Types Of Microchannels Research Articles

Experimental study on flow boiling of fluorocarbon fluid in the pin-ribbed micro-channel with rigid tails

In this work, a novel type of pin-ribbed micro-channel with rigid tails is designed based on the conventional pin-ribbed micro-channel. A comparative experimental study is carried out using fluorocarbon fluid Novec649. The flow boiling heat transfer and pressure drop characteristics are investigated under horizontal/vertical placement at inlet subcooling temperature of 25 °C. The ranges of inlet mass flux and heat flux are 519–1818 kg·m−2·s−1 and 50–500 kW·m−2, respectively. The results show that at a given mass flux, and heat flux of 300–500 kW·m−2, the vertical pin-ribbed micro-channel with rigid tails has the lowest average wall temperature, the largest average heat transfer coefficient, and the smallest total pressure drop, therefore it has the largest j-factor, more than 60% higher than that of the horizontal/vertical channel without rigid-tails. With the aid of a high-speed camera, the localized bubble movement phenomena in horizontal/vertical micro-channel with rigid tails was photographed at a mass flux of 519 kg·m−2·s−1 and a heat flux of 100 kW·m−2. Three types of bubble detachment modes in the wake region at the boiling stable state are observed: natural shedding, one-sided shear and two-sided shear. The bubble detachment diameter under the one-sided shear is more than 23% smaller than that of two-sided shear, and that of the horizontal channel is more than 44% higher than that in the vertical channel, whereas its bubble detachment frequency is only 50% of that in the vertical channel. Therefore, the vertical placement is more helpful for the rigid tails playing a role in the breakup and detachment of bubbles. The experimental results confirm the advantages of adding rigid tails behind the square-rib to enhance the comprehensive heat transfer performance of flow boiling, which can provide a guidance for the structural design of two-phase miniature heat sinks.

Optimal arrangements of inlet and outlet in topology liquid-cooled microchannel heat sink based on Multi-Objective optimization

Different forms of inlet and outlet arrangements in microchannel heat sinks have a significant impact on efficient heat dissipation. In this paper, under the framework of the finite element method coupled with the Method of Moving Asymptotes (MMA), three novel topology structures are proposed. Using Solid Isotropic Material with Penalization Parametrization (SIMP), the topology results with different inlet and outlet arrangements are compared and analyzed, with minimizing the average solid temperature, maximizing the heat transfer capacity and minimizing the power consumption per unit of heat transfer, and 207 sets of results are obtained. The optimized results were analyzed by the Nusselt number (Nu), the friction factor (f) and the Performance Evaluation Criterion (PEC). The results present that the heat transfer performance of the optimized three arrangements in the 207 arrangements are enhanced by 133.6 %, 112.56 % and 135.79 %, respectively, and the PECs improve up to 73.55 %, 65.54 % and 79.78 %, respectively, compared with the horizontal rib inlet and outlet liquid-cooled plate type microchannel heat sink. The results of the present work provide a reference for the optimal design of electronic heat sinks under different working conditions.

Highly efficient fabrication of reentrant microchannels with micro serrated pin fins using a micro staggered multi-edge ball-end milling tool in a single process

