共查询到18条相似文献,搜索用时 75 毫秒
1.
2.
3.
《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
4.
5.
6.
本文建立了纳米颗粒/制冷剂工质换热性能实验台,对实验系统进行了检验,并首次进行了纳米颗粒TiO2/HFC134a工质水平管内的单相对流换热实验研究,纳米颗粒的浓度为0.01、0.025和0.05 g/L,并与纯质HFC134a的结果相比较.结果发现:TiO2/HFC134a工质的单相对流换热系数降低,且随着纳米颗粒浓度的增大,降低程度增大.分析原因纳米颗粒在换热表面的沉积是造成这一结果的关键因素. 相似文献
7.
提出了纳米颗粒水基分散液的力学-化学双重减阻机制,并通过对比岩心切片吸附纳米颗粒前后以及冲刷前后的表面微结构、润湿性的变化,进行了实验验证. 研究结果表明,经纳米颗粒水基分散液处理之后的岩心切片表面表现为强亲水性, 并且存在一层致密的纳米颗粒吸附层;冲刷之后岩心切片表面的纳米颗粒吸附层依然存在, 但其表面已逐渐转变为强/超疏水性,反映了纳米颗粒吸附层表面的表面活性剂被逐渐清洗干净. 注水初期,主要表现为表面活性剂的化学减阻作用.随着注水过程的进行, 主要体现为以疏水表面的滑移效应为主的力学减阻机制.岩心驱替实验结果表明, 纳米颗粒水基分散液驱替后的岩心的水相渗透率平均提高幅度达84.3%, 减阻效果显著,证实了纳米颗粒水基分散液的力学-化学双重减阻机制. 相似文献
8.
9.
10.
纳米流体中悬浮的纳米颗粒可以增强其导热性能已经得到广泛认可,然而纳米流体颗粒增强传热的机理目前尚不清楚.研究表明,纳米颗粒的聚集是纳米流体导热系数增大的重要机制,而且纳米颗粒聚集的形态对纳米流体的导热系数有重要影响,但是目前的导热系数模型大多是建立在Maxwell有效介质理论的"静态"和"均匀分散"假设基础上.本文用平衡分子动力学模拟Cu-Ar纳米流体,采用Green-Kubo公式计算导热系数,采用Schmidt-Ott关系式计算不同聚集形态下的分形维数.对比导热系数与分形维数可以发现:在相同体积分数下,较低的分形维数会有更高的导热系数,分析了分形维数与导热系数的定量关系.此外,通过径向分布函数可以看出纳米颗粒紧密聚集与松散聚集的差异,基液分子在纳米颗粒附近的纳米薄层中处于动态平衡状态.研究结果有助于理解纳米颗粒聚集形态对导热系数的影响机理. 相似文献
11.
E. Veena Gopalan I. A. Al-Omari D. Sakthi Kumar Yasuhiko Yoshida P. A. Joy M. R. Anantharaman 《Applied Physics A: Materials Science & Processing》2010,99(2):497-503
The magnetocaloric properties of cobalt ferrite nanoparticles were investigated to evaluate the potential of these materials
as magnetic refrigerants. Nanosized cobalt ferrites were synthesized by the method of sol–gel combustion. The nanoparticles
were found to be spherical with an average crystallite size of 14 nm. The magnetic entropy change (ΔS
m) calculated indirectly from magnetization isotherms in the temperature region 170–320 K was found to be negative, signifying
an inverse magnetocaloric effect in the nanoparticles. The magnitudes of the ΔS
m values were found to be larger when compared to the reported values in the literature for the corresponding ferrite materials
in the nanoregime. 相似文献
12.
An amorphous acrylic acid (AA) polymer coating was generated on TiO2 nanoparticles through pulse radio frequency (RF) plasma polymerization. The AA plasma synthesis mechanism was studied by its optical emission spectrum. The chemical structures of AA–plasma‐polymer were carefully investigated by Fourier transform infrared spectroscopy (FTIR). The dispersion behaviors of AA‐coated and uncoated TiO2 nanoparticles in glycol solution were characterized by ultraviolet absorbency and particle size distribution measurements. The results showed that the aggregation of TiO2 nanoparticles in glycol solution was effectively lowered and the dispersion was improved a lot after AA–plasma‐polymer coating. The pulse plasma coating parameters played an important role in the dispersion enhancement of TiO2 nanoparticles. By properly regulating the pulse discharge parameters, the system could gain the highest radical–monomer reactions rate, the most compatible functional groups on the nanoparticles, and the best dispersion in the background media. 相似文献
13.
