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Journal articles on the topic 'Microchannel'
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1
Hurtado-Venegas, Ignacio, Víctor A. Martínez, Vasco Diego A., Roberto Ortega-Aguilera, Paula A. Zapata, Francisco A. Cataño, and Alifhers S. Mestra. "Numerical Study About Nanofluids of Spherical and Tube-Shaped TiO2 Nanomaterials on the Thermal Performance and Entropy Generation of Different Cross-Section Microchannel Heat Sinks." Journal of Nanofluids 12, no. 1 (February 1, 2023): 65–77. http://dx.doi.org/10.1166/jon.2023.1911.
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We numerically evaluated the thermal performance of microchannel heat sinks, considering rectangular, hexagonal, and circular cross-sections. Moreover, as a passive heat transfer augmentation technique, dimples were added to improve the rectangular microchannel heat sinks. These simulations use nanofluids based on TiO2 nanoparticles or nanotubes dispersed in bidistilled water as working fluids. The mathematical model considered variable thermophysical properties of the nanofluids; for this purpose, polynomial fittings correlate the dependence of the thermophysical properties on the temperature. We considered a heat flux of q″ = 50 W/cm2 at the microchannel’s lower surface as a boundary condition along with laminar flow conditions. The numerical simulations allowed the Nusselt numbers and entropy generation calculation, which were the basis for the thermal performance calculation. Regarding the effect of TiO2 nanoparticles shape, spherical TiO2 nanoparticles based nanofluids using rectangular microchannels improve the Nusselt number. Moreover, the frictional entropy decreases with nanofluids based on TiO2 nanotubes, but the thermal entropy decreases with nanofluids based on TiO2 nanotubes. Incorporating dimples in the rectangular microchannel enhances the Nusselt numbers and lowers the entropy generation. Considering the Reynolds number range and from the perspective of Nusselt number and entropy generation, we concluded that the microchannels must be operated at a high Reynolds number to improve the microchannel heat sinks thermal performance.
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Doan, Minhhung, Thanhtrung Dang, and Xuanvien Nguyen. "The Effects of Gravity on the Pressure Drop and Heat Transfer Characteristics of Steam in Microchannels: An Experimental Study." Energies 13, no. 14 (July 11, 2020): 3575. http://dx.doi.org/10.3390/en13143575.
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Experiments were carried out to investigate the pressure drop and heat transfer behaviors of a microchannel condenser. The effects of gravity on the condensation of steam in the microchannels were investigated for both horizontal and vertical cases. For the experimental results, the pressure drop of vertical microchannels in the condenser is lower than for horizontal microchannels. In the case of the horizontal microchannel, as the mass flow rate of steam increases from 0.01 g·s−1 to 0.06 g·s−1, the pressure drop increases from 1.5 kPa to 50 kPa, respectively. While the mass flow rate of steam in the vertical microchannel case increases from 0.01 g·s−1 to 0.06 g·s−1, the pressure drop increases from 2.0 kPa to 44 kPa, respectively. This clearly indicates that the gravitational acceleration affects the pressure drop. The pressure drop of the vertical microchannel is lower than that obtained from the horizontal microchannel. In addition, the capacity of the condenser is the same in both cases. This leads to the performance index obtained from the vertical microchannel condenser being higher than that obtained from the horizontal microchannel condenser. These results are important contributions to the research on the condensation of steam in microchannels.
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Wei, Xiaojin, Yogendra Joshi, and Michael K. Patterson. "Experimental and Numerical Study of a Stacked Microchannel Heat Sink for Liquid Cooling of Microelectronic Devices." Journal of Heat Transfer 129, no. 10 (February 23, 2007): 1432–44. http://dx.doi.org/10.1115/1.2754781.
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One of the promising liquid cooling techniques for microelectronics is attaching a microchannel heat sink to, or directly fabricating microchannels on, the inactive side of the chip. A stacked microchannel heat sink integrates many layers of microchannels and manifold layers into one stack. Compared with single-layered microchannels, stacked microchannels provide larger flow passages, so that for a fixed heat load the required pressure drop is significantly reduced. Better temperature uniformity can be achieved by arranging counterflow in adjacent microchannel layers. The dedicated manifolds help to distribute coolant uniformly to microchannels. In the present work, a stacked microchannel heat sink is fabricated using silicon micromachining techniques. Thermal performance of the stacked microchannel heat sink is characterized through experimental measurements and numerical simulations. Effects of coolant flow direction, flow rate allocation among layers, and nonuniform heating are studied. Wall temperature profiles are measured using an array of nine platinum thin-film resistive temperature detectors deposited simultaneously with thin-film platinum heaters on the backside of the stacked structure. Excellent overall cooling performance (0.09°C∕Wcm2) for the stacked microchannel heat sink has been shown in the experiments. It has also been identified that over the tested flow rate range, counterflow arrangement provides better temperature uniformity, while parallel flow has the best performance in reducing the peak temperature. Conjugate heat transfer effects for stacked microchannels for different flow conditions are investigated through numerical simulations. Based on the results, some general design guidelines for stacked microchannel heat sinks are provided.
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Lin, C. M., T. C. Lin, C. M. Tan, and T. H. Tsai. "Computational Modeling of Microchannel Flows on Laboratory Compact Disk (LABCD)." Journal of Mechanics 26, no. 2 (June 2010): 239–47. http://dx.doi.org/10.1017/s1727719100003099.
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AbstractThis paper models and analyzes flows in linear and curved microchannels on a rotating Laboratory Compact Disk (LabCD). The effects of centrifugal force are introduced into the governing equations of the microchannel flow to promote the fluidic velocity in the microchannel. The microchannel types on the LabCD must be designed following a process of mathematical identification. A flow model which takes into account the combined effects of viscosity, capillary forces, pressure difference and rotation is developed. A reduction-order technique is applied to obtain linear and nonlinear governing equations for flows in straight and curviform microchannels, respectively. The analytical solutions for the flow in the tubular microchannel are obtained using the Laplace transform method, while the numerical solutions for the curviform microchannel or microchannel with a varying cross-section are obtained using a piecewise linear method. The results show that the analyzed models are easily presented by a mathematical expression for the case of a tubular microchannel and simulated using a numerical program for the case of special microchannels. The modeling presented in this paper enables the performance of LabCD devices to be significantly enhanced by providing insights into the fluid flow behavior in microchannels of varying configurations under different rotational velocities.
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Hu, Wenju, and Xin Zhang. "Study on the Coupling Effect of Heat Transfer and Refrigerant Distribution in the Flat Tube of a Microchannel Evaporator." Energies 15, no. 14 (July 20, 2022): 5252. http://dx.doi.org/10.3390/en15145252.
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Refrigerant maldistribution severely deteriorates the heat transfer performance of a microchannel evaporator. Compared with the refrigerant distribution among flat tubes along the header, refrigerant distribution among microchannels in the flat tube in the airflow direction has barely been paid attention. In this paper, a heat transfer mathematical model of a microchannel evaporator’s flat tube composed of vertically placed parallel microchannels in the airflow direction was developed. The Refrigerant distribution among the microchannels was evaluated and its influence on heat transfer between air and refrigerant was analyzed. The results showed that the refrigerant distribution and heat transfer performance between air and refrigerant were interrelated and interacted with each other. The temperature of the air leaving the microchannel evaporator changed along the microchannel because of uneven refrigerant distribution among the microchannels, and the air temperature difference between air leaving out of the bottom and the top of the evaporator was approximately 2.13 °C. Ignoring the heat transfer from adjacent microchannels will lead to a small heat transfer deviation for the flat tube; thus, heat transfer among microchannels can be neglected.
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Zhou, Shengnan, Bifen Shu, Zukang Yu, Yan Huang, and Yuqi Zhang. "Experimental Study and Mechanism Analysis of the Flow Boiling and Heat Transfer Characteristics in Microchannels with Different Surface Wettability." Micromachines 12, no. 8 (July 27, 2021): 881. http://dx.doi.org/10.3390/mi12080881.
