Helical Microchannel Research Articles

Direct esterification in helical continuous-flow microreactors under an aqueous environment: optimization, reaction kinetics, and process intensification

This study presents an optimized process for producing long-chain alkyl acrylates via direct esterification in a helical continuous-flow microreactor. Addressing the inefficiencies of traditional batch esterification, such as low energy efficiency and slow mass transfer, this method utilizes continuous-flow chemistry for more effective, eco-friendly, and cost-efficient production. The microreactor, with a 10 m long and 0.5 mm diameter helical microchannel, which active volume was 3.925 ml, was examined for its performance influenced by reactant-catalyst ratios, temperature, and residence time. Results show significantly improved yields of myristyl acrylate (over 89 % in 300 s, respectively) while the residence time was 300 s at 110 ± 10 °C, with a molar ratio of 1-tetradecanol to acrylic acid of 1.3 and a catalyst to acrylic acid molar ratio of 0.1. Additionally, a second-order reaction kinetic model was developed to better understand the reaction dynamics in this setup. This research underscores the potential of integrating helical continuous flow with esterification, offering a novel approach to studying these mechanisms.

The effect of initial temperature and oxygen ratio on air-methane catalytic combustion in a helical microchannel using molecular dynamics approach

In industrial environments where combustion (Com.) is widely carried out, such as steam power plants, gas turbines, etc., the most common way to express the amount of oxygen consumption is its excess percentage in addition to the stoichiometric ratio, and the nearness of a catalyst causes combustion to happen at a high ratio. There are different influential factors in catalytic combustion, such as initial temperature (IT). The current study uses the molecular dynamics (MD) method to examine how the IT and oxygen ratio affect air-methane catalytic combustion in a helical microchannel. The LAMMPS package was used to conduct this investigation. This study examines how simulated structures function during burning in excess oxygen (EO) and oxygen deficiency (OD). Furthermore, palladium was used as a catalyst with an atomic ratio of 4 %. The findings show that raising the IT may enhance its atomic behavior (AB) and thermal performance (TP). The maximum velocity (MV) and maximum temperature (MT) increased from 0.26 Å/ps and 1617 K to 0.45 Å/ps and 1891 K in EO as IT increased from 300 to 700 K. By accelerating the particle velocity, it is anticipated that the catalytic combustion process would proceed more quickly. As a result, after increasing the IT to 700 K, the heat flux (HF), thermal conductivity (TC), and combustion efficiency (CE) increase to 2101 W/m2, 1.23 W/m. K, and 93 %, respectively. On the other hand, the results show that increasing IT affects combustion performance in the presence of OD. In the presence of OD, the MV and CE converge to 0.38 Å/ps and 94 % at 700 K. Therefore. It can be concluded that the atomic ratio of oxygen and the IT can significantly affect combustion process.

Numerical Study for Separation of Particles in Helical Microchannel

Numerical Study for Separation of Particles in Helical Microchannel

Simulation based investigation of Nusselt number and Poiseuille number in helical microchannels

Simulation based work carried out in order to understand the thermohydraulic characteristics of fluid flow in helical microchannel, with circular cross-section, that is subjected to constant heat flux is detailed in this work. Water is used as the fluid in this study and the study is carried out for Reynolds number ranging from 50 to 500. The helical path of the fluid increases the heat transfer coefficient and pressure drop for a specific Reynolds number in comparison with that in a straight microchannel. The increase in heat transfer coefficient and pressure drop associated with the helical microchannel manifests as increased Nusselt number and Poiseuille number. At Reynolds number of 50, the Nusselt number of the helical microchannel is 1.36 times higher than that of the straight microchannel while at Reynolds number of 500, this enhancement increases to 2.33. Regarding Poiseuille number of helical microchannel, it is higher than that of the Poiseuille number of straight microchannel by 1.02 and 1.72 at Reynolds number of 50 and 500, respectively. It is identified from this study that by shifting from straight microchannel to helical microchannel, the enhancement in Nusselt number is higher than the associated penalty, i.e. increase in Poiseuille number.