Feng Zhu Jing Zhang Zhongxue Yang Ying Guo Hua Li Yafei Zhang 《Physica E: Low-dimensional Systems and Nanostructures》2005,27(4):457-461
In this study, the surface of TiO2 nanoparticles was modified through plasma polymerization, which is a dry coating method at room temperature. The surface morphology of TiO2 nanoparticles was characterized by high-resolution transmission electron microscope (HRTEM). The dispersion behavior of TiO2 nanoparticles in water and ethyl glycol was investigated by laser size distribution and ultraviolet–visible absorption spectrum. TiO2 nanoparticles were coated with a thin film through plasma polymerization, which prevents the agglomeration and improves the dispersion behavior of TiO2 nanoparticles. 相似文献
14.
制冷空调系统替代工质的发展现状及方向 总被引:3,自引:0,他引:3
本文主要针对CFC11、CFC12以及HCFC22介绍了目前替代工质的发展现状,阐述了混合工质以及氨、二氧化碳、碳氢化合物等自然工质作为替代工质的特点以及其发展现状,总结了制冷空调系统替代工质的发展方向。 相似文献
15.
V. Goodarzi S. ALI Monemian F. Maleki M. Torabi Angaji 《Journal of Macromolecular Science: Physics》2013,52(3):472-484
In the preparation of nanocomposites, there is competition between the dispersion of nanoparticles and the formation of agglomerates. In this study, radical copolymerization of ethyl acrylate and methyl methacrylate initiated by 2,2‐azobis (isobutyro) nitrile (AIBN) was performed, in the presence of titanium oxide (TiO2) nanoparticles modified in a new approach; a good dispersion of the nanoparticles in the unsaturated polyester (UP) matrix was obtained. The TiO2 nanoparticles were exposed to 3‐(methacryloxy) propyl trimethoxy silane as the coupling agent. The presence of coupling agent‐grafted TiO2 nanoparticles in the copolymerization process resulted in the formation of a polymeric layer on the surface of the TiO2 nanoparticles (doubly modified‐TiO2). The grafting of coupling agent molecules and consequently copolymer macromolecular chains onto the surface of TiO2 nanoparticles was investigated using Fourier transform infrared (FTIR) analysis. It found that the formation of an acrylate layer on the surface of nanoparticles was successful. Then, unsaturated polyester (UP)/TiO2 nanocomposites were prepared. The morphology was studied using transmission electron microscopy (TEM). Mechanical properties and ultraviolet visible (UV/VIS) spectroscopy of various samples, including the doubly modified‐TiO2 nanoparticles, with different nanoparticle inclusions and the unmodified‐TiO2 nanoparticles, were also investigated. The results showed the doubly modified‐TiO2 nanoparticles, compared to those of unmodified‐TiO2, had better nanoparticle dispersion causing improvement in the mechanical properties and UV shielding. 相似文献
16.
Mercapto-terminated linear polymers, which were prepared by a reversible addition-fragmentation chain transfer (RAFT) technique, were used to modify metal nanoparticle surfaces. Au and Ag nanoparticles which are approximately 3–6 nm were used. This modification resulted in easy dispersion of the nanoparticles in polymer resins by simple mixing. The quality of the dispersion was confirmed by UV–Vis spectroscopy and transmission electron microscopy. 相似文献
17.
B. J. Park J. H. Sung K. S. Kim I. Chin 《Journal of Macromolecular Science: Physics》2013,52(1):53-60
Titanium dioxide (TiO2) nanoparticles were modified with poly(methyl methacrylate) (PMMA) to improve the dispersion stability of the nanoparticles in a dielectric medium and to reduce the density mismatch between TiO2 and a dielectric medium for a microcapsule‐type electrophoretic display application. Nanoparticles were coated with PMMA by in situ dispersion polymerization. The PMMA‐coated TiO2 nanoparticles were characterized by fourier transform‐infrared spectrometrey (FT‐IR), electrophoretic light scattering (ELS), and scanning electron microscopy (SEM). Density of PMMA‐coated TiO2 nanoparticles was found to be dependent on the thickness of the PMMA coating on the nanoparticles. An increase of thermal stability of the PMMA layer and the contents of PMMA on the surface of the nanoparticles were measured via thermogravimetric analysis (TGA). 相似文献
18.
阐述了目前HCFCs替代的形势、替代制冷剂和替代技术路线。从各个方面介绍了几种有潜力的单一替代制冷剂R32、R161、R1234yf和R1234ze等。并对将来替代制冷剂的发展进行分析,认为混合制冷剂是大势所趋。 相似文献