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Journal articles on the topic 'Microchannel Heat Transfer'
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1
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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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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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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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.
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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.
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Liu, Dong, and Suresh V. Garimella. "Flow Boiling Heat Transfer in Microchannels." Journal of Heat Transfer 129, no. 10 (December 14, 2006): 1321–32. http://dx.doi.org/10.1115/1.2754944.
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Flow boiling heat transfer to water in microchannels is experimentally investigated. The dimensions of the microchannels considered are 275×636 and 406×1063μm2. The experiments are conducted at inlet water temperatures in the range of 67–95°C and mass fluxes of 221–1283kg∕m2s. The maximum heat flux investigated in the tests is 129W∕cm2 and the maximum exit quality is 0.2. Convective boiling heat transfer coefficients are measured and compared to predictions from existing correlations for larger channels. While an existing correlation was found to provide satisfactory prediction of the heat transfer coefficient in subcooled boiling in microchannels, saturated boiling was not well predicted by the correlations for macrochannels. A new superposition model is developed to correlate the heat transfer data in the saturated boiling regime in microchannel flows. In this model, specific features of flow boiling in microchannels are incorporated while deriving analytical solutions for the convection enhancement factor and nucleate boiling suppression factor. Good agreement with the experimental measurements indicates that this model is suitable for use in analyzing boiling heat transfer in microchannel flows.
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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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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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Cheng, Ping, Hui-Ying Wu, and Fang-Jun Hong. "Phase-Change Heat Transfer in Microsystems." Journal of Heat Transfer 129, no. 2 (September 20, 2006): 101–8. http://dx.doi.org/10.1115/1.2410008.
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Recent work on miscroscale phase-change heat transfer, including flow boiling and flow condensation in microchannnels (with applications to microchannel heat sinks and microheat exchangers) as well as bubble growth and collapse on microheaters under pulse heating (with applications to micropumps and thermal inkjet printerheads), is reviewed. It has been found that isolated bubbles, confined elongated bubbles, annular flow, and mist flow can exist in microchannels during flow boiling. Stable and unstable flow boiling modes may occur in microchannels, depending on the heat to mass flux ratio and inlet subcooling of the liquid. Heat transfer and pressure drop data in flow boiling in microchannels are shown to deviate greatly from correlations for flow boiling in macrochannels. For flow condensation in microchannels, mist flow, annular flow, injection flow, plug-slug flow, and bubbly flows can exist in the microchannels, depending on mass flux and quality. Effects of the dimensionless condensation heat flux and the Reynolds number of saturated steam on transition from annular two-phase flow to slug/plug flow during condensation in microchannels are discussed. Heat transfer and pressured drop data in condensation flow in microchannels, at low mass flux are shown to be higher and lower than those predicted by correlations for condensation flow in macrochannels, respectively. Effects of pulse heating width and heater size on microbubble growth and collapse and its nucleation temperature on a microheater under pulse heating are summarized.
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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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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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Wu, Ge Ping, Jun Wang, and Ping Lu. "Simulation of Flow and Heat Transfer in the MTPV Systems." Applied Mechanics and Materials 448-453 (October 2013): 3291–95. http://dx.doi.org/10.4028/www.scientific.net/amm.448-453.3291.
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Flow and heat transfer characteristics in the microchannel cooling passages with three different types of the MTPV systems are numerically investigated. Reynolds ranged from 100 to 1000 and hydraulic diameter from 0.4mm to 0.8mm. The steady, laminar flow and heat transfer equations are solved in a finite-volume method. The local heat transfer characteristics, thermal resistance, Nusselt numbers, friction factor and pressure losses of the different types are analyzed. A comparison of the heat transfer coefficient, pressure losses and friction factor of the different microchannels are also presented. The heat transfer performance of the rob bundles microchannel is found to be much better than others. However, the rectangular passage has the lowest thermal resistance than the other types of microchannels.
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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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Liu, Yanyu, Tong Su, Xuan Zhang, and Yongou Zhang. "Flow and heat transfer of supercritical LNG in spiral microchannel." E3S Web of Conferences 300 (2021): 01006. http://dx.doi.org/10.1051/e3sconf/202130001006.
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Liquefied natural gas (LNG) is stable and safe, which is why the natural gas is usually liquefied before transported. The heat exchanger is widely used as the key component of vaporizing LNG, and it is composed of a large number of microchannels. This paper mainly analyzes the flow of supercritical LNG in a spiral microchannel, and compares the flow and heat transfer characteristic of spiral microchannel with different pitch. The result was indicative that with the lessen of pitch, the heat transfer is improved, but the flow characteristic is decreased. Compared with the straight channel, the spiral channel with appropriate pitch value can markedly improve the heat transfer properties, but has less effect on the flow characteristic. The discussion also includes the flow and heat transfer of microchannel with different mass flux and heat flux.
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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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Wu, Huajie, and Shanwen Zhang. "Numerical Study on the Fluid Flow and Heat Transfer Characteristics of Al2O3-Water Nanofluids in Microchannels of Different Aspect Ratio." Micromachines 12, no. 8 (July 24, 2021): 868. http://dx.doi.org/10.3390/mi12080868.