Computational study of palladium percentage and oxygen ratio effects on air-methane catalytic combustion in a helical microchannel: A molecular dynamics approach

Combustion is an exothermic chemical process between an explosive substance and an oxidizing agent that is accompanied by heat generation and chemical change of raw materials. Catalysts are used in a combustion process for various reasons, including the speed at which the material reaches equilibrium. Catalysts are chemicals that increase the rate of reaction in chemical processes. The present research investigates the influence of palladium percentage and oxygen ratio on air-methane catalytic combustion in a helical microchannel. For this purpose, the atomic behavior and combustion performance of the simulated sample in the presence of excess oxygen and oxygen deficiency is reported by the molecular dynamics (MD) method. The potential functions used in this paper were Lennard-Jones, the embedded atom model (EAM), and Coulomb. It is concluded that increasing palladium percentage in limited ratios improves the atomic and combustion performance of the simulated structure, and this enhancement is greater in the presence of excess oxygen. In the presence of excess oxygen, the numerical value of maximum density, velocity and temperature converged from 0.138 atom/Å3, 0.33 Å/ps and 523 K to 0.144 atom/Å3, 0.36 Å/ps and 539 K, respectively with increasing palladium percentage from 1 % to 4 %. And by increasing the palladium ratio to 10 %, these numerical values decrease to 0.137 atom/Å3, 0.31 Å/ps and 530 K. Moreover, in the presence of oxygen deficiency, heat flux, thermal conductivity, and combustion efficiency of atomic samples reached 2049 W/m2, 1.23 W/m.K and 90 % after rising palladium to 4 %, and it decreased to 2035 W/m2, 1.19 W/m.K and 86 % by adding 10 % palladium. Therefore, the results indicate that the oxygen and the catalyst (palladium) ratios can benefit the combustion process. These results can optimize the atomic performance and combustion performance of structures essential for use in various industries.

A novel helical descending liquid‐bridge for continuous demulsification

AbstractExisting physical demulsification methods are expensive and offer low separation efficiencies. Therefore, the development of efficient and green continuous demulsification processes has garnered research attention. Inspired by the novel helical liquid bridge flow realized previously by our group, a continuous demulsification method featuring a helically descending liquid bridge was established in this study to treat oil‐in‐water emulsions with low oil contents. First, the formation of the liquid bridge flow was verified. Then, the continuous demulsification of the helically descending liquid bridge was monitored using a high‐speed camera, which helped elucidate the demulsification mechanism. Furthermore, the surface of the helical string was modified to make it oleophilic for improving the demulsification efficiency. The results showed that the helical liquid descent achieved with surface modification led to a competitive separation efficiency of up to 52.94%, which was 27.94% higher than that of other helical microchannel devices with hydrophobic surfaces.

Hydrodynamics of liquid-liquid two-phase flow accounting for the coupling of dean vortices and Poiseuille flow

Hydrodynamics of liquid–liquid (L-L) two-phase flow in a confined helical microchannel are investigated via a VOF-CSF model, and further the influences of continuous phase flowrate, interfacial tension, viscosity ratio, helical screw pitch, helical radius as well as the diameter ratio of droplet to channel were systematically ascertained. To achieve the precise control over the interface deformation in a confined helical microchannel, the correlation equations with several key dimensionless numbers are established to predict the droplet aspect ratio, eccentricity and the minimum liquid film thickness. Especially, the minimum film thickness can be used to distinguish the flow field structures, and when the dimensionless outer minimum liquid film thickness (δ*out) is greater than 0.16, there is only one complete vortex system structure inside the droplet. Otherwise, two vortices are observed. Besides, the Q-criterion is used to quantitatively confirm the disappearance of vortices inside the droplet. Finally, the force field characteristics are also discussed to reveal the corresponding droplet interface deformation mechanisms, and it is found that, the droplet is driven forward by the differential pressure force, and deformed by the shear force along its flow direction. Both of the Dean force and Coriolis force usually control the interface deformation of droplet in the radial direction. The results in our study offer valuable guidance for designing the L-L two-phase flow microsystems to realize the goal of process intensification.

