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The pressure drop at the inlet and outlet of rectangular microchannel is large, and the temperature distribution is uneven; Fractal microchannel is limited by fractal dimension and the number of branches, so its application scope is narrow. A branch and combined-branch microchannel heat sink was designed by combining the advantages of rectangular microchannel and fractal microchannel, and Fluent software was used to numerically simulate its heat dissipation process to study the flow and heat transfer performance when the branch tilt angle inside the microchannel changes. The results show that at the heat flow of 100 W/cm2, when the Re is 970 and the branch tilt angle is 90°, the average temperature of the branch and combined-branch microchannel decreases by 11.9 K, the maximum temperature decreases by 14.2 K, the Nu increases by 85.7%, and the performance evaluation criterion (PEC) is also the best by reaching 1.44. The introduction of branches can increase the heat transfer area inside the microchannel, form a new boundary layer, and generate vortices at the inner side of the branch, effectively improving the heat transfer performance of the microchannel heat sinks, which provides new theoretical basis for optimizing the design of microchannels.

The present study investigates the flow boiling heat transfer and flow pattern of R245fa in a smooth, horizontal microchannel with an inner diameter of 1 mm. The experiments cover a range of mass flux from 300 to 700 kg/m2s and heat fluxes varying between 10 and 94 kW/m2, with corresponding saturation temperature of 23–54 °C. Heat transfer experiment results indicate that the local heat transfer coefficient (HTC) presents two distinct variation trends under different heat and mass flux conditions. In addition, the heat flux is positively correlated with the local HTC at each measure point. Visualization experiment results show that annular flow forms at low vapor quality and significantly influences heat transfer as the primary flow pattern. The flow boiling heat transfer of R245fa in the 1 mm microchannel can be characterized by three regimes: bubble/slug regime, liquid film evaporation regime, and intermittent dryout regime. Thin liquid film evaporation and intermittent dryout during annular flow predominately contribute to heat transfer. Finally, the experimental HTC is compared with five different predictive methods, revealing that the three-zone model proposed by Thome et al. [46] holds immense potential for estimating the local HTC in the microchannel.

Microchannels have attracted significant attention in the thermal management of integrated circuits due to their small geometrical size and high heat transfer efficiency. Motivated by further improving the thermal management capacity of microchannels in multi-cores chips with lower pressure drop penalty, in this paper, a comparative investigation on four different configurations was conducted through numerical simulation for the Reynolds number ranging from 200 to 800 to analyze the comprehensive effects of filling mode and rib arrangement on the flow and heat transfer characteristics, including microchannel completely filled with aligned ribs (MCFAR), microchannel incompletely filled with aligned ribs (MIFAR), microchannel completely filled with staggered ribs (MCFSR) and microchannel incompletely filled with staggered ribs (MIFSR). Moreover, the entropy generation rate is used to estimate the irreversibility of flow and heat transfer based on the second law of thermodynamics. Finally, the performance evaluation criteria (PEC) is adopted to estimate the overall performance. The results show the flow patterns in the MIFAR and the MIFSR are different from those in the MCFAR and the MCFSR due to the incomplete filling mode, which could induce more dramatic disturbance and further break the downstream boundary layer, thus the heat transfer could be enhanced with a lower pressure drop penalty. The analysis of entropy generation rate indicates that entropy generated by heat transfer contributes the majority of the total entropy generation thus enhancing the heat transfer is a more important and effective approach in reducing the irreversibility. Among the four configurations researched, the microchannel MIFAR shows the best overall performance (PEC = 1.76) when Re = 400.

BackgroundAdjacent segmental degeneration after lumbar fusion is one of the common long-term complications after lumbar fusion. With the continuous development of adjacent segmental degeneration, patients who fail conservative treatment often need reoperation to relieve symptoms. In recent years, the technique of bilateral microdecompression through unilateral approach under microchannel has been widely used in the treatment of lumbar degenerative diseases. However, the efficacy of this procedure for adjacent-segment degeneration after lumbar fusion has not been established. Here, we report a case of bilateral microscopic decompression via a unilateral approach through a microchannel in a patient with adjacent segmental degeneration after lumbar fusion.Case reportA 70-year-old male patient was admitted to hospital because of lumbago accompanied by left lower extremity pain, numbness and weakness for 2 years, which aggravated for 2 months. Ten years ago, he underwent PLIF for lumbar spinal stenosis, and recovered well after the operation. According to imaging data and physical examination, the diagnosis was adjacent segmental degeneration after lumbar fusion. Bilateral microdecompression was performed through a unilateral approach under a microchannel. Good clinical outcomes was observed through 1-year postoperative follow-up.ConclusionsThis report reports the successful treatment of a patient with ASD 10 years after lumbar fusion. Bilateral microdecompression via a unilateral approach under a microchannel is a safe and effective method for the treatment of ASD after lumbar fusion with good surgical outcomes.

Microchannel heat sinks play a crucial role in dissipating heat in microelectronic systems in computer data centers. To enhance their thermal performance, this study proposes a combined microchannel design consisting of various cavity shapes and straight ribs, and analyzes its heat transfer and flow performance through numerical simulation. The heat transfer characteristics of microchannel heat sink with different straight rib structures are compared. Moreover, the four parameters including the relative length (α), relative width of the cavity (β), relative length of straight ribs (γ) and relative width of straight ribs (λ) are investigated, and the effects of Reynolds number variation on heat sink Nusselt number (Nu), friction coefficient (f) and thermal enhancement efficiency (η) are studied. The optimization process employs an artificial neural network and a multi-objective genetic algorithm to determine the optimal compromise solution and heat sink model, utilizing the Nusselt number and friction coefficient as evaluation indices. The results show that rectangular rounded straight rib is the straight rib structures with the best comprehensive thermal performance, with an average η approximately 9.7 % higher than that of the non-straight ribbed heat sink model. Furthermore, the variation in the four studied parameters yields distinct effects on the Nusselt number, friction coefficient, and thermal enhancement efficiency. Notably, the optimal performance is achieved when Nu = 13.59679 and f = 0.11855, with corresponding parameter values of α = 0.1575, β = 0.3931, γ = 0.0714, and λ = 1.2149. Ultimately, these results provide valuable insights into the structural optimization of microchannel heat sink cavity and straight rib combination models.

