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
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
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
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 displacement of residual crude oil and enhanced oil recovery from reservoirs of mature oil fields are challenging worldwide and have received intensive attentions in oil and gas industry.In this work,a novel metho...The displacement of residual crude oil and enhanced oil recovery from reservoirs of mature oil fields are challenging worldwide and have received intensive attentions in oil and gas industry.In this work,a novel method for enhanced oil recovery by displacement of oil with bionanofluids was proposed.Microdisplacement hydrodynamics of crude oil in microchannel sand-packed porous media by the bionanofluid were investigated by high-speed imaging.The machine learning models with the extreme gradient boosting(XGBoost) algorithm was developed for the prediction of residual oil saturation during the micro-displacement processes.The residual oil droplets within the porous media after the waterflooding were effectively removed through bionanofluid-flooding,resulting in additional enhanced oil recovery of 39.0%,which is double the recovery achieved by waterflooding at the same displacement velocity.By wavelet-transform image enhancement and the XGBoost algorithm in the machine learning,the residual oil saturations along the porous media were predicted accurately with the mean squared errors of 0.0045 and 0.0030 in the waterflooding and the bionanofluid-flooding,respectively.The results indicated that the machine learning is effective in characterizing the displacement behaviors and the bionanofluid-flooding could be an interesting approach,and thus has potential applications in enhanced oil recovery of waterflooding reservoirs.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
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
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
Combining the advantages of high efficiency,low-pressure drop,and large throughput,the pore arrayenhanced tube-in-tube microchannel(PA-TMC) is a promising microreactor for industrial applications.However,most of the m...Combining the advantages of high efficiency,low-pressure drop,and large throughput,the pore arrayenhanced tube-in-tube microchannel(PA-TMC) is a promising microreactor for industrial applications.However,most of the mass transfer takes place in the upstream pore region,while the contribution of the downstream annulus is limited.In this work,helical wires were introduced into the annulus by adhering to the outer surface of the inner tube.Mixing behavior and mass transfer of liquid-liquid twophase flow in PA-TMC with different helical wires have been systematically studied by a combination of experiments and volume of fluid(VOF) method.The introduction of helical wires improves the overall volumetric mass transfer coefficient KLa by up to 133% and the mass transfer efficiency E by up to 117%.The simulation results show that the helical wire brings extra phase mixing regions and increases the specific interface area,while accelerating the fluid flow and expanding the area of enhanced turbulent dissipation rate.Influences of helical wires in various configurations are compared by the comprehensive index I concerning the pressure drop and mass transfer performance simultaneously and a new correlation between KLa and specific energy consumption φ is proposed.This research deepens the understanding of the mixing behavior and mass transfer in the PA-TMCs and provides practical experience for the process intensification of microchannel reactors.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
Flow boiling in open microchannels offers highly efficient heat transfer performance and has attracted increasing attention in the fields of heat transfer and thermalmanagement of electronic devices in recent years.Ho...Flow boiling in open microchannels offers highly efficient heat transfer performance and has attracted increasing attention in the fields of heat transfer and thermalmanagement of electronic devices in recent years.However,the continuous rise in power density of electronic components imposesmore stringent requirements on the heat transfer capability of microchannel flow boiling.HFE-7100,a dielectric coolant with favorable thermophysical properties,has become a focal point of research for enhancing flow boiling performance in open microchannels.The flow boiling heat transfer performance ofHFE-7100 was investigated in this study by fabricating micro-nano composite structures on the bottom surface of open microchannels