This study investigates the droplet formation for the liquid–liquid two-phase flow within a square T-junction microchannel through numerical simulation using volume of fluid method and experimental visualization usin...This study investigates the droplet formation for the liquid–liquid two-phase flow within a square T-junction microchannel through numerical simulation using volume of fluid method and experimental visualization using high-speed camera imaging.The T-junction microchannel has a cross-sectional width of 0.6 mm and a total length of 27.3 mm.The solution of cyclohexane with 2%and 3%mass concentrations of sorbitan trioleate surfactant were used as the continuous phase,and water was used as the dispersed phase.Slug flow,characteristic of squeezing regime,were predominantly observed.The effects of liquid–liquid two-phase flow rate ratio,and dimensionless number on droplet size,and pressure drop were investigated.The squeezing regime was mapped for 0.0005≤Ca_(c)≤0.0052(capillary number)and 0.1≤q≤10(flow rate ratio).The pressure drops of slugs were in the range from 40 Pa to 200 Pa.The slug lengths were measured between 1 mm and 9 mm.A universal flow map dependent on Ca_(c)Re_(d)^(0.5) are projected to investigate the droplet formation behavior in T-junction microchannel.Correlation expressions are proposed to predict pressure drops and the slug lengths for liquid–liquid two-phase flow in a square T-junction microchannel,using dimensionless numbers such as flow rate ratio and capillary number.The result shows that large continuous phase flow rates facilitate smaller slugs,whereas higher dispersed phase flow rates result in longer shorts.展开更多
Understanding and predicting droplet breakup is essential in droplet-based microfluidic systems,as it enables precise control over droplet manipulation for various applications.In this study,droplet breakup behavior i...Understanding and predicting droplet breakup is essential in droplet-based microfluidic systems,as it enables precise control over droplet manipulation for various applications.In this study,droplet breakup behavior in a T-junction microchannel is investigated under the influence of microchannel geometry using three-dimensional numerical simulations.A theoretical model is developed based on the balance between surface tension and viscous drag forces acting on the droplet,incorporating the effects of geometric parameters on droplet length.This model predicts the critical Capillary number required for breakup to occur.The theoretical predictions are validated using both previous research data and the present numerical simulations.The results show that the model accurately predicts the transition between breakup and non-breakup regimes.Specifically,an increase in sidearm length ratio inhibits droplet breakup and leads to an asymmetric breakup regime.Furthermore,increasing the outlet-to-inlet width ratio also reduces the likelihood of droplet breakup.These findings provide a predictive framework for understanding and controlling droplet dynamics in microfluidic T-junctions,with potential applications in lab-on-a-chip technologies.展开更多
The coalescence behavior of two droplets with different viscosities in the funnel-typed expansion chamber in T-junction microchannel was investigated experimentally and compared with droplet coalescence of the same vi...The coalescence behavior of two droplets with different viscosities in the funnel-typed expansion chamber in T-junction microchannel was investigated experimentally and compared with droplet coalescence of the same viscosity.Four types of coalescence regimes were observed:contact non-coalescence,squeeze non-coalescence,two-droplet coalescence and pinch-off coalescence.For droplet coalescence of different viscosities,the operating range of non-coalescence becomes narrowed compared to the droplet coalescence of same viscosity,and it shrinks with increasing viscosity ratioηof two droplets,indicating that the difference in the viscosity of two droplets is conducive to coalescence,especially when1<η<6.Furthermore,the influences of viscosity ratio and droplet size on the film drainage time(Tdr)and critical capillary number(Ca)c)were studied systematically.It was found that the film drainage time declined with the increase of average droplet size,which abided by power-law relation with the size difference and viscosity ratio of the two droplets:Tdr~(ld)^(0.25±0.04)and Tdr~(η)^(﹣0.1±0.02).For droplet coalescence of same viscosity,the relation of critical capillary number with two-phase viscosity ratio and dimensionless droplet size is Cac=0.48λ^(0.26)l^(﹣2.64),while for droplet coalescence of different viscosities,the scaling of critical capillary number with dimensionless average droplet size,dimensionless droplet size difference and viscosity ratio of two droplets is Cac=0.11η^(﹣0.07)ls^(﹣2.23)l^(0.16)_(d).展开更多
This study focuses on the effect of chemical absorption on the formation dynamic characteristics and initial length of Taylor bubbles.The temporal evolutions of neck width and length of gaseous thread and initial leng...This study focuses on the effect of chemical absorption on the formation dynamic characteristics and initial length of Taylor bubbles.The temporal evolutions of neck width and length of gaseous thread and initial length with and without chemical absorption were investigated with the Capillary number and Hatta number between 0.0010–0.0073 and 1.8–5.8 respectively.The squeezing regime with typical three stages,expansion,squeezing and pinch off is observed for both two processes.Compared with the nonabsorption process,the increase of formation time in the chemical absorption process arises mainly from the expansion stage,and the decrease of initial length is from the necking stage.In addition,the temporal length evolution satisfies the power-law scale with the same exponent but a smaller pre-exponential factor.The correlations of neck width for stage transition and initial length with Hatta number demonstrate the enhancement effect of chemical absorption on bubble formation dynamics and initial length at relatively high chemical reaction rates and long formation time.This study provides insight into the bubble formation mechanism and helps to regulate the bubble initial size with chemical absorption.展开更多
Pseudounipolar neurons in the dorsal root ganglia(DRG),as the central nodes of primary sensory afferents,possess a distinctive T-junction that is not merely a morphological peculiarity but also performs complex roles ...Pseudounipolar neurons in the dorsal root ganglia(DRG),as the central nodes of primary sensory afferents,possess a distinctive T-junction that is not merely a morphological peculiarity but also performs complex roles in rapid,multiplexed shunting and regulation of sensory signals.This specialized geometry enables separation,filtering,and feedback regulation of neuronal signals,thereby coordinating peripheral and central responses at multiple levels.Recent advances,including spatial transcriptomics,single-cell sequencing,super-resolution microscopy,organoid models,and novel electrophysiological methods,have permitted more precise dissection of the T-junction's molecular composition,ion-channel distribution,and electrophysiological properties.Here,we review current knowledge of the T-junction's developmental regulation and multilayered molecular networks,and we detail its functional alterations in both physiological signaling and pathological pain states,with particular emphasis on ion-channel modulation,signal attenuation,and selective transmission mechanisms.Finally,we discuss contemporary pain-intervention approaches and prospects for precision-targeted therapies,aiming to provide a theoretical foundation for future studies in pain physiology and clinical translation.展开更多