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In this paper experiments have been conducted to investigate the flow boiling and heat transfer characteristics in microchannels with three different surface wettability. Three types of microchannels with a super-hydrophilic surface (θ ≈ 0°), a hydrophilic surface (θ = 43°) and an untreated surface (θ = 70°) were prepared. The results show that the average heat transfer coefficient of a super-hydrophilic surface microchannel is significantly higher than that of an untreated surface microchannel, especially when the mass flux is high. The visualization of the flow patterns states that the number of bubble nucleation generated in the super-hydrophilic microchannel at the beginning of the flow boiling is significantly more than that in the untreated microchannel. Through detailed analysis of the experimental data, flow patterns and microchannel surface SEM images, it can be inferred that the super-hydrophilic surface microchannel has more active nucleation cavities, a high nucleation rate and a large nucleation number, a small bubble departure diameter and a fast departure frequency, thereby promoting the flow and heat transfer in the microchannel. In addition, through the force analysis of the vapor-liquid interface, the mechanism that the super-hydrophilic microchannel without dryout under high heat flux conditions is clarified.
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Huang, ZeChen. "Current Status and Prospect of Microchannel Research." Highlights in Science, Engineering and Technology 38 (March 16, 2023): 605–11. http://dx.doi.org/10.54097/hset.v38i.5890.
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The application of microchannel in engineering field is becoming more and more extensive, which has attracted extensive attention of researchers at home and abroad. In the field of microelectronics technology, if the heat cannot be dissipated effectively, the working temperature of electronic devices will be seriously affected. Microchannel is an effective means to solve the heat dissipation problem. This paper shows the research status of microchannels by enumerating the research achievements of microchannels at home and abroad. By using the methods of literature review and comparison, four main problems of microchannel research in China are pointed out: the commercial production of microchannel. The problems caused by the application of micro channels to products, the risk of slow technological innovation is decreasing, the potential for future growth and the lack of uniform industry standards. Finally, the future development and research of microchannel are prospected, and some suggestions are put forward to provide reference for the future research and development of microchannel technology in China.
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Huang, C. Y., and J. S. Li. "Rarefaction Effect on Gas Flow in Microchannels with Various Aspect Ratios." Journal of Mechanics 33, no. 1 (July 1, 2016): N1—N6. http://dx.doi.org/10.1017/jmech.2016.62.
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AbstractThis study investigated the effect of rarefaction on microchannel gas flow by measuring pressure profiles in microchannels with various aspect ratios. Pressure-sensitive paint (PSP) was applied in rectangular microchannels to obtain the global flow field by using detailed pressure data. The effect of rarefaction on the microchannel gas flow was clearly observed in the microchannels through the pressure data obtained using PSP measurements. A nonlinear pressure distribution was observed inside the microchannels, and this distribution decreased as the Knudsen number (Kn) increased because of the rarefaction effect. The dimensionless pressure deviation from the linear assumption dropped from 0.25 to 0 when the outlet Kn number increased to 0.066 in the 100-μm-wide microchannel, and the dimensionless location of the maximum deviation moved upstream because of the gaseous slip at the wall. The nonlinear pressure distribution also decreased in the 50-μm-wide microchannel as the outlet Kn number increased; however, the peak of the maximum deviation could no longer be identified because of the characteristic of the narrow channel.
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Tyrinov, A. I. "TEMPERATURE STABILIZATION OF MICROCHANNEL FLOW." Thermophysics and Thermal Power Engineering 41, no. 1 (December 3, 2018): 20–26. http://dx.doi.org/10.31472/ttpe.1.2019.3.
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The purpose of this work is to determine the nature of the effect of the intensity of slipping the medium on the walls of the microchannel on the temperature stabilization of the flow in the microchannel. To achieve this goal, numerical simulation of the start flow in flat, round, and rectangular microchannels was performed using the Boltzmann Speech Method. The heat exchange in the initial region in flat, round and rectangular microchannels is analyzed. The influence of the fluid acceleration intensity on the stabilization of the flow temperature in the microchannel is determined.
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Yu, Guoqing, Wubin Ding, and Cheng Xu. "Research on the thermal and flow characteristics of novel microchannel PV/T collectors." Thermal Science, no. 00 (2023): 227. http://dx.doi.org/10.2298/tsci230522227y.
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A novel microchannel photovoltaic photothermal collector is investigated, comprising of photovoltaic cells and collectors. Its distinctive feature lies in the flow mode of its microchannels. The novel microchannel investigated in this study is composed of multiple drums, allowing for a non-parallel flow configuration. This distributional flow pattern facilitates enhanced contact between the water flow and the heat transfer surface, thereby resulting in significantly improved heat transfer efficiency. characteristics and flow properties are studied to enhance the thermoelectric performance and broaden the application scope of photovoltaic photothermal collector technology. This study focuses on parallel microchannels and three-passes microchannels for comparison, employing Ansys Fluent to simulate electrical and thermal efficiencies, temperature distribution, velocity field, and pressure field under typical operating conditions. The validity of the model is verified by comparing it with experimental panel surface temperature data. Within this framework, various inlet flow conditions are examined to investigate the collector's temperature profile, standard deviation of temperature distribution, pressure drops, and maximum velocity. Results indicate that under specific circumstances, the heat collection performance of parallel microchannel photovoltaic photothermal collectors is inferior to that of three-passes microchannel counterparts. Both types exhibit reduced efficiency during winter conditions; however, three-passes microchannels experience a more significant decline at 22.4%, compared to 19.7% for parallel microchannels. In terms of flow resistance characteristics, parallel microchannels demonstrate advantages in terms of pressure drops over three-passes configurations as they exhibit nearly 3935 Pa lower values under certain conditions. Regarding temperature uniformity in photovoltaic-photothermal systems, parallel microchannel collectors outperform their three-passes counterparts.
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Atmaramani, Rahul, Bryan Black, Kevin Lam, Vinit Sheth, Joseph Pancrazio, David Schmidtke, and Nesreen Alsmadi. "The Effect of Microfluidic Geometry on Myoblast Migration." Micromachines 10, no. 2 (February 21, 2019): 143. http://dx.doi.org/10.3390/mi10020143.
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In vitro systems comprised of wells interconnected by microchannels have emerged as a platform for the study of cell migration or multicellular models. In the present study, we systematically evaluated the effect of microchannel width on spontaneous myoblast migration across these microchannels—from the proximal to the distal chamber. Myoblast migration was examined in microfluidic devices with varying microchannel widths of 1.5–20 µm, and in chips with uniform microchannel widths over time spans that are relevant for myoblast-to-myofiber differentiation in vitro. We found that the likelihood of spontaneous myoblast migration was microchannel width dependent and that a width of 3 µm was necessary to limit spontaneous migration below 5% of cells in the seeded well after 48 h. These results inform the future design of Polydimethylsiloxane (PDMS) microchannel-based co-culture platforms as well as future in vitro studies of myoblast migration.
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Yu, Hao, Tongling Li, Xiaoxin Zeng, Tianbiao He, and Ning Mao. "A Critical Review on Geometric Improvements for Heat Transfer Augmentation of Microchannels." Energies 15, no. 24 (December 14, 2022): 9474. http://dx.doi.org/10.3390/en15249474.
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With the application of microdevices in the building engineering, aerospace industry, electronic devices, nuclear energy, and so on, the dissipation of high heat flux has become an urgent problem to be solved. Microchannel heat sinks have become an effective means of thermal management for microdevices and enhancements for equipment due to their higher heat transfer and small scale. However, because of the increasing requirements of microdevices for thermal load and temperature control and energy savings, high efficiency heat exchangers, especially microchannels are receiving more and more attention. To further improve the performance of microchannels, optimizing the channel geometry has become a very important passive technology to effectively enhance the heat transfer of the microchannel heat sink. Therefore, in this paper, the microchannel geometry characteristics of previous studies are reviewed, classified and summarized. The review is mainly focused on microchannel geometry features and structural design to strengthen the effect of heat transfer and pressure drop. In addition, the correlation between boiling heat transfer and geometric characteristics of microchannel flow is also presented, and the future research direction of microchannel geometry design is discussed.
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Pelenis, Donatas, Gailius Vanagas, Dovydas Barauskas, Mindaugas Dzikaras, Marius Mikolajūnas, and Darius Viržonis. "Acoustic Streaming Efficiency in a Microfluidic Biosensor with an Integrated CMUT." Micromachines 14, no. 5 (May 8, 2023): 1012. http://dx.doi.org/10.3390/mi14051012.