Microchannels with micro pin fins and reentrant cavities can increase the heat dissipation area and enhance heat transfer, which are promising for high-performance microchannel heat sinks for heat dissipation of high-heat-flux devices. Nevertheless, their fabrication is time-consuming and cost-inefficient for conventional methods. To this aim, we in this study developed a novel micro staggered multi-edge ball end milling tool (SMBMT) to fabricate a unique type of reentrant microchannels with micro serrated pin fins (RMSPF) in a single process. The formation feasibility of the RMSPF was demonstrated, and they were of narrow exit slots with a width of 500 μm on the top, reentrant circular cavities with a diameter of 800 μm at the bottom, and micro serrated pin fins with a width of about 52 μm and a height of 35 μm on the wall surface of reentrant cavities. More microscale serrated pin fins with much smaller sizes than the micro cutting edges of the SMBMT were obtained due to the staggered arrangement and overlapping effect of the multiple micro cutting edges. A geometrical model of the SMBMT with discrete multiple cutting edges was developed by considering the structure of the RMSPF. The formation process mechanism of RMSPF and its chip formation process was investigated with both experiments and finite element (FE) simulations. Compared to conventional micro ball end milling tool (CBM) with continuous cutting edges, the SMBMT suppressed the burr formation inside reentrant microchannels and improved the surface quality, and reduced the cutting force by up to 53 %. The enhanced cutting performance of SMBMT can be attributed to that the multiple discrete cutting edges of SMBMT effectively decreased the contact area of tool-workpiece and the friction between cutting tool and chips. This study offered a highly efficient method to fabricate microchannels with surface microstructures in a single micromilling process, which provided valuable insights for the development of high-performance microchannel heat sinks in a wide range of application areas.

Thermal–Hydraulic Performance Analysis of Combined Heat Sink with Open Microchannels and Embedded Pin Fins

An open type of microchannel with diamond pin fins (OM-DPFs) is introduced for the cooling of high-performance electronic chips. For a Reynolds number (Re) of 247~1173, a three-dimensional model is established to explore the hydrothermal properties of the OM-DPF and compare it to traditional heat sinks with closed rectangular microchannels (RMs), heat sinks with open microchannels (OMs), and the results in the existing research. Firstly, the synergy between tip clearance and pin fins on the hydrothermal properties is discussed. Secondly, the entropy production principle is adopted to analyze the irreversible losses for different heat sinks. Lastly, the total efficiencies of different heat sinks are assessed. The RMs present the worst heat transfer with the lowest friction loss. For the OMs, the temperature and pressure drop are decreased slightly compared to those of the RMs, and the irreversible loss is reduced by 4% at Re = 1173 because of the small tip clearance. But the total efficiency is lower than that of the RMs because the pressure drop advantage is offset by the weak heat transfer. For the OM-DPF, the combined structure has a noticeable impact on the multiple physical fields and hydrothermal characteristics, which present the best thermal performance at the cost of the highest friction loss. The irreversible loss of heat transfer in the OM-DPF is reduced obviously, but the friction irreversible loss significantly increases at high Re values. At Re = 429, the total entropy production of the OM-DPF is reduced by 47.57% compared with the RM. Compared to the OM and the single-pin fin structure in the literature, the total efficiency of the OM-DPF is increased by 14.56% and 40.32% at Re = 614. For a pump power of 0.1 W, the total thermal resistance (Rth) of the OM-DPF is dropped by 23.77% and 21.19% compared to the RM and OM. For a similar Rth, the pump power of the combined structure is 63.64% and 42.86% lower than that of the RM and OM. Thus, the novel combined heat sink can achieve efficient heat removal while controlling the energy consumption of liquid cooling systems, which has bright application prospects.

Bionic Janus microfluidic hydrogen production with high gas–liquid separation efficiency

Water electrolysis offers the advantages of emission-free and highly efficient energy conversion in terms of sustainable energy development and environmental pollution. However, water electrolysis is strongly affected by the detachment of bubbles from the electrodes commonly enabled by buoyancy, thereby reducing the performance of the electrolytic cells in harsh environments like in space. Herein, a bionic Janus microchannels with active gas–liquid separation for water electrolysis is proposed. There is a Janus membrane with superaerophilic top surface and inner micropores over the microchannels, and such a unique type of microchannels can capture and unidirectionally manipulate the hydrogen (H2) bubbles generated on the surface of the electrode during the water electrolysis reaction at high speed with long-term stability. It is worth noting that the gas–liquid separation through the Janus membrane does not hinder the flow of electrolyte in the microchannel due to its hydrophilic inside surfaces, which can maintain the great stability of the electrolysis. Moreover, mimicked leaves and trees for water catalysis are further demonstrated with ultrahigh electrolysis efficiency based on the active detachment of H2 bubbles enabled by Janus micropores. The present bionic Janus microchannels for high-efficient water electrolysis to produce H2 is intended to provide a new power supply solution for human space living and exploration.

