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Microchannel heat sink is widely applied in high-density heat flux devices for its high efficiency in heat dissipation. However, the most effective geometrical configuration of microchannels for best heat transfer augmentation with least pump power penalty is still unknown. In this research, the heat transfer augmentation in a microchannel heat sink with different shaped periodic reentrant cavities on channel sidewalls are numerically studied. Three different kinds of channel structures are introduced, including convex quarter-circular, concave quarter-circular, and inclined shaped reentrant cavities. The comprehensive performances of the proposed microchannels are compared with that of the smooth straight channel, with respect to the pressure drop, friction coefficient, Nusselt number, and performance factor. The results indicate that the comprehensive performance of the microchannel heat sink with periodic reentrant cavities is superior to the smooth straight channel, because its reentrant cavities can strengthen the mixing of fluids and lower the pressure loss. The proposed microchannels can enhance the heat transfer by 1.7 times, reduce the pressure drop by 3.7%–22.4% at Re 648.2, with the heat transfer entropy production decreased by 15.9%–48.2%. The inclined shaped microchannel has the best overall performance factor among the three proposed channels, which achieves up to 1.59 at Re 648.2. [ABSTRACT FROM AUTHOR]

Plasma technology is based on a simple physical principle. When more energy enters the gas, it ionizes and becomes the fourth state of matter, the energy-dense plasma. The studies carried out within the scope of this study were designed to create microchannels on lamellar glass using an improved redesign of the current plasma arc device, which is the main subject of the paper. The created microchannel is examined at the microscale. Experimental analysis was conducted considering the effect of plasma on the effect of microchannel quality. We performed an experimental design study to determine the optimal parameter levels for improving microchannel quality. The predicted results have been validated with the experimental results. An experimental design study provides useful results, such as information about the distance between the probes, pulse duration, and material temperature, which enhances the channel dimensions. The improved device can be utilized effectively to establish microchannel processing in practice. [ABSTRACT FROM AUTHOR]

Microchannel condensers play an essential role in cryogenic two-phase heat management systems due to their efficient heat transfer characteristics. Thus, it is worth conducting an in-depth study on microscale condensation characteristics of cryogenic fluids. This paper delves into the flow condensation process of methane in microchannels. A two-dimensional transient model with high accuracy for cryogenic fluids has been developed by combining a self-defined program for the source term of the phase transition model. The model fully considers the boundary layer thickness and accurately explores the mesh accuracy. The complete condensation flow patterns are captured for various vapor quality, mass flux, and wall subcooling degrees. The injection flow is a unique flow regime for condensation in microchannels. The decrease in wall subcooling degree and increase in mass flux leads to the separation point at the neck of the injected flow moving towards the exit, while the annular flow region is expanding and the flow pattern transition is lagging. The mass flux improves the heat transfer coefficient more significantly at high vapor quality. During injection and bubble flow, the wall shear stress and local heat transfer coefficient are subject to bouncing and oscillations, which may induce fluctuations in the upstream annular flow. The prediction performance of six classical heat transfer correlations is evaluated. The results indicate that the Nie et al. correlation has the highest comprehensive prediction accuracy with MRD and MARD of -5.00 % and 15.83 %, respectively. [ABSTRACT FROM AUTHOR]

Featured Application: The results of the work may be used in the design of cooling systems for electronic components. Cooling of electronic components is of great importance currently. One of the most important methods of integrated circuit cooling is the use of microchannel heat sinks. The aim of this work is to analyze the cooling capacity of zigzag shaped microchannels. The heat exchange for four different microchannels was tested depending on the flow rate of the cooling liquid (water) and the temperature of the cooled element. The system of differential equations that describe fluid flow and heat transport is presented in the paper. The equations were solved using the finite volume method. The work showed that both the increase in the number of zigzag sections and the increase in the flow velocity cause an increase in the flow resistance. In contrast, an increase in the temperature of the cooled element causes a decrease in fluid viscosity, which results in a decrease in flow resistance. From the point of heat exchange, both the increase in the number of segments, the flow rate, and the temperature of the cooled element increase the cooling capacity of the microchannel. Research shows that zigzag shaped microchannels are excellent cooling elements, especially for geometrically small heat sources such as electronic components. [ABSTRACT FROM AUTHOR]

Flow boiling in microchannels has attracted wide attention due to its excellent heat transfer capability, but flow boiling instability is a huge challenge limiting its application. Instability can lead to a series of problems, such as uneven flow distribution, temperature and pressure drop oscillations. This work proposes a novel asymmetric check microvalve (ACMV) structure, exhibiting high ratio of resistance between the reverse and forward flow. The results show the reverse pressure drop of the ACMV structure is 2.06 times that of the forward pressure drop, and the forward flow resistance of the ACMV structure is 16% smaller than that of the conventional inlet restrictor. In addition, bubble dynamics of an isolated bubble in the generated channel under dual outlet condition was numerically investigated. It is found that the bubble grows symmetrically in the rectangular channel upstream and downstream. The distance of bubble movement downstream in the microchannel with ACMV is three times that of the microchannel with inlet restrictor. The microchannel with ACMV can suppress the backflow of isolated bubble better than microchannel with inlet restrictor. Moreover, the growth of the bubble downstream extends the effective evaporation domain, which contributes to the enhanced bubble growth rate. The ACMV is expected to be a potential replacement for the conventional inlet restrictor, which provides a novel and efficient solution for future heat dissipation from high power devices. [ABSTRACT FROM AUTHOR]

Lithium-ion batteries are the direct power sources of electric vehicles, but their high heat flux density restricts their development. Microchannel heat sinks (MCHS) can assist in heat dissipation to overcome this. The distribution of fluid velocity among microchannels has a considerable effect on the performance of MCHS for a water-cooling lithium-ion batteries system. In this paper, a new microchannel heat sink with high depth to width aspect ratio is proposed and the influence of four different aspect ratios on the distribution of fluid velocity among microchannels and heat transfer performance of MCHS was numerically studied by computational fluid dynamics (CFD). The results showed that at the same inlet flow rate, the larger the aspect ratio of the microchannels, the better the uniformity of the internal fluid velocity. The heat performance of microchannel structures with four different aspect ratios for a water-cooling lithium-ion batteries is further investigated experimentally. Compared with the simulation results of the fluid velocity distribution, the coupling effect between the fluid velocity distribution in the microchannels and the heat dissipation performance of a water-cooling lithium-ion batteries is analyzed. The results fully demonstrated that a larger aspect ratio of the microchannels results in a better heat dissipation performance on the surface of the lithium-ion batteries. Optimizing the aspect ratio of the microchannels to facilitate a relatively uniform velocity distribution to improve heat dissipation performance of the water-cooling system may be a key factor to be considered, which provides a new idea for passive thermal management of batteries. [ABSTRACT FROM AUTHOR]