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The study of the influence of the nanoparticle volume fraction and aspect ratio of microchannels on the fluid flow and heat transfer characteristics of nanofluids in microchannels is important in the optimal design of heat dissipation systems with high heat flux. In this work, the computational fluid dynamics method was adopted to simulate the flow and heat transfer characteristics of two types of water-Al2O3 nanofluids with two different volume fractions and five types of microchannel heat sinks with different aspect ratios. Results showed that increasing the nanoparticle volume fraction reduced the average temperature of the heat transfer interface and thereby improved the heat transfer capacity of the nanofluids. Meanwhile, the increase of the nanoparticle volume fraction led to a considerable increase in the pumping power of the system. Increasing the aspect ratio of the microchannel effectively improved the heat transfer capacity of the heat sink. Moreover, increasing the aspect ratio effectively reduced the average temperature of the heating surface of the heat sink without significantly increasing the flow resistance loss. When the aspect ratio exceeded 30, the heat transfer coefficient did not increase with the increase of the aspect ratio. The results of this work may offer guiding significance for the optimal design of high heat flux microchannel heat sinks.
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Anbumeenakshi, C., M. R. Thansekhar, M. Satheeshkumar, and R. Vishnu Gayathri. "Experimental Investigation of Heat Transfer in Coated Microchannels for MEMS Applications." Applied Mechanics and Materials 813-814 (November 2015): 782–86. http://dx.doi.org/10.4028/www.scientific.net/amm.813-814.782.
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The microchannel cooling technique appears to be a viable solution to high heat rejection requirements of today’s high-power electronic devices. The thermal design of the small electronics cooling devices is a key issue that needs to be optimized in order to keep the system temperatures at certain levels. Thus the need of microchannel became vital. This present work investigates the experimental work conducted in a coated rectangular microchannel heat sink of hydraulic diameter of 0.763 mm for a heat input of 250 to 1020 Watt with water to study the heat transfer characteristics with two types of header arrangement such as rectangular header and trapezoidal header. The header plays a significant role in distributing the water in to the channels. The uniform distribution of water leads to uniform heat transfer in microchannels. From the experimental results carried with two types of header arrangements, it was found that coated rectangular microchannel with trapezoidal header gives better heat transfer characteristics for the range of heat inputs.
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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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Pastuszko, Robert, Milena Bedla-Pawlusek, and Robert Kaniowski. "Pool boiling heat transfer for surfaces with microchannels of variable depth." EPJ Web of Conferences 213 (2019): 02063. http://dx.doi.org/10.1051/epjconf/201921302063.
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Experimental investigations of pool boiling heat transfer on microchannels of variable depth were conducted. The experiments were carried out for water and ethanol at atmospheric pressure. Microchannels of variable depth from 0.2 to 2.8 mm and width 0.5 mm were uniformly spaced on base surface with pitch of 1 mm. The comparison of heat transfer coefficients for surfaces with variable and constant depth of microchannels was made. At the low and medium heat fluxes structures with constant microchannel depth showed the best boiling heat transfer performance. EX-FH20 (Casio) camera was used to record the images of the entire surface of the specimen. The bubble growth mechanism on the enhanced surface was different from that of plain surface. Visualization investigations were aimed at identifying nucleation sites and determining the bubble growth cycle. Vapor bubbles generate in microchannel spaces, from where they move towards the fin tips, then grow and depart.
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Wu, Ge Ping, and Ping Lu. "Flow and Heat Transfer in Microchannels of the MTPV Systems." Advanced Materials Research 614-615 (December 2012): 181–85. http://dx.doi.org/10.4028/www.scientific.net/amr.614-615.181.
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Heat transfer and flow characteristics in the microchannel cooling passages with three different types of the MTPV systems are numerically investigated. This investigation covers Reynolds number in the range of 100 to 1000 and heat flux ranged from 50kW/m2 to 150kW/m2. The steady, laminar flow and heat transfer equations are solved in a finite-volume method. Results such as temperature distribution, heat transfer coefficient, pressure drop and friction factor are reported. A comparison of the heat transfer coefficient and friction factor of the different microchannels are also presented. The heat transfer performance of the rod bundles microchannel is found to be much better than others. Both friction factor and heat transfer coefficient are increased as the Reynolds number increased.
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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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Kumar, Valaparla Ranjith, Karthik Balasubramanian, K. Kiran Kumar, Kanishk Bhatia, and Nikhil Tiwari. "Numerical investigation of heat transfer and fluid flow characteristics in circular wavy microchannel with tangentially branched secondary channels." Proceedings of the Institution of Mechanical Engineers, Part E: Journal of Process Mechanical Engineering 233, no. 6 (August 12, 2019): 1304–16. http://dx.doi.org/10.1177/0954408919869543.
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Wavy microchannels have been shown to possess improved heat transfer capabilities because of greater fluid mixing and boundary layer thinning. In this study, fluid flow and heat transfer characteristics of circular wavy microchannels with tangentially branched secondary channels, were numerically investigated. Its heat transfer and fluid flow characteristics were compared with other specific wavy microchannel geometries. Three-dimensional numerical studies were carried out in the Reynolds number range of 100–300 with uniform heat flux wall boundary condition, using Ansys Fluent commercial software. Validation of the model was done with experimental data from literature. Circular wavy microchannels, owing to constant curvature, lead to nearly constant Dean vortices strength. The tangential branched secondary channels helped in further effective fluid mixing and in reinitializing the boundary layer. These phenomena had significant effect on its heat transfer and fluid flow behavior. Circular wavy microchannels with tangentially branched secondary channels, having secondary channel width to primary channel width ratio (ω) equal to 0.25, showed higher overall performance than other designs considered in the present study. Velocity vectors, velocity and temperature contours are presented to explain the fluid flow and heat transfer characteristics. It is observed that circular wavy microchannels with tangentially branched secondary channel design (ω = 0.25) gives 39.36% higher Nusselt number with 21% increased pressure drop as compared to sinusoidal wavy microchannel design. The overall performance factor of circular wavy microchannel with tangentially branched secondary channel design (ω = 0.25) is higher in the Reynolds number range of 100–250 than all other designs considered in this study.