Heat transfer performance of microchannels with different reentrant cavities based on field synergy principle and entropy production analysis

The performance analysis of three types of microchannels with reentrant cavities were investigated in this study. The flow and heat transfer characteristics were analyzed according to the field synergy principle and entropy production. The results indicated that as the Reynolds number ranged from 200 to 1000, the Darcy friction factor of microchannels with reentrant cavities decreased sharply and then slowly. Among microchannels examined, a microchannel with circular reentrant cavities exhibited the smallest Darcy friction factor in the Reynolds number range of 200–1000. The Nusselt number of microchannels with reentrant cavities increased with the Reynolds number range of 200–1000. Among the microchannels, the microchannel with circular reentrant cavities had the largest Nusselt coefficient, from 6.07 to 10.29. According to the principle of field synergy, the heat transfer field of microchannel with circular reentrant cavities had the smallest synergy angle (α), from 85.1°to 83.2°, and the best field synergy. According to an analysis of the entropy production, the entropy production caused by heat transfer in microchannels with reentrant cavities gradually decreased as Reynolds number range from 200 to 1000. The microchannel with circular reentrant cavities had minimal entropy production caused by heat transfer; thus, it had the best heat transfer performance. The flow entropy production of microchannels with reentrant cavities increased with the Reynolds number. Among the microchannels, the microchannel with circular reentrant cavities had the smallest entropy production caused by flow. The present study aims to provide alternative ways to evaluate flow and heat transfer performance of microchannels.

Enhanced solvent extraction of rare earth elements in ultra-high phase ratio with pore-throat microchannels

To enrich and recover low-concentration (101–102 ppm) rare earth elements from ores and industrial wastes, high phase-ratio solvent extraction is favored. However, high phase-ratio solvent extraction is limited by low mass transfer efficiency in the continuous phase due to the insufficient contact between large volume continuous phase and sparse droplets. To realize efficient solvent extraction of rare earth ions from low concentrations (100 ppm) aqueous phase to oil phase with high phase ratio, we introduce a type of microchannel with sequential pore-throat geometry. This sequential pore-throat geometry creates capillary barriers and effectively retains dispersed droplets, leading to a reduction of apparent water–oil volume ratio and thereby major mass transfer enhancement in the continuous phase. We experimentally highlight its advantage over classic uniform microchannel for solvent extraction of rare earth ions under high phase ratios: in a double pore-throat microchannel, extraction equilibrium can be reached within 30 s under high phase ratios of 50–250; for an extreme phase ratio of 500:1, extraction efficiency can achieve 77 % within a quadruple pore-throat channel, while that within a uniform microchannel is only below 40 %. The superiority of sequential pore-throat microchannel for extraction at a high phase ratio is reproduced using different types of rare earth ions. We thus conclude that sequential pore-throat geometry can drastically promote the performance of microfluidic-based solvent extraction at extreme phase ratios, for rare earth enrichment and potentially for other relevant applications.

Effect of Fluoride Layer Growth on the Deposition Rate under Different Microchannel Structures.

In the plasma-enhanced chemical vapor deposition (PECVD) process, a showerhead is used to enhance fluid uniformity in the chamber. The uniformity of the flow field will be affected by changing the microchannel on the showerhead, which in turn directly affects the uniformity of deposition. The showerhead will be etched during the cleaning process due to the presence of HF, which will form a fluoride layer. This layer will cause a decrease in the diameter of the microchannels, resulting in changes in the deposition uniformity. The impact of diameter changes can be reduced by making modifications to the microchannel structure. By adopting a coupling of the Navier-Stokes and Direct Simulation Monte Carlo (NS-DSMC) methods, we obtained the velocity variation of two typical microchannels (equal-diameter type and expansion type) under the same diameter change. The results indicate that compared to the equal-diameter type, the expansion type exhibits a smaller change in velocity for the same change in diameter. For the surface reaction limited regime, a stable velocity leads to a consistent residence time, which is advantageous for maintaining the uniformity of the film thickness. Therefore, compared to the equal-diameter type microchannel, the expansion type can reduce the impact of changes in diameter.