To efficiently remove radioactive nuclides from nuclear industry wastewater and minimize the generation of radioactive secondary waste,this study proposes the concept of a magnetically controlled microchannel adsorber...To efficiently remove radioactive nuclides from nuclear industry wastewater and minimize the generation of radioactive secondary waste,this study proposes the concept of a magnetically controlled microchannel adsorber based on magnetic adsorbents.A novel protocol for achieving high adsorption performance in microchannel adsorbers with periodically distributed particles is developed using the particle-resolved computational fluid dynamics (CFD) method,which addresses the limitations of traditional porous media flow models.To align simulation results more closely with practical scenarios,a typical high-efficiency magnetic adsorbent,magnetic sodium alginate/cobalt-based Prussian blue (M-SA/PB-Co),was synthesized.The M-SA/PB-Co microspheres exhibit a uniform size distribution (300–600 μm),and their Cs^(+) adsorption follows the pseudo-second-order kinetic model with a Langmuir saturated adsorption capacity of 124.84 mg·g^(-1).The performance parameters of M-SA/PB-Co,obtained from characterization and adsorption experiments,were integrated into CFD simulations.CFD results indicate that as the flow velocity increases,the flow field gradually transitions with vortices expanding in scale and streamline bifurcation points shifting rearward.The Cs^(+) concentration decreases progressively along the flow direction,with a more pronounced reduction in the vortex regions downstream of particles.The characteristic velocity and characteristic concentration of specific regions surrounding the particles were extracted based on boundary layer distribution.The amount of concentration reduction of Cs^(+) through particle is positively correlated with the characteristic concentration and negatively correlated with the characteristic velocity.The number of microspheres required in the microchannel adsorber was optimized using the response surface method.Compared with industrial fixed-bed adsorbers,microchannel adsorbers exhibit 8–10 times higher processing capacity,demonstrating significant industrial application potential.展开更多
The synthesis of propylene carbonate(PC)from CO_(2) and propylene oxide(PO)is a typical gas-liquid biphasic system,where gas-liquid mass transfer efficiency significantly influences CO_(2) cycloaddition reactions.Here...The synthesis of propylene carbonate(PC)from CO_(2) and propylene oxide(PO)is a typical gas-liquid biphasic system,where gas-liquid mass transfer efficiency significantly influences CO_(2) cycloaddition reactions.Here,we proposed a microchannel reaction system for the CO_(2) cycloaddition reaction catalyzed by ionic liquid within an aqueous environment.The effect of liquid flow rate,temperature and residence time on gas-liquid flow pattern,catalytic performance and mass transfer were systematically investigated.The results revealed that the PC generation rate reached 560.11 mmol·ml^(−1)·h^(−1)at a 50 cm of flow distance under reaction conditions of 105℃,2.5 MPa,QG=176 ml·min^(−1) and QL=0.3 ml·min^(−1).Variations in mass transfer rate and reaction rate at different flow distances were experimentally studied.The reaction efficiency gradually decreased with increasing flow distance,which were attributed to the reduction of mass transfer caused by decreasing bubble velocity.Optimizing bubble velocity at an appropriate position enhanced reaction efficiency by improving mass transfer,achieving a 97.7%PC yield within 2.85 min.Furthermore,a kinetic model coupling intrinsic kinetics with gas-liquid mass transfer was developed for CO_(2) cycloaddition reaction.The kinetic model was applied to predict PC reaction rates in microchannel reactors at various temperatures and liquid flow rates,achieving an average relative error of 9.6%.展开更多
Droplet-based microfluidics is a transformative technology with applications across diverse scientific and industrial domains.However,predicting the droplet size generated by individual microchannels before experiment...Droplet-based microfluidics is a transformative technology with applications across diverse scientific and industrial domains.However,predicting the droplet size generated by individual microchannels before experiments or simulations remains a significant challenge.In this study,we focus on a double T-junction microfluidic geometry and employ a hybrid modeling approach that combines machine learning with metaheuristic optimization to address this issue.Specifically,particle swarm optimization(PSO)is used to optimize the hyperparameters of a decision tree(DT)model,and its performance is compared with that of a DT optimized through grid search(GS).The hybrid models are developed to estimate the droplet diameter based on four parameters:the main width,side width,thickness,and flow rate ratio.The dataset of more than 300 cases,generated by a three-dimensional numerical model of the double T-junction,is used for training and testing.Multiple evaluation metrics confirm the predictive accuracy of the models.The results demonstrate that the proposed DT-PSO model achieves higher accuracy,with a coefficient of determination of 0.902 on the test data,while simultaneously reducing prediction time.This methodology holds the potential to minimize design iterations and accelerate the integration of microfluidic technology into the biological sciences.展开更多
Bubble breakup at T-junction microchannels is the basis for the numbering-up of gas−liquid two-phase flow in parallelized microchannels. This article presents the bubble breakup in viscous liquids at a microfluidic T-...Bubble breakup at T-junction microchannels is the basis for the numbering-up of gas−liquid two-phase flow in parallelized microchannels. This article presents the bubble breakup in viscous liquids at a microfluidic T-junction. Nitrogen is used as the gas phase, and glycerol-water mixtures with different mass concentration of glycerol as the liquid phase. The evolution of the gas−liquid interface during bubble breakup at the microfluidic T-junction is explored. The thinning of the bubble neck includes the squeezing stage and the rapid pinch-off stage. In the squeezing stage, the power law relation is found between the minimum width of the bubble neck and the time, and the values of exponents α1 and α2 are influenced by the viscous force. The values of pre-factors m_(1) and m_(2) are negatively correlated with the capillary number. In the rapid pinch-off stage, the thinning of the bubble neck is predominated by the surface tension, and the minimum width of the bubble neck can be scaled with the remaining time as power-law. The propagation of the bubble tip can be characterized by the power law between the movement distance and the time, with decreasing exponent as increased liquid viscosity.展开更多
Flow velocity uniformity of the microchannel plate is a major factor affecting the performance of microchannel devices.In order to improve the velocity distribution uniformity of the microchannel plate,we designed two...Flow velocity uniformity of the microchannel plate is a major factor affecting the performance of microchannel devices.In order to improve the velocity distribution uniformity of the microchannel plate,we designed two new microchannel structures:V-type and A-type.The effects of various structural parameters of the manifolds on the velocity distribution are reported.The V-type and A-type microchannel plates had a more uniform velocity distribution compared to the Z-type microchannel plate.The final result showed that it is beneficial for the V-type microchannel plate to obtain a more uniform velocity distribution when the manifold structure parameters are X_(in)=-1,X_(out)=0,Y_(in)=10,Y_(out)=6,Hin=4,H_(out)=1,and R=0.5.展开更多