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Revellin, Rémi, and John R. Thome. "Microchannel Heat Transfer Studies." Heat Transfer Engineering 28, no. 10 (October 2007): 805. http://dx.doi.org/10.1080/01457630701378168.
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Tiwari, Nishant, and Manoj Kumar Moharana. "Comparative study of conjugate heat transfer in a single-phase flow in wavy and raccoon microchannels." International Journal of Numerical Methods for Heat & Fluid Flow 30, no. 7 (November 21, 2019): 3791–825. http://dx.doi.org/10.1108/hff-05-2019-0439.
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Purpose This paper aims to emphasize on studying various geometrical modification performed in wavy and raccoon microchannel by manipulating parameters, i.e. waviness (γ), expansion factor (α), wall to fluid thermal conductivity ratio (ksf), substrate thickness to channel height ratio (dsf) and Reynolds number (Re) for obtaining optimum parameter(s) that leads to higher heat dissipation rate. Design/methodology/approach A three-dimensional solid-fluid conjugate heat transfer numerical model is designed to capture flow characteristics and heat transfer in single-phase laminar flow microchannels. The governing equations are solved using finite volume method. Findings The results are presented in terms of average base temperature, average Nusselt number, pressure drop, dimensionless local heat flux, dimensionless wall and bulk fluid temperature, local Nusselt number and performance factor including axial conduction number. Heat dissipation rate with raccoon microchannel configuration is found to be higher compared to straight and wavy microchannel. With waviness of γ = 0.167, and 0.267 in wavy and raccoon microchannel, respectively, performance factor attains maximum value compared to other waviness for all values of Reynolds number. It is also found that the effect of axial wall conduction in wavy and raccoon microchannel is negligible. Additionally, thermal performance of wavy and raccoon microchannel is compared with straight microchannel. Practical implications In recent past years, much complex design of microchannel has been proposed for heat transfer enhancement, but the feasibility of available manufacturing techniques to fabricate complex geometries is still questionable. However, fabrication of wavy and raccoon microchannel is easy, and their heat dissipation capability is higher. Originality/value This makes the difference in wall and bulk fluid temperature smaller. Thus, present work highlighted the dominance of axial wall conduction on thermal and hydrodynamic performance of wavy and raccoon microchannel under conjugate heat transfer situation.
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Zhang, Xuan, Taocheng Zhao, Suchen Wu, and Feng Yao. "Experimental Study on Liquid Flow and Heat Transfer in Rough Microchannels." Advances in Condensed Matter Physics 2019 (November 23, 2019): 1–9. http://dx.doi.org/10.1155/2019/1974952.
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Although roughness is negligible for laminar flow through tubes in classic fluid mechanics, the surface roughness may play an important role in microscale fluid flow due to the large ratio of surface area to volume. To further verify the influence of rough surfaces on microscale liquid flow and heat transfer, a performance test system of heat transfer and liquid flow was designed and built, and a series of experimental examinations are conducted, in which the microchannel material is stainless steel and the working medium is methanol. The results indicate that the surface roughness plays a significant role in the process of laminar flow and heat transfer in microchannels. In microchannels with roughness characteristics, the Poiseuille number of liquid laminar flow relies not only on the cross section shape of the rough microchannels but also on the Reynolds number of liquid flow. The Poiseuille number of liquid laminar flow in rough microchannels increases with increasing Reynolds number. In addition, the Nusselt number of liquid laminar heat transfer is related not only to the cross section shape of a rough microchannel but also to the Reynolds number of liquid flow, and the Nusselt number increases with increasing Reynolds number.
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Saidi, M. H., and Reza H Khiabani. "Forced Convective Heat Transfer in Parallel Flow Multilayer Microchannels." Journal of Heat Transfer 129, no. 9 (August 30, 2006): 1230–36. http://dx.doi.org/10.1115/1.2739600.
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Abstract In this paper, the effect of increasing the number of layers on improving the thermal performance of microchannel heat sinks is studied. In this way, both numerical and analytical methods are utilized. The analytical method is based on the porous medium assumption. Here, the modified Darcy equation and the energy balance equations are used. The method has led to an analytical expression presenting the average dimensionless temperature field in the multilayer microchannel heat sink. The effects of different parameters such as aspect ratio, porosity, channel width, and the solid properties on the thermal resistance are described. The results for single layer and multilayer heat sinks are compared to show the effectiveness of using multilayer microchannels.
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Kaniowski, Robert, and Robert Pastuszko. "Pool Boiling of Water on Surfaces with Open Microchannels." Energies 14, no. 11 (May 25, 2021): 3062. http://dx.doi.org/10.3390/en14113062.
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Boiling, as the most efficient type of convective heat transfer, is an area of interest in many fields of industry and science. Many works have focused on improving the heat transfer efficiency of boiling by altering the physical and chemical properties of surfaces by using different technological processes in their fabrication. This paper presents experimental investigations into pool boiling on enhanced surfaces with open microchannels. The material of the fabricated surface was copper. Parallel microchannels made by machining were about 0.2, 0.3, and 0.4 mm wide, 0.2 to 0.5 mm deep, and spaced with a pitch equal to twice the width of the microchannel. The experiments were carried out in water at atmospheric pressure. The experimental results obtained showed an increase in the heat flux and the heat transfer coefficient for surfaces with microchannels. The maximum (critical) heat flux was 2188 kW/m2, and the heat transfer coefficient was 392 kW/m2K. An improvement in the maximum heat flux of more than 245% and 2.5–4.9 times higher heat transfer coefficient was obtained for the heat flux range of 992–2188 kW/m2 compared to the smooth surface. Bubble formation and growth cycle in the microchannel were presented. Two static computational models were proposed to determine the bubble departure diameter.