Effects of microchannel width on fluid flow and temperature uniformity

Compact, lightweight and efficient microchannel radiator technology has become an effective way to solve the heat dissipation of microelectronic devices. This article is oriented to the heat dissipation requirements of electronic chips. The heat transfer performance and pressure drop characteristic for microchannel heat exchangers with various widths are investigated in this article to obtain an optimal width design. Results show that for the microchannel with the same width, the mass flow rate in the middle channels is larger than that on both sides. The heat transfer can be enhanced and the uniformity of the temperature distribution is improved by increasing the channel width gradually from the central position. A width distribution expression for an optimal reduction percentage of the channel width is formulated using the performance evaluation criterion for non-uniform channels developed in this article. A wave form microchannel was used to validate the formula for optimal structure design, which shows that the formula is suitable for a different type of microchannel.

Investigation of Overflow-Water-Assisted Femtosecond Laser-Induced Plasma Modulation of Microchannel Morphology

Laser-induced plasma micromachining (LIPMM) process is an effective approach to create microfeatures with high aspect ratio (AR) and reduced heat affected zone (HAZ). Therefore, LIPMM plays a crucial role in improving the morphology of microchannels. In this study, microchannels were fabricated using a femtosecond laser with two distinct sets of process parameters under three different processing methods: overflow-water-assisted laser-induced plasma micromachining (OF-LIPMM), laser direct writing (LDW), and static water laser-induced plasma micromachining (S-LIPMM). Furthermore, single-factor experiments were conducted to systematically analyze the effects of four parameters, namely single-pulse energy, scanning speed, scanning times, and frequency, on the HAZ, AR, and material removal rate (MRR) of the microchannels. Finally, the optimized parameters determined from the single-factor experiments were applied for large-scale grid fabrication on a surface. The experimental results revealed that OF-LIPMM enables the creation of two different kinds of microchannel surfaces: one microchannel was fabricated with a higher AR of 3:1 and a larger HAZ, while another microchannel was created with a lower AR of 1:1 and a reduced HAZ. Moreover, the parameters investigated in the single-factor experiments can be applied to large-scale processing. The results also indicate that variations of the scanning speed, frequency, and single-pulse energy have similar effects on the machining characteristics of the three processing methods. The findings enable the generation of microchannels with favorable morphological characteristics and have significant implications for the large-scale production of both types of microchannels.

Numerical investigation of centrifugal passive cell separation in three types of serpentine microchannels and comparison with fixed platform

Cell separation plays a crucial role in diagnosing and improving a wide range of diseases, such as cancer, which is a severe reason for the death of people in the current decades. Circulating tumor cells (CTCs) inside the blood can be separated from the other whole blood cells to detect early cancer. Inertial methods are more superficial and cost less than the current CTC separation methods. These methods also have great potential in high-throughput separation in lab-on-a-chip (LOC) and lab-on-a-disk (LOD) devices because of secondary flow generation, especially in serpentine-shaped microchannels. The present study considers a continuous process for separating CTCs from the blood sample. This process is utilized in LOD devices, and this platform is also compared with the LOC platform. Moreover, two common types of different serpentine-shaped channels (simple and curved) and a new Omega channel are compared. It should be noted that a direct numerical simulation (DNS) method is used for calculating lift force in the serpentine-shaped channels. The effect of fluid velocity on WBC and CTC separation efficiency in the three mentioned different geometries are investigated in both fixed and rotational platforms, then the best results for each of them are presented. Finally, the best results belonged to the simple serpentine between the three investigated channels, with a separation percentage of 100. Moreover, in comparing the two mentioned platforms, LOD showed a more efficient application in cell separation. In addition, the Omega channel is investigated as a novel serpentine geometry. According to the results, it can be used for particle focusing applications thanks to its 100 percent efficiency at 0.5 m/s in both LOD and LOC platforms.