A study of heat emission during the boiling of distilled water and isopropyl alcohol in a microchannel with a size of 12.5 × 3× 0.2 mm3 has been carried out. To calculate heat emission during boiling in the microchannel, the Kutateladze equation for a flat slot with one-sided heating was used, as well as the Kutepov–Sterman dependences for nucleate boiling under conditions of directional fluid motion and the Danilova dependence for calculating heat emission during boiling. It is established that the Kutepov–Sterman equation yields the minimum deviation from experimental data (no more than 25%). [ABSTRACT FROM AUTHOR]

Nanotechnology in recent years helps researcehers to design flow rate and profile in microsized channel via making surface charge heterogenous. This paper numerically simulates the electroosmotic flow inside a microchannel with non-uniform Zeta potential (ZP). The problem is a two-dimensional, incompressible, steady, and laminar channel flow between two parallel plates. The numerical results show that the flow rate changes compared to a constant ZP by ascending, descending, and parabolic modifications of the wall ZP at the mid-length of the microchannel. Results show that flow volume rate increases by microchannel width from 4 mm3/s to 6.5 mm3/s in best condition. [ABSTRACT FROM AUTHOR]

Increasing processing capacity without modifying the size of electronic devices has made thermal management important in the electronic industry. Commercialized thermal management, such as in a conventional air cooling system, is insufficient for electronic devices with high heat flux dissipation. Pool boiling is a better method for heat transfer because it can dissipate a substantial amount of heat at low wall superheats. This study focused on heat transfer enhancement using passive approaches, including nanostructures and microporous sintered surfaces over open microchannel surfaces and microchannels with pin-fins. In the present work, seven structures were studied in pool boiling, wherein experiments elucidated the effects of microchannels, sintered, and pin fins (micropillar) on boiling heat transfer from a copper chip in a pool of degassed water. Boiling performance is ascertained via critical heat flux (CHF) and heat transfer coefficient (HTC). The best heat transfer performance showed a heat flux of 243.75W/cm2 at 15.46°C on the pin-fins chip, which was 1.9 times the heat flux of the plain chip. The highest HTC was 181.03 kW/(m2 oC) at a heat flux of 172.61 W/cm2 for the microchannel with single pin-fins. The HTC enhancement was 2.8 times greater than the plain surface. It was found experimentally that HTC and CHF improved on all modified surfaces compared to the plain copper chip baseline. [ABSTRACT FROM AUTHOR]

Deep filtration is an important technology for the separation of fine particle pollutants in industrial wastewater. The theoretical core of microchannel separation is the interaction between channel interface and pollutants. Here, microchannels with different shapes and sizes were designed by microfluidic technology and the particle migration process in microchannels was visualized by high-speed camera. This paper studied the effects of apparent depth, inlet structure and channel angle of the interception channel on fluid flow and particle interception. When apparent depth of the interception channel was equidistantly distributed, the flow rate in each channel was uniform, but interception efficiency gradually decreased with the increase of apparent depth. Interception efficiency of the first layer was 16.7 %, while for the 14th layer was only 0.4 %. Interception performance of the upper wall of the inlet of the interception channel was substantially higher than that of the lower wall. The smoother the angle between the interception channel and the mainstream channel was, the better the interception performance. When the angle between the upper and lower walls of the inlet and the mainstream channel was 30° and 60°, respectively, interception efficiency was the optimal, and cumulative interception efficiency of the three filtrations was 92.4 %. Additionally, flow rate and interception efficiency of the interception channel increased with decreasing channel angle. The total interception performance of the 30°–45° group was the optimal, and the total split ratio and total interception efficiency were 65.5 % and 85.5 %, respectively. This provides reference for the change of microchannel structure and the mechanism of particle migration and deposition. [Display omitted] [ABSTRACT FROM AUTHOR]

This paper illustrates the design of a piezoelectric acoustic sensor based on AlN to be used for aero-acoustic measurements. A significant prerequisite for such sensors is a large sound pressure level (SPL) and flat frequency response in the auditory band (20 Hz to 20 kHz). That is why this sensor has been designed to measure upto an SPL of 180 dB. The design of the device has been achieved through the MEMS-CAD tool Coventorware. The Si-diaphragm thickness has been optimized for the desired SPL range using Coventorware for three different sizes of the device, namely 1.5 mm × 1.5 mm, 1.75 mm × 1.75 mm and 2 mm × 2 mm. The cavity developed after the diaphragm formation is connected to the exterior environment through a microchannel. The microchannel was designed for low cut-off frequency. The complete frequency response of all the three sensor structures has been determined. Moreover, a comparison has been drawn among the three devices in terms of parameters such as low cut-off frequency, resonance frequency, and sensitivity to find the optimized device size. The low cut-off frequency, resonance frequency, and flat band sensitivity of the optimized device are 35 Hz, 83 kHz, and 170 µV/Pa, respectively. In addition to this, a proposed fabrication process flow of the device has been presented. [ABSTRACT FROM AUTHOR]