using laser ablation technology.Based on visualization results,a comparative analysis was conducted on the bubble dynamics and flow pattern characteristics of HFE-7100 flow boiling in micronano structured open microchannels(MNSOMC)and smooth-surface open microchannels(SSOMC),to elucidate the enhancement mechanism of micro-nano structures on flow boiling heat transfer in open microchannels.The results indicate that the surface structures and strong wettability of MNSOMC accelerated bubble nucleation and departure.Moreover,bubbles in the channel tended to coalesce along the flow direction,forming elongated slug bubbles with high aspect ratios,which enabled efficient thin film evaporation in conjunction with intense nucleate boiling,thereby significantly enhancing flow boiling heat transfer.Under the experimental conditions of this study,the maximum enhancements in the heat transfer coefficient(HTC)and critical heat flux(CHF)of HFE-7100 inMNSOMC were 33.4%and 133.1%,respectively,with the CHF reaching up to 1542.3 kW⋅m^(−2).Furthermore,due to the superior wettability and capillary wicking capability of the micro-nano composite structures,the significant enhancement in flow boiling heat transfer was achieved without incurring a noticeable pressure drop penalty.展开更多
Understanding the complex interaction between heat and mass transfer in non-Newtonian microflows is essential for the development and optimization of efficient microfluidic and thermal management systems.This study in...Understanding the complex interaction between heat and mass transfer in non-Newtonian microflows is essential for the development and optimization of efficient microfluidic and thermal management systems.This study investigates the magnetohydrodynamic(MHD)thermosolutal convection of a Casson fluid within an inclined,porous microchannel subjected to convective boundary conditions.The nonlinear,coupled equations governing momentum,energy,and species transport are solved numerically using the MATLAB bvp4c solver,ensuring high numerical accuracy and stability.To identify the dominant parameters influencing flow behavior and to optimize transport performance,a comprehensive hybrid optimization framework—combining a modified Taguchi design,Grey Relational Analysis(GRA),and Principal Component Analysis(PCA)—is proposed.This integrated strategy enables the simultaneous assessment of skin friction,Nusselt number,and Sherwood number,providing a rigorous multi-objective evaluation of system performance.Comparative validation with benchmark results from the literature confirms the accuracy and reliability of the present formulation and its numerical implementation.The results highlight the intricate coupling among flow slip,buoyancy effects,and convective transport mechanisms.Increased slip flow enhances axial velocity,while a higher solutal Biot number intensifies concentration gradients near the channel walls.Conversely,a lower thermal Biot number diminishes the temperature field,indicating weaker heat transfer across the boundaries.PCA results reveal that the first principal component(PC1)accounts for most of the system variance,demonstrating the dominant influence of coupled flow and transport parameters on overall system performance.展开更多
The repeated volume variation of lithium(Li)metal anode(LMA)upon Li^(+) plating/stripping,the volatile interface between Li and the electrolyte,and the incessant growth of Li dendrites on Li metal surface have severel...The repeated volume variation of lithium(Li)metal anode(LMA)upon Li^(+) plating/stripping,the volatile interface between Li and the electrolyte,and the incessant growth of Li dendrites on Li metal surface have severely hindered the practical application of Li in constructing high energy-density Li metal batteries(LMBs).Herein,a novel Li host(3D ZnO/CNTs/Cu)featuring ordered microchannels and lithiophilic ZnO species on the inner walls of the microchannels is introduced,which induces the uniform Li^(+) deposition into the microchannels and finally suppresses the formation of Li dendrites.The stable structure of the fabricated 3D Li host can adapt to volume variations upon Li^(+) plating/stripping,thereby enhancing electrochemical performances.Symmetric cells with the 3D ZnO/CNTs/Cu@Li anode exhibited long cycle stability at areal current densities of 0.5 and 2 mA cm^(-2);Full cells maintained a reversible discharge capacity of 105 mAh g^(-1) after 400 cycles at 1C with a capacity retention of 70%.Meanwhile,ex-situ SEM observations proved that the 3D ZnO/CNTs/Cu@Li anode can keep the structural integrity during charging/discharging(or plating/stripping).This work suggested that lithiophilic nanochannels in the Li host can significantly improve the electrochemical performance and safety of LMBs.展开更多
