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1.
以氧化铝为纳米粒子、丙二醇和水为基础液体制备了氧化铝有机纳米流体,分别测量了它的沸点、热导率、比热容和黏度。以1%~5%(体积分数)的氧化铝纳米流体作为冷介质,测试了在车用机油冷却器中的传热系数和流动阻力。试验结果表明,纳米粒子能够显著强化基础液体在机油冷却器中的换热能力,粒子体积分数和流体温度是影响纳米流体热物性的重要因素。氧化铝纳米流体的沸点高于120℃,比热容随体积分数增加而降低,热导率、黏度和在机油冷却器中的传热系数均随粒子体积分数的增加而提高。在试验Ⅱ中,5%(体积分数)纳米流体的平均传热系数比基础液体提高了124.56%,而流动阻力增幅较小。 相似文献
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A comparison between the efficacy of surface boundary structure and presence of nanoparticles on the condensation two-phase flow inside rough nanochannels has been accomplished by applying molecular dynamics procedure to evaluate the thermal conductivity and flow characteristics. Simulation is performed in a computational region with two copper walls containing rectangular rough elements under different saturated temperatures. The main properties of liquid-vapor interface including density and the number of liquid atoms, are obtained. It is observed that the density profile is more affected by nanoparticles than the roughness. Also, compared to the condensation of nanofluid in a smooth nanochannel, the rough wall causes a greater drop in the temperature at the early time steps and by development of liquid films, effects of the wall roughness reduce. At the first of the condensation process, adding nanoparticle causes that transferring argon particles to the liquid phase increases with a steeper slope. Furthermore, heat current autocorrelation function (HCACF) for nanofluid condensation flow over considered correlation time is analyzed and following that the thermal conductivity for different saturated conditions is calculated. It has been represented that at lower temperatures the roughness makes more significant influence on the heat transfer of two-phase flow, while at higher temperatures the importance of nanoparticles prevails. 相似文献
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建立了一套水平气液界面传质模拟装置,利用粒子成像测速仪(PIV)对CO2从乙醇和乙醇纳米流体中解吸过程液相流场进行了观测和分析。传质发生时,在近界面处均观察到了由Marangoni效应造成的湍动。通过对平均速度的分析,发现在乙醇纳米流体中发生的湍动强度和湍动范围较乙醇溶液中大。纳米流体中的Marangoni效应加剧了纳米粒子的布朗运动,引发了纳米流体中的微对流,从而将界面处的湍动传递至液相主体中,导致液相主体的漩涡增多、流体混合加剧,促进了气液传质。 相似文献
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In this study, the performance of stable nanofluid containing SiO_2 nanoparticles dispersed and stabilized in high salinity brine for asphaltene inhibition in dynamic condition is evaluated. In the first stage of this work, the stability of silica nanoparticles in different range of water salinity(0–100000 mg·L~(-1)) is investigated. Next, stable nanofluid containing highest salinity is selected as asphaltene inhibitor agent to inject into the damaged core sample. The estimated values of oil recovery for base case, after damage process and after inhibition of asphaltene precipitation using nanofluid are 51.6%, 36.1% and 46.7%, respectively. The results showed the reduction in core damage after using nanofluid. In addition, the relative permeability curves are plotted for the base case, after damage process and also after inhibition of asphaltene precipitation using nanofluid. Comparison of relative permeability curves shows, relative permeability of oil phase decreased after damage process as compared with the base case. But after using nanofluid the oil relative permeability curve has shifted to the right and effective permeability of oil phase has been improved. 相似文献
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基于经典的核化理论,将纳米流体看成是一个均匀的体系,不考虑颗粒的团聚及其在壁面处的富集和沉积,仅考虑体相纳米颗粒的影响。将纳米颗粒类比为大分子溶质,基液类比为溶剂,则纳米流体便可看作是浓度极稀的溶液,借用溶液热力学的相关理论,并假设气液界面处的颗粒是单层嵌入的方式且排布均匀,分别建立了纳米流体的均相和非均相核化模型,分析探讨颗粒对核化的影响。结果表明,纳米颗粒在界面处的吸附可减小核化的平衡胚泡半径,降低沸腾核化势垒,有利于核化的发生。 相似文献
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对CuO-水纳米流体在6mm多孔球层内进行池沸腾实验研究。实验使用了40nm的CuO纳米颗粒,加以不同浓度的十二烷基苯磺酸钠(SDBS)作为表面活性剂,配成多种不同配比关系的纳米流体。实验结果表明,当表面活性剂浓度与纳米颗粒浓度在0.01%~0.03%(质量分数,下同)之间变化时,两者浓度相近的纳米流体稳定性较好,沸腾传热效果高。其中表面活性剂浓度略高于CuO浓度时,传热效果较好,在SDBS浓度为0.03%、CuO浓度为0.02%时达到最大,为41670W/(m2·K);而纳米颗粒浓度增大时,根据其对纳米流体的稳定性和沉降效应的影响,在不同程度上可增强或削弱沸腾传热。同时对纳米流体的池沸腾进行可视化研究,利用气泡脱离特性对实验结果作了诠释。所得结果可为纳米流体在多孔球层的池沸腾传热特性研究提供有益的研究数据。 相似文献
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Suspensions of nanoparticles (i.e., particles with diameters < 100 nm) in liquids, termed nanofluids, show remarkable thermal