Entropy generation and exergy destruction in two types of wavy microchannels working with various aqueous nanofluids using a multi-phase mixture model

Entropy generation and exergy destruction in two types of wavy microchannels working with various aqueous nanofluids using a multi-phase mixture model

Hydrophobicity induced drag reduction: Perspectives from the slip length

Hydrophobicity has been developed in many areas, whose potentials in drag reduction at microscale have attracted numerous attentions for expanding the practical applications in fields of on chip devices, materials synthesis, and enhanced heat transfer. In this article, we select polydimethylsiloxane (PDMS) as the base material, whose hydrophobic modifications have been well developed. Among them, hydrofluoric acid treated one shows great performance and leads us to two types of microchannels, the straight and U-shaped, with enhanced hydrophobicity (from 91° to 106°). The coefficients of the pressure drop are experimentally measured with the Reynolds number ranging from 0 to 300. The results illustrate that the drag reduction rate reaches at 37.8% for the straight microchannel and 26.8% for the U-shaped microchannel. With the increase in the Reynolds number, the drag reduction effect stays almost constant for the straight channel, while it decreases gradually for the U-shaped channel. The flow impingement induced by a centrifugal force has an important impact on the slip effect that grows with the Re. Next, we adopt the numerical method and the micro-particle imaging velocimetry measurement to analyze the drag reduction effect from perspectives of the slip length. We successfully derive the slip length model correlating the drag reduction effect. Our results not only achieve substantial drag reduction in PDMS microchannels, but also provide a quantitative correlation between hydrophobicity and drag reduction, offering a feasible strategy for extensive applications at microscale, such as fluid actuation, bio-chip analysis, and highly efficient cooling system.

Hybrid acoustic materials through assembly of tubes and microchannels: design and experimental investigation

PurposeThe purpose of this paper is the design and experimental investigation of compact hybrid sound-absorbing materials presenting low-frequency and broadband sound absorption.Design/methodology/approachThe hybrid materials combine microchannels and helical tubes. Microchannels provide broadband sound absorption in the middle frequency range. Helical tubes provide low-frequency absorption. Optimal configurations of microchannels are used and analytical equations are developed to guide the design of the helical tubes. Nine hybrid materials with 30 mm thickness are produced via additive manufacturing. They are combinations of one-, two- and four-layer microchannels and helical tubes with 110, 151 and 250 mm length. The sound absorption coefficient of the hybrid materials is measured using an impedance tube.FindingsThe type of microchannels (i.e. one, two or four layers), the number of rotations and the number of tubes are key parameters affecting the acoustic performance. For instance, in the 500 Hz octave band (α500), sound absorption of a 30 mm thick hybrid material can reach 0.52 which is 5.7 times higher than the α500 of a typical periodic porous material with the same thickness. Moreover, the broadband sound absorption for mid-frequencies is reasonably high with and α1000 > 0.7. The ratio of first absorption peak wavelength to structure thickness λ/T can reach 17, which is characteristic of deep-subwavelength behaviour.Originality/valueThe concept and experimental validation of a compact hybrid material combining a periodic porous structure such as microchannels and long helical tubes are original. The ability to increase low-frequency sound absorption at constant depth is an asset for applications where volume and weight are constraints.

An efficient microreactor with continuous serially connected micromixers for the synthesis of superparamagnetic magnetite nanoparticles

A new microreactor with continuous serially connected micromixers (CSCM) was tailored for the coprecipitation process to synthesize Fe3O4 nanoparticles. Numerical simulation reveals that the two types of CSCM microchannels (V-typed and U-typed) proposed in this work exhibited markedly better mixing performances than the Zigzag and capillary microchannels due to the promotion of Dean vortices. Complete mixing was achieved in the V-typed microchannel in 2.7 s at an inlet Reynolds number of 27. Fe3O4 nanoparticles synthesized in a planar glass microreactor with the V-typed microchannel, possessing an average size of 9.3 nm and exhibiting superparamagnetism, had obviously better dispersity and uniformity and higher crystallinity than those obtained in the capillary microreactor. The new CSCM microreactor developed in this work can act as a potent device to intensify the synthesis of similar inorganic nanoparticles via multistep chemical precipitation processes.