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Kaniowski, Robert, Robert Pastuszko, Milena Bedla-Pawlusek, and Łukasz Nowakowski. "Study of pool boiling heat transfer with FC-72 on open microchannel surfaces." EPJ Web of Conferences 213 (2019): 02038. http://dx.doi.org/10.1051/epjconf/201921302038.
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The paper presents investigations into pool boiling heat transfer for open microchannel surfaces. The experiments were carried out with saturated FC-72 at atmospheric pressure. Parallel microchannels fabricated by machining were about 0.2 to 0.4 mm wide and 0.2 to 0.5 mm deep. Analyzed surfaces with microchannels allowed to obtain heat transfer coefficients within the range of 6.1 – 9.8 kW/m2K, which in relation to the flat surface gives a 3 – 5 - fold increase in HTC. One of the reasons for the increase in the heat transfer coefficient when increasing the heat flux was the growing number of active nucleation sites at the bottom of microchannels and its side surfaces.
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Mikielewicz, Dariusz, and Jan Wajs. "Possibilities of Heat Transfer Augmentation in Heat Exchangers with Minichannels for Marine Applications." Polish Maritime Research 24, s1 (April 25, 2017): 133–40. http://dx.doi.org/10.1515/pomr-2017-0031.
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Abstract In the paper, new trends in the development of microchannel heat exchangers are presented. The exchangers developed in this way can be applied in marine industry. Main attention is focused on heat exchanger design with reduced size of passages, namely based on microchannels. In authors′ opinion, future development of high power heat exchangers will be based on networks of micro heat exchangers.
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Kuznetsov, Vladimir, Alisher Shamirzaev, and Alexander Mordovskoy. "High heat flux flow boiling of refrigerant R236fa in parallel microchannels." EPJ Web of Conferences 196 (2019): 00062. http://dx.doi.org/10.1051/epjconf/201919600062.
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This paper presents the results of an experimental study of the heat transfer during flow boiling of refrigerant R236fa in a horizontal microchannel heat sink. The experiments were performed using closed loop that re-circulates coolant. Microchannel heat exchanger that contains two microchannels with 2x0.4 mm cross-section was used as the test section. The dependence of average heat flux on wall superheat and critical heat flux were measured in the range of mass fluxes from 600 to 1600 kg/m2s and in the range of heat fluxes from 5 to 120 W/cm2. For heat flux greater than 60 W/cm2, nucleate boiling suppression has significant effect on the flow boiling heat transfer, and this leads to decrease of the heat transfer coefficient with heat flux grows.
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Ebrahimi, Amin, Vahid Shahabi, and Ehsan Roohi. "Pressure-Driven Nitrogen Flow in Divergent Microchannels with Isothermal Walls." Applied Sciences 11, no. 8 (April 16, 2021): 3602. http://dx.doi.org/10.3390/app11083602.
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Gas flow and heat transfer in confined geometries at micro-and nanoscales differ considerably from those at macro-scales, mainly due to nonequilibrium effects such as velocity slip and temperature jump. Nonequilibrium effects increase with a decrease in the characteristic length-scale of the fluid flow or the gas density, leading to the failure of the standard Navier–Stokes–Fourier (NSF) equations in predicting thermal and fluid flow fields. The direct simulation Monte Carlo (DSMC) method is employed in the present work to investigate pressure-driven nitrogen flow in divergent microchannels with various divergence angles and isothermal walls. The thermal fields obtained from numerical simulations are analysed for different inlet-to-outlet pressure ratios (1.5≤Π≤2.5), tangential momentum accommodation coefficients, and Knudsen numbers (0.05≤Kn≤12.5), covering slip to free-molecular rarefaction regimes. The thermal field in the microchannel is predicted, heat-lines are visualised, and the physics of heat transfer in the microchannel is discussed. Due to the rarefaction effects, the direction of heat flow is largely opposite to that of the mass flow. However, the interplay between thermal and pressure gradients, which are affected by geometrical configurations of the microchannel and the applied boundary conditions, determines the net heat flow direction. Additionally, the occurrence of thermal separation and cold-to-hot heat transfer (also known as anti-Fourier heat transfer) in divergent microchannels is explained.
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Gonçalves, Inês M., César Rocha, Reinaldo R. Souza, Gonçalo Coutinho, Jose E. Pereira, Ana S. Moita, António L. N. Moreira, Rui Lima, and João M. Miranda. "Numerical Optimization of a Microchannel Geometry for Nanofluid Flow and Heat Dissipation Assessment." Applied Sciences 11, no. 5 (March 9, 2021): 2440. http://dx.doi.org/10.3390/app11052440.
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In this study, a numerical approach was carried out to analyze the effects of different geometries of microchannel heat sinks on the forced convective heat transfer in single-phase flow. The simulations were performed using the commercially available software COMSOLMultiphysics 5.6® (Burlington, MA, USA) and its results were compared with those obtained from experimental tests performed in microchannel heat sinks of polydimethylsiloxane (PDMS). Distilled water was used as the working fluid under the laminar fluid flow regime, with a maximum Reynolds number of 293. Three sets of geometries were investigated: rectangular, triangular and circular. The different configurations were characterized based on the flow orientation, type of collector and number of parallel channels. The main results show that the rectangular shaped collector was the one that led to a greater uniformity in the distribution of the heat transfer in the microchannels. Similar results were also obtained for the circular shape. For the triangular geometry, however, a disturbance in the jet impingement was observed, leading to the least uniformity. The increase in the number of channels also enhanced the uniformity of the flow distribution and, consequently, improved the heat transfer performance, which must be considered to optimize new microchannel heat sink designs. The achieved optimized design for a heat sink, with microchannels for nanofluid flow and a higher heat dissipation rate, comprised a rectangular collector with eight microchannels and vertical placement of the inlet and outlet.