The automotive industry is increasingly focused on developing more energy-efficient and eco-friendly air-conditioning systems. In this context, CO2 microchannel gas coolers (MCGCs) have emerged as promising alternatives due to their low global warming potential (GWP) and environmental benefits. This paper explores the application of machine learning (ML) algorithms to predict the thermohydraulic performance of MCGCs in automotive air-conditioning systems. Using data generated from an experimentally validated numerical model, this study compares various ML techniques, including both linear and nonlinear regression models, to forecast key performance metrics such as refrigerant outlet temperature, pressure drop, and heat transfer rate. Spearman's correlation was employed to develop performance maps, whereas the R2 and MSE metrics were used to evaluate the models' predictive accuracy. The linear models gave around 70% forecasting accuracy for pressure drop across the gas cooler and 97% accuracy for refrigerant outlet temperature, whereas the nonlinear models achieved more accurate predictions, with an accuracy ranging from 71% to 99%. This implies that nonlinear regression generally performs better than linear regression models in assessing the overall thermohydraulic performance of microchannel gas coolers. This research brings forth new ideas on how ML methods can be applied to enhance efficiency and effectiveness in gas coolers, contributing to the development of more eco-friendly automotive air-conditioning systems. [ABSTRACT FROM AUTHOR]

Samarium oxide (Sm 2 O 3), a quintessential lanthanide oxide, garners significant attention in electrocatalysis and photocatalysis. However, the physicochemical properties of precursors and rare earth oxides are hampered by traditional precipitation reactions, mainly due to the asymmetry of time and space. A new anti-clogging strategy based on pneumatic impingement flow is proposed. Subsequently, nano-sized Sm 2 O 3 powder with an ellipsoidal morphology and a median particle size of 70 nm are prepared using the integration of microchannel reaction and microwave heating. Correlation analysis and morphology evolution mechanism reveal intricate relationships among different variables, emphasizing the importance of achieving balance to effectively control crystal properties. Numerical simulations show that the selective heating of microwave make it significantly superior to conventional. Preliminary economic analysis suggests that producing 1 kg of nano-Sm 2 O 3 can yield $57.56. The combination of microchannels and microwaves offers a pathway for the high-value utilization of rare earths and holds significant industrial application prospects. [ABSTRACT FROM AUTHOR]

This study investigates an oil/water two-phase system to assess the potential efficacy of a novel passive mixer in enhancing the liquid-liquid interfacial area within a micro-channel contactor. In this system, two fluids are introduced into a microchannel with a diameter of 800 μm and a length of 20 cm, which is equipped with a stainless-steel helical wire measuring 250 μm in diameter. Throughout the experiments, both fluids are supplied at equal flow rates, and the dominant forces, including attachment and detachment forces, are examined. The results reveal a critical Weber number of 3.8 × 10−³, at which the first detachment occurs. A comparison between microchannels with and without the passive micromixer demonstrates that greater slug breakup occurs in the system incorporating the helical wire micromixer. This innovative configuration results in a significant reduction in slug/droplet size compared to a microchannel without a barrier, decreasing from approximately 600 μm to 390 μm at a flow rate of 0.8 mL/min. Additionally, a flow map is presented, illustrating three distinct flow regimes: flow contains long slug, Slug-droplet flow, and droplet flow regimes, with the droplet flow regime covering the largest area. The findings indicate that the implementation of this innovative passive mixer substantially increases the interfacial area, providing significant advantages for mass transfer applications. [ABSTRACT FROM AUTHOR]

Summary Diffuse large B‐cell lymphoma (DLBCL) represents the most prevalent aggressive B‐cell lymphoma. The group is heterogeneous and the outcome is variable. A variety of approaches have been employed with the objective of improving the stratification of DLBCL patients according to their prognosis, based on the cell of origin. Recently, distinct genetic subtypes of DLBCL have been identified. Given the importance of cell migration in immune cells, the objective of this study was to ascertain whether different genetic subtypes of DLBCL exhibit disparate migration abilities. MCD‐ and EZB‐type DLBCL cell lines were subjected to testing to ascertain their basal velocity in straight microchannels and their ability to overcome tight constrictions of 2 μm. The EZB‐type cell lines showed superior basal migration velocity and constriction passage time, and a similar trend was observed in live cell imaging of native human DLBCL tissue. In addition, MCD‐type DLBCL exhibited significantly elevated levels of nuclear lamin A/C, which is responsible for the stiffness of the nuclear envelope and could thus explain the disparate migration behaviours observed among these subtypes. Our study suggests that different genetic subtypes of DLBCL may not only influence the outcome after therapy but also the motility of the tumour cells. [ABSTRACT FROM AUTHOR]

To enhance the cooling capacity of traditional microchannels for high heat flux electronic devices, a microchannel design with staggered semi-elliptical ribs is proposed in this paper. Through numerical simulations, the flow characteristics of the designed microchannel are compared with those of a smooth one, and the effects of rib width (Wr), rib height (Hr), and rib length (Lr), on the thermal-hydraulic performance are investigated under laminar flow conditions. The results show that the periodically arranged ribs induce periodic vortices within the microchannel, effectively promoting fluid mixing and enhancing heat transfer. Wr and Hr have similar effects on microchannel performance, with an increase in them leading to an enhanced thermal performance at the expense of deteriorated hydraulic performance. Additionally, Lr has a comparatively weaker influence, with both the heat transfer and flow resistance initially growing with increasing Lr and then declining. To strike a balance between the two performances, a multi-objective optimization on the three geometrical parameters is conducted at a Reynolds number (Re) of 440. Combined with simulation data, artificial neural networks are trained as surrogate models, and a multi-objective genetic algorithm is employed to derive the Pareto front. Using the TOPSIS decision-making method, an optimal compromise solution is determined as Wr = 0.2415 mm, Hr = 0.0976 mm, and Lr = 0.6486 mm. Performance testing on the optimized microchannel reveals that it exhibits high heat transfer, middle flow resistance, and excellent overall performance, with the performance evaluation criterion (PEC) falling between 1.572 and 1.723 within the Re range of 220–660. [ABSTRACT FROM AUTHOR]

Split‐and‐recombine (SAR) microreactor is an advanced reactor for chemical process intensification. Bubble flow in the SAR microchannel is an important phenomenon that affects reaction efficiency, however drew little attention before. This study aims to explore the underlying mechanisms of bubble splitting, retraction, and breakup behaviors in a compact SAR microchannel. Two breakup flow patterns, unilateral flow and unilateral alternate flow were identified with symmetric or asymmetric splitting, respectively. Mechanism analysis indicates that the splitting symmetry issue is related to liquid slug size, viscous effect and novel retraction behavior of a splitting filament. The retraction is induced by the interconnection and unequal pressures between the splitting filaments. The correlation between normalized breakup time and Ca number confirms the Capillary‐pressure breakup mechanism for the splitting gas filaments. Two empirical correlations for the two breakup flow patterns were proposed, which illustrate the significant contribution of bubble retraction to the breakup degree. [ABSTRACT FROM AUTHOR]