Numerical assessment of the multi-phase nanofluid flow inside a microchannel during the melting and solidification of PCM in the thermal management of a heatsink

This article presents a numerical simulation of a heatsink with a large number of square pin-fins using the finite element method. A nanofluid passes helical microchannel that is placed inside the heatsink. The two-phase mixture method is employed to simulate the nanofluid flow. The space between the pin-fins and the microchannel in the heatsink is filled with phase change material (PCM). The values ​​of the heatsink temperature (T-HK), including the maximum and average temperature, the temperature of the nanofluid (T-NF) exiting the heatsink, the molten PCM fraction, and the heat transfer coefficient (HTC) are estimated by changing the Reynolds number (Re) ranging from 100 to 500 and the volume fraction of nanoparticles (φ) varying from 0 to 3% up to 500 s. The results demonstrate that an increment in the Re reduces the T-NF exiting the heatsink significantly; however, enhancing the amount of φ decreases it slightly. In 500 s and 250 s, an enhancement in the Re from 100 to 500 intensifies the maximum T-HK by 17.28 and 9.92 °C, respectively. At Re = 100, 200, and 300, the PCM melting process starts in approximately 150, 200, and 250 s, respectively.

Minimum Quantity Lubrication (MQL) multiphase dynamics of a vibration-assisted drilling process

Metalworking fluid (MWF) consumption in machining processes can be minimised using minimum quantity lubrication (MQL). In the vibration-assisted drilling process, the MWF is transported as aerosol (dispersed droplets in gas) to the cutting zone through microchannels inside the drilling tool. Numerical simulations have been applied to elucidate the multiphase flow dynamics of the MWF inside a helical microchannel of a twist drilling tool. Numerical results indicate a transition from the inserted MQL aerosol flow and a wall film already after the first helical bend of the microchannel. The wall film contains > 90 % of the lubricant and is strongly localised on only 10 % of the microchannel circumference at the tool tip. This MQL-flow behaviour has to be considered in future investigations of the processes at the borehole ground, where even more complex phenomena occur.

Effect of a palladium catalyst and initial pressure on methane-air catalytic combustion process in a helical coil microchannel: A molecular dynamics approach

Catalytic combustion is a flame-free process which occurs at low temperatures and reduces less release of nitric oxide (NOx). Although catalysts help reduce the release of toxic gases, they have detrimental environmental effects. Therefore, by simulation these reactions, a constraint on the flammability limits and improving their performance can be achieved. In this research, using the molecular dynamics (MD) simulation, the catalytic combustion process of air-methane was studied in a helical microchannel. Palladium (Pd) was used as the catalyst. The results show that adding a Pd catalyst further improved the simulated structure's thermal performance(TP). The heat flux(HF) and thermal conductivity (TC) of atomic samples increased from 2067 W/m2 and 1.28 W/m.K to 2096 W/m2 and 1.45 W/m.K with an increase in atomic ratio Pd catalyst from 1 to 4%. Finally, the combustion efficiency (CE) converges to 93% in the presence of 4% Pd catalysts. By increasing the initial pressure (IP) from 0 to 10 bar, the maximum density did not change much, and the velocity and temperature values decrease in terms of the limitation in atomic oscillations. Increasing the IP reduces the HF and TC from 2096 W/m2 and 1.45 W/m.K to 1981 W/m2 and 1.19 W/m.K. Regarding different types of combustion processes, such as catalytic combustion, were considered in different types of industrial applications, it is expected to study the effect of the parameters of the atomic ratio of Pd catalyst and the IP, propose an optimal mechanism to create catalytic combustion in real and practical samples.