Microchannels are small-scale channels with unique properties that make them useful in various fields, such as electronics, biomedical engineering, and chemical engineering. This research paper investigates the effect of microchannel geometry on fluid flow behavior at different values of the Reynolds number. A rectangular microchannel with a pattern of obstructions and water as the working fluid was used in this study. Computational fluid dynamics (CFD) simulations were used to investigate the impact of different channel geometrical configurations and different values of the Reynolds number on fluid flow behavior. The results showed that the channel geometrical configuration and the Reynolds number significantly affect fluid flow behavior. A geometry with increasing obstruction heights led to higher values of pressure drop than the geometry with decreasing obstruction heights. This study provides valuable insights into microchannel flow behavior and can be used for the development of optimized microchannel designs for diverse applications. [ABSTRACT FROM AUTHOR]

Heat sinks of copper foam fin microchannels are developed to deal with cooling challenges. The heat sinks consist of fins made of copper foam and channels. The channels are 0.5 mm in width and 1 mm in height, and the fins are 0.5 and 2.0 mm in width. Flow boiling experiments are conducted using R134a at subcooled and saturated inlet conditions. The heat flux is between 22 and 172 W/cm2, and the mass flux ranges from 264 to 1213 kg/(m2 s). The influence of the quality, the heat flux, and the mass flow rate on the heat transfer coefficient is obtained. It is found that wider fin raises the heat transfer coefficient. A correlation is developed based on heat transfer mechanisms, and it predicts the experimental result with a 12% mean absolute error. Compared with a solid fin microchannels heat sink, the heat transfer coefficient of the copper foam fin microchannels is higher (up to 60%) when the heat flux is lower than 100 W/cm2. The copper foam fin microchannels may enhance the heat transfer coefficient and reduce the pressure drop at the same time. [ABSTRACT FROM AUTHOR]

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

Copyright of China Mechanical Engineering is the property of Editorial Board of China 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.)

The vertical microchannels phenomenon is useful in the cooling process of microelectronic devices, fuel cells and MHD (magnetohydrodynamic) micro-pumps. The understanding of this phenomenon makes these flows crucial in industries and engineering products. Objective of this paper is how Dufour, Soret and chemical reaction affect the characteristics of hybrid nanofluid (engine oil + manganese zinc ferrite ( (MnZnFe 2 O 4) + nickel zinc ferrite (NiZnFe 2 O 4) )) flow in a microchannel with two vertical parallel plates. The irreversibility analysis is considered. The bvp4c solver in MATLAB is implemented to compute the transformed system derived from the equations used to describe the present problem. The heat transfer rate and other physical parameters of relevance near both plates are explained using graphs. It has been observed that as the Brinkman number and Dufour numbers increased, the entropy production rate is significantly changed. It is noticed that there is a reduction in Bejan number with the escalation in volume fraction of NiZnFe 2 O 4 ( ϕ Ni ). The skin-friction factor declined with the rate of 0.03114 at 0 ≤ Mn ≤ 3 (near left plate) and decreased in the friction factor is 2.45896 when ϕ Ni is in the range 0 ≤ ϕ Ni ≤ 0.09 (near right plate). It is detected that when Dufour number (Du ) is at 0 ≤ Du ≤ 0.6 , heat transmission rate cuts down by 0.06935 (near the left plate). Sherwood number risen by 0.043153 (near the left plate) when Soret number (Sr ) is set to 0 ≤ Sr ≤ 0.6 . [ABSTRACT FROM AUTHOR]

This paper presents a numerical analysis of the thermal-flow characteristics for a laminar flow inside a rectangular microchannel. The flow of water through channels with thin obstacles mounted on opposite walls was analyzed. The studies were conducted with a low Reynolds number (from 20 to 200). Different heights of rectangular obstacles were analyzed to see if geometrical factors influence fluid flow and heat exchange in the microchannel. Despite of the fact that the use of thin obstacles in the microchannels leads to an increase in the pressure drop, the increase in the height of the obstacles favors a significant intensification of heat exchange with the maximum thermal gain factor of 1.9 for the obstacle height coefficient h/H = 0.5, which could be acceptable for practical application. [ABSTRACT FROM AUTHOR]

Microparticles with multiple internal chambers hold great promise as drug delivery systems due to their ability to sustain the release of drugs with short half‐lives. However, conventional batch methods used for their fabrication have limitations in terms of encapsulation efficiency and particle size distributions, while microfluidic methods suffer from low production efficiency. Herein, a batch‐microfluidic hybrid method is presented for fabricating poly(DL‐lactic‐co‐glycolic acid) (PLGA) polymeric microparticles with uniformly distributed, multiple inner microchambers. A scalable batch method is utilized for primary water‐in‐oil (W/O) emulsions, combined with a precise microfluidic approach for generating controlled secondary emulsions. This approach results in highly uniform PLGA microparticles with tunable size and improved encapsulation efficiency. Additionally, the effect of polydopamine‐based surface hydrophilic modification of microfluidic channels on drug encapsulation efficiency is investigated, achieving an efficiency of approximately 85%. The prepared multichamber PLGA microparticles exhibit an extended‐release profile without initial burst release, demonstrating their potential for sustained drug delivery in various biomedical applications. [ABSTRACT FROM AUTHOR]

The present paper investigates the flow field and heat transfer in a microchannel with incorporating surface hydrophobicity and considering its thickness. The microchannel is under partial magnetic field (MF), which is applied to the top thermal-insulated wall in Hartmann numbers 0 to 30. The results show that at Ha = 0, viscous dissipation (VD) and heat transfer decrease with increasing slip coefficient. Also, raising the Hartmann number (Ha) increases the friction coefficient. The Nusselt number (Nu) reaches its highest value at Ha = 20 for all cases, but then, as the Ha increases, the average Nu reduces. [ABSTRACT FROM AUTHOR]