Due to size limitations, the gas–liquid absorption capacity of a single microchannel is limited, making it difficult to achieve large‐scale CO2 capture. Therefore, the parallel microchannels combining the advantages of high efficiency and large throughput stand out. However, when the operating condition is high gas–liquid flow rate ratio, the liquid phase between bubbles almost disappears after multiple distributions, which affects the amount of gas–liquid absorption. In this study, the numbering‐up of the asymmetric parallel microchannels in the gas–liquid absorption process was investigated by splitting the liquid feed stream in two. The flow patterns under different operating conditions were obtained. The flow and distribution of gas–liquid two‐phase flow were investigated, and the reason of the distribution deterioration caused by appearance of long slug bubbles was explained by the pressure drop distribution. The total liquid mass transfer coefficient and bubble residence time were derived and obtained, and the mass transfer was further discussed. [ABSTRACT FROM AUTHOR]

This study presented a numerical simulation of heat transfer characteristics in a microchannel evaporator for a transcritical CO2 air conditioning system, and the simulated results have been validated by the experimental data. The evaporator consists of 6 passes with 29 flat tubes. Each flat tube has 10 microchannels having a 1.2 × 0.6 mm cross-section. The two-phase flow was simulated in the range of evaporation temperatures from 5 to 15 °C; the mass flow rates of 24.16, 30, and 34.96 g/s; and inlet vapor qualities of 0.5, 0.61, and 0.75, respectively. The results show that the two-phase flow with the evaporative temperature at the inlet of 5, 10, and 15 °C became superheated at the 3rd, the 4th, and the 5th pass, respectively. At the evaporation temperature of 15 °C, the heat transfer coefficient decreases from 8.1 to 3.6 kW/m2 K as the vapor quality increases from 0.75 to 1. With the mass flow rate of 30 g/s, in the tube length range from 0 to 1.1 m, the heat flux achieved around 1.55 kW/m2. The numerical cooling capacity gets the maximum value of 2.85 kW at the evaporative temperature of 10 °C. The numerical results are in good agreement with those obtained from the experimental results and the other published results, with a deviation of less than 10%. [ABSTRACT FROM AUTHOR]

This paper communicates with the entropy generation analysis of Eyring Powell fluid flow through a microchannel in the thermal heat source coefficients. The dimensionless equations of the physical features along with the boundary conditions which are solved by using Homotopy analysis method. An expression of dimensionless velocity and dimensionless temperature are used to determination of the entropy generation number and bejan number explicitly. By using the analytical expression the thermal performances can be improved through the effects of magnetic field, viscous heating, joule heating and convective condition, futhermore it is explaining with graphically. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this paper is to analyze the mechanism of nanofluid enhanced heat transfer in microchannels and promote the application of nanofluids in industrial processes such as solar collectors, electronic cooling and automotive batteries. Design/methodology/approach: The two-phase lattice Boltzmann method was used to calculate the flow and heat transfer characteristics of Al2O3 nanofluids in a microchannel at Re = 50. By comparing the simulation results of pure water, nanofluids without calculated nanoparticle-fluid interaction forces and nanofluids with calculated nanoparticle-fluid interaction forces, the effects of physical properties improvement and interaction forces on flow and heat transfer are quantified. Findings: The findings show that the nanofluid (φ = 3%, R = 10 nm) increases the average Nusselt number by 22.40% at Re = 50. In particular, 16.16% of the improvement relates to nanoparticles optimizing the thermophysical parameters of the base fluid. The remaining 6.24% relates to the disturbance of the thermal boundary layer caused by the interaction between nanoparticles and the base fluid. Moreover, the nanoparticle has a negligible effect on the average Fanning friction factor. Ultimately, we conclude that the nanofluid is an excellent heat transfer working medium based on its performance evaluation criterion, PEC = 1.225. Originality/value: To the best of the authors' knowledge, this research quantifies for the first time the contribution of nanoparticle-liquid interactions and nanofluids physical properties to enhanced heat transfer, advancing the knowledge of the nanoparticle's behavior in liquid systems. [ABSTRACT FROM AUTHOR]

The researchers explored the free convective flow of a hybrid nanofluid in a vertical microchannel with a rectangular cross‐section. Notably, both channel walls were heated alternately, and a transverse magnetic field was applied across the channel. The channel walls had unique properties, one of which was nonslip and the other was exceedingly hydrophobic. The major purpose was to investigate the effects of magnetism and superhydrophobicity on important flow parameters. The differential equations in the investigation were solved, producing accurate results. The study yielded some significant discoveries. First, when heated, the magnetic parameter reduced skin friction on both sides. Second, in both heating conditions, the magnetic field reduced flow rate and velocity. The flow rates in the two reported situations were similar at a crucial temperature jump coefficient. Furthermore, for low‐temperature jump coefficients, heating the superhydrophobic side reduced the Nusselt number whereas heating the nonslip side had no magnetic effect. The percentage change in the value of Nusselt number and velocity decreases continuously with increase in nonlinear density variation with temperature (NDT) parameter and magnetic parameter. The percentage increases in the value of skin friction with increase in temperature jump and slip length but decrease in the percentage of skin friction for the effect of magnetic term and NDT parameter. As the NDT parameter increases, the velocity percentage rises to 50.59% when the superhydrophobic surface is heated and to 84.30% when the nonslip surface is heated. The temperature jump is statistically significant for the value of the Nusselt number and skin friction for the no‐slip surface condition. These discoveries have practical consequences for the design and management of both tiny and large‐scale systems, with possible applications in microfluidics, microelectronics, nanoscience, and nanotechnology. [ABSTRACT FROM AUTHOR]

The formation of double-emulsions or core/shell microdroplets in microchannels, essential for various chemical applications, traditionally relies on costly and time-consuming laboratory methods. In this regard, computational fluid dynamics (CFD) and artificial neural network (ANN) techniques were employed. The present study developed ANN models to predict the relationship between shell thickness and double-emulsion size in a double-T microchannel, using two datasets comprising 180 experimental and CFD data points. Assessing this relationship involved analyzing various input factors, including the Capillary, Weber (case A), and Reynolds numbers (case B) of the core, shell, and continuous phases. Among twelve training algorithms and four activation functions, the Levenberg–Marquardt (LM) algorithm with sigmoidal activation functions (Tansig and Logsig), in contrast to the linear activation functions (Poslin and Purelin), achieved the highest predictive accuracy. Additionally, the predictive accuracy of ANN models was found to be significantly improved when trained using a combination of capillary and Weber numbers, as opposed to models trained only using capillary, Weber, and Reynolds numbers. The optimal neural network architectures were [10 5] neurons for case A (tansig and logsig) and [8] neurons for case B (tansig), yielding coefficients of determination (R2) of 0.99 and 0.98, respectively. These models demonstrated high precision and effective generalization, evidenced by statistical measures such as R2, MSE, RMSE, AAD, %AARD, and computational time. Moreover, their ability to generalize within the training dataset further substantiates their predictive capacity. [ABSTRACT FROM AUTHOR]