Deposition of diamond inside the trenches or microchannels by chemical vapor deposition （CVD） is limited by the diffusion efficiency of important radical species for diamond growth （H, CH3） and the pore depth of t...Deposition of diamond inside the trenches or microchannels by chemical vapor deposition （CVD） is limited by the diffusion efficiency of important radical species for diamond growth （H, CH3） and the pore depth of the substrate template. By ultrasonic seeding with nanodiamond suspension, three-dimensional （3D） penetration structure diamond was successfully deposited in cylindrical microchannels of Cu template by hot-filament chemical vapor deposition. Micro-Raman spectroscopy and scanning electron microscopy （SEM） were used to characterize diamond film and the effects of microchannel depth on the morphology, grain size and growth rate of diamond film were comprehensively investigated. The results show that diamond quality and growth rate sharply decrease with the increase of the depth of cylindrical microchannel. Individual diamond grain develops gradually from faceted crystals into micrometer cluster, and finally to ballas-type nanocrystalline one. In order to modify the rapid decrease of diamond quality and growth rate, a new hot filament apparatus with a forced gas flow through Cu microchannels was designed. Furthermore, the growth of diamond film by new apparatus was compared with that without a forced gas flow, and the enhancement mechanism was discussed.展开更多
Experiments were carried out to investigate the boiling heat transfer characteristics of Al_2O_3-water nanofluids in swirl microchannels under terrestrial gravity and acceleration fields. A centrifuge with a two-meter...Experiments were carried out to investigate the boiling heat transfer characteristics of Al_2O_3-water nanofluids in swirl microchannels under terrestrial gravity and acceleration fields. A centrifuge with a two-meter long rotational arm was used to simulate the acceleration magnitude up to 9 g and three various acceleration directions. Three test sections with different geometric parameters were applied. The volume concentration of Al_2O_3 nanoparticles with an average diameter of 13 nm was varied from 0.07% to 0.1%. The mass flow rate and vapor quality were in ranges of 3–6 kg/h and 0.4–1.0%, respectively. The effects of the mass flow rate, microchannel aspect ratio,vapor quality, nanoparticle volume concentration, and acceleration direction and magnitude were analyzed in a systematic manner. Experimental results showed that the acceleration direction and magnitude had significant influences on the boiling heat transfer. The heat transfer under configuration C was found to be superior to that under configurations A and B. Moreover, the heat transfer coefficient increased with increases of the mass flow rate and the volume concentration and decreased with the aspect ratio.展开更多
Microchannel heat sinks(MCHSs)are promising thermal solutions in miniaturized or compact devices.Lightweight aspect has been given huge emphasis in recent years.Metal-based materials are commonly used to fabricate MCH...Microchannel heat sinks(MCHSs)are promising thermal solutions in miniaturized or compact devices.Lightweight aspect has been given huge emphasis in recent years.Metal-based materials are commonly used to fabricate MCHSs due to their high thermal conductivity.Consequently,MCHSs are heavy due to the high density of these materials albeit the small footprint of MCHSs.Polymer-based materials are interesting alternatives.Despite their poor thermal conductivity,lightweight feature attracts the interest of researchers.Heat transfer is a conjugate process of heat conduction and heat convection.Poor heat conductions aspect may be compensated through enhancement of heat convection aspects.Although polymer-based materials have been used in microscale heat transfer studies,their focus was not on their feasibility.The present study aims to evaluate the feasibility of polymer-based MCHSs as thermal solutions.The effect of thermal conductivity of fabrication materials,including polymer-based PDMS,PTFE,PDMS/MWCNT,and metal-based aluminum,on the thermal performance of MCHSs was investigated and compared at various inlet flow rate,fluid thermal conductivity,and microchannel ratio at different constant heat fluxes using three-dimensional CFD approach.Results showed that the thermal performance of MCHSs was greatly affected by the heat conduction aspect in which poor heat conduction limited the thermal performance improvement due to enhanced heat convection aspects.This suggests polymer-based materials have the potential for heat transfer applications through thermal conductivity enhancement.This was confirmed in the further analysis using a recently proposed high thermal conductivity polymer-based graphite/epoxy MCHS and a hybrid-based PDMS/aluminum MCHS.展开更多