In this study, the magnetic field effect on the hydrodynamics and heat transfer of the laminar flow of a nanofluid in a microchannel with one-sided sudden expansion at a low Reynolds number is investigated. The governing equations including mass, momentum, and energy conservation equations are discretized and solved on a staggered grid using the finite difference method by developing a Fortran code. The simulation results show that at a low Reynolds number, no vortex is formed after the step. In the presence of a magnetic field, the friction coefficient decreases with volume fraction. At a volume fraction of 0.04, this reduction in comparison with water at Hartmann numbers of 20 and 40 is 25 and 18 percent, respectively. By applying the magnetic field, the friction factor increases. For nanofluid with a volume fraction of 0.04, the enhancement of average friction factor in comparison with water at Hartmann numbers of 20 and 40 is 176 and 337 percent, respectively. At a low Reynolds number, the magnetic field effect on the Nusselt number is negligible. The Nusselt number decreases with volume fraction. At a volume fraction of 0.04, a reduction of about 12 percent is observed in the Nusselt number in comparison with water. Examining the performance evaluation criteria shows that applying a magnetic field improves the system's performance. At a Hartmann number of 20 and volume fraction of 0.04, an enhancement of about 11 percent in performance coefficient is observed in comparison with the case that the magnetic field is absent. [ABSTRACT FROM AUTHOR]

Numerical and experimental studies were carried out for the analysis of hydrodynamics and volumetric mass transfer coefficient (kLa) in a cross-T junction microchannel for gas–liquid, two phase flow system. Initially, CO2–water hydrodynamics simulation was performed using ANSYS-FLUENT 2021 R2 and volume of fluid technique. Through the numerical simulation, fluctuation in pressure drop with variation in volume fraction was calculated for the slug flow in a 1 mm hydraulic diameter microchannel. After that mass transfer equations were coupled with the flow equations for CO2–ethyl glycol, CO2–water, and CO2–ethyl alcohol systems to understand the mass transfer mechanism using two film theory concepts. Computational fluid dynamics model was validated by comparing results with the experimental data. An empirical co-relation was also developed to measure the bubble length with its position in the direction of fluid flow. CO2 and solvents velocities were 0.21–0.424 m/s for both the phase. Effect of solvents and film thickness (0.01–0.05 mm) on volumetric mas transfer coefficient were investigated at different temperatures range i.e., T = 298.15 K and 303.15 K (experimental approach) and 298.15–318.15 K (numerical approach). The results obtained in numerical simulation and experimental work show that the total volumetric mass transfer coefficient (range 0.1–0.8 1/s) increases with the gas velocity however, it decreases with increasing film thickness (0.01–0.05 mm) and temperature (T = 298.15 K and 303.15 K). The present work gives an advantage over the conventional channel (e.g., packed bed column) and the other type of T-junction microchannel (e.g., symmetric T-junction) by providing a high mixing rate, interfacial area, and high mass transfer rate. [ABSTRACT FROM AUTHOR]

Copyright of Chinese Journal of Refrigeration Technology is the property of Shanghai Society of Refrigeration 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 Shanghai Jiao Tong University (1006-2467) is the property of Journal of Shanghai Jiao Tong University 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.)

The physics of fluid laminar flow through an idealised deutosternum assembly is used for the first time to review predatory feeding designs over 72 different-sized example species from 16 mesostigmatid families in order to inform the finding of new biological control agents. Gnathosomal data are digitised from published sources. Relevant gnathosomal macro- and micro-features are compared and contrasted in detail which may subtly impact the control of channel- or 'pipe'-based transport of prey liquids around various gnathosomal locations. Relative deutosternal groove width on the mesostigmatid subcapitulum is important but appears unrelated to the closing velocity ratio of the moveable digit. Big mites are adapted for handling large and watery prey. The repeated regular distance between deutosternal transverse ridges ('Querleisten') supports the idea of them enabling a regular fluctuating bulging or pulsing droplet-based fluid wave 'sticking' and 'slipping' along the groove. Phytoseiids are an outlier functional group with a low deutosternal pipe flow per body size designed for slot-like microchannel transport in low volume fluid threads arising from daintily nibbling nearby prey klinorhynchidly. Deutosternal groove denticles are orientated topographically in order to synergise flow and possible mixing of coxal gland-derived droplets and circumcapitular reservoir fluids across the venter of the gnathosomal base back via the hypostome to the prey being masticated by the chelicerae. As well as working with the tritosternum to mechanically clean the deutosternum, denticles may suppress fluid drag. Shallow grooves may support edge-crawling viscous flow. Lateral features may facilitate handling unusual amounts of fluid arising from opportunistic feeding on atypical prey. Various conjectures for confirmatory follow-up are highlighted. Suggestions as to how to triage non-uropodoid species as candidate plant pest control agents are included. [ABSTRACT FROM AUTHOR]

This paper theoretically studied pressure drop variation in microchannels having different cross sections (circular, rectangular, square, trapezoidal, triangular, elliptical, parallel plate, co-centric circles, hexagonal, wavy, smoothed or rounded corners cross sections, and rhombus) for single phase Newtonian fluid (gas and liquid) flow. Based on 41 years (approximately) prior literature (1981–till now), 249 articles were studied and number of correlations of pressure drop calculation in microchannels with or without friction factor equation for four cross sections i.e., rectangular, square, circular, trapezoidal, wavy and triangular is collected and also mentioned their limitations at one place. Other than these four cross sections, there is very few experimental/numerical works was present in the literature. A comparable study was performed for laminar as well as turbulent friction factor to calculate the pressure drop with the help of classical theory for gas and liquid flow in microchannels with circular and rectangular cross sections. Results show wonderful outcomes i.e., correlations of laminar pressure drop study can be extendable for transition and turbulent regime in both types (circular and rectangular) of cross sections of microchannels. In different types of flow regime, it is suggested that for each type of cross section (circular and rectangular) we can go for single correlation for gas/liquid system. It is also investigated that the macro channels pressure drop equations can be used for microchannels up to the certain values of Reynolds number. Basically, this paper provides all possible equations of friction factor related to the microchannels that helps to calculate the pressure drop, is collected at one platform also compared their deviation with conventional channels. [ABSTRACT FROM AUTHOR]