The design and manufacturing of microchannels are crucial aspects of modern micro/nanomanufacturing processes,offering a versatile platform for manipulating and driving micro/nanoparticles or cells.In this study,we pr...The design and manufacturing of microchannels are crucial aspects of modern micro/nanomanufacturing processes,offering a versatile platform for manipulating and driving micro/nanoparticles or cells.In this study,we propose a method for manufacturing microchannels using optically induced dielectrophoresis technology to induce the polymerization of polyethylene glycol diacrylate solution.To overcome limitations related to the light intensity energy and the size of intact microchannels,we design and manufacture microstructures of various shapes with a height of 4µm.Additionally,we simulate and analyze the movement of and forces acting on polystyrene(PS)microspheres at different spatial positions within the microchannels.Finally,we successfully demonstrate applications involving the transport of PS microspheres in custom-fabricated microchannels.This novel biocompatible microchannel manufacturing method is simple and non-biotoxic.It provides a new approach for simulating physiological environments in vitro and cultivating and manipulating cells.展开更多
Micro-grinding has been widely used in aerospace and other industry.However,the small diameter of the micro-grinding tool has limited its machining performance and efficiency.In order to solve the above problems,micro...Micro-grinding has been widely used in aerospace and other industry.However,the small diameter of the micro-grinding tool has limited its machining performance and efficiency.In order to solve the above problems,micro-structure has been applied on the micro-grinding tool.A morphology modeling has been established in this study to characterize the surface of microstructured micro-grinding tool,and the grinding performance of micro-structured micro-grinding tool has been analyzed through undeformed chip thickness,abrasive edge width,and effective distance between abrasives.Then deviation analysis,path optimization and parameter optimization of microchannel array precision grinding have been finished to improve processing quality and efficiency,and the deflection angle has the most obvious effects on the rectangular slot depth,micro-structured micro-grinding tool could reduce 10%surface roughness and 20%grinding force compared to original micro-grinding tool.Finally,the microchannel array has been machined with a size deviation of 2μm and surface roughness of 0.2μm.展开更多
The pivotal role microchannels play in the thermal management of electronic components has,in recent decades,prompted extensive research into methods for enhancing their heat transfer performance.Among these methods,s...The pivotal role microchannels play in the thermal management of electronic components has,in recent decades,prompted extensive research into methods for enhancing their heat transfer performance.Among these methods,surface wettability modification was found to be highly effective owing to its significant influence on boiling dynamics and heat transfer mechanisms.In this study,we modified surface wettability using a nanocomposite coating composed of graphene nano plate(GNPs)and multi-walled carbon nanotubes(MWCNT)and then examined how the modification affected the transfer of boiling heat in microchannels.The resultant heat transfer coefficients for hydrophilic and hydrophilic composite(GNPs+MWCNT)microchannels were,respectively,42.8%and 33.95%higher compared with that of the uncoated surface.These results verify that hydrophilic GNP-based coating significantly improves boiling heat transfer performance.It was observed that a minor increase in contact angle,θfrom 73.142°to 75.73°,resulted in a noticeable decrease in thermal performance.This is attributed to diminished liquid film stability,reduced nucleation site activity,and weakened capillary-driven liquid replenishment.These findings underscore the crucial role of optimized surface wettability in maintaining efficient microchannel boiling.At high mass flux,the GNPS microchannels exhibited maximum pressure drop values,with a pressure drop ratio as high as 36%compared to 29%for the GNPs+MWCNT composite samples.Nevertheless,when a composite hydrophilic–hydrophobic coating was deposited through electrodeposition,the enhancement in heat transfer was less significant.This was probably due to decreased surface uniformity,diminished liquid film stability,and the disruption of effective nucleation behavior,all associated with the slight increase in surface contact angle.The obtained results can be used as guidance for designing advanced cooling surfaces in high-performance microelectronic and energy systems,where precise control of surface characteristics is critical.展开更多
This article aims tomodel and analyze the heat and fluid flow characteristics of a carboxymethyl cellulose(CMC)nanofluid within a convergent-divergent shaped microchannel(Two-dimensional).The base fluid,water+CMC(0.5%...This article aims tomodel and analyze the heat and fluid flow characteristics of a carboxymethyl cellulose(CMC)nanofluid within a convergent-divergent shaped microchannel(Two-dimensional).The base fluid,water+CMC(0.5%),is mixed with CuO and Al2O3 nanoparticles at volume fractions of 0.5%and 1.5%,respectively.The research is conducted through the conjugate usage of experimental and theoretical models to represent more realistic properties of the non-Newtonian nanofluid.Three types of microchannels including straight,divergent,and convergent are considered,all having the same length and identical inlet cross-sectional area.Using ANSYS FLUENT software,Navier-Stokes equations are solved for the laminar flow of the non-Newtonian nanofluid.The study examines the effects of Reynolds number,nanoparticle concentration and type,and microchannel geometry on flow and heat transfer.The results prove that the alumina nanoparticles outperform copper oxide in increasing the Nusselt number at a 0.5% volume fraction,while copper oxide nanoparticles excel at a 1.5%volume fraction.Moreover,in the selected case study,as the Reynolds number increases from 100 to 500,the Nusselt number rises by 56.26% in straight geometry,52.93% in divergent geometry,and 59.10%in convergent geometry.Besides,the Nusselt number enhances by 18.75% when transitioning from straight to convergent geometry at a Reynolds number of 500,and by 19.81%at a Reynolds number of 1000.Finally,the results of the research depict that the use of thermophysical properties derived from the experimental achievements,despite creating complexity in the modeling and the solution method,leads to more accurate and realistic outputs.展开更多
The self-healing function is considered one of the effective ways to address structural damage and improve interfacial bonding in Energetic composite materials(ECMs).However,the currently prepared ECMs with self-heali...The self-healing function is considered one of the effective ways to address structural damage and improve interfacial bonding in Energetic composite materials(ECMs).However,the currently prepared ECMs with self-healing function have problems such as irregular particle shape and uneven distribution of components,which affect the efficient play of self-healing function.In this paper,HMX-based energetic microspheres with self-healing function were successfully prepared by microchannel technology,which showed excellent self-healing effect in both Polymer-bonded explosives(PBXs)and Composite solid propellants(CSPs).The experimental results show that the HMX-based energetic microspheres with different binder contents prepared by microchannel technology show regular shape,HMX crystal particles are uniformly wrapped by self-healing binder(GAPU).When the content of GAPU in HMX-based energetic microspheres is 10%,PBXs show excellent self-healing effect and mechanical safety is improved by 400%(raw HMX vs S4,5 J vs 25 J).As a high-energy component,the burning rate of CSPs is increased by 359.4%,the time(burning temperature>1700℃)is prolonged by 333.3%,and the maximum impulse force is increased by 107.3%(CSP-H vs CSP-S4,0.84 mm/s vs 3.87 mm/s,0.06 s vs 0.26 s,0.82 m N vs 1.70 m N).It also has excellent storage performance.The preparation of HMX-based energetic microspheres with self-healing function by microchannel technology provides a new strategy to improve the storage performance of ECMs and the combustion performance of CSPs.展开更多