A novel AIN monolithic microchannel cooled heatsink for high power laser diode array is introduced.The high power stack laser diode array with an AIN monolithic microchannel heatsink is fabricated and tested.The therm...A novel AIN monolithic microchannel cooled heatsink for high power laser diode array is introduced.The high power stack laser diode array with an AIN monolithic microchannel heatsink is fabricated and tested.The thermal impedance of a 10 stack laser diode array is 0 121℃/W.The pitch between two adjacent bars is 1 17mm.The power level of 611W is achieved under the 20% duty factor condition at an emission wavelength around 808nm.展开更多
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 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the financial supports partially by the National Natural Science Foundation of China(22078296,21576240)the Zhejiang Provincial Natural Science Foundation of China (LD21B060001)。
文摘The displacement of residual crude oil and enhanced oil recovery from reservoirs of mature oil fields are challenging worldwide and have received intensive attentions in oil and gas industry.In this work,a novel method for enhanced oil recovery by displacement of oil with bionanofluids was proposed.Microdisplacement hydrodynamics of crude oil in microchannel sand-packed porous media by the bionanofluid were investigated by high-speed imaging.The machine learning models with the extreme gradient boosting(XGBoost) algorithm was developed for the prediction of residual oil saturation during the micro-displacement processes.The residual oil droplets within the porous media after the waterflooding were effectively removed through bionanofluid-flooding,resulting in additional enhanced oil recovery of 39.0%,which is double the recovery achieved by waterflooding at the same displacement velocity.By wavelet-transform image enhancement and the XGBoost algorithm in the machine learning,the residual oil saturations along the porous media were predicted accurately with the mean squared errors of 0.0045 and 0.0030 in the waterflooding and the bionanofluid-flooding,respectively.The results indicated that the machine learning is effective in characterizing the displacement behaviors and the bionanofluid-flooding could be an interesting approach,and thus has potential applications in enhanced oil recovery of waterflooding reservoirs.
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.
基金the National Natural Science Foundation of China(22208320)the Science and Technology Program of Henan Province(212102210044)The Henan Association for Science and Technology Youth Talent Support Program(2022HYTP026).
文摘Combining the advantages of high efficiency,low-pressure drop,and large throughput,the pore arrayenhanced tube-in-tube microchannel(PA-TMC) is a promising microreactor for industrial applications.However,most of the mass transfer takes place in the upstream pore region,while the contribution of the downstream annulus is limited.In this work,helical wires were introduced into the annulus by adhering to the outer surface of the inner tube.Mixing behavior and mass transfer of liquid-liquid twophase flow in PA-TMC with different helical wires have been systematically studied by a combination of experiments and volume of fluid(VOF) method.The introduction of helical wires improves the overall volumetric mass transfer coefficient KLa by up to 133% and the mass transfer efficiency E by up to 117%.The simulation results show that the helical wire brings extra phase mixing regions and increases the specific interface area,while accelerating the fluid flow and expanding the area of enhanced turbulent dissipation rate.Influences of helical wires in various configurations are compared by the comprehensive index I concerning the pressure drop and mass transfer performance simultaneously and a new correlation between KLa and specific energy consumption φ is proposed.This research deepens the understanding of the mixing behavior and mass transfer in the PA-TMCs and provides practical experience for the process intensification of microchannel reactors.
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funded by the National Natural Science Foundation of China(Grant No.52276047)the Open Fund of NationalKey Laboratory of SpacecraftThermal Control(Grant No.NKLST-JJ-202401011)the Beijing Municipal Science&Technology Commission(Grant No.Z231100006123010).