Using supercritical CO2 as a heat transfer fluid in microchannel receivers is a promising alternative for tower concentrating solar power plants. In this paper, the heat transfer and flow characteristics of supercritical CO2 in microchannels at high temperature are investigated by numerical simulations. The effects of microchannel structure, mass flow rate, heat flux, pressure, inlet temperature and radiation are analyzed and discussed. The results show that higher mass flow rate obtains poorer heat transfer performance with larger flow resistance of supercritical CO2 in microchannels at high temperature. The fluid and wall temperatures, average heat transfer coefficient and pressure drop all increase nearly linearly with the increases in heat flux and inlet temperature in the high-temperature region. Moreover, high pressure contributes to great hydraulic performance with approximate thermal performance. The effect of radiation on thermal performance is more pronounced than that on hydraulic performance. Furthermore, the optimized structures of inlet and outlet headers, as well as those of the multichannel in the microchannels, are proposed to obtain good temperature uniformity in the microchannels with relatively low pressure drop. The results given in the current study can be conducive to the design and application of microchannel receivers with supercritical CO2 as a heat transfer fluid in the third generation of concentrating solar power plants. [ABSTRACT FROM AUTHOR]

Abstract This article presents mixed convection of radiating and reacting Casson nanofluid in microchannel filed with a saturated porous medium with Cattaneo-Christov heat-mass flux model. The Buongiorno’s nanofluid flow model is used to study the effects of the Brownian motion and the thermophoresis whereas the Darcy-Forchheimer model is considered to examine the nanofluid and porous medium interaction. Thereafter, the highly nonlinear system of equations for momentum, energy and concentration are formulated and solved numerically by utilizing the Runge-Kutta-Fehlberg integration scheme with shooting technique. Consequently, the numerical simulation indicates that the Casson fluid parameter and the variable viscosity parameter play a great role in escalating the velocity field and temperature profile however chemical reaction, porous medium, radiation, thermal relaxation time and convective heating control over the temperature profile. Besides, an increase in the thermal relaxation time λ e causes more transfer of heat from the hot microchannel wall to the fluid and thus, fluid temperature distribution is higher for   λ e = 0 . Hence, the Cattaneo-Christov heat flux model is constructive in cooling process as compared to that of the classical Fourier’s law of heat conduction. Furthermore, heat and mass transfer rates are enhancing because of the thermal radiation and solutal Grashof number at both sides of the microchannel walls. Also, the current findings are compared with that of the existing literature and a sound agreement was established. [ABSTRACT FROM AUTHOR]

The control mechanism of the pressure drop and bubble size has a guiding significance for selecting the micropump, the pressure resistance design, and the precise control of the microfluidics. In this study, single-phase flows and gas-non-Newtonian fluid two-phase flows are studied in a microchannel containing curved structures. Sodium carboxymethyl cellulose solutions are used as the non-Newtonian fluids; water and nitrogen are used as Newtonian fluid and gas phases, respectively. The pressure drop and the bubble length are measured. The influences of operating conditions are discussed. The non-Newtonian properties of the solutions are found to affect the parameters measured significantly. The experimental results are compared with the existing models, and the fanning friction factor is used to evaluate the pressure drop. The two-phase flow pressure drop can be predicted by the Lockhart-Martinelli method with a newly developed C-coefficient as a function of the fluid characteristic parameters and microchannel structure parameters. The new correlation for two-phase pressure drop prediction has an error within 18%, smaller than existing models. A new prediction method for the dimensionless bubble length containing the two-phase friction multiplier is also given with an error of 16%. [Display omitted] • A novel microchannel containing curved structures was studied experimentally. • Empirical models for predicting pressure drop and bubble length were developed and compared with existing models. • The prediction accuracy of the pressure drop was improved by considering structural and non-Newtonian fluid parameters. • The prediction accuracy of the bubble length was improved by considering the influence of pressure drop. [ABSTRACT FROM AUTHOR]

[Display omitted] When a liquid is inserted inside a microfluidic channel, embedded within a soft elastomeric layer, e.g. poly(dimethylsiloxane) (PDMS), the thin wall of the channel deforms, due to change in solid–liquid interfacial energy. This phenomenon is known as Elastocapillary effect. The evolution of a new species at this interface too alters the interfacial energy and consequently the extent of deformation. Hence, it should be possible to monitor dynamics of physical and chemical events occurring near to the solid–liquid interface by measuring this deformation by a suitable method, e.g., optical profilometer. Aqueous solution of a metal salt inserted into these channels reacts with Silicon-hydride present in PDMS, yielding metallic nanoparticles at the channel surface. The kinetics of this reaction was captured in real time, by measuring the wall deformation. Similarly, physical adsorption of a protein: Bovine Serum Albumin, on PDMS surface too was monitored. The rate of change in deformation can be related to rate of these processes to extract the respective reaction rate constant. These results show that Elastocapillary effect can be a viable analytical tool for in-situ monitoring of many physical and chemical processes for which, the reaction site is inaccessible to conventional analytical methods. [ABSTRACT FROM AUTHOR]