Copyright of FME Transactions is the property of University of Belgrade, Faculty of Mechanical Engineering and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Flow boiling in microchannels with porous walls has received extensive attention in recent years. Compared with the emphasis on heat transfer, there is a lack of research on the effect of the porous wall structures on the pressure drop characteristics. In this study, systematic experiments are performed to measure the pressure drop of water-vapor two-phase flow in five microchannels with copper foam fins, which consist of nine or six channels and fins of copper foam. The porosities of the foam fins range from 0.78 to 0.82 and ratios of fin width to channel width range from 0.5 to 2. The channels are approximately 0.5 or 1 mm in width and 1 mm in height. Both adiabatic and flow boiling experiments are conducted with water at mass fluxes ranging from 66 to 407 kg/(m2 s). In the adiabatic experiments, the average quality in channels is between 0.017 and 0.846. In the flow boiling experiments, the outlet quality of channels is between 0.040 and 0.863. Slug flow, churn flow, annular flow, and wispy-annular flow are observed in adiabatic experiments. A two-phase frictional pressure drop correlation based on the Lockhart-Martinelli model is developed for copper foam fin microchannels by introducing the effects of the mass flux, porosity, ratio of fin width to channel width, and heating condition step by step. The mean absolute percentage errors of the new correlation are 7.53% for 325 data points under adiabatic conditions and 5.51% for 268 data points under flow boiling conditions, respectively. This work provides insight into the correlations of frictional pressure drop in microchannels with porous walls. [ABSTRACT FROM AUTHOR]

Copyright of Chemical Engineering (China) / Huaxue Gongcheng is the property of Hualu Engineering Science & Technology Co Ltd. and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Engineering for Thermal Energy & Power / Reneng Dongli Gongcheng is the property of Journal of Engineering for Thermal Energy & Power and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

A numerical simulation is conducted to examine the impact of heat source on reactive dynamics of catalytic nanolubricant flow through a horizontal microchannel with convective boundary conditions. The ZnO–SAE50 nanolubricant is important as it reduces the wear in components such as shafts, gaskets, piston bores, and valve mechanisms, offering advantages not commonly observed with other nanofluids. Suitable dimensionless variables are employed to transform the governing equations into a set of ordinary differential equations. The proper boundary conditions are utilized to obtain the numerical results. The results are acquired utilizing Runge–Kutta–Fehlberg fourth, fifth-order method, and validated with the existing solutions. Enhancing the heat source improves the thermal field, thereby boosting the thermal conductivity of the nanolubricant, facilitating improved heat absorption and transmission within the system. Homogeneous-heterogeneous intensities minimize the concentration which improves lubrication efficiency, and optimize heat transfer performance. Further, the drag force decreases with nanoparticle volume fraction and the heat transfer rate is enhanced with the increase in heat source parameter. This study is the first to investigate the ZnO–SAE50 nanolubricant flow in a horizontal microchannel with reactive catalytic reactions and heat sources. The results significantly contribute to improved heat transfer, lubrication, and efficiency across various advanced technological applications like microelectronics, automotive, small-scale heat exchangers, aerospace, and renewable energy.

The purpose of this work is to investigate the effect of thermal radiation on convective heat transfer for an electrically conducting hybrid nanofluid moving perpendicularly through a microchannel with parallel plates heated under isothermal conditions, while subjected to a transverse magnetic field. In this case, one surface exhibited a superhydrophobic slip and temperature jump, whereas the others did not. The objective of the study was to determine the impacts of thermal radiation, heat generation, and magnetism on the volume flow rate, velocity, and bulk temperature when either surface is heated by a constant wall temperature. Our findings reveal that the radiation parameter significantly influences both the Nusselt number and skin friction differently depending on the surface conditions, while also reducing flow rate and bulk temperature. The heat generation parameter similarly affects these variables but varies with the type of surface being heated. Additionally, both the velocity and temperature profiles increase with the porosity parameter and heat generation coefficient, regardless of the heated surface. Statistical analysis confirms the significance of magnetic and heat generation parameters in determining skin friction and the Nusselt number, and streamlines and isotherms illustrating the effects of thermal radiation and magnetism on two different hybrid nanofluids when heated on nonslip and superhydrophobic surfaces were provided. These insights provide valuable information for the design and maintenance of mini- and microdevices in the fields of nanoscience and nanotechnology.

Abstract This study investigates an oil/water two-phase system to assess the potential efficacy of a novel passive mixer in enhancing the liquid-liquid interfacial area within a micro-channel contactor. In this system, two fluids are introduced into a microchannel with a diameter of 800 μm and a length of 20 cm, which is equipped with a stainless-steel helical wire measuring 250 μm in diameter. Throughout the experiments, both fluids are supplied at equal flow rates, and the dominant forces, including attachment and detachment forces, are examined. The results reveal a critical Weber number of 3.8 × 10−³, at which the first detachment occurs. A comparison between microchannels with and without the passive micromixer demonstrates that greater slug breakup occurs in the system incorporating the helical wire micromixer. This innovative configuration results in a significant reduction in slug/droplet size compared to a microchannel without a barrier, decreasing from approximately 600 μm to 390 μm at a flow rate of 0.8 mL/min. Additionally, a flow map is presented, illustrating three distinct flow regimes: flow contains long slug, Slug-droplet flow, and droplet flow regimes, with the droplet flow regime covering the largest area. The findings indicate that the implementation of this innovative passive mixer substantially increases the interfacial area, providing significant advantages for mass transfer applications.

The use of microchannel heat sinks is one of the most popular methods for cooling electronic components. In recent years, fractal microchannels have attracted researchers' attention, leading to increased heat transfer and reduced pressure drop compared to parallel microchannels. In this study, two hybrid nanofluids under laminar flow conditions are used for cooling inside microchannels, and simulations are conducted using COMSOL Multiphysics software. Parameters such as pumping power, maximum temperature, and performance evaluation coefficient are investigated for two hybrid nanofluids, Fe3O4-MoS2 and Fe3O4-Al2O3 (mixed 50%-50% and with a volume fraction of 1% for each nanoparticle). The results indicate that the thermal performance of Fe3O4-MoS2 hybrid nanofluid is superior, leading to a 0.5% improvement in the maximum temperature of the heat sink. On the other hand, the use of this hybrid nanofluid increases pumping power by 9% inside the microchannel. Ultimately, the overall system performance is enhanced with the use of both hybrid nanofluids, and the Fe3O4-MoS2 hybrid nanofluid improves the overall system performance by 3.2%, providing better performance and making it more suitable for cooling microchannel heat sinks.