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The effect of microchannel height on acoustic streaming velocity and capacitive micromachined ultrasound transducer (CMUT) cell damping was investigated. Microchannels with heights ranging from 0.15 to 1.75 mm were used in experiments, and computational microchannel models with heights varying from 10 to 1800 micrometers were simulated. Both simulated and measured data show local minima and maxima of acoustic streaming efficiency associated with the wavelength of the `bulk acoustic wave excited at 5 MHz frequency. Local minima occur at microchannel heights that are multiples of half the wavelength (150 μm), which are caused by destructive interference between excited and reflected acoustic waves. Therefore, microchannel heights that are not multiples of 150 μm are more favorable for higher acoustic streaming effectiveness since destructive interference decreases the acoustic streaming effectiveness by more than 4 times. On average, the experimental data show slightly higher velocities for smaller microchannels than the simulated data, but the overall observation of higher streaming velocities in larger microchannels is not altered. In additional simulation, at small microchannel heights (10–350 μm), local minima at microchannel heights that are multiples of 150 μm were observed, indicating the interference between excited and reflected waves and causing acoustic damping of comparatively compliant CMUT membranes. Increasing the microchannel height to over 100 μm tends to eliminate the acoustic damping effect as the local minima of the CMUT membrane swing amplitude approach the maximum value of 42 nm, which is the calculated amplitude of the freely swinging membrane under the described conditions. At optimum conditions, an acoustic streaming velocity of over 2 mm/s in a 1.8 mm-high microchannel was achieved.
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Kong, Lingjian, and Guangzhe Liu. "Impact of secondary flow on the single-phase flow in spiral microchannels: An experimental study." Advances in Mechanical Engineering 14, no. 9 (September 2022): 168781322211275. http://dx.doi.org/10.1177/16878132221127560.
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Spiral microchannels have a wide range of applications, such as microscale cooling, fluid mixing and particle sorting, in micro-fluidic devices. The flow characteristics of spiral microchannels play an important role in the design and operation of these devices. An experimental study of the laminar flow characteristics in spiral microchannels is conducted for different Reynolds numbers from 51 to 985. Microchannels have rectangular cross sections and follow Archimedean spiral pathways with different spiral and cross-section parameters. The results show that the pressure drop of the spiral microchannel increases with increasing spiral diameter and aspect ratio, but decreases with spiral pitch and hydrodynamic diameter. In addition, the effect of the spiral and cross-section parameters on pressure drop is evident at the high Reynolds number. Under the influence of additional friction caused by the secondary flow, the friction factor of the spiral microchannel is higher than that of the straight channel, and its value increases with the increase in curvature of the microchannel. The correlation of the Poiseuille number in the spiral microchannel is established on the basis of the experimental results, and 95.3% of the experimental data fall within the error band of ±18%.
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Zhang, Donghui, Haiyang Xu, Yi Chen, Leiqing Wang, Jian Qu, Mingfa Wu, and Zhiping Zhou. "Boiling Heat Transfer Performance of Parallel Porous Microchannels." Energies 13, no. 11 (June 10, 2020): 2970. http://dx.doi.org/10.3390/en13112970.
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Flow boiling in microporous layers has attracted a great deal of attention in the enhanced heat transfer field due to its high heat dissipation potential. In this study, flow boiling experiments were performed on both porous microchannels and a copper-based microchannel, using water as the coolant. As the heat flux was less than 80 W/cm2, the porous microchannels presented significantly higher boiling heat transfer coefficients than the copper-based microchannel. This was closely associated with the promotion of the nucleation site density of the porous coating. With the further increase in heat flux, the heat transfer coefficients of the porous microchannels were close to those of the copper-based sample. The boiling process in the porous microchannel was found to be dominated by the nucleate boiling mechanism from low to moderate heat flux (<80 W/cm2).This switched to the convection boiling mode at high heat flux. The porous samples were able to mitigate flow instability greatly. A visual observation revealed that porous microchannels could suppress the flow fluctuation due to the establishment of a stable nucleate boiling process. Porous microchannels showed no advantage over the copper-based sample in the critical heat flux. The optimal thickness-to-particle-size ratio (δ/d) for the porous microchannel was confirmed to be between 2–5. In this range, the maximum enhanced effect on boiling heat transfer could be achieved.
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Xie, Fei, Yun Shan Wang, Wei Wang, Wen Gang Wu, Zhi Hong Li, Gilad Yossifon, and Hsueh Chia Chang. "An Experimental Study on the Side-Opening Filling Process at the Interface between Microchannels with Different Widths." Key Engineering Materials 483 (June 2011): 293–96. http://dx.doi.org/10.4028/www.scientific.net/kem.483.293.
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Micro/nanochannel is of great importance due to its wide applications in micro total analysis system. In a given micro/nanofluidic device, the nanochannel and microchannel can works as function provider and reagent delivering passage, respectively. The easiest way to fabricate micro/nanochannel is depositing material onto a predefined microchannel until nanometer-sized pattern is obtained. Although the deposition process inside the microchannel has been studied before, the filling performance at the side-opening, the connection between microchannels with different widths, is limited studied. The different filling performance at side-opening will lead to a distinct geometrical size. In this work, side-opening filling process during a low pressure chemical vapor deposition of silicon dioxide onto pre-etched microchannels with patterns of straight, triangle and rhombus shapes was preliminarily studied. A filling factor was defined to describe the side-opening filling performance. The present results indicated that the side-opening filling will be affected by the side-opening width, the depth of the microchannel and the microchannel shape.
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Srivastava, Pankaj, and Anupam Dewan. "A study of turbulent heat transfer in convergent-divergent shaped microchannel with ribs and cavities using CFD." Journal of Mechanical Engineering and Sciences 14, no. 1 (March 23, 2020): 6344–61. http://dx.doi.org/10.15282/jmes.14.1.2020.12.0497.
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This paper presents the effects of microchannel shape with ribs and cavities on turbulent heat transfer. Three-dimensional conjugate heat transfer using the SST k-ω turbulence model has been investigated for four different microchannels, namely, rectangular, rectangular with ribs and cavities, convergent-divergent (CD) and convergent-divergent with Ribs and Cavities (CD-RC). The flow field, pressure and temperature distributions and friction factor are analyzed, and thermal resistance and average Nusselt number are compared. The thermal performance of the CD-RC microchannel is found to be better than that of other microchannels considered in terms of an average Nusselt number increased from 16% to 40%. Heat transfer increases due to a strong fluid mixing and periodic interruption of boundary-layer. It is observed that with an increase in Reynolds number (Re), the thermal resitance drops rapidly. The thermal resistance of the CD-RC microchannel is decreased by 30% than that of the rectangular microchannel for Re ranging from 2500 to 7000. However, such design of microchannel loses its heat transfer effectiveness due to a high pumping power at high values of Re.
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Zhao, Jiwen, Kunlong Zhao, Xiaobin Hao, Yicun Li, Sen Zhang, Benjian Liu, Bing Dai, Wenxin Cao, and Jiaqi Zhu. "Numerical Study on the Heat Dissipation Performance of Diamond Microchannels under High Heat Flux Density." Processes 12, no. 8 (August 9, 2024): 1675. http://dx.doi.org/10.3390/pr12081675.
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Heat dissipation significantly limits semiconductor component performance improvement. Thermal management devices are pivotal for electronic chip heat dissipation, with the enhanced thermal conductivity of materials being crucial for their effectiveness. This study focuses on single-crystal diamond, renowned for its exceptional natural thermal conductivity, investigating diamond microchannels using finite element simulations. Initially, a validated mathematical model for microchannel flow heat transfer was established. Subsequently, the heat dissipation performance of typical microchannel materials was analyzed, highlighting the diamond’s impact. This study also explores diamond microchannel topologies under high-power conditions, revealing unmatched advantages in ultra-high heat flux density dissipation. At 800 W/cm2 and inlet flow rates of 0.4–1 m/s, diamond microchannels exhibit lower maximum temperatures compared to pure copper microchannels by 7.0, 7.2, 7.4, and 7.5 °C, respectively. Rectangular cross-section microchannels demonstrate superior heat dissipation, considering diamond processing costs. The exploration of angular structures with varying parameters shows significant temperature reductions with increasing complexity, such as a 2.4 °C drop at i = 4. The analysis of shape parameter ki indicates optimal heat dissipation performance at ki = 1.1. This research offers crucial insights for developing and optimizing diamond microchannel devices under ultra-high-heat-flux-density conditions, guiding future advancements in thermal management technology.
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Gong, Liang, and Bo Wei. "The Characteristics of Fluid Flow and Heat Transfer in Wavy, Dimple and Wavy-Dimple Microchannels." Applied Mechanics and Materials 394 (September 2013): 173–78. http://dx.doi.org/10.4028/www.scientific.net/amm.394.173.