Recent trends of miniaturization and densely packed circuits have necessitated the development of novel cooling methods, especially for emerging fields like flexible microelectronics, biotechnology, and nanotechnology. A polydimethylsiloxane (PDMS) based microchannel flow boiling heat sink can be used for these applications due to its unique properties as such as unique mechanical properties, biocompatibility, optical transparency, etc. PDMS microchannels are fabricated using soft lithography techniques, which involve using a mould to pattern the PDMS material. The mould is created using photolithography, and the PDMS is poured over the mould and cured to create the microchannels. In this study, an effort is made to compare the flow and heat transfer performance of a PDMS microchannel heat sink with different channel shapes, i.e. straight and diverging microchannel heat sinks for different heat flux and mass flux conditions. The PDMS microchannel was fabricated using the soft lithography technique and a flexible laser-induced graphene heater was fabricated and integrated with the developed PDMS microchannel to act as a heat source. Experimentally, the parameters like bubble pattern, pressure drop, exit vapour quality, and corresponding heat transfer coefficient were determined at varying mass and heat flux ranging from 19 to 114 kg m−2s−1 and from 13.3 to 156.6 kW m−2 respectively for both the microchannels. It was observed that the flow in the diverging microchannel is more stable and has a 13% higher heat transfer coefficient value compared to the straight microchannel under similar conditions. Further, a 3D numerical study was carried out to corroborate and elaborate on the results. The heat transfer, flow characteristics, and bubble pattern results show an excellent agreement with experimental results. This work has significant relevance in designing flexible microchannel heat sinks. [ABSTRACT FROM AUTHOR]

Bubble growth behavior significantly influences boiling heat transfer performance, and different microchannel structures and configurations affect bubble growth behavior. To explore the impact of microchannel structures and configurations on the growth behavior of boiling bubbles, two types of microchannel test plates were fabricated on copper substrates using laser machining technology. It was a parallel configuration plate with five different microchannel spacings and a blade vein configuration plate with four different fractal angles. The bubble growth behavior on these two types of surfaces was studied through visual experiments. The results show that smaller microchannel spacing leads to earlier bubble coalescence and departure times under the same degree of superheat. The 3.00 mm microchannel spacing is the critical interfering distance for the parallel configuration plates, while interference behavior occurs for the bubbles on the simulated vein configuration plates at any fractal angle. Furthermore, in different ranges of superheat, the bubble departure diameter increases with increasing superheat, and the frequency of bubble departure initially increases and then decreases with increasing superheat. This study provides experimental data support and design reference for the design of heat transfer plate structures. [ABSTRACT FROM AUTHOR]

High in reliability, multi in function, and strong in tracking and detecting, active phased array antennas have been widely applied in radar systems. Heat dissipation is a major technological barrier preventing the realization of next-generation high-performance phased array antennas. As a result of the advancement of miniaturization and the integration of microelectronics technology, the study and development of embedded direct cooling or heat dissipation has significantly enhanced the heat dissipation effect. In this paper, a novel swept-back fishnet-embedded microchannel topology (SBFEMCT) is designed, and various microchannel models with different fishnet runner mesh density ratios and different fishnet runner layers are established to characterize the chip Tmax, runner Pmax, and Vmax and analyze the thermal effect of SBFEMCT under these two operating conditions. The Pmax is reduced to 72.37% and 57.12% of the original at mesh density ratios of 0.5, 0.25, and 0.125, respectively. The maximum temperature reduction figures are average with little change in maximum velocity and a small increase in maximum pressure drop across the number of fishnet runner layers from 0 to 4. This paper provides a study of the latest embedded thermal dissipation from the dimension of a single chip to provide a certain degree of new ideas and references for solving the thermal technology bottleneck of next-generation high-performance phased array antennas. [ABSTRACT FROM AUTHOR]

Computational fluid dynamics was used and a numerical simulation analysis of boiling heat transfer in microchannels with three depths and three cross-sectional profiles was conducted. The heat transfer coefficient and bubble generation process of three microchannel structures with a width of 80 μm and a depth of 40, 60, and 80 μm were compared during the boiling process, and the factors influencing bubble generation were studied. A visual test bench was built, and test substrates of different sizes were prepared using a micro-nano laser. During the test, the behavior characteristics of the bubbles on the boiling surface and the temperature change of the heated wall were collected with a high-speed camera and a temperature sensor. It was found that the microchannel with a depth of 80 μm had the largest heat transfer coefficient and shortest bubble growth period, the rectangular channel had a larger peak heat transfer coefficient and a lower frequency of bubble occurrence, while the V-shaped channel had the shortest growth period, i.e., the highest frequency of bubble occurrence, but its heat transfer coefficient was smaller than that of the rectangular channel. [ABSTRACT FROM AUTHOR]

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Abstract Molecular diffusive membranes play crucial roles in the field of microfluidics for biological applications e.g., 3D cell culture and biosensors. Hydrogels provide a range of benefits such as free diffusion of small molecules, cost-effectiveness, and the ability to be produced in bulk. Among various hydrogels, Pluronic F127 can be used for cell culture purposes due to its biocompatibility and flexible characteristics regarding its environment. Aqueous solutions of Pluronic F127 shows a reversible thermo-thickening property, which can be manipulated by introduction of ions. As a result, controlled diffusion of ions into the solution of Pluronic F127 can result in a controlled gel formation. In this study, the flow of immiscible solutions of Pluronic and sodium phosphate inside a Y-shaped microchannel is simulated using the level set method, and the effects of volume flow rates and temperature on the gel formation are investigated. It is indicated that the gel wall thickness can decrease by either increasing the Pluronic volume flow rate or increasing both volume flow rates while increasing the saline volume flow rate enhances the gel wall thickness. Below a critical temperature value, no gel wall is formed, and above that, a gel wall is constructed, with a thickness that increases with temperature. This setup can be used for drug screening, where gel wall provides an environment for drug-cell interactions. Article Highlights Parallel flow of Pluronic F127 and saline solutions inside a Y-shaped microchannel results in formation of a gel wall at their interface. The numerical analysis reveals the impact of each inlet flow rate and temperature on gel wall thickness and movement. The findings indicate that the gel wall has a low but steady velocity toward the saline solution. Graphical abstract