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Wu, Ge Ping, Ping Lu, and Jun Wang. "Non-Uniform Heating Condition Effects in Microchannels of the MTPV Systems." Applied Mechanics and Materials 437 (October 2013): 120–23. http://dx.doi.org/10.4028/www.scientific.net/amm.437.120.
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Heat transfer and fluid flow in the microchannel cooling passages of plane cell type MTPV systems are numerically investigated. The Finite Volume method is adopted for the governing equations discretization; The SIMPLE method is applied to deal with the linkage between pressure and velocities. The microscale effects, such as surface roughness and viscous dissipation are taken into account. Influence of non-uniform heating condition on the flow and heat transfer characteristics of the microchannel cooling passage was discussed. The computer simulations were validated by the experiment data. Numerical results confirm that the effects of non-uniform heating condition on fluid flow and heat transfer in microchannels could not be neglected.
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Wu, Ge Ping, and Ping Lu. "Numerical Study of Heat Transfer Enhancement in Microchannels of the MTPV Systems." Applied Mechanics and Materials 316-317 (April 2013): 119–23. http://dx.doi.org/10.4028/www.scientific.net/amm.316-317.119.
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Heat transfer and fluid flow in the microchannel cooling passages with three different types of the MTPV systems are numerically investigated. The heat transfer characteristics and thermal performance of the microchannels are analyzed using different Reynolds numbers and hydraulic diameters. Local heat transfer coefficient, total pumping power, heat transferred are obtained from the simulations and the performance is discussed in terms of heat transfer coefficient and thermal efficiency. Results indicated enhanced performance with the smaller hydraulic diameters, and slighter penalty in pumping power. The increase in Reynolds number cause an increase in the heat transfer coefficient at the expense of decreased thermal efficiency. It is also found that the highest heat transfer coefficient is expected in rod bundles microchannels. However, round microchannels have a better thermal efficiency than others.
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Irandoost Shahrestani, Misagh, Akbar Maleki, Mostafa Safdari Shadloo, and Iskander Tlili. "Numerical Investigation of Forced Convective Heat Transfer and Performance Evaluation Criterion of Al2O3/Water Nanofluid Flow inside an Axisymmetric Microchannel." Symmetry 12, no. 1 (January 7, 2020): 120. http://dx.doi.org/10.3390/sym12010120.
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Al2O3/water nanofluid conjugate heat transfer inside a microchannel is studied numerically. The fluid flow is laminar and a constant heat flux is applied to the axisymmetric microchannel’s outer wall, and the two ends of the microchannel’s wall are considered adiabatic. The problem is inherently three-dimensional, however, in order to reduce the computational cost of the solution, it is rational to consider only a half portion of the axisymmetric microchannel and the domain is revolved through its axis. Hence. the problem is reduced to a two-dimensional domain, leading to less computational grid. At the centerline (r = 0), as the flow is axisymmetric, there is no radial gradient (∂u/∂r = 0, v = 0, ∂T/∂r = 0). The effects of four Reynolds numbers of 500, 1000, 1500, and 2000; particle volume fractions of 0% (pure water), 2%, 4%, and 6%; and nanoparticles diameters in the range of 10 nm, 30 nm, 50 nm, and 70 nm on forced convective heat transfer as well as performance evaluation criterion are studied. The parameter of performance evaluation criterion provides valuable information related to heat transfer augmentation together with pressure losses and pumping power needed in a system. One goal of the study is to address the expense of increased pressure loss for the increment of the heat transfer coefficient. Furthermore, it is shown that, despite the macro-scale problem, in microchannels, the viscous dissipation effect cannot be ignored and is like an energy source in the fluid, affecting temperature distribution as well as the heat transfer coefficient. In fact, it is explained that, in the micro-scale, an increase in inlet velocity leads to more viscous dissipation rates and, as the friction between the wall and fluid is considerable, the temperature of the wall grows more intensely compared with the bulk temperature of the fluid. Consequently, in microchannels, the thermal behavior of the fluid would be totally different from that of the macro-scale.
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Abdelmalek, Zahra, Annunziata D’Orazio, and Arash Karimipour. "The Effect of Nanoparticle Shape and Microchannel Geometry on Fluid Flow and Heat Transfer in a Porous Microchannel." Symmetry 12, no. 4 (April 8, 2020): 591. http://dx.doi.org/10.3390/sym12040591.
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Microchannels are widely used in electrical and medical industries to improve the heat transfer of the cooling devices. In this paper, the fluid flow and heat transfer of water–Al2O3 nanofluids (NF) were numerically investigated considering the nanoparticle shape and different cross-sections of a porous microchannel. Spherical, cubic, and cylindrical shapes of the nanoparticle as well as circular, square, and triangular cross-sections of the microchannel were considered in the simulation. The finite volume method and the SIMPLE algorithm have been employed to solve the conservation equations numerically, and the k-ε turbulence model has been used to simulate the turbulence fluid flow. The models were simulated at Reynolds number ranging from 3000 to 9000, the nanoparticle volume fraction ranging from 1 to 3, and a porosity coefficient of 0.7. The results indicate that the average Nusselt number (Nuave) increases and the friction coefficient decreases with an increment in the Re for all cases. In addition, the rate of heat transfer in microchannels with triangular and circular cross-sections is reduced with growing Re values and concentration. The spherical nanoparticle leads to maximum heat transfer in the circular and triangular cross-sections. The heat transfer growth for these two cases are about 102.5% and 162.7%, respectively, which were obtained at a Reynolds number and concentration of 9000 and 3%, respectively. However, in the square cross-section, the maximum heat transfer increment was obtained using cylindrical nanoparticles, and it is equal to 80.2%.