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The flow and heat transfer characteristics were numerically studied in wave, dimple and wave-dimple microchannels for thermal managements on the chip of Intel i7-996X with heat flux of 0.56 W/mm2.The results show that, in microchannles heat sink, the dimple structure could reduce the flow resistances and the wavy wall could enhance heat transfer. According to the both advantages, two types of microchannel heat sink both with dimples and wavy walls were designed, and the flow and heat transfer characteristics were numerically studied. It is proved that the wave-dimple microchannels heat sink holds the characteristics of enhancing heat transfer with low pressure drop, which implies it has great potential of development and application prospect.
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Tu, Yi, and Yu Zeng. "Comparative Study of the Thermal and Hydraulic Performance of Supercritical CO2 and Water in Microchannels Based on Entropy Generation." Entropy 24, no. 9 (September 16, 2022): 1312. http://dx.doi.org/10.3390/e24091312.
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The excellent thermophysical properties of supercritical CO2 (sCO2) close to the pseudocritical point make it possible to replace water as the coolant of microchannels in application of a high heat flux radiator. The computational fluid dynamics (CFD) method verified by experimental data is used to make a comparison of the thermal hydraulic behavior in CO2-cooled and of water-cooled microchannels. The operation conditions of the CO2-based cooling cases cover the pseudocritical point (with the inlet temperature range of 306~320 K and the working pressure of 8 MPa), and the water-based cooling case has an inlet temperature of 308 K at the working pressure of 0.1 MPa. The channel types include the straight and zigzag microchannels with 90°, 120°, and 150° bending angles, respectively. The analysis result shows that, only when the state of CO2 is close to the pseudocritical point, the sCO2-cooled microchannel is of a higher average heat convection coefficient and a lower average temperature of the heated surface compared to the water-cooled microchannel. The entropy generation rate of the sCO2-cooled microchannel can reach 0.58~0.69 times that of the entropy generation rate for the water-cooled microchannel. Adopting the zigzag structure can enhance the heat transfer, but it does not improve the comprehensive performance represented by the entropy generation rate in the sCO2-cooled microchannel.
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Jawade, Shubham. "Thermal Analysis of Microchannels Heat Sink using Super-hydrophobic Surface." International Journal for Research in Applied Science and Engineering Technology 9, no. 9 (September 30, 2021): 654–57. http://dx.doi.org/10.22214/ijraset.2021.38024.
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Abstract: Electronics devices are the major part of modern technology and with the rapid growth of miniaturizations of electronic devices, the heat dissipation from these devices have been the objective for researchers. This heat dissipation has to done effectively otherwise this will affect the life of device and will result decrement in efficiency. Increasing the heat transfer rates from electronic devices has long been a quest. Microchannel heat sink is one of the best option for removing heat from the electronics devices due to its compact size which provides high surface area to volume ratio that enables higher heat transfer rates. Microchannels are the flow passages having hydraulic diameter ranges from 10 micrometer (µm) to 200µm. Microchannel heat sink enhances the feasibility of electronics device. Microchannels with hydrophobic surface are a promising candidate for cooling of electronics devices, as hydrophobic surface can be used to create friction free regions with a channel which effectively reduce pumping power, flow pressure drop and frictional factor compared to Microchannel without Hydrophobic surface. This paper deals with the detailed behavior of Microchannel with hydrophobic surface. In this work, rectangular cross section with 0.8 mm (800 micron) hydraulic diameter super hydrophobic microchannel is used. Keywords: Microchannel, Hydrophobic surface, Heat transfer rate, Frictional factor.
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Wang, Zhaohui, Weibing Ding, Yiwei Fan, Jian Wang, Jie Chen, and Hongxia Wang. "Design of Improved Flow-Focusing Microchannel with Constricted Continuous Phase Inlet and Study of Fluid Flow Characteristics." Micromachines 13, no. 10 (October 19, 2022): 1776. http://dx.doi.org/10.3390/mi13101776.
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This paper proposed an improved flow-focusing microchannel with a constricted continuous phase inlet to increase microbubble generation frequency and reduce microbubbles’ diameter. The design variables were obtained by Latin hypercube sampling, and the radial basis function (RBF) surrogate model was used to establish the relationship between the objective function (microbubble diameter and generation frequency) and the design variables. Moreover, the optimized design of the nondominated sorting genetic algorithm II (NSGA-II) algorithm was carried out. Finally, the optimization results were verified by numerical simulations and compared with those of traditional microchannels. The results showed that dripping and squeezing regimes existed in the two microchannels. The constricted continuous phase inlet enhanced the flow-focusing effect of the improved microchannel. The diameter of microbubbles obtained from the improved microchannel was reduced from 2.8141 to 1.6949 μm, and the generation frequency was increased from 64.077 to 175.438 kHz at the same capillary numbers (Ca) compared with the traditional microchannel. According to the fitted linear function, it is known that the slope of decreasing microbubble diameter with increasing Ca number and the slope of increasing generation frequency with increasing Ca number are greater in the improved microchannel compared with those in the traditional microchannel.
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SONG, YOON S., and WALTER A. HARGRAVES. "Postprocess Contamination of Flexible Pouches Challenged by In Situ Immersion Biotest." Journal of Food Protection 61, no. 12 (December 1, 1998): 1644–48. http://dx.doi.org/10.4315/0362-028x-61.12.1644.
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Packages were evaluated for leaks by determining microbial penetration through microchannels as a function of test organism concentration, location in a retort, and microchannel diameter and length. A flexible pouch was used in an in situ immersion biotest coupled with a state-of-the-art retort. Microchannel diameters of 10 to 661 μm with 3- and 6-mm lengths were created by placing tungsten wires in vacuum heat-sealed flexible pouches. After removing the wires, these pouches were subsequently heat processed under pressure. They were then biotested in cooling water containing 103 and 106 CFU of motile Enterobacter aerogenes per ml for 30 min and were dried immediately after manual unloading. After incubation at 37°C for 3 days, they were visually examined for contamination. The high-temperature retorting process was shown to decrease microchannel diameters by an average of 20%. Generally, the smaller the microchannel diameter, the greater the percent shrinkage. Statistical analysis of the biotesting data showed that microchannel diameter and length had strong effects on microbial penetration (P < 0.01). Microbial concentration had a borderline significant effect (P < 0.05), but the effect of package location in the retort was not significant. At conservative conditions, such as a 3-mm microchannel length and a cooling water contamination level of 106 CFU/ml, the selected microorganism can penetrate microchannels with diameters as small as 7 μm. However, the minimum microchannel diameter for penetration could be as large as 46 μm at practical conditions of 6-mm microchannel length and contamination levels of 103 CFU/ml.
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Bao, Xiangzhong, Fei Yang, and Xuan Zhang. "Experimental Study of Flow Boiling Regimes Occurring in a Microfluidic T-Junction." Micromachines 14, no. 12 (December 13, 2023): 2235. http://dx.doi.org/10.3390/mi14122235.
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Microchannel flow boiling is an efficient cooling method for high-heat-flux electronic devices. To understand the flow boiling regime in a T-shaped microchannel, this paper prepared T-shaped microchannels of different sizes and designed an experimental platform for the visualization of flow boiling in microchannels, and aimed to study the evolution characteristics of two-phase flow patterns in T-shaped microchannels. The influences of the flow rate and channel size on the boiling flow pattern inside a T-shaped microchannel were experimentally observed and quantitatively described. The results indicate that the occurrence position of the vaporization core gradually migrates from branch channel to main channel as the wall temperature increases. The flow boiling at the bifurcation of the T-shaped microchannel mainly includes the extrusion fracture flow, bubble flow, plug–annular alternating flow and annular flow, in which the annular flow can be further divided into the intermittent annular flow and the stable annular flow. In addition, a high flow rate and small channel size can lead to the disappearance of the bubble flow, and the presence of the bubble flow delays the appearance of the annular flow.
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Gluzdov, D. S., and E. Ya Gatapova. "Modelling corners flow in rectangular microchannel." Journal of Physics: Conference Series 2119, no. 1 (December 1, 2021): 012114. http://dx.doi.org/10.1088/1742-6596/2119/1/012114.
