共查询到18条相似文献,搜索用时 203 毫秒
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纳米颗粒悬浮液池内泡状沸腾的实验研究 总被引:7,自引:0,他引:7
本文对纳米颗粒悬浮液在平壁面上池内沸腾进行了实验研究。实验用的纳米粒子为26 nm的铁粉和13 nm的三氧化二铝纳米粉末,基液为去离子水。分别配成体积浓度为0.1%, 1%和2%的悬浮液。实验结果表明,纳米悬浮颗粒对液体沸腾换热过程的影响会随着纳米颗粒性质,颗粒浓度及热流密度大小的不同而出现不同的效果;加入纳米颗粒后, 对基液沸腾换热的影响存在着两个相反的作用机制,它们分别为:纳米颗粒增强了液体内部的热量迁移能力(热物性的影响)和改变了加热面的表面结构特性(加热面特性的影响)。 相似文献
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纳米颗粒在制冷剂中的分散特性研究 总被引:5,自引:2,他引:5
本文利用沉降观察法和分光光度计吸收测量法,实验研究了纳米颗粒在制冷剂中的分散特性.结果表明:纳米颗粒属性和制冷剂属性对分散稳定性影响较大,制冷剂的极性和介电常数是主要的影响因素. 相似文献
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《工程热物理学报》2016,(9)
为通过表面活性剂抑制纳米制冷剂中的颗粒团聚,需要了解不同种类和浓度的表面活性剂对纳米制冷剂颗粒团聚的影响。本文采用动态光散射技术测量纳米制冷剂中的颗粒尺度,来定量分析纳米制冷剂的颗粒团聚特性;实验所用纳米制冷剂为TiO_2-R141b;表面活性剂种类包括SDBS(阳离子型)、CTAB(阴离子型)和NP-10(非离子型)。实验结果表明,SDBS、CTAB和NP-10均可降低纳米制冷剂的颗粒尺度,即抑制纳米制冷剂中的颗粒团聚。对SBDS、CTAB和NP-10,当其浓度分别为400 mg·L~(-1)、200 mg·L~(-1)和300mg·L~(-1)时纳米制冷剂的颗粒尺度最小,最小值分别是未加表面活性剂时的58.4%、56.9%和38.0%。 相似文献
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考虑在纳米流体中纳米颗粒做布朗运动引起的对流换热, 基于纳米颗粒在纳米流体中遵循分形分布, 本文得到纳米流体对流换热的机理模型. 本解析模型没有增加新的经验常数, 从该模型发现纳米流体池沸腾热流密度是温度、纳米颗粒的平均直径、 纳米颗粒的浓度、纳米颗粒的分形维数、沸腾表面活化穴的分形维数、基本液体的物理特性的函数. 对不同的纳米颗粒浓度和不同的纳米颗粒平均直径与不同的实验数据进行了比较, 模型预测的结果与实验结果相吻合. 所得的解析模型可以更深刻地揭示纳米流体对流换热的物理机理. 相似文献
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R. Mortezazadeh H. Aminfar M. Mohammadpourfard 《Journal of Engineering Thermophysics》2017,26(4):580-597
The nucleate pool boiling heat transfer of ferrofluid on a horizontal plate in the presence of a non-uniform magnetic field has been studied numerically using Eulerian–Eulerian approach. Also, the wall partitioning model was extended to consider the boiling surface modification by the nanoparticles deposition on the heated surface. Adding nanoparticles causes deterioration in the boiling heat transfer coefficient and void fraction. Moreover, applying the magnetic field intensifies these reductions. 相似文献
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In this paper, a fractal model for nucleate pool boiling heat transfer of nanofluids is developed based on the fractal distribution of nanoparticles and nucleation sites on boiling surfaces. The model shows the dependences of the heat flux on nanoparticle size and the nanoparticle volume fraction of the suspension, the fractal dimension of the nanoparticle and nucleation site, temperature of nanofluids and properties of fluids. The fractal model predictions show that the natural convection stage continues r... 相似文献
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Dongsheng Wen 《Journal of nanoparticle research》2008,10(7):1129-1140
Research on nanofluids has progressed rapidly since their enhanced thermal conductivities were identified about a decade ago.
For boiling heat transfer with nanofluids, however, many contradictory results have been reported, which cannot be explained
by conventional theories developed for pure fluids. Recent progress in colloidal science shows that the presence of nanoparticles
could enhance the spreading and wettability of base fluids through a long-range structural disjoining pressure. This article
explores theoretically the influence of structural disjoining pressure to the nucleate boiling heat transfer through a four-zoned
microlayer evaporation model. The influence of particle size, particle concentration, and heat flux on the structural disjoining
pressure and the interfacial shape of the microlayer are investigated. The calculated equilibrium interfacial shape shows
that the meniscus is displaced toward the vapor phase in the presence of nanoparticles, an implication of enhanced wettability.