Investigating the Flow Characteristics of Superhydrophobic U-Shaped Microchannels

Hydrophobicity has been widely reported for its superior behavior in drag reduction, self-cleaning, and anti-corrosion in many areas. Especially in engineering design, the research of the unique property of the slip flow with complex flow patterns is essential for practical applications. In this paper, the flow characteristics of a superhydrophobic U-shaped microchannel are systematically investigated, as the curved part is a fundamental component in microfluids. A slip model is established based on theoretical and experimental solutions. Various types of U-shaped microchannels, radii of curvature, and contact angles are studied with a wide range of Reynolds numbers from 0 to 300. We propose a velocity distribution to examine the non-uniformity of slip velocity on the cross-section. This imbalance is improved with an increase in the apparent contact angle and flow rate, and a decrease in the radius of curvature. The secondary flow and vortices generated by the centrifugal force are enhanced, and their positions are changed due to the slippery boundary. The results show a considerable drag reduction from 10% to 40% with different contact angles. The variation of curvature does not have a decisive impact on the final performance when the surface wettability maintains a steady state. Our research elucidates the physical principle of the slip model in curved channels, showing extensive applications of hydrophobicity in the design of complex microchips and the optimization strategy of heat transfer systems.

Performance prediction of a distributed Joule-Thomson effect cooler with pillars

• Heat transfer and throttling coupling is used to replace the traditional constant enthalpy throttling. • The performance of the J-T cooler is predicted by simulation. • A novel J-T cooler with multi-layer, multi-pillar micro-channels was designed. Hampson type Joule-Thomson (J-T) throttle coolers are widely used for cooling infrared detectors and many electronic components. The conventional J-T throttle coolers are not compact, with low heat transfer efficiency and small cooling capacity. In this paper, a stacked column cluster type microchannel distributed J-T throttle cooler is designed through combining a compact microchannel etched and shaped by photolithography and an atomic diffusion fusion welding process with a J-T throttle cooler. The dimensions of the cooler are 10 mm for the inlet section, 145 mm for the throttling and heat exchange section,10 mm for the expansion chamber, with 6 layers staggered high pressure channels and 6 low pressure channels. The cooling performance of the cooler under various low-temperature and high-pressure operating conditions were studied through simulations, and the results showed that the cold-end temperatures were 158.0, 147.9, 146.1, 144.1, and 141.1 K for an inlet pressure of 5.20 MPa and inlet temperatures of 280.0, 270.0, 260.0, 250.0, and 240.0 K, respectively, with argon as the work gas. The cold-end temperatures were 163.6, 159.4, 156.8, 154.6, and 152.7 K for an inlet pressure of 5.60, 6.00, 6.40, 6.80, and 7.20 MPa respectively in 288.0 K inlet temperature. In the process of working medium flow and heat transfer in the microcolumn group channel of the cooler, the temperature and pressure change significantly. When the working medium in the flow reaches the phase change state, that is, the phase change temperature and pressure reach, due to the gas liquefies and the flow rate drops, the working medium loses the gas throttling refrigeration effect, and the temperature no longer decreases significantly, and the refrigeration temperature is limited by this. In addition, compared with different inlet pressures, when the inlet temperature is 280.0 K, the 5.20 MPa nitrogen throttling refrigeration temperature is close to the argon gas at 2.98 MPa, which are 223.4 K and 234.9 K, respectively. Therefore, high pressure nitrogen can be considered to replace low pressure argon in engineering applications. In view of the problems involved in the research process of traditional micro-channel throttling coolers, the innovative solutions are put forward in this paper, which can bring new innovations and thoughts for the future research and application of such problems.