Abstract This study presented a numerical simulation of heat transfer characteristics in a microchannel evaporator for a transcritical CO2 air conditioning system, and the simulated results have been validated by the experimental data. The evaporator consists of 6 passes with 29 flat tubes. Each flat tube has 10 microchannels having a 1.2 × 0.6 mm cross-section. The two-phase flow was simulated in the range of evaporation temperatures from 5 to 15 °C; the mass flow rates of 24.16, 30, and 34.96 g/s; and inlet vapor qualities of 0.5, 0.61, and 0.75, respectively. The results show that the two-phase flow with the evaporative temperature at the inlet of 5, 10, and 15 °C became superheated at the 3rd, the 4th, and the 5th pass, respectively. At the evaporation temperature of 15 °C, the heat transfer coefficient decreases from 8.1 to 3.6 kW/m2 K as the vapor quality increases from 0.75 to 1. With the mass flow rate of 30 g/s, in the tube length range from 0 to 1.1 m, the heat flux achieved around 1.55 kW/m2. The numerical cooling capacity gets the maximum value of 2.85 kW at the evaporative temperature of 10 °C. The numerical results are in good agreement with those obtained from the experimental results and the other published results, with a deviation of less than 10%.

Zirconia (ZrO2) ceramic has excellent mechanical properties and superior chemical stability, making it widely used in aerospace, microelectronics, biomedicine, and mechanical manufacturing. However, due to its difficult-to-machine characteristics, traditional machining methods struggle with fabricating large-aspect-ratio (LAR) microchannels in zirconia ceramics. This study compares direct laser machining (DLM) and waterjet-assisted laser micromachining (WJALM) in preparing LAR zirconia microchannels, focusing on surface morphology, heat-affected zones, microhardness, chemical and phase composition. Subsequently, parameter experiments of WJALM were carried out to achieve superior machined quality LAR zirconia microchannels by assessing the geometric profile and ablation-area-ratio. Experimental results indicated that WJALM significantly surpasses DLM, achieving a 46 % decrease in areal surface roughness (Sa), WJALM reduced the heat-affected zone depth by approximately 37 % compared to DLM. The WJALM process also enhanced the ablation-area-ratio by 61 %, achieving superior machining quality under optimized conditions of 27 W laser power, 100 mm/s scanning speed, and 8 m/s waterjet velocity.

Improving machinability of various difficult-to-cut materials has become essential in recent years. Out of several parameters, enhancing the delivery method of cutting fluids enhances machinability. Several researchers have previously found that utilising the Minimum Quantity Lubrication technique for cutting fluid delivery has had beneficial effects. Nevertheless, a significantly persisting problem is the ineffective penetration of cutting fluid in certain zones in the chip-tool interface. Microchannel fabrication on cutting tools may help cutting fluids penetrate the chip-tool heat generation zone effectively. However, micro-channelling may also increase the stress concentration on the cutting tool, thus it may promote catastrophic failure. This article aims to discuss the effect of creating a single microchannel on tool rake surfaces to improve the penetrability of the cutting fluid while also determining the change in the tool’s stability. Diversifying the shape of the microchannel by keeping its width unwavering, and changing its nearness from the principle cutting edge, simulations were performed. Further investigations reveal that incorporating microchannels can have a positive impact on cutting fluid delivery without sabotaging the tool’s strength. This inadvertently may help in effective cooling, lubrication and protection of the cutting tool. [ABSTRACT FROM AUTHOR]

Understanding flow characteristics of fluid near rough contact is important for the design of fluid-based lubrication and basic of tribology physics. In this study, the spreading and seepage processes of anhydrous ethanol in the interface between glass and rough PDMS are observed by a homemade optical in-situ tester. Digital image processing technology and numerical simulation software are adapted to identify and extract the topological properties of interface and thin fluid flow characteristics. Particular attention is paid to the dynamic evolution of the contact interface morphology under different stresses, the distribution of microchannels in the interface, the spreading characteristics of the fluid in contact interface, as well as the mechanical driving mechanism. Original surface morphology and the contact stress have a significant impact on the interface topography and the distribution of interfacial microchannels, which shows that the feature lengths of the microchannels, the spreading area and the spreading rate of the fluid are inversely proportional to the load. And the flow path of the fluid in the interface is mainly divided into three stages: along the wall of the island, generating liquid bridges, and moving from the tip side to the root side in the wedge-shaped channel. The main mechanical mechanism of liquid flow in the interface is the equilibrium between the capillary force that drives the liquid spreading and viscous resistance of solid wall to liquid. In addition, the phenomenon of "trapped air" occurs during the flow process due to the irregular characteristics of the microchannel. This study lays a certain theoretical foundation for the research of microscopic flow behavior of the liquid in the rough contact interface, the friction and lubrication of the mechanical system, and the sealing mechanism. [ABSTRACT FROM AUTHOR]

Abstract Microchannel heat exchangers have become the preferred choice in contemporary technologies like electronics, refrigeration, and thermal management systems. Their popularity stems from their compact design and exceptional efficiency, which outperform traditional heat exchangers (HE). Despite ongoing efforts, the optimal microchannels for enhancing heat management, minimizing pressure drop, and boosting overall performance have yet to be identified. This study seeks to deepen our understanding of heat transmission and fluid dynamics within a cross-flow microchannel heat exchanger (CFMCHE). Utilizing numerical modeling, it examines how various physical aspects—such as channel geometry, spacing between channels, the number of channels, and the velocity at the inlet—affect key performance indicators like pressure drop, effectiveness, Nusselt number, and overall efficiency. To enhance the design, we analyze six unique shapes of crossflow microchannel heat exchangers: circular, hexagonal, trapezoidal, square, triangular, and rectangular. We employ the Galerkin-developed weighted residual finite element method to numerically address the governing three-dimensional conjugate partial differential coupled equations. The numerical results for each shape are presented, focusing on the surface temperature, pressure drop, and temperature contours. Additionally, calculations include the efficacy, the heat transfer rate in relation to pumping power, and the overall performance index. The findings reveal that while circular shapes achieve the highest heat transfer rates, they underperform compared to square-shaped CFMCHEs. This underperformance is largely due to the increased pressure drop in circular channels, which also exhibit a 1.03% greater reduction in effectiveness rate than their square-shaped counterparts. Consequently, square-shaped channels, boasting a performance index growth rate of 53.57%, emerge as the most effective design among the six shapes evaluated. Additionally, for the square-shaped CFMCHE, we include residual error plots and present a multiple-variable linear regression equation that boasts a correlation coefficient of 0.8026.

Abstract Metallic microfluidic devices made from powder-bed additive manufacturing systems have received increasing attention, but their feasible channel geometry and complexity are often limited by lack of an effective approach to removing trapped powder particles within the channels or conduits of the sintered parts. Here, we present an innovative approach to fabricating long serpentine, high-aspect-ratio submillimeter channels made of stainless steel 316L (SS) by binder jet printing (BJP) and liquid-phase sintering. We leverage the unique nature of the BJP process, that is printing and consolidation steps are decoupled, enabling us to join two or more parts during the sintering step. Instead of constructing the channel device as a single part, we print multiple parts for easy powder removal and later join them to form enclosed channels. The key innovation lies in adding sintering additives like boron nitrides (BN) to the SS stock powder—at the SS/BN interfaces, liquid phase is locally generated at temperature much lower than the SS melting temperature, facilitating the bonding of the multiple parts as well as the consolidation of parts for near-full density. We systematically vary the sintering temperature to show how it affects the joining quality and the channel shape distortion. The joining quality such as the fracture strengths of the joined samples is measured by a pull test while the shape distortion is characterized by various imaging techniques. The feasibility of the proposed approach is demonstrated by fabricating a 400-mm-long, fully enclosed serpentine channel with a rectangular cross-section of 0.5 mm in width and 1.8 mm in height. The pressure drop across this 3D-printed SS serpentine channels is measured for air flow and compared to a standard gas flow model, showing that the device is free of leakage or clogs.