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Abstract Rectangular microchannels are most common configuration in microfluidics. They can be used in many industries, for example in lab-on-chip devices. Despite standard fluid dynamics, microfluidics has a significant impact of wall boundary conditions on fluid flow. And in microfluidics, we cannot simply set no-slip boundary conditions if our goal is accurate modeling results. In rectangular microchannels, there is another important moment in modeling that is not present in circular pipes. The velocity profile of the fluid depends on the shear stress at the edges and the velocities at the walls of the microchannel change at different points of the cross-sectional wall of the microchannel. The fluid velocity is lower at the corners of a rectangular microchannel. In this paper, a solution is proposed to find a more accurate way to model the fluid flow in a rectangular microchannel by knowing the friction factor without shear stress distribution.
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Yang, Jinshan, Shaoming Dong, David Webster, John Gilmore, and Chengying Xu. "Characterization and Alignment of Carbon Nanofibers under Shear Force in Microchannel." Journal of Nanomaterials 2016 (2016): 1–6. http://dx.doi.org/10.1155/2016/1052478.
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This work presents a novel method to align CNFs by using shear forces in microchannels. Effect of two different microchannel sizes (1 mm × 0.1 mm and 1 mm × 0.2 mm) on CNFs alignment is investigated. SEM images of CNFs preform display significant alignment by both microchannels, which can be interpreted using a second-order alignment tensor and a manual angle meter. In the second-order alignment tensor description, an elongated ellipse can signify high degree of alignment in the direction of the major axis. When the microchannel size is 1 mm × 0.2 mm, the lengths of major and minor axes of the ellipse are 0.982 to 0.018. An angle meter manually shows that 85% of the CNFs are aligned in the direction between 60° and 90° when the microchannel is 1 mm × 0.2 mm. Both methods can demonstrate that better alignment of CNFs can be obtained using the 1 mm × 0.2 mm microchannel.
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Wei, Xiao Ling, Qing Hui Wang, and Min Qiang Pan. "Numerical Simulation of Velocity Distribution among Microchannels with Bifurcation Structures as Manifolds." Advanced Materials Research 108-111 (May 2010): 1009–12. http://dx.doi.org/10.4028/www.scientific.net/amr.108-111.1009.
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Manifold structure shows important effects on the velocity distribution among parallel microchannels. The bifurcation structure was adopted as the manifolds of microchannel array in a plane and a specific case was illustrated to estimate the effects of structural parameters on the velocity distribution using numerical simulation. Simulation result indicated that the velocity distribution appeared to be double W-shape, and somewhat symmetrical. In addition, the velocity values in each W-shape distribution also appeared symmetrical. It also indicated that two bifurcation channels from the same low-level bifurcation channel had different velocity values due to different singular losses. Larger microchannel length, smaller microchannel width or depth, larger RW or RL, suitable RZ were favor in obtaining relatively uniform velocity distribution among microchannels.
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Deng, Daxiang, Guang Pi, Weixun Zhang, Peng Wang, and Ting Fu. "Numerical Study of Double-Layered Microchannel Heat Sinks with Different Cross-Sectional Shapes." Entropy 21, no. 1 (December 25, 2018): 16. http://dx.doi.org/10.3390/e21010016.
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This work numerically studies the thermal and hydraulic performance of double-layered microchannel heat sinks (DL-MCHS) for their application in the cooling of high heat flux microelectronic devices. The superiority of double-layered microchannel heat sinks was assessed by a comparison with a single-layered microchannel heat sink (SL-MCHS) with the same triangular microchannels. Five DL-MCHSs with different cross-sectional shapes—triangular, rectangular, trapezoidal, circular and reentrant Ω-shaped—were explored and compared. The results showed that DL-MCHS decreased wall temperatures and thermal resistance considerably, induced much more uniform wall temperature distribution, and reduced the pressure drop and pumping power in comparison with SL-MCHS. The DL-MCHS with trapezoidal microchannels performed the worst with regard to thermal resistance, pressure drop, and pumping power. The DL-MCHS with rectangular microchannels produced the best overall thermal performance and seemed to be the optimum when thermal performance was the prime concern. Nevertheless, the DL-MCHS with reentrant Ω-shaped microchannels should be selected when pumping power consumption was the most important consideration.
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Jing, Dalei, and Lei He. "Thermal Characteristics of Staggered Double-Layer Microchannel Heat Sink." Entropy 20, no. 7 (July 19, 2018): 537. http://dx.doi.org/10.3390/e20070537.
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The present work numerically studies the thermal characteristics of a staggered double-layer microchannel heat sink (DLMCHS) with an offset between the upper layer of microchannels and lower layer of microchannels in the width direction, and investigates effects of inlet velocity and geometric parameters including the offset of the two layers of microchannels, vertical rib thickness and microchannel aspect ratio on the thermal resistance of the staggered DLMCHS. The present work found that the thermal resistance of the staggered DLMCHS increases with the increasing offset value when the vertical rib thickness is small, but decreases firstly and then increases as the offset value increases when the vertical rib thickness is large enough. Furthermore, the thermal resistance of the staggered DLMCHS decreases with the increasing offset when the aspect ratio is small, but increases with the increasing offset when the aspect ratio is large enough. Thus, for the DLMCHS with a small microchannel aspect ratio and large vertical rib thickness, the offset between the upper layer of microchannels and the lower layer of microchannels in the width direction is a potential method to reduce thermal resistance and improve the thermal performance of the DLMCHS.
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Ranjith Kumar, Valaparla, Karthik Balasubramanian, K. Kiran Kumar, Nikhil Tiwari, and Kanishk Bhatia. "Numerical investigation of fluid flow and heat transfer characteristics in novel circular wavy microchannel." Proceedings of the Institution of Mechanical Engineers, Part E: Journal of Process Mechanical Engineering 233, no. 5 (December 26, 2018): 954–66. http://dx.doi.org/10.1177/0954408918820757.
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In this study, the fluid flow and heat transfer behavior in a novel circular wavy microchannel design is numerically examined and compared with a sinusoidal wavy microchannel. The numerical studies were carried out in the Reynolds number range of 100–300 under a constant heat flux wall boundary condition. The sinusoidal profile has a continuously varying curvature, which peaks at the crests and troughs, and diminishes to naught at each section at the middle of adjacent crests and troughs. On the other hand, the circular profile has a curvature constant in magnitude (and alternating in direction). Heat transfer in wavy microchannels is enhanced by vortex flow induced by centrifugal instability, which in turn depends on the curvature of fluid channel profile. The sinusoidal wavy microchannel has a curvature continuously varying in a large range results in large fluctuations of Nusselt number, while the Nusselt number in the circular channel has smaller fluctuations. Hence, heat transfer performance of the circular wavy microchannel is higher than that of the sinusoidal wavy microchannel. Velocity vectors, velocity contours, and temperature contours are presented to aid the explanation of hydrodynamic and heat transfer characteristics of fluid flow in the novel circular wavy microchannels. The Nusselt number and pressure drop along the channel are also compared with the sinusoidal wavy microchannel using a performance factor.
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Kumar, Shailesh Ranjan, and Satyendra Singh. "Experimental Study on Microchannel with Addition of Microinserts Aiming Heat Transfer Performance Improvement." Water 14, no. 20 (October 18, 2022): 3291. http://dx.doi.org/10.3390/w14203291.
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Microchannel technology rapidly established itself as a practicable solution to the problem of the removal of extremely concentrated heat generation in present-day cooling fields. By implementing a better design structure, altering the working fluids and flow conditions, using various materials for fabrication, etc., it is possible to increase the heat transfer performance of microchannels. Two parameters that affect how well a microchannel transfers heat were only recently coupled, and the complicated coupling of the parameter that affects how well a microchannel sink transfers heat is still not well understood. The newest industrial developments, such as micro-electro-mechanical systems, high performance computing systems, high heat density generating future devices, such as 5G/6G devices, fuel cell power plants, etc., all present thermal challenges that require the use of microchannel technology. In this paper, single-phase flow in microchannels of various sizes, with or without microinserts, is described in terms of its thermal-fluid flow properties, including fluid flow characteristics and heat transfer characteristics considering the compound effects of variations of channel size and addition of microinserts. The trials were carried out using distilled water that had thermo-physical characteristics that varied with temperature. A microchannel with microinserts was developed for managing the high heat generation density equipment. The fluid flow and heat transfer characteristics are explored and analyzed for Reynolds numbers ranges from 125 to 4992, for 1 mm channel size, and from 250 to 9985, for 2 mm channel size. The cooling performance criteria are pressure drop characteristics, heat transfer characteristics, and overall performance, whereas the testing parameters were chosen for the variations in channel size and the addition of microinserts. The influence of inserting microinserts on microchannels is discussed. Results suggest that by inserting microinserts, the performance of the heat transfer of microchannels is significantly improved and, also, fluid flow resistance is increased. The criteria of the thermal performance factor are employed to assess the overall performance of the microchannel. Significant intensification of heat transfer is observed with indication that the addition of microinserts to microchannels and reduction in channel sizes exhibited improved overall performance.