This study numerically investigates the locomotion of active matter over a circular cylinder in a confined microchannel.We consider the effects of cylinder size,swimming Reynolds number on the motion characteristic of...This study numerically investigates the locomotion of active matter over a circular cylinder in a confined microchannel.We consider the effects of cylinder size,swimming Reynolds number on the motion characteristic of three kinds of swimmers.The swimmer’s motion over a cylinder in a microchannel can be classified into seven modes.The cylinder diameter and swimming Reynolds number have no impact on the motion mode of neutral swimmers.When approaching the cylinder,pullers mainly perform periodic motion near the left side of cylinder,the pushers primarily perform periodic motion near the right side of cylinder.The mechanism of the periodic motion is mainly induced by the hydrodynamic interaction between the cylinder,channel walls,and the pressure near the swimmer.As cylinder diameter increases,pushers are more likely to exhibit periodic motion on the surface of cylinder than the pullers.Puller is unable to stabilize on the surface of cylinder at low Reynolds number,it migrates to the right side of cylinder at high Reynolds number,showing a pattern opposite to that observed for pushers.The results provide a possible new path for controlling active matter in microfluidic devices.展开更多
Integrating Bayesian Optimization with Volume of Fluid (VOF) simulations, this work aims to optimize the operational conditions and geometric parameters of T-junction microchannels for target droplet sizes. Bayesian O...Integrating Bayesian Optimization with Volume of Fluid (VOF) simulations, this work aims to optimize the operational conditions and geometric parameters of T-junction microchannels for target droplet sizes. Bayesian Optimization utilizes Gaussian Process (GP) as its core model and employs an adaptive search strategy to efficiently explore and identify optimal combinations of operational parameters within a limited parameter space, thereby enabling rapid optimization of the required parameters to achieve the target droplet size. Traditional methods typically rely on manually selecting a series of operational parameters and conducting multiple simulations to gradually approach the target droplet size. This process is time-consuming and prone to getting trapped in local optima. In contrast, Bayesian Optimization adaptively adjusts its search strategy, significantly reducing computational costs and effectively exploring global optima, thus greatly improving optimization efficiency. Additionally, the study investigates the impact of rectangular rib structures within the T-junction microchannel on droplet generation, revealing how the channel geometry influences droplet formation and size. After determining the target droplet size, we further applied Bayesian Optimization to refine the rib geometry. The integration of Bayesian Optimization with computational fluid dynamics (CFD) offers a promising tool and provides new insights into the optimal design of microfluidic devices.展开更多
With the increasing miniaturization of systems and surging demand for power density,accurate prediction and control of two-phase flow pressure drop have become a core challenge restricting the performance of microchan...With the increasing miniaturization of systems and surging demand for power density,accurate prediction and control of two-phase flow pressure drop have become a core challenge restricting the performance of microchannel heat exchangers.Pressure drop,a critical hydraulic characteristic,serves as both a natural constraint for cooling systems and determines the power required to pump the working fluid through microchannels.This paper reviews the characteristics,prediction models,and optimization measures of two-phase flow pressure drop for low-boiling-point working fluids in microchannels.It systematically analyzes key influencing factors such as fluid physical properties,operating conditions,channel geometry,and flow patterns,and discusses the complex mechanisms of pressure drop under the coupling effect of multi-physical fields.Mainstream prediction models are reviewed:the homogeneous flow model simplifies calculations but shows large deviations at low quality;the separated flow model considers interphase interactions and can be applied to micro-scales after modification;the flow-pattern-based model performs zoned modeling but relies on subjective classification;machine learning improves prediction accuracy but faces the“black-box”problem.In terms of optimization,channel designs are improved through porous structures and micro-rib arrays,and flow rate distribution is optimized using splitters to balance pressure drop and heat transfer performance.This study provides theoretical support for microchannel thermal management in high-power-density devices.展开更多
In this study,the flow boiling characteristics of R1234yf in parallel microchannels were experimentally investigated.The experiments were conducted with heat flux from 0 to 550 kW/m^(2),mass flux of 434,727,and 1015 k...In this study,the flow boiling characteristics of R1234yf in parallel microchannels were experimentally investigated.The experiments were conducted with heat flux from 0 to 550 kW/m^(2),mass flux of 434,727,and 1015 kg/(m2 s),saturation temperatures of 293,298,and 303 K,and inlet sub-cooling of 5,10,and 15 K.The analysis of the experimental results provides the following conclusions:a reduced mass flux and lower subcooling correspond to a diminished degree of superheat at the boiling inception wall;conversely,an elevated saturation temperature results in a reduced amount of superheat at the boiling inception wall.Furthermore,an increase in sub-cooling and saturation temperature will enhance heat transfer efficiency.The wall temperature is mostly influenced by variations in saturation temperature and is minimally related to changes in mass flux and subcooling degree.An increase in mass flux results in a greater pressure drop attributed to heightened frictional pressure loss.The variation in pressure drop with respect to sub-cooling is minimal,while an increased saturation temperature correlates with a reduced pressure drop due to the formation of smaller bubbles and lowered frictional pressure loss at high saturation pressures.This study thoroughly examines and summarizes the effects of mass flow rate,saturation temperature,and subcooling on the flow-boiling heat transfer and pressure drop characteristics of R1234yf.Furthermore,the new correlation has 93.42%of the predicted values fall within a 15%mean absolute error,exhibiting a mean absolute error of 5.75%.It provides a superior method for predicting the flow-boiling heat transfer coefficients of R1234yf in the heat sink of parallel microchannels compared to existing correlations.展开更多
An Fe-doped bimetallic ZnFe-MOF precursor was prepared using a microchannel reactor,and carbonization was conducted to synthesize a bimetallic catalyst(ZnFe-NC).The fundamental reason for the efficient activity of the...An Fe-doped bimetallic ZnFe-MOF precursor was prepared using a microchannel reactor,and carbonization was conducted to synthesize a bimetallic catalyst(ZnFe-NC).The fundamental reason for the efficient activity of the catalyst was determined through an in-depth analysis of its structural composition and close correlation with the oxygen reduction reaction(ORR).The ZnFe-NC catalyst maintains a stable truncated rhombohedral morphology and a rich microporous structure,exhibiting excellent ORR activity and long-term stability.The experimental results show that compared with the reversible hydrogen electrode,it has a high half-wave potential of 0.902 V(E_(1/2)),retains 94%of activity after 35,000 s of stability testing,and exhibits significant methanol tolerance in alkaline media.Density functional theory calculations confirm the synergistic effect between the Zn and Fe sites.Furthermore,the results indicate that the interaction between ZnFe-N_(6)coordination structures reduces the reaction energy barrier,thus enhancing intermediate adsorption during the ORR.展开更多
基金supports for this project from the National Natural Science Foundation of China(22378295).