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YUN, RIN, and YUNHO HWANG. "INFLOW CONDENSATION HEAT TRANSFER CHARACTERISTICS OF CO2 IN MICROCHANNEL." International Journal of Air-Conditioning and Refrigeration 22, no. 02 (April 29, 2014): 1450009. http://dx.doi.org/10.1142/s2010132514500096.
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In this study, we investigated two-phase flow patterns and effects of oil concentration on the heat transfer coefficient and pressure drop of CO 2 undergoing condensation process in a microchannel, and from the data collected, we developed a prediction model of CO 2 condensation heat transfer coefficient in smooth tube and microchannels. The narrow single rectangular channel was utilized to observe flow patterns of CO 2 under the condensation process. Experimental results show that the transition of vapor quality from intermittent flow to annular flow advances with increase of mass flux and with decrease of condensation temperature. The heat transfer coefficient decreased by 50% as compared to that of the pure CO 2 when the oil concentration was increased from 0.7 to 1.2 wt.% for the mass flux of 600 kg ⋅ m-2 ⋅ s-1. The pressure drop slightly decreased with oil concentration as compared to that of pure CO 2. We developed the prediction model for the heat transfer coefficient of CO 2 undergoing condensation process in microchannel by considering the effects of the liquid film thickness and of the interface shape between liquid and vapor phases on the heat transfer coefficient. The present prediction model estimated the experimental data within 18.9% of mean deviation. For the pressure drop in microchannel tubes, the existing models developed by Mishima and Hibiki, and Garimella showed the marginal predictability.
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Jing, Dalei, and Jian Song. "Numerical Studies on the Thermal Performances of Electroosmotic Flow in Y-Shaped Microchannel Heat Sink." Coatings 10, no. 4 (April 13, 2020): 380. http://dx.doi.org/10.3390/coatings10040380.
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This paper numerically studies the thermal performances of electroosmotic flow (EOF) in a symmetric Y-shaped microchannel heat sink (MCHS) having a constant total channel surface area, that is, constant convective heat transfer area. It is found that the average convective heat transfer coefficient of EOF increases with the increasing driven voltage, which is attributed to the increase of EOF flowrate with the increasing driven voltage. However, the maximum MCHS temperature shows an increasing after decreasing trend with the driven voltage owing to the dramatically increasing Joule heating when the voltage is large enough. Further, both the maximum MCHS temperature and average convective heat transfer coefficient are sensitive to the cross-sectional dimensions of the Y-shaped microchannels. The thermal performances of EOF in the Y-shaped MCHS show a strengthening to weakening trend with the increasing daughter-to-parent channel diameter ratio of the Y-shaped microchannel with circular cross-sectional shape, and show a similar strengthening to weakening trend with the increasing daughter-to-parent channel width ratio and the increasing microchannel height of the Y-shaped microchannel with rectangular cross-sectional shape. These cross-sectional dimension dependences of thermal performances are related to the increasing to decreasing trend of EOF flowrate changing with the microchannel cross-sectional dimensions.
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Chen, Liang, Xingchen Li, Runfeng Xiao, Kunpeng Lv, Xue Yang, and Yu Hou. "Flow Boiling of Low-Pressure Water in Microchannels of Large Aspect Ratio." Energies 13, no. 11 (May 27, 2020): 2689. http://dx.doi.org/10.3390/en13112689.
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Flow boiling heat transfer in microchannels can provide a high cooling rate, while maintaining a uniform wall temperature, which has been extensively studied as an attractive solution for the thermal management of high-power electronics. The depth-to-width ratio of the microchannel is an important parameter, which not only determines the heat transfer area but also has dominant effect on the heat transfer mechanisms. In the present study, numerical simulations based on the volume of fraction models are performed on the flow boiling in very deep microchannels. The effects of the depth-to-width ratio on the heat transfer coefficient and pressure drop are discussed. The bubble behavior and heat transfer characteristics are analyzed to explain the mechanism of heat transfer enhancement. The results show the very deep microchannels can effectively enhance the heat transfer, lower the temperature rise and show promising applications in the thermal management of high-power electronics.
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Han, Xiao Wei, Xiao Wei Liu, Li Tian, He Zhang, Yao Liu, and Zhi Gang Mao. "Effect of Joule Heat on Hydrophily of Microchannel." Key Engineering Materials 609-610 (April 2014): 606–10. http://dx.doi.org/10.4028/www.scientific.net/kem.609-610.606.
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We discuss the effect of joule heat which comes from eletroosmosis flow on the microfluidic chip. Our microfluidic chips are fabricated from polymethyl methacrylate (PMMA). As everyone knows, PMMA is a poor conductor of heat, and its transfer coefficient is only 0.19W/m·K in room temperature. So, the heat is generated by eletroosmosis canʼt conduct outside the microchannels of microfluidic chip easily. We research the effect joule heat on walls of microchannels which are made of PMMA. During our study, interior surface of microchannelsʼ hydrophobicity is changed by effect of joule heat.
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Wei, X. J., Y. K. Joshi, and P. M. Ligrani. "Numerical Simulation of Laminar Flow and Heat Transfer Inside a Microchannel With One Dimpled Surface." Journal of Electronic Packaging 129, no. 1 (March 2, 2006): 63–70. http://dx.doi.org/10.1115/1.2429711.