Experimental study of a nanofluid-based photovoltaic/thermal collector equipped with a grooved helical microchannel heat sink

• Energetic and exergetic performances of a nanofluid-based PVT unit are assessed. • The unit is equipped with a grooved helical microchannel heat sink. • Aqueous suspension of magnetite nanoparticles is considered as coolant. • The Staggered PVT unit performs better that the parallel and plain PVT units. • Energetic and exergetic performance of units intensify with boosting Φ nf and M nf . Helical geometry is widely used in heat transfer systems due to the high heat transfer surface and the creation of swirling flow. Grooving the spiral channel can lead to the strengthening of these effects and improve the channel performance. In the present study, the energy and exergy performance of a nanofluid-based photovoltaic thermal unit equipped with a grooved helical microchannel heat sink is investigated experimentally. For this purpose, a plain helical microchannel heat sink, a parallel grooved helical microchannel heat sink and a staggered grooved helical microchannel heat sink are designed and fabricated. The employed nanofluid is the aqueous suspension of Fe 3 O 4 nanoadditives. The experiments were performed at different values of flow rates (20–80 kg/h) and nanoadditive concentrations (0.0–2.0 %). The highest thermal energy/exergy, electrical energy, and their corresponding efficiencies have been recorded at the mass flow rate of 80 kg/h and nanoadditive concentration of 2.0 %. It is seen that the overall energy efficiency of the staggered unit is 17.05 % and it is 6.96 % higher than the plain and parallel unit. Further, the staggered unit demonstrated the highest exergy efficiency (14.67 %) compared to other studied photovoltaic/thermal units.

Co-axial printing of convoluted proximal tubule for kidney disease modeling

Despite the increasing incidence of kidney-related diseases, we are still far from understanding the underlying mechanisms of these diseases and their progression. This lack of understanding is partly because of a poor replication of the diseases in vitro, limited to planar culture. Advancing towards three-dimensional models, hereby we propose coaxial printing to obtain microfibers containing a helical hollow microchannel. These recapitulate the architecture of the proximal tubule (PT), an important nephron segment often affected in kidney disorders. A stable gelatin/alginate-based ink was formulated to allow printability while maintaining structural properties. Fine-tuning of the composition, printing temperature and extrusion rate allowed for optimal ink viscosity that led to coiling of the microfiber’s inner channel. The printed microfibers exhibited prolonged structural stability (42 days) and cytocompatibility in culture. Healthy conditionally immortalized PT epithelial cells and a knockout cell model for cystinosis (CTNS -/-) were seeded to mimic two genotypes of PT. Upon culturing for 14 days, engineered PT showed homogenous cytoskeleton organization as indicated by staining for filamentous actin, barrier-formation and polarization with apical marker α-tubulin and basolateral marker Na+/K+-ATPase. Cell viability was slightly decreased upon prolonged culturing for 14 days, which was more pronounced in CTNS -/- microfibers. Finally, CTNS -/- cells showed reduced apical transport activity in the microfibers compared to healthy PT epithelial cells when looking at breast cancer resistance protein and multidrug resistance-associated protein 4. Engineered PT incorporated in a custom-designed microfluidic chip allowed to assess leak-tightness of the epithelium, which appeared less tight in CTNS -/- PT compared to healthy PT, in agreement with its in vivo phenotype. While we are still on the verge of patient-oriented medicine, this system holds great promise for further research in establishing advanced in vitro disease models.