Such an improved wettability affects the number of active nucleate sites and bubble dynamics significantly, which could be
one of the important parameters that is responsible for the controversy of boiling heat transfer with nanofluids reported
in the literature. 相似文献
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We report the synthesis and self-assembly of different shapes and sizes of FePt nanoparticles. Our study shows that surfactants and solvent play an important role in the synthesis of different shapes and sizes of FePt nanoparticles. Higher boiling point solvents lead to the formation of spherical nanoparticles and low boiling point solvents form cubic nanoparticles. Our studies also indicate that self-assembly of FePt nanoparticles on substrates is a complex process that is sensitive to the concentration of excess surfactant in the nanoparticle solution. 相似文献
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Analytical expressions for nucleate pool boiling heat transfer of nanofluid in the critical heat flux (CHF) region are derived taking into account the effect of nanoparticles moving in liquid based on the fractal geometry theory. The proposed fractal model for the CHF of nanofluid is explicitly related to the average diameter of the nanoparticles, the volumetric nanoparticle concentration, the thermal conductivity of nanoparticles, the fractal dimension of nanoparticles, the fractal dimension of active cavities on the heated surfaces, the temperature, and the properties of the fluid. It is found that the CHF of nanofluid decreases with the increase of the average diameter of nanoparticles. Each parameter of the proposed formulas on CHF has a clear physical meaning. The model predictions are compared with the existing experimental data, and a good agreement between the model predictions and experimental data is found. The validity of the present model is thus verified. The proposed fractal model can reveal the mechanism of heat transfer in nanofluid. 相似文献
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E. Popovici C. Luculescu R. Alexandrescu C. Fleaca F. Dumitrache R. Barjega M. Scarisoreanu E. Dutu A. Barbut I. Morjan E. Vasile 《Applied Surface Science》2012,258(23):9326-9332
The laser synthesis of nanoparticles starting from liquid precursors is particularly suitable as synthesis technique for obtaining nanoparticles. In the present work the laser pyrolysis is performed in a novel setup where the liquid precursor is brought with the aid of an original evaporator system to temperatures in excess of the boiling point and is finally fed into the reactor under the form of heated vapors.The process occurs in the gas phase and ensures the avoidance of the condensation. The temperature control system allows for the maintaining of the overall system temperature below the decomposition temperature and above the boiling. Temperatures up to 500 °C are assured for the mixed precursors. The control of the amount of the active substances is performed upstream, in the liquid phase. The set-up is able to offer safety conditions at the synthesis of substances with high toxicity. This experimental set-up was proposed in order to synthesize TiO2 nanoparticles from TTIP because its boiling temperature is relatively high (239 °C grades). Different analytical techniques such as EDX, TEM, XRD and HRTEM were used in order to evaluate the structural characteristics of the produced nanopowders. 相似文献
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This study investigates flow boiling heat transfer of aqueous alumina nanofluids in single microchannels with particular focuses
on the critical heat flux (CHF) and the potential dual roles played by nanoparticles, i.e., (i) modification of the heating
surface through particle deposition and (ii) modification of bubble dynamics through particles suspended in the liquid phase.
Low concentrations of nanofluids (0.001–0.1 vol.%) are formulated by the two-step method and the average alumina particle
size is ~25 nm. Two sets of experiments are performed: (a) flow boiling of formed nanofluids in single microchannels where
the effect of heating surface modification by nanoparticle deposition is apparent and (b) bubble formation in a quiescent
pool of alumina nanofluids under adiabatic conditions where the role of suspended nanoparticles in the liquid phase is revealed.
The flow boiling experiments reveal a modest increase in CHF by nanofluids, being higher at higher nanoparticle concentrations
and higher inlet subcoolings. The bubble formation experiments show that suspended nanoparticles in the liquid phase alone
can significantly affect bubble dynamics. Further discussion reveals that both roles are likely co-existent in a typical boiling
system. Properly surface-promoted nanoparticles could minimize particle deposition hence little modification of the heating
surface, but could still contribute to the modification in heat transfer through the second mechanism, which is potentially
promising for microchannel applications. 相似文献
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A novel analytical model to determine the heat flux of subcooled pool boiling in fractal nanofluids is developed. The model considers the fractal character of nanofluids in terms of the fractal dimension of nanoparticles and the fractal dimen- sion of active cavities on the heated surfaces; it also takes into account the effect of the Brownian motion of nanoparticles, which has no empirical constant but has parameters with physical meanings. The proposed model is expressed as a function of the subcooling of fluids and the wall superheat. The fractal analytical model is verified by a reasonable agreement with the experimental data and the results obtained from existing models. 相似文献