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Steady, laminar flow and heat transfer, inside a rectangular microchannel with a dimpled bottom surface, are numerically studied. The microchannel is 50×10−6m(50μm) deep and 200×10−6m(200μm) wide. The dimples are placed in a single row along the bottom wall with a pitch of 150×10−6m(150μm). The dimple depth is 20×10−6m(20μm), and the dimple footprint diameter is 98×10−6m(98μm). Fully developed periodic velocity and temperature boundary conditions are used at the inlet and outlet of one unit cell of the dimpled microchannel. Key flow structures such as recirculating flow and secondary flow patterns and their development along the flow directions are identified. The impact of these flow structures on the heat transfer is described. Heat transfer augmentations (relative to a channel with smooth walls) are present both on the bottom-dimpled surface, and on the sidewalls of the channel. The pressure drops in the laminar-microscale flow are either equivalent to, or less than, values produced in smooth channels with no dimples. It is concluded that dimples, proven to be an effective passive heat transfer augmentation for macroscale channels, can also be used to enhance heat transfer inside microchannels.
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Satheeshkumar, M., M. R. Thansekhar, C. Anbumeenakshi, and S. Suresh. "Effect of Geometrical Parameters on Flow Mal-Distribution in a Wavy Microchannel." Applied Mechanics and Materials 813-814 (November 2015): 674–78. http://dx.doi.org/10.4028/www.scientific.net/amm.813-814.674.
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Microchannels are of current interest for use in heat exchangers, where very high heat transfer performance is desired. Microchannels provide very high heat transfer coefficients because of their small hydraulic diameters. In this study, a numerical investigation of fluid flow in microchannels with varying hydraulic diameters is presented. Six channels with wavy shape are considered. Header is the major part in the microchannel, which supplies fluid into different channels. A CFD model was created to simulate the fluid flow in the header and microchannels. In this work, five different shapes of the header were considered namely circular, frustum conical, rectangular, triangular and trapezoidal. The results from these simulations are presented, and it is observed that the flow distribution is significantly affected by geometrical properties of the channel and the header.
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Vinoth, R., M. Parthiban, Naveen Kumar Nagalli, and S. Prakash. "Numerical study of nanofluids effect on heat transfer and pressure drop of triangular microchannel heat sink." International Journal of ChemTech Research 13, no. 1 (2020): 173–80. http://dx.doi.org/10.20902/ijctr.2019.130121.
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The present work deals with study the heat transfer and pressure drop of the triangular microchannel heat sink(MCHS), along different working fluids. The nanofluids such as CuO and Al2O3are used as coolants to enhance the performance of triangular microchannel heat sinks.The modeling and analysis were done with the help of Solid works. The heat transfer performance of the triangular fins were studied with the Reynolds number varying from 96 - 460. Thenumerical result shows that the triangular oblique finned microchannel heat sink has large heat transfer rateof 12.9 % for varying Reynolds number when compared to a straight channel. Similarly, the pressure drop also increases with 38.2% for triangular microchannel flowing nanofluid. Consequently triangular microchannel is enhancing the heat removed in electronics chip cooling
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Nonino, Carlo, and Stefano Savino. "Numerical investigation on the performance of cross-flow micro heat exchangers." International Journal of Numerical Methods for Heat & Fluid Flow 26, no. 3/4 (May 3, 2016): 745–66. http://dx.doi.org/10.1108/hff-09-2015-0393.
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Purpose – The purpose of this paper is twofold: to describe a relevant improvement to an in-house FEM procedure for the heat transfer analysis of cross-flow micro heat exchangers and to study the influence of microchannel cross-sectional geometry and solid wall thermal conductivity on the thermal performance of these microdevices. Design/methodology/approach – The velocity field in each microchannel is calculated separately. Then the energy equation is solved in the whole computational domain. Domain decomposition and grids that do not match at the common interface are employed to make meshing more effective. Some flow maldistribution effects are taken into account. Findings – The results show that larger thermal conductivities of the solid walls and rectangular cross-sectional geometries with higher aspect ratios allow the maximization of the total heat flow rate in the device. However, on the basis of the heat transfer per unit pumping power, the square cross-section could be the best option. Research limitations/implications – The value of the average viscosity is assumed to be different in different microchannels, but constant within each of the microchannels. Practical implications – The procedure can represent a valuable tool for the design of cross-flow micro heat exchangers. Originality/value – In spite of requiring limited computational resources, the improved procedure can take into account flow maldistribution effects stemming from non-uniform microchannel temperatures.
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Jaferian, Vahid, Davood Toghraie, Farzad Pourfattah, Omid Ali Akbari, and Pouyan Talebizadehsardari. "Numerical investigation of the effect of water/Al2O3 nanofluid on heat transfer in trapezoidal, sinusoidal and stepped microchannels." International Journal of Numerical Methods for Heat & Fluid Flow 30, no. 5 (June 19, 2019): 2439–65. http://dx.doi.org/10.1108/hff-05-2019-0377.
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Purpose The purpose of this study is three-dimensional flow and heat transfer investigation of water/Al2O3 nanofluid inside a microchannel with different cross-sections in two-phase mode. Design/methodology/approach The effect of microchannel walls geometry (trapezoidal, sinusoidal and stepped microchannels) on flow characteristics and also changing circular cross section to trapezoidal cross section in laminar flow at Reynolds numbers of 50, 100, 300 and 600 were investigated. In this study, two-phase water/Al2O3 nanofluid is simulated by the mixture model, and the effect of volume fraction of nanoparticles on performance evaluation criterion (PEC) is studied. The accuracy of obtained results was compared with the experimental and numerical results of other similar papers. Findings Results show that in flow at lower Reynolds numbers, sinusoidal walls create a pressure drop in pure water flow which improves heat transfer to obtain PEC < 1. However, in sinusoidal and stepped microchannel with higher Reynolds numbers, PEC > 1. Results showed that the stepped microchannel had higher pressure drop, better thermal performance and higher PEC than other microchannels. Originality/value Review of previous studies showed that existing papers have not compared and investigated nanofluid in a two-phase mode in inhomogeneous circular, stepped and sinusoidal cross and trapezoidal cross-sections by considering the effect of changing channel shape, which is the aim of the present paper.