文摘This study investigates the droplet formation for the liquid–liquid two-phase flow within a square T-junction microchannel through numerical simulation using volume of fluid method and experimental visualization using high-speed camera imaging.The T-junction microchannel has a cross-sectional width of 0.6 mm and a total length of 27.3 mm.The solution of cyclohexane with 2%and 3%mass concentrations of sorbitan trioleate surfactant were used as the continuous phase,and water was used as the dispersed phase.Slug flow,characteristic of squeezing regime,were predominantly observed.The effects of liquid–liquid two-phase flow rate ratio,and dimensionless number on droplet size,and pressure drop were investigated.The squeezing regime was mapped for 0.0005≤Ca_(c)≤0.0052(capillary number)and 0.1≤q≤10(flow rate ratio).The pressure drops of slugs were in the range from 40 Pa to 200 Pa.The slug lengths were measured between 1 mm and 9 mm.A universal flow map dependent on Ca_(c)Re_(d)^(0.5) are projected to investigate the droplet formation behavior in T-junction microchannel.Correlation expressions are proposed to predict pressure drops and the slug lengths for liquid–liquid two-phase flow in a square T-junction microchannel,using dimensionless numbers such as flow rate ratio and capillary number.The result shows that large continuous phase flow rates facilitate smaller slugs,whereas higher dispersed phase flow rates result in longer shorts.
基金funded by the Master,Ph D Scholarship Programme of Vingroup Innovation Foundation(VINIF),code VINIF.2023.Th S.118。
文摘Understanding and predicting droplet breakup is essential in droplet-based microfluidic systems,as it enables precise control over droplet manipulation for various applications.In this study,droplet breakup behavior in a T-junction microchannel is investigated under the influence of microchannel geometry using three-dimensional numerical simulations.A theoretical model is developed based on the balance between surface tension and viscous drag forces acting on the droplet,incorporating the effects of geometric parameters on droplet length.This model predicts the critical Capillary number required for breakup to occur.The theoretical predictions are validated using both previous research data and the present numerical simulations.The results show that the model accurately predicts the transition between breakup and non-breakup regimes.Specifically,an increase in sidearm length ratio inhibits droplet breakup and leads to an asymmetric breakup regime.Furthermore,increasing the outlet-to-inlet width ratio also reduces the likelihood of droplet breakup.These findings provide a predictive framework for understanding and controlling droplet dynamics in microfluidic T-junctions,with potential applications in lab-on-a-chip technologies.
基金supported by the National Natural Science Foundation of China(92034303,91834303 and 21776200)the aid of Program of Introducing Talents of Discipline to Universities(BP0618007)。
文摘The coalescence behavior of two droplets with different viscosities in the funnel-typed expansion chamber in T-junction microchannel was investigated experimentally and compared with droplet coalescence of the same viscosity.Four types of coalescence regimes were observed:contact non-coalescence,squeeze non-coalescence,two-droplet coalescence and pinch-off coalescence.For droplet coalescence of different viscosities,the operating range of non-coalescence becomes narrowed compared to the droplet coalescence of same viscosity,and it shrinks with increasing viscosity ratioηof two droplets,indicating that the difference in the viscosity of two droplets is conducive to coalescence,especially when1<η<6.Furthermore,the influences of viscosity ratio and droplet size on the film drainage time(Tdr)and critical capillary number(Ca)c)were studied systematically.It was found that the film drainage time declined with the increase of average droplet size,which abided by power-law relation with the size difference and viscosity ratio of the two droplets:Tdr~(ld)^(0.25±0.04)and Tdr~(η)^(﹣0.1±0.02).For droplet coalescence of same viscosity,the relation of critical capillary number with two-phase viscosity ratio and dimensionless droplet size is Cac=0.48λ^(0.26)l^(﹣2.64),while for droplet coalescence of different viscosities,the scaling of critical capillary number with dimensionless average droplet size,dimensionless droplet size difference and viscosity ratio of two droplets is Cac=0.11η^(﹣0.07)ls^(﹣2.23)l^(0.16)_(d).
基金This study was supported by the National Natural Science Foundation of China(22008220,21776200,51973196)Natural Science Foundation of Zhejiang Province(LQ21B060009)the Key Research and Development Program of Zhejiang Province(2020C01010).
文摘This study focuses on the effect of chemical absorption on the formation dynamic characteristics and initial length of Taylor bubbles.The temporal evolutions of neck width and length of gaseous thread and initial length with and without chemical absorption were investigated with the Capillary number and Hatta number between 0.0010–0.0073 and 1.8–5.8 respectively.The squeezing regime with typical three stages,expansion,squeezing and pinch off is observed for both two processes.Compared with the nonabsorption process,the increase of formation time in the chemical absorption process arises mainly from the expansion stage,and the decrease of initial length is from the necking stage.In addition,the temporal length evolution satisfies the power-law scale with the same exponent but a smaller pre-exponential factor.The correlations of neck width for stage transition and initial length with Hatta number demonstrate the enhancement effect of chemical absorption on bubble formation dynamics and initial length at relatively high chemical reaction rates and long formation time.This study provides insight into the bubble formation mechanism and helps to regulate the bubble initial size with chemical absorption.
基金supported by grant from the National Key Technology Support Program of the Ministry of Science and Technology of China(No.2021ZD0203204)。
文摘Pseudounipolar neurons in the dorsal root ganglia(DRG),as the central nodes of primary sensory afferents,possess a distinctive T-junction that is not merely a morphological peculiarity but also performs complex roles in rapid,multiplexed shunting and regulation of sensory signals.This specialized geometry enables separation,filtering,and feedback regulation of neuronal signals,thereby coordinating peripheral and central responses at multiple levels.Recent advances,including spatial transcriptomics,single-cell sequencing,super-resolution microscopy,organoid models,and novel electrophysiological methods,have permitted more precise dissection of the T-junction's molecular composition,ion-channel distribution,and electrophysiological properties.Here,we review current knowledge of the T-junction's developmental regulation and multilayered molecular networks,and we detail its functional alterations in both physiological signaling and pathological pain states,with particular emphasis on ion-channel modulation,signal attenuation,and selective transmission mechanisms.Finally,we discuss contemporary pain-intervention approaches and prospects for precision-targeted therapies,aiming to provide a theoretical foundation for future studies in pain physiology and clinical translation.