Waste heat utilization has been prioritized especially in various industries and sectors. Many researchers have developed heat recovery processes by designing suitable waste heat recovery units (WRU), such as heat exchangers, using water as a coolants to receive heat from the waste heat fluid in the production process. The conventional heat exchanger has limitations such as its equipment size, space for installation, and flexibility. The microchannel heat exchanger is one of many ideas for resolving these limitations. Moreover, the coolant on the cold side can be upgraded by adding nanometer-sized solid particles which is called “Nanofluid”. To reduce the high investigation cost and time, a new efficient and cost-effective simulation method was selected to use for investigating the performance of a microchannel heat exchanger with nanofluids in this study. To analyze the heat recovery at low temperature, i.e. around 100–200 °C, nanofluid property predictive models were developed using an artificial neural network (ANN). Then, the predictive models were embedded and integrated into computational fluid dynamics to design a microchannel heat exchanger. It is found that the use of nanofluids improved the heat transfer efficiency of this heat exchanger. The suitable nanofluid types and concentrations were selected based on the thermal–hydraulic​ performance. Here, the 3% weight TiO2/Water fluid with a 1.03 thermal–hydraulic​ performance ratio was found to be the most promising nanofluid for using in this condition.

This study aims to provide condensation heat transfer coefficients of R600a (isobutane) refrigerant under mass fluxes between 50 and 98 kg/m2·s at saturation temperatures of 35 °C, 40 °C and 45 °C. Additionally, experiments are conducted with varying inlet vapour quality to understand its effect on the condensation heat transfer measurement. An aluminium multiport microchannel with a hydraulic diameter (Dh) of 0.399 mm is used, where a plexiglass cover is mounted on the top of the microchannels to observe the flow conditions. A 1D heat transfer through the aluminium block is assumed, and heat flux through the refrigerant to the coolant is measured to obtain condensation heat transfer coefficients of R600a. The results showed that decreasing saturation temperature and increasing vapour quality increase the condensation heat transfer coefficient. Increasing refrigerant mass flux increases the heat transfer coefficient up to a specific mass flux. It is observed that the effect of inlet vapour quality becomes significant as introduced quality decreases due to increasing fluctuation.

In the pursuit of enhancing thermal management for miniaturized electronic devices, our study delves into the impact of entry effects on Ledinegg instability and flow maldistribution within parallel microchannels. Utilizing a coupled model that incorporates phase change and pressure drop dynamics in boiling flow, we examine microchannels characterized by a 50 length-to-diameter ratio and a 200 μm hydraulic diameter. Our findings unveil a significant influence of entry effects, which narrow the total flow excursion interval, thereby bolstering system stability. Specifically, as the heat flux escalates from 5 W/cm2 to 120 W/cm2, the entry effects increasingly mitigate flow instability and maldistribution in parallel channels, diminishing the total flow rate range susceptible to flow instability by 4.73% and 47.52%, while narrowing the total flow rate range corresponding to uneven flow distribution by 4.70% and 46.75%, respectively. Furthermore, entry effects expand the inlet subcooling range necessary for stabilizing the parallel channel system by 38.89% and 1000%. This research not only underscores the importance of considering entry effects in microchannel design but also opens avenues for further exploration into enhancing thermal management solutions.

A CFD simulation of the condensation flow of R600a and R290 within microchannels was conducted to explore the effect of mass flux, hydraulic diameter, and vapour quality on heat transfer rate and pressure drop. Data obtained from CFD simulations were used to develop new heat transfer and pressure drop correlations for the condensation flows of R600a and R290, which are climate-friendly refrigerants. Steady-state numerical simulations of condensation flow of refrigerants were carried out inside a single circular microchannel with diameters varying between 0.2 and 0.6 mm. The volume of fluid approach was used in the proposed model, calculating the interface phase change using the Lee model. The CFD simulation model was validated via a comparison of the simulation results with the experimental data available in the literature. It is found that the newly developed Nu number correlation shows a deviation, with an Ave-MAE of 11.16%, compared to those obtained by CFD simulation. Similarly, the deviation between friction factors obtained by the newly proposed correlation and those obtained by CFD simulation is 20.81% Ave-MAE. Widely recognized correlations that are applicable to the condensation of refrigerants within small-scale channels were also evaluated by comparing newly developed correlations. It is concluded that the newly proposed correlation has a higher accuracy in predicting the heat transfer coefficient and pressure drop. This situation can contribute to the creation of a sustainable system via the use of microchannels and climate-friendly refrigerants, like R600a and R290.

The use of polymer microspheres is becoming increasingly widespread. Along with their most common applications, they are beginning to be used in the synthesis of photonic crystals, microstructure analysis and multiplexed diagnostics for disease control purposes. This paper presents a simple mathematical model that allows us to study the transport mechanisms involved in the deformation of an elastic microchannel under the flow stream of a power-law fluid. In particular, we analyze the momentum transfer to a non-Newtonian fluid (Polydimethylsiloxane, PDMS) due to the deformation of the elastic ceiling of a rectangular microchannel. Hooke’s law is used to represent the stress–deformation relationship of the PDMS channel ceiling. Stop-flow lithography is modeled, and the pressure exerted by the deformed PDMS ceiling on the fluid when the microchannel returns to its original form is taken into account. It is found that the response time of the elastic ceiling deformation increases with the channel width and length and decreases with the channel height independently of the power-law exponent of the injected fluid. However, an increase in the power-law exponent beyond unity causes an increase in the wall-deformation response time and the maximum deformation of the channel height compared to a Newtonian fluid.