and optical property changes from the base liquid at low particle loadings. Recent studies also indicate that selected nanofluids
may improve the efficiency of direct absorption solar thermal collectors. To determine the effectiveness of nanofluids in
solar applications, their ability to convert light energy to thermal energy must be known. That is, their absorption of the
solar spectrum must be established. Accordingly, this study compares model predictions to spectroscopic measurements of extinction
coefficients over wavelengths that are important for solar energy (0.25 to 2.5 μm). A simple addition of the base fluid and
nanoparticle extinction coefficients is applied as an approximation of the effective nanofluid extinction coefficient. Comparisons
with measured extinction coefficients reveal that the approximation works well with water-based nanofluids containing graphite
nanoparticles but less well with metallic nanoparticles and/or oil-based fluids. For the materials used in this study, over
95% of incoming sunlight can be absorbed (in a nanofluid thickness ≥10 cm) with extremely low nanoparticle volume fractions
- less than 1 × 10-5, or 10 parts per million. Thus, nanofluids could be used to absorb sunlight with a negligible amount of viscosity and/or
density (read: pumping power) increase. 相似文献
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Copper (Cu)‐doped polymethylmethacrylate (PMMA) composites were prepared by soapless emulsion polymerization. In this process, copper nanoparticles were modified by sodium oleate (SOA) and the surface property of Cu nanoparticles changed from hydrophilic to hydrophobic. The hydrophobic Cu nanoparticles could not only avoid the oxidation of Cu in air but also improve the compatibility between Cu nanoparticles and PMMA. The TEM micrographs revealed that Cu nanoparticles were encapsulated in PMMA polymer microspheres. In addition, the uniform Cu/PMMA composite microspheres could be synthesized in such a soapless emulsion polymerization process. It was worth mentioning that the friction property in oil was well improved when little nanocomposites were added into the base oil, which indicated that the composites can be widely used in lubricating oil. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011 相似文献
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Kuznetsov AV 《Nanoscale research letters》2011,6(1):100
The aim of this article is to propose a novel type of a nanofluid that contains both nanoparticles and motile (oxytactic)
microorganisms. The benefits of adding motile microorganisms to the suspension include enhanced mass transfer, microscale
mixing, and anticipated improved stability of the nanofluid. In order to understand the behavior of such a suspension at the
fundamental level, this article investigates its stability when it occupies a shallow horizontal layer. The oscillatory mode
of nanofluid bioconvection may be induced by the interaction of three competing agencies: oxytactic microorganisms, heating
or cooling from the bottom, and top or bottom-heavy nanoparticle distribution. The model includes equations expressing conservation
of total mass, momentum, thermal energy, nanoparticles, microorganisms, and oxygen. Physical mechanisms responsible for the
slip velocity between the nanoparticles and the base fluid, such as Brownian motion and thermophoresis, are accounted for
in the model. An approximate analytical solution of the eigenvalue problem is obtained using the Galerkin method. The obtained
solution provides important physical insights into the behavior of this system; it also explains when the oscillatory mode
of instability is possible in such system. 相似文献
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In this article, laminar flow-forced convective heat transfer of Al2O3/water nanofluid in a triangular duct under constant wall temperature condition is investigated numerically. In this investigation,
the effects of parameters, such as nanoparticles diameter, concentration, and Reynolds number on the enhancement of nanofluids
heat transfer is studied. Besides, the comparison between nanofluid and pure fluid heat transfer is achieved in this article.