基金Dalian distinguished young scholars program(2022RJ17)the Dalian excellent young talents program(2023RY037)provided funding for this study.
文摘To efficiently remove radioactive nuclides from nuclear industry wastewater and minimize the generation of radioactive secondary waste,this study proposes the concept of a magnetically controlled microchannel adsorber based on magnetic adsorbents.A novel protocol for achieving high adsorption performance in microchannel adsorbers with periodically distributed particles is developed using the particle-resolved computational fluid dynamics (CFD) method,which addresses the limitations of traditional porous media flow models.To align simulation results more closely with practical scenarios,a typical high-efficiency magnetic adsorbent,magnetic sodium alginate/cobalt-based Prussian blue (M-SA/PB-Co),was synthesized.The M-SA/PB-Co microspheres exhibit a uniform size distribution (300–600 μm),and their Cs^(+) adsorption follows the pseudo-second-order kinetic model with a Langmuir saturated adsorption capacity of 124.84 mg·g^(-1).The performance parameters of M-SA/PB-Co,obtained from characterization and adsorption experiments,were integrated into CFD simulations.CFD results indicate that as the flow velocity increases,the flow field gradually transitions with vortices expanding in scale and streamline bifurcation points shifting rearward.The Cs^(+) concentration decreases progressively along the flow direction,with a more pronounced reduction in the vortex regions downstream of particles.The characteristic velocity and characteristic concentration of specific regions surrounding the particles were extracted based on boundary layer distribution.The amount of concentration reduction of Cs^(+) through particle is positively correlated with the characteristic concentration and negatively correlated with the characteristic velocity.The number of microspheres required in the microchannel adsorber was optimized using the response surface method.Compared with industrial fixed-bed adsorbers,microchannel adsorbers exhibit 8–10 times higher processing capacity,demonstrating significant industrial application potential.
基金supported by the National Key Projects for Fundamental Research and development of China(2020YFA0710202)the China Postdoctoral Science Foundation(2024M761567)Shandong Postdoctoral Science Foundation(SDCX-ZG-202400271).
文摘The synthesis of propylene carbonate(PC)from CO_(2) and propylene oxide(PO)is a typical gas-liquid biphasic system,where gas-liquid mass transfer efficiency significantly influences CO_(2) cycloaddition reactions.Here,we proposed a microchannel reaction system for the CO_(2) cycloaddition reaction catalyzed by ionic liquid within an aqueous environment.The effect of liquid flow rate,temperature and residence time on gas-liquid flow pattern,catalytic performance and mass transfer were systematically investigated.The results revealed that the PC generation rate reached 560.11 mmol·ml^(−1)·h^(−1)at a 50 cm of flow distance under reaction conditions of 105℃,2.5 MPa,QG=176 ml·min^(−1) and QL=0.3 ml·min^(−1).Variations in mass transfer rate and reaction rate at different flow distances were experimentally studied.The reaction efficiency gradually decreased with increasing flow distance,which were attributed to the reduction of mass transfer caused by decreasing bubble velocity.Optimizing bubble velocity at an appropriate position enhanced reaction efficiency by improving mass transfer,achieving a 97.7%PC yield within 2.85 min.Furthermore,a kinetic model coupling intrinsic kinetics with gas-liquid mass transfer was developed for CO_(2) cycloaddition reaction.The kinetic model was applied to predict PC reaction rates in microchannel reactors at various temperatures and liquid flow rates,achieving an average relative error of 9.6%.
文摘Droplet-based microfluidics is a transformative technology with applications across diverse scientific and industrial domains.However,predicting the droplet size generated by individual microchannels before experiments or simulations remains a significant challenge.In this study,we focus on a double T-junction microfluidic geometry and employ a hybrid modeling approach that combines machine learning with metaheuristic optimization to address this issue.Specifically,particle swarm optimization(PSO)is used to optimize the hyperparameters of a decision tree(DT)model,and its performance is compared with that of a DT optimized through grid search(GS).The hybrid models are developed to estimate the droplet diameter based on four parameters:the main width,side width,thickness,and flow rate ratio.The dataset of more than 300 cases,generated by a three-dimensional numerical model of the double T-junction,is used for training and testing.Multiple evaluation metrics confirm the predictive accuracy of the models.The results demonstrate that the proposed DT-PSO model achieves higher accuracy,with a coefficient of determination of 0.902 on the test data,while simultaneously reducing prediction time.This methodology holds the potential to minimize design iterations and accelerate the integration of microfluidic technology into the biological sciences.
基金supports for this project from State Key Laboratory of Chemical Safety(SKLCS–2024001)are gratefully acknowledged。
文摘Bubble breakup at T-junction microchannels is the basis for the numbering-up of gas−liquid two-phase flow in parallelized microchannels. This article presents the bubble breakup in viscous liquids at a microfluidic T-junction. Nitrogen is used as the gas phase, and glycerol-water mixtures with different mass concentration of glycerol as the liquid phase. The evolution of the gas−liquid interface during bubble breakup at the microfluidic T-junction is explored. The thinning of the bubble neck includes the squeezing stage and the rapid pinch-off stage. In the squeezing stage, the power law relation is found between the minimum width of the bubble neck and the time, and the values of exponents α1 and α2 are influenced by the viscous force. The values of pre-factors m_(1) and m_(2) are negatively correlated with the capillary number. In the rapid pinch-off stage, the thinning of the bubble neck is predominated by the surface tension, and the minimum width of the bubble neck can be scaled with the remaining time as power-law. The propagation of the bubble tip can be characterized by the power law between the movement distance and the time, with decreasing exponent as increased liquid viscosity.
基金supported by Scientific Research Project of Guangdong Provincial Department of Education(2024KQNCX152).
文摘Flow velocity uniformity of the microchannel plate is a major factor affecting the performance of microchannel devices.In order to improve the velocity distribution uniformity of the microchannel plate,we designed two new microchannel structures:V-type and A-type.The effects of various structural parameters of the manifolds on the velocity distribution are reported.The V-type and A-type microchannel plates had a more uniform velocity distribution compared to the Z-type microchannel plate.The final result showed that it is beneficial for the V-type microchannel plate to obtain a more uniform velocity distribution when the manifold structure parameters are X_(in)=-1,X_(out)=0,Y_(in)=10,Y_(out)=6,Hin=4,H_(out)=1,and R=0.5.
基金funded by the National Natural Science Foundation of China(Project No.62273289)The Youth Innovation Science and Technology Support Program of Shandong Province(Project No.2022KJ274)+1 种基金Natural Science Foundation of Shandong Province(Grant No.ZR2024MF007)Graduate Innovation Foundation of Yantai University,GIFYTU.