文摘Flow boiling in open microchannels offers highly efficient heat transfer performance and has attracted increasing attention in the fields of heat transfer and thermalmanagement of electronic devices in recent years.However,the continuous rise in power density of electronic components imposesmore stringent requirements on the heat transfer capability of microchannel flow boiling.HFE-7100,a dielectric coolant with favorable thermophysical properties,has become a focal point of research for enhancing flow boiling performance in open microchannels.The flow boiling heat transfer performance ofHFE-7100 was investigated in this study by fabricating micro-nano composite structures on the bottom surface of open microchannels using laser ablation technology.Based on visualization results,a comparative analysis was conducted on the bubble dynamics and flow pattern characteristics of HFE-7100 flow boiling in micronano structured open microchannels(MNSOMC)and smooth-surface open microchannels(SSOMC),to elucidate the enhancement mechanism of micro-nano structures on flow boiling heat transfer in open microchannels.The results indicate that the surface structures and strong wettability of MNSOMC accelerated bubble nucleation and departure.Moreover,bubbles in the channel tended to coalesce along the flow direction,forming elongated slug bubbles with high aspect ratios,which enabled efficient thin film evaporation in conjunction with intense nucleate boiling,thereby significantly enhancing flow boiling heat transfer.Under the experimental conditions of this study,the maximum enhancements in the heat transfer coefficient(HTC)and critical heat flux(CHF)of HFE-7100 inMNSOMC were 33.4%and 133.1%,respectively,with the CHF reaching up to 1542.3 kW⋅m^(−2).Furthermore,due to the superior wettability and capillary wicking capability of the micro-nano composite structures,the significant enhancement in flow boiling heat transfer was achieved without incurring a noticeable pressure drop penalty.
文摘Understanding the complex interaction between heat and mass transfer in non-Newtonian microflows is essential for the development and optimization of efficient microfluidic and thermal management systems.This study investigates the magnetohydrodynamic(MHD)thermosolutal convection of a Casson fluid within an inclined,porous microchannel subjected to convective boundary conditions.The nonlinear,coupled equations governing momentum,energy,and species transport are solved numerically using the MATLAB bvp4c solver,ensuring high numerical accuracy and stability.To identify the dominant parameters influencing flow behavior and to optimize transport performance,a comprehensive hybrid optimization framework—combining a modified Taguchi design,Grey Relational Analysis(GRA),and Principal Component Analysis(PCA)—is proposed.This integrated strategy enables the simultaneous assessment of skin friction,Nusselt number,and Sherwood number,providing a rigorous multi-objective evaluation of system performance.Comparative validation with benchmark results from the literature confirms the accuracy and reliability of the present formulation and its numerical implementation.The results highlight the intricate coupling among flow slip,buoyancy effects,and convective transport mechanisms.Increased slip flow enhances axial velocity,while a higher solutal Biot number intensifies concentration gradients near the channel walls.Conversely,a lower thermal Biot number diminishes the temperature field,indicating weaker heat transfer across the boundaries.PCA results reveal that the first principal component(PC1)accounts for most of the system variance,demonstrating the dominant influence of coupled flow and transport parameters on overall system performance.
基金supported by the Science Foundation of Zhejiang Sci-Tech University(18062299-Y)。
文摘The repeated volume variation of lithium(Li)metal anode(LMA)upon Li^(+) plating/stripping,the volatile interface between Li and the electrolyte,and the incessant growth of Li dendrites on Li metal surface have severely hindered the practical application of Li in constructing high energy-density Li metal batteries(LMBs).Herein,a novel Li host(3D ZnO/CNTs/Cu)featuring ordered microchannels and lithiophilic ZnO species on the inner walls of the microchannels is introduced,which induces the uniform Li^(+) deposition into the microchannels and finally suppresses the formation of Li dendrites.The stable structure of the fabricated 3D Li host can adapt to volume variations upon Li^(+) plating/stripping,thereby enhancing electrochemical performances.Symmetric cells with the 3D ZnO/CNTs/Cu@Li anode exhibited long cycle stability at areal current densities of 0.5 and 2 mA cm^(-2);Full cells maintained a reversible discharge capacity of 105 mAh g^(-1) after 400 cycles at 1C with a capacity retention of 70%.Meanwhile,ex-situ SEM observations proved that the 3D ZnO/CNTs/Cu@Li anode can keep the structural integrity during charging/discharging(or plating/stripping).This work suggested that lithiophilic nanochannels in the Li host can significantly improve the electrochemical performance and safety of LMBs.