This innovative study investigates the flow of ternary hybrid nanofluid containing gyrotactic microorganisms in microchannel. The magnetic field, thermophoresis, and Brownian motion effects are analyzed. The transformation of the PDEs system into ODEs is carried out by using the group transformation method. The innovative findings examine the Newtonian and non-Newtonian models derived from the system of ODEs. Several graphs illustrate how different parameters affect the velocity profile, temperature, concentration, and microorganisms. The power-law index value increases the fluid flow velocity by about 9% at n = 3, 36% at n = 4 relative to the case of n = 2.5 at the center of the boundary layer. Moreover, the ternary hybrid nanofluid exhibits a greater temperature compared to the nanofluid. The current results are compared to the researchers' findings to confirm the validity of the obtained results. When the Prandtl number is between 6 and 10, the Nusselt number reaches 45.49%.

With the rise of third-generation semiconductors, electronic devices are evolving towards high-power, miniaturization, and integration. Traditional heat dissipation technologies are no longer sufficient to meet the heat dissipation requirements of high heat flux in third-generation semiconductor devices. Temperature accumulation has become a major cause of device failure. Diamond-based materials have excellent thermal properties. Efficient heat dissipation technology based on these materials has become a key direction to solve the high heat flux dissipation problem. This article summarizes the development of diamond-based materials and the main methods for preparing surface microchannels. It reviews the application and development trends of diamond-based materials in the field of efficient heat dissipation. The development and application of diamond-based materials for efficient heat dissipation technology can provide technical support for addressing the problem of high heat flux dissipation.

The development of microchannel manufacturing technology has led to a growing interest in using them as heat exchangers. Microchannels are used to control the temperature of equipment and components that generate a high amount of heat flux. Heat transfer can be further increased by dispersing particles (nano-sized particles) with a low volume fraction into the base fluid (nanofluid). A nanofluid can change the thermophysical properties of a base fluid and improve its thermal performance. The purpose of this study was to examine the heat transfer characteristics of oil-based nanofluid within wavy microchannels in series and parallel arrangements of microchannels. In order to examine the performance of each microchannel separately and to make it easier to draw their diagrams, they are named 1 and 2. Experiments were performed on TiO2 and SiO2 oil-based nanofluids in volume fractions of 0.05 and 0.1, flow rates of 0.5, 1.0, and 1.5 lit/min, and inlet temperatures of 40°C, 45°C, 50°C, 55°C. The results show an increase in the Nusselt number of the base fluid up to 41.8% in the series arrangement and also a decrease in the surface temperature in the series arrangement compared to the parallel arrangement. Also, TiO2 and SiO2 nanofluids with a volume fraction of 0.1 caused the highest increase in heat transfer, up to 56% and 52.7% in parallel arrangement and up to 45.8% and 42% in series arrangement compared to the base fluid, respectively. The pressure drop of the test section in series arrangement was up to 82.1% higher than parallel.

The objective of this review article is to provide a comprehensive analysis of the latest research on microchannel heat sinks, with a particular focus on single-phase flow, flow boiling, and coating microchannels. The review aims to highlight the progress made in this field and identify the challenges that need to be addressed to promote the widespread adoption of microchannel heat sinks. The review article examines the research on microchannel heat sinks and analyzes the findings related to single-phase flow, flow boiling, and coating microchannels. The analysis of single-phase flow in microchannels covers the impact of various parameters, including channel size, fluid properties, and flow conditions, on the heat transfer rate. The analysis of flow boiling in microchannels includes the identification of the potential advantages and challenges associated with this technique, as well as the strategies developed to mitigate these issues. The analysis of coating microchannels examines the effects of surface coatings on flow behavior and heat transfer performance. The review finds that microchannel heat sinks have gained significant attention due to their potential for high heat transfer rates in a compact size. The analysis of single-phase flow reveals that the heat transfer rate is proportional to the channel diameter and inversely proportional to the fluid viscosity. Increasing the flow rate results in higher heat transfer rates and pressure drops. The analysis of flow boiling reveals that this technique can significantly increase the heat transfer rate compared to single-phase flow. However, it can also lead to flow instability, wall superheat, and premature drying. The review identifies strategies to mitigate these issues, including using different surface coatings, enhancing nucleation, and optimizing channel geometry. The analysis of coating microchannels shows that coatings can alter the surface energy, wettability, and roughness of the channel walls, affecting the flow behavior and heat transfer performance. Coatings made from materials such as metals, polymers, and self-assembled monolayers have been investigated, and their effects on the flow of boiling heat transfer have been analyzed. The review highlights the need for further research to address the challenges associated with microchannel heat sinks, including flow instability and premature drying. Additionally, the review suggests that there is a need for more comprehensive studies on the effects of different surface coatings on flow behavior and heat transfer performance. Future research can also explore the potential of other materials for coating microchannels and investigate new strategies to optimize channel geometry and enhance nucleation. The review article concludes that the progress made in understanding microchannel heat transfer is significant, but further research is necessary to realize the full potential of microchannel heat sinks.

CO2 laser machining is a cost effective and time saving solution for fabricating microchannels on polymethylmethacrylate (PMMA). Due to the lack of research on the incubation effect and ablation behavior of PMMA under high-power laser irradiation, predictions of the microchannel profile are limited. In this study, the ablation process and mechanism of a continuous CO2 laser machining process on microchannel production in PMMA in single-pass and multi-pass laser scan modes are investigated. It is found that a higher laser energy density of a single pass causes a lower ablation threshold. The ablated surface can be divided into three regions: the ablation zone, the incubation zone, and the virgin zone. The PMMA ablation process is mainly attributed to the thermal decomposition reactions and the splashing of molten polymer. The depth, width, aspect ratio, volume ablation rate, and mass ablation rate of the channel increase as the laser scanning speed decreases and the number of laser scans increases. The differences in ablation results obtained under the same total laser energy density using different scan modes are attributed to the incubation effect, which is caused by the thermal deposition of laser energy in the polymer. Finally, an optimized simulation model that is used to solve the problem of a channel width greater than spot diameter is proposed. The error percentage between the experimental and simulation results varies from 0.44% to 5.9%. [ABSTRACT FROM AUTHOR]