In microchannels where there is a change in the direction of flow, the difference in path length between the inner and outer walls or boundaries can play an effective role in dispersion. This research focuses on studying the fluid flow and heat transfer of a hybrid nanofluid in a microchannel under electroosmotic flow. A structural optimization is applied to reduce dispersion, and the results of the optimized geometry are compared with the original geometry. The results show that the heat transfer is improved due to the new geometry configuration. If only the study of heat transfer is considered, it is recommended to use the optimal geometry with a low volume fraction and a high electric potential. Although the nanofluid's performance in increasing heat transfer is failed due to the low flow rate, the enhanced heat transfer can be achieved through optimized geometry or high electric potential. The results of this research can be applied to the design of more advanced and efficient microfluidic devices with multifaceted objectives.

Issues related to the heavy consumption of fossil fuels namely coal and oil have necessitated development of renewable energy sources as alternatives. Solar photovoltaic (PV) modules are one of the most attractive options for electricity generation by use of solar energy as the most abundant renewable energy source. One of the main disadvantages of PV cells is their relatively low efficiencies that leads to low power generation intensity. In this regard, concentrators can be applied to exploit further electricity per area of the cell; however, it causes increase in the temperature and consequently reduce the efficiency. To overcome the efficiency degradation due to the temperature increase, thermal management of cell has been introduced and applied recently. One of the efficient active techniques for cooling PV cells is making use of microchannels for circulation of coolants inside it. This article reviews the research works implemented on the use of microchannels as thermal management unit of PV cells. According to the findings it can be concluded that performance of this cooling techniques is influenced by variety of factors like the coolant mass flow rate, configuration and characteristics of microchannels, thermophysical properties of coolant and heat transfer mechanisms. It is reported that employment of microchannels with modified architecture can lead to better thermal management and consequently higher efficiency of the cells. Furthermore, it is found that use of modified coolants, i.g. nanofluids, would result in higher heat removal and electrical efficiency. One of the main challenges in use of microchannels for thermal management is its manufacturing and related difficulties and issues.

A nanofluid (NF) is a mixture of metallic or non-metallic nanoparticles (NPs) suspended in a fluid. The high activity and energy of the surface atoms of NPs cause them to stick together and aggregate in the base fluid (BF). This leads to instability, changes in the NF concentration, and fouling and obstruction of the flow path, which reduces the NF's thermal conductivity (TC). In this study, the effect of copper oxide NPs on atomic behavior and the aggregation procedure in a water/CuO NF flow in a microchannel was explained using a Molecular Dynamics (MD) simulation procedure. For this purpose, various physical parameters, such as density, temperature, velocity, aggregation time (AT), and potential energy (PE), were calculated. The results show that after 1 ns, the temperature and PE converged to 300 K and −553088 eV. By CuO NPs number increasing among H2O molecules, the maximum ratio of density, temperature, and V profiles reached 1.60 g/cm3, 0.0122 Å/ps, and 303 values. The aggregation process in simulated NF was varied by these atomic changes. From a numerical point of view, by CuO NPs number increasing from 2 to 3 NPs, the AT reduced by 1.15 ns to 1.01 ns. Furthermore, this atomic evolution was investigated by PE changed from −652411 to −660258 eV.

Understanding of mass transfer in gas-liquid slug flow is imperative to design and optimize micro-reactors. There exist extensive studies on symmetric bubbles by the phase volume monitor technique, whereas deformed bubbles are rarely studied due to the limitation of volume calculation methods. In this work, CO2-water and N2-water two-phase flows were investigated in a square microchannel, obtaining annular flow, slug flow, and bubbly flow. A flow pattern map was then proposed and compared with the literature. A 3D slicing technique was developed to measure the volume and interfacial area of bubble, including symmetric bubbles and deformed bubbles, by slicing the bubble along the streamwise direction. Scaling laws of the important parameters that characterize the micro-reactors were proposed. Mass transfer coefficients kLa were quantified from the time-changing volume. The empirical correlation involving dimensionless numbers were fitted, which shows accurate predictive performance for mass transfer coefficients in this study and literatures. The bigger index of Reynolds number ReG indicated that gas flow condition is the main influencing factor during mass transfer process. To have a better universality, a new semi-theoretical model involving the ratio of the size of the liquid and gas phases LL/LG was developed based on the Pigford and Higbie penetration theory because experimental data confirms that the degree of bubble deformation is related to LL/LG. The semi-theoretical model shows a satisfactory agreement over the whole range of slug flow in this study.

Microparticles with multiple internal chambers hold great promise as drug delivery systems due to their ability to sustain the release of drugs with short half‐lives. However, conventional batch methods used for their fabrication have limitations in terms of encapsulation efficiency and particle size distributions, while microfluidic methods suffer from low production efficiency. Herein, a batch‐microfluidic hybrid method is presented for fabricating poly(DL‐lactic‐co‐glycolic acid) (PLGA) polymeric microparticles with uniformly distributed, multiple inner microchambers. A scalable batch method is utilized for primary water‐in‐oil (W/O) emulsions, combined with a precise microfluidic approach for generating controlled secondary emulsions. This approach results in highly uniform PLGA microparticles with tunable size and improved encapsulation efficiency. Additionally, the effect of polydopamine‐based surface hydrophilic modification of microfluidic channels on drug encapsulation efficiency is investigated, achieving an efficiency of approximately 85%. The prepared multichamber PLGA microparticles exhibit an extended‐release profile without initial burst release, demonstrating their potential for sustained drug delivery in various biomedical applications.