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Jiang, Weiyu, Lili Sun, Jijin Mao, Zhang Donghui, and A. Levtsev. "Effect of Copper Particles Shape on the Heat Transfer Characteristics of Porous Microchannels During Boiling of Working Fluid." Bulletin of Science and Practice 7, no. 4 (April 15, 2021): 286–94. http://dx.doi.org/10.33619/2414-2948/65/32.
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In this paper, the heat transfer performance of porous microchannels sintered with spherical and dendritic copper particle is compared. The working fluid is deionized water. For uniform particle size sample, the dendritic-particle microchannel presents better boiling heat transfer performance than the spherical-particle one. It includes higher critical heat flux (CHF), which was related to the connected pore structure of the dendritic copper powder. For mixed particle size sample, the dendritic-particle microchannel also shows higher heat transfer coefficient and CHF. At high heat flux, the dendritic-particle microchannel can effectively suppress the pressure pulsation and maintain a relatively stable flow boiling state in the microchannel.
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Zhang, Dengying, Wenqiang Xing, Weiren Li, Shengming Liu, Yanli Dong, Lichun Zhang, Fengzhou Zhao, Jun Wang, and Zheng Xu. "Fabrication of Multiple Parallel Microchannels in a Single Microgroove via the Heating Assisted MIMIC Technique." Micromachines 13, no. 3 (February 25, 2022): 364. http://dx.doi.org/10.3390/mi13030364.
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For the first time, multiple parallel microchannels in a single microgroove have been fabricated by the heating-assisted micromolding in capillaries technique (HAMIMIC). Microchannel development, cross-sectional shape, and length were all explored in depth. The factors affecting the cross-sectional shape and length of the double-microchannel were also discussed. Finally, a special-shaped PDMS guiding mold was designed to control the cross-sectional shape and length of multiple parallel microchannels for controlled growth. The HAMIMIC technique provides a low-cost, straightforward, and repeatable way to create multiple parallel microchannels in a single microgroove, and will promote the progress of bifurcated vessels and thrombus vessels preparation technology.
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JING, DALEI, JIAN SONG, and YI SUI. "HYDRAULIC AND THERMAL PERFORMANCES OF LAMINAR FLOW IN FRACTAL TREELIKE BRANCHING MICROCHANNEL NETWORK WITH WALL VELOCITY SLIP." Fractals 28, no. 02 (March 2020): 2050022. http://dx.doi.org/10.1142/s0218348x2050022x.
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This work theoretically studies the effects of wall velocity slip on the hydraulic resistance and convective heat transfer of laminar flow in a microchannel network with symmetric fractal treelike branching layout. It is found that the slip can reduce the hydraulic resistance and enhance the Nusselt number of laminar flow in the network; furthermore, the slip can also affect the optimal structure of the fractal treelike microchannel network with minimum hydraulic resistance and maximum convective heat transfer. Under the size constraint of constant total channel surface area, the optimal diameter ratio of microchannels at two successive branching levels of the symmetric fractal treelike microchannel network with a minimized hydraulic resistance is only dependent on branching number [Formula: see text] in the manner of [Formula: see text] for no slip condition, but decreases with the increasing slip length, the increasing branching number and the increasing length ratio of microchannels at two successive branching levels for slip condition. The convective heat transfer of the treelike microchannel network is independent on the diameter ratio for no slip condition, but displays an increasing after decreasing trend with the increasing diameter ratio for slip condition. The symmetric treelike microchannel network with the worst convective heat transfer performance is the network with diameter ratio equaling one for slip condition.
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Huang, Xiang, Wei Zhou, Daxiang Deng, Bin Liu, and Kaiyong Jiang. "The Impacts of Surface Microchannels on the Transport Properties of Porous Fibrous Media Using Stochastic Pore Network Modeling." Materials 14, no. 24 (December 8, 2021): 7546. http://dx.doi.org/10.3390/ma14247546.
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A stochastic pore network modeling method with tailored structures is proposed to investigate the impacts of surface microchannels on the transport properties of porous fibrous media. Firstly, we simplify the original pore network extracted from the 3D images. Secondly, a repeat sampling strategy is applied during the stochastic modeling of the porous structure at the macroscale while honoring the structural property of the original network. Thirdly, the microchannel is added as a spherical chain and replaces the overlapped elements of the original network. Finally, we verify our model via a comparison of the structure and flow properties. The results show that the microchannel increases the permeability of flow both in the directions parallel and vertical to the microchannel direction. The microchannel plays as the highway for the pass of reactants while the rest of the smaller pore size provides higher resistance for better catalyst support, and the propagation path in the network with microchannels is more even and predictable. This work indicates that our modeling framework is a promising methodology for the design optimization of cross-scale porous structures.
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Fang, Kun, Kuijing Song, Tiesong Lin, and Haitao Jiang. "Optimization of brazing process and structure lightweight design for diamond microchannel." Journal of Physics: Conference Series 2535, no. 1 (June 1, 2023): 012005. http://dx.doi.org/10.1088/1742-6596/2535/1/012005.
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Abstract The application of diamond material significantly improves the heat dissipation capability of liquid cooling microchannels, solving the bottleneck problem of heat dissipation for highly integrated electronic components and thus promoting the development of a new generation of military electronic equipment. In this study, diamond microchannels with ultra-high heat flux density were reliably vacuum-brazed by using AgCuTi filler metal in a high vacuum furnace. Microstructure and properties of diamond brazing joints were studied and effect of brazing temperature and time was analyzed. The optimal brazing process parameters were obtained as follows: a vacuum level of <1×10−5 Pa, brazing temperature of 840°C, brazing pressure of 0.5–3 bars and holding time of 10 min. Following vacuum-brazing experiment, the brazing residual stress and working stress of the diamond microchannel were analyzed by finite element simulation. The wall thickness of the diamond microchannel was optimized. The minimum wall thickness, which was 0.4 mm, was obtained for the diamond microchannel with dimensions of 14 mm × 10 mm × 1.3 mm. On that basis, the influence of brazing pressure on the brazing filler overflow in the diamond microchannel brazing process was studied. It was showed that when the pressure was below 1 bar, the overflow of brazing filler from the brazing seam could be controlled to a minimum, especially suitable for brazing precision. The formation of residues in the diamond microchannel was thereby avoided basically, and a diamond microchannel heat sink with good performance was obtained.
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Abidin, Ummikalsom, Burhanuddin Yeop Majlis, and Jumril Yunas. "Design, Simulation and Fabrication of Polydimethylsiloxane (PDMS) Microchannel for Lab-on-Chip (LoC) Applications." Applied Mechanics and Materials 819 (January 2016): 420–24. http://dx.doi.org/10.4028/www.scientific.net/amm.819.420.
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Microchannel of micron-to milimeter in dimension has been immensely used for fluid handling in transporting, mixing and separating biological cells in Lab-on-Chip (LoC) applications. In this paper, design, simulation and fabrication of Polydimethylsiloxane (PDMS) microfluidic channel are presented. The microchannel is designed with one inlet and outlet. A reservoir or chamber is proposed as an extra component in the microchannel design for ease of separating the intended biological cells as used in LoC magnetic separator and micro-incubator. Finite Element Analysis (FEA) shows laminar flow characteristic is maintained in the proposed microchannel design operating at volumetric flow rate between 0.5 to 1000 μL/min. In addition, pressure drop data across the microchannel are also been obtained from the FEA in determining the safe operation limit of the microchannel. The PDMS microchannels of two different chamber geometries have been successfully fabricated using replica molding technique from SU-8 negative photoresist mold. The fabricated SU-8 mold and the PDMS microchannel structure dimension are characterized using Scanning Electron Microscopy (SEM). Reversible bonding of PDMS microchannel layer and PDMS tubing layer has successfully accomplished by activating the PDMS surfaces using corona discharge. The preliminary testing of the microchannel confirmed its function for LoC continuous flow applications.