Sometimes, because of pressure drop limitations, the need for non-circular ducts arises in many heat transfer applications.
The low heat transfer rate of non-circular ducts is one the limitations of these systems, and utilization of nanofluid instead
of pure fluid because of its potential to increase heat transfer of system can compensate this problem. In this article, for
considering the presence of nanoparticl: es, the dispersion model is used. Numerical results represent an enhancement of heat
transfer of fluid associated with changing to the suspension of nanometer-sized particles in the triangular duct. The results
of the present model indicate that the nanofluid Nusselt number increases with increasing concentration of nanoparticles and
decreasing diameter. Also, the enhancement of the fluid heat transfer becomes better at high Re in laminar flow with the addition
of nanoparticles. 相似文献
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《Ceramics International》2022,48(21):31728-31737
Microchannel technology is an effective method to solve the heat transfer of microelectronics. Nanofluids are considered to have great application potential in microchannel heat exchangers. In this experiment, β-cyclodextrin (β-CD) was used to modify ZrO2 nanoparticles. The morphology, functional group, and crystal structure of the nanoparticles before and after modification were studied. Ethylene glycol aqueous solution-based nanofluids were prepared using a two-step method. Its physical properties were studied. The modified nanofluid has better stability. The thermal conductivity of the nanofluid was measured and the mathematical model was analyzed. The results showed that the nanofluid with a concentration of 0.10 vol% was 37.82% higher than the base fluid at 60 °C. The results of the mathematical analysis indicate that the fabrication of nanofluids using β-cyclodextrin-modified ZrO2 has great potential for application in heat transfer in microelectronic microchannels. 相似文献
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非离子表面活性剂的加入对水基纳米微流体在小直径管中的减阻作用(英文) 总被引:2,自引:0,他引:2
The goal of this research was to determine the impact of nonionic surfactants on drag reduction effect in water and metal oxide nanofluid. Two nonionic surfactants (Rokacet O7 and Rokanol K7) and copper(Ⅱ) oxide water-based nanofluid were examined. Friction factors in a 4 mm diameter pipe for the Reynolds number between 8000 and 50000 were determined. Results showed that addition of nonionic surfactants caused the decrease of friction factor in water and nanofluid. The drag reduction effect was similar in both cases. Presence of nanoparticles in the system has no great influence on drag reduction effect. 相似文献
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A. Kazemi-Beydokhti S. Zeinali Heris M. Shariati-Niasar A. A. Hamidi 《Chemical Engineering Communications》2013,200(5):593-611
The present research reports nanofluid effective thermal conductivity enhancements (ETCE) using an accurate transient short hot wire method system. Preparation of nanofluids was carried out through a two-step method with highly powered pulses similar to that for nanoparticle dispersion in base fluids. Parameters affecting nanofluid heat conductivity such as concentration, sizes, and material of nanoparticle? type of base fluid, temperature, ultrasonic mixing time, and elapsed time after preparation were studied. In the present study, nanoparticles of Al, Al2O3, CuO, SnO2, TiO2, and SiO2 with base fluids of water and ethylene glycol were used. Parameters like concentration, size, temperature, and the type of base fluid showed more noticeable effect on the effective thermal conductivity than the others, and mixing time had the least effect. The results showed that any increase in concentration and temperature, and also any decrease in size of nanoparticles and time elapsed after nanofluid preparation, leads to the ETCE of the nanofluid. However, the effects of nanoparticle material, base fluid, and mixing time on thermal conductivity of the nanofluid showed varying trends. Last, a number of mathematical models for prediction of thermal conductivity of nanofluids were applied. 相似文献
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Investigation of the effect of magnetic field on mass transfer parameters of CO2 absorption using Fe3O4‐water nanofluid 下载免费PDF全文