Although methods for generating human induced pluripotent stem cell (hiPSC)-derived motor nerve organoids are well established, those for sensory nerve organoids are not. Therefore, this study investigated the feasibility of generating sensory nerve organoids composed of hiPSC-derived sensory neurons using a microfluidic approach. Notably, sensory neuronal axons from neurospheres containing 100,000 cells were unidirectionally elongated to form sensory nerve organoids over 6 mm long axon bundles within 14 days using I-shaped microchannels in microfluidic devices composed of polydimethylsiloxane (PDMS) chips and glass substrates. Additionally, the organoids were successfully cultured for more than 60 days by exchanging the culture medium. The percentage of nuclei located in the distal part of the axon bundles (the region 3−6 mm from the entrance of the microchannel) compared to the total number of cells in the neurosphere was 0.005% for live cells and 0.008% for dead cells. Molecular characterization confirmed the presence of the sensory neuron marker ISL LIM homeobox 1 (ISL1) and the capsaicin receptor transient receptor potential vanilloid 1 (TRPV1). Moreover, capsaicin stimulation activated TRPV1 in organoids, as evidenced by significant calcium ion influx. Conclusively, this study demonstrated the feasibility of long-term organoid culture and the potential applications of sensory nerve organoids in bioengineered nociceptive sensors. [ABSTRACT FROM AUTHOR]

This paper describes a method for fabricating microfluidic electronics with 3D interconnected networks by direct ink writing (DIW)‐based 3D printing. Existing 3D printing technologies have yet to simultaneously realize 1) direct printing of interconnected multilayered microchannels without supporting materials or post‐processing and 2) integration of electronic elements with microchannels during the process of printing. This research aims to develop a method to fabricate support‐free microchannels consisting of silicone sealant without the collapse of the extruded structure while integrating electronic elements during the fabrication by DIW. The injection of liquid metal into 3D‐printed microchannels allows the formation of electrical connections between 3D conductive networks and the embedded electronic elements, enabling the fabrication of flexible and stretchable liquid metal antenna coils. To demonstrate a practical application, 1) a skin‐attachable radio‐frequency identification (RFID) tag using a commercial skin‐adhesive plaster as a substrate and 2) free‐standing flexible wireless light‐emitting devices with a small footprint (21.4 mm × 15 mm) for potential implantable applications are produced. This technology will offer a new capability to realize the automated fabrication of stretchable printed circuits with 3D configuration of electrical circuits consisting of liquid metals. [ABSTRACT FROM AUTHOR]

Microchannels are widely prepared for application in aerospace, refrigeration and air conditioning. To understand the mechanism of material removal, ablation threshold dependent on scanning speed is investigated, which is related to the effective number of laser pulses and the incubation coefficient. For the smaller number of pulses, the material is removed by weak ablation due to vaporization. For the lager number of pulses, the material is removed by strong ablation due to the combined vaporization and phase explosion. To obtain high-quality microchannel on the K24, the surface morphology is measured by scanning electron microscope (SEM). It is found that morphologies of microchannels are strongly dependent on the laser parameters, especially the laser power and scanning speed have the strongest effect on the morphology. Meanwhile, the oxidation reaction is found on the zone of microchannels. Furthermore, the geometry of microchannel is predicted and compared to that of experimental measured. The results indicate that the predicted geometry is well agreement with those experimental results. Finally, the relationship between material removal rate and laser parameters is investigated. This work not only promotes the recognition of the mechanism of material removal by femtosecond laser on high-temperature alloy, but also presents effective guidance for achieving high-quality machining of microchannel. [ABSTRACT FROM AUTHOR]

In the present numerical simulation, laminar single‐phase and two‐phase nanofluid flows are investigated inside a rectangular microchannel with the vortex generators. Rhombic vortex generators with different attack angles are used for a better mixture of fluid. Water/MgO nanofluid is used as the working fluid in the volume fractions of nanoparticles φ = 0‐4% in Reynolds numbers of Re = 1‐300 at the two‐dimensional space. The presence of vortex generators with attack angles of λ = 0‐45°, and simultaneous investigation of heat transfer and flow hydrodynamic parameters distinguish this research from other similar studies. Obtained results revealed that using nanofluid with higher volume fractions, slip boundary condition on the hot wall, and using vortex generator with higher λ lead to significant enhancement of heat transfer. Also, the value of pressure drop augmentation is caused by the increase of φ and λ is significant at higher Reynolds numbers. Unlike the increase of φ, by increasing Reynolds number, the effect of slip boundary condition becomes considerable on the reduction of entropy generation. The behavior of entropy generation graphs with slip velocity boundary condition on the wall is different from the no‐slip boundary condition at Re = 300. The behavior of average entropy generation is different in the various φ, Reynolds numbers, and λ in the no‐slip boundary condition for single‐phase and two‐phase models. Also, the two‐phase model estimates flow behavior with less irreversibility. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Refrigeration is the property of Journal of Refrigeration Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Refrigeration is the property of Journal of Refrigeration Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Cylindrical column with packed stationary phase is the workhorse of liquid chromatography systems. These stationary phases are commonly classified on the basis of different form factors namely, beads and monoliths for protein chromatography. Monolithic rods are one of the important geometries derived from polymers through complex polymerization schemes with additional requirements such as cross-linkers and specific reaction conditions. To address these practical difficulties and enable ease of fabrication at laboratory scale, acrylic copolymers are hypothesized to perform as a monolithic stationary phase suitable for protein chromatography. The present work proposes a rapid fabrication technique to obtain monolithic rods that could be reconditioned without any of the above additional steps. It is characterized with monolith diameter that could be controlled using acrylic copolymer concentration. Formation of the copolymeric stationary phase inside microchannel led to annular geometry and in turn, demonstrated fabrication of moon-shaped channels (MSCs) for the first time in literature. An online monitoring system facilitated tracer breakthrough analysis with MSCs to report sharp peak front and an estimate of channel void volume. Breakthrough curves with single protein validated the selection of blue dextran as tracer and indicated retention of proteins due to electrostatic interactions on the functional copolymer surface. [ABSTRACT FROM AUTHOR]

The article presents the results of an analytical study of the flow dynamics in a microdiffuser. An expression for the velocity profile is obtained with account for slip effects. The effect of the Knudsen number on the velocity profiles is shown. The effect of the microdiffuser angle on the flow velocity profile and the friction coefficient is analyzed. The opening angle of the microdiffuser was determined, at which slip effects do not affect the velocity profile. [ABSTRACT FROM AUTHOR]