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Doganay, Serkan, Levent Cetin, Mehmet Akif Ezan, and Alpaslan Turgut. "Magnetic Field Distributions inside Magnetically Driven Nanofluids for Thermal Management of CPUs." E3S Web of Conferences 162 (2020): 03005. http://dx.doi.org/10.1051/e3sconf/202016203005.
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Herein a magnetic actuation strategy is proposed to manipulate magnetic nanofluids in CPU thermal management applications. The proposed concept consists of a multi-circular microchannel unit and a rotating permanent magnet. A set of numerical simulations have been carried out to evaluate the influences of (i) magnet diameter, (ii) distance between the magnet and the microchannel, and (iii) shape of the magnet on magnetic flux densities (MFD) inside microchannels with Fe3O4 magnetic nanofluid. The results indicated that the MFD on the magnetic nanofluid significantly varies along with the radial position within the microchannel.
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Xue, Lihong, Chunsheng Guo, Yuankun Zhang, Yanfeng Xu, and Baorui Li. "Parametrical Study on the Capillary Flowing Characteristics of the Parallel Microchannel Array." Crystals 12, no. 7 (July 7, 2022): 950. http://dx.doi.org/10.3390/cryst12070950.
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The flow mechanism within a silicon-based micro heat sink plays a crucial role in two-phase thermal dissipation technology. In this study, the effect of geometrical properties on the flow behavior within a silicon-based array parallel microchannel as the evaporator of a silicon-based micro loop heat pipe (s-mLHP) is experimentally and numerically investigated. Here, three arrayed microchannels with different aspect ratio (AR) parameters (depth of 180 μm and AR of 6, 9, and 15) are specially fabricated. A visual experiment platform is established to observe and measure capillary properties of microchannels characterized by the suction distance. In addition, a validated numerical model (the maximum deviation less than 38.3%) is applied to simulate the flow characteristics of microchannels with different ARs. Numerical solutions show that the microchannel with ARs taken between 3 and 4 achieves the best capillary pumping performance within the studied range (suction distance up to 0.8 mm), which provides a theoretical basis for further exploration of silicon-based microchannel array with the optimal flow and thermal performance.
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Wang, Xinhui, Antony Seng Kai Kho, Jinghang Liu, Tianyu Mao, Michael D. Gilchrist, and Nan Zhang. "Mechanistic Modelling of Coupled UV Energy Penetration and Resin Flow Dynamics in Digital Light Processing (DLP)-Based Microfluidic Chip Printing." Micromachines 16, no. 2 (January 21, 2025): 115. https://doi.org/10.3390/mi16020115.
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Digital light processing (DLP) technology has emerged as a promising approach for fabricating high-precision microfluidic chips due to its exceptional resolution and rapid prototyping capabilities. However, UV energy penetration and resin flow dynamics during layer-by-layer printing introduce significant challenges for microchannel printing, particularly in controlling microchannel over-curing. In this study, a novel 3D DLP over-curing interaction model (DLP-OCIM) was developed to investigate the coupled effects of UV energy penetration and directional resin flow on the over-cured structure formation of microchannels. COMSOL Multiphysics 6.1 simulations incorporating UV light propagation, photopolymerization kinetics, and resin flow dynamics revealed that microchannel over-curing is a result of both energy infiltration through previously cured layers and periodic resin flow induced by the peeling process. Experimental validation using linear and annular microfluidic chips demonstrated that increasing layer thickness induces progressive over-curing, leading to inclined cross-sectional structures. Additionally, the microchannel geometry and size significantly influence resin flow patterns, with shorter transverse microchannels producing flatter over-cured profiles compared to their longitudinal counterparts. This study provides the first comprehensive analysis of the dynamic interplay between UV energy penetration and resin flow during DLP-based microchannel fabrication, offering valuable process insights and optimization strategies for enhancing shape fidelity and printing accuracy in high-resolution microfluidic chips.
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Wan Mohd. Arif Aziz Japar, Nor Azwadi Che Sidik, R. Saidur, Natrah Kamaruzaman, Yutaka Asako, Siti Nurul Akmal Yusof, and Mohd Nizam Lani. "Hybrid Microchannel Heat Sink with Sustainable Cooling Solutions: Numerical Model Validation." CFD Letters 14, no. 4 (May 6, 2022): 91–117. http://dx.doi.org/10.37934/cfdl.14.4.91117.
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Miniaturization and utilization of low-dimensional structures of recent electronic devices have witnessed some new micro cooling methods which can fulfil the cooling demand for the electronic devices. Microchannel heat sink (MCHS) is one of the micro cooling method which appears as a promising method that can provide high heat transfer rate due to small hydraulic diameter. Furthermore, microchannel heat sink is easy to be fabricated compare to other micro cooling device. Due to fast development in electronic industry, hybrid microchannel heat sink with optimal design has received a great deal of attention in order to provide sustainable cooling solutions. However, most of the studies of hybrid microchannel heat sink only provided the numerical analysis without any validation of the proposed design experimentally. This is very important since it also will determine whether the proposed hybrid microchannel heat sink can be fabricated or not. Therefore, the aim of this article is to validate the numerical model of hybrid microchannel heat sink (TC-RR-SC MCHS) experimentally. The validation result showed that the maximum discrepancy between both simulation and experimental analyses for Nusselt number and friction factor were 15.8% and 17.4%, respectively, which is less than 20%. The different number of microchannels between the simulated TC-RR-SC MCHS and fabricated TC-RR-SC MCHS is one of the factors that contribute to the data discrepancy. Furthermore, the poor finishing during the fabrication process also another factor because the burrs and debris at the top and bottom surface of microchannels affect the convective heat transfer area and the flow area of fluid.
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Xue, Yufan, Chunsheng Guo, Xiaoxiao Gu, Yanfeng Xu, Lihong Xue, and Han Lin. "Study on Flow Characteristics of Working Medium in Microchannel Simulated by Porous Media Model." Micromachines 12, no. 1 (December 26, 2020): 18. http://dx.doi.org/10.3390/mi12010018.
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As a phase change evaporator, a microchannel array heat exchanger is of great significance in the field of microscale heat dissipation. The performance of which strongly depends on the flow resistance, capillary force, and other factors. In order to improve the heat dissipation efficiency, it is necessary to perform an in-depth study of the characteristics of microchannel flow using numerical simulation. However, the current simulation model requires high computational cost and long simulation time. To solve this problem, this paper simplifies the numerical simulation of the rectangular parallel array microchannels by building the basic flow model based on the concept of porous media. In addition, we explore the effect of aspect-ratio (AR), hydraulic diameter, inlet velocity, and other parameters of fluid flow behavior inside the microchannels. Meanwhile, a user-defined function (UDF) is formulated to add the capillary force into the model to introduce capillary force into the porous media model. Through the above research, the paper establishes the porous media model for single-phase and gas-liquid two-phase flow, which acts as a simplification of microchannel array simulation without grossly affecting the results obtained. In addition, we designed and manufactured experiments using silicon-based microchannel heat exchangers with different-ratios, and combined with the visualization method to measure the performance of the device and compared them with simulation results. The theoretical model is verified through the suction experiment of array microchannel evaporator capillary core. The simplified model of microchannel array significantly saves the computational cost and time, and provides guidance for the related experimental researches.
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Jiang, Bingyan, Laiyu Zhu, Liping Min, Xianglin Li, Zhanyu Zhai, and Dietmar Drummer. "Characterization of Microchannel Replicability of Injection Molded Electrophoresis Microfluidic Chips." Polymers 11, no. 4 (April 2, 2019): 608. http://dx.doi.org/10.3390/polym11040608.
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Microfluidic chips have been widely applied in biochemical analysis, DNA sequencing, and disease diagnosis due to their advantages of miniaturization, low consumption, rapid analysis, and automation. Injection molded microfluidic chips have attracted great attention because of their short processing time, low cost, and mass production. The microchannel is the critical element of a microfluidic chip, and thus the microchannel replicability directly affects the performance of the microfluidic chip. In the current paper, a new method is proposed to evaluate the replicability of the microchannel profile via the root mean square value of the actual profile curve and the ideal profile curve of the microchannel. To investigate the effects of injection molding parameters (i.e., mold temperature, melting temperature, holding pressure, holding time, and injection rate) on microchannel replicability, a series of single-factor experiments were carried out. The results showed that, within the investigated experimental range, the increase of mold temperature, melt temperature, holding pressure, holding time, and injection rate could improve microchannel replicability accuracy. Specifically, the microchannels along the flow direction of the polymer melt were significantly affected by the mold temperature and melt temperature. Moreover, the replicability of the microchannel was influenced by the distance from the injection gate. The effect of microchannel replication on electrophoresis was demonstrated by a protein electrophoresis experiment.