文摘The design and manufacturing of microchannels are crucial aspects of modern micro/nanomanufacturing processes,offering a versatile platform for manipulating and driving micro/nanoparticles or cells.In this study,we propose a method for manufacturing microchannels using optically induced dielectrophoresis technology to induce the polymerization of polyethylene glycol diacrylate solution.To overcome limitations related to the light intensity energy and the size of intact microchannels,we design and manufacture microstructures of various shapes with a height of 4µm.Additionally,we simulate and analyze the movement of and forces acting on polystyrene(PS)microspheres at different spatial positions within the microchannels.Finally,we successfully demonstrate applications involving the transport of PS microspheres in custom-fabricated microchannels.This novel biocompatible microchannel manufacturing method is simple and non-biotoxic.It provides a new approach for simulating physiological environments in vitro and cultivating and manipulating cells.
基金co-supported by the Enterprise Innovation and Development Joint Program of the National Natural Science Foundation of China(No.U20B2032)Open Project Funding of State Key Laboratory for High Performance Tools(GXNGJSKL-2024-08)+1 种基金Open Foundation of the State Key Laboratory of Intelligent Manufacturing Equipment and Technology(IMETKF2023005)Introduced Innovative Scientific Research Team Project of Zhongshan(the tenth batch)(CXTD2023008)。
文摘Micro-grinding has been widely used in aerospace and other industry.However,the small diameter of the micro-grinding tool has limited its machining performance and efficiency.In order to solve the above problems,micro-structure has been applied on the micro-grinding tool.A morphology modeling has been established in this study to characterize the surface of microstructured micro-grinding tool,and the grinding performance of micro-structured micro-grinding tool has been analyzed through undeformed chip thickness,abrasive edge width,and effective distance between abrasives.Then deviation analysis,path optimization and parameter optimization of microchannel array precision grinding have been finished to improve processing quality and efficiency,and the deflection angle has the most obvious effects on the rectangular slot depth,micro-structured micro-grinding tool could reduce 10%surface roughness and 20%grinding force compared to original micro-grinding tool.Finally,the microchannel array has been machined with a size deviation of 2μm and surface roughness of 0.2μm.
文摘The pivotal role microchannels play in the thermal management of electronic components has,in recent decades,prompted extensive research into methods for enhancing their heat transfer performance.Among these methods,surface wettability modification was found to be highly effective owing to its significant influence on boiling dynamics and heat transfer mechanisms.In this study,we modified surface wettability using a nanocomposite coating composed of graphene nano plate(GNPs)and multi-walled carbon nanotubes(MWCNT)and then examined how the modification affected the transfer of boiling heat in microchannels.The resultant heat transfer coefficients for hydrophilic and hydrophilic composite(GNPs+MWCNT)microchannels were,respectively,42.8%and 33.95%higher compared with that of the uncoated surface.These results verify that hydrophilic GNP-based coating significantly improves boiling heat transfer performance.It was observed that a minor increase in contact angle,θfrom 73.142°to 75.73°,resulted in a noticeable decrease in thermal performance.This is attributed to diminished liquid film stability,reduced nucleation site activity,and weakened capillary-driven liquid replenishment.These findings underscore the crucial role of optimized surface wettability in maintaining efficient microchannel boiling.At high mass flux,the GNPS microchannels exhibited maximum pressure drop values,with a pressure drop ratio as high as 36%compared to 29%for the GNPs+MWCNT composite samples.Nevertheless,when a composite hydrophilic–hydrophobic coating was deposited through electrodeposition,the enhancement in heat transfer was less significant.This was probably due to decreased surface uniformity,diminished liquid film stability,and the disruption of effective nucleation behavior,all associated with the slight increase in surface contact angle.The obtained results can be used as guidance for designing advanced cooling surfaces in high-performance microelectronic and energy systems,where precise control of surface characteristics is critical.
文摘This article aims tomodel and analyze the heat and fluid flow characteristics of a carboxymethyl cellulose(CMC)nanofluid within a convergent-divergent shaped microchannel(Two-dimensional).The base fluid,water+CMC(0.5%),is mixed with CuO and Al2O3 nanoparticles at volume fractions of 0.5%and 1.5%,respectively.The research is conducted through the conjugate usage of experimental and theoretical models to represent more realistic properties of the non-Newtonian nanofluid.Three types of microchannels including straight,divergent,and convergent are considered,all having the same length and identical inlet cross-sectional area.Using ANSYS FLUENT software,Navier-Stokes equations are solved for the laminar flow of the non-Newtonian nanofluid.The study examines the effects of Reynolds number,nanoparticle concentration and type,and microchannel geometry on flow and heat transfer.The results prove that the alumina nanoparticles outperform copper oxide in increasing the Nusselt number at a 0.5% volume fraction,while copper oxide nanoparticles excel at a 1.5%volume fraction.Moreover,in the selected case study,as the Reynolds number increases from 100 to 500,the Nusselt number rises by 56.26% in straight geometry,52.93% in divergent geometry,and 59.10%in convergent geometry.Besides,the Nusselt number enhances by 18.75% when transitioning from straight to convergent geometry at a Reynolds number of 500,and by 19.81%at a Reynolds number of 1000.Finally,the results of the research depict that the use of thermophysical properties derived from the experimental achievements,despite creating complexity in the modeling and the solution method,leads to more accurate and realistic outputs.
基金support given by the Fundamental Research Program of Shanxi Province(Grant No.202203021212152)。
文摘The self-healing function is considered one of the effective ways to address structural damage and improve interfacial bonding in Energetic composite materials(ECMs).However,the currently prepared ECMs with self-healing function have problems such as irregular particle shape and uneven distribution of components,which affect the efficient play of self-healing function.In this paper,HMX-based energetic microspheres with self-healing function were successfully prepared by microchannel technology,which showed excellent self-healing effect in both Polymer-bonded explosives(PBXs)and Composite solid propellants(CSPs).The experimental results show that the HMX-based energetic microspheres with different binder contents prepared by microchannel technology show regular shape,HMX crystal particles are uniformly wrapped by self-healing binder(GAPU).When the content of GAPU in HMX-based energetic microspheres is 10%,PBXs show excellent self-healing effect and mechanical safety is improved by 400%(raw HMX vs S4,5 J vs 25 J).As a high-energy component,the burning rate of CSPs is increased by 359.4%,the time(burning temperature>1700℃)is prolonged by 333.3%,and the maximum impulse force is increased by 107.3%(CSP-H vs CSP-S4,0.84 mm/s vs 3.87 mm/s,0.06 s vs 0.26 s,0.82 m N vs 1.70 m N).It also has excellent storage performance.The preparation of HMX-based energetic microspheres with self-healing function by microchannel technology provides a new strategy to improve the storage performance of ECMs and the combustion performance of CSPs.