基金Project(21271188) supported by the Nature Science Foundation of China
文摘Deposition of diamond inside the trenches or microchannels by chemical vapor deposition （CVD） is limited by the diffusion efficiency of important radical species for diamond growth （H, CH3） and the pore depth of the substrate template. By ultrasonic seeding with nanodiamond suspension, three-dimensional （3D） penetration structure diamond was successfully deposited in cylindrical microchannels of Cu template by hot-filament chemical vapor deposition. Micro-Raman spectroscopy and scanning electron microscopy （SEM） were used to characterize diamond film and the effects of microchannel depth on the morphology, grain size and growth rate of diamond film were comprehensively investigated. The results show that diamond quality and growth rate sharply decrease with the increase of the depth of cylindrical microchannel. Individual diamond grain develops gradually from faceted crystals into micrometer cluster, and finally to ballas-type nanocrystalline one. In order to modify the rapid decrease of diamond quality and growth rate, a new hot filament apparatus with a forced gas flow through Cu microchannels was designed. Furthermore, the growth of diamond film by new apparatus was compared with that without a forced gas flow, and the enhancement mechanism was discussed.
基金the financial support from the Youth Talent Plan of Beijing of China (No. YETP 1087)
文摘Experiments were carried out to investigate the boiling heat transfer characteristics of Al_2O_3-water nanofluids in swirl microchannels under terrestrial gravity and acceleration fields. A centrifuge with a two-meter long rotational arm was used to simulate the acceleration magnitude up to 9 g and three various acceleration directions. Three test sections with different geometric parameters were applied. The volume concentration of Al_2O_3 nanoparticles with an average diameter of 13 nm was varied from 0.07% to 0.1%. The mass flow rate and vapor quality were in ranges of 3–6 kg/h and 0.4–1.0%, respectively. The effects of the mass flow rate, microchannel aspect ratio,vapor quality, nanoparticle volume concentration, and acceleration direction and magnitude were analyzed in a systematic manner. Experimental results showed that the acceleration direction and magnitude had significant influences on the boiling heat transfer. The heat transfer under configuration C was found to be superior to that under configurations A and B. Moreover, the heat transfer coefficient increased with increases of the mass flow rate and the volume concentration and decreased with the aspect ratio.
基金supported by The Murata Science Foundation[grant numbers 015ME0-031]。
文摘Microchannel heat sinks(MCHSs)are promising thermal solutions in miniaturized or compact devices.Lightweight aspect has been given huge emphasis in recent years.Metal-based materials are commonly used to fabricate MCHSs due to their high thermal conductivity.Consequently,MCHSs are heavy due to the high density of these materials albeit the small footprint of MCHSs.Polymer-based materials are interesting alternatives.Despite their poor thermal conductivity,lightweight feature attracts the interest of researchers.Heat transfer is a conjugate process of heat conduction and heat convection.Poor heat conductions aspect may be compensated through enhancement of heat convection aspects.Although polymer-based materials have been used in microscale heat transfer studies,their focus was not on their feasibility.The present study aims to evaluate the feasibility of polymer-based MCHSs as thermal solutions.The effect of thermal conductivity of fabrication materials,including polymer-based PDMS,PTFE,PDMS/MWCNT,and metal-based aluminum,on the thermal performance of MCHSs was investigated and compared at various inlet flow rate,fluid thermal conductivity,and microchannel ratio at different constant heat fluxes using three-dimensional CFD approach.Results showed that the thermal performance of MCHSs was greatly affected by the heat conduction aspect in which poor heat conduction limited the thermal performance improvement due to enhanced heat convection aspects.This suggests polymer-based materials have the potential for heat transfer applications through thermal conductivity enhancement.This was confirmed in the further analysis using a recently proposed high thermal conductivity polymer-based graphite/epoxy MCHS and a hybrid-based PDMS/aluminum MCHS.
文摘A novel AIN monolithic microchannel cooled heatsink for high power laser diode array is introduced.The high power stack laser diode array with an AIN monolithic microchannel heatsink is fabricated and tested.The thermal impedance of a 10 stack laser diode array is 0 121℃/W.The pitch between two adjacent bars is 1 17mm.The power level of 611W is achieved under the 20% duty factor condition at an emission wavelength around 808nm.