Metallic microfluidic devices made from powder-bed additive manufacturing systems have received increasing attention, but their feasible channel geometry and complexity are often limited by lack of an effective approach to removing trapped powder particles within the channels or conduits of the sintered parts. Here, we present an innovative approach to fabricating long serpentine, high-aspect-ratio submillimeter channels made of stainless steel 316L (SS) by binder jet printing (BJP) and liquid-phase sintering. We leverage the unique nature of the BJP process, that is printing and consolidation steps are decoupled, enabling us to join two or more parts during the sintering step. Instead of constructing the channel device as a single part, we print multiple parts for easy powder removal and later join them to form enclosed channels. The key innovation lies in adding sintering additives like boron nitrides (BN) to the SS stock powder—at the SS/BN interfaces, liquid phase is locally generated at temperature much lower than the SS melting temperature, facilitating the bonding of the multiple parts as well as the consolidation of parts for near-full density. We systematically vary the sintering temperature to show how it affects the joining quality and the channel shape distortion. The joining quality such as the fracture strengths of the joined samples is measured by a pull test while the shape distortion is characterized by various imaging techniques. The feasibility of the proposed approach is demonstrated by fabricating a 400-mm-long, fully enclosed serpentine channel with a rectangular cross-section of 0.5 mm in width and 1.8 mm in height. The pressure drop across this 3D-printed SS serpentine channels is measured for air flow and compared to a standard gas flow model, showing that the device is free of leakage or clogs. [ABSTRACT FROM AUTHOR]

The purpose of this study is to explore the boiling heat transfer performance of microchannel flow under the combination of two enhanced technologies of pin electrodes and phase separation structure. Therefore, a parallel bidirectional microchannel heat sink was proposed to realize the gas-phase separation by switching high and low pressure for the downstream and countercurrent microchannels. Ethanol was taken as an experimental working fluid, while the modified polyvinylidene fluoride (PVDF) was as a gas-liquid phase separation tool. Then the flow boiling experiment was carried out under the conditions of inlet supercooling at 10 °C and effective heat flux range of 48.08 -87.29 kW/m², where other experimental conditions remained the same. Furthermore, the heat transfer enhancement factor of saturated boiling heat transfer coefficient (Fht) was introduced to investigate the boiling heat transfer mechanism in the microchannel under the combination of the number of pores in different phase separation structures (4-hole PSS-1, 6-hole PSS-2, 10-hole PSS-3) (Phase Separation Structure, PSS) and different electric field strengths (200, 400 and 600 V). The results show that the heat transfer performance of the microchannel under the action of the single-phase separation structure and the pin electrodes was effectively improved under the same working conditions, compared with the ordinary microchannel (0 V without electric field and 0-hole PSS-0 without phase separation structure). The number of opening holes shared a strong correlation with the enhanced heat transfer of the phase separation structure. The maximum Fht of the phase separation structure was 1.14 at a heat flux of 80 kW/m², with an increase in the number of opening holes. There was the strengthening effect of the electric field on small or confined bubbles, with small lengths and diameters. An outstanding strengthening was found under the condition of low and medium heat flux, such as the maximum Fht under pin electrodes was 1.20 at a heat flux of 65 kW/m². The heat transfer performance of the microchannel was further improved under the combined role of phase separation structure and pin electrodes, in which the maximum Fht was 1.29. In addition, the electric field was introduced to improve the strengthening effect of the phase separation structure at low heat flux density. The phase separation structure also effectively enhanced the strengthening effect of the electric field at high heat flux density, indicating the synergistic effect. In addition, the comparison was made on the effects of phase separation structure and electric field enhancement on the heat transfer of micro-channel boiling under the condition of mass flow rate (86.11 and 172.11 kg/(m²·s) of the two groups. The results show that the strengthening effect of phase separation during the boiling heat transfer of the microchannel was weakened at the high mass flow rate, compared with the low one. The strengthening effect of the electric field was enhanced, according to the influence of fluid flow rate. And there was little difference in the enhanced effect of boiling heat transfer under the two mass flow rates. The finding can provide a strong reference for the phase separation structure combined with the electric field. [ABSTRACT FROM AUTHOR]

VOF model and user-defined function were applied to simulate the flow boiling process of water in microchannel with V-cavities. The effects of V-cavity asymmetry (ε) and distribution on the bubble growth and detachment and the transition of gas-liquid two-phase flow in microchannel were analyzed. The results show that the magnitude of the V-cavity asymmetry can change the bubble detachment diameter and detachment time. The bubble detachment diameter of the V-cavity with asymmetry ε of 1.0 is 0.063 mm and 0.025 mm smaller than that of the V-cavity with ε of 0 and ε of 0.5, and the bubble detachment time is shortened by 5.20 ms and 2.40 ms, respectively. The transition of gas-liquid two-phase flow from bubbly flow to confined bubble flow is 2.7 mm backward along the flow direction, and the occupied area of the segment annular flow in microchannel is reduced slightly. When the V-cavity with ε of 1.0 has different distribution along the flow direction, the gas-liquid two-phase flow in microchannel presents different characteristics. The V-cavity with increasingly dense distribution can better inhibit the coalescence of bubbles in microchannel without segment annular flow, which can ensure the existence of liquid film near the wall to avoid the local drying for improving the stability and reliability of flow boiling heat transfer in microchannel. [ABSTRACT FROM AUTHOR]

Metal matrix composites (MMC) have found applications in places where the utilization of conventional materials is limited. This also includes areas of micro- and meso-applications. However, micromachining of metal matrix composites by conventional methods poses difficulties due to the heterogeneous nature of the material and the presence of hard reinforcement particles. Micro-ED milling is a versatile micromachining process used to machine hard engineering materials. It employs a simple cylindrical cross-section tool, which is rotated and fed in predefined paths to generate intricate 3D features with good dimensional accuracy and surface finish. In order to study the machining performance of micro-ED milling process on metal matrix composites, micro-ED milling of AA6063-4 wt.% SiC composite fabricated by ultrasonic-assisted stir casting was carried out. The tool feed rate and tool rotation speed are important parameters as they aid in debris evacuation and influence material removal. So, the effect of tool feed rates, tool rotation speeds and discharge energies on the surface morphology and surface roughness of the machined channels were studied. The surface roughness parameters, namely Sa and Sq, were considered for the study. The least surface roughness, Sa and Sq, was observed at 2 µm/s for all the investigated discharge energies. [ABSTRACT FROM AUTHOR]

In this study, a simulation has been performed to investigate the effect of circular perforated pinfins on the performance of microchannel heat sink by varying the number of holes and their locations on the pinfins. A total of ten configurations are considered in this work including a plain microchannel (without pinfin) and a solid pinfin case. The study was conducted on a single-phase flow using deionized water as coolant and the Reynolds numbers range from 150 to 350 when a constant heat flux of 100W/cm2 has been applied at the heated base wall of a heat sink. The results obtained indicate that the location, as well as the number of perforations, affects the heat transfer capacity and pressure drop that occurs in the microchannel. However, the outcomes of the present analysis contradict the findings for thermal airflows when identical cases have been applied to the micro heatsink. According to the present analysis case 1 (perforation at the underside of the pinfin) has the maximum Nusselt number followed by case 2 (perforation at the mid of the pinfin) and case 3 (perforation at the topside of the pinfin) whereas the minimum pressure drop is achieved by case 8 (four equidistant perforations) among pinfin configurations. The highest performance factor is achieved by case 1 at a low Reynolds number while case 6 (perforation at the underside and topside) performs best at a higher Reynolds number. [ABSTRACT FROM AUTHOR]