Mohammad Hossein Karimi Darvanjooghi Maedeh Pahlevaninezhad Ali Abdollahi Seyyed Mohammadreza Davoodi 《American Institute of Chemical Engineers》2017,63(6):2176-2186
In this study, the enhancement of physical absorption of carbon dioxide by Fe3O4‐water nanofluid under the influence of AC and DC magnetic fields was investigated. Furthermore, a gas‐liquid mass transfer model for single bubble systems was applied to predict mass transfer parameters. The coated Fe3O4 nanoparticles were prepared using co‐percipitation method. The results from characterization indicated that the nanoparticles surfaces were covered with hydroxyl groups and nanoparticles diameter were 10–13 nm. The findings showed that the mass transfer rate and solubility of carbon dioxide in magnetic nanofluid increased with an increase in the magnetic field strength. Results indicated that the enhancement of carbon dioxide solubility and average molar flux gas into liquid phase, particularly in the case of AC magnetic field. Moreover, results demonstrated that mass diffusivity of CO2 in nanofluid and renewal surface factor increased when the intensity of the field increased and consequently diffusion layer thickness decreased. © 2016 American Institute of Chemical Engineers AIChE J, 63: 2176–2186, 2017 相似文献
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In this paper, response surface methodology(RSM) based on central composite design(CCD) is applied to obtain an optimization design for the fuel rod's diameter and distance cooled by turbulent Al_2O_3–water nanofluid for a typical pressurized water reactor(PWR). Fuel rods and nanofluid flow between them are simulated 3D using computational fluid dynamics(CFD) by ANSYS-FLUNET package software. The RNG k–ε model is used to simulate turbulent nanofluid flow between the rods. The effect of different nanoparticles concentration is also investigated on the Nusselt number from heat transfer efficiency view point. Results reveal that when distance parameter(a) is in the minimum level and diameter parameter(r) is in the maximum possible level, cooling the rods will be better due to higher Nusselt number in this situation. Also, using the different nanoparticles on the cooling process confirms that Al_2O_3 averagely 17% and TiO_2 10% improve the Nusselt numbers. 相似文献
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Seyedeh‐Saba Ashrafmansouri Mohsen Nasr Esfahany 《American Institute of Chemical Engineers》2016,62(3):852-860
The performance of a spray liquid‐liquid extraction column at two mass‐transfer directions was experimentally studied in the presence of silica nanoparticles. Toluene‐based nanofluid drops containing 0.0005–0.01 vol % silica nanoparticles were dispersed in aqueous phase and acetic acid (AA) transfer between phases was investigated. The experiments were performed at fixed volumetric flow rates of dispersed and continuous phases. Maximum enhancement of 47.4% and 107.5% in overall mass‐transfer coefficient, respectively, for mass‐transfer direction of dispersed to continuous phase and vice versa were achieved for drops with 0.001 vol % silica nanoparticles. These enhancements can be referred to Brownian motion of nanoparticles and induced microconvection. The results showed that nanoparticles are more effective in augmenting AA transfer from continuous to dispersed phase. Probable reason is that smaller diameter and lower internal turbulence of drops in this transfer direction increase dispersed phase resistance potential to be manipulated by Brownian motion of nanoparticles. © 2015 American Institute of Chemical Engineers AIChE J, 62: 852–860, 2016 相似文献
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Silver nanoparticles were produced by electrical explosion of wires in liquids with no additive. In this study, we optimized
the fabrication method and examined the effects of manufacturing process parameters. Morphology and size of the Ag nanoparticles
were determined using transmission electron microscopy and field-emission scanning electron microscopy. Size and zeta potential
were analyzed using dynamic light scattering. A response optimization technique showed that optimal conditions were achieved
when capacitance was 30 μF, wire length was 38 mm, liquid volume was 500 mL, and the liquid type was deionized water. The
average Ag nanoparticle size in water was 118.9 nm and the zeta potential was -42.5 mV. The critical heat flux of the 0.001-vol.%
Ag nanofluid was higher than pure water. 相似文献