resolution transmission electron microscopy. L25(56) orthogonal experiments were performed in order to assess the effect of each factor on the particle size of anatase nanopowders. Finally, the residence time R value was 50.734, which was much larger than R values for other factors, highlighting residence time as the key factor determining anatase nanoparticle size.

A spiral microreactor for improved stability and performance for catalytic combustion of propane

Numerical CFD simulations are used to demonstrate the performance characteristics of a novel spiral geometry, which is used for catalytic micro-combustion in this work. This reactor has catalytic channel, with inlet at the center and spiraling outwards. The spiral microreactor geometry allows preheating of the cold inlet owing to heat exchange with the hot products flowing in co-current direction in the adjacent channel. Results indicate that the spiral is more stable than the straight channel reactor, due to the transverse heat transfer between adjacent channels in the spiral reactor. 2D simulations are performed to comprehensively analyze the role of this heat recirculation on the thermal management and stability of catalytic combustion of propane/air mixtures; and the spiral microreactor is compared with the well-studied straight channel microreactor. Axial and transverse temperature profiles at various design and operating conditions are analyzed for a better understanding of heat recirculation in this geometry. Effect of various parameters viz. equivalence ratio (ϕ), inlet velocity (u0), wall thermal conductivity (ks) and number of turns (N) on the spiral reactor’s stability and performance is presented.

Synthesis of iron oxide nanoparticles in a continuous flow spiral microreactor and Corning® advanced flow™ reactor

AbstractIn the present work, synthesis of iron oxide nanoparticles (NPs) using continuous flow microreactor (MR) and advanced flow™ reactor (AFR™) has been investigated with evaluation of the efficacy of the two types of MRs. Effect of the different operating parameters on the characteristics of the obtained NPs has also been investigated. The synthesis of iron oxide NPs was based on the co-precipitation and reduction reactions using iron (III) nitrate precursor and sodium hydroxide as reducing agents. The iron oxide NPs were characterized using transmission electron microscopy (TEM), Fourier transform infrared spectroscopy, and X-ray diffraction (XRD) analysis. The mean particle size of the obtained NPs was less than 10 nm at all flow rates (over the range of 20−60 ml/h) in the case of spiral MR, while, in the case of AFR™, the particle size of NPs was below 20 nm with no specific trend observed with the operating flow rates. The XRD and TEM analyses of iron oxide NPs confirmed the crystalline nature and nanometer size range, respectively. Further, magnetic properties of the synthesized iron oxide NPs were studied using electron spin resonance spectroscopy; the resonance absorption peak shows theg-factor values as 2.055 and 2.034 corresponding to the magnetic fields of 319.28 and 322.59 mT for MR and AFR™, respectively.

Scale-Up Investigation of the Continuous Phase-Transfer-Catalyzed Hypochlorite Oxidation of Alcohols and Aldehydes

The use of bleach to oxidize alcohols with the aid of a phase-transfer catalyst (PTC) offers several benefits over traditional oxidants: low material cost, mild reaction conditions, and no metallic waste. Mass transport limitations often dictate overall reaction rates of such PTC reactions, and continuous-flow reactors with superior mass and heat transport performance are consequently used to enhance their rates. Three PTC hypochlorite oxidation reactions are chosen to illustrate scaling of PTC reactions from microfluidic to mesoscale systems [Corning Low Flow Reactor (LFR) and Advanced Flow Reactor (AFR)]. The successful scaling from microliters per hour in microreactors to intermediate milliliters per minute without sacrificing mass transport performance leads to significant increases in production rate and constitutes an efficient flow reactor scaling approach. The production rate increases up to 700 times in the scaling process from a spiral microreactor to the LFR and then to the AFR.

A hybrid microreactor/microwave high-pressure flow system of a novel concept design and its application to the synthesis of silver nanoparticles

This article reports on a microreactor/microwave high-pressure flow hybrid apparatus of a novel concept design, which includes both the microreactor and a spiral reactor, and its efficient use in the synthesis of silver nanoparticles of relatively uniform sizes (4.3±0.7nm) under microwave irradiation. By contrast, under otherwise identical experimental conditions but with conventional heating, the nanoparticle size was non-uniform (8.3±2.7nm) and the spiral reactor walls were covered with a silver mirror deposit. Formation of the nanoparticles was monitored by UV–visible spectroscopy (plasmonic absorption band; LSPR), TEM and by small-angle X-ray scattering (SAXS). Both the spiral microreactor and the spiral quartz reactor of the hybrid system played an important role in the synthesis, with the microreactor providing the environment wherein mixing of the aqueous solution of [Ag(NH3)2]+ and the solution of glucose (the reducing agent) and poly(N-vinyl-2-pyrrolidone) (PVP; stabilizer/dispersing agent) occurred. The microwaves provided the thermal energy to effect a uniform growth of the silver nanoparticles at temperatures above 120°C. Mixing the two solutions by conventional methods (no microreactor) failed to yield such nanoparticles even under microwave irradiation and no formation of a silver mirror occurred in the inner walls of the spiral reactor.

Segmented flow synthesis of Ag nanoparticles in spiral microreactor: Role of continuous and dispersed phase

This work focuses on understanding the effect of segmented flow on the nanoparticle size distribution in a unidirectionally expanding spiral microreactor, where secondary flows are prevalent in the absence of segmentation. Stearic acid sophorolipid reduced/capped Ag NPs were synthesized in the aqueous phase and air or kerosene was used as inert phases for creating the gas–liquid and liquid–liquid segmented flow, respectively. While, in one case the reactant phase is in the form of dispersed phase slugs, in the other case it is in the form of continuous phase, each exhibiting a different behavior. The slug sizes and the slip velocity, both of which govern the nature of internal mixing in the reactant phase slug controlled the nanoparticle size distribution. This observation was consistent for both, gas–liquid and liquid–liquid segmented flows. The micromixer having smaller orifice diameter yielded smaller slugs and also a narrow particle size distribution. In general, the particle sizes were much smaller for gas–liquid flow rather than for liquid–liquid flow. Because of the unidirectionally expanding spiral geometry of the channel, at any given condition, unsteady behavior of slugs due to continuously varying radius of curvature results in variation in the slip velocity along the length of microchannel. This effect was seen to further narrow the particle size distribution than alone by the segmented flow.