Effect of using a heatsink with nanofluid flow and phase change material on thermal management of plate lithium-ion battery

The thermal management of a lithium-ion battery employing a heatsink is evaluated in this study.The heatsink employs nanofluids (NFs) and phase change material (PCM) and has a revolutionary shape. The NFs flows through a helical microchannel (MCH) into the heatsink. A number of pin-fins with a spiral arrangement are used in the heatsink. The MCHs are filled with nano-PCM containing graphene nanoparticles. This study is performed in a time interval of 0 to 500 s at the Reynolds number (Re) range of 100 to 500. NFs outlet temperature (T-O), maximum (T-M) and average temperature (T-A) of PCM, heat transfer coefficient (HTC) and amount of molten PCM at different times, and different Re are estimated. COMSOL Multiphysics software is employed to do the simulations. The results demonstrate that the amount of molten PCM is enhanced except for Re = 500 until all the PCM inside the heatsink is melted. At Re ≥ 500, the PCM melting process does not occur within the heatsink and the PCM remains solid. The output temperature of NFs and PCM temperature are intensified with time. An increment in the Re reduces the amount of NFs temperature at the outlet as well as the T-A and T-M of PCM inside the heatsink. The amount of HTC between PCM and NFs depends on Re and increases over time.

Two-phase mixture simulation of the performance of a grooved helical microchannel heat sink filled with biologically prepared water-silver nanofluid: Hydrothermal characteristics and irreversibility behavior

• A novel heatsink with grooved helical microchannels is suggested. • Biologically synthesized water-Ag nanofluid is considered as the working fluid. • First and second law analysis of nanofluid flow inside the heatsink are evaluated. • Heatsink with staggered grooved helical channels has best first-law performance. • Grooving the helical channel entails an increment in the entropy generation. The present paper investigates the influence of using two grooved channel geometries on the hydrothermal performance of a helical microchannel heat sink. The results were compared with those obtained for the plain channel geometry. Based on the results, the highest flow mixing is observed for the staggered grooved configuration. Moreover, the convective heat transfer coefficient enhances by nearly 70% and 17% for the MCHS with the staggered and parallel grooved channels, respectively, as compared to that with the plain channel. The influence of Reynolds number ( Re ) escalation on the convective heat transfer coefficient is insignificant, while a 21% increase is obtained when NF concentration is increased from 0% to 1%. Furthermore, the increase of φ in the grooved configurations is more effective than that in the plain configuration. In addition, the lowest thermal resistance and temperature uniformity factors were obtained for the staggered grooved configuration. Besides, the parallel grooved configuration represents the highest frictional entropy generation rates among the three studied geometries due to the considerable reduction of the fluid flow cross-section area between the groove ribs. The highest heat transfer coefficient and pressure drop are associated with the staggered grooved configuration. For the plain, parallel grooved, and staggered grooved configurations, the increase of Re from 500 to 2000 escalates the NF pressure drop by 2730%, 4420%, and 4460%, respectively. Therefore, the highest performance evaluation criterion of more than unity was obtained for the MCHS with the staggered grooved channels for the studied range of Re (500–2000). The numerical analysis was also performed to evaluate the influence of groove pitch on the hydrothermal performance of the staggered groove channel for the pitch range of 0.15 mm to 0.75 mm. The results demonstrated that the highest PEC is associated with the groove pitch of 0.75 mm.

Study of Microchannels Fabricated Using Desktop Fused Deposition Modeling Systems.

Microfluidic devices are used to transfer small quantities of liquid through micro-scale channels. Conventionally, these devices are fabricated using techniques such as soft-lithography, paper microfluidics, micromachining, injection moulding, etc. The advancement in modern additive manufacturing methods is making three dimensional printing (3DP) a promising platform for the fabrication of microfluidic devices. Particularly, the availability of low-cost desktop 3D printers can produce inexpensive microfluidic devices in fast turnaround times. In this paper, we explore fused deposition modelling (FDM) to print non-transparent and closed internal micro features of in-plane microchannels (i.e., linear, curved and spiral channel profiles) and varying cross-section microchannels in the build direction (i.e., helical microchannel). The study provides a comparison of the minimum possible diameter size, the maximum possible fluid flow-rate without leakage, and absorption through the straight, curved, spiral and helical microchannels along with the printing accuracy of the FDM process for two low-cost desktop printers. Moreover, we highlight the geometry dependent printing issues of microchannels, pressure developed in the microchannels for complex geometry and establish that the profiles in which flowrate generates 4000 Pa are susceptible to leakages when no pre or post processing in the FDM printed parts is employed.