基金supported by the Major Program of the National Natural Science Foundation of China(Grant No.12132015)the National Natural Science Foundation of China(Grant Nos.12202392 and 12372251)the Joint Funds of the National Natural Science Foundation of China(Grant No.U2006221).
文摘This study numerically investigates the locomotion of active matter over a circular cylinder in a confined microchannel.We consider the effects of cylinder size,swimming Reynolds number on the motion characteristic of three kinds of swimmers.The swimmer’s motion over a cylinder in a microchannel can be classified into seven modes.The cylinder diameter and swimming Reynolds number have no impact on the motion mode of neutral swimmers.When approaching the cylinder,pullers mainly perform periodic motion near the left side of cylinder,the pushers primarily perform periodic motion near the right side of cylinder.The mechanism of the periodic motion is mainly induced by the hydrodynamic interaction between the cylinder,channel walls,and the pressure near the swimmer.As cylinder diameter increases,pushers are more likely to exhibit periodic motion on the surface of cylinder than the pullers.Puller is unable to stabilize on the surface of cylinder at low Reynolds number,it migrates to the right side of cylinder at high Reynolds number,showing a pattern opposite to that observed for pushers.The results provide a possible new path for controlling active matter in microfluidic devices.
基金support from National Key Research and Development Program of China(2023YFC3905400)the Strategic Priority Research Program of the Chinese Academy of Sciences(XDA0490102)National Natural Science Foundation of China(22178354,2242100322408374).
文摘Integrating Bayesian Optimization with Volume of Fluid (VOF) simulations, this work aims to optimize the operational conditions and geometric parameters of T-junction microchannels for target droplet sizes. Bayesian Optimization utilizes Gaussian Process (GP) as its core model and employs an adaptive search strategy to efficiently explore and identify optimal combinations of operational parameters within a limited parameter space, thereby enabling rapid optimization of the required parameters to achieve the target droplet size. Traditional methods typically rely on manually selecting a series of operational parameters and conducting multiple simulations to gradually approach the target droplet size. This process is time-consuming and prone to getting trapped in local optima. In contrast, Bayesian Optimization adaptively adjusts its search strategy, significantly reducing computational costs and effectively exploring global optima, thus greatly improving optimization efficiency. Additionally, the study investigates the impact of rectangular rib structures within the T-junction microchannel on droplet generation, revealing how the channel geometry influences droplet formation and size. After determining the target droplet size, we further applied Bayesian Optimization to refine the rib geometry. The integration of Bayesian Optimization with computational fluid dynamics (CFD) offers a promising tool and provides new insights into the optimal design of microfluidic devices.
基金supported by the Beijing Municipal Science&Technology Commission(Z231100006123010).
文摘With the increasing miniaturization of systems and surging demand for power density,accurate prediction and control of two-phase flow pressure drop have become a core challenge restricting the performance of microchannel heat exchangers.Pressure drop,a critical hydraulic characteristic,serves as both a natural constraint for cooling systems and determines the power required to pump the working fluid through microchannels.This paper reviews the characteristics,prediction models,and optimization measures of two-phase flow pressure drop for low-boiling-point working fluids in microchannels.It systematically analyzes key influencing factors such as fluid physical properties,operating conditions,channel geometry,and flow patterns,and discusses the complex mechanisms of pressure drop under the coupling effect of multi-physical fields.Mainstream prediction models are reviewed:the homogeneous flow model simplifies calculations but shows large deviations at low quality;the separated flow model considers interphase interactions and can be applied to micro-scales after modification;the flow-pattern-based model performs zoned modeling but relies on subjective classification;machine learning improves prediction accuracy but faces the“black-box”problem.In terms of optimization,channel designs are improved through porous structures and micro-rib arrays,and flow rate distribution is optimized using splitters to balance pressure drop and heat transfer performance.This study provides theoretical support for microchannel thermal management in high-power-density devices.
基金supported by the Beijing Municipal Science&Technology Commission(Z231100006123010).
文摘In this study,the flow boiling characteristics of R1234yf in parallel microchannels were experimentally investigated.The experiments were conducted with heat flux from 0 to 550 kW/m^(2),mass flux of 434,727,and 1015 kg/(m2 s),saturation temperatures of 293,298,and 303 K,and inlet sub-cooling of 5,10,and 15 K.The analysis of the experimental results provides the following conclusions:a reduced mass flux and lower subcooling correspond to a diminished degree of superheat at the boiling inception wall;conversely,an elevated saturation temperature results in a reduced amount of superheat at the boiling inception wall.Furthermore,an increase in sub-cooling and saturation temperature will enhance heat transfer efficiency.The wall temperature is mostly influenced by variations in saturation temperature and is minimally related to changes in mass flux and subcooling degree.An increase in mass flux results in a greater pressure drop attributed to heightened frictional pressure loss.The variation in pressure drop with respect to sub-cooling is minimal,while an increased saturation temperature correlates with a reduced pressure drop due to the formation of smaller bubbles and lowered frictional pressure loss at high saturation pressures.This study thoroughly examines and summarizes the effects of mass flow rate,saturation temperature,and subcooling on the flow-boiling heat transfer and pressure drop characteristics of R1234yf.Furthermore,the new correlation has 93.42%of the predicted values fall within a 15%mean absolute error,exhibiting a mean absolute error of 5.75%.It provides a superior method for predicting the flow-boiling heat transfer coefficients of R1234yf in the heat sink of parallel microchannels compared to existing correlations.
基金financially supported by Xinjiang Science and Technology Program(No.2023TSYCCX0118)Bingtuan Science and Technology Program(No.2023AB033)。
文摘An Fe-doped bimetallic ZnFe-MOF precursor was prepared using a microchannel reactor,and carbonization was conducted to synthesize a bimetallic catalyst(ZnFe-NC).The fundamental reason for the efficient activity of the catalyst was determined through an in-depth analysis of its structural composition and close correlation with the oxygen reduction reaction(ORR).The ZnFe-NC catalyst maintains a stable truncated rhombohedral morphology and a rich microporous structure,exhibiting excellent ORR activity and long-term stability.The experimental results show that compared with the reversible hydrogen electrode,it has a high half-wave potential of 0.902 V(E_(1/2)),retains 94%of activity after 35,000 s of stability testing,and exhibits significant methanol tolerance in alkaline media.Density functional theory calculations confirm the synergistic effect between the Zn and Fe sites.Furthermore,the results indicate that the interaction between ZnFe-N_(6)coordination structures reduces the reaction energy barrier,thus enhancing intermediate adsorption during the ORR.