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Lu, Kaijie, Chunju Wang, Changrui Wang, Xueliang Fan, Fei Qi, and Haidong He. "Topological structures for microchannel heat sink applications – a review." Manufacturing Review 10 (2023): 2. http://dx.doi.org/10.1051/mfreview/2022035.
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The microchannel heat sink (MCHS) has the advantages of small heat transfer resistance, high heat transfer efficiency and small size, which exhibits good heat transfer performance in the field of active heat dissipation of electronic devices integrated with high heat flux density. In this paper, the application of MCHS in thermal management is reviewed in recent years, and the research progress of microchannel topology on enhancing heat transfer performance is summarized. Firstly, the research progress on the cross-sectional shape of the microchannel shows that the heat transfer area and fluid flow dead zone of the microchannel is the keys to affecting the heat transfer performance; Secondly, the microchannel distribution and the bionic microchannel structure have a great role in enhancing heat transfer performance, especially in microchannel temperature uniformity; Thirdly, the disturbing effect caused by interrupted structures in microchannels such as ribs and concave cavities has become a hot topic of research because it can weaken the thermal boundary layer and increase heat dissipation. Finally, the commonly used MCHS materials and cooling media are summarized and introduced. Based on the above reviews of MCHS research and applications, the future trends of MCHS topologies are presented.
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Pan, Minqiang, Hongqing Wang, Yujian Zhong, Tianyu Fang, and Xineng Zhong. "Numerical simulation of the fluid flow and heat transfer characteristics of microchannel heat exchangers with different reentrant cavities." International Journal of Numerical Methods for Heat & Fluid Flow 29, no. 11 (November 4, 2019): 4334–48. http://dx.doi.org/10.1108/hff-03-2019-0252.
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Purpose With the increasing heat dissipation of electronic devices, the cooling demand of electronic products is increasing gradually. A water-cooled microchannel heat exchanger is an effective cooling technology for electronic equipment. The structure of a microchannel has great impact on the heat transfer performance of a microchannel heat exchanger. The purpose of this paper is to analyze and compare the fluid flow and heat transfer characteristic of a microchannel heat exchanger with different reentrant cavities. Design/methodology/approach The three-dimensional steady, laminar developing flow and conjugate heat transfer governing equations of a plate microchannel heat exchanger are solved using the finite volume method. Findings At the flow rate range studied in this paper, the microchannel heat exchangers with reentrant cavities present better heat transfer performance and smaller pressure drop. A microchannel heat exchanger with trapezoidal-shaped cavities has best heat transfer performance, and a microchannel heat exchanger with fan-shaped cavities has the smallest pressure drop. Research limitations/implications The fluid is incompressible and the inlet temperature is constant. Practical implications It is an effective way to enhance heat transfer and reduce pressure drop by adding cavities in microchannels and the data will be helpful as guidelines in the selection of reentrant cavities. Originality/value This paper provides the pressure drop and heat transfer performance analysis of microchannel heat exchangers with various reentrant cavities, which can provide reference for heat transfer augmentation of an existing microchannel heat exchanger in a thermal design.
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Zhuang, Xiaoru, Haitao Wang, Haoran Lu, Zhi Yang, and Hao Guo. "Numerical Investigation of Heat Transfer and Flow Characteristics of Supercritical CO2 in Solar Tower Microchannel Receivers at High Temperature." Energies 16, no. 18 (September 6, 2023): 6445. http://dx.doi.org/10.3390/en16186445.
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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.
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Galieva, Karina, Iskandar Garifullin, Eduard Batyrshin, and Olga Solnyshkina. "Experimental analysis of fluid dynamics in microchannels featuring two-scale fin pin arrays." EPJ Web of Conferences 321 (2025): 01006. https://doi.org/10.1051/epjconf/202532101006.
Full textAbstract:
Optimizing the geometry of internal microchannel structures is critical to the design of efficient microfluidic devices. This study addresses the pressing issue of understanding how the distribution of circular cross-section pins within microchannels affects integral hydrodynamic performance. We employ a comprehensive experimental methodology combining high-speed imaging, optical microscopy, and microfluidic platform fabrication using polydimethylsiloxane based on the lab-on-a-chip technology. A series of experiments were conducted under varying pressure drops to assess the throughput of microchannel structures with different fin pin configurations. Results demonstrate a significant reduction in microchannel throughput upon the introduction of a secondary porosity scale.
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Zhuang, Jian, Ya Jun Zhang, Da Ming Wu, Li Zhu Liu, Cheng Jun Sun, Wei Wang, and Shui Xing Liu. "Effects of Wall Slip on Filling Flow for Polymer Melt in Micro Injection Molding." Key Engineering Materials 609-610 (April 2014): 617–22. http://dx.doi.org/10.4028/www.scientific.net/kem.609-610.617.
Full textAbstract:
Effect of wall slip on melt filling flow behaviors in micro injection molding are investigated based on analysis of wall slip mechanism for polymer melt flowing at filling stage. By means of comparisons, slip coefficients in different microchannels are confirmed. With finite element method, the relationship between slip velocity and inlet flow rate or length-diameter ratio is analyzed. The results indicate that the wall slip happen for polymeric melt in microchannels, and slip coefficients are related with the size characteristics of microchannels. Moreover, wall slip velocity has the size effect and increase with the decrease of the section size of microchannels, which cause melt velocity distribution to smooth. At the same time, slip velocity is proportional to length-diameter ratio of microchannel, namely when wall shear stress is uniform, the slip velocity rises with increasing length-diameter ratio of microchannel.
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Kozioł, Paweł, Piotr Jaworski, Karol Krzempek, Viktoria Hoppe, Grzegorz Dudzik, Fei Yu, Dakun Wu, Meisong Liao, Jonathan Knight, and Krzysztof Abramski. "Fabrication of Microchannels in a Nodeless Antiresonant Hollow-Core Fiber Using Femtosecond Laser Pulses." Sensors 21, no. 22 (November 16, 2021): 7591. http://dx.doi.org/10.3390/s21227591.
Full textAbstract:
In this work, we present femtosecond laser cutting of microchannels in a nodeless antiresonant hollow-core fiber (ARHCF). Due to its ability to guide light in an air core combined with exceptional light-guiding properties, an ARHCF with a relatively non-complex structure has a high application potential for laser-based gas detection. To improve the gas flow into the fiber core, a series of 250 × 30 µm microchannels were reproducibly fabricated in the outer cladding of the ARHCF directly above the gap between the cladding capillaries using a femtosecond laser. The execution time of a single lateral cut for optimal process parameters was 7 min. It has been experimentally shown that the implementation of 25 microchannels introduces low transmission losses of 0.17 dB (<0.01 dB per single microchannel). The flexibility of the process in terms of the length of the performed microchannel was experimentally demonstrated, which confirms the usefulness of the proposed method. Furthermore, the performed experiments have indicated that the maximum bending radius for the ARHCF, with the processed 100 µm long microchannel that did not introduce its breaking, is 15 cm.
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Huang, Binghuan, Haiwang Li, and Tiantong Xu. "Experimental Investigation of the Flow and Heat Transfer Characteristics in Microchannel Heat Exchangers with Reentrant Cavities." Micromachines 11, no. 4 (April 12, 2020): 403. http://dx.doi.org/10.3390/mi11040403.
Full textAbstract:
The application of microchannel heat exchangers is of great significance in industrial fields due to their advantages of miniaturized scale, large surface-area-to-volume ratio, and high heat transfer rate. In this study, microchannel heat exchangers with and without fan-shaped reentrant cavities were designed and manufactured, and experiments were conducted to investigate the flow and heat-transfer characteristics. The impact rising from the radius of reentrant cavities, as well as the Reynolds number on the heat transfer and the pressure drop, is also analyzed. The results indicate that, compared with straight microchannels, microchannels with reentrant cavities could enhance the heat transfer and, more importantly, reduce the pressure drop at the same time. For the ranges of parameters studied, increasing the radius of reentrant cavities could augment the effect of pressure-drop reduction, while the corresponding variation of heat transfer is complicated. It is considered that adding reentrant cavities in microchannel heat exchangers is an ideal approach to improve performance.