Analysis of mixing in a helical microchannel

Examining fluid flow inside a monolithic, three-dimensionally oriented, microfluidic channel is experimentally challenging because it does not permit a laser sheet to be effectively applied; tracking microscopic tracer particles is difficult; and monolithic construction prevents access to any material inside. We overcome these problems with an approach which captures the flow both along the channel axis and in a plane perpendicular to it, yet lets us capture the flow pattern over a wide Reynolds number range. Our observations corroborate results from flow simulations.

Liquid‐liquid two‐phase flow patterns in a new helical microchannel device

Flow patterns of liquid‐liquid two‐phase fluids in a new helical microchannel device were presented in this paper. Three conventional systems were considered: kerosene‐water, n‐butyl acetate‐water, and butanol‐water. Six different flow patterns, slug flow, continuous parallel flow, discontinuous deformation parallel flow, discontinuous deformation parallel‐droplet flow, droplet‐slug flow, and filiform‐droplet flow, were observed. The influence of interfacial tension, microchannel structure, and rotation rate on two‐phase flow patterns were studied, and a universal flow pattern map was presented and discussed. The systems without mass transfer (0.1 g/g (10 %) tri‐n‐butyl phosphate (TBP)‐water, 0.2 g/g (20 %) TBP‐water, and 0.8 g/g (80 %) TBP‐water) and the system with mass transfer (0.8 g/g (80 %) TBP‐0.62 g/g (62 %) H3PO4) were used to verify the validity of the proposed universal flow pattern map in predicting flow patterns. The results showed that the former compared with the latter can be predicted more accurately by the universal flow pattern map.

Liquid–liquid two-phase mass transfer characteristics in a rotating helical microchannel

Abstract In this work, the mass transfer characteristics of two immiscible fluids were investigated in a rotating helical microchannel with hydraulic diameter of 932 μm. Aqueous phosphoric acid solution and 80% tri-n-butyl phosphate (TBP) in kerosene were selected for the investigation of mass transfer performance in quartz glass/high density polyethylene (HDPE) microchannel. High dispersion between the two immiscible fluids can be obtained in the microchannel due to the intensifying action of centrifugal force, and the majority of the droplets with average diameter of 20–100 μm were produced in the microchannel. The flow rate and rotation speed were found to have great effects on the extraction efficiency and average residence time. The empirical correlation of average residence time based on experimental data was developed by theoretical analysis and data fitting method, and a mathematical model of the mass transfer coefficient in dispersed phase was proposed.

Three-dimensional multiphase CFD modeling of thermal–hydraulic characteristics of nanofluid flow in helical microchannels

Forced convection heat transfer of two different types of water-based nanofluids (Al2O3, TiO2) was investigated numerically. In this numerical investigation, mixture two-phase model was considered and the governing equations were discretized based on the finite element method. The developed model agrees well with the experimental data for the two straight and helical microchannel tubes. The presented model covers the helical microchannel with different axial pitches and curvature ratios. The obtained results showed that geometrical parameters (curvature ratio and axial pitch) with a combination of nanofluid types and concentration have impressive effects on thermal performance and pressure drop. The results revealed that the Nu number was about 14% higher compared to pure water for the helical-containing Al2O3 nanofluids. Moreover, addition of both nanoparticles had negligible effect on friction factor in helical microchannel. The optimum operating conditions which are most economical from an industrial point of view were evaluated using the effectiveness parameter (η).

Flow through triple helical microchannel

Flow analysis in triple-helical micro-channels via \textmu{}-PIV experiments and 3D simulations show generation of strong secondary flow at the channel cross-section. Such flow is expected to significantly enhance mixing between liquids in the laminar regime useful for a host of microfluidic applications.