A new type of liquid-cooled channel thermal characteristics analysis and optimization based on the optimal characteristics of 24 types of channels

The battery thermal management system (BTMS) is an important guarantee that the batteries of new energy vehicles work efficiently and safely, so it is particularly important to design a liquid cooling channel with good cooling performance and low power consumption. Based on 6 types of common local channel geometries (square, triangular, diamond, trapezoid, hexagonal, etc.), 24 types of liquid-cooled plate channel structures were proposed by adding V- and X-shaped differential flow channel inside. Analyzed the flow characteristics, pressure drop and heat transfer characteristics of the 24 different types of liquid-cooled channels, to clarify the reasons for the differences in heat dissipation level and pressure drop of each type of micro channel, and to obtain the optimal channel types. For the structural parameters of the optimal channel types, the NSGA-II algorithm was used for multi-objective optimization. Compared to CFD simulation results, the relative errors were within 3%. To further improve the comprehensive performance of the liquid-cooled plate, the optimized model would be analyzed for channel arcing. The optimized results showed an average temperature reduction of 0.36°C (1.01%) and a pressure drop reduction of 132.43Pa (64.72%) compared to the base model. The optimal channel features obtained in this study will provide a reference for the selection of channel types and local feature optimization.

Pool boiling heat transfer characteristics of a stepped microchannel structured heating surface

Structured heating surfaces modify the bubble ebullition cycle in pool boiling, thereby enhancing heat transfer. The present work explores an innovative structured heating surface for heat transfer enhancement in pool boiling. Two types of microstructured, i.e., stepped microchannels (SMC) and stepped-segmented microchannels (SSMC) surfaces, have been fabricated on a heating surface, and their heat transfer characteristics are experimentally investigated. Saturated pool boiling experiments are performed with deionized water at atmospheric pressure, and the performance of both the structured surfaces is compared with a plain copper heating surface. All three heating surfaces are fabricated using a wire-EDM process with the same footprint area of 10 × 10 mm2. The SSMC structured surface exhibits the maximum heat transfer coefficient (HTC) and results in 296% heat transfer enhancement compared to the plain copper surface. The surface also makes a 224% enhancement in the critical heat flux (CHF) compared to the plain copper surface. Compared to the plain copper surface, the SMC structured surface shows an enhancement of 200% in HTC and 162% in CHF. For the same operating conditions, the SSMC structured surface shows better pool boiling heat transfer characteristics than the similar structured surfaces reported in the literature. More nucleation sites, better bubble evolution along the expanding cross-section stepped channel, and efficient rewetting of the heating surface contribute to the excellent thermal performance of the SSMC structured surface.

Elasto-Inertial Particle Focusing in Microchannel with T-Shaped Cross-Section

Recently, particle manipulation in non-Newtonian fluids has attracted increasing attention because of a good particle focusing toward the mid-plane of a channel. In this research, we proposed a simple and robust fabrication method to make a microchannel with various T-shaped cross-sections for particle focusing and separation in a viscoelastic solution. SU-8-based soft lithography was used to form three different types of microchannels with T-shaped cross-sections, which enabled self-alignment and plasma bonding between two PDMS molds. The effects of the flow rate and geometric shape of the cross-sections on particle focusing were evaluated in straight microchannels with T-shaped cross-sections. Moreover, by taking images from the top and side part of the channels, it was possible to confirm the position of the particles three-dimensionally. The effects of the corner angle of the channel and the aspect ratio of the height to width of the T shape on the elasto-inertial focusing phenomenon were evaluated and compared with each other using numerical simulation. Simulation results for the particle focusing agreed well with the experimental results both in qualitatively and quantitatively. Furthermore, the numerical study showed a potential implication for particle separation depending on its size when the aspect ratio of the T-shaped microchannel and the flow rate were appropriately leveraged.