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Cheong, Wong Kok, and Fashli Nazhirin bin Ahmad Muezzin. "Heat Transfer of a Double Layer Microchannel Heat Sink." Applied Mechanics and Materials 479-480 (December 2013): 411–15. http://dx.doi.org/10.4028/www.scientific.net/amm.479-480.411.
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A numerical study is conducted to predict the effects of physical parameters of a double layer microchannel heat sink on heat transfer. The physical parameters investigated are the channel height and channel width for different flow orientation at the upper and lower channels. For the range of Reynolds number investigated, results show that parallel flow configuration leads to better heat transfer performance than counter flow. Lower thermal resistance can be achieved in a double-layered microchannel heat sink with higher channel height and lower channel width.
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Kaniowski, Robert, Robert Pastuszko, Joanna Kowalczyk, and Łukasz Nowakowski. "Bubble departure diameter determination for pool boiling on surface with microchannels." E3S Web of Conferences 70 (2018): 02008. http://dx.doi.org/10.1051/e3sconf/20187002008.
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The paper presents visualization investigations into pool boiling heat transfer for open microchannel surfaces. The experiments were carried out with saturated water, ethanol, FC-72 and Novec-649 at atmospheric pressure. Parallel microchannels fabricated by machining copper sample were about 0.2 to 0.5 mm wide and 0.2 to 0.5 mm deep. The diameter of departing bubble was calculated for the microchannel surface on the basis of buoyancy force and surface tension force balance. The visualization carried out was aimed at determining the diameters of the departing bubbles at various heat fluxes for four working fluids.
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Moshizi, S. A. "Forced convection heat and mass transfer of MHD nanofluid flow inside a porous microchannel with chemical reaction on the walls." Engineering Computations 32, no. 8 (November 2, 2015): 2419–42. http://dx.doi.org/10.1108/ec-02-2015-0035.
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Purpose – The purpose of this paper is to focus on convective heat and mass transfer characteristics of Cu-water nanofluid inside a porous microchannel in the presence of a uniform magnetic field. The walls of the microchannel are subjected to constant asymmetric heat fluxes and also the first order catalytic reaction. To represent the non-equilibrium region near the surfaces, the Navier’s slip condition is considered at the surfaces because of the non-adherence of the fluid-solid interface and the microscopic roughness in microchannels. Design/methodology/approach – Employing the Brinkman model for the flow in the porous medium and the “clear fluid compatible” model as a viscous dissipation model, the conservative partial differential equations have been transformed into a system of ordinary ones via the similarity variables. Closed form exact solutions are obtained analytically based on dimensionless parameters of velocity, temperature and species concentration. Findings – Results show that the addition of Cu-nanoparticles to the fluid has a significant influence on decreasing concentration, temperature distribution at the both walls and velocity profile along the microchannel. In addition, total heat transfer in microchannel increases as nanoparticles add to the fluid. Slip parameter and Hartmann number have the decreasing effects on concentration and temperature distributions. Slip parameter leads to increase velocity profiles, while Hartmann number has an opposite trend in velocity profiles. These two parameters increase the total heat transfer rate significantly. Originality/value – In the present study, a comprehensive analytical solution has been obtained for convective heat and mass transfer characteristics of Cu-water nanofluid inside a porous microchannel in the presence of a uniform magnetic field. Finally, the effects of several parameters such as Darcy number, nanoparticle volume fraction, slip parameter, Hartmann number, Brinkman number, asymmetric heat flux parameter, Soret and Damkohler numbers on total heat transfer rate and fluid flow profiles are studied in more detail. To the best of author’s knowledge, no study has been conducted to this subject and the results are original.
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Muwanga, R., and I. Hassan. "Local Heat Transfer Measurements in Microchannels Using Liquid Crystal Thermography: Methodology Development and Validation." Journal of Heat Transfer 128, no. 7 (December 14, 2005): 617–26. http://dx.doi.org/10.1115/1.2193541.
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Microchannel heat transfer governs the performance of the microchannel heat sink, which is a recent technology aimed at managing the stringent thermal requirements of today’s high-end electronics. The microencapsulated form of liquid crystals has been well established for use in surface temperature mapping, while limited studies are available on the use of the un-encapsulated form. This latter form is advantageous since it offers the potential for high spatial resolution, which is necessary for microgeometries. A technique for using un-encapsulated thermochromic liquid crystals (TLCs) in order to measure the local heat transfer coefficient in microchannel geometries is shown in the present study. Measurements were made in a closed loop facility combined with a microscopic imaging system and automated data acquisition. A localized TLC calibration was used to account for a non-uniform coating and variation of lighting conditions. Three test section configurations were investigated with each subsequent configuration arising due to a shortfall in the previous. Two of these configurations are comprised of single wall heated rectangular channels, while the third is a circular tube channel. Validation results are also presented; overall, the methods developed and utilized in this study have been shown to provide the local heat transfer coefficient in microchannels.
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Rahman, Muhammad Mustafizur. "Measurements of heat transfer in microchannel heat sinks." International Communications in Heat and Mass Transfer 27, no. 4 (May 2000): 495–506. http://dx.doi.org/10.1016/s0735-1933(00)00132-9.
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Takahashi, Ichiro, and Eisuke Ishikawa. "Microchannel Heat Sink Based on Boiling Heat Transfer." Transactions of the Japan Society of Mechanical Engineers Series B 61, no. 584 (1995): 1498–504. http://dx.doi.org/10.1299/kikaib.61.1498.
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